Haemopoiesis

Question 1

List features of haematopoietic stem cells.

Answer 1

Perpetual life.
Ability to extensively proliferate.
Self-renewable.
Pluripotency (ability to differentiate into other cells).

Question 2

Across the lifespan, where does haematopoiesis occur?

Answer 2

Embryonic:
Aorta gonad mesonephros (AGM) region and yolk sac up until week 6 gestation.
Foetal liver from 6-22 weeks.
Bone marrow begins to take over from then on and becomes predominant after birth.

Question 3

In which bones is bone marrow found?

Answer 3

pelvic bones, ribs, spine (vertebral bodies), skull, proximal bones of arms/legs (femur, humerus).

Question 4

Briefly describe erythropoiesis.

Answer 4

The process by which RBCs are generated. (colony forming unit - erythrocytes from megakaryocytes erythroblast progenitors (MEP) from committed myeloid precursors (CMP) from haemopoetic stem cell.
Regulated by erythropoietin (EPO). EPO is synthesised and secreted by the kidneys in response to low oxygen tension within the tubules.
EPO stimulates RBC precursors. EPO stimulates blasts via a JAK/STAT pathway. Also role of erythroferrone, which travels to the liver to shut down hepcidin (negative regulator of iron absorption), to increase iron levels for erythropoiesis.

Question 5

Briefly describe granulopoiesis.

Answer 5

The process by which mature granulocytes are produced in the bone marrow from a myeloid stem cell (haemopoietic stem cell to committed myeloid precursor to granulocyte and monocyte progenitor).
Regulated by GCSF (granulocyte colony stimulating factor) and IL-6

Question 6

Briefly describe how an infection can result in granulopoiesis.

Answer 6

1. LPS from bacterial infection presented to immune cell, monocyte or fibroblast.
2. Monocyte releases IL-6.
3. Fibroblast stromal cell release MCSF (macrophage colony stimulating factor)
4. M-CSF stimulates the release of ADAM (a-disintegrin and metaproteinase enzyme)
5. ADAM travels to other immune cells and cleaves off their IL-6-R (IL6 receptor).
6. IL-6-R binds to IL-6 and forms a complex, which travels to the bone marrow to stimulate increased production.

Question 7

Briefly describe thrombopoiesis (megakaryopoiesis).

Answer 7

The process by which platelets from megakaryocytes are produced in bone marrow. (haemopoietic stem cell to committed myeloid progenitor to megakaryocyte erythroblast progenitor to colony forming unit - megakaryocyte).
Megarkaryocytes undergo repeated chromosome replication to 16-64n, and platelets budd off the surface of these big cells.
Thrombopoietin is the primary regulator, produced in the liver

Question 8

What is the term for too many RBCs in circulation?

Answer 8

Polycythaemia.

Question 9

What is the term for too many platelets in circulation?

Answer 9

Thrombocytosis, thrombocythaemia.

Question 10

What is the term for too many WBCs in circulation?

Answer 10

leucocytosis, leukaemia.

Question 11

What is the term for too few RBCs in circulation?

Answer 11

Anaemia

Question 12

What is the term for too few platelets in circulation?

Answer 12

Thrombocytopenia.

Question 13

What is the term for too few WBCs in circulation?

Answer 13

Leucopenia, lymphopenia, neutropenia.