homeostasis Flashcards
Role of insulin
Insulin made in beta cell of islets of langerhans, pancreas
Released and travels in blood
- insulin binds to specific receptors on target cells (muscle or liver)
- causes vesicles containing glucose channel proteins to fuse with cell membrane (eg GLUT4)
- this increases permeability to glucose (liver and muscles take up more glucose)
- increased FACILITATED DIFFUSION of glucose into target cell
- reduces blood glucose level
activates enzymes to convert glucose to glycogen (glycogenesis)
Role of glucagon
Glucagon made in alpha cells of islets of langerhans
Released into blood to target organs
- glucagon binds to a specific receptor on target cell (liver or muscles)
- stimulates enzymes to convert glycogen to glucose - glycogenolysis
- stimulates enzymes that create new glucose from glycerol and amino acids - gluconeogenesis
- increase amount of glucose to be released into blood, raise levels
role of adrenaline
increases blood glucose levels
- released from adrenal glands
- released when stressed, exercising or low glucose
binds to specific receptors on target cells (liver cells)
activates enzymes that hydrolyse glycogen into glucose (glycogenolysis)
gets body ready for action by creating more glucose for muscles to respire
Second messenger of adrenaline and glucagon
- bind to specific complementary receptors on target cell
- activates adenylate cyclase
- this converts ATP into cyclic AMP (cAMP)
(chemical signal called a second messenger) - cAMP activates protein kinase A (activates chain of reactions)
- breaks down glycogen into glucose (glycogenolysis)
into blood by facilitated diffusion
describe ultrafiltration
afferent article takes blood into glomerulus and leaves through efferent
- efferent is smaller in diameter
- puts blood under high pressure
liquid and small molecules forced out of capillary and into Bowmans capsule
- passes through capillary wall, basement membrane and epithelium of capsule
larger molecules (protein and blood cells) remain in blood
glomeular filtrate passed along rest of nephron
describe selective reabsorption
happens along PCT, loop of Henle and DCT
epithelium of PCT has microvilli - large surface area
useful solutes reabsorbed by active transport and facilitated diffusion
water reabsorbed by osmosis
contents of urine
- water and dissolved salts
- urea
shouldn’t contain:
- proteins
- blood cells - both too big
- glucose (reabsorbed)
describe osmoregulation
kidneys regulate water potential of the blood
- water lost by sweat and urine
low water potential - more water reabsorbed from tubules to blood
- less, more concentrated urine
high water potential - less water reabsorbed by osmosis
- urine more dilute, more water lost
water reabsorbed along nephron
regulated by loop of henle, DCT and collecting duct
- volume reabsorbed regulated by hormones
how is water reabsorbed?
maintains a sodium ion gradient
- top of ascending limb, Na+ pumped into medulla by active transport
ascending limb impermeable to water - no water moves out
- creates low water potential in medulla (high concentration of ions)
- low water potential in medulla means water moves out descending limb by osmosis
water in medulla reabsorbed into blood
- Na+ diffuse out of bottom of ascending limb
- lowers water potential further in medulla
(ascending limb impermeable, doesn’t absorb) - gradient (low potential in medulla) causes
-water to move out of DCT by osmosis - into blood
- water to move out of collecting duct by osmosis - also reabsorbed
Adaptations of cells in PCT for absorption
Microvilli to increase surface area
Many carrier proteins for FD, active transport and co-transport
Many mitochondria for ATP for active transport
what happens when there is a decreased water potential in blood?
due to lack of water, sweating or solutes in diet
- detected by osmoreceptors in hypothalamus
- increased impulses to posterior pituitary gland - more ADH released
- causes DCT and collecting duct to become more permeable to water
- more water reabsorbed by osmosis into blood - small amounts of concentrated urine produced
what happens when there is an INCREASED water potential in blood?
1, detected by osmoreceptors in hypothalamus
- fewer impulses sent to poster pituitary gland - less ADH released
- causes DCT and collecting duct to become less permeable to water
- less water reabsorbed by osmosis into blood - large volume of dilute urine lost
how does ADH increase the permeability of the nephron?
