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Module 103: The Heart, Lungs and Blood > Theme 2: Lecture 1 - Erythrocytes (Red Blood Cells) > Flashcards

Theme 2: Lecture 1 - Erythrocytes (Red Blood Cells) Flashcards

1
Q

Why is Hb needed to carry O2?

A

It ‘s poorly soluble in plasma

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2
Q

How much moreO2 is carried on Hb than dissolved in the plamsa in normal arterial blood?

A

70X

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3
Q

How is it possible for arterial PO2 to be normal but hypoxia to occur?

A

If there is no Hb to carry the O2

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4
Q

Why do you need O2?

A

Oxidative phosphorylation produces more energy than anaerobic glycolysis

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5
Q

Cooperativity

A
  • Biochemical phenomenon displayed by proteins with multiple subunits, which depend on each other
  • Enzymes or receptors that have multiple binding sites have an increased or decreased affinity to a ligand upon binding a ligand at a different binding site
  • I.e. O2 is more likely to bind to a Hb that already has one O2 bound to it than a Hb that doesn’t
  • O2 binding leads to more O2 binding and O2 release leads to more O2 release
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6
Q

What does Hb do?

A

Picks up O2 in the lungs and releases it in the tissues

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7
Q

How much of a RBC is Hb

A

95% of dry weight

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8
Q

Describe Hb

A
  • Each Hb has 4 subunits
  • Each subunit has a small haem group (616 Da) and a large globin group (17 000 Da)
  • Has allosteric properties: cooperativity
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9
Q

Describe haem

A
  • A porphyrin ring
  • Rigid
  • 2D
  • Highly coloured due to presence of iron
  • Conjugated to one Ferrous Fe2+ (not Ferric Fe3+)
  • The site of O2 binding
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10
Q

HbA

A
  • Made up of 2 alpha subunits and 2 beta subunits

- AKA maternal Hb

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11
Q

HbF

A
  • Made up of 2 alpha subunits and 2 gamma subunits

- Binds O2 more strongly than HbA

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12
Q

What Hb do healthy adults have?

A

Mostly HbA and a small percentage of HbF

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13
Q

The Bohr effect

A
  • Because of the carbonic anhydrase reaction: A higher blood CO2 level leads to a lower blood pH
  • A higher blood CO2 level and lower pH leads to a lower affinity of Hb to O2
  • CO2 and H+ bind Hb but at a different site from O2
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14
Q

How is CO2 transported in the blood?

A
  • 10% dissolved in plasms
  • 22% as carbamino Hb
  • 68% as HCO3-
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15
Q

Carbamino Hb

A

CO2 combines reversibly with Hb-NH2 to form Hb-N-H(COOH) to transported in the blood

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16
Q

How is CO2 carried as HCO3- in the blood?

A
  • CO2 diffuses into RBC
  • CO2 combines with H2O in the carbonic anhydrase reaction to form H+ and HCO3-
  • Hb- combines with H+ to form HHb (Hb essentially acts as a buffer)
  • A band 3 protein (chloride bicarbonate exchanger) transports HCO3- out of the cell and Cl- into the cell
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17
Q

Chloride shift

A

More Cl- inside RBCs in venous blood than in arterial blood due to transport of CO2

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18
Q

Myoglobin

A

Similar to haemoglobin but found in the muscle and doesn’t have multiple subunits

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19
Q

Oxygen binding curve of myoglobin shape

A

Hyperbolic due to it having a high affinity to oxygen

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20
Q

Oxygen binding curve of haemoglobin shape

A

Sigmoidal (S) shape due to cooperativity of haemoglobin

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21
Q

What causes Hb to have a lower affinity for O2

A
  • CO2
  • H+
  • Cl-
  • 2,3-DPG

Therefore muscle activity encourages Hb to release O2

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22
Q

What is 2,3-DPG

A

2,3 diphosphoglycerate OR 2,3 bisphosphoglycerate OR 2,3 BPG

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23
Q

What does 2,3-DPG do

A

Binds to Hb and lowers the affinity for O2

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24
Q

At what concentration is 2,3-DPG found in erythrocytes

A

5mM (quite high)

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25
Q

Relationship between foetal Hb and 2,3-DPG

A
  • Foetal Hb has a lower affinity for 2,3-DPG than adult Hb

- This means foetal Hb has a higher binding affinity for O2 than HbA

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26
Q

What is the main driver to increase respiratory rate?

A

H+ in the CSF (not H+ in the blood)

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27
Q

How is respiratory rate increased

A
  • CO2 gas can get into CSF (H+ in blood is slow to get to CSF)
  • Once CO2 is in the CSF it makes carbonic acid and H+
  • Medullary receptors (how the brain controls breathing) sample from the interstitial and CSF
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28
Q

Erythrocytes appearance

A
  • Biconcave disc
  • Anucleate, lack organelles
  • 7 um diameter, 2 um height
  • Contain haemoglobin
  • Red when oxygenated
29
Q

Erythrocytes function

A
  • “Bag” of haemoglobin
  • Transport O2 and CO2
  • Survive ~120 days
  • Very flexible – fold and stack in blood vessels
30
Q

Haematocrit/Packed cell volume (PCV)

A

measurement of the proportion of blood that is made up of cells

31
Q

Mean Cell Haemoglobin (MCH)

A

Amount of Hb in a single cell

32
Q

Mean corpuscular volume (MCV)

