section 3 (7) explain how the processes of filtration and reabsorption in the mammalian nephron regulate body fluid composition

Question 1

What is a nephron?

Answer 1

• the fundamental unit of a kidney
• a microscopic tubule
• each kidney contains millions of nephrons

Question 2

What are the 4 functional parts of a nephron?

Answer 2

1) bowman’s capsule
2) proximal convoluted tubule
3) loop of Henle
4) distal convoluted tubule→ leads to → collecting duct

Question 3

What is the glomerulus?

Answer 3

• a spherical network of capillaries

- Serves as the first stage in the filtering process of the blood carried out by the nephron in its formation of urine.

Question 4

What is the Bowmans capsule?

Answer 4

• the enlarged part of the nephron tubule; double-walled sac

Question 5

What happens in the proximal convoluted tubule?

Answer 5

• reabsorption of all organic nutrients (amino acids, glucose) and some ions

Question 6

What happens in the descending loop of Henle?

Answer 6

• walls are permeable to water, not salts

- water exits as a result of the salty environment→ concentration of filtrate increases

Question 7

What happens in the ascending loop of Henle?

Answer 7

• walls are permeable to salts, not water

- sodium ions are pumped out and into the medulla, so that water can leave passively in the descending loop

Question 8

What happens in the distal convoluted tubule?

Answer 8

• reabsorption of salts and bicarbonate

Question 9

What happens in the collecting ducts?

Answer 9

• walls permeable to water but not salts

- the concentration of urine increases as water leaves passively into the salty medulla

Question 10

Where does filtration happen?

Answer 10

• between the glomerulus and the Bowmans capsule

Question 11

What causes part of the blood to be forced into the Bowmans capsule?

Answer 11

• high blood pressure in the glomerulus

- high permeability of capillary walls

Question 12

What is the fluid that enters the Bowman’s capsule?

Answer 12

• Glomerular filtrate
• contains water containing dissolved substances e.g. glucose, amino acids, salts, nitrogenous wastes
• blood cells and large proteins do not pass through into the filtrate (retained in the blood on account of their large size)

Question 13

What is the progression of Glomerular filtrate?

Answer 13

Fills the hollow part of the Bowmans capsule → travels the length of nephron → reaches collecting duct as urine because of a change in chemical composition on account of addition/ removal of various substances

Question 14

Give a basic overview of reabsorption

Answer 14

• occurs from the glomerular filtrate in the nephron tubule to the blood from the capillaries
• at the proximal and distal tubules in the loop of Henle, materials from the Glomerular filtrate that can be reused are selectively reabsorbed into the large capillary network and interstitial fluid
• surrounding capillaries lead to larger vessels and then eventually to the renal vein which leads filtered blood back into the bloodstream
• substances reabsorbed include water and solutes (e.g glucose, amino acids, ions)

Question 15

outline solute reabsorption

Answer 15

• all amino acids and glucose are reabsorbed in the proximal tubule
• some ions and some minerals are reabsorbed in the proximal and distal tubules
• occurs by facilitated diffusion and active transport
• urea is no reabsorbed

Question 16

outline water reabsorption

Answer 16

• as solutes are reabsorbed, so is water through osmosis
• 99% of the glomerular filtrate (only 1% is excreted in urine)
• occurs mainly in the collecting duct

Question 17

What is secretion?

Answer 17

• involves the removal of toxic substances from the blood capillaries to the filtrate by active transport
• secreted substances include: urea, uric acid, ammonia, ions and drugs (penicillin etc)