Semester 1

Question 1

Where is the thorax located?

Answer 1

Between the neck and abdomon

Question 2

What does the thoracic skeleton consist of?

Answer 2

The sternum, ribs, costal cartilages and thoracic vertebrae

Question 3

What is the main role of the thoracic skeleton?

Answer 3

It protects vital organs in chest and upper abdomen.
Contracts to assist inspiration.

Question 4

What are the 2 main openings of the thorax?

Answer 4

The superior thoracic aperture found superiorly and the inferior thoracic aperture located inferiorly.

Question 5

Which strucrures bound the superior thoracic aperture?

Answer 5

The bones of the upper thorax; manubrium of sternum, the first pair of ribs, and the body of the vertebra T1.

Question 6

Which strucrures bound the inferior thoracic aperture?

Answer 6

Its almost completely bound by the diaphragm, separating it from the abdominal cavity.

Question 7

Name some of the contents of the thorax?

Answer 7

• Heart
• Lungs
• Oesophagus
• Trachea
• main bronchi
• Thymus
• Vagus and phrenic nerves
• Sympathetic trunks and ganglia
• Thoracic duct
• Lymph nodes
• Major systemic and pulmonary vasculature

Question 8

Name the 3 parts of the sternum

Answer 8

1. Superior part is the manubrium
2. The middle and largest part is the body
3. The inferior, smallest part is the xiphoid process

Question 9

What is the sternal angle?

Answer 9

Junction of the manubrium and body

Question 10

What is the jugular notch?

Answer 10

The depression on the superior surface of the manubrium

Question 11

Which substance directly attaches the true ribs to the sternum?

Answer 11

Costal cartilage.

Question 12

What is the role of the costal cartilage?

Answer 12

The elasticity of the thoracic cage and prevent various blows to the chest from fracturing the sternum and/or ribs.

Question 13

What are articulations formed between the true ribs and the sternum?

Answer 13

Sternocostal joints

Question 14

What is the name for the ribs directly attached to the sternum (1-7)?

Answer 14

True ribs

Question 15

What is the name for the ribs indirectly attached to the sternum (8-10)?

Answer 15

False ribs/vertebrochondral ribs

Question 16

What is the name for the ribs not attached to the sternum (11-12)?

Answer 16

Floating ribs/vertebral ribs

Question 17

What is the ‘head’ of the rib?

Answer 17

A projection at the posterior end of the rib that contains a pair of articular facets

Question 18

What is the name of the joint whereby the ribs articulate with the vertebrae?

Answer 18

A vertebrocostal joint.

Question 19

What is the neck of the rib?

Answer 19

Constricted portion of a rib just lateral to the head.

Question 20

What is the neck of the rib?

Answer 20

Constricted portion of a rib just lateral to the head.

Question 21

What is the tubercle of the rib?

Answer 21

A knoblike structure on the posterior surface, where the neck joins the body.

Question 22

Define the lateral costotransverse ligament

Answer 22

The nonarticular part of the tubercle attaches to the transverse process of a vertebra

Question 23

Define the costal angle

Answer 23

A short distance beyond the tubercle, an abrupt change in the curvature of the shaft occurs.

Question 24

Define the costal groove

Answer 24

The inner surface of the rib that protects the intercostal blood vessels and a small nerve.

Question 25

Describe the articulation of the ribs with the thoracic vertebrae

Answer 25

• The posterior portion of the rib connects to a thoracic vertebra by its head and the articular part of a tubercle.
• The facet of the head fits into either a facet on the body of one vertebra (T1 only) or into the demifacets of two adjoining vertebrae.
• The articular part of the tubercle articulates with the facet of the transverse process of the vertebra

Question 26

Describe the articulation of the costochondral joint

Answer 26

The lateral end of the costal cartilage articulates with the sternal end of the rib.

Question 27

Describe the articulation of the interveterbral joint

Answer 27

Adjacent verterbral bodies bound together by IV disc

Question 28

Describe the articulation of the costoverterbral joint

Answer 28

Head of each rib with superior demi/costal facet of vertebral body.
Tubercle of rib with transverse process of vertebrae.

Question 29

Describe the articulation of the interchondral joint

Answer 29

Between costal cartilage of 6th-9th ribs

Question 30

Describe the articulation of the sternocostal joint

Answer 30

Articulation of the 1st costal cartilages with the manubrium of the sternum.
2nd-7th costal cartilages with the body of the sternum.

Question 31

Describe the articulation of the sternoclavicular joint

Answer 31

Clavicle with manubrium of sternum and 1st costal cartilage.

Question 32

Describe the articulation of the manubriosternal joint

Answer 32

Articulation of manubrium and body of sternum

Question 33

Describe the articulation of the xiphoisternal joint

Answer 33

Articulation bewteen xiphoid process and body of sternum

Question 34

What are the main muscles of the thorax?

Answer 34

-Diaphragm
-Intercostal muscles

Question 35

What is the origin and insertion of the thorax?

Answer 35

Origin: Xiphoid process, inner surface lower 6 ribs, lumbar attachment via crura and arcuate ligaments.
Insertion: Large, trefoil-shaped central tendon

Question 36

Which nerve supplies the thorax?

Answer 36

Left and right phrenic nerves C3-C5.

Question 37

Describe the action of the diaphragm in inspiration

Answer 37

Inspiration starts with the 2 domes of the diaphragm flattening to bring muscle fibres into a position to pull down the central tendon. The central tendon then becomes fixed and continued muscular contraction lifts the ribs and sternum (bucket and pump handle action) to increase thoracic volume, decreasing pressure, drawing air in (atmospheric pressure greater than pulmonary pressure).

Question 38

Which 3 sugroups make up the intercostal muscles?

Answer 38

-External
-Internal
-Innermost

Question 39

Describe the 2 main functions of the intercostals

Answer 39

-Pull the ribs up/down to assist inspiration/expiration
-Fill the gaps between ribs, creating airtight cavity. Fibres run obliquely between adjacent ribs, the 3 layers at different angles.

Question 40

Describe the action of the external intercostals apon the ribs?

Answer 40

External intercostal muscles pull the ribs upwards (upon contraction/inspiration) to increase the volume of the thorax.

Question 41

Describe the action of the internal intercostals apon the ribs?

Answer 41

Internal intercostal muscles pull the ribs downwards (upon contraction/expiration) to decrease the volume of the thorax.

Question 42

What is the role of accessory muscles in the thorax?

Answer 42

Recruited to increase ventilation by patients with laboured breathing.

Question 43

What is the origin and insertion of the external intercostal muscles?

Answer 43

Origin: Inferior border of the rib
Insertion: Superior border of the rib

Question 44

What is the origin and insertion of the internal intercostal muscles?

Answer 44

Origin: Superior border of the rib
Insertion: Inferior border of the rib

Question 45

Which nerve supplies the intercostals?

Answer 45

Thoracic spinal nerves T2-T12

Question 46

Describe the role of the levatores constorum

Answer 46

Elevate ribs in inspiration. 12 small muscles on either side of the thorax running between traverse process and ribs below.

Question 47

Describe the role of the serratus posterior superior

Answer 47

Asssists inspiration.

Question 48

Describe the role of the serratus posterior inferior

Answer 48

Assists expiration

Question 49

Describe the role of the transverse thoracics?

Answer 49

Assists expiration

Question 50

Describe the process of quiet inspiration

Answer 50

• Contraction of the diaphragm flattens its domes
• Volume of the thorax increased, which lowers intrapleural pressure and causes air to be drawn into the lungs
• At the same time, the abdominal wall relaxes, allowing the abdominal contents to be displaced downwards as the diaphragm flattens.
• The intercostal muscles can expand the ribcage by two movements:
• Forward movement of the lower end of the sternum
• Upward and outward movement of the ribs, as the external intercostal muscles contract.
• The intercostal muscles mainly prevent deformation of the tissue between the ribs, which would otherwise lower the volume of the thoracic cage

Question 51

Is quiet expiration an active or passive process?

Answer 51

Passive and there is no direct muscle action.
During inspiration, the lungs are expanded against their elastic recoil. This recoil is sufficient to drive air out of the lungs in expiration.

Question 52

Describe the process of forced inspiration

Answer 52

In addition to the action of the diaphragm:
* Scalene muscles and sternocleidomastoids raise the ribs anteroposteriorly, producing movement at the manubriosternal joint.
* Intercostal muscles are more active and raise the ribs to a far greater extent than in quiet inspiration.
* The 12th rib, which is attached to quadratus lumborum, allows forcible downward movement of the diaphragm.
* Arching the back using erector spinae also increases thoracic volume.
* During respiratory distress, the scapulae are fixed by trapezius muscles. The rhomboid muscles and levator scapulae, pectoralis minor and serratus anterior raise the ribs. The arms can be fixed (e.g., by holding the back of a chair), allowing the use of pectoralis major.

Question 53

Describe the process of forced expiration?

Answer 53

Elastic recoil of the lungs is reinforced by contraction of the muscles of the abdominal wall. This forces the abdominal contents against the diaphragm, displacing the diaphragm upwards
In addition, quadratus lumborum pulls the ribs down, adding to the force at which the abdominal contents are pushed against the diaphragm. Intercostal muscles prevent outward deformation of the tissue between the ribs.

Question 54

Describe the pump and bucket handle mechanism

Answer 54

• During respiration the anteroposterior, transverse and vertical diameters of the thorax change, resulting in changes in thoracic volume.
• Vertical diameter changes are due to contraction and relaxation of the diaphragm.
• Movement of the 2nd to 5th ribs during inspiration occurs about an axis along the rib neck through the costovertebral and costotransverse joints, causing their anterior ends to be raised (‘pump handle’ movement). Because the 1st rib is firmly attached to the manubrium, movement of its anterior end is slight: the longer 2nd to 5th ribs lift the body of the sternum upwards and forwards, resulting in bending of the manubriosternal joint and an increase in the anteroposterior diameter of the thorax.
• In inspiration movement of the 8th to 10th ribs occurs about an axis through the costovertebral and sternocostal joints, causing the shaft of the rib to move outwards and upwards (‘bucket handle’ movement), widening the infrasternal angle to increase the transverse diameter of the thorax.
• Ribs 11 and 12 have little influence on movement but provide firm attachment for the diaphragm.
• During expiration reverse movements of the ribs and sternum occur, decreasing the anteroposterior and transverse diameters.

Question 55

Describe the boundaries of the thorax

Answer 55

Bounded superiorly superior thoracic aperture
Bounded posteriorly by posterior thoracic aperture
Bounded laterally and posteriorly by ribcage and intercostal muscles
12 thoracic vertebrae posteriorly
Sternum anteriorly
Diaphragm inferiorly
Abdomon superiorly

Question 56

What is the role of the sternocleidomastoids and scalenes?

Answer 56

Used for a more forceful inhalation, raise the ribs anteroposteriorly increasing intrathoracic volume.

Question 57

What is the role of the abdominal muscles?

Answer 57

Used for a more forceful exhalation. Elastic recoil of the lungs is reinforced by contraction of the muscles of the abdominal wall; this forces the abdominal contents against the diaphragm, displacing the diaphragm upwards.

Question 58

What is the role of the quadratus lumborum?

Answer 58

Attached to the 12th rib, allows forcible downward movement of the diaphragm.

Question 59

What’s the role of errector spinae?

Answer 59

Arching the back to increase thoracic volume.

Question 60

What is the role of trapezius muscles?

