Gas exchange

Question 1

External respiration

Answer 1

exchange of oxygen at the alveoli

exchange of carbon dioxide at the alveoli

Question 2

Internal respiration

Answer 2

exchange of oxygen at the tissue

exchange of carbon dioxide at the tissue

Question 3

Air composition

Answer 3

nitrogen- 597 mmHg
oxygen- 159mmHg
water- 2.5mmHg
carbon dioxide- 0.3mmHg

total partial pressure- 760mmHg

Question 4

Kpa to mmHg

Answer 4

mmHg= Kpa x 7.5

Question 5

Movement of gases

Answer 5

conducting zone by bulk flow

respiratory zone by diffusion

Question 6

Alveoli and capillary interface

Answer 6

oxygen dissolves in and diffuses through the surfactant
through alveolar wall
through capillary wall
into plasm
into RBC
combined with haemoglobin
carbon does the reverse

Question 7

Capillary and tissue interface

Answer 7

Bulk flow of blood to tissue
diffusion through RBC wall
through plasma
through capillary wall 
through tissue membrane
into mitochondria

Question 8

Dalton’s Law

Answer 8

total pressure of mixture of nonreacting gases is the sum of the partial pressures exerted by each of the gases in the mixture

Question 9

Henry’s law

Answer 9

the amount of gas in a solution depends on the partial pressure of the gas and it’s solubility

pressure decrease
gas’s ability to dissolve decrease

Question 10

Carbon dioxide

Answer 10

in air has a low partial pressure but high solubility

Question 11

Oxygen

Answer 11

in air has a high partial pressure but low solubility

Question 12

Diffusion

Answer 12

movement of gas from a high partial to a low partial pressure

dependent on
temperature
movement of molecule
diffusion gradient

Question 13

Ficks law

Answer 13

rate of diffusion is

directly proportional to-
surface area
diffusion gradient

inversely proportional to
-diffusion difference

the higher the surface area, the greater the diffusing ability of the gas, the greater the diffusion gradient and the shorter the diffusion pathway the greater the rate of diffusion

Question 14

Alveolar oxygen exchange

Answer 14

mixed venous blood contains 40mmHg partial Po2

alveoli air contains 104mmHg partial Po2

movement of oxygen from the alveoli to the venous blood occur

equilibrium reached after 0.25 seconds

Question 15

Oxygen exchange

Answer 15

oxyhaemoglobin doesn’t contribute to Po2 of capillary blood

once haemoglobin is saturated only oxygen in plasma contributes to partial pressure which the equals the alveolar partial pressure

there transfer of oxygen is perfusion limited

Question 16

Perfusion

Answer 16

passage of fluid through the circulatory system or lymphatic system to an organ or a tissue, usually referring to the delivery of blood to a capillary bed in tissues

Question 17

oxygen exchange in exercise

Answer 17

blood move more quickly through capillaries

no limit on diffusion or perfusion as capillaries are recruited

partial pressure are maintained

RBC pass through without oxygen being picked up but more capillaries and lung surface are recruited as oxygen demand increases

Question 18

Disease

Answer 18

patients with abnormal alveolar/ capillary interface
thickened barrier of exchange surfaces
diffusion of oxygen is reduced
suffer from diffusion limitations
limits exercise tolerance

application not ficks law

Question 19

Alveolar carbon dioxide exchange

Answer 19

mixed venous blood contain 45mmHg Pco2
alveolar Pco2 is 40mmHg
small diffusion gradient
as co2 is more soluble reaches equilibrium in 0.25 seconds

Question 20

Capillary and tissue interface

Answer 20

Bulk flow of blood to tissue
diffusion through RBC wall
through plasma
through capillary wall 
through tissue membrane
into mitochondria

Question 21

Inspiration

Answer 21

The respiratory centre in the medulla oblongata sends impulses to initiate inspiration, the muscles of inspiration are initiated and contract, Accessory muscles include sternocleidomastoid, scalene, pectorals minor, sertatus anterior. The diaphragm contracts and descends. The rib cage swings up and out, increasing the volume within the thorax. The intrapulmonary pressure starts to drop. The pleural pressure in the pleural space becomes more negative as the rib cage moves up and out. Intrapulmonary pressure becomes less than atmospheric pressure. Air is moved into the lungs down concentration gradient until equilibrium is reached and air movement stops.

Question 22

Expiration

Answer 22

The respiratory centre in the medulla oblongata stops initiating inspiration, respiratory muscles relax, diaphragm moves up as the ribcage moves down and in. the lungs recoil due to the elastic recoil, intra pulmonary pressure rises, intrapleural pressure becomes less negative air moves down a concentration gradient until equilibrium is reached.