Topic 4 Excretory System: Urine Formation

Question 1

• Fluid that goes through the glomerulus (afferent arteriole -> glomerulus -> efferent arteriole) to the rest of the nephron is called filtrate, which is pushed into Bowman’s capsule. Particles that are too large to filter through the glomerulus (such as blood cells or albumin) remain in the circulatory system.
• This is a passive process that is driven by the hydrostatic pressure of blood

Answer 1

1. Filtration

Question 2

• Glucose, salts, and amino acids are reabsorbed from filtrate and return to the blood. This process takes place primarily in the PCT via active transport.
• The only passive transport here is the movement of water and the leaving of bicarbonate
• At the DCT, NaCl and bicarbonate are actively reabsorbed, allowing water to passively follow

Answer 2

2. Reabsorption

Question 3

• Substances such as acids, bases, ammonia, drugs, and ions are secreted by both passive and active transport from the peritubular capillaries and into the nephron

Answer 3

3. Secretion

Question 4

• When were dehydrated, the volume of fluid in the bloodstream is low, so we need to make small amounts of concentrated urine (and increase our blood fluids). ADH prevents water loss; it increases water retention by making the collecting duct more permeable to water. When blood pressure is low, aldosterone increases reabsorption of Na+ by the DCT and collecting duct, which increases water retention.

Answer 4

4. Concentration

Question 5

1. Filtration occurs in renal corpuscle
2. Reabsorption/secretion occurs mostly in PCT
3. Filtrate becomes more concentrated as it moves down the Loop or Henle (passive movement of water out of tube)
4. Filtrate becomes more dilute as it moves up the ascending loop (passive and active transport of salts out of Loop, but no movement of water)
5. DCT dumps into collecting duct
6. Filtrate becomes more concentrated again as it descends the collecting duct because the surrounding medulla is salty, causing water to leave
7. The collecting duct leads to multiple renal calyces
8. Renal calyx empties into renal pelvis
9. Drains to ureter
10. Drains to urinary bladder
11. Urethra

Answer 5

Recap