Components and function of the blood (Theme 2)

Question 1

Methods of transporting CO2 in the blood.

Answer 1

Most of it is in bicarbonate form, 68%.

22% as carbaminohaemoglobin

10% dissolved in plasma (more soluble that O2)

Question 2

Fetal haemoglobin (HbF)

Answer 2

HbF contains 2 alpha and 2 gamma units.

HbF has a very low affinity to 2,3-DPG, this maintains the T state, retaining for oxygen.

HbF has a much higher affinity to O2 than adult haemoglobin (HbA)

Question 3

Oxygen transport in the blood

Answer 3

Oxygen is poorly soluble in plasma: only 0.003ml of O2 is present per 100ml of plasma/ mm Hg.

Most of O2 is carried in haemoglobin (Hb): 1.39ml of O2 is carried by Hb/ g of blood.

Question 4

Haemoglobin

Answer 4

Quaternary protein that is the primary mode of transport for O2 in the blood. Makes up 95% of RBC dry weight.

Structure:
4 polypeptide chains- 2 alpha, 2 beta.
One Fe2+ in the haem group, the group gives it colour.

Mechanism with O2:
Each unit carries one O2 molecule. Binding of one O2 causes confirmation change= cooperativity of other units.

Release of one O2 molecule from one unit also triggers the release from other units.

Question 5

Average amount of Hb in adults.

Answer 5

In males: 13-17 g/dL

In females: 12-16 g/dL

Question 6

Myoglobin

Answer 6

Oxygen storage in muscles.

Only has one polypeptide change so does not undergo cooperativity.

Has higher affinity to O2 than HbA but lower than HbF.

Question 7

Respiratory control of O2 in the blood.

Answer 7

Respiratory control is either triggered by fall in O2 lower than 88% or a rise in H+ in the cerebrospinal fluid (CSF)
O2 below 90% is clinically significant so CSF control is more mandatory.

CO2 reacts with water in the CSF, producing H+. This is picked up in medullary receptors.

H+ in the blood is only picked up by chemoreceptors in the aortic and carotid bodies.

Question 8

Erythrocytes

Answer 8

Red blood cells produced via erythropoiesis (branch from haemopoiesis).

Cells is biconcave and anucleate.

Life span- mature RBC last 120 days.

Contain Hb which is the primary transport of O2 in the blood.

Question 9

Average hematocrit in adults

Answer 9

Haematocrit- the ratio of volume RBCs to total blood volume

Males: 40-52%

Females: 36- 48%

Question 10

Mean corpuscular volume

Answer 10

Volume of red blood cells

80-100 fL (femtolitre)

Question 11

Erythropoiesis

Answer 11

The development of red blood cells.

During embryogenesis: occurs in the liver, spleen, lymph nodes and yolk sac.
After birth occurs in the bone marrow.
After 20 years, occurs in membranous bones.

Development from stem cells-
1. Derive from hematopoietic MULTIPOTENT stem cells.

2. Become multipotent myeloid progenitor cells.
3. Cell becomes committed and undergoes maturity into erythrocytes under terminal differentiation.

Question 12

General development of mature cells from stem cells.

Answer 12

1. Derived from MULTIPOTENT stem cells
2. Become multipotent progenitor cells.
3. Undergo commitment and become lineage-committed progenitor cells.
4. Proliferates then undergoes terminal differentiation to form mature cells.

Question 13

Erythropoietin

Answer 13

Cytokine made in the kidneys used especially in the early haematopoietic stages, in the bone marrow .

Used as a drug to combat anaemia in the forms: Epogen/Procrit, Aranesp.

Question 14

Methemoglobinemia

Answer 14

Anaemia where O2 cannot sufficiently bind to Hb due to Fe2+ in the haem group (ferrous), being oxidised to Fe3+ (ferric).

Causes:
Hereditary decrease of NADH (reducing agent)
Congenital mutation of Hb
Toxic substances

Question 15

CO poisoning

Answer 15

CO has affinity to Hb 250x stronger than O2.

Low levels of CO displaces O2, as it prevents O2 from binding.
Symptoms:
Dizziness, nausea, headaches.

Treatment: 95 % O2 (compared to usual 21%) and 5 % CO2.

Question 16

Reticulocytes

Answer 16

Immature RBCs, precursor of erythrocytes.

Life span= 2 days.

Reticulocyte indications: bone marrow activity
Low count= Erythropoiesis is low,
High count= haemolytic anaemia (erythrocytes are dying so bone marrow compensates by making more reticulocytes).

Question 17

Polycythaemia

Answer 17

Blood is very viscous due to very high RBC count.

This can clog vessels and cause stroke/ ischaemia.

Physiological polycythaemia:
Increase in RBCs due to living in higher altitudes. Homeostatic response to low O2 levels.
Endurance athletes train at higher altitudes to increase RBCs, increasing O2 carrying capacity.

Polycythemia vera:
Blood cancer that causes bone marrow to produce too many RBCs.
Likelihood of developing increases with age.
Treatment: venesection (phlebotomy), essential controlled blood letting, with a needle.

Question 18

Pernicious anaemia

Answer 18

Malabsorption of vitamin B12 due to loss of intrinsic factor from gastric parietal cells.

Intrinsic factor is vital for the absorption of vit B12 in the gut.

Question 19

Megaloblastic anaemia

Answer 19

Bone marrow produces megaloblast, large immature red blood cells.

Can occur as a result of B12 or folic acid deficiency

Question 20

Microcytic hypochromic anaemia

Answer 20

Anaemia, presented as very small RBCs. Mean corpuscular volume is <80 fL.

Cause: iron deficiency, unable to make haem group, causing it to be ‘hypochromic’

Question 21

Vitamin B12

Answer 21

Vitamin that forms thymidine, essential for the synthesis of DNA.

Essential in RBCs, skin and gametogenesis.

Deficiency can cause anaemia, like pernicious anaemia.
Deficiency risk factors:
Old Age
Veganism
Lymphoma
Haemolytic anaemia
Pregnancy

Question 22

Folic acid

Answer 22

Folic acid is a B vitamin essential for the body to make DNA, RNA, and metabolise amino acids for cell division.

Can only be obtained from diet/ supplement.

Deficiency can cause anemia, such as megaloblastic anaemia.

Question 23

Role of iron in red blood cells.

Answer 23

65% of iron is stored in RBCs, in haem.

30% are in intracellular storage:
Ferritin
Hemosiderin

Storage in the reticuloendothelial system:
Liver, spleen, RBC, bone marrow, macrophages, monocytes

Iron deficiency can lead to anaemia- like microcytic hypochromic anaemia

Question 24

Mean cell haemoglobin (MCH)

Answer 24

The average amount of Hb in each red blood cell.

Average = 27-34 pcg