Can urine be isotonic

Answer 1

yes, urine can be isotonic ,hypotonic or even hypertonic, under normal conditions the body adjust that mainly through kidney, the main factor is vasopressin or Anti-diuretic hormone "ADH" which activate aquaporins receptor to increase water re-absorption back into blood, the regulator key in increase or decrease of ADH is the osmoreceptors in the hypothalamus.

Under normal conditions, your body always keep plasma osmolarity nearly equal 300 mosm, that can be achieved via numerous mechanisms ,one of will be the hypothalamus, but there are several accidental or pathological factors that can alter that heamostasis, some related to urine (ex:nephrogenic Diabetes inspidus, SIADH) , other related to plasma its self (ex: sever skin burning can cause lagre portion of plasma oxidation, hemorrhage), or other ways of dehydration (ex: vomiting or diarrhea in gastroenteritis, excessive sweating via skin or lungs), or just by other specific dysfunction of organ(s) that lead to alter haemostasis (ex: congestive heart failure, excessive mineralocorticoids in some adrenal disorders), or by other factors like neurogenic polydipsia or chronic Alcoholism.....