RS: Blood Gases

Question 1

What are the 2 types of breathing?

Answer 1

1. Voluntary

2. Involuntary

Question 2

How is voluntary (rhythmic) breathing controlled?

Answer 2

Controlled by sensory feedback receptors that are sensitive to partial pressure of carbon dioxide and oxygen, as well as pH.

Question 3

What is voluntary breathing?

Answer 3

The overriding of involuntary breathing mechanisms during certain situations.

Question 4

How is the diaphragm innervated?

Answer 4

Innervated by the phrenic nerves

Question 5

How is the intercostal muscles innervated?

Answer 5

By intercostal nerves

Question 6

When are the diaphragm and intercostal muscles innervated?

Answer 6

In times of need to trigger the appropriate muscles to contract and trigger inspiration or expiration, for the process of ventilation.

Question 7

Where is the inspiratory centre situated?

Answer 7

In the medulla oblongata

Question 8

What are the 3 regions of the respiratory centre?

Answer 8

1. Dorsal respiratory group
2. Ventral respiratory group
3. Pontine respiratory group

Question 9

What is the function of the dorsal respiratory group?

Answer 9

Integrates input from the stretch receptors and the chemoreceptors in the periphery.
The dorsal respiratory group is involved in maintaining a constant breathing rhythm by stimulating the diaphragm and intercostal muscles to contract, resulting in inspiration.

Question 10

What happens when activity in the dorsal respiratory group ceases?

Answer 10

When activity in the DRG ceases, it no longer stimulates the diaphragm and intercostals to contract, allowing them to relax, resulting in expiration.

Question 11

What is the function of the ventral respiratory group?

Answer 11

Generates the breathing rhythm and integrates data coming into the medulla.
The ventral respiratory group is involved in forced breathing, as the neurons in the VRG stimulate the accessory muscles involved in forced breathing to contract, resulting in forced inspiration. It also stimulates the accessory muscles involved in forced expiration to contract.

Question 12

What is the function of the pontine respiratory group?

Answer 12

Influences and modifies the medulla oblongata functions.

Question 13

Describe the structure of the pontine respiratory group

Answer 13

The pontine respiratory group consists of the apneustic and pneumotaxic centers.

Question 14

What is the apneustic region of the pontine respiratory group?

Answer 14

The apneustic center is a double cluster of neuronal cell bodies that stimulate neurons in the DRG, controlling the depth of inspiration, particularly for deep breathing.

Question 15

What is the pneumotaxic region of the pontine respiratory group?

Answer 15

The pneumotaxic center is a network of neurons that inhibits the activity of neurons in the DRG, allowing relaxation after inspiration, and thus controlling the overall rate.

Question 16

How does inspiration arise?

Answer 16

Inspiration arises as a result of the progressive increase in the number of activated inspiratory neurones that increases the strength of the respiratory muscles.

Question 17

How does expiration arise?

Answer 17

Expiration occurs as a result of the activation of inhibitory neurons which cause the inhibition if inspiratory neurons and activation of expiratory neurons. Expiratory neurons receive input from pons, lung stretch receptors, and other sources to trigger the relaxation of respiratory muscles.

Question 18

Describe the rhythmic breathing processes of inspiration

Answer 18

Respiratory centre triggered by respiratory neurons to send nerve signals. Diaphragm and external intercostal muscles contract. Inspiration.

Question 19

How long does inspiration take?

Answer 19

Roughly 2 seconds

Question 20

How long does expiration take?

Answer 20

Roughly 3 seconds

Question 21

Describe the rhythmic breathing processes of expiration

Answer 21

Respiratory centre receives signal to inhibit inspiratory neurons and activate expiratory neurons. Stops nerve signals so diaphragm and external intercostal muscles relax, and internal costal muscles and abdominal muscles contract. Expiration.

Question 22

What inputs does the respiratory centre receive to alter rhythmic breathing?

Answer 22

Inputs from central chemoreceptors in the medulla oblongata and peripheral chemoreceptors associated with the aorta and carotid bodies, that are both sensitive to carbon dioxide, oxygen and pH.

Question 23

What are the central chemoreceptors found?

Answer 23

In the medulla oblongata. Ventrolateral surface of medulla oblongata has a chemosensitive area that is anatomically distinct from, but synaptically connected to, the respiratory control centre.

Question 24

Where are the peripheral chemoreceptors found?

Answer 24

Associated with the aorta and carotid bodies

Question 25

What is significant about the chemoreceptors in the medulla oblongata?

Answer 25

Sensitive to pH, but hydrogen ions cannot cross the blood brain barrier (BBB). Arterial carbon dioxide can cross the BBB and enter the cerebrospinal fluid where it is converted to hydrogen ions, which then directly stimulates chemoreceptors.

Question 26

What chemoreceptors are responsible for the greatest increase in ventilation in response to a sustained increased in carbon dioxide?

Answer 26

Chemoreceptors in the medulla oblongata

Question 27

Describe the action and signalling cascade of the peripheral chemoreceptors

Answer 27

Chemoreceptors are contained within small nodules associated with the aortic arch and the carotid artery. Chemoreceptors receive blood via small arterial branches.
Carotid and aortic bodies send sensory information to the medulla via the glossopharyngeal nerve (IX) and vagus nerves (X) respectively.

Question 28

How are the chemoreceptors in the peripheral similar to those in the medulla oblongata?

Answer 28

Not stimulated directly by carbon dioxide but by hydrogen ions, from the conversion of carbon dioxide to carbonic acid, and its eventually breakdown to hydrogen and hydrogen carbonate ions. Peripheral chemoreceptors also respond to other circulating acids eg. Lactic Acids.

Question 29

What is the roles of the carotid bodies?

Answer 29

Primary role is to monitor the levels of carbon dioxide in the blood and report this to the medulla.

Carotid bodies also monitor oxygen levels in the blood, but only trigger responses when partial pressure falls below 60 mmHg.

Question 30

How do carotid bodies send sensory information, with regards to carbon dioxide levels, to the medulla?

Answer 30

Via the glossopharyngeal nerve (IX)

Question 31

How do aorta bodies send sensory information, with regards to carbon dioxide levels, to the medulla?

Answer 31

Via the vagus nerves (X)

Question 32

What is the blood plasma pH maintained at?

Answer 32

7.35-7.45

Question 33

How blood plasma pH regulated?

Answer 33

By the regulation of carbon dioxide by the lungs and the regulation of bicarbonate ions and hydrogen ions by the kidneys.

Question 34

Where do the hydrogen ions in the blood come from?

Answer 34

The hydrogen ions in blood come from volatile acids (carbonic acid) and non-volatile acids (lactic acid, fatty acids). Non-volatile acids hydrogen ions are often buffered by hydrogen carbonate ions, resulting in the formation of carbonic acid.

Question 35

What is acidosis?

Answer 35

A fall in blood plasm pH below 7.35 often caused by inadequate ventilation.

Question 36

How is acidosis compensated for?

Answer 36

Hyperventilation

Question 37

What is alkalosis?

Answer 37

A rise in blood plasma pH above 7.45, often caused by excessive ventilation (panic attack). Induces cerebral vasoconstriction.

Question 38

How is alkalosis compensated for?

Answer 38

Hypoventilation

Question 39

How does ventilation ensure blood plasma pH is maintained?

Answer 39

Ventilation usually adjusts to match metabolism (carbon dioxide production) in order to maintain a steady state blood pH; arterial carbon dioxide therefore remains relatively constant.