Chapter 12 Homeostasis - Lecture Notes

Chapter 12: Homeostasis Students should be able to: 1. 2.

Define homeostasis. Identify and name the hairs, sweat glands and blood vessels of the skin. 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. State the nervous system – brain, spinal cord and nerves. Describe how the 3 parts of the nervous system serve to coordinate/regulate bodily functions.

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12.1 Homeostasis 12.1.1 • •

12.1.2 •

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Definition Maintenance of a constant internal environment (steady state) in the mammalian body Derived from Greek: (homoio = same, stasis= standstill)

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 ________ Mammalians o So-called “warm-blooded” because… o Can maintain a _________ body temperature Analogy with air-conditioning systems o 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 _______ ___ again o A similar “system” is present in the body of mammals  such systems work under the “Negative Feedback Control”

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12.2 The Mammalian Skin 12.2.1

Structure

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12.3 Functions of the components of the Mammalian Skin 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

Arterioles in the skin dilate (becomes wider) More blood flow through skin Sweat glands become active  produce more sweat More sweat evaporates from the skin surface  remove latent heat Breathing 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 sweat Metabolic process of body speed up  more heat is produced Hair erector muscles contracts  still air trapped between hairs (goose pimples) Body muscles contract  Shivering Increase heat production

Help raise body temp 3 to normal

12.3.3

Blood Vessels near the skin Vasoconstriction

Vasodilation

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12.3.4

Coordinating Role of the brain

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