Red Blood Cells Flashcards
1
Q
erythrocyte definition
A
A red blood cell, which in humans is typically a biconcave disc without a nucleus
2
Q
How can erythrocytes be visualised in blood?
A
- smear blood on slide, add H&E- stain pink due to protein haemoglobin- no blue as they have no nuclei
- scanning EM
3
Q
3 shapes of red blood cells, what causes the differences?
A
discocyte, stomatocyte, echinocyte
shape depends on water content, due to the osmotic effects of solutes- especially ions
4
Q
discocyte explained
A
the shape that a rbc takes when not subjected to external stress
7.5-8.7 μm in diameter and 1.2-2.2 μm in thickness
5
Q
stomatocytes structure
A
erythrocytes with a slit-like central pallor, giving the appearance of a coffee bean- bowl shape
6
Q
how are stomatocytes formed?
A
lost its biconcave structure due to membrane defect
stomatocytosis often due to alterations in membrane permeability, leading to increase in cell volume
form in low blood acidic pH
7
Q
Echinocyte structure
A
red blood cell with an abnormal cell membrane characetrised by many small, evenly spaced thorny projections
8
Q
synonym for echinocytes
A
Burr cells
9
Q
Why are echinocytes formed?
A
Echinocytosis- reversible condition of red blood cells
often occurs during sampling blood due to EDTA ( an anticoagulant) producing the artefact.
also associated with disease- such as cirrhosis, and vitamin E deficiency
10
Q
Inner structure of erythrocytes
A
- annucleate
- no mitochondria- rely solely on anaerobic respiration
- haemoglobin
- enzymes
- ions
11
Q
advantages of being annucleate
A
- better surface- volume ratio, thus improves gas exchange
- improved deformability- able to fit through capillaries
- less work for heart as a pump, as the red blood cells have a smaller mass
12
Q
How many kg does the heart pump per minute?
A
3kg of erythrocytes
13
Q
disadvantages of being anucleate
A
- no further protein synthesis or repair- cells wear out
- requires vast new replacement cell production
- terminally differentiate, therefore cannot adapt to changes in conditions
14
Q
turnover of erythrocyte
A
120 DAYS
15
Q
How do erythrocytes survive without mitochondria?
A
- energy required is very small, only for ion pumps
- solely depend upon glucose- glycolysis
- glycolytic intermediate- 2,3 bisphosphoglycerate is produced by erythrocyte enzyme. This shifts the curve to enable oxygen to dissociate
16
Q
Haemoglobin brief structure
A
globin protein- alpha 2 and beta 2 (tetramer)
haem prosthetic group- one Fe2+ per haem
forms 2/3 of the body’s iron
17
Q
haemoglobin function
A
binds to oxygen, enabling it to be carried around the body
carbon dioxide binds to the haemoglobin, forming carbaminohaemoglobin
18
Q
How else is carbon dioxide transported around the body?
A
via the bicarbonate buffer system
- co2 diffuses into the red blood cells
- carbonic anhydrase converts the co2 into carbonic acid
- carbonic acid is unstable, so dissociates into bicarbonate ions and hydrogen ions
- since carbon dioxide is quickly converted into bicarbonate ions, a concentration gradient is maintained, enabling co2 to continually diffuse into cells
19
Q
How does carbon dioxide become released?
A
- bicarbonate ion transported out of red blood cell into the plasma, in exchange for a chloride ion (known as the chloride shift)
- when the blood reaches the lungs, the bicarbonate ion is transported back into the red blood cell in exchange for chloride
- H+ dissociates from the haemoglobin and binds to the bicarbonate ion, forming carbonic acid intermediates
- carbonic anyhydrase then converts the carbonic acid back into CO2
- CO2 then expelled during exhalation
20
Q
Intracellular K+ and Na+ conc
A
na+ = 6mM
K+ = 100-140 mM
21
Q
Extracellular K+ and Na+ conc
A
Na+= 140mM
K+ = 3.5-5 mM
22
Q
How is this maintained?
A
Na+ - K+ ion exchanger present in cell membrane
23
Q
How do red blood cells flow through blood vessels?
A
- erythrocytes deform to squeeze through arterioles and capillaries
- occupy the central axis of the vessel- plasma rich at circumference
- blood is viscoelastic- meaning it changes shape with flow rate
- form a rouleaux- pile up on each other
24
Q
anomalous viscosity of blood definition
A
The measure of the resistance of blood to flow- the thickness and stickiness of blood.
Viscosity of blood increases with decreased velocity
25
Why is blood flow low in small vessels?
adherence of RBCs to each other, forming a rouleaux and to vessel walls
shear forces no longer enough to deform the RBC, so they appear my rigid
26
what factors increase the viscosity of blood? + explained
Hematocrit- one unit increase in haematocrit can cause up to a 4% increase in blood viscosity
red blood cell aggregation- rouleaux formation
plasma viscosity- depends on water content and macromolecular components
low temperatures
27
Where does the energy fro viscoelasticity come from?
primarily due to the elastic energy that is stored in the deformation of red blood cells
energy transferred to the blood from the heart is partially stored in the elastic structure, whilst the remaining energy is stored in the kinetic motion of the blood
28
How do rouleauxs form?
At rest or very small shear rates, the cells aggregate and stack together in an energetically favourable manner.
due to the attraction of charged groups on the surface of cells and the presence of fibrinogen and globulins
29
different physiological solution conditions and their osmotic effects on erythrocytes
isotonic- rouleaux
hypotonic- lysis
hypertonic- shrivelled, crenated cells
30
What causes the cells to burst?
cell membrane contains aquaporins, which allows fluid to cross the membrane
31
How much water permeates the rbc?
