Blood (Anatomy)

Question 1

Describe the morphological features of the formed elements of blood

Answer 1

Erythrocytes

• Biconcave discs.
• Anucleate and lack major organelles.

Neutrophils (granulocyte)

• Nucleus has 2-5 lobes.
• Numerous cytoplasmic granules.

Eosinophils

• Bilobed nucleus.
• Large refractile granules.

Basophils (granulocyte)

• Largest type of granulocyte.
• Irregularly-lobed nucleus.
• Numerous large overlying granules which often obscure the nucleus.
• Granules contain histamine and heparin.

Lymphocytes (Agranulocyte)
- Nucleus is spherical and densely stained.

Monocytes

• Large cells.
• Kidney-shaped nucleus.

Platelets

• Small cell fragments.
• Consist of a marginal bundle of actin filaments, alpha and delta granules, and an open canalicular system of membranous vesicles.

Question 2

Describe the relative abundance of each of the elements in a sample of normal blood

Answer 2

• Erythrocytes = 45% of whole blood
• Leukocytes = <1% of whole blood
• Neutrophils = 60-70% of total white blood cells
• Eosinophils = 3% of circulating white blood cells
• Basophils = <1% of circulating white blood cells
• Lymphocytes = 20-25% of circulating white blood cells
• Monocytes = 3-8% of circulating white blood cells
• Platelets = 55% of whole blood

Question 3

Describe the formation (haemopoiesis) of the elements of blood from stem cells found in the bone marrow

Answer 3

Haematopoiesis

• Occurs in the bone marrow.
• All blood cells develop from a pluripotential haemopoietic stem cell found in the marrow.
• The pluripotent stem cell ultimately produces all the different types of blood cell via a series of mitotic divisions.
• Pluripotent stem cells give rise to multipotent haemopoietic progenitors.
• Lymphoid progenitors give rise to B and T cells.
• Myeloid progenitors give rise to red blood cells, granulocytes, monocytes, megakaryocytes etc.

Question 4

What is an immature red blood cell called and why is it called this

Answer 4

• Reticulocyte

- Still retains reticulum

Question 5

What is the process of erythrocyte production and describe it

Answer 5

Name: Erythropoiesis

• Begins when a haemopoietic cell becomes an erythrocyte colony-forming unit (ECFU) which has receptors for erythropoietin (EPO), a hormone secreted by the kidneys.
• EPO stimulates the ECFU to transform into an erythroblast.
• The erythroblasts multiply, build up a large cell population, and synthesise haemoglobin.
• When this task is complete, the nucleus shrivels and is discharged from the cell.
• The cell is now called a reticulocyte.
• Reticulocytes leave the bone marrow and enter the bloodstream. In a day or two the last of the reticulin disintegrates and the cells becomes a mature erythrocyte.

Question 6

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Answer 6

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