Unit 5 Respiratory System

Question 1

what does the respiratory system allow?

Answer 1

1. exchange of gasses between atmosphere and blood
2. homeostatic regulation of body pH
3. protection from inhaled pathogens and irritating substances
4. vocalization

Question 2

what are the 4 processes of the respiratory system

Answer 2

1. gas exchange between atmosphere and lungs (ventilation)
   -air moves into lungs (inspiration/inhalation)
   -air moves out of lungs (expiration/exhalation)
2. gas exchange between lungs and blood (CO2 and O2)
3. transport of gases by blood (CO2 and O2)
4. exchange of gases between blood and tissues

Question 3

systems/surfaces of the respiratory system

Answer 3

1. conducting system (airways)
2. exchange surface (alveoli)
3. pumping system (bones and muscles of thorax)

Question 4

conducting system

Answer 4

-passage or airways (lead from environment to the exchange surface)
-respiratory system can be divided into 2 parts:
1. upper respiratory tract
-mouth
-nasal cavity
-pharynx
-larynx
2. lower respiratory tract
-trachea
-bronchi
-bronchioles
-lungs

Question 5

exchange surface

Answer 5

-alveoli (sites of gas exchange)
-tiny hollow sacs found at the ends of the terminal bronchiole
-wrapped with an extensive capillary network which covers 80-90% of the alveolar surface
-gas exchange occurs by diffusion between alveoli and capillary
-blood vessels of the pulmonary circulation allow for exchange with alveoli
-low oxygen blood exits the right ventricle of the heart
-goes into the pulmonary arteries via the pulmonary trunk (two pulmonary arteries)
rate of blood flow is high because al the output of the right ventricle goes to the lungs versus whole body for the blood leaving the left ventricle
-however blood pressure is low relative to the systemic circuit (right ventricle does not pump as forcefully as the left ventricle

Question 6

what are the types of alveoli cells

Answer 6

-two types of alveoli cells:
1. type I (large but thin)
-rapid gas diffusion
2. type II (smaller but thicker)
-synthesize and secrete surfactant (disrupt cohesive forces of water molecules)

Question 7

pumping system

Answer 7

-bones and muscles of the thorax allow for ventilation (inspiration and expiration)
-relation of the lungs to the chest wall
-closed compartment by the neck muscles and connective tissue at the top and the diaphragm at the bottom
-wall is formed by the ribs and intercostal muscles
-each lung is surrounded by the pleural sac which forms a double membrane around each lung
-the pleura is filled with fluid that acts as a lubricant

Question 8

muscles of inspiration and expiration

Answer 8

Inspiration
-sternocleido-mastoids
-scalenes
-external intercostal
-diaphragm

Expiration
-internal intercostal
-abdominal muscles
-these muscles only contract in active expiration
-in passive expiration the inspiration muscles only relax

Question 9

mixture of gases

Answer 9

-total pressure of a mixture of gases is the sum of the partial pressure of the individual gases
- gases move from areas of high pressure to areas of low pressure
-volume and pressure of a gas are inversely related
-amount of gas will dissolve in a liquid is determined by:
a. partial pressure of the gas
b. solubility of the gas in the liquid

Question 10

partial pressure

Answer 10

-partial pressure = P(atm) x % fo gas in atmosphere
-pressure volume relationships are described by boyles law: P1V1=P2V2
-pressure volume relationship is critical for ventilation
-during inspiration and expiration the volume of the thoracic cavity changes which causes changes in the alveolar pressure
-changes in alveolar pressure are the driving force for air flow
-there are no muscles in the lung itself (the lungs cannot change volume on their own)
-the lungs are passive elastic structures
-pressure inside the lungs is the alveolar pressure
-pressure outside the lungs is the pressure in the intrapleural fluid

Question 11

what does the volume depend on

Answer 11

1. transpulmonary pressure (difference between alveolar pressure and intrapleural pressure)
2. the degree of elasticity of the lungs
   -pressure inside the lungs is the alveolar pressure
   -pressure outside the lungs is the pressure in the intrapleural fluid

