Water balance control and its effect on blood pressure

Water Balance Control

The body possesses a homeostatic mechanism known as water balance control, which maintains the right amount of water in the body.
This balance is vitally important, as both dehydration (too little water) and overhydration (too much water) can result in harmful effects on the body.
The body constantly loses water through sweating, breathing, urine, and faeces. It replenishes this water mainly through drinking and eating.

Roles of Kidneys in Water Balance

Kidneys play a crucial role in maintaining water balance by adjusting the amount of water that is reabsorbed during the formation of urine.
This process is based on the concentration of hormones, such as anti-diuretic hormone (ADH) and aldosterone, in the blood.
The more concentrated the blood, the more water the kidneys reabsorb, and the less water lost in urine.

Anti-diuretic Hormone (ADH) and Water Balance

ADH, also known as vasopressin, is a hormone released by the pituitary gland in response to dehydration or low blood volume.
ADH communicates with the kidneys, increasing the reabsorption of water and thus reducing the amount of urine produced.
This process effectively concentrates the urine and lowers the amount of water loss through urine when the body is dehydrated.

Aldosterone and Water Balance

Aldosterone is a hormone produced by the adrenal glands that works to conserve sodium, secrete potassium, and increase water retention.
With more sodium conserved by the kidneys, water retention increases to maintain the balance of electrolytes in the body.
Aldosterone assists in maintaining correct blood volume and pressure.

Effect of Water Balance on Blood Pressure

Regulation of water in the body also directly impacts blood pressure. Too much water can increase blood volume and lead to high blood pressure.
Conversely, too little water can decrease blood volume causing low blood pressure.
Through water balance control, the kidneys contribute directly to the regulation of blood pressure.

Renin-Angiotensin-Aldosterone System (RAAS)

RAAS is a hormone system that regulates blood pressure and fluid balance.
When blood volume is low, the kidneys secrete the enzyme renin. This initiates a chain of reactions resulting in the production of angiotensin II, a potent vasoconstrictor, which narrows blood vessels and stimulates the production of aldosterone.
Aldosterone then stimulates the kidneys to retain more sodium and water, thus increasing blood volume and blood pressure.
This coordinated response between the kidneys and adrenal glands allows the body to maintain proper hydration and control blood pressure.