Homeostasis Flashcards
What is homeostasis
the maintenance of a constant internal environment
What does homeostasis regulate
- PH
- Blood glucose
- temperature
Why is it important for glucose and PH and temperature levels to not be too high
If PH too high or low = enzymes denature
If BG high = water potential of blood decrease = water moves out of cells and die
If temp too high = enzymes denature
What are negative feedback loops
And what are the advantages of multiple feedback loops
- mechanism that restores systems to original
- multiple mechanisms = better control as body able to to respond in multiple ways
- can only work within a certain range = if change is too great = cannot return to normal
Gylcogenesis
Glucose to glycogen
Glycogenolysis
Glycogen to glucose
Gluconeogenesis
Glycerol + amino acids to glucose
Forms glucose from non-carbohydrate molecules
What hormone is released if BG too high
Insulin
Detection and action of BG too high
1- High BG detected by Beta cells in pancreas / islets of langerhans
2- insulin secreted to muscles and liver
3- insulin binds to muscle cell + increase number of glucose channel proteins in cell membrane = increase glucose uptake + rate of respiration
4- insulin binds to liver cell = glucose to glycogen ( glycogenesis)
What hormones are released if BG to low
Glucagon + adrenaline
Detection and action of BG too low
1- low BG detected by Alpha cells in pancreas/ islets of Langerhans
2- glucagon secreted
3- glucagon binds to liver cells =
- glycogen to glucose
- glycerol + AA/Non-carbohydrates to glucose
4- glucagon slows down rate of respiration = less glucose used up
Action of adrenaline
1- secreted from adrenal gland in Low BG
2- binds to liver cells:
- activate glycogen to glucose
- inhibit glucose to glycogen
3- promotes glucagon secretion + inhibits insulin secretion
Difference between primary and secondary messengers
Primary = do not enter cell = bind to cell membrane + trigger action in cell (hormones)
Secondary = inside cell= activated by primary binding to membrane + cause the change ( cyclic AMP)
Steps in control of low blood glucose for a secondary messenger ( what happens inside cells) - complex
1- Glucagon/adrenaline bind to cell membrane of liver cells
2- binding activates Adenyl cyclase = converts ATP to Cyclic AMP (cAMP)
3- cAMP activates protein kinase A = results in group of reactions that cause glyconeolysis
(glycogen to glucose)
Action of secondary messengers in low BG (action inside cell)
- simple
1- hormone binds to cell
2- adrenal cyclase causes ATP to cyclic AMP
3- cAMP activates protein kinase
4- glycogen to glucose
What is type 1 diabetes
- beta cells damaged + no longer produce insulin = BG cannot be regulated
What is hyperglycaemia
- BG too high + nothing to counteract
What is the treatment for type 1 diabetes
- insulin shots or pump
Type 1 develops in childhood
What is type 2 diabetes
- beta cells do not produce SUFFICIENT insulin = blood glucose cannot be regulated / hyperglycaemia
Treatment for type 2 diabetes
- eating healthy + exercise
Type 2 develops in later life + is linked to obesity
What is a way to measure glucose concentration
Colorimetry and Dilution Series
= identifies BG conc in urine
Steps of colorimetry
1- prepare urine samples
2- prepare calibration curve = with known concentrations
3- incubate test tubes
4- use colorimeter
5- record results
What reagent is used in colorimetry and what colour does it turn in glucose
Benedict’s reagent
Blue to red
In glucose
What is osmoregulation
Control of water potential in blood
Where does osmoregulation take place
- kidneys/ Nephrons
- kidneys absorb more or less water according to water potential of blood
What are nephrons and what are the 5 key structures
Functional unit of kidney
1- Bowman’s capsule
2- Afferent + efferent arterioles
3- Proximal convoluted tubule
4- Loop of Henle
5- Collecting duct
What is the bowman’s capsule
- Cup-shaped beginning of tubules
- surrounds glomerulus = network of capillaries
- layer is made of Podocytes = specialised epithelial cells
Afferent and efferent arterioles
Afferent = blood flow into glomerlus
Efferent = blood flow out of glomerulus
Afferent is wider = causes high blood pressure in capillaries
Proximal convoluted tubule (PCT)
