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Physiology > lecture 2 - blood: introduction to haemoglobin > Flashcards

lecture 2 - blood: introduction to haemoglobin Flashcards

1
Q

average amount of blood in human body

A

female adults – average of 5 litres

male adults – average of 5.5 litres

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2
Q

what is blood?

A

a connective tissue

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3
Q

blood functions

A
  • gas transport & exchange
  • distributing solutes
  • immune functions
  • maintains body temp
  • regulates blood clotting
  • maintaining pH
  • maintaining BP
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4
Q

what solutes does plasma transport?

A

ions
nutrients
hormones
metabolic waste

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5
Q

blood constituents

A

consists of a complex liquid (plasma) in which the cells are suspended
• erythrocytes: RBCs
• leukocytes: WBCs
• thrombocytes: platelets

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6
Q

if blood is places in a test tube (with anticoagulant) how will the cells settle?

A

the heavier cells will settle to the bottom of the tube

top layer = plasma
55% and lightest layer
soluble materials - mostly water

middle layer = buffy coat
1%
WBCs and platelets

bottom layer =  RBCs
44% 
the haematocrit (packed cell volume) represents the % of total blood volume occupied by RBCs
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7
Q

normal haematocrit for males & females

A 
females = 42%
males = 45%
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8
Q

functions of plasma

A

thermoregulation

transport

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9
Q

components of plasma

A
  • water
  • plasma proteins
  • dissolved small molecules
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10
Q

how does water influence blood viscosity?

A

less water = thicker blood = sluggish flow

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11
Q

4 plasma proteins

A
  • serum albumin
  • globulins
  • clotting proteins (fibrinogen)
  • regulatory proteins
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12
Q

what % of plasma volume is taken up by plasma proteins?

A

around 8%

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13
Q

serum albumin

A
  • 55% of plasma proteins
  • maintains osmotic pressure of plasma
  • assists in transport of lipids & steroid hormones
  • large protein synthesised in the liver
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14
Q

globulins

A
  • 38% of plasma proteins
  • bind to and transport ions, hormones and lipids
  • immune proteins: antibodies or gammaglobulins, made by leukocytes
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15
Q

clotting proteins (fibrinogen)

A
  • 7% of plasma proteins
  • essential for blood clotting
  • synthesised in the liver
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16
Q

what is the remaining 1% of plasma proteins?

A

regulatory proteins such as enzymes, proenzymes and hormones

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17
Q

how can plasma proteins be identified?

A

by electrophoresis - separation by size and charge

can be a diagnostic tool - electrophoretic patterns of plasma proteins change in a number of clinical conditions

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18
Q

what is cirrhosis?

A

liver disease (cirrhosis) has many causes, including cancer, alcoholism, and viral hepatitis

results in progressive decrease in production of plasma proteins; leads to decreased colloidal osmotic pressure; results in fluid loss to extracellular spaces, producing severe edema in the abdomen; termed ascites

decline in clotting factor levels also causes easy bruising and delays clotting; may be fatal

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19
Q

structure and function of RBCs

A

indented, disc shaped cells

primary function is oxygen transport

enables efficient oxygen transport

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20
Q

what is the volume of a RBC?

A

80-96 femtolitres

referred to as mean cell volume (MCV)

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21
Q

what are microcytic RBCs?

A

small RBCs

found in iron deficiency anaemia

22
Q

what are macrocytic RBCs?

A

large RBCs

found in folate (vitamin B9) deficiency anaemia

23
Q

what is erythropoiesis?

A

RBC formation

24
Q

what happens in erythropoiesis?

A

1) comes from hematopoietic stem cells
2) become an erythrocyte CFU - becomes committed to becoming a RBC
3) pro-erythroblast develops into an early erythroblast - iron needs to be present here
4) late erythroblast is where the nucleus starts to shrink and is ejected from the cells along with other organelles
5) reticulocytes then become erythrocytes

25
Q

order of formation in erythropoiesis

A
  • red bone marrow
  • hematopoietic stem cells
  • erythrocyte CFU
  • proerythroblast
  • early erythroblast
  • late erythroblast
  • reticulocyte
  • erythrocyte
26
Q

erythrocyte synthesis

A
  • a feedback loop
  • takes about 26 days
  • starts in bone marrow
  • finishes in blood vessels
  • EPO in the kidneys is what stimulates red bone marrow to increase erythropoietin to increase the RBC count
27
Q

erythrocytes: end of life

A
  • squeezing through capillaries causes damage
  • with age cells become fragile and easily rupture
  • recognised by monocytes which engulf old RBCs and take them to liver and spleen
  • haemoglobin is decomposed to heme and globin
28
Q

how are the heme components of the blood recycled?

A

heme minus the iron is converted to biliverdin and then to bilirubin, which is secreted in bile from the liver - bile pigments eventually leave the body in faeces and urine

the iron is transported in the blood by the protein transferrin and stored by the protein ferritin in the liver

29
Q

how are the erythrocyte membrane proteins and globin proteins of the blood recycled?

