Red cells (3) Flashcards
Where are all blood cells derived from?
- bone marrow
- multipotent haemopoietic stem cells (HSCs), which give rise to lymphoid stem cells and myeloid stem cells
What is haemopoiesis?
- 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
What follows the myeloid stem cell/precursor in the origin of blood cells?
granulocyte (–> basophil, eosinophil, neutrophil), monocyte (–> macrophage), mast cell, erythrocyte, megakaryocyte (–> thrombocyte)
What follows the lymphoid stem cell in the origin of blood cells?
B cell/ B lymphocyte (–>plasma cell), T cell/T lymphocyte, NK cell
What are the 2 essential characteristics of HSCs?
- 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
How does a myeloid stem cell/precursor give rise to erythrocytes?
myeloid stem cell–> proerythroblast–> early, intermediate, late erythroblast–> erythrocytes
How does a myeloid stem cell/precursor give rise to erythrocytes?
myeloid stem cell–> proerythroblast–> erythroblasts–> erythrocytes
What is erythropoietin?
- glycoprotein synthesised mainly in kidney (also in liver) in response to hypoxia
- growth factor for normal erythropoiesis
- stimulates bone marrow to produce more RBCs
What is the main function of erythrocytes?
transport oxygen from lungs to tissues- binds to Fe2+ in haem groups of haemoglobin
What is the structure of adult haemoglobin?
- 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
How does haemoglobin differ at birth?
fetal haemoglobin (F) has 2 alpha and 2 gamma globin chains
What are the sources of iron and their comparative absorption?
- 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
Why is iron absorption tightly controlled by hepcidin?
- only 1-2mg per day absorbed, bc no physiological mechanism to excrete iron
- excess iron can be toxic to heart and liver
Why are vitamin B12 and folate needed for the development of red blood cells?
- 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
What are sources of vitamin B12?
- meat
- liver and kidney
- fish
- oysters and clams
- eggs
- milk and cheese
- fortified cereals
What are sources of folic acid?
- green leafy vegetables
- cauliflower
- brussels sprouts
- liver and kidney
- whole grain cereals
- yeast
- fruit
How is vitamin B12 absorbed?
- in stomach, B12 combines w/ IF made in gastric parietal cells
- in small intestine, B12-IF binds to receptors in ileum then is absorbed
What are causes of vitamin B12 deficiency?
- inadequate intake
- inadequate secretion of IF e.g. pernicious anaemia
- malabsorption
Where are red blood cells destroyed and what happens to the iron inside?
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
What is a microcyte?
a RBC that is smaller than normal
What does normocytic mean?
describes RBCs that are of normal size or anaemia w/ normal sized RBCs
What is a macrocyte?
a red cell that is larger than normal
What are the 3 types of macrocyte?
- round macrocyte
- oval macrocyte
- polychromatic macrocyte
What is the area of central pallor?
- cells shaped like discs
- not much Hb in middle
- about 1/3 of diameter is pale
What is hypochromia?
cells have a larger area of central pallor than normal–> indicates lower Hb content and flatter cells
(often goes w/ microcytosis)
What is polychromasia?
inc. blue tinge in cytoplasm of RBC–> indicates that cell is young
(also macrocytic)
What special stain is used to detect reticulocytes?
new methylene blue- stains for higher RNA content
less subjective than detecting polychromasia
What is reticulocytosis?
inc. numbers of reticulocytes (immature RBCs)
- -> may occur as a response to bleeding or RBC destruction
What is anisocytosis?
RBCs show more variation in size than is normal- some macrocytic, some microcytic
What is poikilocytosis?
RBCs show more variation in shape than is normal
What are some examples of poikilocytes?
- spherocyte
- irregularly contracted cell
- sickle cell
- target cell (has a dot in middle)
- elliptocyte
- fragment (piece of RBC)
What are target cells?
RBCs w/ an accumulation of Hb in area of central pallor
–> may indicate obstructive jaundice, liver disease, haemoglobinopathies, hyposplenism
What are sickle cells?
RBC in crescent shape
–> results from polymerisation of HbS, which is much less soluble thatn HbA in deoxygenated form
When does HbS occur?
when 1 or 2 copies of an abnormal beta globin gene are inherited
What affects ‘normal’?
- age
- gender
- ethnic origin
- physiological status
- altitude
- nutritional status
- cigarette smoking
- alcohol intake
What is a reference range?
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
How do we determine the 95% range of data with a normal/Gaussian distribution?
mean value +- 2SD
