Peripheral chemoreceptors

Question 1

what is a chemoreceptor?

Answer 1

a receptor that responds to a change in the chemical composition of the blood or fluid surrounding it

Question 2

what are the 2 types of chemoreceptors ?

Answer 2

• peripheral chemoreceptors
• central chemoreceptors

Question 3

Where are the peeipheral chemoreceptors located?

Answer 3

• carotid bodies at the bifurcation of the common carotid artery
• in the aortic bodies above and below aortic arch
• paraganglia - along length of vagus nerve

Question 4

what structures are the peipheral chemoreceptors in close association to?

Answer 4

the arterial baroreceptors

Question 5

what is the function of the caroid bodies?

Answer 5

they monitor oxygen supply to the brain

Question 6

what are the 2 types of cells present in the carotid bodies?

Answer 6

• type 1 glomus cell
• type 2 glomus cell

Question 7

Describe type 1 glomus cells

Answer 7

• close apposition to the endings of afferent carotid sinus nerve
• they release lots of intense light as they are full of dopamine and other NT’s

Question 8

Describe the type 2 glomus cells

Answer 8

• lack dense vesicles - they dont release intense light
• they represent about 20% of the carotid body cells

Question 9

which cells are the initial site of sensory transduction in the carotid body?

Answer 9

the type 1 cells

Question 10

how do the type 1 cells respond to hypoxia?

Answer 10

• they** release neurotransmitters** which causes** depolarisation** of the nearby afferent nerve endings, leading to an increase in sensory discharge

Question 11

what are the carotid bodies sensitive to?

Answer 11

• decreases in arterial PO2 - ie hypoxia
• increases in H+ concentration and PCO2

Question 12

what are examples of the neurotransmitters released in response to hypoxia?

Answer 12

• dopamine
• Ach
• ATP
• ROS
• Cytokines

Question 13

what do the peripheral arterial chemoreceptors increase their firing rate in response to?

Answer 13

• increased arterial PCO2
• increased arterial K+
• decrease arterial PO2
• decreased arterial PH

Question 14

what is hypoxic hypoxia?

Answer 14

insufficient O2 to the lungs eg blocked airway, altitude and COPD

Question 15

what is stagnant hypoxia?

eg in state of shock or cardiac arrest

Answer 15

failure to transport sufficient O2 due to inadequate blood flow

Question 16

what is anaemic hypoxia?

eg in situations with carbon monoxide posioning

Answer 16

reduced oxygen carrying capacity of blood due to reduced haemoglobin

Question 17

what is histotoxic hypoxia?

Answer 17

impaired oxygen use by tissues

Question 18

what situations cause hypoventilation?

Answer 18

• central
• spinal injury
• neuromuscular disorders
• lung disease
• airway obstruction

Question 19

what are the 3 main physiological responses to hypoxia?

Answer 19

• immediate hyperventilation
• increased cardiac output
• systemic vasodilatation - to get blood moving fast

Question 20

what are the longer term adaptations to hypoxia?

Answer 20

• transcription factors eg Hypoxia-inducible factors
• secondary polycythaemia - increase red blood cell production

Question 21

at what pressure in mmHg do the peripheral chemoreceptors start to become sensitive to changes in arterial PO2?

Answer 21

500mmHg

Question 22

what receptors are responsible for all the increases in ventilation that occur in response to arterial hypoxemia?

Answer 22

the peripheral chemoreceptors

Question 23

Describe the sequence of events of hypoxia causing hyperventilation

Answer 23

• less inspired oxygen
• decrease in alveolar oxygen
• decrease in arterial oxygen
• the peripheral chemoreceptors start firing
• this causes the respiratory muscles to contract via reflex through the medullary respiratory neurons
• this causes an increase in ventilation
• returns alveolar and arterial oxygen to normal