Cardiovascular And Respiratory

Question 1

How does blood flow through the heart?

Answer 1

1) Deoxygenated blood enters the right atrium of the heart through the vena cava and then passes through the tricuspid valve into the right ventricle. It is then ejected through the pulmonary valve and the pulmonary artery into the lungs.
2) Oxygenated blood from the lungs enters the left atrium of the heart through the pulmonary veins and then passes through the mitral valve into the left ventrcile. It is then ejected through the aortic valve and the aorta into the body.

Question 2

What are the semilunar valves?

Answer 2

The aortic and the pulmonary valves are collectively known as the semilunar valves. They are located between the ventricles and the major outflow vessels; aorta and pulmonary artery.

Question 3

What are the atrioventricular valves?

Answer 3

The mitral (bicuspid) and tricuspid valves are collectively known as the atrioventricular valves. They are located between the atria and the ventricles. The mitral valve is in the left ventricle and the tricuspid valve in the right ventricle.

Question 4

What is the function of the internodal tracts?

Answer 4

These tracts are composed of specialised conducting fibres that transmit the electrical signal along the myocardium of the atria.

Question 5

What is the function of the sinoatrial (SA) node?

Answer 5

This nodes generates the primary pacemaking signal, and is located in the upper wall of the right atrium.

Question 6

What is the function of the Purkinje fibres?

Answer 6

Electrical activation of these specialised conducting fibres results in contraction of the ventricles.

Question 7

What is the function of the atrioventricular node?

Answer 7

Like the SA node, the AV node also has pacemaker activity. Transmission through this node corresponds to the P-R interval in the electrocardiogram (ECG).

Question 8

What is the function of the bundle of His

Answer 8

This is a collection of myocytes (specialised muscle cells) that lie in the interventricular septum and also contribute to the P-R interval of the ECG. They transmit electrical impulses from the AV node to the point of the apex of the fascicular branches via the bundle branches at the intraventricular septum.

Question 9

How can the main anatomical features of the heart be broadly categorised?

Answer 9

The main anatomical components of the heart can be broadly categorised as:

1) Muscle cells (cardio-myocytes): can contract and relax in response to electrical stimuli. Essential for pumping blood around the body
2) Specialised electrical cells: cells that create spontaneous currents and those that transmit currents exist within the heart. Essential for regulating contraction of the cardio-myocytes
3) Vessels: the major blood vessels are responsible for transporting blood in and out of the heart, whilst the coronary blood vessels are responsible for supplying blood to the heart

Question 10

What is the Sinoatrial (SA) node?

Answer 10

This is the pacemaker of the heart: usually beating at ~60-100 bpm. It is located at the junction of crista terminalis; upper wall of right atrium & opening of superior vena cava.

Question 11

What is the Atrioventricular (AV) node?

Answer 11

This also has pacemaker activity: slow calcium mediated action potential, but it is usually the SA node that controls heart beat. It is located at the Triangle of Koch at the base of right atrium.

Question 12

What are the Bundle of His & bundle branches?

Answer 12

These are internodal tracts (connect the AV and SA nodes) made of specialised myocytes. From the AV node: Bundle of His leads to the branches at the intraventricular septum, which lead to the apex.

Question 13

What are the Purkinje fibres?

Answer 13

These are specialised conducting fibres, which propagate the electrical current along the ventricles of the heart.

Question 14

Outline nodal cell action potential (AP)

Answer 14

• Nodal AP only has 3 phases (0, 3 & 4)
• Upstroke (⇡) due to Ca2+ influx
• Repolarisation (⇣) due to K+ efflux
• Nodal cells do not have a resting membrane potential - only a pre-potential, which is due to Na+ influx through a ‘funny’ channel

Question 15

What are action potential profiles?

Answer 15

Different parts of the heart have different action potential shapes. This is caused by different ion currents flowing and different ion channel expression in cell membrane.

Question 16

Outline cardiac (ventricular) muscle action potential

Answer 16

• Compared to nerves, cardiac AP is long (200-300 ms vs. 2-3 ms)
• Duration of AP controls duration of contraction of heart
• Long, slow contraction is required to produce an effective pump
• AP has 5 phases numbered 0(upstroke), 1 (early repolarisation), 2 (plateau), 3 (repolarisation) and 4 (resting membrane potential)
• Absolute refractory period (ARP) = time during which no AP can be initiated regardless of stimulus intensity
• Relative refractory period (RRP) = period after ARP where an AP can be elicited but only with larger stimulus strength

Question 17

What are the 3 main exogenous systems able to modulate the activity of the heart?

