Excretion

Question 1

Where does ultrafiltration occur?

Answer 1

In the renal/bowman’s capsule.

Question 2

What are the different arterioles?

Answer 2

• arteriole into the glomerulus (afferent-arriving) is wider
• arteriole out (efferent - exiting) is narrower

Question 3

Where does selective reabsorption take place?

Answer 3

At proximal convulated tubule.

Question 4

What is selective reabsorption?

Answer 4

“Useful materials” that were filtered out of blood are returned. E.g. glucose, amino acids, vitamins , hormones.
- some urea is reabsorbed to the blood by diffusion.

Question 5

What is the proximal convoluted tubule lined with?

Answer 5

• lined with epithelial cells.
  Microvilli -> increases SA for reabsorption
  Mitochondria -> used for active transport.

Question 6

Describe how glucose is transported from lumen of the tubule into the blood.

Answer 6

1- sodium ions actively transported out of cells into tissue fluid via Na+/K+ pump. Increases in Na+ in epithelial cells.
2- glucose and amino acids diffuse into blood capillaries (facilitated diffusion).
3- glucose or amino acids enter cells with sodium ions by facilitated diffusion via co-transport.

Question 7

Where does the reabsorption of water take place?

Answer 7

Loop of Henle.

Question 8

What are the effects of reabsorption of water?

Answer 8

• makes tissue fluid in the medulla increasingly hypertonic (salty via ions) compared to the filtrate in the nephron.
• achieved with countercurrent system

Question 9

Features of the ascending limb.

Answer 9

• impermeable to water and contains a Na+ and Cl- pump.
• ions are actively transported out of filtrate into surrounding tissue fluid. Water would follow by osmosis, but it can’t as ascending limb is impermeable to water.

Question 10

Features of descending limb.

Answer 10

-impermeable to ions and permeable to water.
- some water leaves loop by osmosis.
- filtrate becomes more concentrated as it descends.
- Tissue fluid becomes more salty (hypertonic) and becomes more conc at base of medulla.

Question 11

Adaptations to hot climates in terms of water reabsorption.

Answer 11

• animals in desert have longer loop of henle so that the medulla can become increasingly slaty (concentrated) to increase reabsorption of water.

Question 12

what happens in distal convoluted tubule?

Answer 12

• substances are actively transported from blood into filtrate. Has membrane pump for active transport and regulated by hormones.These include:
• H+(for pH homeostasis)
• K+ (for salt homeostasis).
• ethanol
• toxins
• drugs

Question 13

What happens in collecting duct?

Answer 13

Homeostatic control of blood water potential.

Question 14

What’s included in this homeostatic control?

Answer 14

• Hypothalamus has osmoreceptors -> sensitive to water potential of the blood.
• Stimulates neurosecretory cells in hypothalamus -> secretes ADH..
• ADH molecules then travel along the axons of the neurosecretory cells to the prosterian pituitary gland where they are stored. ADH alters the permeability if the walls of the collecting duct of the nephron to water.

Question 15

ADH vs no ADH.

Answer 15

ADH:
- made in hypothalamus in brain
- causing collecting duct to reabsorb more water
- maintains water potential of blood
- less urine made
- urine is more concentrated and therefore dark in colour
No ADH:
- causes collecting duct to reabsorb less water
- reduces water level in blood
- more urine is made
-urine is less concentrated and therefore pale in colour

Question 16

ADH is a protein hormone. Describe how its secretion into the blood will cause a cell in the collecting duct to reabsorb more water.

Answer 16

1- ADH bind to receptor
2- Activates adenyl cyclase ATP -> cAMP
3- cAMP activates protein kinase A.
4- protein kinase A stimulates release of aquaporin
5- inc aquaporin in cell surface memb
6- inc osmosis