Gas Exchange + Control of Breathing

Question 1

Dalton’s Law

Answer 1

• In a mixture, each gas will contribute their pressures in direct proportion with it’s percentage
• Direction of diffusion is determined by partial pressure of the gas
• Alveolus –> blood –> tissue

Question 2

What happens as atmospheric air enters the alveoli?

Answer 2

• PO2 decreases because of increase of:
  
  • PH20: water vapour from mucous membranes
  • PCO2: stale air is mixed in w the fresh air
• PCO2 increases due to addition from blood

Question 3

What happens as air moves form alveoli to atmosphere?

Answer 3

• PO2 increases (due to mixing with dead air)

- PCO2 decreases (mixing w dead air)

Question 4

Pulmonary edema: Diffusion barrier

Answer 4

• Too much fluid within the alveoli = makes diffusion of O2 too slow
• CO2 is soluble in water so doesn’t affect it

Question 5

Ventilation/Perfusion mismatches

Answer 5

High V/Q ratio: not enough perfusion of a well ventilated area

• Apex of lung (naturally)
• Pulmonary embolism (no BF but open airways)

Low V/Q ratio: not enough ventilation of a well perfused area

• Asthma
• Lung cancer
• Base of lung (naturally because of gravity)

Question 6

How is V/Q mismatch corrected?

Answer 6

Pulmonary arterioles!

• Arterioles relax if PCO2 is low or PO2 is high (high V/Q)
• Arterioles constrict is PC02 is high or PO2 is low (low V/Q, hypoxic pulmonary vasoconstriction - pulmonary vascular SMCs have O2 sensors)
  
  • Sends blood to other alveoli that are well ventilated

NOTE: can’t adjust airway diameters –> only pulmonary arterioles for V/Q

Question 7

Forms of hemoglobin

Answer 7

• Adult (A)
• Fetal (F): higher affinity for 02 than A form (need strong hold on mom’s O2)
• Sickle (S): crystallizes within the cell –> cells don’t live as long but same affinity

Question 8

Hemoglobin cooperativity

Answer 8

• After Hb binds to 1 O2, it becomes easier to bind the next 3
• Non-linear O2-Hb disassociation curve

Question 9

Benefits of the shape of the 02-Hb curve

Answer 9

• Flat top allows lots of O2 pickup respiratory failure (huge swings of O2 only affects the saturation a bit)
• Steep portion allows tissue to pull off as much O2 as needed (small change in O2 = huge change)

Question 10

The shifted O2-Hb curve

Answer 10

• Shifted to the right
• Tissues with high metabolism change the curve because of:
  
  • Increased PCO2
  • Increased temperature
  • Decreased pH (more H+)
  • Increased loss to the tissues during time of need

Question 11

Dorsal respiratory group

Answer 11

• Sends bursts of neural activity to the muscles of inspiration during normal quiet breathing (in medulla)
• Pacemaker cells that send out the neural signals

Question 12

Ventral respiratory group

Answer 12

• Sends outputs to accessory muscles during forced breathing (acts with the dorsal RG)

Question 13

Pontine respiratory group

Answer 13

• Collects information about blood chemistry/emotional state and sends the corrective input to the dorsal & ventral groups (in pons)

Question 14

Respiratory center inputs

Answer 14

• Temp, emotion, pain, anal sphincter stretching
• O2, CO2 and H+ changes (baroreceptors + chemoreceptors)
• Increased breathing when activity increases
• Hering-Breuer reflex prevents over inflation
• Irritant receptors: cough reflex

Question 15

Central chemoreceptors

Answer 15

• On ventral surface of medulla
• Senses H+ levels in CSF (influenced by CO2)
• Provides input to respiratory centres to maintain CO2

Question 16

Peripheral chemoreceptors