Answer 60

They fix the scapulae.

Question 61

What’s the role of the rhomboid muscles, levator scapulae, pectoralis minor and serratus anterior?

Answer 61

They all raise the ribs/forced inspiration

Question 62

Roughly give the size of the heart

Answer 62

The sized of a closed fist

Question 63

Where does the heart rest?

Answer 63

Lies in the mediastinum, an anatomical region that extends from the sternum to the vertebral column, from the first rib to the diaphragm, and between the lungs

Question 64

What is the base of the heart?

Answer 64

The base of the heart is opposite the apex and is its posterior aspect. It is formed by the atria of the heart, mostly the left atrium.

Question 65

What is the apex of the heart?

Answer 65

The pointed apex is formed by the tip of the left ventricle and rests on the diaphragm. It is directed anteriorly, inferiorly, and to the left.

Question 66

Which 3 veins does the right atrium recieve blood from?

Answer 66

The superior vena cava, inferior vena cava, and coronary sinus

Question 67

What is the partition between the right and left atria called?

Answer 67

The interatrial septum

Question 68

What is the partition between the right and left atria called?

Answer 68

The interatrial septum

Question 69

What is the name of the valve between the right atria and ventricles?

Answer 69

Tricuspid Valve/Right Atrioventricular valve

Question 70

Define the chordae tendineae

Answer 70

Tendon-like cords connected to the tricuspid and bicuspid valves, which in turn are connected to papillary muscles.

Question 71

What is the partition between the right and left ventricles called?

Answer 71

Interventricular septum

Question 72

Which major vessel is connected to the right ventricle?

Answer 72

Pulmonary artery- takes deoxygenated blood from the heart to the lungs via the pulmonary trunk.

Question 73

Which major vessel suplies the left atrium?

Answer 73

The 4 Pulmonary veins

Question 74

Name the valve that separates the left atrium and left ventricle

Answer 74

Bicuspid/mitral/atrioventricular valve

Question 75

Which chamber of the heart has the thickest walls?

Answer 75

Left ventricle

Question 76

How thick is the left ventricle?

Answer 76

10–15 mm

Question 77

Which vessels are supplied by the left ventricle?

Answer 77

• Blood passes from the left ventricle through the aortic valve (aortic semilunar valve) into the
  ascending aorta
• Some of the blood in the aorta flows into the coronary arteries, which branch from the
  ascending aorta and carry blood to the heart wall.
• Remainder of the blood passes into the arch of the aorta and descending aorta (thoracic aorta
  and abdominal aorta).
• Branches of the arch of the aorta and descending aorta carry blood throughout the body.

Question 78

Why do the atria have considerably thinner walls than the ventricles?

Answer 78

The atria deliver blood under less pressure into the adjacent ventricles. Because the ventricles pump blood under higher pressure over greater distances, their walls are thicker

Question 79

Why is the muscular wall of the left ventricle considerably thicker than the right ventricle.

Answer 79

Although the right and left ventricles act as two separate pumps that simultaneously eject equal volumes of blood, the right side has a much smaller workload. It pumps blood a short distance to the lungs at lower pressure, and the resistance to blood flow is small.
The left ventricle pumps oxygenated blood great distances to all other parts of the body at higher pressure, and the resistance to blood flow is larger. Therefore, the left ventricle works much harder than the right ventricle to maintain the same rate of blood flow, so the walls are thicker to enable more forceful contractions, delivering blood under high pressure.

Question 80

Define ‘pericardium’

Answer 80

The membrane that surrounds and protects the heart.

Question 81

What are the 2 main parts of the pericardium?

Answer 81

The superficial fibrous pericardium and the deeper serous pericardium

Question 82

Give the function of the fibrous pericardium

Answer 82

The fibrous pericardium prevents overstretching of the heart, provides protection, and anchors the heart in the mediastinum.
The fibrous pericardium near the apex of the heart is partially fused to the central tendon of the diaphragm and therefore aids movement of the diaphragm, as in deep breathing, facilitates the movement of blood by the heart.

Question 83

Give the location of the fibrous pericardium

Answer 83

It resembles a bag that rests on and attaches to the diaphragm; its open end is fused to the connective tissues of the blood vessels entering and leaving the heart.

Question 84

What is the composition of the fibrous pericardium

Answer 84

Composed of tough, inelastic, dense irregular connective tissue

Question 85

Give the composition of the serous pericardium

Answer 85

Serous pericardium is a thinner, more delicate membrane that forms a double layer around the heart.
The outer parietal layer of the serous pericardium is fused to the fibrous pericardium. The inner visceral layer of the serous pericardium, which is also called the epicardium is one of the layers of the heart wall and adheres tightly to the surface of the heart.
* Between the parietal and visceral layers of the serous pericardium is a thin film of lubricating serous fluid, ‘pericardial fluid’.
* The space that contains the few millilitres of pericardial fluid is called the pericardial cavity.

Question 86

What is the function of the pericardial fluid?

Answer 86

Reduces friction between the layers of the serous pericardium as the heart moves.

Question 87

Give the 3 layers that make up the heart wall

Answer 87

The epicardium (external layer), the myocardium (middle layer), and the endocardium (inner layer).

Question 88

Describe the epicardium

Answer 88

The epicardium is composed of two tissue layers. The outermost is called the visceral layer of the serous pericardium. This thin, transparent outer layer of the heart wall is composed of mesothelium. Beneath the mesothelium is a variable layer of delicate fibroelastic tissue and adipose tissue.
The adipose tissue predominates and becomes thickest over the ventricular surfaces, where it houses the major coronary and cardiac vessels of the heart. The epicardium imparts a smooth, slippery texture to the outermost surface of the heart. The epicardium contains blood vessels and lymphatics that supply the myocardium.

Question 89

Describe the myocardium

Answer 89

The middle myocardium is responsible for the pumping action of the heart and is composed of cardiac muscle tissue. It makes up approximately 95% of the heart wall. The muscle fibers are wrapped and bundled with connective tissue sheaths composed of endomysium and perimysium. The cardiac muscle fibers are organized in bundles that swirl diagonally around the heart and generate the strong pumping actions of the heart.

Question 90

Describe the endocardium

Answer 90

The innermost endocardium is a thin layer of endothelium overlying a thin layer of connective tissue. It provides a smooth lining for the chambers of the heart and covers the valves of the heart. The smooth endothelial lining minimizes the surface friction as blood passes through the heart. The
endocardium is continuous with the endothelial lining of the large blood vessels attached to the heart.

Question 91

Describe the composition of the fibrous skeleton of the heart

Answer 91

The fibrous skeleton consists of 4 dense connective tissue rings that surround the valves of the heart, fuse with one another, and merge with the interventricular septum:
-Pulmonary fibrous ring
-Aortic fibrous ring
-Right atrioventricular fibrous ring
-Left atrioventricular fibrous ring

Question 92

Give the function of the fibrous skeleton of the heart

Answer 92

• In addition to forming a structural foundation for the heart valves, the fibrous skeleton prevents overstretching of the valves as blood passes through them.
• It also serves as a point of insertion for bundles of cardiac muscle fibres and acts as an electrical insulator between the atria and ventricles.

Question 93

Give the function of valves

Answer 93

The valves of the heart are structures which ensure blood flows in only one direction.

Question 94

Describe the composition of valves

Answer 94

They are composed of connective tissue and endocardium (the inner layer of the heart).

Question 95

List all the valves found in the heart

Answer 95

• Atrioventricular valves: The tricuspid valve and mitral (bicuspid) valve. They are located between the atria and corresponding ventricle.
• Semilunar valves: The pulmonary valve and aortic valve. They are located between the ventricles and their corresponding artery, and regulate the flow of blood leaving the heart.

Question 96

Describe the mechanism behind the opening and closing of the atrioventricular valves

Answer 96

• When an AV valve is open, the rounded ends of the cusps project into the ventricle.
• When the ventricles are relaxed, the papillary muscles are relaxed, the chordae tendineae are
  slack, and blood moves from a higher pressure in the atria to a lower pressure in the ventricles
  through open AV valves
• When the ventricles contract, the pressure of the blood drives the cusps upward until their edges
  meet and close the opening. At the same time, the papillary muscles contract, which pulls on and
  tightens the chordae tendineae. This prevents the valve cusps from everting (opening into the
  atria) in response to the high ventricular pressure. If the AV valves or chordae tendineae are damaged, blood may regurgitate into the atria when the ventricles contract.

Question 97

Describe the mechinism behind the opening and closing of the semi-lunar valves

Answer 97

Made up of three crescent moon–shaped cusps.
* Each cusp attaches to the arterial wall by its convex outer margin.
* The SL valves allow ejection of blood from the heart into arteries but prevent backflow of blood into the ventricles. The free borders of the cusps project into the lumen of the artery.
* When the ventricles contract, pressure builds up within the chambers. The semilunar valves open when pressure in the ventricles exceeds the pressure in the arteries, permitting ejection of blood from the ventricles into the pulmonary trunk and aorta.
* As the ventricles relax, blood starts to flow back toward the heart. Arteriole pressure exceeds ventricular pressure. This backflowing blood fills the valve cusps, which causes the free edges of the semilunar valves to contact each other tightly and close the opening between the ventricle and artery.

Question 98

Which vessels does the left coronary artery branch into?

Answer 98

• Circumflex artery
• Left Anterior Descending artery (LAD)

Question 99

What do the left coronary arteries supply?

Answer 99

• Circumflex artery - supplies blood to the left atrium, side and back of the left ventricle
• Left Anterior Descending artery (LAD) - supplies the front and bottom of the left ventricle and the front of the septum

Question 100

What does the right coronary artery branch into?

Answer 100

• Right marginal artery
• Posterior descending artery

Question 101

What does the right artery supply?

Answer 101

• Right atrium, right ventricle, bottom portion of both ventricles and back of the septum

Question 102

Describe ‘Collateral Circulation’

Answer 102

• A network of tiny blood vessels, and, under normal conditions, not open.
• When the coronary arteries narrow to the point that blood flow to the heart muscle is limited (coronary artery disease), collateral vessels may enlarge and become active. This allows blood to flow around the blocked artery to another artery nearby or to the same artery past the blockage, protecting the heart tissue from injury.

Question 103

Give features of the autorhythmic fibres

Answer 103

• a network of specialised cardiac muscle fibres which are self-excitable.
• generate action potentials that trigger heart contractions.
• during embryonic development, only about 1% of the cardiac muscle fibres become autorhythmic fibres

Question 104

Give functions of the autorhythmic fibres

Answer 104

1. They act as a pacemaker, setting the rhythm of electrical excitation that causes contraction of the heart.
2. They form the cardiac conduction system, a network of specialized cardiac muscle fibres that provide a path for each cycle of cardiac excitation to progress through the heart. The conduction system ensures that cardiac chambers become stimulated to contract in a coordinated manner, which makes the heart an effective pump. Problems with autorhythmic fibres can result in arrhythmias (abnormal rhythms) in which the heart beats irregularly, too fast, or too slow.

