Red cells (3)

Question 1

Where are all blood cells derived from?

Answer 1

• bone marrow

- multipotent haemopoietic stem cells (HSCs), which give rise to lymphoid stem cells and myeloid stem cells

Question 2

What is haemopoiesis?

Answer 2

• the process by which the body produces blood cells
• haem= blood… poiesis= making
• occurs in adults mainly in bone marrow, esp. pelvis, femur and sternum

Question 3

What follows the myeloid stem cell/precursor in the origin of blood cells?

Answer 3

granulocyte (–> basophil, eosinophil, neutrophil), monocyte (–> macrophage), mast cell, erythrocyte, megakaryocyte (–> thrombocyte)

Question 4

What follows the lymphoid stem cell in the origin of blood cells?

Answer 4

B cell/ B lymphocyte (–>plasma cell), T cell/T lymphocyte, NK cell

Question 5

What are the 2 essential characteristics of HSCs?

Answer 5

• can self-renew–> some daughter cells remain as HSCs, a pool is not depleted
• can differentiate to mature progeny–> other daughter cells follow a differentiation pathway

Question 6

How does a myeloid stem cell/precursor give rise to erythrocytes?

Answer 6

myeloid stem cell–> proerythroblast–> early, intermediate, late erythroblast–> erythrocytes

Question 7

How does a myeloid stem cell/precursor give rise to erythrocytes?

Answer 7

myeloid stem cell–> proerythroblast–> erythroblasts–> erythrocytes

Question 8

What is erythropoietin?

Answer 8

• glycoprotein synthesised mainly in kidney (also in liver) in response to hypoxia
• growth factor for normal erythropoiesis
• stimulates bone marrow to produce more RBCs

Question 9

What is the main function of erythrocytes?

Answer 9

transport oxygen from lungs to tissues- binds to Fe2+ in haem groups of haemoglobin

Question 10

What is the structure of adult haemoglobin?

Answer 10

• made up of 4 subunits
• 2 alpha globin chains, 2 beta
• each chain bounds to a haem group, consisting of a ferrous iron held in a porphyrin ring

Question 11

How does haemoglobin differ at birth?

Answer 11

fetal haemoglobin (F) has 2 alpha and 2 gamma globin chains

Question 12

What are the sources of iron and their comparative absorption?

Answer 12

• haem iron (ferrous Fe2+) from animal products- best absorbed
• non-haem (ferric Fe3+) iron from food- requires reducing substances (vit C, ascorbic acid) for absorption

Question 13

Why is iron absorption tightly controlled by hepcidin?

Answer 13

• only 1-2mg per day absorbed, bc no physiological mechanism to excrete iron
• excess iron can be toxic to heart and liver

Question 14

Why are vitamin B12 and folate needed for the development of red blood cells?

Answer 14

• they are needed for dTTP synthesis (necessary for making thymidine)
• DNA synthesis needs 4 immediate precursors, including dTTP
• therefore, deficiency affects DNA synthesis and thus, cell division
• cells larger than normal, and not enough cells

Question 15

What are sources of vitamin B12?

Answer 15

• meat
• liver and kidney
• fish
• oysters and clams
• eggs
• milk and cheese
• fortified cereals

Question 16

What are sources of folic acid?

Answer 16

• green leafy vegetables
• cauliflower
• brussels sprouts
• liver and kidney
• whole grain cereals
• yeast
• fruit

Question 17

How is vitamin B12 absorbed?

Answer 17

• in stomach, B12 combines w/ IF made in gastric parietal cells
• in small intestine, B12-IF binds to receptors in ileum then is absorbed

Question 18

What are causes of vitamin B12 deficiency?

Answer 18

• inadequate intake
• inadequate secretion of IF e.g. pernicious anaemia
• malabsorption

Question 19

Where are red blood cells destroyed and what happens to the iron inside?

Answer 19

RBCs destroyed after 120 days by macrophages in the spleen–> macrophages store the iron released from haemoglobin breakdown–> transferred as ferritin–> returns to bone marrow

Question 20

What is a microcyte?

Answer 20

a RBC that is smaller than normal

Question 21

What does normocytic mean?

Answer 21

describes RBCs that are of normal size or anaemia w/ normal sized RBCs

Question 22

What is a macrocyte?

Answer 22

a red cell that is larger than normal

Question 23

What are the 3 types of macrocyte?

Answer 23

• round macrocyte
• oval macrocyte
• polychromatic macrocyte

Question 24

What is the area of central pallor?

Answer 24

• cells shaped like discs
• not much Hb in middle
• about 1/3 of diameter is pale

Question 25

What is hypochromia?

Answer 25

cells have a larger area of central pallor than normal–> indicates lower Hb content and flatter cells
(often goes w/ microcytosis)

Question 26

What is polychromasia?

Answer 26

inc. blue tinge in cytoplasm of RBC–> indicates that cell is young
(also macrocytic)

Question 27

What special stain is used to detect reticulocytes?

Answer 27

new methylene blue- stains for higher RNA content

less subjective than detecting polychromasia

Question 28

What is reticulocytosis?

Answer 28

inc. numbers of reticulocytes (immature RBCs)

- -> may occur as a response to bleeding or RBC destruction

Question 29

What is anisocytosis?

Answer 29

RBCs show more variation in size than is normal- some macrocytic, some microcytic

Question 30

What is poikilocytosis?

Answer 30

RBCs show more variation in shape than is normal

Question 31

What are some examples of poikilocytes?

Answer 31

• spherocyte
• irregularly contracted cell
• sickle cell
• target cell (has a dot in middle)
• elliptocyte
• fragment (piece of RBC)

Question 32

What are target cells?

Answer 32

RBCs w/ an accumulation of Hb in area of central pallor

–> may indicate obstructive jaundice, liver disease, haemoglobinopathies, hyposplenism

Question 33

What are sickle cells?

Answer 33

RBC in crescent shape

–> results from polymerisation of HbS, which is much less soluble thatn HbA in deoxygenated form

Question 34

When does HbS occur?

Answer 34

when 1 or 2 copies of an abnormal beta globin gene are inherited

Question 35

What affects ‘normal’?

Answer 35

• age
• gender
• ethnic origin
• physiological status
• altitude
• nutritional status
• cigarette smoking
• alcohol intake

Question 36

What is a reference range?

Answer 36

derived from a carefully defined reference population

• samples collected from healthy volunteers w/ defined characteristics
• analysed using same instrument and techniques that will be used for patient samples
• data analysed by appropriate statistical technique

Question 37

How do we determine the 95% range of data with a normal/Gaussian distribution?

Answer 37

mean value +- 2SD