Respiration

Question 1

Ficks law of diffusion?

Answer 1

Smaller the distance and greater the surface area = greater rate of diffusion

Question 2

Type 1 alveoli cells?

Answer 2

Make up the wall of the alveoli

Question 3

Type 2 alveoli cells?

Answer 3

Secrete pulmonary surfactant

Question 4

Law of LaPlace?

Answer 4

(2 x surface tension) / radius = inward pressure
Therefore, smaller radius = higher inwards pressure

Question 5

What causes the lungs to return to their pre-inspiration size?

Answer 5

Alveolar surface tension - elastic recoil

Question 6

Role of pulmonary surfactant?

Answer 6

Decreases alveolar surface tension
- reduces recoil / prevents smaller alveoli from collapsing into larger ones

Question 7

Why does pulmonary surfactant decrease surface tension in smaller alveoli more compared to larger ones?

Answer 7

Because the surfactant molecules are more crowded

Question 8

Define the transmural pressure gradient

Answer 8

The pressure gradient between the alveolar pressure (same as atmospheric) and the intrapleural pressure (4 mmHg less than atmospheric). Means there is more pressure pushing out from inside than pressure pushing in from outside

Question 9

Role of transmural pressure gradient?

Answer 9

Keeps the alveoli open and forces the lungs to expand with expansion of the thoracic cavity

Question 10

Explain how pneumothorax occurs

Answer 10

Hole in the lung or chest pierces the pleural sac, causing the pressure to equilibriate with atmospheric pressure. Abolishes the transmural pressure gradient, causing it to collapse. Rib cage will spring out

Question 11

Define newborn respiratory distress syndrome

Answer 11

Insufficient pulmonary surfactant cause by premature birth. Results in poorly compliant lungs due to increased alveoli surface tension + increased transmural pressure gradient. Would need massive effort to inflate the lungs

Question 12

Boyle’s law? + application

Answer 12

P = 1 / V
As chest volume increases, pressure decreases - allowing air to enter lungs as the alveolar pressure is now less than atmospheric

Question 13

Muscles involved in active expiration?

Answer 13

Internal intercostal muscles and abdominal muscles

Question 14

Name 2 factors keeping alveoli open

Answer 14

• pulmonary surfactant
• transmural pressure gradient

Question 15

Name 2 forces promoting alveolar collapse

Answer 15

• alveolar surface tension
• elasticity of pulmonary connective tissue

Question 16

Define tidal volume

Answer 16

The volume entering and leaving the lungs during a single breath

Question 17

Define residual volume

Answer 17

Minimal volume of air remaining in lungs after maximal expiration
Cannot be measured using spirometer

Question 18

Compare pulmonary and alveolar ventilation

Answer 18

Alveolar excludes the ‘dead space’ volume and reveals how much air is actually reaching alveoli. Pulmonary is the total volume of air inspired and expired

Question 19

If V/Q = more than 1, what are the control mechanisms?

Answer 19

• increase in Oxygen causes local vessel dilation to increase blood flow
• decrease in CO2 causes contraction of smooth muscle = more airway resistance = reduced airflow

Question 20

What can increased CO2 cause?

Answer 20

Respiratory acidosis
CO2 in blood forms carbonic acid. Reduced CO2 would make blood alkaline

Question 21

What could cause V / Q to be less than 1?

Answer 21

Asthma attack.
More perfusion than ventilation

Question 22

V / Q < 1 control mechanisms?

Answer 22

Want to increase air flow by dilating airways and decrease blood flow by constructing vessels

Question 23

Would too much CO2 in the blood cause alkalosis or acidosis? Explain.

Answer 23

Acidosis. There would be more CO2 induced H+ ions in blood

Question 24

Which part of the brainstem houses the respiratory control centre?

Answer 24

Medulla (+ pons)

Question 25

Compare the dorsal and ventral respiratory groups?

Answer 25

Dorsal = in control during quiet breathing - innervates the diaphragm
Ventral = takes over control during increased ventilation. Innervates both inspiratory and expiratory muscles

Question 26

Where does the respiratory control centre receive input from?

Answer 26

Central chemo receptors

Question 27

What do central chemoreceptors detect?

Answer 27

The pH of the extra cellular fluid in the brain

Question 28

What do peripheral chemoreceptors detect?

Answer 28

Oxygen partial pressure + pH of blood

Question 29

Where are peripheral chemoreceptors located

Answer 29

In aortic arch and carotid bodies

Question 30

Which chemoreceptors will detect hypoxia

Answer 30

Peripheral

Question 31

The hypoxic urge to breathe occurs when?

Answer 31

Partial pressure of O2 below 60

Question 32

Describe the hypoxic urge to breathe mechanism.

Answer 32

When pO2 <60, the peripheral chemoreceptors send messages to medullary respiratory centre to increase ventilation

Question 33

What does an increase in PCO2 do to the brain?

Answer 33

Increases carbonic acid = lowers the pH. This is recognised by the central chemoreceptors which respond by innervating the respiratory centre causing an increase in ventilation

Question 34

Consequence of CO2’s high diffusion coefficient?

Answer 34

Diffuses faster than O2, does not require as high of a concentration gradient, and is removed by exhalation much easier

Question 35

Explain renal compensation of respiratory acidosis

Answer 35

With chronic elevation of CO2, the kidneys respond by retaining bicarbonate ions which neutralise the excess H+ to bring the pH back to normal levels

Question 36

Explain how renal compensation of respiratory acidosis knocks out central chemoreceptors? What impact does this have

Answer 36

The kidneys increase bicarbonate concentration to neutralise the blood pH. The bicarbonate can eventually diffuse across the BBB to also neutralise the excess H+ there. As a result, the central chemoreceptors are not detecting an abnormal pH, so they do not innervate the respiratory centre. Causes respiration to slow down. Eventually slows so much that the pO2 drops to a point where the hypoxic urge to breathe kicks in

Question 37

Which chemoreceptors are responsible for mediating non-CO2 induced alkalosis or acidosis?

Answer 37

Peripheral

Question 38

How long does it take for renal compensatory mechanisms to kick in?

Answer 38

Hours to days

Question 39

Compare apnea and dyspnea

Answer 39

Apnea = subconsciously ‘forgets’ to breathe - e.g. sleep apnea
Dypsnea = consciously feels that their ventilation is inadequate

Question 40

How can you tell if a person is hyperventilating based on a blood gas report?

Answer 40

CO2 will be low

Question 41

If bicarb levels are within the normal range, what does this indicate?

Answer 41

The acidosis must be acute, because the kidney’s compensatory mechanisms have not kicked in yet

Question 42

What is a condition where the PA-aO2 might be above 10?

Answer 42

Asthma - indicates a physiological shunt

Question 43

With prolonged renal compensation, patients might become dependent on…?

Answer 43

The hypoxic drive to breathe

Question 44

If the CO2 is low but the pH is acidic, what could this indicate?

Answer 44

Acidity is not due to the respiratory system. Could be metabolic acidosis

Question 45

Compensatory mechanism for metabolic acidosis?

Answer 45

Low pH recognised by peripheral chemoreceptors only (bc ions cannot cross BBB), causing innervation of medullary respiratory centre, causing increased ventilation