Question 105

Describe the process of cardiac excitation

Answer 105

1. Cardiac excitation begins in the sinoatrial (SA) node, located in the right atrial wall just inferior and lateral to the opening of the superior vena cava. SA node cells do not have a stable resting potential. Rather, they repeatedly depolarize to threshold spontaneously. The spontaneous depolarization is a pacemaker potential. When the pacemaker potential reaches threshold, it triggers an action potential. Each action potential from the SA node propagates throughout both atria via gap junctions in the intercalated discs of atrial muscle fibers. Following the action potential, the two atria contract at the same time.
2. By conducting along atrial muscle fibers, the action potential reaches the atrioventricular (AV) node, located in the interatrial septum, just anterior to the opening of the coronary sinus. At the AV node, the action potential slows considerably as a result of various differences in cell structure in the AV node. This delay provides time for the atria to empty their blood into the ventricles.
3. From the AV node, the action potential enters the atrioventricular (AV) bundle (also known as the bundle of His). This bundle is the only site where action potentials can conduct from the atria to the ventricles. (Elsewhere, the fibrous skeleton of the heart electrically insulates the atria from the ventricles.) The atrioventricular bundle (bundle of His) is a continuation of the specialised tissue of the AV node, and serves to transmit the electrical impulse from the AV node to the Purkinje fibres of the ventricles.
   It descends down the membranous part of the interventricular septum, before dividing into two main bundles:
   * Right bundle branch - conducts the impulse to the Purkinje fibres of the right ventricle
   * Left bundle branch - conducts the impulse to the Purkinje fibres of the left ventricle
   * The Purkinje fibres (sub-endocardial plexus of conduction cells) are a network of specialised cells. They are abundant with glycogen and have extensive gap junctions. These cells are located in the subendocardial surface of the ventricular walls and are able to rapidly transmit cardiac action potentials from the atrioventricular bundle to the myocardium of the ventricles.
4. This rapid conduction allows coordinated ventricular contraction (ventricular systole) and blood is moved from the right and left ventricles to the pulmonary artery and aorta respectively.

Question 106

Which factors do cardiac output depend on?

Answer 106

Heartrate
Stroke volume

Question 107

What can cause a change in heart rate?

Answer 107

Exercise
Exessive bleeding
Increase bp/increase hr

Question 108

Which factors are involved in the regulation of heartrate?

Answer 108

Autonomic nervous system
Hormones released by adrenal medullae (epinephrine and norepinephrine)

Question 109

Where is the cardiovascular centre located?

Answer 109

Medulla oblongata

Question 110

Describe the role of the cardiovascular centre

Answer 110

This region of the brain stem receives input from a variety of sensory receptors and from higher brain centres, such as the limbic system and cerebral cortex. The cardiovascular centre then directs appropriate output by increasing or decreasing the frequency of nerve impulses in both the sympathetic and parasympathetic branches of the ANS to increase or decrease heartrate respectively.

Question 111

Describe how heart rate is regulated by the autonomic nervous system.

Answer 111

-A wave of electrical excitation spreads out from the sinoatrial node (SAN) across both atria, causing them to contract.
-A layer of non-conductive tissue prevents the wave crossing to the ventricles.
-The wave of excitation enters the atrioventricular node (AVN).
-The atrioventricular node, conveys a wave of electrical excitation between the ventricles along the Purkyne tissue muscle fibres, collectively making up the bundle of His.
-The bundle of His conducts the wave through the atrioventricular septum to the base of the ventricles, where the bundle branches into smaller fibres of Purkyne tissue.
-The wave of excitation is released from the Purkyne tissue, causing the ventricles to contract quickly at the same time, from the bottom of the heart upwards.

Question 112

How do chemoreceptors control heartrate?

Answer 112

-When blood has a high concentration of carbon dioxide, the pH is lowered.
-Chemoreceptors detect this pH change and increase the frequency of nervous impulses to the centre in the medulla oblongata that increases heart rate.
-This centre increases the frequency of impulses via the sympathetic nervous system to the sinoatrial node. This increases the rate of increases the rate of production of electrical waves by the sinoatrial node and therefore increases the heart rate.
-The increased blood flow that this causes leads to more carbon dioxide being removed by the lungs and so the carbon dioxide concentration of the blood returns to normal
-As a consequence the pH of blood rises to normal and the chemoreceptors in the wall of caratoid arteries and aorta reduce the frequency of nerve impulses to the medulla oblongata.
-The medulla oblongata reduces the frequency of impulses to the sinoatrial node, therefore leading to reduction in heart rate.

Question 113

How does exercise affect cardiac output?

Answer 113

-Increased muscular activity
-More carbon dioxide produced by tissues by increased respiration
-Blood pH lowered
-Chemical receptors in carotid arteries increase frequency of impulses to medulla oblongata.
-Centre in medulla oblongata that speeds heart rate, increases frequency of impulses to SA node via the sympathetic nervous system.
-SA node increases heart rate.
-Increased blood blow removed carbon dioxide faster.

Question 114

How do baroreceptors control heart rate when blood pressure is too high?

Answer 114

Pressure receptors transmit more nervous impulses to the centre in the medulla oblongata that decreases heart rate. This centre sends impulses via the parasympathetic nervous system to the sinoatrial node of the heart which leads to decrease in heart rate.

Question 115

Suppose the parasympathetic nerve connections from the medulla oblongata to the sinoatrial node were out. Suggest what might happen if a persons blood pressure increases above normal

Answer 115

Blood pressure remains high because the parasympathetic system is unable to transit nerve impulses to the SA node, which decreases heart rate and so lowers blood pressure.

Question 116

The nerve connecting the carotid artery to the medulla oblongata of a person is cut. This person then undertakes some strenuous exercise. Suggest what might happen to the persons heart rate?

Answer 116

Heart rate remains as it was before taking exercise, blood pressure increases and carbon dioxide concentration of blood rises (lowering pH). The changes are detected by pressure and chemical receptors in the wall of the carotid arteries. As the nerve from here to the medulla oblongata is cut, no nerve impulse can be sent to centres that control heart rate.

Question 117

The nerve connecting the carotid artery to the medulla oblongata of a person is cut. This person then undertakes some strenuous exercise. Suggest what might happen to the persons carbon dioxide concentration?

Answer 117

Blood CO2 concentration increased as a result of increased respiration during exercise.

Question 118

Describe how ECGs relate to Conducting systems

Answer 118

• In a typical record, three clearly recognizable waves appear with each heartbeat
• The first, called the P wave, is a small upward deflection on the ECG. The P wave represents atrial depolarization, which spreads from the SA node through contractile fibres in both atria.
• The second wave, called the QRS complex, begins as a downward deflection, continues as a large, upright, triangular wave, and ends as a downward wave. The QRS complex represents rapid ventricular depolarization, as the action potential spreads through ventricular contractile fibers.
• The third wave is a dome-shaped upward deflection called the T wave. It indicates ventricular repolarization and occurs just as the ventricles are starting to relax. The T wave is smaller and wider than the QRS complex because repolarization occurs more slowly than depolarization.
• During the plateau period of steady depolarization, the ECG tracing is flat.

Question 119

Define ‘systole’

Answer 119

The period of contraction that the heart undergoes while it pumps blood into circulation

Question 120

Define ‘diastole’

Answer 120

The period of relaxation that occurs as the chambers fill with blood

Question 121

Describe how ECGs relate to the cardiac cycle

Answer 121

1. A cardiac action potential arises in the SA node. It propagates throughout the atrial muscle and down to the AV node in about 0.03 sec. As the atrial contractile fibres depolarize, the P wave appears in the ECG.
2. After the P wave begins, the atria contract (atrial systole). Conduction of the action potential slows at the AV node because the fibres there have much smaller diameters and fewer gap junctions. The resulting 0.1-sec delay gives the atria time to contract, thus adding to the volume of blood in the ventricles, before ventricular systole begins.
3. The action potential propagates rapidly again after entering the AV bundle. About 0.2 sec after onset of the P wave, it has propagated through the bundle branches, Purkinje fibres, and the entire ventricular myocardium. Depolarization progresses down the septum, upward from the apex, and outward from the endocardial surface, producing the QRS complex. At the same time, atrial repolarization is occurring, but it is not usually evident in an ECG because the larger QRS complex masks it.
4. Contraction of ventricular contractile fibres (ventricular systole) begins shortly after the QRS complex appears and continues during the S–T segment. As contraction proceeds from the apex toward the base of the heart, blood is squeezed upward toward the semilunar valves.
5. Repolarization of ventricular contractile fibres begins at the apex and spreads throughout the ventricular myocardium. This produces the T wave in the ECG about 0.4 sec after the onset of the P wave.
6. Shortly after the T wave begins, the ventricles start to relax (ventricular diastole). By 0.6 sec, ventricular repolarization is complete and ventricular contractile fibres are relaxed.

Question 122

Describe atrial systole

Answer 122

• During atrial systole, which lasts about 0.1 sec, the atria are contracting. At the same time, the ventricles are relaxed.
• Depolarization of the SA node causes atrial depolarization, marked by the P wave in the ECG.
• Atrial depolarization causes atrial systole. As the atria contract, they exert pressure on the blood within, which forces blood through the open AV valves into the ventricles.
• Atrial systole contributes a final 25 mL of blood to the volume already in each ventricle. The end of atrial systole is also the end of ventricular diastole. Thus, each ventricle contains about 130 mL at the end of diastole. This blood volume is called the end-diastolic volume (EDV).
• The QRS complex in the ECG marks the onset of ventricular depolarization.

Question 123

Describe ventricular systole

Answer 123

• During ventricular systole, which lasts about 0.3 sec, the ventricles are contracting. At the same time, the atria are relaxed in atrial diastole.
  Ventricular depolarization causes ventricular systole. As ventricular systole begins, pressure rises inside the ventricles and pushes blood up against the AV valves, forcing them shut. For about 0.05 seconds, both the SL and AV valves are closed. This is the period of isovolumetric contraction.
• Continued contraction of the ventricles causes pressure inside the chambers to rise sharply. When left ventricular pressure surpasses aortic pressure at about 80 mmHg and right ventricular pressure rises above the pressure in the pulmonary trunk, both SL valves open. At this point, ejection of blood from the heart begins. The period when the SL valves are open is ventricular ejection and lasts for about 0.25 sec. The pressure in the left ventricle continues to rise to about 120 mmHg, and the pressure in the right ventricle climbs to about 25–30 mmHg.
• The left ventricle ejects about 70 mL of blood into the aorta and the right ventricle ejects the same volume of blood into the pulmonary trunk. The volume remaining in each ventricle at the end of systole, about 60 mL, is the end-systolic volume (ESV). * The T wave in the ECG marks the onset of ventricular repolarization.

Question 124

How do you calculate stroke volume?

Answer 124

Stroke volume, the volume ejected per beat from each ventricle, equals end-diastolic volume minus end-systolic volume: SV = EDV − ESV. At rest, the stroke volume is about 130 mL − 60 mL = 70 mL (a little more than 2 oz).

Question 125

Describe diastole

Answer 125

• During the relaxation period, which lasts about 0.4 sec, the atria and the ventricles are both relaxed. As the heart beats faster and faster, the relaxation period becomes shorter and shorter, whereas the durations of atrial systole and ventricular systole shorten only slightly.
• Ventricular repolarization causes ventricular diastole. As the ventricles relax, pressure within the chambers falls, and blood in the aorta and pulmonary trunk begins to flow backward toward the regions of lower pressure in the ventricles. Backflowing blood catches in the valve cusps and closes the SL valves. The aortic valve closes at a pressure of about 100 mmHg. Rebound of blood off the closed cusps of the aortic valve produces the dicrotic wave on the aortic pressure curve. After the SL valves close, there is a brief interval when ventricular blood volume does not change because all 4 valves are closed. This is the period of isovolumetric relaxation.
• As the ventricles continue to relax, the pressure falls quickly. When ventricular pressure drops below atrial pressure, the AV valves open, and ventricular filling begins. The major part of ventricular filling occurs just after the AV valves open. Blood that has been flowing into and building up in the atria during ventricular systole then rushes rapidly into the ventricles. At the end of the relaxation period, the ventricles are about three-quarters full. The P wave appears in the ECG, signaling the start of another cardiac cycle.