Question 12

movement of air

Answer 12

• Ventilation is the exchange of air between the atmosphere and lungs
• Airways serve an important role in conditioning the air before it reaches the lungs
• The airways need to:
  1. Warm air to 37°C to maintain core body temp and protect alveoli
  2. Add water vapour to air to prevent drying of epithelia
  3. Filter out foreign material
• Airways are lined with ciliated epithelia that secrete a watery saline solution
• Cells move Cl- from ECF into the cell via the NKCC –> Cl- transported to lumen of airway via apical anion channel
• Na+ moves between cells from ECF to lumen –> [ ] gradient of NaCl draws water towards the lumen creating the watery saline solution
• Cilia are covered with mucus that is secreted by goblet cells
• Mucus contains immune cells (e.g. macrophages) that kill invaders
• Mucus is moved up to the pharynx (mucus escalator)
• Transferred to the digestive tract where additional bacteria are destroyed
• Medical conditions can complicate ventilation
• For example, Cystic Fibrosis (CF)
• Inherited condition
• Result of mutations in a C1 channel
• Cystic fibrosis transmembrane conductance regulator (CFTR)
• In CF the Cl- channel is defective
• This defect prevents the appropriate secretion of water to create the watery saline layer in the lumen
• Cilia are trapped in thick and sticky mucus
• Blocks airways –> difficulty breathing
• Prevents proper removal of bacteria –> repeated infections
• Eventually, over-active immune cells start to destroy the lung –> lethal

Question 13

the respiratory cycle

Answer 13

• The respiratory cycle has two steps –> Inspiration and Expiration

Step 1: Inspiration
1. Somatic motor neurons trigger contraction of diaphragm and inspiratory muscles
2. Thorax expands –> increases thoracic volume
3. Alveolar and intrapleural pressure decreases
4. Lungs expand resulting in air flowing into lungs

Step 2: Expiration
1. Impulses from somatic motor neurons stop
2. Diaphragm and thoracic muscles relax which returns thorax to their original positions –> decrease volume (elastic recoil)
3. Alveolar and intrapleural pressure increases
4. Elastic recoil of the lungs decreases lung volume –> air flows out of the lungs

• Note that during quiet breathing, expiration is a passive process
• i.e. passive expiration depends on elastic recoil of the thoracic muscles and the lungs
• During exercise or heavy breathing expiration is active
• i.e. active expiration depends on contraction of internal intercostals & abdominal muscles

Question 14

intrapleural pressure

Answer 14

• Intrapleural pressure is normally sub-atmospheric –> arises during fetal development
• Having lower pressure in the pleural fluid (outside the lung) than inside the lung (at rest) helps keep the lung expanded and open
• If air gets into the pleural cavity –> intrapleural pressure increases
• Pressure difference is abolished –> the lung collapses
• This is a condition called pneumothorax (or collapsed lung)
• Treatment –> apply suction to remove the air and seal the hole

Question 15

Factors for breathing

Answer 15

• The work required to breathe depends on two main factors:
  1. Compliance (stretchability) of the lungs
  2. The resistance of air flow in the airways

Question 16

lung compliance

Answer 16

• Definition: the ability for the lung to stretch
• The lower the lung compliance, the harder it is to expand the lungs
• People with low lung compliance breath shallowly and rapidly
• High lung compliance indicates that the lungs stretch easily –> easier to breathe

Question 17

lung elastance

Answer 17

• Definition: degree and/or speed of return to resting volume after lung is stretched
• When the lung elastance is low, the lung does not return to resting volume passively
• Expiration must be active not passive

Question 18

airway resistance

Answer 18

• Resistance is determined primarily by airway diameter: Remember –> R = 8Ln/pi r^4
• Normally the work needed to overcome airway resistance is low relative to work needed to overcome resistance to stretch, but: mucus accumulation from allergies or infections can greatly increase resistance of the airways
• Bronchiole diameter can be affected by the nervous system, hormones and paracrines
• CO2 causes bronchodilation
• Histamine released in response to tissue damage or allergic reactions causes bronchoconstriction
• Severe allergic reactions can cause difficulty breathing
• Neural control of bronchioles:
• Primarily by parasympathetic neurons that cause bronchoconstriction
• Reflex designed to protect lower respiratory tract from inhaled irritants
• No significant sympathetic inervation
• Hormonal control of bronchioles is done primarily via circulating epinephrine
• Through beta 2 receptors in smooth muscle of bronchioles –> relax muscles to dilate bronchioles
• Used as a treatment for asthma

