3.6.4.3 - CONTROL OF BLOOD WATER POTENTIAL Flashcards
alport syndrome (AS) is an inherited disorder that affects the kidney glomeruli of both men and women. affected individuals have proteinuria (high quantities of protein in their urine)
suggest how AS could cause proteinuria (2)
- affects/damages basement membrane OR more protein channels in basement membrane
- proteins can pass into the glomerular filtrate
describe how ultrafiltration occurs in a glomerulus (3)
- high hydrostatic pressure
- two named small substances pass out - water, urea, glucose, ions, urea
- through pores in capillary endothelium
furosemide is a drug used to remove excess fluid from the body. scientists investigated the effect of this drug on the volume of urine produced by human volunteers.
furosemide inhibits the absorption of sodium and chloride ions from the filtrate produced in the nephrons.
explain how furosemide causes an increase in the volume of urine produced (3)
- water potential of filtrate decreased
- less water reabsorbed by osmosis from the filtrate
- collecting duct/PCT/DCT is where osmosis occurs
osmoreceptors are specialised cells that respond to changes in the water potential of the blood.
give the location of osmoreceptors in the body of a mammal (1)
hypothalamus
when a person is dehydrated, the cell volume of an osmoreceptor decreases.
explain why (2)
- water potential of blood will decrease
- water moves from osmoreceptor into blood by osmosis
stimulation of osmoreceptors can lead to secretion of the hormone ADH.
describe and explain how the secretion of ADH affects urine produced by the kidneys (4)
- permeability of membrane to water is increased
- more water absorbed from collecting duct
- smaller volume of urine
- urine becomes more concentrated
in a mammal, urea is removed from the blood by the kidneys and concentrated in the filtrate.
describe how urea is removed from the blood (2)
- hydrostatic pressure
- causes ultrafiltration at Bowman’s capsule
- through basement membrane
explain how urea is concentrated in the filtrate (3)
- reabsorption of water by osmosis
- at the PCT
- at the DCT
- active transport of ions/glucose creates gradient (give context)
describe how ultrafiltration produces glomerular filtrate (5)
- hydrostatic pressure
- small molecules - amino acids, urea, water, ions
- pass through basement membrane/acts as filter
- protein too large to go through
- presence of podocytes/pores in capillaries
some people who have diabetes do not secrete insulin.
explain how a lack of insulin affects reabsorption of glucose in the kidneys of a person who does not secrete insulin (4)
- high concentration of glucose in blood
- high concentration of glucose in filtrate
- reabsorbed by facilitated diffusion/active transport
- requires proteins
- these are saturates/working at maximum rate
- not all glucose absorbed, so some lost in urine
some desert mammals have long loops of henle and secrete large amounts of ADH.
explain how these two features are adaptations to living in desert conditions (6)
- more water reabsorbed/less lost in urine
- by osmosis
- from collecting duct
- due to longer loop of henle
loop of henle:
5. sodium ions absorbed from filtrate in ascending limb
6. gradient established in medulla
ADH:
7. acts on collecting duct
8. makes cells more permeable by inserting aquaporins in plasma membranes
the urine of a non-diabetic person does not contain glucose. explain why (2)
- glucose leaves the blood at the kidney
- but then is reabsorbed in proximal convoluted tubule
a high blood glucose concentration could cause glucose to be present in the urine of a diabetic person. suggest how (2)
- high concentration of glucose in the filtrate
- cannot all be reabsorbed
a test for glucose in urine uses immobilised enzymes on a plastic strip test. one of these enzymes is glucose oxidase.
explain why the test strip detects glucose and no other substance (2)
- active site has specific tertiary structure
- only glucose can form enzyme-substrate complex
if the glomerular filtrate of a diabetic person contains a high concentration of glucose, they produce a larger volume of urine.
explain why (3)
- glucose in filtrate lowers water potential
- lower water potential gradient
- so less water reabsorbed by osmosis