Homeostasis and Negative Feedback Mechanisms Unit 1: Wellness and Homeostasis

Homeostasis Homeostasis: The body’s maintenance of a stable internal environment. For example, if the temperature outside is -30˚C , your body needs to maintain a temperature inside of 37 ˚C Your internal temperature may drop, so the body needs to make certain corrections to fix this.

Negative Feedback Most homeostatic systems operate on negative feedback Negative feedback restores homeostasis by fixing the initial change in the internal environment (by doing the opposite of what is happening). The basic function of Negative Feedback Mechanisms is to prevent small changes from becoming too large.

Involve the receptor, control centre, and effector components, which work together in a circuit. Receptors Receive information/stimulus about that change in the environment, sends information to control centre Control Centre Determines an appropriate response to the stimulus and sends signal to effector. Effector Creates a response that changes conditions in the internal environment

Three important homeostatic systems in the human body that depend upon negative feedback mechanisms to maintain equilibrium are: 1. Thermoregulation The maintenance of body temperature. The hypothalamus (a part of the human brain) controls (with hormones) sweat glands, shivering, or vasodilation/vasoconstriction

Thermoregulation May Involve:   1. Increasing muscle contraction (E.g. movement or shivering) 2. Changing the rate of metabolic heat production Secrete hormones that increase metabolism (E.g. epinephrine)

3. Altering amount of blood flowing to the skin. Dilation of blood vessels allows blood to flow close to surface of skin and more heat being lost to the environment. 4. Cooling by evaporative heat loss We can lose water from our respiratory tract surfaces by increasing our breathing rate. We can lose water across the skin by sweating. Thermoregulation in Animals: http://www.youtube.com/watch?v=NJEBfl_Lkno  

In Thermoregulation… Receptors – Nerve cells (warm and cold receptors) 2. Control Center – Hypothalamus in the brain Heating center – controls shivering, goose bumps, erection of hair, and constriction of blood vessels Cooling center – controls sweating, breathing rate, and dilation of blood vessels. 3. Effectors – Muscles and Hormones (E.g. diaphragm and adrenal glands)

2. Osmoregulation The maintenance of water balance. The hypothalamus controls (with hormones) increased absorption of water as well as thirst. We take in most of our water from food or drink, and we lose water by urinating, defecating, and evaporation (breathing and sweating)

Regulation of water is important because our cells cannot survive a net gain or loss of water. For example: A loss of 1% of our body fluid causes thirst A loss of 5% of our body fluid results in extreme pain or collapse.   A loss of 10% of our body fluid can cause death.

In osmoregulation: OSMERECEPTORS – monitor the salt and water concentration of the blood HYPOTHALAMUS – triggers the release of hormones to signal the removal or reabsorption of water KIDNEYS – absorbs or excretes water

3. Waste Management The maintenance of excretion. The kidneys, liver, lungs, skin, and stomach are involved in the elimination of various waste products. This will be covered further in a later unit.

See “Negative Feedback Mechanisms” Diagram for Temperature Control 2b. Negative Feedback Mechanism Diagram.docx