Excretion Long Answers

Question 1

How is urea formed and stored?

Answer 1

-formed in the liver
-delamination converts amino acids into keto acids and ammonia
-ammonia is highly toxic so cannot accumulate in the body
-ammonia then enters the ornithine cycle
-here it is combined with CO2 to produce urea
-urea is then passed into the blood and transported to the kidneys
It is then filtered and stored as urine in the bladder

Question 2

How does osmoregulation correct a decrease in blood water content?

Answer 2

• osmoreceptors in the hypothalamus detects a decrease in blood water potential
• the osmoreceptor cells shrink because of low water potential and water moving out by osmosis
• stimulating neurosecretory cells to release ADH
• ADH travels to posterior pituitary gland where it is stored
• when neurosecretory cells are stimulated, ADH is released into the bloodstream
• ADH acts on the cells of the collecting duct, causing a chain of enzyme controlled reactions
• this results in vesicles carrying aquaporins fusing to a cell membrane
• this causes more water to be reabsorbed