A

they are broken down into amino acids, some of which are used to make new erythrocytes

30
Q

what is glucose-6-phosphate dehydrogenase (G6PD) deficiency?

A
  • favisim
  • the 2nd most common enzyme defect
  • X-linked, recessive genetic disorder
  • predisposes to RBC breakdown when exposed to certain environmental triggers
31
Q

why does glucose-6-phosphate dehydrogenase (G6PD) deficiency cause the breakdown of RBCs?

A

RBCs lack mitochondria so rely on the pentose phosphate pathway (PPP) to produce the energy needed to produce glutathione (G6PD is part of the PPP)

no G6PD = no glutathione = inability to resist oxidative stress

results in damage to RBC and breakdown in the spleen

can result in anaemia, newborn jaundice and kidney damage

32
Q

what does haemoglobin do?

A

enables erythrocytes to transport oxygen

33
Q

what does a haemoglobin molecule consist of?

A

the globin part - made up of 4 protein chains

4 iron containing haem groups - each iron atom can reversibly bind 1 molecule of oxygen

34
Q

the haem (heme) group

A
  • an iron containing pigment
  • consists of a porphyrin ring containing 1 atom of iron
  • appears relish when combined with oxygen and blueish when deoxygenated
35
Q

what are the 4 types of globins?

A

alpha
beta
gamma
delta

36
Q

how are globins normally distributed in humans?

A

97% of adults have 2 alphas and 2 betas (HbA)

2.5% of adults have 2 alphas and 2 deltas (HbA2)

foetuses have 2 alphas and 2 gammas (HbF)

37
Q

Hb’s ability to bind oxygen is governed by..

A
  • partial pressure of oxygen (pO2)
  • number of free oxygen binding sites available in the molecules
  • O2 binding is cooperative
38
Q

what 2 forms does Hb exist in?

A

relaxed (r) form:
• has high O2 affinity
• exists at high pO2
• firmly binds oxygen

taut (t) form:
• low O2 affinity
• exists at low pO2
• releases oxygen

39
Q

what else can Hb bind to apart from oxygen?

A
  • carbon dioxide
  • the acidic hydrogen ion portion (H+) of carbonic acid
  • carbon monoxide
  • regulatory molecules NO
40
Q

what are the 2 major classes of inherited disorders for Hb production?

A

haemoglobinopathies
• abnormal globin chains are made
• sickle cell anaemia

the thalassaemias
• normal globin chains are made but in decreased amounts OR are absent due to defects at the level of gene expression

41
Q

what is sickle cell anaemia?

A
  • genetic disease
  • caused by a mutation in the beta globin gene
  • a glutamic acid residue is replaced by valine in the protein
  • resultant haemoglobin polymerises at low pO2 forming long crystals of HbS - this causes RBCs to deform and become sickle shaped
42
Q

how does sickle cell anaemia work?

A
  • sticky patches give it the sickle shape and makes them rigid
  • leads to damage and a reduction in the amount of RBCs
  • they become trapped within small blood vessels and block them
  • this deprived the downstream tissues of oxygen and causes ischemia (lack of oxygen) and infarction (cell death as a result of lack of oxygen)
43
Q

what is ischemia?

A

lack of oxygen

44
Q

what is infarction?

A

cell death as a result of lack of oxygen

45
Q

sickle cell anaemia vs sickle cell trait

A
  • homozygous = sickle cell anaemia
  • heterozygous = sickle cell trait
  • most common in afro-caribbean population
  • sickle cell trait is 50% protective against mild malaria & 90% protective against sever malaria
46
Q

what are the thalassemias?

A

group of diseases where synthesis of 1 or both of the alpha or beta globins is reduced

disease severity varies from minor, intermediate or major

either caused by:
• gross deletion of 1 or more globin genes
• gene mutation

47
Q

what are the 2 classes of thalassemias?

A

alpha:
• production of alpha globin is deficient
• found predominantly in India and surrounding areas

beta:
• production of beta globin is defective
• predominantly in mediterranean region

48
Q

alpha thalassemia

A
  • production of alpha globins is reduced
  • leads to excess of beta chains - unstable tetramers of four beta chains form (HbH)
  • leads to abnormal O2 dissociation curves & RBC damage
  • short lived RBCs - anaemia
  • produced ‘golf ball’ cells after staining under a microscope
49
Q

beta thalassemia

A
  • relative excess of alpha chains
  • do not form tetramers
  • bind to and damage RBC membranes
  • form toxic aggregates at high concs
  • results in iron overload - organ damage

treatment: iron chelation therapy otherwise patients accumulate potentially fatal iron levels

50
Q

alpha or beta thalassemia diagnosis by electrophoresis

A

alpha: reduced HbA and presence of HbH
beta: production of beta globins is reduced or absent, decreased HbA on

51
Q 
what is: 
• HbA 
• HbA2
• HbF 
• HbH
A
  • HbA = 2 alpha and 2 beta
  • HbA2 = 2 alpha and 2 delta
  • HbF = 2 alpha and 2 gamma
  • HbH = 4 beta
52
Q

what are the 3 main functions of blood?

A

transport
protection
regualtion

Physiology (29 decks)

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