Body Systems: Excretory System (Water Balance And Hormones)

Question 1

Water balance and hormones:

Answer 1

-Antidiuretic hormone (ADH).
-Acts on the distal tubule and the collecting duct.
-cause the kidneys to increase water reabsorption.
-urine becomes more concentrated.
-*decreased urine output due to less water in the urine = less volume.

Question 2

ADH balance:

Answer 2

•no ADH present:
-distal tubule and collecting duct impermeable to water.
-large volume of dilute urine produced.
•ADH present:
-distal tubule and collecting duct permeable to water.
-small volume of concentrated urine produced.

Question 3

Osmoreceptors and ADH:

Answer 3

•osmoreceptors in the hypothalamus (brain) detect changes in blood concentration (called osmotic pressure).
•decreased water intake (dehydration) or increased water loss (diarrhea, vomiting, hemorrhage) results in more concentrated blood.
•the pituitary gland (brain) is signalled to release ADH—> acts on the kidneys.
•the kidney reabsorbs water into the blood.
•this reduces the water in the urine and produces more concentrated urine.

Question 4

Behavioural response: sensation of thirst:

Answer 4

•body cells are dehydrated—> osmoreceptors shrink—> blood solute concentration increases—> feel thirsty.
•fluid consumed—> blood becomes more dilute and solute concentration in blood decreases—> lowers osmotic pressure of blood.
•osmoreceptors swell and the pituitary gland is signalled—> stop releasing ADH—> less water is reabsorbed from the nephrons.
•excess water consumed is excreted in urine—> larger urine output.

Question 5

Kidneys and blood pressure:

Answer 5

•need high blood pressure in the glomerulus for filtration to take place.
•higher blood volume = higher blood pressure.
•low blood pressure and blood volume = dehydration.
•a complex of cells near the glomerulus contains blood pressure receptors (called baroreceptors).
•low blood pressure is detected by these receptors and causes the release of a hormone called aldosterone.

Question 6

Aldosterone:

Answer 6

-a hormone produced in the adrenal glands.
-increased Na+ reabsorption (active).
-increased water reabsorption (passive).
-the increased water reabsorption leads to increased blood volume = increased blood pressure.

Question 7

Maintaining pH balance:

Answer 7

-pH of body is 7.3-7.5.
1. An acid-base balance is maintained by buffer systems that prevents changes in pH by adding or removing H+ ions.
2. Changes in breathing rate:
-an increased breathing rate (respiration) pulls the reaction to the right to generate CO2 more quickly.
3. Kidney actions: to excrete more H+ and reabsorb HCO3- as needed to maintain normal blood pH.
-if the blood is too acidic, H+ is excreted and HCO3- is reabsorbed (urine is usually acidic).
-if the blood is too basic, H+ is not excreted and HCO3- is not reabsorbed.

Question 8

Where does absorption from aldosterone occur?

Answer 8

The distal tubule and collecting duct.