Lecture 16 - Haemopoiesis

Question 1

What is haemopoiesis?

What kind of cells are blood cells derived from?

Answer 1

• The production of blood cells and platelets that occurs in bone marrow
• From haemopoietic stem cells which become common progenitor cells - these progenitor cells must differentiate into their lineage bound cells.

Question 2

What is meant by the term “selection” in terms of haemopoiesis?

Answer 2

Selection means that not all blood cells produced make it out of the bone marrow. 250 mil erythrocytes produced per day - only 40% make it into blood. Many are killed via apoptosis (particularly if they are not adequately synthesised).

Question 3

What is the process by which erythrocytes are formed? What growth factor is required?
What features do RBC’s have?

Answer 3

• Erythropoiesis
• Erythropoietin
• Last 120 days, degraded by liver/spleen - take 20 seconds to circulate entire body.

Question 4

How does the structure/contents of erythrocytes relate to its function?

Answer 4

1) Biconcave to increase SA for diffusion of gases
2) No nucleus to maximise oxygen holding capabilities
3) No mitochondria to ensure no oxygen is used up
4) Contain Hb to increase affinity of oxygen binding

Question 5

Describe what happens from a proerythroblast to RBC during erythropoiesis.
What is the cell in the final step before the nucleus is removed called? What does high amount of this cell in the blood tell us?

Answer 5

• Starting with a pro erythroblast, there is a large nucleus and lots of RNA. The cell nucleus gradually shrinks and RNA is moved along with it.
• Reticulocytes - high amounts in blood indicate significant blood loss (as more RBC’s are clearly being synthesised).

Question 6

What is erythropoietin released in response to and from where?
How does erythropoietin increase RBC population?

Answer 6

• Erythropoietin is released from the kidney after it senses hypoxia (low O2 levels)
• This stops apoptosis of erythrocyte progenitor cells
• It is made in the liver during fetal life and taken over by the kidney at birth.

Question 7

What is granulopoiesis?
Why are granulocytes named granulocytes?
What do they do?
What are the 3 main types of granulocyte?

Answer 7

• Production of granulocytes within bone marrow
• Due to abundant presence of granules in their cytoplasm
• Mediate inflammatory reactions by releasing cytokines, IL’s & leukotrienes.
• Neutrophil, eosinophil & basophil

Question 8

What are neutrophils?
What does their nucleus look like?
What are their functions?

Answer 8

• The most abundant WBC (60%) and the first line defence against bacteria.
• Multilobuled nucleus with lots of granules in cytoplasm
• They kill bacteria via phagocytosis, are involved in antigen presentation and produce neutrophil extracellular traps (NETS) as well as undergoing respiratory burst

Question 9

What growth factor stimulates granulocyte production? When is it released?
How does it do this?

Answer 9

• Granulocyte-colony stimulating factor (G-CSF)
• In response to inflammation
• by acting on bone marrow, increasing the number of circulating neutrophils or making them mature faster.

Question 10

What are the role of basophils?
What does their nucleus look like?
What do their granules contain?

Answer 10

• Release histamine which causes vasodilation & mediates hypersensitivity reactions.
• Bilobed nucleus (2 lobes)
• Histamine & Heparin

Question 11

What do eosinophils do?
What does their nucleus look like?
What do their granules contain?

Answer 11

• Phagocytose pathogens and fight parasitic worms
• 2 nuclear lobes
• Anthelminthic proteins to fight parasitic worms and cell component destroying enzymes.

Question 12

What are monocytes called when they are in tissues?
What is the role of these cells?
What does their nucleus look like?

Answer 12

• Monocytes in blood, macrophages in tissues
• First line of defence, to phagocytose pathogens and present foreign antigens
• Unilobular horse shoe nucleus

Question 13

What is thrombopoiesis?
What is the role of thrombocytes?
What are their main features?

Answer 13

• Formation of thrombocytes (platelets) in bone marrow
• Have special receptors in surface that cause aggregation of platelets
• No nucleus, biconvex shape, contain vast amounts of proteins and clotting factors.

Question 14

How does thrombopoiesis occur and what is it upregulated by?

Answer 14

• Breakdown of each megakaryocyte creates 2-3,000 platelets

- Upregulated by thrombopoietin in the liver

Question 15

What is lymphopoiesis?

Answer 15

The production of lymphocytes (T, B & Natural Killers)

Question 16

What is the main role of B-lymphocytes?

Where does maturation occur?

Answer 16

• To produce antibodies - each B cell is specific to 1 antigen. Plays a part in humoral adaptive immunity and can activate T-cells.
• In the bone marrow - and then in intestines, spleen and lymph nodes.

Question 17

What is the role of T-lymphocytes?

Where do they migrate to from the bone marrow?

Answer 17

• Kill virus infected cells, neoplastic cells and transplanted tissue
• Activate B-cells to make antibodies with IL-4
• Have large nucleus with small rim of cytoplasm
• They migrate to thymus to mature, then stored in lymphoid organs

Question 18

What is plasma?

What are its constituents?

Answer 18

• Makes up majority of circulating volume as it is the watery component of blood and supporting medium for all circulating blood cells.
• 92% water, 8% protein and some ions
• Important proteins include albumin (for oncotic pressure), clotting factors and hormones.