Answer 17

1) The brain/central nervous system: can effect immediate changes through nerve activity or slower changes through hormonal activity
2) The kidneys: the heart and kidneys share a bi-directional regulatory relationship usually through indirect mechanisms
3) The blood vessels: by regulating the amount of blood that goes to and from the heart the blood vessels are able to influence cardiac activity.

Question 18

What is the autonomic nervous system?

Answer 18

This system consists of 2 components: the cardio-regulatory centre & the vasomotor centres in the medulla.

Question 19

What is the function of the parasympathetic nervous system?

Answer 19

This is known as the ‘Rest & digest’ system. When activated, it decreases heart rate (HR), by affecting the pre-potential of the AP within the SA nodal cell, thus decreasing the slope of phase 4. It leaves from the medulla and goes via the vagus nerve to the heart.

Question 20

What is the function of the sympathetic nervous system?

Answer 20

This is known as the ‘fight or flight’ response. It increases heart rate (HR), known as positive chronotropy, by increasing the slope of phase 4, which causes determines how quick the return to the repolarisation phase can be, thus causing a decrease in time. The force of contraction (inotropy) – increases Ca2+ dynamics.

Question 21

Outline the anatomy of the PNS

Answer 21

1) The parasympathetic nerves arise from the cranial and sacral parts of the spinal chord.
2) Pre-ganglionic fibres use acetylcholine (ACh) as neurotransmitter
3) PNS post ganglionic neurotransmitter is ACh
4) PNS is important for controlling the heart rate

Question 22

Outline the anatomy of the SNS

Answer 22

1) The sympathetic nerves arise from the thoracic vertebra and the lumbar vertebra.
2) Pre-ganglionic fibres use ACh as their neurotransmitter
3) SNS post ganglionic neurotransmitter is noradrenaline
4) Nicotinic ACh receptors transmit the signal to the pre- to the post-ganglionic nerves in the SNS
5) SNS is important for controlling the circulation

Question 23

Where is the vasomotor centre (VMC) located?

Answer 23

The VMC is located bilaterally in reticular substance of medulla & lower third of pons.

Question 24

What is the vasomotor centre (VMC) composed of?

Answer 24

It is composed of:

1) Vasoconstrictor (pressor) area
2) Vasodilator (depressor) area
3) Cardio-regulatory inhibitory area

Question 25

What is the function of the vasomotor centre (VMC)?

Answer 25

The VMC transmits impulses distally through spinal cord to almost all blood vessels.

Question 26

What effect do higher centres of the brain have on the VMC?

Answer 26

Many higher centers of the brain, such as the hypothalamus, can exert powerful excitatory or inhibitory effects on the VMC.

Question 27

What do the lateral portions of the VMC control?

Answer 27

The lateral portions of VMC control heart activity by influencing heart rate and contractility.

Question 28

What is the function of the medial portion of the VMC?

Answer 28

The medial portion of VMC transmits signals via the vagus nerve to heart, these tend to decrease heart rate.

Question 29

Outline cardiac innervation

Answer 29

The PNS inhibits the SA node, whilst the SNS stimulates the SA node:

1) In the PNS input, ACh acts on M2 Muscarinic receptors on the cell membrane of a SA nodal cell. Via the G-protein, known as the GI protein, it causes the inhibition of adenylyl cyclase, which converts or prevents the conversion of ATP to protein kinase A (PKA).
2) In the SNS input, noradrenaline (NA) acts on beta-1-receptors on the cell membrane of a SA nodal cell. Via the G-protein, known as the GS protein, it causes the stimulation adenylyl cyclase, which converts ATP to PKA.

Question 30

How do the kidneys regulate heart function?

Answer 30

The heart and kidneys share a bi-directional regulatory relationship usually through indirect mechanisms (i.e. the CNS & the blood vessels). In terms of exogenous regulation of the heart, the kidneys regulate blood volume and can impact blood pressure. It is through these ‘intermediaries’ that the kidneys regulate cardiac function, it does not have a direct impact on the heart.

Question 31

How does the the CNS affect the kidneys?

Answer 31

Afferent sympathetic nerves innervated the kidneys. These nerve increase renal activity activity, by decreasing glomerular filtration, which then decreases Na+ excretion: thereby increasing blood volume, using the hormone aldosterone.

Question 32

How does a change in renal blood volume affect cardiac function?

Answer 32

The change in blood volume, as a result of the SNS activities, will then go on to have an impact on cardiac function. The blood volume is detected by venous volume receptors

Question 33

How does SNS affect renal blood pressure?

