Nephron in kidney

Nephron is a functional unit of the kidney. Its main function is to regulate water and soluble substances by filtering the blood, reabsorbing what is needed and excreting the rest as urine. Each of your kidneys is made up of about a million filtering units called nephrons.

Blood flows into the kidney through the renal artery. This large blood vessel branches into smaller and smaller blood vessels until the blood reaches the nephrons. Each nephron is made up of a very small filter, called a glomerulus, which is attached to a tubule. As blood passes through the nephron, fluid and waste products are filtered out.

The nephrons work through a two-step process: the glomerulus filters blood, and the tubule returns needed substances to the blood and removes wastes.

Multisegmented tubule—composed of the proximal convoluted tubule, the loop of Henle, and the distal convoluted tubule—which reabsorbs the “good” (water and nutrients) and secretes the “bad” (metabolic waste products) from the glomerular filtrate, also called primitive urine.

Reabsorption occurs next to filtration. In this process, several components of the glomelular filtrate that are vital for body functioning are transferred back to the blood. It takes place in proximal convoluted tubule, Loop of Henle, distal convoluted tubule and collecting duct.
Nephron in kidney

Function of kidney: Balance the body's fluids

One of the key tasks of the kidneys is to regulate fluid and electrolyte balance by controlling the volume and composition of the urine. These adjustments are essential because the osmolarity of body fluids must be around 300 milliosmols/liter.

All the cells in the body, apart from those of the outer skin, are surrounded by a fluid called the extracellular fluid (ECF).

80% of ECF is interstitial fluid (which includes lymph, synovial fluid, cerebrospinal fluid, GI tract fluids, and fluids in the eyes and ears), and 20% of ECF is blood plasma.

For the cells of the body to work properly, the extracellular fluid needs to have a stable composition of salts - such as potassium and sodium - and acidity (often referred to as pH).

The kidneys are the most important organs for regulating the characteristics of body fluids. This regulation is apparent in the control of
*Blood volume,
*Extracellular fluid volume and
*Osmolality of body fluids.

Osmotic pressure (created by the dissolved electrolytes in body fluids) and hydrostatic pressure (created by the water in body fluids) are the main forces behind any molecular movement between body compartments.

99 % of water and Na is re-absorbed by tubules to maintain osmotic balance. If more Na is excreted, this leads to water excretion and dehydration.

The kidneys are central to maintaining these correct balances and the effective functioning of all the cells of the body.

Thirst also plays a vital role in controlling some characteristics of body fluids. The salt and water balance is maintained by a series of hormones acting on the kidney. The kidneys recognize and act upon a series of messages that vary according to how much fluid is drunk.

If an excess of fluid is drunk, the body fluids become more diluted, and the kidneys excrete a more dilute urine, getting rid of the excess that has been taken in.
Function of kidney: Balance the body's fluids