antidiuretic hormone

Question 1

Too much water or too little salts → water potential is raised above the norm

Answer 1

• osmoreceptors of hypothalamus not stimulated → pituitary secretes less ADH → collecting duct walls less permeable so medulla absorbs less water from the collecting ducts → large volume of dilute urine formed → blood plasma returns to normal concentration
• thirst receptors are not stimulated → no feeling of thirst little water drunk

Question 2

Too little water or too much salt → water potential is lowered below the norm

Answer 2

• osmoreceptors of hypothalamus stimulated → pituitary secretes more ADH → collecting duct walls more permeable so medulla absorbs more water from the collecting ducts → small volume of concentrated urine formed → blood plasma returns to normal concentration
• thirst receptors are stimulated → feeling of thirst, water likely to be drunk