- site of selective re-absorption
-after Glomelar filtrate produced in bowman’s capsule= glucose + water reabsorbed through PCT
Loop of Henle
Produces a low water potential + high solute/Na+ conc in medulla of kidney
2 parts:
Ascending limb= impermeable to water
Descending limb = permeable to water
“Down below all to go”
Collecting duct
Water reabsorbed into blood via collecting duct
- amount of water reabsorbed depend on water potential of blood
Eg: low water potential = more water absorbed
What is the first stage of osmoregualtion
Formation of glomelar filtrate
- takes place in bowman’s capsule
Stages in formation Glomelar filtrate
1- pressure filtration - capillary entering is wider than capillary leaving glomerlus = High BP = Fluid forced out of capillary
2- fluid forced out pores in capillary epithelial cells
3- small molecules filter through the pores whereas large molecules cannot fit
4- Podocytes - inner layer of bowman’s capsule = finger like projections
- substance passes from blood = to bowman’s capsule
This is glomelar filtrate
Stages of selective reabsorption in proximal convoluted tubule (long)
1- Na+ actively transported from PCT epithelial cells to blood
2- Conc of Na+ decrease in epithelial cells
3- Na+ diffuse with glucose + other small molecules in glomelar filtrate to epithelial cells via Co-transport
4- conc in epithelial cellsincrease = diffusion into capillary/blood
(The blood pressure is high = substances in blood carried away fast = maintains diffusion gradient
5- movement of glucose + S molecules into blood lowers water potential in blood + increases it in PCT= water moves into blood by osmosis
6- substances not selectively re absorbed = excreted as waste (Urine)
Stages of selective reabsorption in proximal convoluted tubule (simple)
1- active transport by Na-K pump
2- diffusion with Co-transport proteins of S molecules + Na+
3- reabsorption of small molecules by diffusion
4- reabsorption of water by osmosis
What are podocytes
Epithelial cells of bowman’s capsule
Specialised finger like projections that increase Surface area of bowman’s capsule = gaps between the podocytes allows substances to pass through
Action of water reabsorption in loop of henle
1- Na+ actively transported out of Top of ascending limb into tissue fluid of Medulla
2- Na+ diffuse from bottom of ascending limb to medulla = overall effect of decrease in water potential in medulla + increase in Na+ conc
3- descending limb is permeable to water = water in tubule/limb diffuse out by osmosis due to low water P
4- Water that moves into Medulla re absorbed into blood
Overall idea of reabsorption of water
- overall effect of ascending + descending limb = create low water potential in tissue fluid of Medulla + surrounding collecting duct
- water in collecting duct diffuse out via osmosis = water reabsorbed by bloodstream
What does the volume of water reabsorbed into blood depend on
Permeability of collecting duct
What does the permeability of collecting duct depend on
Water potential of blood
- if water potential is high + collecting duct less permeable = less water reabsorbed
- If water potential is low = collecting duct more permeable = more water reabsorbed
What does ADH influence in osmoregualtion
- affect’s permeability of PCT + collecting duct
= controls how much water is reabsorbed
Secretion and action of ADH
1- Osmoreceptors in hypothalamus (area of brain) shrink or swell depending on blood water potential
2- if water P is low = osmoreceptor cells shrink = detected by Posterior pituitary gland
3- ADH released
4- ADH bind to receptors on PCT + collecting duct = vesicles with aquaporins fuse with cell membrane
(Aquaporins are protein channels for water , more channels = permeability increase = more water reabsorbed
ADH effect on urine concentration
More ADH = more water Reabsorbed + less water In urine = urine is more concentrated
What happens to substance in collecting duct + PCT that is not reabsorbed
Collecting duct connect to Ureter
- Ureter carries urine/ left over molecules to bladder to wait to be excreted (weeing)
What’s the basement membrane
In between the pores in capillary of glomerulus and podocytes of bowman’s capsule
The basement membrane acts as a filter = stops large protein molecules from getting through
