Hemopoiesis: Blood Cell Formation

Question 1

Where are blood cells produced

Answer 1

1. In embyro the yolk sac is the primary site
2. In the third trimester of pregnancy the bone marrow supersedes the yolk sac
3. In adults the stem cells in the bone marrow produce blood cells
4. The spleen and liver can also form red blood cells (sites of haemopoiesis)

Question 2

How is yellow marrow different to red marrow

Answer 2

Yellow marrow contains adipose tissue and is inert whereas red bone marrow contains stem cells involved in hematopoiesis. As a child ages red marrow is gradually replaced with yellow marrow

Question 3

What are the features of stem cells in haemopoeisis

Answer 3

1. Self renew
2. Multipotent - capable of differentiating into all cell types within one lineage of blood cell
3. Replicate slowly

Question 4

Explain the role of the erythroblastic island

Answer 4

1. Found in the bone marrow
2. Composed of a central macrophage surrounded by erythrocyte precursors
3. Allows erythroblast development, differentiation and proliferation

Question 5

How is hemopoiesis controlled
How is thrombopoiesis (formation of platelets) controlled

Answer 5

1. Controlled by erythropoietin - a hormone produced in the kidney (main) and liver that promotes blood cell growth via glycosylation
2. Controlled by thrombopoietin, but negative feedback occurs since platelets bind and degrade thrombopoietin, called platelet number self-regulation

Question 6

How is erythropoietin controlled

Answer 6

Gene for erythropoietin contains enhancer regions that act as oxygen sensors
This region binds hypoxia-inducible factor (HIF2) triggering expression

Question 7

Explain what neutrophils are (leukocyte)

Answer 7

1. Neutrophils are types of phagocytes
2. Make up 50-80% of circulating leukocytes
3. Have a single, multi-lobed nucleus
4. Function as non specific immune response to pathogens since they contain blue granules of proteases and anti-microbe molecules e.g. defensins
5. Circulate for 7-10 hours

Question 8

Explain what eosinophils are (leukocyte)

Answer 8

1. Kill parasites that cannot be digested
2. Bind to antibodies on parasites, dissolving their cell surface
3. Involved in allergies
4. Stain with eosin
5. Mechanism of action is Phagocytic

Question 9

Basophils and mast cells explained (leukocyte)

Answer 9

1. Basophils are the circulating version of mast cells, which exist in the mucosa and connective tissue
2. Involved in the acute inflammatory response
3. Allergy and hypersensitivity due to histamine release
4. Defend against larger parasites but not by phagocytosis

Question 10

Monocytes (leukocyte)

Answer 10

1. The largest leukocytes involved in Phagocytic defence
2. Circulate for a few hours before migrating into tissues
3. Enlargen and turn into macrophages
   4.

Question 11

Humoral immunity

Answer 11

1. Humoral immunity is immunity provided by secreting antibodies, proteins and peptides into extracellular fluids
2. Antibodies - proteins made in response to antigen detection
3. Cytokines - stimulates or inhibits cell differentiation
4. Interleukins - enable communication between leukocytes
5. Chemokines - induces chemotaxis and leukocyte activation