Answer 33

The SNS also causes an increase in renin secretion, which leads to an increase in angiotensin-II production: thereby causing vasoconstriction & increasing blood pressure. This change in blood pressure will also have an impact on cardiac function. Angiotensin-II also causes the release of aldosterone, which has an impact on blood volume.

Question 34

What do sympathetic nerves innervated in the kidneys?

Answer 34

Sympathetic nerve fibres innervate both the afferent & efferent arterioles of the glomerulus and nephron tubule cells.

Question 35

Outline the function of the afferent arteriolar of the glomerulus

Answer 35

1) These are the primary site of sympathetic activity, noradrenaline activates the alpha-1-adrenoceptor and causes vasoconstriction. Vasoconstriction causes a reduction in the glomerular filtration rate, which reduces the amount Na+ to filtered, thereby increasing blood volume. This leads to increased chronotropy (heart beat) and inotropy (muscle contraction).
2) Juxtaglomerular cells are the site of synthesis, storage & release of renin. The sympathetic nerves act on beta-1-adrenoceptors, which stimulate renin secretion. This subsequently increases aldosterone secretion and thereby also blood volume.

Question 36

How do blood vessels affect cardiac function?

Answer 36

Similar to the kidneys, the heart and the blood vessels share a bi-directional regulatory relationship usually through indirect mechanisms (i.e. the CNS & the kidneys). In terms of exogenous regulation of the heart, the blood vessels regulate blood pressure and blood volume, which impacts cardiac function.

Question 37

What are the 2 main circuits of blood vessels?

Answer 37

1) The cardiopulmonary circuit - large pulmonary vessels

2) The arterial circuit - aortic arch, carotid sinus & afferent arterioles of kidneys

Question 38

Outline the function of the cardiopulmonary circuit

Answer 38

1) These are large vessels that act as volume sensors (also atria & right ventricle): they send signals though glossopharyngeal & vagus nerves.
2) A decrease in filling (caused by blood vessels) causes a decrease in baroreceptor firing, leading to an increase in sympathetic nerve (SNS) activity. This then increases heart rate.
3) Distention (increase in filling) caused an increase in baroreceptor firing, causing a decrease in SNS activity. This then decreases heart rate.

Question 39

Outline the function of the arterial circuit

Answer 39

1) These are vessels that act as pressure sensors: they send signals through the glossopharyngeal & vagus nerves.
2) A decrease in pressure causes a decrease in baroreceptor firing, which leads to an increase in SNS activity. This then leads to increased heart rate.
3) An increase in pressure causes an increase in baroreceptor firing, which leads to a decrease in SNS activity. This then leads to decreased heart rate.

Question 40

What are the 2 circulations in the body?

Answer 40

The two circulations are the pulmonary and the systemic.

Right heart —> lungs —> left heart —> body.

Question 41

What affects venous volume distribution?

Answer 41

The veins and venules contain 61% of the blood in the body.

Venous volume distribution is affected by peripheral venous tone, gravity, skeletal muscle pump & breathing.

Question 42

What does central venous pressure determine?

Answer 42

Central venous pressure (mean pressure in the right atrium) determines amount of blood flowing back to heart (filling and distention). This in turn determines stroke volume (using Starling’s Law of the Heart). Increased central venous pressure will. Abuse an immediate increase in baroreceptor firing.

Question 43

What does constriction determine in veins?

Answer 43

In veins, constriction reduces compliance and increases venous return.

Question 44

What does constriction determine in arterioles?

Answer 44

The arterioles and capillaries only contain 7%, constriction determines:

1) Blood flow to downstream organs
2) Mean arterial blood pressure
3) The pattern of blood flow to organs

Question 45

What are the local mechanisms for regulating blood flow?

Answer 45

These are intrinsic to the smooth muscle (or closely associated. They are important for reflex local blood flow regulation within an organ.

Question 46

What are the endothelium-derived mediators in local mechanisms of blood flow regulation?

Answer 46

1) Nitric oxide (NO): potent vasodilator, which diffuses into vascular smooth muscle cells.
2) Prostacylin: vasodilator that also has antiplatelet & anticoagulant effects
3) Thromboxane A2 (TXA2): vasoconstrictor that is also heavily synthesised in platelets
4) Endothelins (ET): vasoconstrictors generated from nucleus of endothelial cells

Question 47

What are are the systemic mechanisms for regulating blood flow?

Answer 47

These are extrinsic to the smooth muscle and include the autonomic nervous system & circulating hormones.

Question 48

What are the non-endothelium-derived mediators in systemic mechanisms of blood flow regulation?

