the kidneys

Question 1

what is the function of the Nephron?

Answer 1

• to filter the blood to remove waste and selectively reabsorb useful substances back into the blood.

Question 2

what does the urine contain?

Answer 2

-water
-dissolved salts
-urea
-other small substances such as hormones and excess vitimans

Question 3

what the urine NOT contain and why?

Answer 3

-protein and blood cells as they are too large to be filtered out of the blood
- glucose as all glucose is reabsorbed by active transport at the selective reabsorption stage in the proximal covuluted tubule

Question 4

where does ultrafiltration occur?

Answer 4

-bowmans capsule

Question 5

what occurs in the ultrafiltration process?

Answer 5

• blood enters via the afferent arteriole and splits into smaller capillaries (glomerus)
  -this causes high hydrostatic pressure
• water and small molecules e.g glucose and mineral ions are forced out of the capillaries, forming the glomerus filtrate
  -large proteins and blood cells are too big to pass through the capillary endothelium, so thye remian in the blood
  -blood leaves via efferent arteriole

Question 6

where does selective reabsorption occur?

Answer 6

-in the proximal convoluted tubulew

Question 7

what happens during selective reabsorption?

Answer 7

• 85% of glomerus filtrate is reabsorbed back into the blood, leaving urea and excess minerals behindi

Question 8

give the adaptations of the cells lining the proximal convulted tubule

Answer 8

• lots of mitochondria to provide energy for active transport
  -microvilli to provide a larger surface area for absorption

Question 9

steps of selective reabsorption.

Answer 9

• the conc of sodium ions in the proximal convulutes tubule decreases as sodium ions are actively transported out of the PCT cells into blood capillaries
• due to the conc gradient, sodium diffuses down the conc gradient from lumen of PCT into the cells lining the PCT , co transport carries glucose with it
  -glucose can then diffuse from the PCT epithilial vell into the blood stream

Question 10

where is the sodium ion conc maintained?

Answer 10

-in the loop of henle

Question 11

what is the function of the Loop of Henle?

Answer 11

-maintains a sodium ion gradient to enable reabsorption of water

Question 12

How to maintain a sodium ion conc gradient by the Loop of Henle?

Answer 12

-mitochondria in the walls of the cells provide energy to acticvely transport sodium ions out of the loop of henle
-the accumilation of sodium outside the nephron in the medulla, lowers the water potential
- so water diffuses out by osmosis into the interstatial space and then the blood capillaries (water reabsorbed into the blood)
-at the base of the ASCENDING limb some sodium are transported out by diffusion (very dilute )

Question 13

where is water reabsorbed?

Answer 13

• at the Distal Convuluted Tubule and the collecting duct

Question 14

steps of reabsoprtion

Answer 14

• due to all sodium being transported out of Loop of Henle, when filtrate reaches Distil convulted tubule its very dilute
  -filtrate moves into Distal convuluted tubule and collecting duct, this section of medulla is very concentrated
• therefore even more water diffuses out of the DCT
  -what remains is transported to form urine