Respiratory - Alveolar ventilation

Question 1

What is the alveolar volume?

Answer 1

The difference between the tidal volume and the dead-space (i.e. the volume of fresh air that goes into the lungs per breath)

Question 2

What is the purpose of alveolar ventilation?

Answer 2

Maintains the partial pressures of O2 and CO2 in the blood as it controls the amount of O2 and CO2 available for gas exchange

Question 3

What is the equation for the rate of alveolar ventilation?

Answer 3

V_T = tidal volume

V_D = dead space

f_R = frequency of breathing

Question 4

What is pulmonary ventilation? How does it differ from alveolar ventilation?

Answer 4

Pulmonary = the amount of air that goes into the lungs per min (tidal volume)

Alveolar = the amount of fresh air that gets to the alveoli per min

Question 5

What is hypo and hyper ventilation?

Answer 5

Hypo = low rate of breath

Hyper = high rate of breath

Question 6

What remains constant during hypo or hyper ventilation? Why?

Answer 6

The amount of CO2 and O2 going into/out of the blood remains constant because the energy consumption doesn’t change much (increased breathing rate has negligible energy increase)

Question 7

What changes during hypo and hyper ventilation? How does it change?

Answer 7

The partial pressures of CO2 and O2 change

Hypo-ventilation causes increased PCO2 and decreased PO2

Hyper-ventilation causes increased PO2 and decreased PCO2

Question 8

How does hyperventilation change the oxyhemoglobin equilibrium?

Answer 8

Hyperventilation causes decreased CO2 which causes a shift to the left in the equilibrium therefore less O2 gets dropped off per pressure drop

Question 9

What causes and what happens due to a decrease in the CO2 in the alveoli?

Answer 9

Hyperventilation causes an increase of arterial pH (more basic) as there is a decrease PCO2 in the alveoli and arteries (CO2 is removed from the lungs more which means that more CO2 is removed from the blood)

Question 10

What causes and what happens due to an increase in the CO2 in the alveoli?

Answer 10

Hypoventilation causes a decrease of arterial pH (more acidic) as there is an increase of PCO2 in the alveoli and arteries (CO2 can accumulate for longer in alveoli therefore more diffuses into the blood)

Question 11

What does large changes in blood pH due to hyper and hypo ventilation lead to?

Answer 11

Hyper = alkalotic coma

Hypo = acidotic coma or lack of oxygen

Question 12

What is the bodies responsiveness to PO2 for the respiration rate? Explain

Answer 12

It is relatively unresponsive as the rate of breathing only measurably increases once the oxygen levels are near critical and this response varies greatly among people

Question 13

What senses the oxygen levels in the body?

Answer 13

Chemoreceptors

Question 14

What is the bodies responsiveness to pH for the respiration rate? Explain

Answer 14

The body is very sensitive to changes as the acidity increases but this then decreases rapidly as well. This is because it is damaging the nervous system so it is not a direct response to O2 levels

Question 15

What is the bodies responsive to CO2 for the respiration rate? Explain

Answer 15

There is a very strong relationship between CO2 and respiratory rate. The respiratory rate begins to fall way after ~10% CO2 because the patient goes into a acidotic coma

Question 16

Where does the respiratory rhythm originate from?

Answer 16

From the medullary centres (in the medulla oblongata FYI)

Question 17

What are apart of the medullary centres that control respiration? What do they control?

Answer 17

Dorsal respiratory group (DRG) are active during inspiration

Ventral respiratory group (VRG) are active throughout the breath (inspiration, expiration and in the transition)

Question 18

How does the respiratory system control the volume of breath? Where are the sensors located?

Answer 18

Slowly adapting stretch receptors that are located in the walls of the bronchi and bronchioles send signals via myelinated vagus nerve to the medullary centres. Activating these receptors stops inspiration.

Question 19

How does the respiratory system respond to particles? What are some of these particles?

Answer 19

Irritant sensors in the airways activate myelinated and unmyelinated C-fibres in the vagus nerve causing reflex constriction of the bronchioles, coughing, rapid shallow breathing and increased mucous secretion

The irritant sensors respond to noxious mechanic and chemical stimuli (smoke, smog, pollen….), histamine from allergic reactions and lung hyperinflation

Question 20

How is PCO2 measured? Where are these sensors?

Answer 20

Using chemoreceptors in:

• the carotid bodies (chemoreceptors off the carotid vessels [vessels going to and from the brain])
• the aortic bodies (chemoreceptors off the aorta)
• central chemoreceptors on the ventral (front) of the medulla

Question 21

What makes the carotid and aortic bodies ideal for measuring PCO2?

Answer 21

They are located just before/after important organs (carotid before/after the brain, aortic after the heart) and are highly vascularised (have a high blood flow relative to their metabolic needs)

Question 22

How do the carotid and aortic bodies transmit their information about the CO2 concentration?

Answer 22

Carotid bodies via the carotid sinus nerves which connects with the glossopharyngeal nerve IX (sympathetic nerve FYI)

Aortic bodies via the vagus nerve (parasympathetic nerve FYI)

Question 23

What does the central chemoreceptors measure?

Answer 23

the pH of the cerebrospinal fluid

Question 24

Label the diagram

Answer 24

Question 25

What is the function of the carotid sinus?

Answer 25

It measures the blood pressure

Question 26

What do the carotid vessels go into/out of?

Answer 26

The brain

Question 27

What is the ventral medulla surrounded by?

Answer 27

Cerebrospinal fluid

Question 28

What is a challenge the ventral medulla faces in measuring the pH of the blood?

Answer 28

protons cannot cross the blood brain barrier to get to the ventral surface of the medulla

Question 29

How can the ventral medulla measure pH without protons being able to cross the blood brain barrier?

Answer 29

CO2 can easily diffuse across all membranes and gets into the cerebrospinal fluid. In here it can form the weak acid carbonic acid which disassociates to produce a proton therefore can measure the acidity

Question 30

What are the two measure which ventilation is most sensitive to (i.e. what changes in the air we breathe are we most sensitive to)?

Answer 30

• Peripheral PCO2 (in the carotid and aortic bodies)
• Ventral medullary pH (the pH of the cerebrospinal fluid surrounding the medulla)

Question 31

What is this result of this graph showing?

Answer 31

The top graph is when PCO2 is kept a constant 42.6mmHg and the PO2 is dropped.

The bottom graph is when PO2 is decreased and PCO2 is not controlled.

It shows that the respiratory system is hypersensitive to oxygen concentration but only when PCO2 is not influencing the respiratory rate. This is because, as seen in the bottom graph when PCO2 decreases due to hyperventilation, PCO2 is the MAIN driving factor for the respiratory rate but when it is not influencing the respiratory rate, the body is very sensitive to decreasing PO2