Question 126

Define cardiac output

Answer 126

Cardiac output (CO) is the volume of blood ejected from the left ventricle (or the right ventricle) into the aorta (or pulmonary trunk) each minute.

Question 127

How is cardiac ouput calculated

Answer 127

• CO=SV×HR

Question 128

Define End Systolic Volume (ESV)

Answer 128

The volume of blood in the ventricles at the end of systole. It is the lowest volume of blood in the ventricles at any point of the cardiac cycle.

Question 129

What are the main factors that affect ESV

Answer 129

Afterload
Contractibility of the heart

Question 130

Define End Diastolic Volume (EDV)

Answer 130

The volume of blood in the ventricles at the end of diastole.

Question 131

Describe the anatomical locations position of the conducting system of the heart

Answer 131

Sinoatrial Node in right atrium.
Atrioventricular node between right and left atria and ventricles (Interatrioventricular septum)
Bundle of His between AV node and bundle branches
Right and left bundle branches in interventricular septum
Purkinje fibres in endocardium

Question 132

Define ‘Lung volume’

Answer 132

The volume of gas held in the lungs.

Question 133

How are lung volumes measured?

Answer 133

Spirometre

Question 134

Give the 4 lung volumes

Answer 134

Tidal Volume
Inspiratory Reserve Volume
Expiratory Reserve Volume
Residual Volume

Question 135

Define tidal volume

Answer 135

Volume of air breathed in and out in a single breath

Question 136

Define Inspiratory Reserve Volume

Answer 136

Volume of air breathed in by a maximum inspiration at the end of a normal inspiration

Question 137

Define Expiratory Reserve Volume

Answer 137

Volume of air that can be expelled by a maximum effort at the end of a normal expiration

Question 138

Define Residual Volume

Answer 138

Volume of air remaining in lungs at the end of maximum expiration.

Question 139

What are pulmonary capacities?

Answer 139

A combination of 2 or more volumes.

Question 140

Define Inspiratory Capacity and give the calculation

Answer 140

IC= TV+IRV
Volume of air breathed in by a maximum inspiration at the end of a normal expiration

Question 141

Define Functional Residual Capacity and give the calculation

Answer 141

FRC= ERV+RV
Volume of air remaining in the lungs at the end of a normal expiration. Acts as a buffer against extreme changes in alveolar gas levels with each breath.

Question 142

Define Vital Capacity and give the calculation

Answer 142

VC= IRV+TV+ERV
Volume of air that can be breathed in by a maximum inspiration following a maximum expiration.

Question 143

Define Total Lung Capacity

Answer 143

TLC=VC+RV
The total volume of air that can be held by the lungs.
Only a fraction of TLC is used in normal breathing.

Question 144

After exhalation, the lungs are not completely emptied of air, why is this?

Answer 144

This is useful physiologically, as a completely deflated lung requires significantly more energy to inflate it than one in which the alveoli have not completely collapsed. Even following a maximum respiratory effort (forced expiration), some air remains within the lungs.

Question 145

Why is there still a residual volume?

Answer 145

This occurs because as the expiratory muscles contract during forced expiration, all the structures within the lungs (including the airways) are compressed by the positive intrapleural pressure. Consequently, the smaller airways collapse before the alveoli empty completely, meaning some air
remains within the lungs; this is known as the residual volume (RV).

Question 146

Describe what happens in quiet breathing after the tidal volume has been expired

Answer 146

• Pressure outside the chest is equal to pressure inside the alveoli (i.e., atmospheric pressure).
• Elastic forces tending to collapse the lung are balanced by the elastic recoil trying to expand the chest.
• This creates a subatmospheric (negative) pressure in the intrapleural space.
• The lung volume at this point is known as functional residual capacity (FRC).

Question 147

Describe how Residual Volume and Functional Residual Capacity can be measured

Answer 147

Nitrogen washout, helium dilution and plethysmography

Question 148

How can disease affect lung volumes?

Answer 148

Disease affects lung volumes in specific patterns, depending on the pathological processes.

Question 149

What are the 3 types of lung disease

Answer 149

Obstructive, restrictive or mixed

Question 150

What is an obstructive disorder

Answer 150

This group of disorders is characterized by obstruction of normal air flow caused by airway narrowing, which if not reversed, leads to hyperinflation of the lungs as air is trapped behind closed airways.
An example of an obstructive lung disease where a patient develops gas trapping and hyperinflation is chronic obstructive pulmonary disease (COPD).

Question 151

How do obstructive disorders affect lung volumes?

Answer 151

• The RV is increased as gas that is trapped cannot leave the lung, and the RV:total lung capacity (TLC) ratio increases.
• In patients with severe obstruction, air trapping can be so extensive that vital capacity is decreased.

Question 152

What is a restrictive disorder?

Answer 152

Restrictive disorders result in stiffer lungs that cannot expand to normal volumes. An example of a restrictive lung disorder is Idiopathic pulmonary fibrosis.

Question 153

How do restrictive disorders affect lung volumes?

Answer 153

All the subdivisions of volume are decreased and the RV:TLC ratio will be normal or increased (where vital capacity has decreased more quickly than RV).

Question 154

Define FEV1 (forced expiratory volume in 1 second)

Answer 154

FEV1 is the volume of air expelled in the first second of a forced expiration, starting from full inspiration.

Question 155

Define FVC (the forced vital capacity)

Answer 155

FVC is a measure of total lung volume exhaled; the patient is asked to exhale with maximal effort after a full inspiration.

Question 156

How can FEV1 and FVC be measured

Answer 156

Spirometre

Question 157

Which factors affect FEV1 and FVC

Answer 157

Height, age and sex of the patient.

Question 158

Explain the FEV1:FVC ratio

Answer 158

The FEV1:FVC ratio is a more useful measurement than FEV1 or FVC alone. FEV1 is 80% of FVC in normal subjects. The FEV1:FVC ratio is an excellent measure of airway limitation and allows us to differentiate obstructive from restrictive lung disease

Question 159

How is the FEV1:FVC ratio affected in obstructive disorders?

Answer 159

• High intrathoracic pressures generated by forced expiration cause premature closure of the
  airways with trapping of air in the chest
• FEV1 is reduced much more than FVC
• FEV1:FVC ratio is reduced (< 80%)

Question 160

How is the FEV1:FVC ratio affected in restrictive disorders?

Answer 160

• Both FEV1 and FVC are reduced, often in proportion to each other
• FEV1:FVC ratio is normal or increased (> 80%)

Question 161

What does the upper respiratory system include?

Answer 161

The upper respiratory system includes the nose, nasal cavity, pharynx, and associated structures

Question 162

What does the lower respiratory system include?

Answer 162

The lower respiratory system includes the larynx, trachea, bronchi, and lungs.

Question 163

Define ‘pulmonary ventilation’

Answer 163

Breathing- the inhalation and exhalation of air and involves the exchange of air betrween the atmosphere and the alveoli of the lungs. Inhalation permits oxygen to enter the lungs and exhalation permits carbon dioxide to leave the lungs.

Question 164

Define ‘External pulmonary respiration’

Answer 164

The exchange of gases between the alveoli of the lungs and the blood in pulmonary capillaries acorss the respiratory membrane. In the process, pulmonary capillary blood gains oxygen and loses carbon dioxide.

Question 165

Define Internal pulmonary respiration

Answer 165

Internal respiration is the exchange of gases between blood in systemic capillaries and tissue cells. In this step the blood loses oxygen and gains carbon dioxide. Within cells, the metabolic reactions that consume oxygen and give off carbon dioxide duiring the production of ATP are termed cellular respiration.

Question 166

What are the 2 fundamental parts of the respiratory system

Answer 166

-The conducting zone
-The respiratory zone

Question 167

Describe the conducting zone

Answer 167

The conducting zone consists of a series of interconnecting cavities and tubes both outside and within the lungs. These include the nose, nasal cavity, pharynx, larynx, trachea, bronchi, bronchioles, and terminal bronchioles; their function is to filter, warm, and moisten air and conduct it into the lungs.

Question 168

Describe the respiratory zone

Answer 168

The respiratory zone consists of tubes and tissues within the lungs where gas exchange occurs. These include the respiratory bronchioles, alveolar ducts, alveolar sacs, and alveoli and are the main sites of gas exchange between air and blood.

Question 169

Describe the gross structure of the lungs and pleura

Answer 169

• The lungs extend from the diaphragm to just slightly superior to the clavicles and lie against the ribs anteriorly and posteriorly
• The broad inferior portion of the lung, the base, is concave and fits over the convex area of the diaphragm.
• The narrow superior portion of the lung is the apex.
  *The surface of the lung lying against the ribs, the costal surface, matches the rounded curvature of the ribs.
• The mediastinal (medial) surface of each lung contains a region, the hilum, through which bronchi, pulmonary blood vessels, lymphatic vessels, and nerves enter and exit
• These structures are held together by the pleura and connective tissue and constitute the root of the lung.
• Medially, the left lung also contains a concavity, the cardiac notch, in which the apex of the heart lies.
• Due to the space occupied by the heart, the left lung is about 10% smaller than the right lung.
• Although the right lung is thicker and broader, it is also somewhat shorter than the left lung because the diaphragm is higher on the right side, accommodating the liver that lies inferior to it.
• The oblique fissure divides the left lung into two lobes. The oblique and horizontal fissures divide the right lung into three lobes.
• The lungs almost fill the thorax
• The apex of the lungs lies superior to the medial third of the clavicles, and this is the only area that can be palpated.
• The anterior, lateral, and posterior surfaces of the lungs lie against the ribs. The base of the lungs extends from the sixth costal cartilage anteriorly to the spinous process of the tenth thoracic vertebra posteriorly.
• The pleura extends about 5 cm (2 in.) below the base from the sixth costal cartilage anteriorly to the twelfth rib posteriorly.

Question 170

What does the hilum (root) of the lung consist of?

Answer 170

• Bronchi
• Vessels: pulmonary artery and vein
• Nerves
• Lymph nodes and lymphatic vessels
• Pulmonary ligament.

Question 171

Describe the oblique fissures

Answer 171

• One or two fissures divide each lung into sections called lobes
• Both lungs have an oblique fissure, which extends inferiorly and anteriorly; the right lung also has a horizontal fissure.
• The oblique fissure in the left lung separates the superior lobe from the inferior lobe.
• In the right lung, the superior part of the oblique fissure separates the superior lobe from the inferior lobe; the inferior part of the oblique fissure separates the inferior lobe from the middle lobe, which is bordered superiorly by the horizontal fissure.

Question 172

Describe the lobar bronchi

Answer 172

*Each lobe receives its own lobar bronchus. Thus, the right main bronchus gives rise to three lobar bronchi called the superior, middle, and inferior lobar bronchi, and the left main bronchus gives rise to superior and inferior lobar bronchi.