250 times the cell volume
32
Brief erythrocyte membrane structure
anchoring proteins- spectrin, ankyrin, band 3
glycoproteins with external carbohydrate
33
How are the anchoring proteins bound together?
spectrin dimers form a lattice bound to underlying actin filaments and ankyrin
this anchors the spectrin lattice to the glycophorins and band 3 proteins- enable red blood cells to maintain their shape
34
Ankyrin function
protein that links the bilayer to the membrane skeleton through the interaction of cytoplasmic domains
35
spectrin function
cytoskeletal protein that lines the intracellular side of the plasma membrane
maintains plasma membrane integrity and cytoskeletal structure
36
Band 3 function
anion transport protein- mediates the exchange of chloride and bicarbonate ions across plasma membranes
37
What shortens the life span of red blood cells?
abnormal shape, accelerated clearance
38
Explain abnormal shape
Mutated haemoglobin- thalassaemias, sickle cell anaemia
cytoskeletal proteins altered- hereditary spherocytosis
39
Explain accelerated clearance
overactive phagocytosis in spleen and liver, due to autoimmune disease or the macrophages are too active
40
What causes erythrocyte ageing?
inactivation of cellular enzymes and many membrane transporters
increased haemoglobin oxygen affinity and decreased cellular deformability of aged red blood cells
products of proteolytic degradation of Band 3 accumulate
41
How are aged erythrocytes removed from circulation?
Bind immunoglobin G
erythrophagocytosis
42
Erythrophagocytosis stages
1. ageing red blood cell undergoes changes in its plasma membrane
2. selectively recognised by macrophages
3. leads to phagocytosis in the spleen and liver
43
How is a low RBC count prevented?
erythopoiesis is the same rate as eryptosis
44
anaemia definition
condition which leads to a decrease in the total amount of RBCs, haemoglobin or a lowered ability of the blood to carry oxygen around the body
45
anaemia symptoms
tiredness, weakness, shortness of breath, poor ability to exercise
46
Causes of anaemia
impaired RBC production, increased RBC destruction, blood loss
47
how are anaemias differentiated + 3 divisions of anaemia
different diseases dependent on the shape of blood cell- microcytic, normocytic, macrocyctic
48
Anaemia due to lack of...
Iron and vitamins- B12 or folate
49
Example of B12 deficiency anaemia
pernicious anaemia- immune system attacks healthy cells in the stomach
prevents the body absorbing vitamin B12 from food
50
Causes of ion deficiency anaemia
lack of iron in diet, o heavy periods
51
Folate and B12 function
work together to during the purine and thymidylate syntheses and dna synthesis
52
sickle cell anaemia explained
An individual inherits two abnormal copies of the haemoglobin gene- in chromosome 11
leads to sickle shaped red blood cells
low oxygen tension promotes sickling and damage to the cell membranes, which decreases elasticity
53
How does sickle cell disease damage organs?
causes a vaso-occlusive crisis that causes the obstruction of capillaries and restrict blood flow to an organ
splenic sequestration crisis- vaso-occlusion increases the risk of infection from encapsulated organisms- leads to an acute, painful enlargement of the spleen
54
process that produces more erythrocytes
hematopoeisis
55
process of hematopoeisis stages
1. all blood cells arise from a single hemopoietic stem cell in the bone marrow
2. give rise to two majr lineages of progenitor cells- myeloid an lyphoid
3. myeloid cells divide into different types of colony forming units- the erythroid lineage of erythrocytes
4. each of these progenitor cell lineages produce precursor cells that gradually assume the morphologic characteristics of the mature, functional cell type they become
56
where does the process of hematopoeisis take place?
red bone marrow
57
key features of stem cells
1. self renew
| 2. differentiate to next stage
58
Who investigated the pluripotency of cells in the bone marrow?
Till and McCullough
59
Explain Till and McCullough experiment
1. irradiated a female mouse, killing her bone marrow
2. inserted a cell suspension containing male red blood cells, male bone marrow and male spleen into the female mouuse
3. within 8-14 days, the spleen was shown to be full of erythrocytes, suggesting that the red blood cell population had been repopulated
60
list sources of haemopoietic stem cells
adult bone marrow, liver in foetus, embryonic yolk sac, umbilical cord
61
erythropoiesis definition
the formation of a terminally differentiated red blood cell. Requires approximately a week and involves 3-5 cell divisions between the progenitor cell and the functional cell
62
Changes that take place during erythropoiesis
cell and nuclear volume decrease
nucleoli diminish in size and disappear
gradual decrease in number of polyribosomes
increase in the amount of haemoglobin
mitochondria and other organelles slowly disappear
63
important growth factor in erythropoiesis
Erythropoietin (EPO)
64
where is EPO produced? + when?
The kidneys. Produced by interstitial fibroblasts
in response to cellular hypoxia (when a region of the body is deprived of oxygen)
65
EPO function
stimulates production of mRNA for the protein components of haemoglobin
66
EPO mechanism of action
C
67
two different types of blood group
ABO and Rh
68
explain ABO blood typing
presence of alpha or beta glycorproteins on the outer cell membrane
alpha and beta are dominant to i but are co dominant
69
explain Rh blood typing
blood typing system of 49 defined blood group antigens
main antigens are D,C,E,e and c
70
what does rh negative mean?
there's no d
inherits two d which means has no rhesus protein