- ADH binds to specific receptors on target cell - DCT or CD
- causes vesicles containing aquaporins fuse with cell membrane
- more water can be reabsorbed through more aquaporins
why must temperature be kept stable?
too high - enzymes denature
- molecule vibrate too much, hydrogen bonds break, tertiary structure changes
- shape of active site changed, not complementary
- doesn’t work as catalyst, metabolic reactions slower
too low - enzyme activity reduced
- less kinetic energy, more slower
- slows rate of metabolic reactions
why must pH be kept stable?
too high or low - enzymes denature
- hydrogen bonds holding tertiary structure break
- shape of enzymes active site changes
- no longer works as catalyst
- metabolic reactions less efficient
work best a optimum pH
why must blood glucose be kept constant?
cells need glucose for energy - used as respiratory substrate
concentration effects water potential of blood
too high - reduced water potential
- water molecules diffuse out of cells into blood by osmosis
- causes cells to shrivel up and die
too low - cells unable to work
- cant carry out activities as not enough glucose to provide energy from respiration
how do homeostatic systems work?
receptors detect when level is too high or low
information communicated via the nervous systems or hormonal system
effectors respond to counteract changes - bring levels back to normal
negative feedback mechanisms - restore normal levels
positive feedback
amplifies the change
= further from normal level
not involved in homeostasis as doesn’t maintain stable environment
used in activation, eg blood clot
or when systems stop working
eg hypothermia, too cold
what changes blood glucose levels?
rise after eating food containing carbohydrate
fall after exercise - more glucose used in respiration to release energy
negative feedback of blood glucose concentration
- pancreas detects HIGH concentration
- beta cells secrete insulin
- insulin binds to receptors on liver and muscle cells
cells take up more glucose
glycogenesis - less glucose in blood
- pancreas detects LOW concentration
- alpha cells secrete glucagon
- glucagon binds to receptors on liver cells
glycogenolysis
gluconeogenesis - cells release glucose into blood
type 1 diabetes
beta cells can’t produce insulin
after eating, blood glucose levels remain high
glucose in urine as kidney can’t reabsorb it all
treated with insulin injections
- monitored so blood glucose levels don’t drop too low
type 2 diabetes
lack of exercise, obesity, age
beta cells don’t produce enough insulin or body cells don’t respond to it
- insulin receptors don’t work so don’t take up enough glucose
- blood glucose higher than normal
treated with healthy diet and weight loss
can cause other issues eg kidney failure
ways to reduce risk of type 2
- diet low in fat, sugar and salt
- regular exercise
- lose weight
done through education of healthy lifestyles
reduced advertising of junk food
some companies aim to make products healthier
- use sugar alternatives
- reduce sugar, fat and salt in products
but need to make profits
how in the concentration of a glucose solution determined?
colorimetry
quantitative Benedict’s reagent - heated with glucose, goes blue to pale
use colorimeter to measure light absorbance
higher concentration, the more blue is lost (paler) decreasing absorbance
colorimetry
make several glucose solutions of different known concentrations
- serial dilution technique
add 10cm3 glucose to first
5cm3 distilled water to other
- use pipette to take 5cm3 from first
- add to second, mix
- take half (5) to add to third etc
do quantitative Benedict’s test on each solution
- plus a negative control
add same volume and heat in water bath
use colorimeter with red filter to measure absorbance
plot on calibration curve
- can text unknown solutions but calibrating them and testing them against curve
hyperglycaemia
blood glucose level too high
effects water potential of blood
cells can shrivel and die (water moves out into blood)
hypoglycaemia
blood glucose too low
- may be due to injections
not enough glucose to provide cells with energy from respiration
can’t carry out activities
how is glucose reabsorbed?
reabsorbed in PCT
- by active transport
why can diabetes cause high blood pressure?
high blood glucose concentration
= lower water potential of blood
more water moves into blood by osmosis
= larger volume, more pressure
what does each section of the nephron do?
glomerulus = ultrafiltration
PCT = reabsorbs glucose
loop of henle = maintains Na+ gradient, causes:
water leaves: descending, DCT, CD
- by osmosis
(permeability of DCT and CD affected by ADH)
why is glucose is a diabetics urine?
high concentration in blood
too much glucose to be reabsorbed along PCT
carrier proteins working at maximum/ saturated
so not all reabsorbed, remain in urine
