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Physiology > lecture 4 - blood: blood groups > Flashcards

lecture 4 - blood: blood groups Flashcards

1
Q

what are blood groups?

A

a classification of blood based on the presence (or absence) of inherited antigenic substances on the surface of RBCs

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2
Q

what is an antigen?

A

a molecule that induces an immune response

those on RBCs will mount are red blood cell surface antigens

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3
Q

how many blood group systems are there?

A

30

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4
Q

how do we get our blood groups?

A

they are inherited and represent contributions from both parents

an individual always almost has the same blood group for life but it may change due to infection, malignancy, autoimmune disease or after a bone marrow transplant

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5
Q

what is the ABO system

A

determined by the terminal sugar structure in the surface of RBCs

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6
Q

what are the major sugars in the ABO system?

A 
fucose
galactose 
N-acetylgalactosamine 
N-acetylglucosamine 
sialic acid
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7
Q

what genes control the ABO system?

A

genes ABO and H

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8
Q

what do the ABO and H genes encode?

A

glycotransferases

• enzymes that transfer monosaccharides to polysaccharide chains

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9
Q

what are the alleles of the ABO gene?

A

A, B and O

A and B are dominant to O
O allele codes a truncated, non-functional proteins

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10
Q

what are the alleles of the H gene?

A

H and h

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11
Q

what does the H allele code for?

A

fucosyl transferase (FUT1) which converts precursor substance on RBCs to H antigen

H substance is required for A and B antigen production

adds a fucose to the terminal galactose

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12
Q

what does the h allele code for?

A

a non-functional protein

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13
Q

what substances do HH, Hh and hh individuals make?

A

HH make H substance
Hh make H substance
hh dont make H substance

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14
Q

hh individuals

A

dont possess a functioning copy of the FUT1 gene

bombay phenotype

no ill effect but people with this blood group can only have transfusions from others with the same blood group

may have functional A or B genes but as they don’t have a functional FUT1 they cannot make substance H so can’t make ABO antigens

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15
Q

where is the ABO gene located?

A

chromosome 9

the A and B alleles differ by 7 nucleotide substitutions

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16
Q

what is the A transferase enzyme?

A

N-acetyl galactosamine transferase

17
Q

what is the B transferase enzyme?

A

galactose transferase

18
Q

what happens if an individual has both A and B transferases?

A

they add either galactose or N-acetyl galactosamine to the galactose on the glycoprotein H substance

results in blood cells having both sugar chains on their surface

19
Q

what are the 2 subgroups of blood group A?

A

A1 and A2

these react differently to a particular antibody (anti-A1)

in transfusion the A1 and A2 blood groups are interchangeable

20
Q

how does A1 react with anti-A1?

A

RBCs with the A1 phenotype react with anti-A1 and make up about 80% of blood group A

21
Q

how does A2 react with anti-A1?

A

RBCs with the A2 phenotype do not react with anti-A1 and make up 20% of blood group A

22
Q

functions of the A and B substances

A

unknown

O people are healthy, suggesting antigen function is not important

some disease susceptibility has been linked to ABO phenotypes

may have an evolutionary importance

23
Q

what are blood group antigens also known as?

A

agglutinogens

antibodies raised against them are agglutinins

24
Q

the rhesus group

A

system of greatest clinical relevance

named after the rhesus monkey

rhesus antigens are proteins unlike ABO antigens which are sugars

25
Q

what is the main antigen in the rhesus group?

A

the D antigen

26
Q

how are you Rh+?

A 
homozygous domiant (DD)
heterozygous (Dd)
27
Q

how are you Rh-?

A

homozygous recessive (dd)

28
Q

what do anti-Rh(D) antibodies do?

A

destroy any Rh(D)+ RBCs they come into contact with

29
Q

what blood type is the universal recipient?

A

AB+

• has A, B and Rh antigens on the RBC surface

30
Q

what blood type is the universal donor?

A

O-

• has no antigens on the RBC surface

31
Q

what is haemolytic disease of the newborn?

A

destroys the RBCs causing anaemia and jaundice

can kill the baby

32
Q

how does haemolytic disease of the newborn occur?

A
  • Rh+ father
  • Rh- mother carrying her first Rh+ foetus - Rh antigens from the developing foetus can enter the mothers blood during delivery
  • in response to the foetal Rh antigens, the mother will produce anti-Rh antibodies
  • if the woman becomes pregnant with another Rh+ foetus, her anti-Rh antibodies will cross the placenta and damage the foetal RBCs
33
Q

how can you prevent haemolytic disease of the newborn?

A

Rh-ve mothers will be given anti-D immunoglobulin (normally in the third trimester) which will remove any foetal Rh+ve blood in her circulation before she can make her anti-D antibodies

34
Q

what are other blood group antigens?

A
  • the lewis family of antigens
  • the P family
  • the Forssman antigen

Physiology (29 decks)

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