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Homeostasis, homeostasis is the maintenance of a constant internal…
Homeostasis
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Osmoregulation
Describe the stimulus response pathway of osmoregulation when there's a DECREASE in the water potential of the blood
Describe the stimulus response pathway of osmoregulation when there's a INCREASE in the water potential of the blood
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Ultrafiltration
Describe how the structure of the nephron and its associated blood vessels are adapted to
the process of ultrafiltration. [8]
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- homeostasis is the maintenance of a constant internal environment
- a negative feedback loop is used to maintain homeostatic balance
- a receptor detects a stimulus/factor/parameter
- the receptor sends info. about the changes they detect through the nervous system to a central control in the brain or spinal cord (the central control receives an input)
- the central control instructs an effector to carry out a response (output)
- the factor/parameter returns to normal
- the factor/parameter fluctuates around a set point
- The blood in the glomerular capillaries is separated from the lumen of the Bowman’s capsule by two cell layers (the endothelium of the capillary and epithelial cells (have podocytes) which make up the inner lining of the Bowman's capsule) and a basement membrane (made up of a network of collagen + glycoproteins)
- Blood contains ions, proteins, O2, glucose, urea, red blood cells, white blood cells
- This all filters through the podocytes and endothelium gaps
- The basement membrane stops large proteins (a relative molecular mass of more than 69,000) from diffusing through the basement membrane
- Red and white blood cells are also too large so they remain in the blood
- Because of this the water potential in the afferent arteriole remains lower than in the glomerular filtrate
- afferent arteriole has a larger diameter then the efferent arteriole => to produce more hydrostatic pressure in glomerulus => the pressure forces the water to move into the Bowman's capsule
- afferent arteriole has a larger diameter then the efferent arteriole (1) => to produce more hydrostatic pressure in glomerulus (1) => the pressure forces the water to move into the Bowman's capsule (1)
- podocytes (1)
- basement membrane acts as a selective barrier/filter (1) allows H2O/solutes/ions to pass through (1)
- basement membrane (1) - is made up of a network of collagen + glycoproteins (1) => stops large protein (a relative molecular mass of more than 69,000) (1) and red & white blood cells from diffusing through the basement membrane (1)
- gaps (1) in the endothelium (1) of the capillary
- Na+ - K+ pumps in the basement membrane (of the proximal convoluted tubule pump sodium ions out of the cells (of the cells of the proximal convoluted tubule) into the blood by active transport
- This lowers the conc. of sodium ions inside the cell so they diffuse into it down their conc./ion gradient using co-transporter molecules by facilitated diffusion
- this allows glucose + amino acids to move into the cells at the same time (against their conc. gradient)
- this increases the water potential of the filtrate (in the lumen) and decreases the water potential of the blood
- water moves down its water potential by osmosis from the filtrate through the cells into the blood
- thermoreceptors receptors in the skin detect decrease in temp. of surroundings and the hypothalamus detect decrease in blood temp.
- the hypothalamus sends impulses that activate physiological responses:
- Vasoconstriction - muscles of the walls of the arterioles that supply blood to capillaries near the skin contract => narrows the lumens => reduces supply of blood to the capillaries so less heat is lost from the blood
- Shivering - the involuntary contraction of skeletal muscles generates heat which is absorbed by the blood
- Raising body hairs - contraction of the muscles attached to the hairs, increasing the depth of fur so trapping air close to the skin. The air provides insulation
- Decreasing the production of sweat - this reduces the loss of heat by evaporation from the skin surface
- Increasing the secretion of adrenaline - increases the rate of heat production in the liver
- thermoreceptors receptors in the skin detect increase in temp. of surroundings and the hypothalamus detect increase in blood temp.
- the hypothalamus sends impulses that activate physiological responses:
- Vasodilation - the muscles in the arterioles in the skin relax => allowing more blood to flow through the capillaries => so heat is lost to the surroundings
- Lowering body hairs - muscles attached to the hairs relax so they lie flat => reducing the depth of fur => reducing the layer of insulation
- Increasing sweat production - sweat glands increase the production of sweat which evaporates on the surface of the skin so removing heat from the body
- folded basement membrane - to increase surface area
- epithelial cells w/ microvilli - to increase surface area
- epithelial cells have tight junctions - so no fluid or dissolved substances can cross so everything has to go through the cell
- many mitochondria - to provide ATP for Na+ - K+ pump - active transport
- microvilli - to increase surface area for more co-transporters
- capillary - near the outer surface of the proximal convoluted tubule to decrease diffusion difference
*cuboidal epithelial cells (in the proximal convoluted tubule)
- decrease in water potential of blood
- osmoreceptors in the hypothalamus
- detect decrease in the water potential of the blood
- osmoreceptors shrink
- send impulse to pituitary gland
- stimulates pituitary gland to release ADH
- ADH binds to receptor proteins in the cell surface membranes of collecting duct cells
- this activates an enzyme on the inside of the cell
- the cells contain ready made vesicles containing aquaporins
- (when the enzymes are activated) the vesicles move to the cell membrane
- then fuse with the cell membrane
- this increases the permeability of the membrane of the collecting duct to water
- more water moves from the lumen by osmosis to the epithelial cells then into the blood
- concentrated urine
- normal water potential of blood
Make paper notes on:
Deamination
Selective reabsorption in the loop of Henle
Draw pictures of ultrafiltration, reabsorption in the proximal convoluted tubule, reabsorption in the loop of Henle, glucose conc.
