You have probably noticed that urine is not always the same. the body is capable of adjusting the volume and the osmolarity of its urine output depending on a number of factors. the kidneys are regulated by hormones such as antidiuretic hormone (adh) and aldosterone. these hormones are secreted in response to changes in the animal's internal water and salt balance. for example, sweating or blood loss can disrupt water and/or salt balance in the body, leading to a hormonal response that returns the system to homeostasis. mechanisms for adjusting blood volume or osmolarity include increasing water and/or sodium reabsorption in the nephrons and collecting ducts. how do the following stimuli affect water and sodium (na+) reabsorption in the kidneys?
match each item to appropriate category
1) eating salty food
2) blood loss
3) alcohol consumption
4) aldosterone release
5) severe diarhea
6) sweating
7) diabetes insipidus
8) caffine consumption
9) adh secretion
10) dehydration due to inadequate water intake

a) increases both water and na+ reabsorption
b) does not increase water or na+ reabsorption
c) increases water reabsorption

1) eating salty food= c) increases water reabsorption

2) blood loss= a)increases both water and Na+ reabsorption

3) alcohol consumption= a) Increases both water and Na+ reabsorption

4) Aldosterone release= a) Increases both water and Na+ reabsorption

5) Severe diarrhea= a) Increases both water and Na+ reabsorption

6) Sweating=  a) Increases both water and Na+ reabsorption

7)   diabetes insipidus= c) Increases water reabsorption

8)  caffeine consumption= b) does not increase water or Na+ reabsorption.

9) ADH secretion= c) increases water reabsorption

10) dehydration due to inadequate water intake= c) increases water reabsorption.

Explanation:

1) eating salty food

An acute renal Na+ conversion occurs because of eating salty food and is mediated by angiotensin II enzymes and aldosterone. Aldosterone promotes the conversion of sodium in sweating and feces. Increased water intake is also indicative of diluting excess of Na+ also known as dilutional hyponatremia.  

2) blood loss

Blood loss cause release of angiotensin II enzyme which has a vasoconstrictor effect and immediately improves blood pressure. This enzyme causes constriction of both afferent and efferent arterioles in the kidneys and reduces the glomerular filtration rate (GFR). As a result, decrease in fluid loss from kidneys helps in preserving the blood pressure.

3) alcohol consumption

Low sodium blood levels are reported in alcoholic patients due to electrolyte disorder and reset of cerebral osmolarity.

4) Aldosterone release

Aldosterone is also known as the salt-retaining hormone and is released in response to decrease Na+ and increased K+ in plasma. Therefore, Na+ reabsorption by the nephrons is promoted by water retention.

5) severe diarrhea

Severe diarrhea is also managed by secretion of aldosterone from the pituitary gland. This hormone is responsible for increased water and sodium reabsorption from the distal convoluted tubule in the kidneys.

6) sweating

Sweating is responsible for loss of electrolytes i.e. Na+ and Cl. Hence, aldosterone hormone is released which increases the reabsorption of both Na+ and water.

7) diabetes insipidus

People suffering from nephrogenic diabetes insipidus excretes large amount of diluted urine and has severe dehydration. ADH is released to control the excessive urination and reduce hypernatremia.

8) caffeine consumption

Caffeine containing beverages does not cause serious fluid loss or increase Na+ retention. However, they may produce a mild diuretic effect and increase urgency to urinate but does not cause dehydration.

9) ADH secretion

ADH is produced by the hypothalamus in response to increase in blood osmolarity and causes water retention by decreasing urine volume.

10) dehydration due to inadequate water intake

Chronic regulation of increased plasma sodium is performed with release of anti-diuretic hormone (ADH). Na+ imbalance occurs due to abnormal water intake and decrease amount of water is indicative of hypernatremia. Hence, increased thirst mechanism is initiated by ADH and fluid retention is observed.

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