Special Circulations III: Skin and Splanchnics

Question 1

What is a determinant of blood flow?

Answer 1

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.

Question 2

What is a regulator of blood flow?

Answer 2

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.

Question 3

What is the most important factor in regulation of skin blood flow?

Answer 3

Neural Control

Question 4

What is the main function of cutaneous circulation?

Answer 4

It is to maintain a constant body temperature, NOT to supply nutrients, as the skin has very low nutrient requirements.

Question 5

What is the cutaneous vasculature most efficient at?

Answer 5

It is most efficient at the promotion of heat loss, so humans climatize better in heat than in cold

Question 6

What happens to the O2-hemoglobin relationship in low temperatures?

Answer 6

It decreases the dissociation of O2 from hemoglobin and this increased retention results in more oxyhemoglobin and makes arterial blood deep red.

Question 7

What are the resistance vessels in the skin?

Answer 7

Arterioles

Arteriovenous Anastamoses

Question 8

What are the arteriovenous anastamoses?

Answer 8

They shunt blood from the arterioles to venules and bypass the capillary beds. They are solely under sympathetic neural control.

Question 9

Do the AV anastamoses respond to local metabolic regulation?

Answer 9

No. They are only controlled by sympathetics.

Question 10

Where is apical skin?

Answer 10

Nose
Lips
Ears
Fingertips

Question 11

What are the characteristics on apical skin?

Answer 11

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.

Question 12

Where is non-apical skin?

Answer 12

In the rest of the body

Question 13

What are the characteristics of non-apical skin?

Answer 13

Lack AV anastamoses

Innervated by cholinergic sympathetic fibers that release ACh from the postganglionics and produce vasodilation.

Question 14

Describe the neural control of apical skin.

Answer 14

The AV anastamoses are innervated by sympathetic adrenergic nerves and stimulation will cause sympathetic vasoconstriction. Removal of the stimulation will cause passive vasodilation.

Question 15

Describe the neural control of non-apical skin.

Answer 15

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.

Question 16

How is temperature regulation controlled?

Answer 16

Controlled by major sensory sites in the hypothalamus

Question 17

How do they respond to increases in internal temperature?

Answer 17

Withdrawal of the sympathetic nerve activity and vasodilation will result. Blocking the sympathetic nerve activity will result in maximum vasodilation.

Question 18

How do they respond to decreases in internal temperature?

Answer 18

Sympathetic activity will activate and cause vasoconstriction to decrease blood flow.

Question 19

In normothermic conditions, what is the extent of the baroreceptor reflex?

Answer 19

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.

Question 20

In hyperthermic conditions, what is the extent of the baroreceptor reflex?

Answer 20

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.

Question 21

What happens to response to an increase in the BP under warm conditions?

Answer 21

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.

Question 22

Which blood vessels freeze first?

Answer 22

Smaller blood vessels

Question 23

How does cutaneous blood flow change in exercise?

Answer 23

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.

Question 24

What is the splanchnic circulation?

Answer 24

It consists of the blood supply to the abdominal organs of digestion, liver, pancreas and spleen.

Question 25

What are the major vessels of the splanchnic region?

Answer 25

Celiac Artery Superior Mesenteric Artery Inferior Mesenteric Artery

Question 26

Describe the countercurrent flow in the intestinal system.

Answer 26

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.

Question 27

What blood flows into the portal vein?

Answer 27

It collects blood from the capillaries of the intestine, stomach, pancreas and spleen and it enters the capillaries of the liver.

Question 28

What is the pressure in the portal vein like compared to the vena cava?

Answer 28

The pressure in the portal vein is 10 mmHg and is only slightly higher than that of the vena cava.

Question 29

What can portal hypertension result from?

Answer 29

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.

Question 30

What are some of the effects of portal hypertension?

Answer 30

It can cause edema formation and ascites. It can cause esophageal varices, umbilical varices and hemorrhoids.

Question 31

During an increase in metabolism, how do the metabolites affect splanchnic circulation?

Answer 31

The metabolites, CO2, H+ and adenosine will occur with the decrease of O2 and both cause vasodilation.

Question 32

What happens to splanchnic circulation with a decrease in the metabolism?

Answer 32

Vasoconstriction will occur and blood flow will be decreased.

Question 33

What is the primary determinant of intestinal blood flow?

Answer 33

Rate of transport of solutes across the mucosal epithelium. This is increased with increased metabolism.

Question 34

During intestinal contractions, what happens to the blood flow?

Answer 34

It will decrease due to the compression of the blood vessels just as in the heart.

Question 35

What are the auto regulatory factors in the intestines?

Answer 35

Metabolites or osmolarity will cause vasodilation, with the opposite occurring in their absence.

Question 36

What effects do the hormones, cholecystokinin and neurotensin have on the gastrointestinal circulation?

Answer 36

They induce vasodilation

Question 37

What is the major neural influence on intestinal blood flow?

Answer 37

Postganglionic sympathetic vasoconstriction

Question 38

What results from the activation of alpha-adrenergic receptors?

Answer 38

Vasoconstriction

Question 39

What results from the activation of beta-adrenergic receptors?

Answer 39

Vasodilation

Question 40

What happens to the splanchnic circulation during exercise?

Answer 40

It will vasoconstrict and blood will be shunted away to muscles.

Question 41

How does parasympathetic activity affect splanchnic circulation?

Answer 41

It will indirectly stimulate intestinal blood flow as the Para-NS will activate intestinal motility and that will increase metabolism.

Question 42

What is postprandial hyperemia?

Answer 42

Food ingestion causes the increase of intestinal blood flow through metabolic, mechanical, hormonal and neural influences. Fat and carbohydrates are better at inducing hyperemia.