homeostasis

homeostasis

the maintenance of a relatively stable internal environment despite fluctuations in the external environment

aspects of internal environment that need to be regulated

core body temp; ph; concentration of glucose, oxygen and carbon dioxide in blood; blood pressure; concentration of metabolic wastes

homeostatic mechanisms

work to maintain homeostasis; main sensory and controlling body systems: nervous system (fast) and hormonal system (slow); operate through feedback loops

negative feedback loop

a circular situation in which the body responds to a stimulus, with the response altering the original stimulus

negative feedback

when the body’s response has the effect of reducing or eliminating the stimulus that caused it

positive feedback

when the body’s response has the effect of reinforcing or intensifying the stimulus that caused it

components of the feedback system

stimulus: a change in the environment
receptors: sensory cells that detect changes
modulator: control centre that processes the messages received by the receptor
effector: muscles or glands that make the necessary adjustments
response: the reaction from the effector
feedback: response changes original stimulus

how heat is generated in the body

body processes; heat gained by environment; illness; stress/emotions; medications; increase in adrenaline

how heat is lost from the body

evaporation from water in body and lungs; warm air breathed out; voiding of warm urine and feces; radiation of body heat; conduction and convection

normal body temperature of humans

37.6 degrees celsius: cells function optimally

location of thermoreceptors

central (hypothalamus) and peripheral (skin)
detect temperature of blood

radiation

transfer of heat emitted as infrared radiation by objects.

conduction

transfer of heat by direct contact between particles.

convection

transfer of heat by convection currents
only occurs in liquids and gases

evaporation

change of state from liquid to gas

physiological response to fall in body temp

Constriction of blood vessels in the skin
Less sweat produced
Shivering
Increase in secretion of adrenaline and thyroxine

behavioural response to fall in body temp

Put on more/warmer clothes
take a warm shower
sit in front of a heater
Decrease surface area
Increase voluntary activity

physiological response to rise in body temp

Dilation of blood vessels in the skin
Sweat is produced
Decrease the secretion of thyroxine.
Change blood flow to skin

behavioural response to rise in body temp

Wear less/lighter clothes
take a cool shower
sit in the shade/fan yourself
Increase surface area
Reduce voluntary activity

vasodilation

the widening of blood vessels, which increases blood flow and lowers blood pressure

vasoconstriction

the narrowing (constriction) of blood vessels by small muscles in their walls

glucose

simple carb, source of energy for cellular respiration, sugar in the blood

glycogen

complex carb, made up of long chains of glucose molecules, glucose is stored as glycogen

liver - regulation of blood sugar

converts glucose into glycogen for storage, converts glycogen into glucose for release into the blood

glucagon

raises blood glucose levels through glycogenolysis and gluconeogenesis

insulin

lowers blood glucose level through glycogenesis and lipogenesis

glycogenesis

to make glycogen (glucose --> glycogen)

Gluconeogenesis

to make glucose from non- carbohydrate sources (amino acids or fats--> glucose)

Glycogenolysis

to breakdown glycogen (glycogen --> glucose)

cortisol

glucocorticoid, increase blood glucose levels, stimulates glycogenolysis, and increases the rate of gluconeogenesis

adrenaline

increases blood glucose level, stimulates glycogenolysis, lactic acid is converted to glucose, insulin receptors become more sensitive

hyperglycemia

abnormally high blood glucose level

hyperglycemia symptoms

thirst, urination, feeling hungry and tired, blurred vision

hyperglycemia causes

taking too little insulin, too many carbs/sugars, not exercising enough

thirst reflex in maintaining water balance

1. Water concentration of blood plasma decreases; osmotic pressure of the blood is increased; mouth becomes dry

2. Osmoreceptors in the thirst center of the hypothalamus are stimulated

3. Person feels thirsty

4. Person responds to the feeling of thirst by drinking

5. Water drunk is absorbed into the blood from the alimentary canal

6. Water leaves the blood and the extracellular and intercellular fluids return to their normal concentration

dehydration

When 2% or more of body fluid lost, in elderly, thirst reflex less effective, Can lead to thirst, head aches, low blood pressure, and dizziness

water intoxication

body fluids become diluted and cells take in extra water due to osmosis, can happen if you lose lots of water through sweating and replace with plain water. Lightheadedness , vomiting and collapse.

intracellular fluid

Fluid contained within the cells of an organism 2/3 of total body water

extracellular fluid

Fluid that is outside the cells of an organism 1/3 of total body water

plasma

1/4 of extracellular fluid, the fluid part of the blood

intercellular fluid

3/4 of the extracellular fluid, found in lymph, cerebrospinal fluid, synovial fluid in joints, fluids of eyes and ears, chest and abdominal cavities and around the heart, alimentary canal and kidney filtrate

role of intercellular fluid

surrounds body cells and acts as a medium for exchanging substances between capillaries (vascular fluids) and the cytoplasm of cells

nutrient movement

Oxygen and nutrients diffuse from capillaries into tissue fluid and then into cells following a concentration gradient, glucose and amino acids may also be transported by facilitated diffusion or active transport.

waste removal

Metabolic wastes like carbon dioxide (CO₂) and urea move from cells into tissue fluid and then diffuse into capillaries, where they are transported for excretion, CO₂ diffuses into the blood, where it dissolves in plasma or binds to haemoglobin before being transported to the lungs

water movement

Water moves by osmosis from areas of low concentration to areas of high concentration (inside cells or blood plasma). The lymphatic system helps return excess tissue fluid to the bloodstream, preventing swelling

excretion

the removal from the body of the waste products of metabolism, maintain constant concentration of materials in body fluid

filtration

substances are separated from a fluid by passing it through a membrane or filter, occurs in renal capsule

selective reabsorption

substances are reabsorbed back into the bloodstream from the filtrate in the kidneys

tubular secretion

substances are actively transported from the blood into the tubular fluid