1. Circulation through Special Regions

2. Circulation through Special Regions
Circulations considered:
Coronary circulation
Cerebral circulation
Circulation through the skin
Renal circulation
Pulmonary circulation

3. Coronary Circulation
Although the heart contains blood, the myocardium must be supplied by arteries, like any other organ.
Two major coronary arteries
Both 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

4. Coronary Circulation Left ventricle
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
Right ventricle

5. Coronary Circulation Left ventricle
Subendocardial muscle are furthest away from main arteries
Subendocardial muscle are the most likely to suffer from ischaemia
Right ventricle
Subendocardial
muscle
endocardium

6. Coronary Circulation Left ventricle
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
Right ventricle

7. Coronary Circulation SYSTOLE DIASTOLE Left ventricle Left ventricle
Right ventricle
Right ventricle

8. Coronary Circulation During systole
Left 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

9. systole
systole

10. Effect of heart rate on coronary blood flow
systole
systole
Effect of heart rate on coronary blood flow
Increased heart rate
Shorter diastole
Reduced LV blood flow

11. 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

12. Cerebral Circulation
Cerebral circulation is part of contents enclosed within a rigid container – the skull
Non-expandable space
Any 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

13. 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

14. Cerebral Circulation Regulation Autoregulation is well developed
However, the total cerebral circulation is dependent on other factors too

15. Cerebral Circulation Regulation
Autoregulation 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

16. 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

17. 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
CUSHING
REFLEX
Raised blood pressure, bradycardia

18. 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

19. Skin Circulation Regulation – mainly by central nechanisms
Has a rich sympathetic supply
Under the control of the vasomotor centre
Influenced by the temperature centre

20. Skin Circulation
Skin
Capillary
Venule
Small artery

21. Skin Circulation
Shunting blood from arterial to venous side bypassing capillaries help in temperature regulation
Skin
Capillary
Arterio-venous shunt
Venule
Small artery