6.4.3 - Control of blood water potential Flashcards
Identify 2 features of the Bowman’s capsule which enables ultrafiltration to take place. Explain how it aids ultrafiltration. (4)
- The efferent arteriole is narrower than the afferent arteriole
- Generating high blood pressure
- The endothelium of the glomerular capillary has pores / the basement membrane (between the capillary and the Bowman’s capsule) is made up of a mesh of fibres / the Bowman’s capsule epithelium has (extensions called) podocytes which wrap around the capillary
- Enabling small molecules to pass through (from the blood in the glomerulus into the Bowman’s capsule) but stops blood cells and proteins
Describe how ultrafiltration occurs in a glomerulus. (3)
- High blood/hydrostatic pressure
- Two named small substances pass out e.g. water, glucose, ions, urea
‘accept correct named ions, mineral ions/minerals, amino acids/small proteins - (Through small) gaps/pores/fenestrations in (capillary) endothelium
‘accept epithelium for endothelium’ - (And) through (capillary) basement membrane
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 / cells (to water) is increased
- More water absorbed from / leaves distal tubule / collecting duct
- Smaller volume of urine
- Urine becomes more concentrated
Describe how urea is removed from the blood. (2)
- Hydrostatic pressure
- Causes ultrafiltration (Allow description of ultrafiltration) at Bowman’s capsule / glomeruli / renal capsule
- Through basement membrane
- Enabled by small size urea molecule
Explain how urea is concentrated in the filtrate. (3)
- Reabsorption of water / by osmosis
- At the PCT / descending LoH
- At the DCT / CD
- Active transport of ions / glucose creates gradient (in context)
Describe how ultrafiltration produces glomerular filtrate. (5)
- Blood pressure / hydrostatic pressure
- Small molecules / named example
- Pass through basement membrane / basement membrane acts as filter
- Protein too large to go through / large so stays behind
- Presence of pores in capillaries / presence of podocytes
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 in tubule / in filtrate
- Reabsorbed by facilitated diffusion / active transport
- Requires proteins / carriers
- These are working at maximum rate / are saturated
- Not all glucose is reabsorbed / some is lost in urine
Some desert mammals have long loops of Henle and secrete large amounts of antidiuretic hormone (ADH). Explain how these two features are adaptations to living in desert conditions. (6)
- More water (from filtrate) reabsorbed / returned to blood / less lost in urine
- By osmosis
- From collecting duct / from end of second convoluted tubule
- Due to longer loop of Henle
- Sodium / chloride ions absorbed from filtrate in ascending limb
- Gradient established in medulla / concentration of ions increases down medulla
- Acts on collecting duct / distal convoluted tubule / second convoluted tubule
- Makes cells more permeable / inserts aquaporins in plasma membranes
A diabetic person and a non-diabetic person each ate the same amount of glucose. One hour later, the glucose concentration in the blood of the diabetic person was higher than that of the non-diabetic person. Explain why. (2)
- Lack of insulin / reduced sensitivity of cells to insulin
- Reduced uptake of glucose by cells / liver / muscles
- Reduced conversion of glucose to glycogen
If the glomerular filtrate of a diabetic person contains a high concentration of glucose, he produces a larger volume of urine. Explain why. (3)
- Glucose in filtrate lowers water potential
- Lower Ψ gradient / less difference in Ψ filtrate − Ψ plasma
- Less water reabsorbed by osmosis
In some forms of kidney disease, proteins from the blood plasma are found in the urine. Which part of the nephron would have been damaged by the disease to cause proteins from blood plasma to be present in the urine? Explain your answer. (3)
- Glomerulus / Bowman’s capsule / renal capsule
- Basement membrane
- Proteins are large (molecules) / proteins cannot normally pass through filter /proteins can only pass through if filter damaged
