homeostasis Flashcards
what is homeostasis?
phsiological control system which maintains the internal environment within restricted limits.
why is homeostasis important?
important to maintain
-a stable core temperature
pH- important for enzyme activity
blood glucose concentration
tissue fluid
all cells are bathed in tissue fluid
maintaining constant internal environment
protecting organisms from changes in external environment.
gives organisms a degree of independence.
what is negative feedback?
when any deviation from the normal value is restored to the original.
involes the nervous system and often involves hormones
when will blood glucose concentration increase and decrease?
increases after eating a meal containing carbohydrates
decreases after exercise/ not eating for a while
what are changes in blood glucose concentration detected by?
the pancreas
contains endocrine cells in the islet of langerhans
release insulin or glucagon to restore blood glucose concentration.
beta cells and insulin
rise in blood glucose is detected by beta cells in the isle of langheran.
beta cells secrete insulin which reduces blood glucose concentration by:
activates enzymes whicb convert excess glucose into glycogen
glucose in the blood converted to glycogen in cells.
liver cells become more permeable to glucose.
alpha cells and glucagon
when blood glucose concentration decreases. this is detected by alpha cells in the islest of langharan.
alpha cells secrete glucagon, which increases the blood glucose concentration as
adrenal glands secrete adrenaline
second messanger model occurs to activate enzymes to hydrolyse glycogen.
glucogenesis
mainly occurs in liver
excess glucose is converted into glycogen when blood lgucose concentration is too high.
glycogenolysis
glycogen is hydrolysed back into glucose when blood glucose concentration is too low
gluconeogenesis
amino acids used to produce glucose
when all the glycogen has been hydrolysed into glucose and the bodfy still needs more glucose, it is produced from carbohydrate stores in the liver.
how insulin reduces blood glucose concentration
binds to receptors on target cell
changes quartneraty structure of channel protein- mor eglucose absorbed via facilitated diffusion
more carrier proteins in cell membrane- more glucose absorbed.
actives enzyme which converts glucose to glycogen.
glycoygenesis in liver
diabetes and the types
diabetes is when you cannot control your blood glucose concentration
type 1 diabetes
cells do not produce enough insulin
develops during childhood
can be due to autoimmune disease in which beta cells are attacked.
treatment- insulin injections
type 2 diabetes
develops in older adults
due to lack of exercise, diet, obesity
treatements- regular intake of carbohydrates, increased exercise, sometimes insulin injections
temperature
too low- not enough kinetic energy- fewer enzyme substrate complexes formed
too high- enzymes denatured.
pH
deviation from optimum temperature cause enzymes to denature
blood glucose concentration
too low- cells die as glucose needed for respiration
too high- lowers cells water potential- water leaves cells via osmosis- causes lysis/bursting of organelles.
what is positive feedback?
deviation from optimum stimualtes change that results in even bigger deviation from optimum.
why may blood water potential be too low and what impact does this have?
blood water potential can be too low due to
not drinking enough water
too many ions lost from the diet
water moves via osmosis from cells to blood
causes crenation/shriveling
mechanism response- more water reabsorbed into cells from tubules in nephron via osmosis
urine is more concentrated as contains less water
why may blood water potential be too high and what impact does this have?
drinking too much water
not enough salt in diet
can cause lysis/bursting as water moves via osmosis into cells from the blood.
response mechanism- less water reabsorbed from tubules in nephron via osmosis
urine is more dilute as it contains more water
what happens when the blood water potential is too low?
water leaves the osmoreceptors via osmosis
stimulates hypothalamus to produce more ADH
what happens when the blood water potential is too high?
water enters the osmoreceptors via osmosis
stimulates hypothalamus to produce less ADH
where is ADH produced and how is it transported?
ADH produced by hypothalamus
moves to posterior pituatary
travels into capilleries and into blood
transported in blood to target organ, the kidney.
effect of ADH/antidieuretic hormone
increases the permeability of the collecting duct and DCT
more water leave the nephron
more water reabsorbed into blood
urine more concentrated
ADH binds to receptors on the cell membrane of the DCT and collecting duct
activates phosphorylase enzyme in the cell
causes vesicles containing aquaporin to fuse with membrane
aquaporin embeded in membrane
makes collecting duct and DCT more permeable to water
so more water leaves the nephron and is reabsorbed into the blood.
aquaporins are channel proteins which transport water
more aquaporins- more water leaves the collecting duct and DCT and is reabsorbed into the blood.
when blood water potential falls
detected by osmoreceptors in the hypothalamus
hypothalamus produces more ADH
travels from hypothalamus to posterior pituatry to blood where it travels to kidney/target organ
more water leaves collecting duct and DCT
more water re absorbed into blood
when blood water potential is too high
detected by osmoreceptors in the hypothalamus
hypothalamus produces less ADH
walls of collecting duct and DCT less permeable to water
less water reabsorbed into blood
urine more dilute- contains more water
