Week 1 .4

Question 1

What is ventilation?

Answer 1

Air getting to the alveoli in L/min

Question 2

How does perfusion and ventilation vary across the lung?

Answer 2

Ventilation exceeds perfusion at the apex of the lung and perfusion exceeds ventilation at the base. This is based on gravity

Based on alveolar pressure and arterial pressure

Question 3

Where in the lungs is there a balance in alveolar and arterial pressure?

Answer 3

Around rib 3

Question 4

What is shunt and when does it occur?

Answer 4

Shunt occurs when we have mismatch - perfusion is greater than ventilation. Blood passes poorly ventilated alveoli and thus isn’t oxygenated. Blood returns to heart having not undergone gas exchange. This is shunt

Question 5

What is alveolar dead space?

Answer 5

Ventilation exceeds perfusion so more air is in alveoli than can participate in gas exchange.

Question 6

In which situations do we find alveolar dead space? (2)

Answer 6

At the apex of the lungs to a small extent, but usually in pulmonary embolisms when blood flow is restricted

Question 7

How do we solve alveolar dead space issue?

Answer 7

Blood vessels near highly ventilated alveoli vasodilate so more O2 can get out of alveoli and CO2 can diffuse in.

Additionally, low levels of CO2 in alveoli cause bronchoconstriction, which reduces ventilation

Question 8

How do our lungs overcome mismatch where perfusion>ventilation?

Answer 8

When lungs are hypoxic, blood vessels going by poorly ventilated alveoli vasoconstrict so less blood can match low ventilation levels, and its blood is diverted to better ventilated alveoli

Also increased CO2 in alveoli causes bronchodilation, which allows more ventilation to occur

Question 9

How much o2 is is found in the blood and how is it organised?

Answer 9

200ml/L. 3ml in plasma and 197ml in haemoglobin (98%)

Question 10

What determines the amount of O2 carried in haemoglobin?

Answer 10

The pO2 in arterial plasma (100mmHg)

Question 11

How much O2 and CO2 do our tissues metabolise?

Answer 11

250ml/min O2 and 200ml/min CO2

Question 12

If our haemoglobin is fully saturated, how much O2 is being carried in the blood? How much of this isn’t used for our tissues?

Answer 12

1000ml. Our cardiac output is 5L/min and we have 200ml/L O2 in our blood, 200*5 = 1000ml/min.

Our tissues only require 250ml/min so we have 75% O2 reserve

Question 13

How is the partial pressure gradient maintained between alveoli and capillary when O2 is being diffused? How long does the transfer take?

Answer 13

Returning blood has 40mmHg O2. This means O2 is sucked into capillary, then Haemoglobin immediately sucks this O2 in to fill 4 spaces. When all the haem is stuffed full, the RBC is fully saturated and the blood reaches 100mmHg. Takes 0.25 seconds

Question 14

What’s the pO2 and percentage saturation in venous blood?

Answer 14

pO2 is 40mmHg and 75% O2 saturated haemoglobin

Question 15

What can cause anaemia? (3)

Answer 15

• Iron deficiency (lack of haemoglobin)
• Vitamin B12 deficiency (makes RBC’s)
• Haemorrhage (loss of RBC’s)

Question 16

What is anaemia?

Answer 16

Condition which reduces O2 carrying ability of blood. All haem is still saturated with O2, but there’s less haem, thus less O2

No change to pO2 in alveoli as there’s no ventilation change, thus no change in arterial pO2 as no lung issues

Question 17

What 4 factors affect O2 haemoglobin saturation?

Answer 17

pH, CO2, temp and DPG

Question 18

What causes the affinity of haem to O2 to decrease? Consider 3 factors

Answer 18

exercise causes lower pH due to lactic acid production. CO2 rises as we metabolise O2 faster. Body temp goes up. This means our tissues need more O2 so haem releases it and less than 75% O2 saturated haem returns to lungs

Graph shifts right.

Question 19

What causes the affinity of haem to O2 to increase? Consider 3 factors.

Answer 19

In hypothermia, pH increases, CO2 decreases and body temp decreases. Haem holds onto O2. Your body needs O2 but you cant access it.

Question 20

What is the significance of DPG?

Answer 20

It is a by-product of RBC’s. When RBC works harder, it releases DPG which reduces haem’s affinity to O2 so more O2 is released. RBC’s release DPG in hypoxic situations

Question 21

Why is carbon monoxide poisoning dangerous? What’re the symptoms? (4)

Answer 21

Has affinity to haem 250X stronger than to O2, so displaces it

Nausea, headache, anaemia, hypoxia.

Question 22

How is CO2 distributed in transport?

Answer 22

7% stays in plasma dissolves
23% binds to haemoglobin to corm carbamino compound
70% converts to H2CO3-, then dissociates into H+ and CO3-
H+ is buffered in RBC by deoxyhaemoglobin
CO3- exits, changing spots with Cl-, and travels in plasma

Question 23

How is CO2 released from blood and exchanged with O2?

Answer 23

Haem would rather bind to O2. The exact opposite process happens. CO2 diffuses out down conc gradient and into alveoli down partial pressure gradient (46mHg to 40mmHg)