Flashcards in Special Circulations III: Skin and Splanchnics Deck (42)
What is a determinant of blood flow?
It is a factor that is related to and affects the blood flow, but it is not actively changed in order to regulate blood flow. An example is aortic pressure, which affects blood flow, but is not a regulator.
What is a regulator of blood flow?
It is a factor that is not only related to and affects the blood flow, but it also actively changes and regulates the blood flow. An example is metabolic regulation through various metabolites.
What is the most important factor in regulation of skin blood flow?
What is the main function of cutaneous circulation?
It is to maintain a constant body temperature, NOT to supply nutrients, as the skin has very low nutrient requirements.
What is the cutaneous vasculature most efficient at?
It is most efficient at the promotion of heat loss, so humans climatize better in heat than in cold
What happens to the O2-hemoglobin relationship in low temperatures?
It decreases the dissociation of O2 from hemoglobin and this increased retention results in more oxyhemoglobin and makes arterial blood deep red.
What are the resistance vessels in the skin?
What are the arteriovenous anastamoses?
They shunt blood from the arterioles to venules and bypass the capillary beds. They are solely under sympathetic neural control.
Do the AV anastamoses respond to local metabolic regulation?
No. They are only controlled by sympathetics.
Where is apical skin?
What are the characteristics on apical skin?
High surface to volume ratio that favors heat loss.
They have no sweat glands and have special AV anastamoses called glomus bodies that facilitate heat loss.
Where is non-apical skin?
In the rest of the body
What are the characteristics of non-apical skin?
Lack AV anastamoses
Innervated by cholinergic sympathetic fibers that release ACh from the postganglionics and produce vasodilation.
Describe the neural control of apical skin.
The AV anastamoses are innervated by sympathetic adrenergic nerves and stimulation will cause sympathetic vasoconstriction. Removal of the stimulation will cause passive vasodilation.
Describe the neural control of non-apical skin.
NE will stimulate sympathetic constriction. But non-apical also has active vasodilation that is caused by sympathetic cholinergic fibers via sweat dependent release of bradykinin.
How is temperature regulation controlled?
Controlled by major sensory sites in the hypothalamus
How do they respond to increases in internal temperature?
Withdrawal of the sympathetic nerve activity and vasodilation will result. Blocking the sympathetic nerve activity will result in maximum vasodilation.
How do they respond to decreases in internal temperature?
Sympathetic activity will activate and cause vasoconstriction to decrease blood flow.
In normothermic conditions, what is the extent of the baroreceptor reflex?
The baroreceptor reflex in the skin only exerts a small effect on the total peripheral resistance due to only 5-10% of the cardiac output being in the cutaneous vessels.
In hyperthermic conditions, what is the extent of the baroreceptor reflex?
In heat stress, the total skin flow increases dramatically, up to 60%. This decrease in the BP will result in a significant basoreceptor vasoconstriction of the cutaneous vessels to help maintain the BP. However, the BP cannot be maintained as well due to the competing temperature regulated vasodilation.
What happens to response to an increase in the BP under warm conditions?
It will cause the withdrawal of the sympathetic nerve activity and result in vasodilation, which has little effect due to the apical vessels already being dilated.
Which blood vessels freeze first?
Smaller blood vessels
How does cutaneous blood flow change in exercise?
During exercise, sympathetic stimulation will vasoconstrict the skin to move blood to the active muscle, but the heat production will stimulate vasodilation for blood loss. Continued exercise will result in the net vasodilation of the skin vessels.
What is the splanchnic circulation?
It consists of the blood supply to the abdominal organs of digestion, liver, pancreas and spleen.
What are the major vessels of the splanchnic region?
Superior Mesenteric Artery
Inferior Mesenteric Artery
Describe the countercurrent flow in the intestinal system.
Arteries parallel to the veins in the villi
and the venules coming out have absorbed
Na and it diffuses into the arterioles and
increases the osmolarity of the arterioles and
increases the blood flow.
What blood flows into the portal vein?
It collects blood from the capillaries of the intestine, stomach, pancreas and spleen and it enters the capillaries of the liver.
What is the pressure in the portal vein like compared to the vena cava?
The pressure in the portal vein is 10 mmHg and is only slightly higher than that of the vena cava.
What can portal hypertension result from?
It can result from increases in either the vena cava pressure or hepatic vascular resistance, which are the result of congestive heart failure and cirrhosis respectively.