Circulation through Special Regions
Circulations considered:• Coronary circulation• Cerebral circulation• Circulation through the skin
• Renal circulation• Pulmonary circulation
Coronary Circulation
Although the heart contains blood, the myocardium must be supplied by arteries, like any other organ. Two major coronary arteriesBoth arise from the root of the aorta (aortic sinuses)Major arteries run on the surface of the heart Branches go into the myocardium between muscle fibres to supply the myocardium
Coronary Circulation
Left ventricle is thicker – blood needs to go further from the major arteries
Left ventricle is more likely to suffer from ischaemia than the right ventricle
Left ventricle
Right ventricle
Coronary Circulation
Subendocardial muscle are furthest away from main arteries
Subendocardial muscle are the most likely to suffer from ischaemia
Left ventricle
Right ventricle
endocardium
Subendocardialmuscle
Coronary Circulation
Pressure in the left ventricle is greater; blood vessels going through the left ventricle are compressed more during systole
Left ventricle is more likely to suffer from ischaemia than the right ventricle
Left ventricle
Right ventricle
Coronary Circulation
During systoleLeft ventricular pressure is slightly higher than aortic
(and therefore coronary artery) pressure Very little blood flow to the left ventricular myocardium
during systole, significant flow occurs only in diastole
Right ventricular pressure is lower than aortic (and therefore coronary artery) pressure Blood flow to right ventricle continues during systole
and diastole
Effect of heart rate on coronary blood flow
systole systole
Increased heart rate
Shorter diastole
Reduced LV blood flow
Coronary Circulation
Regulation – No significant control by sympathetic nerves to
arterioles Regulated by metabolic needs – flow increases when
the work of the heart increases (Note: sympathetic stimulation increases activity of the heart) Hypoxia - the main vasodilator Adenosine Hypercapnia, lactate, H+
Autoregulation – present but not a major regulatory mechanism
Cerebral Circulation
Cerebral circulation is part of contents enclosed within a rigid container – the skullNon-expandable spaceAny increase in any one of contents
Take space from others Increase intracranial pressure
Blood flow should not increase significantly; if it does intracranial pressure will increase
Cerebral Circulation
Brain is a critical organ Contains vital centres Regulates critical functions of the body
Function can not be compromised
Blood flow can not be allowed to decrease significantly
Cerebral Circulation
Regulation
Autoregulation is well developed
However, the total cerebral circulation is dependent on other factors too
Cerebral Circulation
RegulationAutoregulation is not the only regulatory mechanism
Increase in CO2 is the main stimulus for cerebral vasodilatation – hypercapnia is a cause of raised intracranial pressure
Hypoxia is a less potent stimulus for cerebral vasodilatation
Circulating hormones / chemicals have no effect Autonomic nervous system has little influence on the
cerebral blood flow
Cerebral Circulation
Regulation Metabolic factors are the most important regulators Parts of the brain become more active / less active
depending on what the individual is doing
These metabolic influences change the blood flow to different parts of the brain to meet the metabolic demands of the different parts, but the total blood flow to the brain remains mostly unchanged Redistribution
Cerebral Circulation
Effect of increased intracranial pressure Blood flow tends to get reduced Body attempts to compensate by increasing the arterial
blood pressure Increased pressure affects the medullary centres and
cause bradycardia
Increased intracranial pressure
Raised blood pressure, bradycardia
CUSHINGREFLEX
Skin Circulation
Little metabolic change from time to time ( except for the sweat gland activity, which is related to temperature control
Plays a major role in blood pressure and temperature control
Skin Circulation
Regulation – mainly by central nechanisms Has a rich sympathetic supply Under the control of the vasomotor centre Influenced by the temperature centre
Skin Circulation
Shunting blood from arterial to venous side bypassing capillaries help in temperature regulation
Skin
Venule
Capillary
Small artery
Arterio-venous shunt