33. Pulmonary circulation. Special circulations: coronary, cerebral, splanchnic, cutaneous.
Covers pulmonary circulation, including how hypoxia makes pulmonary vessels constrict rather than dilate, then moves through coronary circulation with its venous drainage and local metabolic control. It goes on to cerebral circulation, covering the blood-brain barrier, autoregulation and ischaemia timings, followed by splanchnic flow with the spleen's blood reservoir role and ascites, and ends with cutaneous circulation and the two types of skin resistance vessels. Five recap questions close the note.
Topic 33 of 104 in the MU Sofia syllabus for Physiology (Medicine, Year 2). The free AceMed note covers it in 6 sections, about 1,069 words (7 min of reading), with 26 flashcards.
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Pulmonary circulation. Special circulations: coronary, cerebral, splanchnic, cutaneous.
Pulmonary Circulation:-
Coronary Circulation
Cerebral Circulation
Splanchnic Circulation:-
Cutaneous Circulation
Pulmonary Circulation:-
The pulmonary circulation is the system of blood vessels that transports deoxygenated blood from the heart to the lungs for oxygenation and then returns the oxygenated blood back to the heart.
The pulmonary arteries, originating from the right ventricle, carry deoxygenated blood to the lungs, while the pulmonary veins carry oxygenated blood back to the left atrium.
Unlike systemic vessels, pulmonary vessels are wider and possess less musculature, leading to significantly lower pulmonary vascular resistance compared to systemic vascular resistance.
This lower resistance, coupled with lower pressure, minimizes fluid filtration from capillaries into the alveoli.
Hypoxia, a condition of low oxygen levels, uniquely triggers vasoconstriction in the pulmonary circulation, unlike the systemic circulation where it causes vasodilation. This mechanism helps to direct blood flow away from poorly oxygenated lung areas, optimizing the use of available oxygen.
Coronary Circulation
The coronary circulation is the network of blood vessels responsible for supplying the heart muscle itself with oxygenated blood.
The left and right coronary arteries, branching from the left ventricle, encircle the heart to deliver blood.
Venous blood from the heart drains into the coronary sinus, which empties into the right atrium via the V. cardiaca magna, V. cardiaca media, and V. cardiaca parva.
The heart muscle has a high capillary density with numerous open capillaries, facilitating efficient blood and oxygen delivery to the myocardial cells.
The heart extracts a large amount of oxygen from the blood, approximately 14ml per 100ml of blood.
The regulation of coronary blood flow is primarily governed by local metabolic factors, with hypoxia playing a crucial role.
When myocardial activity increases, as during systole, a temporary oxygen debt occurs due to the compression of coronary vessels. To compensate, local hypoxia triggers vasodilation, increasing blood flow and restoring oxygen supply.
Adenosine, a short-acting vasodilator, also contributes to increased blood flow when needed.
While neural regulation has a minor role in coronary circulation, both alpha-receptors (vasoconstriction) and beta2-receptors (vasodilation) are present.
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