Question 173

Describe the segmental bronchi

Answer 173

*Within the lung, the lobar bronchi give rise to the segmental bronchi, which are constant in both origin and distribution—there are 10 segmental bronchi in each lung. The portion of lung tissue that each segmental (tertiary) bronchus supplies is called a bronchopulmonary segment.

Question 174

What is the pleural membrane (pleura)

Answer 174

Each lung is enclosed and protected by a double-layered serous membrane.

Question 175

What is the paritial pleura?

Answer 175

The superficial layer lining the wall of the thoracic cavity.

Question 176

What is the visceral pleura?

Answer 176

The deep layer, covers the lungs themselves.

Question 177

What is the visceral pleura?

Answer 177

The deep layer, covers the lungs themselves.

Question 178

What is the pleural cavity?

Answer 178

A small space between the visceral and parietal pleurae which contains a small amount of lubricating fluid secreted by the membranes.
Separate pleural cavities surround the left and right lungs.

Question 179

Give the function of the pleaural fluid

Answer 179

Pleural fluid reduces friction between the membranes, allowing them to slide easily over one another during breathing.
Pleural fluid also causes the two membranes to adhere to one another, a phenomenon called surface tension.

Question 180

Define atmospheric pressure (Patm)

Answer 180

Pressure at the entrance of the respiratory tract.

Question 181

Define alveolar pressure (PA)

Answer 181

Pressure inside the lungs.

Question 182

Explain the mechansim of respiration in relation to pressure

Answer 182

Pressure differences in the lungs generate air flow.
Respiratory muscles generate these pressure differences.
If PA = Patm, no air flow occurs
If PA<Patm, air flows into the lungs
If PA>Patm, air flows out of the lungs

Question 183

Explain Boyle’s Law

Answer 183

Boyle’s Law states that at a fixed temperature, the pressure and volume of an ideal gas are inversely proportional, so as volume of air within the lungs increases, the pressure decreases.
Atmospheric pressure is always the same, therefore the alveolar pressure needs to change to achieve airflow.
When the diaphragm flattens, thoracic volume increases, intrapleural pressure decreases, so air flows into the lungs.
In expiration, relaxation of muscles of the chest wall allows the elastic recoil of the lungs to cause contraction of the lungs, reducing thoracic volume and increasing intrapleural pressure and thus expulsion of gas.

Question 184

Describe the process of inspiration

Answer 184

-The external intercostal muscles contract, whilst the internal intercostal muscles relax
-The ribs are pulled upwards and outwards, increasing the volume of the thorax.
-The diaphragm muscles contract, causing it to flatten, also increasing the volume of the thorax.
-The increased volume of the thorax results in reduced pressure in the lungs.
-Atmospheric pressure is now greater than pulmonary pressure, so air is forced into the lungs.

Question 185

Describe the process of expiration

Answer 185

-The internal intercostal muscles contract, whilst the external intercostal muscles relax
-The ribs are pulled downwards and inwards, decreasing the volume of the thorax.
-The diaphragm muscles relax, so it’s pushed up again by the contents of the abdomen that were compressed during inspiration, decreasing the volume of the thorax.
-The decreased volume of the thorax results in increased pressure in the lungs.
-Pulmonary pressure is now greater than atmospheric pressure, so air is forced out of the lungs.

Question 186

Give the surface markings of the lungs

Answer 186

The apices of the lung extend above the level of the medial third of the clavicles.
* The lower borders of the lung are:
* T6 - mid-clavicular line
* T8 - mid-axillary line
* T10 - posteriorly
* The lower borders of the pleura are:
* T8 - mid-clavicular line
* T10 - mid-axillary line
* T12 - posteriorly
* The upper lobe is in front of the lower lobe and thus the area of lung behind the anterior aspect of the chest wall is mainly the upper lobe; in the right lung the
middle lobe also contributes significantly to the anterior aspect (between T4 and T6 anteriorly). From the posterior aspect, the chest wall encloses the lower lobes
of each lung.
* In the right lung the oblique fissure runs from the spinal process of T3 posteriorly to the level of T6 anteriorly; The transverse fissure is at T4.
* Left lung has upper and lower lobes only. The middle lobe is replaced by a small segment called the lingula

Question 187

Give the surface markings of the lungs

Answer 187

The apices of the lung extend above the level of the medial third of the clavicles.
* The lower borders of the lung are:
* T6 - mid-clavicular line
* T8 - mid-axillary line
* T10 - posteriorly
* The lower borders of the pleura are:
* T8 - mid-clavicular line
* T10 - mid-axillary line
* T12 - posteriorly
* The upper lobe is in front of the lower lobe and thus the area of lung behind the anterior aspect of the chest wall is mainly the upper lobe; in the right lung the
middle lobe also contributes significantly to the anterior aspect (between T4 and T6 anteriorly). From the posterior aspect, the chest wall encloses the lower lobes
of each lung.
* In the right lung the oblique fissure runs from the spinal process of T3 posteriorly to the level of T6 anteriorly; The transverse fissure is at T4.
* Left lung has upper and lower lobes only. The middle lobe is replaced by a small segment called the lingula

Question 188

Give examples of accessory muscles of respiration, describing how they support with breathing

Answer 188

The sternocleidomastoids and scalenes may be used for a more forceful inhalation, raise the ribs anteroposteriorly increasing intrathoracic volume.
The abdominal muscles may be used for a more forceful exhalation. Elastic recoil of the lungs is reinforced by contraction of the muscles of the abdominal wall; this forces the abdominal contents against the diaphragm, displacing the diaphragm upwards.
Intercostal muscles are more active and raise the ribs to a far greater extent than in quiet inspiration
The 12th rib, which is attached to quadratus lumborum, allows forcible downward movement of the diaphragm.
Arching the back using erector spinae also increases thoracic volume.
Scapulae are fixed by trapezius muscles.
The rhomboid muscles and levator scapulae, pectoralis minor and serratus anterior raise the ribs. The arms can be fixed (e.g., by holding the back of a chair), allowing the use of pectoralis major.
Levatores constorum- Elevate ribs in inspiration. 12 small muscles on either side of the thorax running between traverse process and ribs below.
Serratus posterior superior- Help inspiration.
Serratus posterior inferior- Assist expiration.
Transverse thoracics- Assist expiration, lie on inner surface of anterior thoracic wall running from superior surface xiphoid process, sternum and costal cartilage.

Question 188

Give examples of accessory muscles of respiration, describing how they support with breathing

Answer 188

The sternocleidomastoids and scalenes may be used for a more forceful inhalation, raise the ribs anteroposteriorly increasing intrathoracic volume.
The abdominal muscles may be used for a more forceful exhalation. Elastic recoil of the lungs is reinforced by contraction of the muscles of the abdominal wall; this forces the abdominal contents against the diaphragm, displacing the diaphragm upwards.
Intercostal muscles are more active and raise the ribs to a far greater extent than in quiet inspiration
The 12th rib, which is attached to quadratus lumborum, allows forcible downward movement of the diaphragm.
Arching the back using erector spinae also increases thoracic volume.
Scapulae are fixed by trapezius muscles.
The rhomboid muscles and levator scapulae, pectoralis minor and serratus anterior raise the ribs. The arms can be fixed (e.g., by holding the back of a chair), allowing the use of pectoralis major.
Levatores constorum- Elevate ribs in inspiration. 12 small muscles on either side of the thorax running between traverse process and ribs below.
Serratus posterior superior- Help inspiration.
Serratus posterior inferior- Assist expiration.
Transverse thoracics- Assist expiration, lie on inner surface of anterior thoracic wall running from superior surface xiphoid process, sternum and costal cartilage.

Question 189

Describe the structure of the nose

Answer 189

The lateral wall of the nasal cavity consists of bony ridges called conchae or turbinates which provide a large surface area covered in highly vascularized mucous membrane to warm and humidify inspired air.
* Under each turbinate, there is a groove or meatus.
* The paranasal air sinuses (frontal, sphenoid, ethmoid and maxillary) drain into these meatuses via small ostia, or openings.

Question 190

Describe the gross structure of the pharynx

Answer 190

• The pharynx extends from the base of the skull to the inferior border of the cricoid cartilage,
  where it is continuous anteriorly with the trachea and posteriorly with the oesophagus. It is
  described as being divided into three parts: the nasopharynx, oropharynx and laryngopharynx,
  which open anteriorly into the nose, mouth and larynx, respectively
• The pharynx is part of both the respiratory and gastrointestinal systems.
• The nasopharynx is situated above the soft palate and opens anteriorly into the nasal cavities at
  the choanae (posterior nares).
• During swallowing, the nasopharynx is cut off from the oropharynx by the soft palate. The
  nasopharynx contains the opening of the eustachian canal (pharyngotympanic or auditory tube)
  and the adenoids, which lie beneath the epithelium of its posterior wall.

Question 191

Describe the gross structure of the pharynx

Answer 191

• The pharynx extends from the base of the skull to the inferior border of the cricoid cartilage,
  where it is continuous anteriorly with the trachea and posteriorly with the oesophagus. It is
  described as being divided into three parts: the nasopharynx (Ciliated pseudostratified columnar epithelium), oropharynx (Nonkeratinized stratified squamous epithelium) and laryngopharynx(Nonkeratinized stratified squamous epithelium), which open anteriorly into the nose, mouth and larynx, respectively
• The pharynx is part of both the respiratory and gastrointestinal systems.
• The nasopharynx is situated above the soft palate and opens anteriorly into the nasal cavities at
  the choanae (posterior nares).
• During swallowing, the nasopharynx is cut off from the oropharynx by the soft palate. The
  nasopharynx contains the opening of the eustachian canal (pharyngotympanic or auditory tube)
  and the adenoids, which lie beneath the epithelium of its posterior wall.

Question 192

Describe the structure of the larynx

Answer 192

The larynx is continuous with the trachea at its inferior end. At its superior end, it is attached to the U-shaped hyoid bone and lies below the epiglottis of the tongue. The larynx consists of a cartilaginous skeleton linked by a number of membranes. This cartilaginous skeleton comprises the epiglottis, thyroid, arytenoid and cricoid cartilages.
Made of Nonkeratinized stratified squamous epithelium above vocal folds and Ciliated pseudostratified columnar epithelium below.

Question 193

Give functions of the larynx

Answer 193

1. As an open valve, to allow air to pass when breathing.
2. Protection of the trachea and bronchi during swallowing. The vocal folds close, the epiglottis is pushed back covering the opening to the larynx, and the larynx is pulled upwards and forwards beneath the tongue (preventing aspiration).
3. Speech production (phonation).

Question 194

Describe the structure of the trachea

Answer 194

The trachea is a cartilaginous and membranous tube of about 10 cm in length. It extends from the
larynx to its bifurcation at the carina (at the level of the fourth or fifth thoracic vertebra). The trachea is approximately 2.5 cm in diameter and is supported by C-shaped rings of hyaline cartilage. The rings are completed posteriorly by the trachealis muscle.
Made of Ciliated pseudostratified columnar epithelium

Question 195

Give the important relations of the trachea within the neck

Answer 195

1. The thyroid gland, which straddles the trachea, with its two lobes positioned laterally, and its
   isthmus anterior to the trachea with the inferior thyroid veins.
2. The common carotid arteries, which lie lateral to the trachea.
3. The oesophagus, which lies directly behind the trachea, and the recurrent laryngeal nerve, which
   lies between these two structures.

