Excretion of waste Flashcards Preview

BIOMOLECULES AND CELLS > Excretion of waste > Flashcards

Flashcards in Excretion of waste Deck (16)
Loading flashcards...
1
Q

What is the function of the thick ascending limb?

A
  • Actively pumps out NaCl
  • is impermeable to water so water does not follow
  • NaCl raises the solute concentration in the surrounding interstitial fluid of the renal medulla
2
Q

What is the function of the thin descending limb?

A
  • highly permeable to water but not to Na+ or Cl-
  • bc the surrounding interstitial fluid tissue is more concentration, water exits the descending loop by omsosis
  • thus the renal fluid in the descending limb becomes more concentrated
3
Q

What happens in the distal convoluted tubule?

A
  • the renal fluid is LESS concentrated than the interstitial fluid
  • reabsorption of salts, amino acids etc occurs.
  • Some water moves out by osmosis
  • renal fluid becomes iso-osmotic with the interstitial fluid
4
Q

What happens as the filtrate moves down the collecting duct?

A

• it becomes highly concentrated as water is drawn out due to the high solute concentration in the interstitial fluid of the medulla

5
Q

Describe the movement of urea

A
  • some urea leaks from the collecting duct into the interstitial fluid of medulla, adding to increased osmotic concentration in renal medulla
  • urea diffuses back into ascending limb and is returned to the collecting duct
6
Q

What is the function of ADH (Antidiuretic hormone - aka vasopressin)?

A
  • controls the permeability of the collecting duct to water - thus the amount of water reabsorbed from urine
  • ADH stimulates expression of aquaporin 2 which is a water channel in the collecting duct cell membranes.
7
Q

What signals does the brain receive for it to stimulate thirst?

A
  • the amount of water in the body is too low

* some elements in the blood, such as sodium, are too concentrated

8
Q

Explain with reference to kidney function the hormonal control of blood volume if blood pressure is too low.

A
  • blood pressure is too low - kidney releases renin
  • renin converts angiotensinogen to ang 1
  • then converting enzyme ACE converts ang 1 to active form ang2
  • ang2 stimulates adrenal cortex to release aldesterone
  • there is enhanced Na+ reabsorption in the kidney and H2O is reserved
9
Q

What effect angiotensin 2 have on the body?

A
  • constriction of peripheral blood vessels (increase pressure)
  • release of aldosterone (enhances Na+ reabsorption and hence water reabsorption in distal convoluted tubule and collecting duct)
  • stimulation of thirst and drinking
10
Q

What happens in the hypothalamus if blood osmolarity increases?

A
  • high blood osmolarity or low blood pressure/volume
  • stimulates the posterior pituitary to release ADH
  • ADH increases permeability of distal tubule and collecting duct to H2O - water is conserved to restore the osmolarity
11
Q

What receptors detect osmolarity?

A

Osmoreceptors in the hypothalamus

• they also detect changes in blood pressure

12
Q

What happens if there is a mutation to the vasopressin/ADH gene?

A
  • mice cannot produce AD/vasopressin so its kidneys don’t return water to the blood but instead secrete it
  • mice is always drinking water to replenish the water lost in the urine
13
Q

Why does alcohol increase frequency of urination?

A
  • high blood alcohol levels block production of vasopressin in the pituitary gland
  • kidney does not return water to the blood
  • excess urination leads to dehydration and loss of electrolytes (K+, Mg2+)
14
Q

what is RAAS?

A

Renin-Angiotensin - Aldosterone System

• An important autoregulatory mechanism is renin release by kidney when blood pressure falls

15
Q

How is a decrease in blood pressure detected by the kidney?

A
  • blood volume influences the pressure in the glomerulus which is regulated to maintain the glomerular filtration rate
  • small changes in blood pressure are detected by baroreceptors in the afferent arterioles
16
Q

Where are large decrease in blood volume detected?

A

Juxtaglomerular cells of the kidney