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- increase on water potential of blood
- osmoreceptors in the hypothalamus
- detect increase in the water potential of blood
- osmoreceptors swell up
- send impulses to pituitary gland
- stimulates pituitary gland to STOP secreting ADH
- aquaporins move out of the cell surface membrane of the collecting duct cells, back into the cytoplasm as part of vesicles
- this makes the collecting duct cells impermeable to water
- the filtrate moves down the collecting duct without losing any water
- dilute urine
- normal water potential of blood
- a cells and b cells in the islets of Langerhans in the pancreas detect rise in blood glucose
- b cells in the pancreas secrete insulin
- insulin is a protein so it cannot pass through the plasma membrane
- it binds to a receptor
The role of insulin:
- it activates an enzyme
- the enzyme creates vesicles carrying glucose transporters
- the vesicles move to and fuse with the cell membrane
- inserting glucose transporters into the plasma membrane
- most common is GLUT 4
- glucose is then converted into glycogen (glycogenesis)
- and used in respiration
- Insulin also activates glucokinase
- glucokinase phosphorylates glucose
- so it's too big to leave through GLUT
- Insulin stimulates phosphofructokinase
- these enzymes add more glucose to glycogen
- making the glycogen granules bigger
- the blood glucose conc. returns to normal by negative feedback
- blood glucose conc. decreases
- the a and b cells in the islets of Langerhans in the pancreas detect the decrease in blood glucose
- the a cells respond by secreting glucagon
- b cells respond by stopping the secretion of insulin
- the decrease in conc. of insulin in the blood reduces the rate of uptake of glucose by liver and muscle cells
- glucagon binds to receptors in the cell surface membranes of liver cells
- this activates a G protein
- the G protein activates an enzyme in the membrane which catalyses the conversion of ATP to cyclic AMP (a secondary messenger)
- cyclic AMP binds to kinase enzymes in the cytoplasm which activates an enzyme cascade
- kinase enzymes activates enzymes by phosphorylating them
- the enzyme cascade leads to the activation of glycogen phosphorylase
- activated glycogen phosphorylase catalyses the hydrolysis of glycogen to glucose
- the glucose diffuses out of the cell through GLUT 2 transporter proteins into the blood
In the case of adrenaline:
- the adrenaline binds to a G protein
- and same process
- Dipsticks for detecting glucose contain the enzymes glucose oxidase and peroxidase
- these 2 enzymes are immobilised on a small pad at 1 end of the stick
- the pad is immersed in urine
- if it contains glucose, glucose oxidase catalyses a chemical reaction in which glucose is oxidised into gluconolactone + hydrogen peroxide
- peroxidase catalyses a reaction between hydrogen peroxide and a colourless chemical in the pad to form a brown compound
- O2 produced oxidises the colourless chemical to produce a range of colour
- the resulting colour of the pad is matched against a colour chart
- the chart shows colours that indicate different conc. of glucose
- the more glucose present, the darker the colour
Problem with urine tests:
They DON'T indicate current blood glucose conc.
They indicate whether the conc. was higher than the renal threshold
Biosensors can be used to measure blood glucose conc. by:
- the pad contains glucose oxidase which reacts with the glucose in the blood sample to produce gluconolactone
- an electric current is generated
- the current is detected by an electrode, amplified and gives a numerical value of blood glucose conc.
- the greater the current, the greater the reading on the biosensor, the greater the blood glucose conc.
Stomata open in response to:
- increasing light intensity
- low CO2 conc. in the air spaces within the leaf
Stomata close in response to:
- darkness
- high CO2 conc. in the air spaces of the leaf
- low humidity
- high temp.
- water stress, when the supply of water from the roots is limited and/or there are high rates of transpiration
- proton pumps in the cell surface membranes actively transport H+ ions out of guard cells
- this cause a lower H+ ion conc. inside the cells
- this causes the inside of the cells to become negatively charged
- the negative charge causes K+ channel proteins to open so K+ ions diffuse into the cell down an electrochemical gradient by facilitated diffusion
- this lowers the water potential
- water moves into the cell by osmosis down a water potential gradient through aquaporins in the membrane
- volume of guard cells increases => turgid => stoma opens
- thin outer walls expand causing => cells curve apart
Advantages of biosensors over dipsticks:
- gives the actual reading of blood glucose conc.
- re-usable
- quantitative => more precise reading
- thick inelastic inner walls
- thin outer walls
- Guard cells have ABA receptors on their cell surface membranes
- when ABA binds to these, it inhibits the proton pump to stop H+ ions being pumped out of the cells
- ABA also stimulates the movement of Ca+ ions into the cytoplasm from the vacuole through the cell surface membrane and tonoplast
- Ca+ acts as a second messenger to activate channel proteins to open that allow negatively charged ions and K+ to leave the guard cells
- At the same time Ca+ ions also stimulate the closure of the channel proteins so K+ ions can’t enter
- the loss of ions raises the water potential of the cells
- water moves out by osmosis
- guard cells become flaccid and the stomata close
- cells are turgid
- stomata close when the hydrogen proton pumps stop and K+ ions diffuse out of the guard cells through K+ channels and enter neighbouring cells
- this causes a high water potential in the cells
- water leaves the guard cells by osmosis
- guard cells become flaccid
- stoma close