Topic 7: Red blood cells and the haemoglobin

Question 1

What should be mentioned in this topic?

Answer 1

• Red blood cells
• Hemoglobin
• Age effect
• Transport of Blood Gases
• Hemoglobin as a buffer
• Degradation of the hemoglobin
• Factors affecting RBC Synthesis

Question 2

Red Blood Cells:

Answer 2

- No mitochondria
Average lifetime: 
Horse, dog - 120 days
Cattle, Swine – 60
Birds – 30

Question 3

Red Blood Cells:

Hemoglobin amount

Answer 3

120-180g/L

35% haemoglobin concentration

Question 4

Red Blood Cells:

• Mean Corpuscular Hemoglobin Concentration (MCHC)
• Mean Corpuscular Hemoglobin (MCH)
• Mean Corpuscular Volume (MCV)

Answer 4

MCHC: Hb/Ht – 5mmol/L
MCH: Hb/RBC – 0.45fmol/db
MCV: Ht/RBC – 80-100 femtoliter/pc

Question 5

Red Blood Cells:

Hemolysis

Answer 5

Red blood cells can undergo osmotic hemolysis. Hemolysis is the leakage or disruption of blood cells.

• RBC in isotonic solution – Cell does not change
• RBC in hypotonic solution – Water flows into cell, cell swells up - bursts
• RBC in hypertonic solution – Water leaves cell and cell shrinks.

Hemolysis can be brought about by:

• Physical effects
  
  • Freezing, Dissolving, Shaking, Shocking
• Chemical effects
  
  • Acids, Liposolvents, Surface tension reducers
• Toxins
  
  • Bacterial, Snake, Plant

Question 6

Red Blood Cells:

Osmotic resistance

Answer 6

RBCs can adapt to these slight changes easily. This is called osmotic resistance.
The minimal resistance is 70-120mmol/L NaCl. The maximal resistance is 50-90mmol/L NaCl Osmotic resistance is due to spectrin protein molecules on the internal side of the membrane giving it flexibility. These molecular springs are fixed forming a net on the internal side of the cell by ankyrine, actin and smaller connective molecules.

Question 7

Haemoglobin

Answer 7

It is the pigment colouring the red blood cells and plays a main role in the transport of the blood gases and the forming of the blood’s buffer capacity.
Synthesis requires Fe, Cu, Co, Mn, Zn, Pyridoxin B6 among others.

Question 8

Haemoglobin:

ferro-protoporphyrine

Answer 8

The haem is a ferro-protoporphyrine. In the porphyrine base, iron only has 4 coordination sites. The two other valences involved are bound to the imidazole ring of the protein under and over the porphyrine base. Only the iron atom can bind the Oxygen reversibly – Oxygenation (not oxidation). The oxygenated derivative is methaemoglobin. This binds oxygen irreversibly and is produced under normal conditions too but it is reversed by the methaemoglobin-reductase – NADPH system.

Question 9

Haemoglobin:

Structure

Answer 9

The structure of globin determines the characteristics of oxygen binding. The structure allows allosteric stimulation and is able to bind new oxygen even stronger after accepting the former one.

Question 10

Haemoglobin:

Age effect.

Answer 10

HB-F has a smaller affinity to the 2,3-DPG than the Hb-A due to its amino acid sequence. Normally this binds to the haemoglobin decreasing its Oxygen affinity enabling transfer of oxygen from mother to fetus. Complete lack of the 2,3-DPG increases the oxygen affinity of the haemoglobin to such a high degree that it binds oxygen irreversibly. Important in case of long term storage of blood.

Hb-A = 2 alpha + 2 beta chains 
Hb-F = 2 alpha + 2 gamma chains

Question 11

Transport of gases:

O2

Answer 11

• Binds to Fe2+

- 1 hem binds 1O2

Question 12

Transport of gases:

CO2

Answer 12

• Carbamino-haemoglobin
• Responsible for about 20% of the complete CO2 blood-transport
• Hb-NH2 + CO2 = Hb-N-COOH

Question 13

Transport of gases:

CO

Answer 13

• Binds reversibly though with 200 times larger affinity than to Oxygen

Question 14

Transport of gases:

OH and Cl radicals

Answer 14

• Binds irreversibly

Question 15

Haemoglobin as Buffer

Answer 15

Hb- anion is one of the two most important buffer bases in the blood. Buffer action is ensured by:
- HHb/Hb-
- 35% of the buffer capacity of the blood is provided by haemoglobin. The
deoxygenated Hb is a better proton acceptor than the oxygenated one

Question 16

Degradation of the Haemoglobin

Answer 16

During the degradation of the haemoglobin phagocytes convert the HEM part to bilirubin. Albumin binds bilirubin in the circulation. This is called bilirubin-I or indirect bilirubin or non-conjugated bilirubin.

Bilirubin dissociated from the albumin and it is taken up by the hepatocytes. A major proportion of bilirubin is conjugated with glucuronic acid, while the rest with the other molecules. This is called bilirubin-II.
Bilirubin is exreted to the bile and ends up in the gut where it is first deconjugated by the bacteria and further degradation products (stercobilinogen, stercobilin and urobilinogen) are produced. Most of the UBG is absorbed in the gut and transported back to the liver where it is converted back to bilirubin. Some is excreted by the kidney.

Question 17

Factors affecting RBC Synthesis:

Answer 17

• Oxygen supply
• Kidney status
• Age