Answer 48

1) Kinins: bind to receptors on endothelial cells & stimulate NO synthesis – vasodilator effects
2) Atrial natriuretic peptide (ANP): secreted from the atria in response to stretch – vasodilator effects to reduce BP
3) Vasopressin (ADH): secreted from pituitary gland. Binds to V1 receptors on smooth muscle to cause vasoconstriction
4) Noradrenaline/Adrenaline: secreted from adrenal gland (& SNS); causes vasoconstriction
5) Angiotensin II: potent vasoconstrictor from the renin-angiotensin-aldosterone axis. Also stimulates ADH secretion.

Question 49

What are the 4 distinct groups of nuclei found in the medulla oblongata essential for breathing?

Answer 49

The 4 distinct groups of nuclei found in the pontine and medullary regions, important to the generation control of the intrinsic rate and rhythm of breathing are the:

1) Dorsal respiratory group (medullary) - Inspiratory centre, main ‘controller’ of inspiration, set the ‘rate’ of breathing. Works synergistically and antagonistically with the ventral respiratory group m
2) Ventral respiratory group (medullary) - Expiratory centre, inactive during quiet breathing. Inhibits apneustic centre
3) Apneustic centre (pontine) - Stimulates activity in DRG, inhibited by pulmonary afferents
4) Pneumotaxic centre (pontine) - The ‘inspiratory off switch’, regulates depth & frequency

DIVE: Dorsal Inspire Ventral Expire

Question 50

Outline the relationships between the groups of the medulla oblongata

Answer 50

1) As inspiration and expiration cannot occur simultaneously, both groups act as an inhibitor to the other.
2) The apnuestic centre stimulates and activates the dorsal respiratory group.
3) The pneumotaxic centre inhibits the dorsal respiratory group.
4) The ventral respiratory group inhibits the apneustic centre.

Question 51

Outline the respiratory pacemaker - quiet breathing

Answer 51

1) As action potentials come in at a given amplitude and frequency, the frequency ramps up steadily, until it activates the pneumotaxic centre. 2) This creates a cessation of the rhythm, so inspiration ceases to occur.
3) After a period of latency, the apneustic centre, starts to help programme the rhythm into the dorsal respiratory group.

Question 52

Outline the innervation of the diaphragm

Answer 52

C3,C4 and C5 are responsible for what becomes the phrenic nerve. Arising from these spinal and coalescing into a single nerve fibre is the main motor nerve that innervates the diaphragm.

Question 53

Outline the function and location of the intercostal muscles

Answer 53

The internal and external intercostal muscles, sitting between the ribs. The external intercostal muscles are attached to the lateral aspects of the ribs and are responsible for inspiration. The internal intercostal muscles are responsible for expiration.

Question 54

Outline chemosensitivity in the medulla

Answer 54

1) In normal circulation, there is “continuous capillaries”. Although there is a certain amount of space (water-filled gap junction) between the capillaries that are not at the endothelial cells, they are not technically fenestrations/holes/big gaps, so the capillaries are deemed continuous.
2) The blood-brain barrier (BBB) is also formed of “continuous capillaries”, however, there’s a supporting feature creating tight junctions. Nerve cells help more tightly pack the capillary endothelial cells to prevent any leakage from the cells. This restricts the substances that can come out of the blood and enter the cerebrospinal fluid (CSF) and into brain tissue.

Question 55

What is the importance of carbonic acid in breathing?

Answer 55

Carbon dioxide and water can combine to form carbonic acid, which can dissociate into protons and bicarbonate. These protons create the drive to breathe, as they are a product of metabolism. If the energy created by tissues increases or decreases, this directly results in a change in proton concentration, which the body needs to mitigate for.

Question 56

Can protons and bicarbonate cross the BBB?

Answer 56

Protons and bicarbonates (HCO3-) are charged molecules, so are unable to diffuse across the lipid bilayer of the endothelial cells. Moreover, the cells lack the channels required to be able to process the molecules across.

Question 57

How are protons and bicarbonate produced in the CSF?

Answer 57

Protons and bicarbonate exist in equilibrium with dissolved carbon dioxide, in the capillaries. Carbon dioxide is able to freely diffuse across the BBB. Once beyond the BBB, carbon dioxide can participate in a reaction with water to form protons and bicarbonate.

Question 58

What is the function of the protons generated in the CSF?

Answer 58

The protons generated in the CSF can then interact with the afferent fibres in the medulla, to take the signal straight to the dorsal respiratory group to determine the type of rate and rhythm that should be created.

Question 59

What are irritant receptors?

Answer 59

These are afferent receptors embedded within and beneath the airway epithelium of the trachea. Stimulation of these receptors leads a short reflex that results in coughing: which involves forceful expiration against a closed glottis with sudden glottal opening & high velocity expulsion of air.