Question 196

Describe the struture of the respiratory tree (bronchi)

Answer 196

• Inside the thorax, the trachea divides into the left and right primary bronchi at the carina.
• The right main bronchus is shorter and more vertical than the left (for this reason, inhaled foreign bodies are more likely to pass into the right lung).
• The primary bronchi within each lung divide into secondary or lobar bronchi.
• The lobar bronchi divide again into tertiary or segmental bronchi.
• The airways continue to divide, always splitting into two daughter airways of progressively smaller calibre until eventually forming bronchioles.
  Bronchi made of Ciliated pseudostratified columnar epithelium

Question 197

Give the location and function of the conducting zone

Answer 197

Airways proximal to the respiratory bronchioles. Involved in air movement by bulk flow to the end respiratory units.

Question 198

Give the location and function of the respiratory zone

Answer 198

Airways distal to the terminal bronchiole
Involved in gaseous exchange.

Question 199

Describe the structure of the acnius

Answer 199

The acinus is the part of the airway involved in gaseous exchange. The acinus consists of:
* Respiratory bronchioles, leading to the alveolar ducts.
* Alveolar ducts, opening into two or three alveolar sacs, which in turn open into several alveoli.
Multiple acini are grouped together and surrounded by parenchymal tissue, forming a lung lobule. Lobules are separated by interlobular septa.

Question 200

What is the blood air interface?

Answer 200

• The blood–air interface is a term that describes the site at which gaseous exchange takes place within the lung.
• Average surface area of the alveolar–capillary membrane = 50–100 m2.
• Average thickness of alveolar–capillary membrane = 0.4 mm.
  Short diffusion distance for efficient gas exchange.

Question 201

Describe the structure of alveoli

Answer 201

• The alveoli are microscopic blind-ending air pouches forming the distal termination of the respiratory tract; there are 150–400 million in each normal lung. The alveoli open into alveolar sacs and then into alveolar ducts.
• Simple squamous epithelium, 1 squamous cell thick- very thin, short diffusion distance
• Most gaseous exchange occurs in the alveoli. Because alveoli are so numerous, they provide the majority of lung volume and surface area. The majority of alveoli open into the alveolar sacs.
• Communication between adjacent alveoli is possible through perforations in the alveolar wall, called pores of Kohn.
• The alveoli are lined with type I and type II pneumocytes, which sit on a basement membrane.
• Type I pneumocytes are structural, whereas type II pneumocytes produce surfactant.

Question 202

What is the function of alveolar macrophages?

Answer 202

• The most numerous of all cells in the lung are the alveolar macrophages (dust cells), which drift through the alveolar lumens and the connective tissue between them clearing up debris through phagocytosis.
• These macrophages “eat” the dust particles that escape from mucus in the higher parts of the respiratory tract, as well as other debris that is not trapped and cleared out by your mucus.
• If your lungs are infected or bleeding, the macrophages also function to phagocytize bacteria and loose blood cells.
• At the end of each day, as many as 100 million of these alveolar macrophages will expire as they ride up the mucociliary escalator to be swallowed at the esophagus and digested.

Question 203

What is Collateral Ventilation?

Answer 203

Provides alternate pathways for airflow upon obstruction.

Question 204

What are the interalveolar pores of Kohn?

Answer 204

The interalveolar pores of Kohn are epithelial-lined openings between adjacent alveoli
The pores of Kohn are usually filled with fluid and only open in response to a high pressure gradient across them. The fluid may contain alveolar lining fluid, components of surfactant, and macrophages.
There are between 13 and 21 pores in each alveolus

Question 205

What are the bronchoalveolar canals of Lambert?

Answer 205

The bronchoalveolar canals of Lambert are communications that reached from respiratory bronchioles to the alvelar ducts. They have a muscular wall with possible regional airflow control.

Question 206

What are the interbronchiolar channels of Martin?

Answer 206

The interbronchiolar channels of Martin have a diameter of 30 μm and are found between respiratory bronchioles and terminal bronchioles

Question 207

Describe Nonkeratinized stratified squamous epithelium

Answer 207

• Consists of cells arranged in layers upon a basal membrane.
• Only one layer is in contact with the basement membrane; while the other layers are adhered
  to one another to maintain structural integrity.
• This type of epithelium is well suited to areas in the body subject to constant abrasion, as it
  is the thickest layer.
• Additionally, this layer can be sequentially sloughed off and replaced before the basement membrane is exposed.
• Non-keratinised surfaces must be kept moist by bodily secretions to prevent them from
  drying out.

Question 208

Describe Ciliated pseudostratified columnar epithelium

Answer 208

• Pseudostratified columnar epithelia are tissues formed by a single layer of cells
  that give the appearance of being made from multiple layers, especially when seen in cross section. The nuclei of these epithelial cells are at different levels leading to the illusion of being stratified. However, this tissue is made of a single layer of cells and each cell is in
  contact with the basement membrane.
• The coordinated action of cilia on longer columnar cells facing the lumen moves the mucus along with the particulate matter away from the lung.

Question 209

Describe Golblet Cells

Answer 209

• a specialized type of epithelial cell that secrete mucins, which are significant components of mucus
• most often found in the respiratory and gastrointestinal tracts, where they make up part of the surface epithelium. The secretion of mucus in these tracts lubricates and protects the lining of the organs
• The increased activity or number of goblet cells has been associated with some diseases.

Question 210

Describe club/clara cells

Answer 210

• Nonciliated bronchiolar epithelial cells found in the mucosa of the terminal bronchioles
• Secrete a club cell secretory protein which has antioxidant and immune-modulatory functions

Question 211

Describe the structure of bronchioles

Answer 211

• The epithelium here is ciliated and cuboidal but contains some Clara cells, which are non-ciliated and secrete proteinaceous fluid. Bronchioles contain no cartilage, meaning these airways must be kept open by radial traction, and there are no glands in the submucosa. The smooth-muscle layer is prominent. Adjusting the tone of the smooth-muscle layer alters airway diameter, enabling
  resistance to air flow to be effectively controlled.
  Made of Ciliated simple columnar epithelium.

Question 212

Describe the structure of respiratory bronchioles

Answer 212

The respiratory bronchioles are lined by ciliated cuboidal epithelium, which is surrounded by smooth muscle. Clara cells are present within the walls of the respiratory bronchioles. Goblet cells are absent but there are a few alveoli in the walls; thus, the respiratory bronchiole is a site for gaseous exchange.

Question 213

Describe the physical defence system of the lungs

Answer 213

• Filtering at the nasopharynx
• Swallowing
• Irritant C-fibre nerve endings (receptors stimulated which leads to contraction of the smooth muscle)
• Cough reflex
• Mucociliary clearance

Question 214

Describe the humoral defence system of the lungs

Answer 214

• Antimicrobial peptides (short protein structures, antibacterial, e.g. lysozymes)
• Surfactant (plays a role in defence, e.g. SpA)
• Immunoglobulins ( contained in mucus secretions, directed against specific antigens)
• Complement (high concentration during inflammation, propagates inflammatory response)
• Antiproteases (type of enzyme, breaks down destructive proteases released from e.g. neutrophils)

Question 215

Give 2 examples of cellular defence of the lungs

Answer 215

Alveolar macrophages
Neutrophils

Question 216

Give the function of alevolar macropahes

Answer 216

• Ingest bacteria by phagocytosis
• Initiate and amplify inflammatory response

Question 217

Give the function of neutrophils

Answer 217

• Predominant cells recruited in the acute inflammatory response
• Emigrate from intravascular space to alveolar lumen, and here intracellular killing of bacteria takes place ( 2 mechanisms, oxidative and non-oxidative)

Question 218

Define the Mucociliary Escalator

Answer 218

“Mucociliary clearance is an innate defense mechanism that protects the pulmonary system from the harmful consequences of inhaled agents, including those of biological, chemical, and physical
nature. Ciliated cells, which line the surface epithelium of the airways, provide the force necessary for mucociliary clearance by the coordinated beating of their cilia.”

Question 219

Describe the 2 layers of the mucus film

Answer 219

1. Periciliary fluid (sol) layer about 6 μm deep, immediately adjacent to the surface of the epithelium. The mucus here is hydrated by epithelial cells. This reduces its viscosity and allows movement of the cilia.
2. Superficial gel layer about 5–10 μm deep. This is a relatively viscous layer forming a sticky blanket, which traps particles.

Question 220

Describe the role of the cilia

Answer 220

• The cilia beat synchronously at 1000–1500 strokes per minute. Coordinated movement causes the superficial gel layer, together with trapped particles, to be continually transported towards the mouth at 1–3 cm/min. The mucus and particles reach the trachea and larynx where they are swallowed or expectorated.

Question 221

Which factors inhibit mucociliary clearance?

Answer 221

• Tobacco smoke
• Cold air
• Drugs e.g. general anaesthetic, so implications for this following surgery
  Cystic Fibrosis – ineffective mucociliary clearance

Question 222

Define the ‘cough reflex’

Answer 222

The cough reflex is an important defence mechanism which clears the airways of irritants by forcefully expelling air from the respiratory tract.

Question 223

Describe the inspiratory phase of the cough reflex

Answer 223

Irritation of cough receptors causes the vocal cords to open more widely, allowing more air to enter the lungs. The external intercostal muscles and diaphragm then contract causing expansion of the chest cavity, facilitating movement of air into the lungs, and increasing intra-thoracic pressure.

Question 224

Describe the compression phase of the cough reflex

Answer 224

The epiglottis and vocal cords close, trapping the air within the lungs. There is expiration against the closed epiglottis, causing a further increase in intra-thoracic pressure.

Question 225

Describe the expiratory phase of the cough reflex

Answer 225

The internal intercostal muscles and abdominal muscles contract to depress the thoracic cavity. The vocal cords relax, and the epiglottis opens. This releases the pressure from the lungs and causes air and the irritant to be rapidly expelled.

Question 226

Briefly describe the cough reflex arc

Answer 226

-Receptors: mechanical/chemical
-Afferent nerves
-Reflex Arc: cough centre: NTS medulla
-Efferent nerves
-Expiratory muscles: cough

Question 227

Describe the sensory afferent pathway of the cough reflex arc

Answer 227

• The cough reflex arc is initiated by irritation of cough receptors, for example, mechanoreceptors
  or chemoreceptors. Irritants are detected by these receptors and they send sensory
  information to afferent nerves. Receptors are found in the trachea, main carina, branching
  points of large airways, and more distal smaller airways; also, they are present in the pharynx.

Question 228

Describe the central pathway of the cough reflex arc

Answer 228

Sensory information travels to the nucleus tractus solitarius (NTS) of the medulla. The vagus
nerve then synapses with motor neurons, delivering information to effector muscles and
causing the cough reflex to occur.

Question 229

Describe the motor efferent pathway of the cough reflex arc

Answer 229

• Various respiratory muscles contract to allow initiation of the cough reflex.
• The diaphragm contracts to become flattened which increases the thoracic cavity space
• The laryngeal muscles contract to close the vocal cords
• The external intercostal muscles contract to change the space available in the thoracic cavity
• Rectus abdominis contracts to depress the rib cage and decrease space in the thoracic cavity

Question 230

Describe the muscocillary escalator and the role it plays in pulmonary defence (12 marks)

Answer 230

Mucociliary clearance deals with a lot of the large particles trapped in the bronchi and bronchioles and debris brought up by alveolar macrophages.
* Respiratory epithelium is covered by a layer of mucus secreted by goblet cells and submucosal glands.
* The mucus film is divided into two layers
* Periciliary fluid (sol) layer immediately adjacent to the surface of the epithelium. The mucus here is hydrated by epithelial cells. This reduces its viscosity and allows movement of the cilia.
* Superficial gel layer, a relatively viscous layer forming a sticky blanket, which traps particles.
* Coordinated movement of the cilia causes the superficial gel layer, together with trapped particles, to be continually transported towards the mouth
* The mucus and particles reach the trachea and larynx where they are swallowed or expectorated.

