The Kidneys- BP

Question 1

Structure of Kidneys?

Answer 1

Outer region called Cortex, Middle region called Medulla

Question 2

role of kidneys?

Answer 2

filters blood (removes urea, excess salts, excess water – combined known as urine)

Question 3

why move urea?

Answer 3

toxic waste product made from excess amino acids

Question 4

why remove excess salts and water?

Answer 4

maintain correct water potential and pressure in blood

Question 5

how do the kidneys filter?

Answer 5

• made up of millions of nephrons
• each nephron filters the blood producing urine

Question 6

Structure of Nephron?

Answer 6

1st part = Bowmans Capsules
2nd part = Proximal Convoluted Tubule
3rd part = Loop of Henle
4th part = Distal Convoluted Tubule
5th part = Collecting Duct

Question 7

Bowmans Capsule?

Answer 7

• start of nephron
• site of ultrafiltration (where blood is filtered)
• occurs between specialised capillaries called Glomerulus and Bowmans Capsule

Question 8

Proximal Convoluted Tubule?

Answer 8

• second part of the nephron
• site of selective reabsorption
• all the glucose/amino acids and some of the salts/water are sent back into blood
  (from lumen of PCT, through cells lining PCT, into blood)

Question 9

How does the proximal convoluted tubule work?

Answer 9

• salts (sodium ions) are actively transported from cells lining the PCT into the blood
• this lowers sodium ion concentration in the cells
• sodium ions diffuse from the lumen of the PCT into the cells
• as sodium ions move, they pull in glucose and amino acids with them via co-transport
• glucose and amino acids build up in the cell, then diffuse into the blood
• the movement of salt/glucose/amino acids into the blood, lowers it’s water potential, so water follows into blood by osmosis

Question 10

Loop of Henle?

Answer 10

• third part of the nephron
• site of further water reabsorption
• occurs by hairpin countercurrent multiplier

Question 11

How does the loop of henle work?

Answer 11

• sodium and chloride ions are actively transported out of the ascending limb of the loop of henle into the surrounding medulla of kidney
• this lowers water potential of medulla
• so water moves out of the descending limb of loop of henle (and collecting duct) by osmosis into the medulla
• this water then moves into the blood
• the sodium and chloride ions then diffuse into the descending limb of loop of henle so the above process can be repeated

Question 12

Distal Convoluted Tubule?

Answer 12

 fourth part of nephron
 site of further salt reabsorption
 corrects required salt balance between blood and urine

Question 13

collecting duct?

Answer 13

• final part of nephron
• site of further water reabsorption and osmoregulation
• end up being left with urine that is sent into the ureter to the bladder
• water reabsorption occurs by the hairpin countercurrent multiplier
• amount of water being reabsorbed is controlled at this stage, this is known as osmoregulation

Question 14

what happens in the collecting duct if water levels become too low?

Answer 14

• osmoreceptors in hypothalamus shrink
• this stimulates the release of ADH from the posterior part of the pituitary gland
• ADH stimulates the cells lining the collecting duct to increase the number of aqauporins (water channels)
• so more water moves from the collecting duct back into blood
• so less water is lost in the urine

Question 15

what is osmoregulation?

Answer 15

the process by which the hypothalamus controls water potential of the blood

Question 16

what happens in the collecting duct if water levels become too high?

Answer 16

• less ADH released
• less aquaporins in collecting duct
• less water moves from collecting duct into blood
• more water lost in urine (reduces overhydration)

Question 17

what happens in the Bowman’s capsule?

Answer 17

• glomerulus located in the middle of an arteriole
• afferent arteriole before glomerulus is wide, efferent arteriole after glomerulus is narrow
• so build up of hydrostatic pressure in the glomerulus pushes fluid and small substances from the glomerulus into the bowmans capsule
• small substances filtered = glucose, amino acids, salts, urea
• only small substances can pass through the 3 layers
  (endothelium of glomerulus, basement membrane, podocytes of bowmans capsule)
• results in glomerular filtrate in bowmans capsule
  (water + glucose/amino acids/salts/urea)
• the job of the rest of the nephron is to send all the glucose/amino acids and some of the salts/water back into the blood [reabsorption]