Blood Constituents
Red blood cells
o Carry oxygen to tissues
White blood cells
o Function primarily as defence to infection
Platelets
o Primarily prevent blood loos by coagulation and clotting
Plasma
o Transport medium for nutrients, plasma proteins, growth factors and
clotting factors
Erythropoiesis
Life span of RBC is 100-120 days
20 seconds to circulate
Erythropoietin stimulates RBC production
Red Blood Cell
Biconcave disc
No nucleus
Diffusion of O2 and CO2
At the lungs, oxygen diffuses into the blood
o Oxygen reacts with and attaches to haemoglobin
o This oxygenation reaction with haemoglobin produces excess H+
ions which react with HCO3- to produce H2CO3
o The carbonic acid decomposes to CO2 which diffuses out of the
blood
Haemoglobin
Per Hb molecule
o 2 alpha chains
o 2 beta chains
, o 4 heme groups carrying iron
Each subunit 17kDa
Heme
o Iron held in porphyrin ring
o Iron co-ordinates with 4 nitrogen
o Oxygen binds to Fe2+ to become oxygenated
o If Fe2+ becomes oxidised to Fe3+ so no longer able to bind to
oxygen
Oxygen Binding
Sigmoidal curve
o Once oxygen binds, the next oxygen binds more readily due to
conformational change
Oxygen tension at the placenta is lower than arterial pressure
o This means that foetal Hb (HbF) has a higher affinity to bind oxygen
at low pressure
o HbF can release oxygen at even lower pressure to ensure
oxygenation of foetal tissues
Glycated HbA
o HbA can be glycated to give 3 forms
A1a, A1b and A1c
This is due to high plasma glucose levels
o Hb A1c is a indication of diabetes mellitus
Ontogeny
Ontogeny is where haematopoiesis takes
This takes place in the sternum, pelvis and femurs in the bone marrow
It can also occur extramedullary in certain pathological conditions
Haematopoiesis
Haematopoiesis is required for the production and development of blood
cells
It is needed for
o Transport of oxygen
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