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Homeostasis homeostasis – constant physiological adjustments of the body in response to external environment changes also known as dynamic equilibrium What happens to your body when you exercise?

body temperature increases O 2 levels being used up increased cellular metabolism evaporation of sweat to cool off heart rate increases to increase blood flow (to get O 2 levels back up) pancreas signals breaking down of biomolecules to get energy needed to exercise Exercise and Homeostasis

Homeostatic Control System 1. Receptor – organs that detect changes or sense when conditions are not within “normal” range 2. Control Centre – organs which process information it receives from the receptor and send signals to another part of the body 3. Effector – coordinating centre sends signals to an organ / tissue which will normalize the original organ

dynamic equilibrium

Analogy Response No heat produced Room temperature decreases Heater turned off Set point Too hot Set point Control center: thermostat Room temperature increases Heater turned on Too cold Response Heat produced Set point dynamic equilibrium

Feedback Systems negative feedback system - buildup of the end product of the system shuts the system off blood pressure drops brain nerve pathway blood pressure rises heart rate increases arteries constrict The response counteracts further change in the same direction

Feedback Systems positive feedback (feed-forward) system - a change in some variable that triggers mechanisms that amplify the change progesterone decrease uterus endocrine system oxytocin increased contractions

Thermoregulation Process by which animals maintain an internal temperature within a tolerable range. Critical to survival because biochemical and physiological processes are sensitive to changes in temperature. Enzymatic reactions Properties of membranes

Modes of Heat Exchange Radiation is the emission of electromagnetic waves by all objects warmer than absolute zero. Radiation can transfer heat between objects that are not in direct contact, as when a lizard absorbs heat radiating from the sun. Evaporation is the removal of heat from the surface of a liquid that is losing some of its molecules as gas. Evaporation of water from a lizard’s moist surfaces that are exposed to the environment has a strong cooling effect. Convection is the transfer of heat by the movement of air or liquid past a surface, as when a breeze contributes to heat loss from a lizard’s dry skin, or blood moves heat from the body core to the extremities. Conduction is the direct transfer of thermal motion (heat) between molecules of objects in direct contact with each other, as when a lizard sits on a hot rock.

Balancing Heat Loss and Gain 1. Insulation 2. Circulatory Adaptations 3. Cooling by Evaporative Heat Loss 4. Adjusting Metabolic Heat Production

Insulation Feathers, hair or fat layers Reduces the flow of heat between an animal and its environment Lowers the energy cost of keeping warm

In mammals, the insulating material is associated with the integumentary system (skin, hair and nails) Hair Sweat pore Muscle Nerve Sweat gland Oil gland Blood vessels Adipose tissue Hypodermis Dermis Epidermis

Most land animals and birds react to cold by raising their fur or feathers Traps a thicker layer of air Increasing its insulating power (the more still air = more insulation!)

Goosebumps Raise hair on our body Inherited from our furry ancestors We rely more on a layer of fat just beneath the skin

Circulatory Adaptations We can alter the amount of blood (and hence heat) flowing between the body core and the skin. Vasodilation Muscles in superficial blood vessels relax Increases the diameter of vessels = more blood Increases heat transfer, releasing heat energy to surroundings.

Vasoconstriction Muscles in superficial blood vessels contract Smaller diameter of blood vessels = less blood Reduces heat transfer, preventing heat loss Keeps blood (and heat) in interior of body where it is needed

Evaporative Heat Loss When environmental temperatures are above body temperature animals Sweat, pant, bathe, spread saliva over body surfaces Heat is carried away with water molecules as they change into a gas

Adjusting Metabolic Heat Production Shivering and Moving - Heat production is increased by muscle activity Non-shivering Thermogenesis (NST) - Certain hormones can cause mitochondria to increase their metabolic activity and produce heat instead of ATP Brown Fat – Specialized tissue for rapid heat production (has higher conc’n of mitochondria)

What regulates our temperature? Hypothalamus - contains a group of nerve cells that function as a thermostat

Body temperature decreases; thermostat shuts off cooling mechanisms. Increased body temperature (such as when exercising or in hot surroundings) Homeostasis: Internal body temperature of approximately 36–38°C Body temperature increases; thermostat shuts off warming mechanisms. Decreased body temperature Vasoconstriction, diverting blood from skin to deeper tissues and reducing heat loss from skin surface. Skeletal muscles rapidly contract, causing shivering, which generates heat. Thermostat in hypothalamus activates warming mechanisms. Cold Response

Thermostat in hypothalamus activates cooling mechanisms. Sweat glands secrete sweat that evaporates, cooling the body. Vasodilation, Blood vessels relax and fill with warm blood; heat radiates from skin surface. Body temperature decreases; thermostat shuts off cooling mechanisms. Increased body temperature Homeostasis: Internal body temperature of approximately 36–38°C Heat Response

Extreme Cold Why does your body allow you to get frost bite? Why is hypothermia such a concern?

Classwork/Homework Section 7.1 – Pg. 337 #1-5, 7-9 Section 7.2 – Pg. 341 # 1-9,11