Gas exchange

Question 1

Define ventilation

Answer 1

Ventilation - the movement of air through the conduction passages between the atmosphere and the lungs.

Question 2

Define diffusion

Answer 2

Diffusion - the movement of molecules from an area of high concentration to an area of low concentration.

Question 3

Define perfusion

Answer 3

Perfusion - the process in which blood is forced to flow through a network of microscopic vessels within biologic tissue, allowing exchange of oxygen and other molecules across semipermeable microvascular walls.

Question 4

Define External Respiration AND Internal Respiration

Answer 4

External Respiration - Occurs between alveolus and pulmonary capillaries.

Internal Respiration - Occurs between the systemic capillaries and body tissues.

Question 5

Describe FOUR factors which promote External Respiration.

Answer 5

1. Short diffusion distance between alveolus and capillary - In health lungs the respiratory membrane is 0.5 - 1ym thick so gas exchange is very rapid and efficient
2. Large surface area of alveoli - surface area of alveoli is a huge 70 m2. The greater the surface area the more gas that can diffuse across it in a given time.
3. Abundance of capillaries surround alveoli - With adequate transit time for blood through the capillaries. It take 0.25 secs for exchange of O2 and CO2 between alveoli and capillaries. Transit time for blood on pulmonary capillaries is 0.75 sec.
4. Moist alveolar surface - to allow the respiratory gases to dissolve (gases dissolve before diffusion).

Question 6

Define Partial Pressure

Answer 6

Partial pressure - Partial pressure gradients drive O2 and CO2 across the membrane.

Question 7

State where is PO2 is highest and the effect on O2 binding with haemoglobin

Answer 7

The partial pressure of O2 in the alveolus is higher than the partial pressure in the pulmonary capillaries which contain deoxygenated blood.
The greater the difference in PO2, the faster oxygen will combine with haemoglobin, until the available haemoglobin molecules are fully saturated.

Question 8

State where PCO2 is highest and the effect on CO2 diffusion

Answer 8

The partial pressure of carbon dioxide in blood is higher than in the alveolus, the greater the difference in partial pressure of CO2 across between the capillary and the alveolus, the faster it will diffuse.

Question 9

State the percentage of oxygen transported by Hb

Answer 9

98.5%

Question 10

Identify the ways carbon dioxide is transported in blood

Answer 10

70% is carried as bicarbonate ions.
7% is dissolved in plasma
23% bound to haemoglobin in red blood cells

Question 11

State which method transports the largest amount of CO2 and how it does this

Answer 11

The highest proportion of CO2 is transported in the blood plasma as bicarbonate ions.