Review

Haematopoiesis (1)

Creating new blood cells. The process that ensures the delivery of appropriate cell types in the appropriate numbers when needed.

Red blood cells characteristics (1)

• Carry oxygen in the body

• 20-30 trillion in the body

• Lifespan up to 120 days

• Produced 4000 million per day

White blood cells characteristics (1)

• Fight infection in the body

• Survive around 5-10 days on average (may be less during infection)

• Make 10,000 million per day

Platelets characteristics (1)

• Small cell fragments that promote clotting

• Survive minutes to days

• Produce 400,000 million/day

• Too many blocks vessels 

• To fewcauses bleeding and bruising

What cells can multipotent haematopoietic stem cells give arise to? (1)

Megakaryocyte (—> platelets), erythrocytes, monocytes, neutrophils, basophil, eosinophil

How can stem cells differentiate (1)

Into different maturing precursor blood types or can self-renew to produce more identical stem cells and maintain stem cell number

Proliferating precursor cells allow _____ in production (1)

rapid change

How many cycles does a proliferating haematopoietic cells go through (1)

19

What is the “stem cell niche” (1)

Local hormones “cytokines”

Adhesive proteins

Supporting “stromal” cells

How long does it take for stem cells to make replacement cells (1)

20 days

Proliferating cell summary (1)

1. Proliferating cells have many cycles of replication

2. Proliferating cells cannot self-renew

3. Many proliferating cells die

4. The cell types formed may be directed

Cytokines (1)

Small locally active hormones. They act together to control the production of blood cells 

Erythropoietin (Epo) (1)

Epo is to ensure that the red cell number is sufficient to deliver oxygen to tissues whatever the need. Oxygen supply requires sufficient red cells- but an excess number is dangerous so this must be controlled. It acts mainly on red cells precursors it enhances their survival and increases maturation

Mechanism behind Epo (1)

Oxygen level is sense in the kidney, if levels drop then Epo secretion is increased. When red cells numbers are sufficient then oxygen level is restored and Epo secretion is reduced again.

** Responding to the O₂ , not necessarily red cell numbers

Granulocyte colony stimulation factor (G-CSF) (1)

It is to ensure that the neutrophil number and function is sufficient to fight infection without overproduction. It must provide a baseline number to protect the body, but also respond very rapidly during infection with no upper limit to number and improved function. Acting mainly on the late granulocyte precursors and increases maturation rate and granule formation to massively increase output and function

G-CSF mechanism (1)

Body detects infection or inflammation , G-CSF is released by endothelial cells causing increased neutrophil formation release and infections. Once that stimulus is resolved then the G-CSF production stops and its effects cease

Thrombopoietin (Tpo) (1)

It is to ensure that there are always enough platelets to prevent haemorrhage. It must achieve the correct number of platelets. It acts mainly on megakaryocytes precursors within the proliferating pool to increase number and rate of maturation

Tpo mechanism (1)

Produced in fairly constant amounts by the liver but control is achieved because mature platelets are able to bind to the Tpo and destroy it. If platelet numbers are high the level of Tpo is reduced, if numbers are low (like after bleeding) Tpo level rises to stimulate production of platelets 

Cytokines almost always work by altering _________ (1)

cell death in proliferating pool