Physiology

Question 1

What is the primary function of the lungs?

Answer 1

To provide a surface for the exchange of O2 and CO2 between atmospheric air and blood

Question 2

Define ‘external respiration’

Answer 2

Breathing and exchange of blood gases with the atmosphere

Question 3

Define ‘internal respiration’

Answer 3

Properties of respiratory and circulatory sytems to deliver O2 from air to mitochondria for cellular respiration and transport of CO2 from cells to lungs

Question 4

Which structures make up the conducting zone?

Answer 4

Trachea, bronchi, bronchioles, terminal bronchioles

Question 5

Which structures make up the respiratory zone?

Answer 5

Respiratory bronchi, alveolar ducts, alveolar sacs

Question 6

How do gas molecules move into the respiratory zone?

Answer 6

No forward bulk air flow, movement is by diffusion. A concentration gradient is required for this.

Question 7

What is Vᴇ ?

Answer 7

Tidal breath/volume expired. It is divided into the respiratory and conducting zones.

Question 8

What is Vᴀ ?

Answer 8

Alveolar ventilation (respiratory zone)

Question 9

What is Vᴅ ?

Answer 9

Dead space volume (conducting zone). Is always constant, but can be altered by smooth muscle in airway walls.

Question 10

What is the relationship between Vᴇ, Vᴀ and Vᴅ?

Answer 10

Vᴇ = Vᴀ + Vᴅ

Question 11

What are the implicationsn for animals that pant?

Answer 11

Causes a reduced alveolar ventilation but dead space ventilation is constant. Causes a reduced tidal breath and very little air reaches the resp zone. Air is forced over the wet surface of the airways causing water to evaporate and the blood to cool

Question 12

Describe the blood supply to the lungs

Answer 12

Mixed deoxygenated venous blood from the body enters the right atrium. It is pumped in the pulmonary artery (R and L) from the right ventricle to the lungs where it forms dense pulmonary circulation.
Pulmonary vein brings oxygenated blood back to the heart into the L atrium.
Conducting airways are supplied by bronchial circulation derived from the aorta (common carotid artery) - systemic circulation

Question 13

Which nerves innervate the intercostal muscles and diaphragm?

Answer 13

Intercostal muscles - intercostal nerve (somatic)
Diaphragm - phrenic nerve (somatic)
Both nerves arise from the medulla oblongata

Question 14

Describe breathing

Answer 14

1. Diaphragm and external intercostals contract to expand the thoracic cavity (ribs move laterally and diaphragm flattens
2. Creates a -ve pressure int he lungs which draws air into them
3. Diaphragm and intercostal muscles relax, causing lungs to recoil
4. Lungs pull chest wall and diaphragm back to resting position
   * visceral and parietal pleura are closely adhered, allows lungs to expand*
   * movement of abdominal contents helps to expel air in quadropeds*

Question 15

Define ‘pneumothorax’

Answer 15

Trauma causes the seal between the 2 sheets of pleura to break. Lungs won’t expand.

Question 16

Describe alveolar epithelium

Answer 16

Wet inner surface with attractive forces between neighbouring water molecules. Causes surface tension. To prevent collapse, some air is always retained in the alveoli and some cells produce a surfactant to reduce surface tension.

Question 17

What is normal atmospheric pressure?

Answer 17

760mmHg

Question 18

What is the pressure in the trachea and why is it lower than atmospheric?

Answer 18

149mmHg

Trachea is warm, air contains water vapour which exerts its own partial pressure.

Question 19

What is the pressure in the alveoli?

Answer 19

100mmHg

CO2 has a substantial presence in alveolar air which causes a reduction in Po2. O2 is also being driven into the blood.

Question 20

What is the pressure in pulmonary venous blood?

Answer 20

96mmHg

Should equilibriate with alveolar air but some arterial blood moves into the venous system (bronchial venous shunt)

Question 21

What is the pressure in arterial blood?

Answer 21

92mmHg

Question 22

What is the pressure in sytemic veins?

Answer 22

40mmHg

Question 23

How is external respiration regulated?

Answer 23

Chemoreceptors inform the brain respiratory centre (medulla) which adjusts breathing rate to compensate for conditions.

Question 24

What is the role of carotid bodies?

Answer 24

Located in carotid arteries and contain O2 receptors which measure O2 tension in the blood. Connected to medulla by parasympathetic nerves. A decrease in [O2] stimulates medulla.

Question 25

What is the role of CO2 receptors?

Answer 25

Carotid fluid forms CSF which perfuses the medulla. Changes in [CO2] are deteted by central CO2 receptors in the medulla.
More sensitive, alveolar ventilation is adjusted accordingly.

Question 26

How is CO2 carried in the blood?

Answer 26

A little can be dissolved in blood plasma.
Some reacts with amino groups on plasma protein to form carboamino groups (limited by H+; 5%)
Diffuses into RBC corpuscle which contains carbonic anhydrase which hydrates CO2 to carbonic acid. This dissociates to bicarbonate and H+ (90%).
Bicarbonate diffuses out of corpuscle and Cl- in (chloride shift). H+ accepted by Hb in place of O2.

Question 27

Explain how gases are transferred in the lungs

Answer 27

1. At rest, RBC spends 0.75s in transit over an alveolus
2. Venous blood arrives at the lung with a tension of 40mmHg
3. Blood and alveolar PO2 equilibriate within 0.25s
4. During exercise, transit time is reduced to 0.25s
5. Disease of the alveoli thickens the diffusional barrier and limits O2 uptake by slowing down equilibrium time
6. Low PAo2, O2 diffusion will be slower and pulmonary venous blood tension will be lower
7. Anaemia doesn’t affect )2 diffusion so PO2 reaches a normal level
8. Increased lung barrier thickness /airway occlusion/decreased PatmO2 is defined as hypoxic hypoxia