A

value that describes the average size of red blood cells

33
Q

Normal PVC range

A

Males: 40-52%
Females: 36-48%

34
Q

Normal MCH

A

27-34 pg

35
Q

Normal MCV

A

80-100 fL

36
Q

Normal Hb range

A

Males: 13-17 g/dL
Females: 12-16 g/dL

37
Q

Erythropoiesis

A

The development of RBCs

38
Q

Where does erythropoiesis take place in the body after birth

A
  • The bone marrow only

- After 20, in membranous bone only

39
Q

Where does erythropoiesis take place in the body in embryogenesis

A
  • Liver
  • Spleen
  • Lymph node
  • Yolk sac
40
Q

Haematopoiesis

A

The development of all blood cells

41
Q

Describe the general process of development from stem cells

A

Multipotent stem cells => Multipotent progenitor cells => Lineage committed progenitor cells => Mature cells

42
Q

Erythroblast

A

Nucleated cell in the stages of development into a RBC

43
Q

What stages does a haematopoietic stem cell go through to mature into a erythrocyte

A
  • Haematopoietic stem cell
  • Burst forming unit-erythroid (BFU-E)
  • Colony forming unit-erythroid (CFU-F)
  • Erythroblast
  • Reticulocyte
  • Erythrocyte
44
Q

Which stages of erythropoiesis are dependant on erythropoietin?

A

Burst forming unit-erythroid to erythroblast

45
Q

Which stages of erythropoiesis are iron dependant?

A

Erythroblasts to erythrocytes

46
Q

What is erythropoietin (EPO)

A

A cytokine/hormone that drives erythropoiesis

47
Q

Where is (EPO) made

A

In the kidney in response to hypoxia in the kidney

48
Q

What is EPO used for?

A
  • Medically to stimulate erythropoiesis (there’s a risk of severe off target effects)
  • Performance enhancing drug for athletes
49
Q

What are reticulocytes

A

-RBC precursor before the nucleus and organelles are expelled

50
Q

How long do reticulocytes last in the blood

A

2 days (become RBCs after that)

51
Q

How is the reticulocyte count used as a diagnostic in anaemias

A
  • Indicator of bone marrow activity
  • High in haemolytic anaemias (homeostatic response)
  • Low when erythropoiesis is low
  • Machine counts cells and detects those with basophilic material (eg DNA) in them
52
Q

What is methaemoglobinaemia

A
  • Hb cannot transport O2

- Fe in haemoglobin is oxidized (Fe3+) instead of usual ferrous (Fe2+)

53
Q

What causes methaemoglobinaemia

A
  • Congenital globin mutations (Hb M)
  • Hereditary decrease of NADH
  • Toxic substances
54
Q

Carbon Monoxide poisoning

A
  • Hb cannot transport O2
  • Due to CO Displacing O2 from Hb as they have the same binding site
  • Affinity for CO is 250X stronger
  • Low levels of CO can completely displace most O2
  • PO2 dissolved in blood remains normal
  • Lethal
55
Q

Treatment for CO poisoning

A
  • 95% O2 and 5% CO2
  • The CO2 makes the Hb have a lower affinity for CO, this helps to temporarily knock off the CO molecules so the high levels of o2 can grab onto any vacated spaces
56
Q

Polycythaemias

A
  • Increased number of RBCs (PCV)
  • Causes increased viscosity of blood
  • Clogs up blood vessels
57
Q

Physiological polycythaemia

A

Increased number of RBCs caused by living at high altitude

58
Q

Polycythaemia vera

A
  • Is a neoplasm
  • Often asymptomatic
  • Risk of thrombotic events
  • Affects all ages but risk increases with age
  • Possibly genetic
59
Q

Treatment for polycythaemia vera

A
  • No cure

- Treated with venesection

60
Q

Venesection

A

Removal of excess blood by blood letting

61
Q

Why is Vitamin B12 and Folic acid important

A
  • Important for rapidly dividing tissue
  • Essential for forming DNA (thymidine)
  • Nuclear maturation fails (if deficient)
  • Important in RBCs, Skin, Gametogenesis
62
Q

What does Vitamin B12 and Folic acid deficiency cause?

A

-Megaloblastic anaemia (macrocytic)

These are large, fragile RBCs cells

63
Q

What causes Vitamin B12 and Folic acid deficiency?

A
  • Diet
  • Malabsorption
  • Increased utilisation
64
Q

Pernicious anaemia

A

Vitamin B12 deficiency causing anaemia because the stomach fails to produce intrinsic factor which is essential for the absorption of B12 from the digestive tract

65
Q

What is vitamin B12 and Folic acid deficiency treated by?

A
  • Oral folic acid

- Intramuscular hydroxocobalamin

66
Q

How is iron stored intracellularly

A
  • Ferritin - An immediately form of stored iron, it’s small and dispersed
  • Haemosiderin - A more insoluble storage form made when the apoferritin stores are overwhelmed, forms in large clusters
67
Q

Where is iron stored in the body

A

In reticulo endothelial system:

Liver, spleen, erythrocytes, bone marrow, macrophages/monocytes

68
Q

What does depleting all the iron stores in the body lead to?

A

Anaemia, specifically microcytic and hypochromic cells

69
Q

Why is it easy to be iron deficient

A
  • Only a small % of dietary iron absorped

- Lose roughly 1mg of iron a day (more in pregnancy, menstruation, peptic ulcers)

Module 103: The Heart, Lungs and Blood (51 decks)

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