Haematopoiesis

Question 1

What is haematopoiesis

Answer 1

Production of new blood cells

Question 2

Numbers

Answer 2

420 billion each day
175 billion RBCs
70 billion WBCs
175 billion platelets

If needed production can increase by 5-10 times

Question 3

What are HSCs

Answer 3

Haematopoietic Stem Cell.
A multipotent stem cell (can differentiate into multiple but limited types of cell)

Question 4

Stem cell potency

Answer 4

Question 5

How do they provide so many blood cells per day

Answer 5

Intrinsic and extrinsic factors regulate the balance of symmetric and asymmetric cell division to maintain HSC number and blood cell production.

HSCs give rise to all blood cell types via committed oligopotent progenitor cell intermediates

Question 6

What is symmetric and asymmetric division

Answer 6

Symmetric - stem cell divides into 2 stem cells
Asymmetric - Parent divides to produce 2 daughter cells which are different. Eg. One remains a stem cell, one becomes a differentiated or progenitor cell

Question 7

What is primitive haematopoiesis and definitve haematopoeisis, then after that

Answer 7

Haematopoeisis during embryonic deveolpemt in the yolk sac where blood cells are produced in the mesoderm layer for the first 0-6 weeks.

Definite haematopoeisis continues after for 2-7 months being produced from the AGM region, populating the foetal liver, thymus and spleen.

After 7 months HSCs populate bone marrow, the most important primray site of haematopoeisis from then onwards.

Question 8

What is the haemotopoietic niche

Answer 8

The specialised microenvironment in the bone marrow supporting, regulating and maintaining the HSCs.

Question 9

Summary of part 2

Answer 9

Specific combinations of cytokines, transcription factors and cell signalling molecules drive the multipotent progenitor cells down specific lineage pathways when differentiating into specific cell types

Combination of general and lineage specific transcription factors enhance or repress gene expression of cell specific genes

Megakaryotocyte maturation involves preparing cells to make platelets

Erythroocyte maturation involves synthesis of haemoglobin and enucleation

Platelet release from megakaryocytes occur via proplatelet formation