Circulation 9 Flashcards
Describe total skin blood flow percentages.
Receives about 5-10% of cardiac output normally, but can vary from near zero to >7 liters/min
What is different about the regulation of blood flow in the skin than other areas of the body?
Neural control is more important than local metabolic control
Describe the primary function of cutaneous circulation.
Maintain constant body temperature by convective transport of heat to the body surface. Skin has a small nutritive/oxygen demand
To which climate do humans better acclimate: heat or cold, and why?
Heat. Alterations in blood flow can increase heat loss up to 30x, but only cut down heat loss by a factor of 10.
In which situation would you find each of the following colors of skin: pale, cyanotic, reddish, and bright pink?
Pale - decreased blood flow
Cyanotic - desaturated hemoglobin
Reddish - fully saturated hemoglobin
Bright pink - carbon monoxide poisoning
Describe why cold causes red skin.
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
Two types of resistance vessels in skin
Arterioles and arteriovenous anastomoses
Describe the arterioles of the skin.
They have some basal tone, and are controlled by both sympathetic innervation and local regulatory factors
Describe arteriovenous anastomoses in the skin.
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.
Where is apical skin?
Present on the nose, lips, ears, fingertips, hands, and feet.
Describe apical skin.
Favors heat loss due to high surface-to-volume ratio. Contains glomus bodies.
Glomus bodies
Specialized AV anastomoses that help facilitate heat loss
Where is non-apical skin?
Anywhere else, other than the hands, feet, nose, lips, ears, and fingertips.
Describe non-apical skin.
Almost completely lacks the anastomoses. Contains sympathetic innervation that vasodilates.
Innervation of apical skin
Receive sympathetic adrenergic innervation with basal vsoconstriction.
Innervation of non-apical skin
As well as sympathetic vasoconstriction, there is also active vasodilation by sympathetic cholinergic fibers through release of bradykinin.
Primary control of temperature regulation
Major sensory sites in the hypothalamus and less by receptors located in the spinal cord
What change in nerve activity happens with increased internal temperature?
Withdrawal of sympathetic nerve activity and vasodilation.
What change in nerve activity occurs after decrease in internal temperature?
Activation of sympathetic nerve activity and vasoconstriction
Regulation of blood pressure and cutaneous blood flow in a normothermic person
Blood flow will not change total peripheral resistance/blood pressure significantly
Regulation of blood pressure and cutaneous blood flow in a person in heat stress
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.
Order of events with frostbite
- Under 0 degrees C, temperature drops 0.5 degrees per minute
- Microvasculature freezes first
- Venous system freezes before arterial system
Mechanisms of frostbite injury
Direct thermal damage to cells
Direct cell damage from ice crystals
Microvascular stasis, thrombus, ischemia
Reperfusion inflammation
Competing effects of cutaneous blood vessels during exercise
Sympathetic stimulation vasoconstricts, but internal metabolic heat production vasodilates for heat loss.
Net vasodilation after initial vasoconstriction
Splanchnic organs receive __% of cardiac output in a resting, fasting individual
25
Countercurrent flow system
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
What happens with solutes in countercurrent flow?
They can diffuse from the venules back into the arterioles to increase arterial osmolarity and, overall, blood flow to that region.
The portal vein collects blood from . . .
capillary beds of the intestine, stomach, and spleen
Normal pressure in the portal vein
10 mmHg
Portal hypertension can result from two things. What are they?
Increases in vena cava pressure (as with CHF) or hepatic vascular resistance (such as cirrhosis, hepatitis B or C)
Portal hypertension is a value above __ mmHg.
25
In episodes of portal hypertension, where does the blood flow, and what can that cause?
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
Regulation factors of intestinal blood flow
Local factors, hormonal factors, and neural factors
Intestinal blood flow is determined primarily by . . .
the rate of active transport of solutes across the mucosal epithelium
Total intestinal blood flow often __ during intestinal contractions due to . . .
decreases; compression of blood vessels
Does autoregulation occur in the intestines?
Yes.
Which hormones are the only ones that affect intestinal circulation?
Cholecystokinin and neurotensin (both vasodiliators)
Biggest neural influence on intestinal blood flow
Postganglionic sympathetic vasoconstriction
Parasympathetic activity indirectly stimulates intestinal blood flow by . . .
stimulating intestinal motility and glandular secretions, which, in turn, increases metabolism
Postprandial hyperemia
Food ingestion increases intestinal blood flow through a complex interplay of metabolic, mechanical, hormonal, and neural influences
Postprandial hyperemia based on gut content
Partially digested fats and carbohydrates are especially effective in inducing hyperemia