Question 19

assessment of pulmonary function

Answer 19

• Pulmonary function is assessed to determine the amount of air a person moves during quiet breathing and maximal breathing effort
• Tests use a spirometer –> instrument that measures movement of air during breathing
• Assessment of pulmonary function using a spirometer allows for diagnosis of many diseases
• e.g. asthma, emphysema, chronic bronchitis

Question 20

lung volumes

Answer 20

• Four lung volumes that can be measured as air moves during breathing:
  1. V(T)–> Tidal Volume–> amount of air moved in a single normal inspiration or expiration
  2. Inspiratory Reserve Volume –> IRV –> maximum amount of air that can be inspired above tidal volume
  3. ERV –> Expiratory Reserve Volume –> amount of air that can be exhaled after a normal expiration
  4. RV –> Residual Volume –> amount of air left in the lungs after maximal expiration
• The sum of two or more lung volumes is called a capacity
• Vital Capacity –> VC
• The maximum amount of air that can be voluntarily moved into or out of the respiratory system
• VC= IRV + ERV + V(T)
• Total Lung Capacity > TLC
  TC = Vital capacity + Residual volume

Question 21

efficiency of breathing

Answer 21

• Estimate the effectiveness of breathing by measuring the total pulmonary ventilation –> minute volume –> MV
• MV (mL/min) = Vr (mL/breath) X respiratory rate (breaths/min)
• There is anatomic dead space located in the airways –> no gas exchange
• Air in trachea, bronchi and bronchioles does not participate in gas exchange
• Alveolar volume = VT - dead space
• Effectiveness of ventilation determined by the rate and depth of breathing
  Because of the dead space, increase in depth of breathing is most important
• Alveolar ventilation is the amount of air that reaches the alveoli each minute
• A more accurate indicator of efficiency of ventilation
  Alveolar ventilation = ventilation rate X alveolar volume
• Ventilation is matched to alveolar blood flow –> the body attempts to match air flow and blood flow to maximize gas exchange in the capillary beds that surround the alveoli
• Alterations in blood flow in the lungs depends primarily local control exerted by O levels in the interstitial fluid around the arteriole surrounding the alveoli
• Increases in tissue PO2 result in vasodilation in the arteriole
• If ventilation of alveoli in an area of the lung decreases, then tissue O2 in that area also decreases
• Decreases in tissue PO2 result in vasoconstriction in the arteriole
• Overall, this diverts blood away from the under-ventilated areas –> ensures that blood travels to areas of the lungs that would ensure that oxygen is available to be picked up

Question 22

rate of diffusion across the lungs is…

Answer 22

1. Proportional to partial pressure gradient
2. Proportional to the available surface area
3. Inversely proportional to the thickness of the membranes
4. Greatest over short distances

Question 23

what is the partial pressure gradient influenced by

Answer 23

1. Composition of inspired air
   - Affected by altitude
2. Alveolar ventilation
   - Can be affected by:
   - Changes in airway resistance –> e.g. asthma
   - Changes in lung compliance –> e.g. fibrosis

Question 24

inside normal alveoli

Answer 24

• Inside normal alveoli the PO2 will be normal and the PO2 inside the capillary will also be normal

Question 25

Diseases and conditions that impact gas exchange

Answer 25

a. Emphysema –> destruction of alveoli
- Physical loss of alveolar surface area
-PO2 normal or low in alveoli
-PO2 low in capillary

b. Fibrotic Lung Disease
- Scarring thickens the alveolar membrane
-PO2 normal or low in alveoli
-PO2 low in capillary

c. Pulmonary Oedema
- Increase in interstitial fluid in lungs leads to increase in diffusion distance
-PO2 normal in alveoli
-Large distance between alveoli and capillary
-PO2 low in capillary

d. Asthma
- Increase airway resistance decrease ventilation
-Bronchiole constricted
-PO2 low in alveoli
- PO2 low in capillary

Question 26

gas transport in blood

Answer 26

• Gases are transported throughout the body either dissolved in plasma or in the RBCs