Question 60

What are stretch receptors?

Answer 60

These are afferent receptors stimulated during excessive inflation of the lungs. They send signals to respiratory centres to inhibit the dorsal respiratory group and apneustic centre and stimulate pneumotaxic ventral respiratory group. Inspiration inhibited & expiration stimulated

Question 61

What are J-receptors?

Answer 61

These are afferent receptors, found in the juxta-alveolar, that are sensitive to oedema (swelling due to excess fluid) and pulmonary capillary engorgement. They increase breathing frequency.

Question 62

What is volitional apnoea?

Answer 62

This is the act of holding ones breath for as long as possible. Static apnoea is a discipline in which one holds their breath under water for as long as possible.

Question 63

Outline the steps of volitional apnoea

Answer 63

1) As one ventilates, their arterial oxygen and carbon dioxide are fairly stable.
2) As one begins to hold their breath, oxygen is no longer replenished through ventilation, meaning that there’s a steady decay in the amount of oxygen and a steady accumulation of carbon dioxide.
3) As the carbon dioxide increases, a threshold is reached as protons accumulate beyond the BBB, thus stimulating the medulla to breath in.
4) Eventually, the overwhelming urge to breathe takes hold, and one is forced to ventilate.

Question 64

What is an acid?

Answer 64

An acid is any molecule that has a loosely bound H+ ion that it can donate. H+ ions are also called protons (because an H atom with a +1 valency has no electrons or neutrons). A greater concentration of H+ ions refers to a lower pH (discussed later).

Question 65

Why must blood acidity be regulated?

Answer 65

The acidity of the blood must be tightly regulated as marked changes will alter the 3D structure of proteins (enzymes, hormones, protein channels). Fortunately, blood has an enormous buffering capacity (identified by Pitt’s and Swan), that can react als,it immediately to imbalances.

Question 66

What is a base?

Answer 66

A base is an anionic (negatively charged ion) molecule capable of reversibly binding protons (to reduce the amount that are ‘free’).

Question 67

What is the pH scale?

Answer 67

The tiny numbers for [H+] are inconvenient to use. Sørensen scaled the data using a log10 transformation, making the numbers much more manageable, although negative. This was easily fixed by applying a minus sign to the equation. The inverse function of log is (10x), using this we can calculate [H+] from pH.

1) -log10[H+] = pH
2) [H+] = 10^(-pH)

Question 68

What are alkalaemia and acidaemia?

Answer 68

1) Alkalaemia: Refers to high-than-normal pH of blood.

2) Acidaemia: Refers to a lower-than-normal pH of blood.

Question 69

What are alkalosis and acidosis?

Answer 69

1) Alkalosis: Describes circumstances that will decrease [H+] and increase pH. An alkalosis will need an acidosis to correct.
2) Acidosis: Describes circumstances that will increase [H+] and decrease pH. An acidosis will need an alkalosis to correct.

Question 70

How can changes in ventilation alter pH?

Answer 70

Changes in ventilation can stimulate a rapid compensatory response to change CO2 elimination and therefore alter pH.

Question 71

How can changes in bicarbonate and proton conc. in the kidney alter pH?

Answer 71

Changes in HCO3- and H+ retention/secretion in the kidneys can stimulate a SLOW compensatory response to increase/decrease pH.

Question 72

What are chemoreceptors?

Answer 72

These are specialised cells loafed at the bifurcation of the carotid arteries on the aortic arch, in specialised structures called carotid bodies. These cells are sensitive to protein and carbon dioxide concentration in the blood. The location of the cells is especially important as the blood which passes through here goes to the brain, and they sit next to carotid baroreceptors, which measure the blood pressure heading to the brain.

Question 73

Outline the link between emotional change and ventilation

Answer 73

A multitude of afferent signals that affect breathing. The limbic system, where many emotions are processed, being very close to the brain stem can provide signals, as well as things that come from the special senses (e.g. sight, smell, taste, hear) can plug into the specialised region of the brain and can fuel an emotional drive to breathe.

Question 74

Outline the link between exercise and changes to breathing

Answer 74

Efferents from primary motor cortex to gross skeletal musculature partly innervate the respiratory control centre in the medulla, notifying it to increase breathing. Proprioceptive afferents from muscle spindles & golgi tendon organs innervate the medulla on way to brain.

Question 75

Outline the link between the skin and changes to breathing

Answer 75

The cold shock ventilator response is a central reflex of deep breathing which occurs when a large area of the body is immersed in water (<10°C). This prevents one from holding their breath for more than 5-10 seconds, resulting in an inspiratory gasp/hyperventilation.