Question 231

Give the 3 processes of gaseous exchange

Answer 231

• Pulmonary ventilation
• External respiration
• Internal respiration

Question 232

Describe external respiration

Answer 232

• diffusion of O2 from air in the alveoli of the lungs to blood in pulmonary capillaries and the diffusion of CO2 in the opposite direction
• deoxygenated blood (depleted of some O2) coming from the right side of the heart is converted into oxygenated blood (saturated with O2) that returns to the left side of the heart
• blood flows through the pulmonary capillaries, picks up O2 from alveolar air and unloads CO2 into alveolar air
• each gas diffuses independently from the area where its partial pressure is higher to the area where its partial pressure is lower.

Question 233

Describe the saturation values of external respiration

Answer 233

• O2 diffuses from alveolar air, where its partial pressure is 105 mmHg, into the blood in pulmonary capillaries, where PO2 is only 40 mmHg in a resting person.
• If you have been exercising, the PO2 will be even lower because contracting muscle fibers are using more O2. Diffusion continues until the PO2 of pulmonary capillary blood increases to match the PO2 of alveolar air, 105 mmHg.
• Because blood leaving pulmonary capillaries near alveolar air spaces mixes with a small volume of blood that has flowed through conducting portions of the respiratory system, where gas exchange does not occur, the PO2 of blood in the pulmonary veins is slightly less than the PO2 in pulmonary capillaries, about 100 mmHg.
• While O2 is diffusing from alveolar air into deoxygenated blood, CO2 is diffusing in the opposite direction. The PCO2 of deoxygenated blood is 45 mmHg in a resting person, and the PCO2 of alveolar air is 40 mmHg. Because of this difference in PCO2, carbon dioxide diffuses from deoxygenated blood into the alveoli until the PCO2 of the blood decreases to 40 mmHg.
  Exhalation keeps alveolar PCO2 at 40 mmHg. Oxygenated blood returning to the left side of the heart in the pulmonary veins thus has a PCO2 of 40 mmHg.

Question 234

Describe internal respiration

Answer 234

• The left ventricle pumps oxygenated blood into the aorta and through the systemic arteries to systemic capillaries.
• The exchange of O2 and CO2 between systemic capillaries and tissue cells is called internal respiration or systemic gas exchange.
• As O2 leaves the bloodstream, oxygenated blood is converted into deoxygenated blood. Unlike external respiration, which occurs only in the lungs, internal respiration occurs in tissues throughout the body.

Question 235

Describe the saturation values of internal respiration

Answer 235

• The PO2 of blood pumped into systemic capillaries is higher (100 mmHg) than the PO2 in
  tissue cells (40 mmHg at rest) because the cells constantly use O2 to produce ATP. Due to this
  pressure difference, oxygen diffuses out of the capillaries into tissue cells and blood PO2
  drops to 40 mmHg by the time the blood exits systemic capillaries.
• CO2 diffuses in the opposite direction. Because tissue cells are constantly producing CO2, the
  PCO2 of cells (45 mmHg at rest) is higher than that of systemic capillary blood (40 mmHg). As
  a result, CO2 diffuses from tissue cells through interstitial fluid into systemic capillaries until
  the PCO2 in the blood increases to 45 mmHg. The deoxygenated blood then returns to the
  heart and is pumped to the lungs for another cycle of external respiration.

Question 236

Describe the composition of proteins

Answer 236

Proteins are complex macromolecules (polymers). They have high molecular weight and are made up of structural units (monomers) called amino acids.
Amino acids are the protein’s building units. They are organic compounds made up of hydrogen, oxygen, carbon and nitrogen atoms. Amino acids are made up of a basic group (amino group NH2), an acidic group (carboxyl group COOH), a hydrogen atom, and a terminal group R which differs from one amino acid to another.
* Amino group, carboxyl group, R group (changes)
* The combination of two amino acids is called a dipeptide compound, and the protein chain formed of several amino acids is called a polypeptide.

Question 237

How much oxygen is transported in blood plasma?

Answer 237

1.5% (due to the relative insolubility of oxygen in water)

Question 238

How much oxygen is transported in red blood cells/haemoglobin?

Answer 238

98.5%

Question 239

Describe the structure of haemoglobin

Answer 239

• Haemoglobin is a globular protein which is an oxygen-carrying pigment found in vast quantities in red blood cells
• It has a quaternary structure as there are four polypeptide chains. These chains or subunits are globin proteins (two α–globins and two β–globins) and each subunit has a prosthetic haem group
• The four globin subunits are held together by disulphide bonds and arranged so that their hydrophobic R groups are facing inwards (helping preserve the three-dimensional spherical
  shape) and the hydrophilic R groups are facing outwards (helping maintain its solubility)
• The arrangements of the R groups is important to the functioning of haemoglobin. If changes occur to the sequence of amino acids in the subunits this can result in the properties of haemoglobin changing.
• The prosthetic haem group contains an iron II ion (Fe2+) which is able to reversibly combine with an oxygen molecule forming oxyhaemoglobin and results in the haemoglobin appearing
  bright red
• Each haemoglobin with the four haem groups can therefore carry four oxygen molecules (eight oxygen atoms)

Question 240

What is the function of haemoglobin?

Answer 240

Haemoglobin is responsible for binding oxygen in the lung and transporting the oxygen to tissue to be used in aerobic metabolic pathways
As oxygen is not very soluble in water and haemoglobin is, oxygen can be carried more efficiently around the body when bound to the haemoglobin

Question 241

Give the function of the ferrous group

Answer 241

• The presence of the haem group (and Fe2+) enables small molecules like oxygen to be bound more easily because as each oxygen molecule binds it alters the quaternary structure (due to alterations in
  the tertiary structure) of the protein which causes haemoglobin to have a higher affinity for the subsequent oxygen molecules and they bind more easily
• The existence of the iron II ion (Fe2+) in the prosthetic haem group also allows oxygen to reversibly bind as none of the amino acids that make up the polypeptide chains in haemoglobin are well suited to binding with oxygen

Question 242

Describe the affinity of haemoglobin for carbon monxide compared to oxygen

Answer 242

• The affinity of haemoglobin for carbon monoxide is 245-fold higher than that for oxygen Therefore, haemoglobin will preferentially bind irreversably to carbon monoxide over oxygen following an exposure.
• This decreases the oxygen carrying capacity of the blood and alters the dissociation curve of oxyhaemoglobin.
  As a result, the rate at which oxygen is delivered to cells is reduced, interfering with cellular respiration and causing tissue hypoxia.

Question 243

Describe the relatishsp between haemoglobin and the partial pressure of oxygen

Answer 243

The higher the PO2, the more O2 combines with Hb.

Question 244

Give the 3 ways carbon dioxide is transported throughout the body

Answer 244

-Dissolved in blood - 7%
-Carbamino compounds - 23%
-Bicarbonate ions – 70%

Question 245

Describe the transport of carbon dioxide dissolved in the blood

Answer 245

CO2 is dissolved in blood plasma. On reaching the lungs, it diffuses into alveolar air and is exhaled.

Question 246

Describe the transport of carbon dioxide in carbamino compounds

Answer 246

CO2 combines with the amino groups of amino acids and proteins in blood to form carbamino compounds.
Because the most prevalent protein in blood is haemoglobin (inside red blood cells), most of the CO2 transported in this manner is bound to haemoglobin.
The main CO2 binding sites are the terminal amino acids in the two alpha and two beta globin chains.
Haemoglobin that has bound CO2 is termed carbaminohaemoglobin (Hb–CO2).
The formation of carbaminohaemoglobin is greatly influenced by PCO2. For example, in tissue capillaries
PCO2 is relatively high, which promotes formation of carbaminohaemoglobin. But in pulmonary capillaries,
PCO2 is relatively low, and the CO2 readily splits apart from globin and enters the alveoli by diffusion.

Question 247

Describe the transport of carbon dioxide in bicarbinate ions

Answer 247

As CO2 diffuses into systemic capillaries and enters red blood cells, it reacts with water in the presence of the enzyme carbonic anhydrase (CA) to form carbonic acid, which dissociates into H+ and HCO3−:
Thus, as blood picks up CO2, HCO3− accumulates inside RBCs. Some HCO3− moves out into the blood plasma, down its concentration gradient.
In exchange, chloride ions (Cl−) move from plasma into the RBCs. This exchange of negative ions, which maintains the electrical balance between blood plasma and RBC cytosol, is known as the chloride shift.
The net effect of these reactions is that CO2 is removed from tissue cells and transported in blood plasma as HCO3−. As blood passes through pulmonary capillaries in the lungs, all of these reactions reverse and CO2 is exhaled.

Question 248

Describe and explain the shape of an oxygen dissociation curve

Answer 248

• When the PO2 is high, haemoglobin binds with large amounts of O2 and is almost 100% saturated. When PO2 is low, haemoglobin is only partially saturated. In other words, the greater the PO2, the more O2 will bind to haemoglobin, until all the available haemoglobin molecules are saturated.
• In pulmonary capillaries, where PO2 is high, a lot of O2 binds to haemoglobin (has high affinity for oxygen). In tissue capillaries, where the PO2 is lower, haemoglobin does not hold as much O2, and the dissolved O2 is unloaded via diffusion into tissue cells (hb has low affinity for oxygen)
• Note that haemoglobin is still 75% saturated with O2 at a PO2 of 40 mmHg, the average PO2 of tissue cells in a person at rest, only 25% of the available O2 unloads from haemoglobin and is used by tissue cells under resting conditions.
• When the PO2 is between 60 and 100 mmHg, haemoglobin is 90% or more saturated with O2 , thus, blood picks up a nearly full load of O2 from the lungs even when the PO2 of alveolar air is as low as 60 mmHg. The Hb–PO2 curve explains why people can still perform well when they have certain cardiac and pulmonary diseases, even though PO2 may drop as low as 60 mmHg.
• Note also in the curve that at a considerably lower PO2 of 40 mmHg, haemoglobin is still 75% saturated with O2. However, oxygen saturation of Hb drops to 35% at 20 mmHg.
• Between 40 and 20 mmHg, large amounts of O2 are released from haemoglobin in response to only small decreases in PO2. In active tissues such as contracting muscles, PO2 may drop well below 40 mmHg. Then, a large percentage of the O2 is released from haemoglobin, providing more O2 to
  metabolically active tissues.

Question 249

GIve factors which affect the affinity of haemoglobin for oxygen

Answer 249

Acidity
Partial pressure of Carbon Dioxide
Temperature
BPG

Question 250

Explain how acidity affects haemoglobin affinity

Answer 250

• When pH decreases (CO2 conc increases), the entire oxygen–haemoglobin dissociation curve shifts to the right; at any given PO2, Hb is less saturated with O2, a change termed the Bohr effect.
• The Bohr effect works both ways: An increase in H+ in blood causes O2 to unload from haemoglobin, and the binding of O2 to haemoglobin causes unloading of H+ from haemoglobin.
• The explanation for the Bohr effect is that haemoglobin can act as a buffer for hydrogen ions (H+). But when H+ ions bind to amino acids in haemoglobin, they alter its structure slightly, decreasing its oxygen-carrying capacity.
• Thus, lowered pH drives O2 off haemoglobin, making more O2 available for tissue cells. By contrast, elevated pH increases the affinity of haemoglobin for O2 and shifts the oxygen–haemoglobin dissociation curve to the left.

