Control of breathing Lecture 12

Question 1

Briefly describe peripheral chemoreceptors

Answer 1

Carotid bodies and aortic bodies involved with blood gas and acid-base homeostasis- respond to PO2, PCO2 and pH Intrinsically sensitive to oxygen Functional unit is the glomerulus (type 1 or glomus cells)

Question 2

Describe the process of sensing hypoxia

Answer 2

Low oxygen in blood➡ O2 sensor in PM of glomus cell➡ inhibition of K channels– cell depolarisation- voltage-gated calcium channel open- Calcium influx➡ neurosectretion of ATP/ACh/DA➡ afferent action potentials

Question 3

How might hypoxia be sensed in glomus cells

Answer 3

1. Hypoxia inhibits oxidative phosphorylation which increases AMP:ATP ratio which activates AMP kinase which inhibits K channels 2. In hypoxia conditions haem oxygenase 2 (HO-2) is inhibited so it does not generate CO so cystathionine-gamma-lyase (CSE)-regulated H2S generation is not inhibited so H2S closes K channels and the cell becomes depolarised

Question 4

Describe central chemoreceptors

Answer 4

Ventral sites eg. retrotrapezoid nucleus Dorsal sites eg. solitary tract nucleus Midline sites Glial cells? Generate 80% of the total response to CO2 Inhibited by hypoxia The non-polar H2O and CO2 diffuse through the BBB and form HCO3 and H which are sensed by central chemoreceptors➡ medullary respiratory neurones➡ adjustment of ventilation

Question 5

What is the relationship between gas velocity pressure and size of airways

Answer 5

Lower pressure in larger airways Higher velocity in larger airways Increased gas velocity causes decreasing pressure- Bernoulli Increased turbulent flow in larger airways Pressure falls more quickly in turbulent flow- Reynolds

Question 6

What is the equal pressure point?

Answer 6

If the pressure in the airways is less than or equal the P(Pl) the airway will collapse unless it is in large airways with cartilage (Pressure falls along the airways because of Bernoulli and Reynolds)

Question 7

Describe peak expiratoiry flow?

Answer 7

Greatest at total lung capacity -surfactant is least effective ie. Large surface tension - able to generate greatest positive P(Pl) to prevent aoitrway collapse - airway resistance at lowest