Blood - Red Blood Cells

Question 1

Erythrocytes

Answer 1

5 billion RBC/ml blood
Shape: Biconcave disk
Large surface area
Favours diffusion
Diameter: 8um
Thickness: 2um

Question 2

Membrane flexibility and capillaries

Answer 2

Erythrocyte membranes are highly flexible allowing them to pass through narrow capillaries

99% of the blood vessels in the body are capillaries

Capillaries only hold 5% of the total blood

Question 3

Hypotonic vs Hypertonic

Answer 3

Hypotonic: Cells swell and lose shape
Hypertonic: Cells collapse but rigid cytoskeleton remains intact

Question 4

Red blood cell production

Answer 4

30000000000000 red blood cells
Each lives 120 days
Therefore every day 250000000000
This requires 3000000 nee cells to be synthesised every second

Question 5

Steps to control erythropoiesis

Answer 5

1. The kidneys detect reduced O2-carrying capacity of the blood
2. When less O2 is delivered to the kidneys, they secrete the hormone erythropoietin into the blood
3. Erythropoietin stimulates erythropoiesis by the bone marrow
4. The additional circulating erythrocytes increases the O2-carrying capacity of the blood
5. The increased O2-carrying capacity relieves the initial stimulus that triggered erythropoietin secretion

Question 6

Haem Groups

Answer 6

Four iron-containing, non-protein groups bound to the polypeptides

Each haem group can reversibly combine with one molecule of O2

Iron is present as Fe2+ which gives blood it’s red colour

Oxygenated Hb is bright red

Deoxygenated Hb is dark red

One harmoglobin molecule can carry 4 molecules of O2

O2 is poorly soluble in the plasma so 98.5% is carried in the blood bound to haemoglobin