F2144 -2- Excretion

Question 0

Outline the process by which water is reabsorbed in the kidney.

Answer 0

Medulla tissue fluid has a VERY LOW WATER POTENTIAL

1) DESCENDING LIMB: Na+ and Cl- diffuse into the tubule fluid as there is a high concentration of these ions in the tissue fluid; water moves out of the tubule fluid via OSMOSIS due to the very low water potential in the medulla.
2) LOWER ASCENDING LIMB - as ionic potential is now also quite high in the tubule fluid, some of the Na+ and Cl- ions begin to diffuse out into the medulla tissue fluid again.
3) UPPER ASCENDING LIMB - the process of diffusion slows as the diffusion gradient becomes less dramatic, so active transport is used in the ascending limb to remove a large number of Cl- and Na+ ions from the tubule fluid, keeping the ion concentration in the medulla high.
4) DISTAL CONVOLUTED TUBULE - this part is in the cortex of the kidney and not the medulla, so NOTHING HAPPENS TO WATER HERE.
5) COLLECTING DUCT - this passes through the medulla once more, and so a lot of osmosis occurs to remove lots of water into the capillaries due to the very low water potential in the medulla. Finally, urine passes down the collecting duct to pelvis (pale bit in middle of Kidney before the ureter).

Question 1

Structure of a nephron (in order)

Answer 1

• Afferent arteriole (from renal artery)
• Glomerulus (efferent arteriole diverges)
• Bowman’s Capsule
• Proximal Convoluted Tubule (PCT)
• Descending limb of Loop of Henle
• Ascending limb of Loop of Henle
• Distal Convoluted Tubule (DCT)
• Collecting Duct (to ureter)

Note: the efferent arteriole loops around the nephron, tracing it all the way along until the collecting duct, where it parts ways to feed into the renal vein.

Note: Ureter -> Bladder -> Urethra

Question 2

Definition of excretion

Answer 2

The removal of metabolised waste products from the body, such as urea.

Question 3

Osmoreceptors

Answer 3

Receptor cells that monitor the water potential of the blood and detect any changes.

Question 4

Osmoregulation

Answer 4

The control and regulation of the water potential if the blood and body fluids.

Question 5

Peritoneal dialysis

Answer 5

A form of treatment for kidney patients in which dialysis fluid is pumped into the body cavity so that exchange can occur across the peritoneal membrane (abdominal membrane in the patients body).

Question 6

Dialysis (non-peritoneal) plus haemodialysis

Answer 6

Dialysis is the use of a partially permeable membrane to filter the blood. The DIALYSIS MEMBRANE is a partially permeable membrane that separates the dialysis fluid from the patient’s blood in a dialysis machine. DIALYSIS FLUID is a complex solution that matches the composition of normal body fluids.

In HAEMODIALYSIS blood is taken from a vein and passed through a dialysis machine so that exchange can occur across an artificial partially permeable membrane.

Question 7

Advantages and disadvantages of a kidney transplant

Answer 7

ADVANTAGES:
•Freedom from time-consuming dialysis
•Diet is less limited
•A better quality of life (eg allowed to travel)
•No longer seeing oneself as chronically ill

DISADVANTAGES:
•Need immunosuppressants for the life of the kidney
•Need major surgery under a general anaesthetic
•Risks of surgery include infection, bleeding and damage to surrounding organs
•Frequent checks for signs of organ rejection
•Side effects: anti-rejection medicines cause fluid retention and high blood pressure; immunosuppressants increase susceptibility to infections.

Question 8

Selective Reabsorption occurring at the Proximal Convoluted Tubule where 85% of the glomerular filtrate is reabsorbed.

Answer 8

P. 45 in textbook