Circulation 9

Question 1

Describe total skin blood flow percentages.

Answer 1

Receives about 5-10% of cardiac output normally, but can vary from near zero to >7 liters/min

Question 2

What is different about the regulation of blood flow in the skin than other areas of the body?

Answer 2

Neural control is more important than local metabolic control

Question 3

Describe the primary function of cutaneous circulation.

Answer 3

Maintain constant body temperature by convective transport of heat to the body surface. Skin has a small nutritive/oxygen demand

Question 4

To which climate do humans better acclimate: heat or cold, and why?

Answer 4

Heat. Alterations in blood flow can increase heat loss up to 30x, but only cut down heat loss by a factor of 10.

Question 5

In which situation would you find each of the following colors of skin: pale, cyanotic, reddish, and bright pink?

Answer 5

Pale - decreased blood flow
Cyanotic - desaturated hemoglobin
Reddish - fully saturated hemoglobin
Bright pink - carbon monoxide poisoning

Question 6

Describe why cold causes red skin.

Answer 6

Decreased temperature in the tissue will decrease the amount of oxygen unloading that takes place, increasing the amount of oxyhemoglobin that gives a reddish color

Question 7

Two types of resistance vessels in skin

Answer 7

Arterioles and arteriovenous anastomoses

Question 8

Describe the arterioles of the skin.

Answer 8

They have some basal tone, and are controlled by both sympathetic innervation and local regulatory factors

Question 9

Describe arteriovenous anastomoses in the skin.

Answer 9

Shunts blood from the arterioles to venules and venous plexuses, bypassing capillary beds. ONLY under sympathetic control. No basal tone, no reactive hyperemia or autoregulation.

Question 10

Where is apical skin?

Answer 10

Present on the nose, lips, ears, fingertips, hands, and feet.

Question 11

Describe apical skin.

Answer 11

Favors heat loss due to high surface-to-volume ratio. Contains glomus bodies.

Question 12

Glomus bodies

Answer 12

Specialized AV anastomoses that help facilitate heat loss

Question 13

Where is non-apical skin?

Answer 13

Anywhere else, other than the hands, feet, nose, lips, ears, and fingertips.

Question 14

Describe non-apical skin.

Answer 14

Almost completely lacks the anastomoses. Contains sympathetic innervation that vasodilates.

Question 15

Innervation of apical skin

Answer 15

Receive sympathetic adrenergic innervation with basal vsoconstriction.

Question 16

Innervation of non-apical skin

Answer 16

As well as sympathetic vasoconstriction, there is also active vasodilation by sympathetic cholinergic fibers through release of bradykinin.

Question 17

Primary control of temperature regulation

Answer 17

Major sensory sites in the hypothalamus and less by receptors located in the spinal cord

Question 18

What change in nerve activity happens with increased internal temperature?

Answer 18

Withdrawal of sympathetic nerve activity and vasodilation.

Question 19

What change in nerve activity occurs after decrease in internal temperature?

Answer 19

Activation of sympathetic nerve activity and vasoconstriction

Question 20

Regulation of blood pressure and cutaneous blood flow in a normothermic person

Answer 20

Blood flow will not change total peripheral resistance/blood pressure significantly

Question 21

Regulation of blood pressure and cutaneous blood flow in a person in heat stress

Answer 21

Total ski blood flow can approach 60% of cardiac output, causing a decrease in blood pressure that, through the baroreceptor reflex, causes a vasoconstriction of blood vessels in the skin that is not well-controlled. Overall, BP drops.

Question 22

Order of events with frostbite

Answer 22

• Under 0 degrees C, temperature drops 0.5 degrees per minute
• Microvasculature freezes first
• Venous system freezes before arterial system

Question 23

Mechanisms of frostbite injury

Answer 23

Direct thermal damage to cells
Direct cell damage from ice crystals
Microvascular stasis, thrombus, ischemia
Reperfusion inflammation

Question 24

Competing effects of cutaneous blood vessels during exercise

Answer 24

Sympathetic stimulation vasoconstricts, but internal metabolic heat production vasodilates for heat loss.
Net vasodilation after initial vasoconstriction

Question 25

Splanchnic organs receive __% of cardiac output in a resting, fasting individual

Answer 25

25

Question 26

Countercurrent flow system

Answer 26

Arrangement of microvessels in an intestinal villus. Incoming arteriole courses up the center and branches into many capillaries on its way to the tip. Arterioles and venules run parallel

Question 27

What happens with solutes in countercurrent flow?

Answer 27

They can diffuse from the venules back into the arterioles to increase arterial osmolarity and, overall, blood flow to that region.

Question 28

The portal vein collects blood from . . .

Answer 28

capillary beds of the intestine, stomach, and spleen

Question 29

Normal pressure in the portal vein

Answer 29

10 mmHg

Question 30

Portal hypertension can result from two things. What are they?

Answer 30

Increases in vena cava pressure (as with CHF) or hepatic vascular resistance (such as cirrhosis, hepatitis B or C)

Question 31

Portal hypertension is a value above __ mmHg.

Answer 31

25

Question 32

In episodes of portal hypertension, where does the blood flow, and what can that cause?

Answer 32

First leads to edema, but the pressure then causes blood to flow through anastomoses into systemic veins of the lower esophagus, stomach, and rectum, which can cause hemorrhoids and ruptured esophageal varices

Question 33

Regulation factors of intestinal blood flow

Answer 33

Local factors, hormonal factors, and neural factors

Question 34

Intestinal blood flow is determined primarily by . . .

Answer 34

the rate of active transport of solutes across the mucosal epithelium

Question 35

Total intestinal blood flow often __ during intestinal contractions due to . . .

Answer 35

decreases; compression of blood vessels

Question 36

Does autoregulation occur in the intestines?

Answer 36

Yes.

Question 37

Which hormones are the only ones that affect intestinal circulation?

Answer 37

Cholecystokinin and neurotensin (both vasodiliators)

Question 38

Biggest neural influence on intestinal blood flow

Answer 38

Postganglionic sympathetic vasoconstriction

Question 39

Parasympathetic activity indirectly stimulates intestinal blood flow by . . .

Answer 39

stimulating intestinal motility and glandular secretions, which, in turn, increases metabolism

Question 40

Postprandial hyperemia

Answer 40

Food ingestion increases intestinal blood flow through a complex interplay of metabolic, mechanical, hormonal, and neural influences

Question 41

Postprandial hyperemia based on gut content

Answer 41

Partially digested fats and carbohydrates are especially effective in inducing hyperemia