12HBY Body Temp and BGL Homeostasis - Ch 5

Also includes general homeostasis info

Homeostasis

. the ability of an organism to maintain a constant internal environment, despite changes in internal or external conditions, in order to maintain optimal functioning of metabolic processes

Negative feedback

. activated when internal or external conditions change from optimal conditions

. negative feedback is when the response reduces or counteracts the stimulus

. allows the body and body cells to return towards its normal set point

Stimulus-response model

stimulus

receptor

modulator

effector

response

4 examples of homeostasis

1. Body temperature of 37^oC:

•Allows chemical reactions within cells to proceed at the correct pace

•Allows proteins to maintain correct shape

2. Neutral fluid pH

•Allows chemical reactions within cells to proceed at correct pace

•Helps with management of CO₂ levels

3. Steady supply of glucose for cellular respiration

4. Steady supply of oxygen for cellular respiration

Thermoregulation

. The regulation of body temperature

. the balance of heat gain and heat loss in order to maintain a constant internal body temperature independent of the environmental temperature

Human Body temp and why

. humans are endotherms who maintain a core body temp of 37 degrees for optimal enzyme function

Main modulator for thermoregulation

. Hypothalamus

What are temperature changes detected by

1. central thermoreceptors in hypothalamus: detect changes in blood temp (core body temp)

2. peripheral thermoreceptors in skin: detect external temp changes and send nerve impulses to hypothalamus

How does the hypothalamus produce a response from thermoreceptors

. sends nerve impulses via the autonomic nervous system to effectors in the skin, muscles and glands, and via sympathetic nerves to the adrenal medulla

How does heat production relate to metabolism and metabolic rate

. heat is a by-product of metabolism

. rate of heat production is the metabolic rate

5 sources of heat production

1. cellular respiration in all body cells: the fundamental source of heat

2. skeletal muscle activity: the greatest contributor, increases dramatically during exercise

3. Shivering: rapid, involuntary contraction and relaxation of skeletal muscles, triggered by hypothalamus via the autonomic nervous system in cold conditions

4. The Liver: highly active at rest, continuous biochemical reactions produce significant heat

5. Adrenal medulla: stimulated by hypothalamus via sympathetic nerves, secretes adrenaline + noradrenaline, which increases the rate of cell respiration + metabolism, increasing heat production

What does heat transfer depend on

. the temperature gradient between the internal and external environments

Heat balance

. occurs when there is a balance between heat gain and heat loss

. is the purpose of thermoregulation

List the ways an organism loses and gains heat

1. conduction

2. convection

3. radiation

4. evaporation (for heat loss only)

Describe conduction as a method of heat transfer

. the transfer of heat by direct contact between particles

—> for heat loss: removal of heat when a hotter body directly touches a cooler solid body/object

. water conducts heat faster than air

. a large SA:V ratio increases the contact with the environment, so can increase the rate of heat exchange

—> smaller SA:V ratio decreases the heat transfer with the environment due to less direct contact

. solids are the best conductors as their particles are the closest together, then liquids followed by gases being the worst conductors (air is an insulator)

Describe convection as a method of heat transfer

. the transfer of heat by the movement of liquids or gases, in the form of currents of rising and falling fluid (convection currents)

—> for heat loss: heat being lost from body through gases or liquid, like when a cooler gas passes over a hotter body and takes this heat from the body

. the faster the rate of fluid movement, the faster the heat is transferred

. warmer fluids are less dense so rise

. cooler fluids are more dense so fall

. eg: wind

Describe radiation as a method of heat transfer

. the transfer of heat (and energy) in the form of electromagnetic infrared waves (radiation) being emitted by objects

—> for heat loss: heat is lost by electromagnetic radiation, where infrared waves are emitted from a hotter body and absorbed by a cooler body

. emission and absorption of heat is greater with dark colours and larger SA:V ratio

. an object will lose heat if it is warmer than its surroundings and will gain heat if it’s cooler than it’s surroundings

Describe evaporation as a method of heat transfer

. the process of a liquid forming a gas (eg.vapour), which absorbs heat energy

—> for heat loss: increased sweating results in increased evaporation of moisture from the skin surface which absorbs heat energy and thus increases heat loss from body

. convection increases the rate of evaporation

. rate of evaporation is faster in drier air than humid air