Respiratory Physiology Lecture 7 Part 30: Chemical control of respiration

Question 1

What things might influence PO2, PCO2, and H+ Concentration?

Answer 1

Small variations in arterial PCO2 and PO2 occur with activities such as sleep, exercise, talking, and panting

Question 2

What causes increases in chemical control of ventilation?

Answer 2

Hypoxia (Low PO2), hypercapnia (HighPCO2), and acidosis (Low pH in blood) all cause an increase in ventilation, which tends to raise PO2, to lower PCO2, and to raise pH

Question 3

What have a key role in chemical control of ventilation?

Answer 3

Peripheral and central chemoreceptors have a KEY role in chemical control of ventilation

Question 4

chemoreceptors

Answer 4

specialized structures that sense changes in PO2, PCO2 and pH; Provide drive to centres in brain stem that control respiratory activity (mostly dorsal and ventral)

Question 5

What are the peripheral chemoreceptors?

Answer 5

Outside CNS

Carotid and Aortic Bodies

• Peripheral chemoreceptors (carotid and aortic bodies) detect changes in arterial blood oxygen and initiate reflexes that are important for maintaining homeostasis during hypoxemia. … Peripheral chemoreceptors are critical for ventilatory acclimatization at high altitude.

Question 6

What do carotid and aortic bodies primarly sense?

Answer 6

They sense primarily hypoxia (Low arterial PO2) but are also sensitive to pH

Question 7

Carotid bodies

Answer 7

The carotid body is a small cluster of chemoreceptor cells, and supporting sustentacular cells. The carotid body is located in the adventitia, in the bifurcation (fork) of the common carotid artery, which runs along both sides of the neck.

Question 8

characteristics of carotid bodies

Answer 8

• Extremely small
• Chemosensitive
• Highly vascularized
  
  • The largest of any tissue in the body, 40x more than brain
• High metabolic rate
  
  • 2- to 3- fold greater than that of the brain
  • PO2, PCO2, and pH in the carotid body capillaries is virtually the same as in the systemic arteries

Question 9

What two cells make up carotid bodies?

Answer 9

• Type I (Glomus cells) → the chemosensitive cells
  
  • Drive response, change in ventilation if change in P_O2 levels
• Type II (Sustentacular cells) → act as support in the CB

Question 10

glomulus cells

Answer 10

Glomus type I cells are secretory sensory neurons that release neurotransmitters in response to hypoxemia (low pO2), hypercapnia (high pCO2) or acidosis (low pH). Signals are transmitted to the afferent nerve fibers of the sinus nerve and may include dopamine, acetylcholine, and adenosine.

Question 11

Characteristics of glomulus cells

Answer 11

Neuron-like characteristics

• Have a variety of voltage-gated ion channels
• Depolarization triggers action potentials (Their firing rate increases)
• Have numerous intracellular vesicles containing a variety of neurotransmitters: acetylcholine, dopamine, norepinephrine, substance P, met-encephalin
• Stimulation causes the release of these neurotransmitters and controls the firing of the sensory nerve endings

Question 12

What happens when NT are released from the glomulus cells?

Answer 12

The NT release excites the glossopharyngeal nerve and drives the input back to the dorsal respiratory group in the brain stem and will excite prebot and pfNG in order to increase the respiratory drive to muscles and therefore ventilation. Usually happens with low PO2 level

Question 13

primary stimulus for the peripheral chemoreceptors

Answer 13

A decrease in arterial PO2 is the primary stimulus for the peripheral chemoreceptors

Question 14

What are glomus cells sensitive to?

Answer 14

• Glomus cells display an increase in firing rate with lowering of PO2
• Glomus cells are also sensitive to changes in PCO2 and pH (Increase response to hypoxia)

Question 15

Range of stable P_O2 ventilation

Answer 15

Ventilation is stable over 60 - 120 mmHg range of arterial PO2

Question 16

When does stimulation of peripheral chemoreceptors occur with P_O2 changes?

Answer 16

Stimulation of peripheral chemoreceptors occurs at arterial P_O2 values below 60 mmHg

Question 17

Response pathway to hypoxia mediated by peripheral chemoreceptors

Answer 17

Question 18

How do the periperal chemoreceptors control respiratory muscles?

Answer 18

Peripheral chemoreceptors activate dorsal and ventral respiratory group neurons in the medulla in order to control centrally the activity of the respiratory muscles via:

↑ Contractions

↑ Ventilation

Question 19

Ventilatory Changes with Changes in Arterial P_CO2

Answer 19

Do not normally breathe in gas containing high CO2 but some pulmonary diseases such as emphysema cause the body or retain CO2 resulting in increased arterial PCO2 that increase ventilation. Usually this is associated with H+ concentration