Section 2: Formation of Blood Cells

Question 1

How is the number of erythrocytes and platelets regulated?

Answer 1

Via negative feedback systems, so their numbers remain fairly stable.

Question 2

Define haemopoiesis

Answer 2

The process by which formed elements develop.

Question 3

Where does haemopoiesis occur in the 6 months following fertilisation of an egg, and in the last 3 months before birth and during life?

Answer 3

First 6 months before birth: yolk sac of the embryo, then the liver, spleen, thymus and lympth nodes.
Last 3 months before birth and till death: red bone marrow.

Question 4

What is red bone marrow, and where is it found in a certain bone tissue?

Answer 4

Highly vascularised connective tissue found between trabeculae in spongy bone tissue.

Question 5

Where in the body is red bone marrow chiefly found?

Answer 5

In the bones of the axial skeleton, pectoral and pelvic girdles, and the proximal epiphyses of the humerus and femur.

Question 6

What are pluripotent stem cells?

Answer 6

Cells that have the ability to differentiate into many different types of cells.

Question 7

What is the percentage of pluripotent stem cells present in red bone marrow?

Answer 7

0.05 - 0.1%

Question 8

What are pluripotent stem cells derived from?

Answer 8

The mesenchyme: the tissue from which all connective tissue develops.

Question 9

How does the quantity of red bone marrow present in the body change over time?

Answer 9

In new borns,: all bone marrow is red and active.
With age: red bone marrow in the medullary cavity of lone bones becomes less active and develops into yellow bone marrow.

Question 10

How does yellow bone marrow revert back into red bone marrow, and under what conditions does this happen?

Answer 10

Under severe conditions (such as excessive blood loss), pluripotent stem cells are transferred from red bone marrow to yellow bone marrow, making the yellow bone marrow active.

Question 11

What are the two types of stem cells that pluripotent stem cells can develop into?

Answer 11

Myeloid and lymphoid.

Question 12

What cells can myeloid stem cells make?

Answer 12

1) Erythrocytes
2) Platelets
3) Monocytes
4) Basophils
5) Eosinophils
6) Neutrophils
7) Mast cells

Question 13

What cells can lymphoid stem cells make?

Answer 13

1) Lymphocytes

2) Natural killer cells

Question 14

What other cells, that don’t derive from myeloid or lymphoid stem cells, can pluripotent stem cells also develop into?

Answer 14

1) Adipocytes
2) Reticular cells
3) Osteoblasts
4) Chondroblasts
5) Muscle cells

Question 15

What are reticular cells?

Answer 15

Cells that produce reticular fibres which forms the stroma: the framework surronding red bone marrow cells.

Question 16

What are progenitor cells?

Answer 16

Cells that give rise to specific formed elements.

Question 17

What stem cells develop into progenitor cells?

Answer 17

They are formed from some myeloid stem cells.

Question 18

Give two facts about progenitor cells.

Answer 18

1) They are not capable of reproducing themselves.

2) They cannot be distinguished under a microscope.

Question 19

What does CFU stand for?

Answer 19

Colony forming units.

Question 20

Give three examples of CFUs.

Answer 20

1) CFU-E: Erythrocytes
2) CFU-Meg: Megakaryocytes –> Platelets
3) CFU-GM: Granulocytes –> neutrophils, and macrophages.

Question 21

What cells are CFUs?

Answer 21

Progenitor cells.

Question 22

What cell forms formed elements over many cell divisions?

Answer 22

Precursor cells.

Question 23

Give two examples of precursor cells.

Answer 23

1) Monoblasts –> monocytes

2) Eosinophilic myeloblasts –> eosinophils

Question 24

Which cell cannot be distinguished under a microscope and which cell have recognisable shapes?

Answer 24

1) Can’t be distinguished: progenitor cells.

2) Recognisable shapes: precursor cells.

Question 25

What are haemopoietic growth factors?

Answer 25

Hormones that regulate the differentiation and proliferation of particular progenitor cells.

Question 26

What is the function of erythropoietin?

Answer 26

Increases the number of erythrocyte precursor cells.

Question 27

Where is erythropoietin produced?

Answer 27

Between tubules in the kidneys.

Question 28

What affect does renal failure have on erythropoietin, and what are the consequences?

Answer 28

Renal failure = less erythropoietin produced = less erythrocytes = decreased hematocrit = reduced ability to transport oxygen around the body.

Question 29

What is the function of thrombopoietin?

Answer 29

Stimulate megakaryocytes to develop into platelets.

Question 30

Where is thrombopoietin produced?

Answer 30

The liver.

Question 31

Name two haemopoietic growth factors.

Answer 31

Erythropoietin and thrombopoietin.

Question 32

What are cytokines?

Answer 32

Small glycoproteins produced by erythrocytes, leucocytes, macrophages, fibroblasts, and endocrine cells.

Question 33

What are the two functions of cytokines?

Answer 33

1) Several cytokines regulate the development of different blood cells by stimulating the proliferation of progenitor cells.
2) Regulate the activity of non-specific defences and immune responses.

Question 34

What are the two important families that stimulate leucocyte formation?

Answer 34

1) Interleukins.

2) Colony-stimulating factors (CSFs).

Question 35

Which arteries do blood reach the red bone marrow via?

Answer 35

Nutrient and metaphyseal arteries.

Question 36

What are sinuses?

Answer 36

Enlarged, leaky capillaries that surrond red bone marrow cells and reticular fibres.

Question 37

How do formed blood cells leave the red bone marrow?

Answer 37

Via sinuses and other blood vessels, then via nutrient and periosteal veins.

Question 38

Out of leucocytes and all other formed elements which further divide when out of red bone marrow, and which do not?

Answer 38

Leucocytes = further divide. 
Others = do not.