what are the roles of the cardiovascular system?
supply oxygen and metabolic fuel to tissues
remove metabolic waste from tissues
defence against pathogens
what is oxidation?
loss of electrons
what is an oxidising agent?
a substance that is reduced so that it can oxidise another molecule
give examples of oxidising agents in anaerobic bacteria
sulphate
nitrate
sulphur
what does oxidation do to a substrate?
simplifies the electronic structure
releases energy
what is reduction?
gain of electrons
what does reduction do to substrates?
allows complex molecules to be made from simple ones
requires energy
when are oxidation reactions irreversible?
when they release a large amount of energy
what does NAD stand for?
nicotinamide adenine dinucleotide
how is NAD used in the body?
NADH gives electrons
NAD can store electrons
give an equation for NAD to NADH
NAD+ + H+ + 2e- –> NADH
what is microcytic anaemia?
smaller than usual RBCs
what is microcytic anaemia?
larger than usual RBCs
what are reticulocytes?
immature RBCs that have just left the bone marrow
what % of RBCs are reticulocytes?
1-2%
how long does it take for reticulocytes to turn into mature RBCs?
1 day after being in circulation
how is the rRNA arranged in reticulocytes?
reticular, mesh-like structure
what does a blood smear with high levels of reticulocytes show?
lots of haemolysis
why can RBCs not repair themselves?
they don’t have a nucleus or organelles
how long do RBCs survive in the bloodstream?
120 days
why do RBCs require a small amount of ATP?
maintain the Na+ pumps in the cell membranes
actin filaments
how do RBCs make ATP?
glycolysis
what is the glucose uptake system in RBCs?
glut1 - works by facilitated diffusion
what is the pH of RBCs?
low - acidic
why do RBCs contain antioxidants? name an antioxidant
to protect haemoglobin against oxidative stress
vitamin C
describe the process of an RBC being destroyed?
ageing RBC undergoes changes to its plasma membrane
recognised by phagocytes
undergoes phagocytosis in the spleen, liver and bone marrow
what is a haem group?
porphyrin ring with a ferrous iron centre
what does hexavalent mean?
can form 6 bonds with surrounding atoms
how many electrons does ferrous iron have in its outer shell and how are they arranged?
6 d electrons
4 in one plane held to nitrogen atoms in the porphyrin ring
one bound to a histidine group underneath the porphyrin ring
one sticking out
why does oxygen form a weak reversible bond to haemoglobin?
oxygen cannot get close enough to remove the electron fully because of steric hindrance
what causes steric hindrance in a haemoglobin molecule?
3D folding of the subunit
what makes up a haemoglobin molecule?
4 subunits each with a haem group attached
4 polypeptide chans connected by salt bridges, hydrogen bonds and hydrophobic interactions
what is methaemoglobin?
haemoglobin with ferric iron
when is methaemoglobin made?
over time, RBCs gradually accumulate methaemoglobin so they can no longer carry oxygen
what does methaemoglobin reductase do?
converts methaemoglobin back to haemoglobin
what does methaemoglobin reductase rely on?
NADH
what percentage of people’s haemoglobin is methaemoglobin?
1-2%
what is methaemoglobinemia and what causes it?
abnormally high Methaemoglobin
genetics or exposure to chemicals
how does a high level of methaemoglobin lead to the death of a RBC?
markers on the surface of the RBC change
change is detected by the cells of the liver and spleen
they signal to dendritic cells and macrophages
how do individuals with methaemoglobin reductase deficiency compensate for the defect?
make more RBCs than normal
polycythemia
what are the subunits of adult haemoglobin?
2 alpha
2 beta
what are the subunits of fetal haemoglobin?
2 alpha
2 gamma
what is an advantage of fetal haemoglobin having a higher affinity for oxygen?
can remove it more easily from placental blood
what does 2,3 DPG stand for and what does it do?
2-3 diphosphateglycerate
enhances ability of RBCs to release oxygen in hypoxic tissue
binds to beta subunit as it starts to deoxygenate and increases steric hindrance
define percent saturation
proportion of haemoglobin bound to oxygen
how can % Hb be measured?
pulse oximeter
uses a laser to detect the colour of blood which is a good indicator of levels of venous blood
what should be the levels of % Hb in healthy individuals?
96-99%
what is hypoxaemia?
arterial oxygen saturation below 90%
what shape is the oxygen/haemoglobin curve?
sigmoid shape
how does heat shift the oxygen/haem curve?
heat shifts curve to the right
how does pH shift the oxygen/haem curve?
low pH shifts the curve to the right
describe the structure of myoglobin
single subunit with haem group on it
how does myoglobin act as an oxygen store?
loads O2 as Hb unloads it
only releases O2 when pO2 is very low and Hb cannot supply O2 fast enough
where does the myoglobin curve lie with respect to the HbA curve?
to the left - has a higher affinity for oxygen
what is rhabdomyolysis?
the process of myoglobin being released from damaged muscle tissue
how can myoglobin cause acute kidney failure?
rhabdomyolysis occurs
myoglobin is filtered by the kidneys
toxic to the renal tubular epithelium
causes acute renal failure
what controls haematocrit levels?
erythropoietin (EPO)
where is EPO released from?
interstitial cells in the kidneys
what part of the body does EPO act on?
bone marrow
describe the negative feedback loop of EPO raising haematocrit levels
normal haematocrit = 45% haematocrit falls renal hypoxia EPO increases stimulates RBC production in the bone marrow haematocrit levels restored
how is CO2 carried in red blood cells?
CO2 converted to bicarbonate via carbonic anhydrase
bicarbonate diffuses out of RBC
chloride moves in to maintain the electrical neutrality (chloride shift)
how is CO2 removed from the blood in the lungs?
venous blood containing bicarbonate brought to the lungs
bicarbonate re-enters RBC and converted back to CO2
CO2 diffuses into alveoli air space
chloride leaves the RBC to balance the electrical charge of bicarbonate entering