Topic 4 Excretory System: Different Notes

Question 1

• The macula densa, an area of closely packed specialized cells lining the DCT, monitor the filtrate pressure in the DCT. If the blood pressure is low, then via the granular cells → secrete renin → angiotensin cascade → tells adrenal cortex to synthesize aldosterone → more water is reabsorbed from the DCT and the blood pressure rises and is restored to normal
• Note that selective permeability of the tubules establishes an osmolarity gradient in the surrounding interstitial fluid. Also note that urine is hypertonic to the blood and contains a high urea and solute concentration.

Answer 1

Juxtaglomerular Apparatus

Question 2

• Created by entering and exiting of solutes, and increases from cortex to medulla

Answer 2

Osmolarity Gradient

Question 3

• Because descending loop is permeable to water and ascending loop is permeable to salts and ions, the medulla is very salty and facilitates water reabsorption
• The innervations of the sympathetic nervous system primarily affect the afferent arterioles (constrict it -> reduced using output)
• Humans filter and reclaim a lot of fluid from the bloodstream through the kidney each day (about 180 L) and 1-2 L are excreted per day

Answer 3

Counter Current Multiplier

Question 4

• Nitrogen is a waste product
  o Aquatic animals: excrete NH3 and NH4 directly into water
  o Mammals, sharks, and amphibians: convert NH3 into urea
  o Birds, insects, reptiles: secrete uric acid (is insoluble in water and is excreted as a solid to conserve water)
   Allantois: in bird eggs, the allantois is a special sac that keeps nitrogenous waste in the form of uric acid away from the embryo

Answer 4

Nitrogenous Waste Products

Question 5

• Excess CO2, waste O2, and H2O (gas) lease via diffusion through the stomata and lenticels via transpiration

Answer 5

Excretion in Plants