Overview
This lecture explains how the body regulates its core temperature through mechanisms involving the skin, blood vessels, and smooth muscle control, focusing on vasodilation and vasoconstriction.
Heat Production and the Need for Regulation
- Exercise increases muscle activity, producing excess heat in the body.
- The body must maintain a core temperature of 98.6°F for optimal chemical reactions.
- Sweating and skin involvement are ways the body gets rid of extra heat.
Skin Structure and Heat Loss
- The skin acts as insulation, preventing rapid heat loss in cold conditions.
- Blood vessels called arterioles supply the skin and form capillary beds near the surface.
- Capillary beds increase surface area for exchange and play a key role in heat dissipation.
Mechanism of Vasodilation and Heat Loss
- Capillaries near the skin’s surface act like “windows” for heat escape.
- In hot conditions, the body widens (dilates) these capillaries—this process is called vasodilation.
- Vasodilation allows more blood (and heat) to flow near the skin, increasing heat loss.
Mechanism of Vasoconstriction and Heat Conservation
- In cold conditions, capillaries narrow (vasoconstriction), reducing blood flow to the skin.
- Vasoconstriction conserves heat by minimizing heat loss through the skin.
- This is why skin and extremities feel cold in low temperatures.
Control of Blood Vessel Size
- Blood vessels have smooth muscle cells in their walls.
- Contraction of smooth muscle narrows vessels (vasoconstriction); relaxation widens them (vasodilation).
- Nerve signals regulate smooth muscle contraction and thus vessel size.
Key Terms & Definitions
- Core Body Temperature — The internal temperature the body maintains for optimal function, typically 98.6°F.
- Vasodilation — Widening of blood vessels to increase blood flow and heat loss.
- Vasoconstriction — Narrowing of blood vessels to decrease blood flow and conserve heat.
- Arteriole — A small branch of an artery leading to capillaries.
- Capillary Bed — Network of tiny blood vessels for substance exchange between blood and tissues.
- Smooth Muscle — Muscle in vessel walls controlling diameter via contraction and relaxation.
Action Items / Next Steps
- Review how nerve signals regulate smooth muscle cells in blood vessels.
- Read supplemental materials on thermoregulation and homeostasis.