Chapter 12: Homeostasis

Students should be able to:

1. Define homeostasis.2. Identify and name the hairs, sweat glands and blood vessels of the

skin.3. Describe the maintenance of a constant body temperature in Man

by(a) Temperature receptors in the skin.(b) Sweating and shivering.(c) Blood vessels near the skin.(d) Coordinating role of the brain.

4. State the nervous system – brain, spinal cord and nerves.5. Describe how the 3 parts of the nervous system serve to

coordinate/regulate bodily functions.

12.1 Homeostasis

12.1.1 Definition Maintenance of a constant internal environment (steady state) in

the mammalian body Derived from Greek: (homoio = same, stasis= standstill)

12.1.2 Negative feedback control External Environment Temperature

o As external temperature changes body internal temp ____o When in hot sun, our body tends to get _______o When in the cold, our body tends to get ________

Mammalianso So-called “warm-blooded” because…o Can maintain a _________ body temperature

Analogy with air-conditioning systemso When we first switch on the air-con, the fans will turn at its

maximum speed, cooling the place ________o However, as the temperature reaches its programmed level,

the thermostat causes fans to automatically _____ its speed o When temp reaches its programmed level, the fans ______

____o When temp starts to increase as more people fill the room,

the fans will start to _______ ___ againo A similar “system” is present in the body of mammals

such systems work under the “Negative Feedback Control”

12.2 The Mammalian Skin

1

12.2.1 Structure

12.3 Functions of the components of the Mammalian Skin

2

12.3.1 Temperature Receptors in the Skin Nerve endings found in epidermis & the dermis Form receptors

o Function: Sense pain, pressure or temperature changes in the external environment

o For example: Touch receptors gives us a sensation of pain Temperature Receptors: Gives us a sensation of temperature

changes in the surroundings

12.3.2 Sweating & Shivering

12.3.3 Blood Vessels near the skinVasoconstriction Vasodilation

3

Arterioles in the skin dilate (becomes wider)More blood flow through skin

Sweat glands become active produce more sweatMore sweat evaporates from the skin surface remove latent heatBreathing becomes more rapid help remove heat

Metabolic process of body slows down less heat is produced

Arterioles in the skin constrict (becomes smaller)Less blood flow through skin

Sweat glands become less active produce less / no sweatMetabolic process of body speed up more heat is producedHair erector muscles contracts still air trapped between hairs (goose pimples)Body muscles contract Shivering

Increase heat production

Help raise body temp to normal

12.3.4 Coordinating Role of the brain

4

5

6