Chapter 5 - Homeostasis

homeostasis

• maintainence of a relatively constant internal environment

• maintain optimum condition for cellular function

positive feedback

• response amplifies stimulus(change in internal environment)

• EG: childbirth - as head of fetus push against cervix, brain stimulate pituitary gland to secrete oxytocin, oxytocin stimulate increase uterine contractions and push fetus towards cervix

negative feedback

• response by effectors initiated in opposing direction of stimulus to conteract change

• EG: core body temp

thermoregulation - core body temp HIGH

thermoregulation - core body temp LOW

heat gain/loss by

• excretion

• metabolism

• conduction

• convection

• evaporation

• thermal radiation

excretion

• warm urine and faeces

• warm air exhaled

metabolism

• cellular respiration produce heat and energy

conduction

• heat transferred between objects in direct contact with each other

thermal radiation

• emission of heat into space around a warm object

• OR gain heat by radiation

convection

• moving air/water transfer heat

• heat move down thermal gradient

• heated air/water constantly move away from body

evaporation

• evaporation of water from body surface COOL body

peripheral thermoreceptors

• in skin

• provide info about external environment

central thermoreceptors

• in hypothalamus and internal organs

• provide info about core body temp

modulator

control centre responsible for processing info from receptor and sending signals to effector

hyperthErmia

• temp and humidity high

• body temp rise, above set point

hypOthermia

• person core body temp fall below 33 celc

• metabolic rate so low that heat production unable to replace heat loss

heat exhaustion

• extreme sweating and vasodilation

• loss of water, reduced blood pressure

blood glucose levels ABOVE set point

blood glucose levels BELOW set point

adrenal cortex

• secretes cortisol

• stimulate glycogenolysis(glycogen to glucose)

• stimulate protein breakdown, gluconeogenesis(amino acids to glucose)

adrenal medulla

• secrete adrenaline and noradrenaline

• stimulate glycogenolysis(glycogen to glucose)

nephron system

process of ultrafiltration/formation of filtrate

• afferent arteriole has larger diameter than efferent arteriole

• hydrostatic pressure high in glomerulus

• pushes plasma through filtration barriers

• form filtrate in capsular space

reabsorption of water in PCT

• glucose and ions axtively transported back into plasma from tubule to peritubular capillaries

• filtrate has HIGH water potential

• plasma have LOW water potential

• water diffuse down water potential gradient via osmosis

• water diffuse back into PCT

blood osmotic pressure HIGH(solute conc in blood high)

blood osmotic pressure LOW(solute conc in blood low)

blood carbon dioxide conc HIGH

blood carbon dioxide conc LOW