Module 6- Control of blood water potential Flashcards
Outline ultrafiltration to form glomerular filtrate
Afferent wider than efferent capillary –> increased hydrostatic pressure –> Small molecules pushed through capillary pores/endothelium –> Basement membrane acts as filter –> Bowmans capsule [filtrate] –> Gaps between podocytes–> Large proteins and blood cells left behind in glomerulus
Outline selective reabsorption of glucose and water in proximal convoluted tubule
- Cotransporter takes in Na+ against concentration gradient and Glucose down concentration gradient
- Na+ pumped out of cell using Na+/K+ pump.
- Glucose moves to medulla and then blood via facilitated diffusion.
- Water potential in epithelial cell lowers
- Water moves into cell via osmosis and then on to medulla and blood
- 100% glucose and amino acids should be reabsorbed
Outline selective reabsorption of water in Loop of Henle by maintaining a gradient of sodium ions
- Na+ actively transported out of the ascending limb [requires ATP].
- Water potential of medulla lowered.
- Ascending limb impermeable to water.
- Water leaves descending limb via osmosis [from filtrate to medulla and then blood].
- Some Na+ diffuses into descending limb.
- Longer the Loop of Henle – more water reabsorbed
- Apex of loop has the most concentrated filtrate
Outline osmoregulation in the Distal Convoluted Tubule and the collecting duct
- Osmoreceptors in the hypothalamus detect water levels of blood.
- Posterior pituitary gland releases ADH, if dehydrated
- ADH binds to specific complementary receptors on target cells in Distal convoluted tubule and collecting duct.
- Phosphorylase activated
- Increased inclusion of water channels in membrane
- Increase reabsorption of water via osmosis from filtrate to medulla to blood
- Urine becomes more concentrated and lower in volume.
How does dialysis work?
Dialysis fluid concentration gradients are manipulated so that no glucose or amino acids are lost. All of urea is removed.
Give negatives of dialysis
- Blood thinners required – can lead to blood clotting issues
- Quality of life issues – time consuming.
- Infection risk in hospital
Give negatives of kidney transplant
- Difficulty to find donor match.
- Immunosuppressant drugs required.
- New transplant needed after 9 years.
- Surgical risks.
2 marks
A high blood glucose concentration could cause glucose to be present in the urine of a diabetic person. Suggest how
- large amount of glucose in filtrate
- Cannot all be reabsorbed
3 marks
If the glomerular filtrate of a diabetic person contains a high concentration of glucose, he produces a larger volume of urine. Explain why.
- Glucose in filtrate lowers water potential
- Lower water potential gradient
- Less water reabsorbed via osmosis
3 marks
Explain how urea is concentrated in the filtrate
Reabsorption of water by osmosis
At the PCT / descending LoH
At the DCT / CD
Active transport of ions / glucose creates gradient (in context)
6 marks
Humans can produce urine which is more concentrated than their blood plasma.
Explain the role of the loop of Henle in the absorption of water from the filtrate.
- In the ascending limb sodium ions actively removed
- Ascending limb impermeable to water
- In descending limb sodium(ions) diffuse in
- Descending limb water moves out
- Low water potential
- The longer the loop, the lower the water potential in medulla
- Water leaves collecting duct
- By osmosis / down water potential gradient
4 marks
Explain the role of ADH in the production of concentrated urine.
- When water potential of the blood too low
- Detected by receptors in the hypothalamus
- Pituitary releases more ADH
- ADH increases the permeability/ opens channels for water in the DCT / collecting duct
- More water is reabsorbed into the blood
- By osmosis down the water potential gradient
2 marks
When a person’s dehydrated, the cell volume of an osmoreceptor falls. Explain why
- Water potential of blood will decrease
- Water moves from osmoreceptor into blood via osmosis
2 marks
The kangaroo rat is a small desert mammal. It takes in very little water in its food and it rarely
drinks. Its core body temperature is 38 °C.
The kangaroo rat takes in some water by feeding and drinking. Describe another method by
which the kangaroo rat could obtain water.
From aerobic respiration
4 marks
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.
- High concentration of glucose in blood
- High concentration in filtrate
- Reabsorbed by F.D
- Requires carrier proteins
- These are saturated
- Not all glucose is reabsorbed / some is lost in urine
