3.6.4.3 Control of blood water potential

Question 1

2 kidney function

Answer 1

Excretion
Osmoregulation

Question 2

Kidney Structure

Answer 2

Cortex & Medulla

Renal Artery / Veins
pyramids
Pelvis
Ureter (urine) –> Bladder

Nephron

Question 3

3 process in nephron + brief description

Answer 3

Ultrafiltration – Blood is filtered out of the glomerulus at the Bowman’s capsule to form filtrate
Selective reabsorption – Usable materials are reabsorbed in convoluted tubules (both proximal and distal)
Osmoregulation – The loop of Henle establishes a salt gradient, which draws water out of the collecting duct

Question 4

nephron structure

Answer 4

Bowman’s Capsule
Glomerulus
Proximal Convoluted Tubule
Loop of Henle
Distal Convoluted Tubule
Collecting Duct

Vasa Recta (throughout)

Question 5

Ultrafiltration process in Nephron

Answer 5

• Hydrostatic pressure is high in the glomerulus.
• Fluid (water, salts, urea, glucose, amino acids) is forced out into the capsule.
• Fluid moves through fenestrations between the endothelial cells of the capillary and the spaces between the podocytes.
• Cells and proteins are too large to pass through and remain in the blood.

1. Blood is filtered by the basement membrane, which lies between the glomerulus and Bowman’s capsule
2. Glomerular blood vessels are fenestrated (have pores) which means blood can freely exit the glomerulus
3. The podocytes of the Bowman’s capsule have gaps between their pedicels, allowing for fluid to move freely into the nephron

The basement membrane is size-selective and restricts the passage of blood cells and large proteins.

Question 6

Reabsorption process in Nephron (amino Acid) - cotransport

Answer 6

• Sodium ions are actively pumped out of the PCT by the Na+K+ATPase pump using ATP.
• Sodium ions inside the cell are at a lower concentration than in the lumen.
• Sodium moves into the cell from the lumen down its concentration gradient through a carrier (cotransport) protein.
• AA moves in with it against its concentration gradient, creating a high concentration inside the cell.
• AA moves into the blood by facilitated diffusion from a high concentration inside to a low concentration in the blood where it is quickly removed by the flow, maintaining a concentration gradient.

Question 7

3 adaptation of the cell for reabsorption

Answer 7

1. Microvilli / Folded cell-surface membrane provide a large surface area
2. Many channel/carrier proteins for facilitated diffusion;
3. Many carrier proteins for active transport;
4. Many channel/carrier proteins for co-transport;
   Accept ‘cotransport protein’ for type of transport protein.
5. Many mitochondria produce ATP OR Many mitochondria for active transport;
6. Many ribosomes to produce carrier/channel proteins;
   Accept abundant rough endoplasmic reticulum for many ribosomes, but abbreviation is not enough.

Question 8

Describe another method by which the animal live in extreme dry places could obtain water. [2]

Answer 8

It could produce metabolic water
Using oxygen & aerobic respiration

from water (product) + fatty acid

Question 9

How diabetes lead to glucose appear in urine

Answer 9

High blood Glucose (>10 mol dm -3)
Filtrate — Cotransporter Saturated = Renal threshold
Not all glucose is reabsorbed
some appear in urine

Question 10

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. [6]

Answer 10

The loop of Henle operates a counter-current multiplier system.
In the ascending limb sodium ions are actively removed from the tubule into medulla tissue
Water does not follow by osmosis because the ascending limb impermeable to water (no aquaporines)
As a result, a Na+ (salt) gradient is formed in the interstitial fluid of the medulla
The longer the loop / the deeper into medulla, the lower the water potential in medulla / interstitial fluid;
The descending limb is permeable to water, so water moves out of the tubule by osmosis;
As the filtrate moves through the collecting duct / DCT, water moves out by osmosis / down water potential gradient (present of ADH - reabsorb into blood)

Question 11

Anti-diuretic hormone (ADH)

where it produce
the use

Answer 11

• Secreted from the posterior pituitary gland when blood water potential is low
• regulates the level of water reabsorption in the collecting duct
• detect by osmoreceptor cell in hypothalamus (shrink/ swell)

Question 12

How does ADH lead to reabsorption of water in collecting duct

Answer 12

ADH bind to complementary receptor on collecting duct/ DTC
more aquaporines in membrane (stimulated)
Addition of channel protein into membrane
increase permeability
Water enter by osmosis

Question 13

why no conc change in pct ?

Answer 13

reabsorption of water by osmosis happen at the same time when glucose and amino acid being absorb.

Question 14

the difference in con and volume after going through limb and overall

Answer 14

descending limb
- higher concentration
- less volume

ascending limb
- lower concentration
- no volume change

overall
- same concentration
- lower volume

Question 15

Concentration calculation

Answer 15

C₁ = concentration of starting “stock” solution
V₁ = initial volume taken

C₂ = concentration of final “dilute” solution

V₂= final volume

C₁V₁ = C₂V₂