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Summary specialised circulations
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Summary of specialised circulations
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Specialised Circulations: Heart and SkinThere are various types of circulation within the body, these include:
Coronary
Cutaneous
Cerebral
Pulmonary
Skeletal muscle
Splanchnic (gut, liver, pancreas)
This lecture focuses on the coronary and cutaneous circulatory system
When looking at specialised circulation we can break it down into three parts in
order to study it:
1. Specialised Requirements – E.g. For heart, what special requirements does the
heart have that the coronary circulation provides
2. Special Features – So in order to fulfill the specialised requirements there will be
certain structural and thus functional changes in the circulation
3. Special Problems – E.g. what are the specialised problems of the coronary
circulation (related to structure and function)
Coronary Circulation
1) Special Requirements
Our heart needs a huge basal supply of oxygen, at rest it requires 20x more than
resting skeletal muscle. It also needs to be able to increase O 2 supply in proportion to
the demand (increase in cardiac work requires increase oxygen supply).
2) Special Features: Structural
Structurally we are able to supply this high demand of O 2 because of the high
capillary density there is (no. of capillaries per cardiac muscle cell). This is important
because with a high capillary density it gives a large surface area for O2 transfer and
reduces the diffusion distance to the myocytes. Both of these together increases the
speed of passive diffusion of CO2 removal and O2 uptake. This is because time taken
for diffusion (t) is proportional to distance squared (X 2).
, As can be seen cardiac myocyte fibres are much smaller cells than skeletal and they
are still receiving lots of capillaries hence the density of capillaries is much higher.
This allows us to provide high oxygen even at rest.
3) Special Features: Functional
At rest, the coronary circulation has a very high blood flow (10x the flow per weight
than the rest of the body). It does this by basal nitric oxide release (releasing of NO)
causing vasodilatation. This much wider radius of vessels increases blood flow. Also
at rest the heart is also able to extract much higher amounts of oxygen (75%) than
the rest of the body (25%).
During metabolic hyperaemia [(e.g. in exercise), increase in blood flow), coronary
blood flow increases in proportion to the demand, there is production of vasodilators
(adenosine/other factors) and these out compete sympathetic vasoconstriction.
Circulating adrenaline also dilates coronary vessels due to abundance of β2
adrenoceptors (PKA pathway).
When you get the increased blood flow there is increased ability for uptake of fatty
acids (which the heart prefers for metabolism) to provide more work and less uptake
of glucose (not preferred substrate). Note potentially increased fatty acid uptake
could cause potential problems.
Oxygen unloading to myocardium
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