lecture 2 - blood: introduction to haemoglobin

Question 1

average amount of blood in human body

Answer 1

female adults – average of 5 litres

male adults – average of 5.5 litres

Question 2

what is blood?

Answer 2

a connective tissue

Question 3

blood functions

Answer 3

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

Question 4

what solutes does plasma transport?

Answer 4

ions
nutrients
hormones
metabolic waste

Question 5

blood constituents

Answer 5

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

Question 6

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

Answer 6

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

Question 7

normal haematocrit for males & females

Answer 7

females = 42%
males = 45%

Question 8

functions of plasma

Answer 8

thermoregulation

transport

Question 9

components of plasma

Answer 9

• water
• plasma proteins
• dissolved small molecules

Question 10

how does water influence blood viscosity?

Answer 10

less water = thicker blood = sluggish flow

Question 11

4 plasma proteins

Answer 11

• serum albumin
• globulins
• clotting proteins (fibrinogen)
• regulatory proteins

Question 12

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

Answer 12

around 8%

Question 13

serum albumin

Answer 13

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

Question 14

globulins

Answer 14

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

Question 15

clotting proteins (fibrinogen)

Answer 15

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

Question 16

what is the remaining 1% of plasma proteins?

Answer 16

regulatory proteins such as enzymes, proenzymes and hormones

Question 17

how can plasma proteins be identified?

Answer 17

by electrophoresis - separation by size and charge

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

Question 18

what is cirrhosis?

Answer 18

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

Question 19

structure and function of RBCs

Answer 19

indented, disc shaped cells

primary function is oxygen transport

enables efficient oxygen transport

Question 20

what is the volume of a RBC?

Answer 20

80-96 femtolitres

referred to as mean cell volume (MCV)

Question 21

what are microcytic RBCs?

Answer 21

small RBCs

found in iron deficiency anaemia

Question 22

what are macrocytic RBCs?

Answer 22

large RBCs

found in folate (vitamin B9) deficiency anaemia

Question 23

what is erythropoiesis?

Answer 23

RBC formation

Question 24

what happens in erythropoiesis?

Answer 24

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

Question 25

order of formation in erythropoiesis

Answer 25

* red bone marrow * hematopoietic stem cells * erythrocyte CFU * proerythroblast * early erythroblast * late erythroblast * reticulocyte * erythrocyte

Question 26

erythrocyte synthesis

Answer 26

* 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

Question 27

erythrocytes: end of life

Answer 27

* 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

Question 28

how are the heme components of the blood recycled?

Answer 28

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

Question 29

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

Answer 29

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

Question 30

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

Answer 30

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

Question 31

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

Answer 31

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

Question 32

what does haemoglobin do?

Answer 32

enables erythrocytes to transport oxygen

Question 33

what does a haemoglobin molecule consist of?

Answer 33

the globin part - made up of 4 protein chains 4 iron containing haem groups - each iron atom can reversibly bind 1 molecule of oxygen

Question 34

the haem (heme) group

Answer 34

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

Question 35

what are the 4 types of globins?

Answer 35

alpha beta gamma delta

Question 36

how are globins normally distributed in humans?

Answer 36

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)

Question 37

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

Answer 37

* partial pressure of oxygen (pO2) * number of free oxygen binding sites available in the molecules * O2 binding is cooperative

Question 38

what 2 forms does Hb exist in?

Answer 38

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

Question 39

what else can Hb bind to apart from oxygen?

Answer 39

* carbon dioxide * the acidic hydrogen ion portion (H+) of carbonic acid * carbon monoxide * regulatory molecules NO

Question 40

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

Answer 40

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

Question 41

what is sickle cell anaemia?

Answer 41

* 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

Question 42

how does sickle cell anaemia work?

Answer 42

* 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)

Question 43

what is ischemia?

Answer 43

lack of oxygen

Question 44

what is infarction?

Answer 44

cell death as a result of lack of oxygen

Question 45

sickle cell anaemia vs sickle cell trait

Answer 45

* 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

Question 46

what are the thalassemias?

Answer 46

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

Question 47

what are the 2 classes of thalassemias?

Answer 47

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

Question 48

alpha thalassemia

Answer 48

* 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

Question 49

beta thalassemia

Answer 49

* 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

Question 50

alpha or beta thalassemia diagnosis by electrophoresis

Answer 50

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

Question 51

``` what is: • HbA • HbA2 • HbF • HbH ```

Answer 51

* HbA = 2 alpha and 2 beta * HbA2 = 2 alpha and 2 delta * HbF = 2 alpha and 2 gamma * HbH = 4 beta

Question 52

what are the 3 main functions of blood?

Answer 52

transport protection regualtion