Question 251

Describe how concentration of CO2 affects haemoglobin affinity

Answer 251

CO2 also can bind to haemoglobin, and the effect is similar to that of H+ (shifting the curve to the right). As PCO2 rises, haemoglobin releases O2 more readily (lower affinity).
* PCO2 and pH are related factors because low blood pH (acidity) results from high PCO2. As CO2 enters the blood, much of it is temporarily converted to carbonic acid (H2CO3), a reaction catalyzed by an enzyme in red blood cells called carbonic anhydrase (CA):
* The carbonic acid thus formed in red blood cells dissociates into hydrogen ions and bicarbonate ions. As the H+ concentration increases, pH decreases. Thus, an increased PCO2 produces a more acidic environment, which helps release O2 from haemoglobin. During exercise, lactic acid—a by-product of anaerobic metabolism within muscles—also decreases blood pH. Decreased PCO2 (and elevated pH) shifts the saturation curve to the left

Question 252

Describe how temperature affects affinity of haemoglobin

Answer 252

• As temperature increases, so does the amount of O2 released from haemoglobin.
• Heat is a by-product of the metabolic reactions of all cells, and the heat released by contracting muscle fibres tends to raise body temperature.
• Metabolically active cells require more O2 and liberate more acids and heat.
• The acids and heat in turn promote release of O2 from oxyhaemoglobin.
• Fever produces a similar result. In contrast, during hypothermia (lowered body temperature) cellular metabolism slows, the need for O2 is reduced, and more O2 remains bound to haemoglobin (a shift to the left in the saturation curve).

Question 253

Describe how temperature affects affinity of haemoglobin

Answer 253

• As temperature increases, so does the amount of O2 released from haemoglobin.
• Heat is a by-product of the metabolic reactions of all cells, and the heat released by contracting muscle fibres tends to raise body temperature.
• Metabolically active cells require more O2 and liberate more acids and heat.
• The acids and heat in turn promote release of O2 from oxyhaemoglobin.
• Fever produces a similar result. In contrast, during hypothermia (lowered body temperature) cellular metabolism slows, the need for O2 is reduced, and more O2 remains bound to haemoglobin (a shift to the left in the saturation curve).

Question 254

Describe how BPG affects affinity of haemoglobin

Answer 254

• A substance found in red blood cells called 2,3-bisphosphoglycerate (BPG) decreases the affinity of
  haemoglobin for O2 and thus helps unload O2 from haemoglobin.
• BPG is formed in red blood cells when they break down glucose to produce ATP in a process called
  glycolysis
• When BPG combines with haemoglobin by binding to the terminal amino groups of the two beta globin chains, the haemoglobin binds O2 less tightly at the haem group sites. The greater the level of BPG, the more O2 is unloaded from haemoglobin. Certain hormones, such as thyroxine, human growth hormone, epinephrine, norepinephrine, and testosterone, increase the formation of BPG.

Question 255

Give the normal values for arteriole blood gases

Answer 255

• pH: 7.35 – 7.45
• pO2: 10 – 14kPa
• pCO2: 4.5 – 6kPa
• Base excess (BE): -2 – 2 mmol/l
• HCO3: 22 – 26 mmol/l
• SaO2 = 95-100%

Question 256

Define ‘oxygen uptake’

Answer 256

Oxygen uptake (VO2) is the amount of oxygen that the body takes up and utilizes.

Question 257

How is oxygen uptake measured?

Answer 257

Oxygen uptake can be measured by gas analysis of the oxygen content of inspired air vs. the oxygen content of expired air.
During exercise at a constant workload, VO2 increases exponentially at the start of exercise until it reaches the point at which oxygen supply matches oxygen demand and then it plateaus, this plateau is termed steady-state.

Question 258

Define ‘maximal oxygen uptake’

Answer 258

Maximal oxygen uptake (VO2max) is the maximal amount of oxygen that the body can uptake and
utilize and is the gold standard measure of exercise capacity. VO2max is the point at which oxygen
uptake plateaus and shows no further increase in response to additional workload.

Question 259

Which factors can affect VO2 max?

Answer 259

Gender
Height
Weight
Lung function
Fitness level
Activity they are performing. VO2max is exercise-specific and is greater for activities involving large muscle groups.

Question 260

Define ‘Global Oxygen Delivery’

Answer 260

Global oxygen delivery (DO2) is the total amount of oxygen delivered to the tissues in the entire body per minute, regardless of the distribution of blood flow. It is the product of total blood flow or cardiac output (CO) and the oxygen content of arterial blood and is usually expressed in ml O2/min.

Question 261

How is oxygen delivery calculated

Answer 261

Oxygen Delivery (mL O2/min) = CaO2 x CO

Question 262

How is carbon dioxide transported around the body (6 marks)

Answer 262

Under normal resting conditions, each 100 mL of deoxygenated blood contains the equivalent of 53 mL of gaseous CO2, which is transported in the blood in three main forms.
Dissolved in plasma 7%
Combined with globin carbaminoglobin 23%
Dissolved in plasma as bicarbonate ions 70%
Carbon dioxide plus water in presence of carbonic anhydrase forms carbonic acid dissociates into hydrogen ions

Question 263

Define ‘homeostasis’

Answer 263

“Homeostasis is the state of steady internal chemical and physical conditions maintained by living systems.”

Question 264

What is a chemoreceptor?

Answer 264

• Cell that responds to chemical compounds to give an impulse to a sensory nerve, Two sets of chemoreceptors
• Oxygen receptors which are in the peripheral nervous system
• Carbon dioxide receptors which are found both peripherally and centrally

Question 265

What is a mechanoreceptor?

Answer 265

• Mechanoreceptors are sensory receptors that respond to mechanical deformation of the receptor or surrounding tissue.

Question 266

What are stretch receptors?

Answer 266

Respond to the stretching of muscles by giving impulses to the central nervous system (CNS)

Question 267

What are proprioreceptors?

Answer 267

Cells that monitor body changes brought about by muscular movement to give an impulse to the central nervous system to co-ordinate movement.

Question 268

What are juxtacapillary receptors?

Answer 268

Cells that cause an increase in breathing rate as reflex response, thought to be involved in the sensation of dyspnea.

Question 269

What is a nociceptor?

Answer 269

Cells that respond to a pain stimulus by giving impulses to the central nervous system.

Question 270

Define nucleus

Answer 270

Nucleus is a collection of neuronal cell bodies within the central nervous system.
The neurons in one nucleus usually have roughly similar connections and functions.
Nuclei are connected to other nuclei by tracts, the bundles (fascicles) of axons (nerve fibers) extending from the cell bodies.

Question 271

Describe the Pneumotaxic Centre

Answer 271

• is in the upper aspect of the pons
• controls the fine tuning of respiratory rate and depth.
• sends signals inferiorly and can influence the VRG (expiratory centre)and DRG (inspiratory centre)
• Inhibits inspiration, which allows for the transition from inspiration to expiration.
• It decreases tidal volume.
• Transitioning occurs as a response to stimulus from peripheral receptors

Question 272

Describe the Apneustic Centre

Answer 272

• controls prolonged breathing
• receives peripheral stimulus from stretch receptors
• sends signals to the VRG and DRG to trigger inspiration
• It increases tidal volume
• If there is damage to the Pneumotaxic Centre the DRG and VRG would only receive signals from the Apneustic Centre,it cannot inhibit transition from inspiration to expiration, and undergoes prolonged inspiration called apneustic breathing

Question 273

Describe the Dorsal Respiratory Group DRG (inspiratory)

Answer 273

• is located in medial aspect within the medulla
• Has two functions
  o Receives peripheral stimulus signals from the stretch receptors, proprioceptors,
  Juxtacapillary receptors, and both central and peripheral chemoreceptors.
  o Sends signals to the external intercostals and diaphragm to cause inspiration

Question 274

Describe the Ventral Respiratory Group VRG (expiratory)

Answer 274

Is in the anterior aspect of the medulla
o Controls expiration via sending expiratory signals

Question 275

What do chemoreceptors respond to?

Answer 275

• Chemoreceptors monitor blood gas tensions, PaCO2, PaO2 and pH, and help keep minute volume appropriate to the metabolic demands of the body. Therefore, chemoreceptors respond to:
  *Hypercapnia
  *Hypoxia
  *Acidosis.
• The most important factor controlling the rate and depth of breathing is the effect of carbon dioxide on the central chemoreceptors.

Question 276

Describe the role of central chemoreceptors

Answer 276

o 80% of the drive for ventilation is a result of stimulation of the central chemoreceptors.
o When they are inactivated, respiration ceases.
o These receptors are readily depressed by drugs (e.g., opiates and barbiturates).
o respond to hydrogen ion concentration within the surrounding brain tissue and cerebrospinal fluid (CSF) and low partial pr0essure of oxygen (less than 60mmHg)
* Raised hydrogen ion concentration increases ventilation.
* Lowered hydrogen ion concentration decreases ventilation.
* Increase in pCO2 levels leads to increased carbonic acid in CSF. This leads to increase in protons in CSF. Central chemoreceptors are stimulated, leads to increased ventilation and increase in blood pH, bringing it back to normal level.

Question 277

Describe the location of central chemoreceptors

Answer 277

o located in the brainstem on the ventrolateral surface of the medulla
o they are anatomically separate from the medullary respiratory control centre.

Question 278

Describe the role of peripheral chemorecptors

Answer 278

Stimulation of peripheral chemoreceptors
has both cardiovascular and respiratory effects. Of the two receptor groups, the carotid bodies have the greatest effect on respiration.

Question 279

Describe the location of peripheral chemoreceptors

Answer 279

Carotid sinus and aortic arch

Question 280

What are peripheral chemorecptors sensitive to?

Answer 280

PaO2
*PaCO2
*pH
*Blood flow
*Temperature.

Question 281

Describe the carotid bodies

Answer 281

• The carotid bodies contain two different types of cells. Type I and Type II cells
• There is a rich blood supply to the carotid bodies (blood flow per mass of tissue far exceeds that to the brain); venous blood flow, therefore, remains saturated with oxygen.
• It is believed that type I (glomus) cells are activated by hypoxia and release transmitter substances that stimulate afferents to the brainstem.

Question 282

List stimuli that increase breathing rate and depth

Answer 282

Voluntary hyperventilation
Increase in arterial blood PCO2 above 40 mmHg/H+
Decrease in arterial blood PO2 from 105 mmHg to 50mmHg
Increased activity of propriorecpetors
Increased body temperature
Prolonged pain
Decreased blood pressure
Stretching of anal sphincter

Question 283

List stimuli that decrease breathing rate/depth

Answer 283

Voluntary hypoventilation
Decrease in arterial blood PCO2 below 40mmHg/H+
Decrease in arterial blood PO2 below 50 mmHg
Decreased activity of propriorecetors
Decrease in body temperature/sudden cold stimulus (causes apnea)
Severe pain (causes apnea)
Increase in blood pressure
Irritation of phharynx/larynx (causes apnea)