Question 27

transport of oxygen

Answer 27

• Oxygen has low solubility in plasma
• therefore most O2 is transported by RBC
• Within RBCs O2 is bound by haemoglobin
• Blood loss results in less of O carrying capacity –> a blood transfusion is required to restore capacity, but in emergencies this is not always possible
• Each haemoglobin molecule can bind up to 4 oxygen molecules (4 haeme groups)
• Oxygen binds reversibly with iron in hame group
• Haemoglobin bound to oxygen = oxyhemoglobin –> HbO2
• Unbound haemoglobin = deoxyhaemoglobin –> Hb
  Percent saturation of haemoglobin: % of available binding sites that are bound to oxygen
• Carbon monoxide is a competitive inhibitor of O2 binding
• Prevents oxygen binding
• Under normal conditions, increasing alveolar PO2 does not have much effect on percent saturation of haemoglobin

Question 28

transport of carbon dioxide

Answer 28

• Carbon dioxide is transported by three mechanisms:

1. Dissolved in plasma
   - CO is more soluble in body fluids than oxygen; however, cells produce more CO2 than can be carried in plasma
2. Interact with proteins (including haemoglobin via 4 terminal amine groups on the protein)
   - Forms carbaminohaemoglobin (Hb * CO2)
   - Deoxy-haemoglobin interacts more readily with CO2 than oxy-haemoglobin
3. Converted to bicarbonate
   - The majority of CO2 entering the blood is converted by reaction catalyzed by carbonic anhydrase (present in RBCs) –> the H+ formed by this reaction binds to Hb
   - The bicarbonate ions are moved out the RBC by a transporter protein which
   exchanges HCO3- for Cl- in a process is known as the chloride shift

• When venous blood reaches lungs the PCO2 of alveoli is lower than blood
• CO2 dissolved in plasma diffuses into alveoli and then CO2 in BC diffuses into plasma
• Equilibrium of CO2-bicarbonate reaction is shifted
• Bicarbonate ions move from plasma into RBCs and then bicarbonate and Ht form carbonic acid and then CO2 –> catalyzed by carbonic anhydrase
• CO2 diffuses out of RBC into plasma and then alveoli

Question 29

muscle control of ventilation

Answer 29

• Diaphragm and intercostals are skeletal muscles
• Skeletal muscle cannot contract spontaneously
• Therefore, they are innervated by somatic motor neurons
• Contraction of the respiratory skeletal muscles is initiated in the medulla oblongata (brain)
• There is a network of neurons called the central pattern generator in the medulla oblongata
• These neurons have intrinsic rhythmic activity (i.e. fire a signal at a rhythmic rate)
• There are two nuclei in the medulla oblongata associated with respiration
  a. Dorsal respiratory group (DRG) –> inspiratory neurons (I neurons)
• Control external intercostal muscles & diaphragm (muscles of inspiration)
  b. Ventral respiratory group (VRG) –> active expiration neurons (E neurons)
• Control internal intercostal & abdominal muscles (active expiration)

Question 30

regulation by chemoreceptors

Answer 30

• Chemoreceptors modify or adjust the rhythmicity of the central pattern generator neurons
• There are two sets of chemoreceptors responsible for this regulation:
  1. Peripheral Chemoreceptors
• Located in carotid bodies –> glomus cells
• Sense changes in PO2 and pH of plasma or increase in PCO2
• Decrease PO or decreased pH or increase in PCO2 –> increase ventilation
• Most circumstances pH and PCO2 are important
• Plasma PO2 must change radically before a signal is sent

2. Central Chemoreceptors
   - Located in medulla oblongata –> most important chemical controller of ventilation
   - increase PCO2 in arterial blood –> increase ventilation
   - CO2 crosses blood brain barrier into cerebrospinal fluid (CSF)-> activates central chemoreceptors via changes in pH caused by the production of carbonic acid
   - CO2 + H20 <–> H2CO3 <–> HCO3- + H+
   - Sense changes of H+ in CSF and not H+ in arterial blood

Question 31

regulation by mechanoreceptors

Answer 31

• In some circumstances mechanoreceptors also control ventilation to protect the lungs
• There are two types of mechanoreceptors:

1. Irritant receptors: located in airway mucosa
   - Stimulation triggers parasympathetic neurons that innervate bronchiolar smooth muscle –> bronchoconstriction
2. Stretch receptors: located in airway smooth muscle
   - Triggered if lungs are over-inflated
   - Terminate ventilation –> Hering-Breuer inflation reflex
   - Reflex does not happen during quite breathing or mild exertion