Role Of The Nephron In Osmoregulation

Question 1

1. Describe the formation of glomerular filtrate by ultrafiltration

Answer 1

1. Blood enters the kidney through the renal artery which branches frequently to give arterioles, each of which enters the Bowmans capsule of the nephron.
2. This arteriole is called the afferent arteriole and it divides to give a complex of capillaries known as the glomerulus
3. The glomerulus capillaries later merge to form the efferent arteriole, which then subdivides into the capillaries, which wind their way around the various tubules of the nephron before combining to form the renal vein
4. As the diameter of the afferent arteriole is greater than that of the efferent arteriole, there is a build up of hydrostatic pressure within the glomerulus
5. As a result, water, glucose and mineral ions are squeezed out of the capillary and into the bowmans capsule to form the glomerular filtrate
6. Blood cells and proteins cannot pass across into the bowmans capsule as they are too large, so stay in the blood
7. The substances that enter the bowmans capsule are called the glomerular filtrate

Question 2

What is the movement of the filtrate out of the glomerulus is resisted by what?

Answer 2

Capillary epithelial cells

Connective tissue of the blood capillary

Epithelial cells of renal capsule

Hydrostatic pressure of the fluid in the bowmans capsule space

The low water potential of the blood in the glomerulus

Question 3

How is the barrier adapted to let filtrate through

Answer 3

Podocytes on inner layer of bowmans capsule- have spaces between them for filtrate to pass between them

Endothelium of glomerular capillaries has spaces between its cells, that can allow fluid to pass between them

Question 4

How is the proximal convoluted tubules adapted to reabsorb substances into the blood by having epithelial cells that have :

Answer 4

Microvilli to provide a large SA to reabsorb substances from the filtrate

Infoldings at their bases to give large SA to transfer reabsorbed substances into the blood capillaries

A high density of mitochondria to provide ATP for active transport

Question 5

2. Describe the process of reabsorption of glucose and water by the proximal convoluted tubule

Answer 5

1. Sodium ions are actively transported out of the cells lining the proximal convoluted tubule into blood capillaries which carry them away. The sodium ion concentration of these cells is therefore lowered
2. Sodium ions now diffuse down a concentration gradient from the lumen of the proximal convoluted tubule into the epithelial lining cells but only through special carrier proteins by facilitated diffusion
3. These carrier proteins are of specific types, each of which carries another molecule ( glucose, amino acids) along with sodium ions. (Co transport)
4. The molecules which have been co transported into the cells of the proximal convoluted tubule then diffuse into the blood. As a result, all the glucose and most other valuable molecules are reabsorbed as well as water