blood cell physiology

Question 1

where do all blood cells originate in

Answer 1

bone marrow

Question 2

what are blood cells ultimately derived from

Answer 2

multipotent haemopoietic stem cells

Question 3

what 2 types of stem cells do multipotent haemopoietic stem cells give rise to

Answer 3

lymphoid stem cells, myeloid stem cells

Question 4

what 4 types of cells are derived from myeloid stem cells

Answer 4

red cells (erythroid), granulocytes, monocytes, platelets (megakaryocyte)

Question 5

how are stem cells able to self-renew and produce mature progeny

Answer 5

have ability to divide into two cells with different characteristics: one another stem cell, and the other a cell capable of differentiating to mature progeny

Question 6

myeloid stem cell to erythrocyte maturation pathway in bone marrow (mitosis so divides into 2 etc.)

Answer 6

myeloid stem cell -> proerythroblast -> (early -> mid -> late) erythroblast (leaves nucleus behind for macrophage digestion by squeezing cytoplasm out of endothelium) -> erythrocyte

Question 7

what is the process of red cell production called and where does it occur

Answer 7

erythropoiesis in bone marrow

Question 8

what does erythropoiesis require, and where and when is this synthesised

Answer 8

requires erythropoietin, which is synthesised mainly in the kidney in response to hypoxia

Question 9

% of erythropoietin synthesised in kidney and liver

Answer 9

kidney: 90%, liver: 10%

Question 10

what cells synthesise erythropoietin in the kidney

Answer 10

juxtatubular interstitial cells

Question 11

what cells synthesise erythropoietin in the liver

Answer 11

hepatocytes and interstitial cells

Question 12

where is erythropoietin secreted into and where does it go

Answer 12

capillaries to reach bone marrow

Question 13

intravascular life span of red cells and significance

Answer 13

120 days, allowing transfusion to be possible

Question 14

main and other function of red cells

Answer 14

main function: transport oxygen, other function: transport some CO2 (most transported in plasma)

Question 15

fate of red cells

Answer 15

destroyed by phagocytic cells of spleen (also liver and other cells of reticulo-endothelial system)

Question 16

define anisocytosis

Answer 16

red cells that show more variation in size than normal

Question 17

define poikilocytosis

Answer 17

red cells that show more variation in shape than normal

Question 18

define microcytosis, and how to tell what normal size should be vs lymphocyte

Answer 18

red cells are smaller than normal; diameter of nucleus of lymphocyte should be similar to diameter of red cell

Question 19

define macrocytosis

Answer 19

red cells are larger than normal

Question 20

define microcyte

Answer 20

red cell smaller than normal (microcytic)

Question 21

define macrocyte

Answer 21

red cell larger than normal (macrocytic)

Question 22

3 specific types of macrocyte

Answer 22

round, oval or polychromatic

Question 23

why do normal red cells have about 1/3 of diameter pale

Answer 23

result of disc shape (centre has less Hb so is paler when dyed)

Question 24

define hypochromia

Answer 24

cells have a larger area of central pallor than normal (hypochromic)

Question 25

cause of hypochromia

Answer 25

lower Hb content and concentration, and a flatter cell

Question 26

what often goes with hypochromia

Answer 26

microcytosis as often have same underlying cause e.g. iron deficiency causing inadequate amounts of Hb, or thalassaemia B major

Question 27

define hyperchromia

Answer 27

cells lack central pallor (hyperchromic)

Question 28

2 causes of apparent hyperchromia

Answer 28

thicker than normal, or abnormal shape

Question 29

2 important types of hyperchromia

Answer 29

spherocytes, irregularly contracted cells

Question 30

define spherocytes

Answer 30

cells approx. spherical in shape so lack central pallor

Question 31

cause of spherocyte formation

Answer 31

result from loss of cell membrane (e.g. hereditary where membrane not tethered to underlying cytoskeleton) without loss of equivalent amount of cytoplasm, so cell is forced to round up

Question 32

define irregularly contracted cells

Answer 32

cells irregular in outline but smaller than normal cells, and have lost central pallor (irregular shape and contracted as dense and small)

Question 33

cause of irregularly contracted cell formation

Answer 33

result from oxidant damage to cell membrane and Hb (e.g. some food, chemicals etc.)

Question 34

define polychromasia

Answer 34

increased blue tinge to cytoplasm of red cell as ribosomes (more blue, the younger it is)

Question 35

what does polychromasia indicate

Answer 35

red cell is young, as first red cell to leave bone marrow but is larger than mature erythrocyte

Question 36

how to identify young red cells reliably so they can be counted as not subjective

Answer 36

reticulocyte stain, which exposes living red cells to new methylene blue, which precipitates as a network (“reticulum”); expressed as % of total red cells

Question 37

6 poikilocyte variety of shapes

Answer 37

spherocytes, irregularly contracted cells, sickle, target, elliptocytes, fragments

Question 38

define target cell

Answer 38

cells with an accumulation of Hb in centre of area of centrl pallor

Question 39

when do target cells occur

Answer 39

obstructive jaundice, liver disease, haemoglobinopathies, hyposplenism

Question 40

define elliptocyctes

Answer 40

cells elliptical in shape

Question 41

when do elliptocytes occur

Answer 41

in hereditary elliptocytosis and in iron deficiency (so often larger central pallor - hypochromia - and microcytic cells)

Question 42

define sickle cell

Answer 42

cells sickle or crescent shaped

Question 43

when do sickle cells occur

Answer 43

result from polymerisation of haemoglobin S when present in a high concentration due to low oxygen tension

Question 44

define fragments (schistocytes)

Answer 44

small pieces of red cells

Question 45

what do fragments indicate

Answer 45

red cell has fragmented

Question 46

define rouleaux

Answer 46

stacks of red cells (resemble pile of coins)

Question 47

when do rouleaux occur

Answer 47

result from alterations in plasma proteins (normally repel each other, but if increase in Ig then repelling force negated, so common in infection)

Question 48

agglutinates vs rouleaux

Answer 48

irregular clumps, not tidy stacks

Question 49

when do agglutinates occur

Answer 49

result from antibody on cell surface

Question 50

define Howell-Jolly body; where formed and removed

Answer 50

nuclear remnant in red cell (same dark purple colour); form in bone marrow and removed by spleen

Question 51

commonest cause of Howell-Jolly body

Answer 51

lack of splenic function

Question 52

define erythrocytosis

Answer 52

too many red cells

Question 53

define reticulocytosis

Answer 53

too many reticulocytes (immature red cells)

Question 54

symptom vs sign, using iron deficiency as example

Answer 54

symptom: something patient feels and comes to doctor about e.g. tiredness, shortness of breath; signs: something doctor detects e.g. pallor