Renal urea handling is the part of renal physiology

Renal physiology

Renal physiology is the study of the physiology of the kidney. This encompasses all functions of the kidney, including reabsorption of glucose, amino acids, and other small molecules; regulation of sodium, potassium, and other electrolytes; regulation of fluid balance and blood pressure;...

 that deals with the reabsorption

Reabsorption

In physiology, reabsorption or tubular reabsorption is the flow of glomerular filtrate from the proximal tubule of the nephron into the peritubular capillaries, or from the urine into the blood...

 and secretion

Secretion

Secretion is the process of elaborating, releasing, and oozing chemicals, or a secreted chemical substance from a cell or gland. In contrast to excretion, the substance may have a certain function, rather than being a waste product...

 of urea

Urea

Urea or carbamide is an organic compound with the chemical formula CO2. The molecule has two —NH2 groups joined by a carbonyl functional group....

. Movement of large amounts of urea across cell membranes is made possible by urea transporter

Urea transporter

An urea transporter is a membrane transport protein, transporting urea. Humans and other mammals have two types of urea transport proteins, UT-A and UT-B. The UT-A proteins are important for renal urea handling and are produced by alternative splicing of the SLC14A2 gene...

 proteins.

Urea allows the kidney

Kidney

The kidneys, organs with several functions, serve essential regulatory roles in most animals, including vertebrates and some invertebrates. They are essential in the urinary system and also serve homeostatic functions such as the regulation of electrolytes, maintenance of acid–base balance, and...

s to create hyperosmotic urine (urine that has more ions in it--is "more concentrated"--than that same person's blood plasma

Blood plasma

Blood plasma is the straw-colored liquid component of blood in which the blood cells in whole blood are normally suspended. It makes up about 55% of the total blood volume. It is the intravascular fluid part of extracellular fluid...

). Preventing the loss of water in this manner is important if the person's body needs to save water in order to maintain a suitable blood pressure

Blood pressure

Blood pressure is the pressure exerted by circulating blood upon the walls of blood vessels, and is one of the principal vital signs. When used without further specification, "blood pressure" usually refers to the arterial pressure of the systemic circulation. During each heartbeat, BP varies...

 or (more likely,) in order to maintain a suitable concentration of sodium

Sodium

Sodium is a chemical element with the symbol Na and atomic number 11. It is a soft, silvery-white, highly reactive metal and is a member of the alkali metals; its only stable isotope is 23Na. It is an abundant element that exists in numerous minerals, most commonly as sodium chloride...

 ions in the blood plasma.

About 40% of the urea filtered is normally found in the final urine, since there is more reabsorption than secretion along the nephron

Nephron

The renal tubule is the portion of the nephron containing the tubular fluid filtered through the glomerulus. After passing through the renal tubule, the filtrate continues to the collecting duct system, which is not part of the nephron....

.

It is regulated by antidiuretic hormone, which controls the amount reabsorbed in the collecting duct system

Collecting duct system

The collecting duct system of the kidney consists of a series of tubules and ducts that connect the nephrons to the ureter. It participates in electrolyte and fluid balance through reabsorption and excretion, processes regulated by the hormones aldosterone and antidiuretic hormone.There are several...

 and secreted into the loop of Henle

Loop of Henle

In the kidney, the loop of Henle is the portion of a nephron that leads from the proximal convoluted tubule to the distal convoluted tubule. Named after its discoverer F. G. J...

.

Overview table

Characteristic	proximal tubule Proximal tubule The proximal tubule is the portion of the duct system of the nephron of the kidney which leads from Bowman's capsule to the loop of Henle.-Structure and appearance:...			loop of Henle Loop of Henle In the kidney, the loop of Henle is the portion of a nephron that leads from the proximal convoluted tubule to the distal convoluted tubule. Named after its discoverer F. G. J...			Distal convoluted tubule Distal convoluted tubule The distal convoluted tubule is a portion of kidney nephron between the loop of Henle and the collecting duct system.- Physiology :It is partly responsible for the regulation of potassium, sodium, calcium, and pH...	Collecting duct system Collecting duct system The collecting duct system of the kidney consists of a series of tubules and ducts that connect the nephrons to the ureter. It participates in electrolyte and fluid balance through reabsorption and excretion, processes regulated by the hormones aldosterone and antidiuretic hormone.There are several...
	S1	S2	S3	descending limb Descending limb of loop of Henle The descending limb of loop of Henle is the portion of the renal tubule constituting the first part of the loop of Henle.-Physiology:The permeability is as follows:...	thin ascending limb Thin ascending limb of loop of Henle The thin ascending limb of loop of Henle is a sub-portion of the loop of Henle in the juxtamedullary nephron of the kidney. The thin ascending limb is impermeable to water, and is also permeable to ions in particular Na and Cl...	thick ascending limb Thick ascending limb of loop of Henle The thick ascending limb of loop of Henle also known as distal straight tubule, is a segment of the nephron in the kidney. It can be divided into two parts: that in the renal medulla, and that in the renal cortex.-Medullary thick ascending limb:...		connecting tubule Connecting tubule In the kidney, the collecting tubule is a tubular segment of the renal collecting duct system that connects the distal convoluted tubule to the cortical collecting duct.-Classification:...	initial collecting tubule	cortical collecting ducts	medullary collecting ducts
reabsorption (% compared to filtered amount)	50										70
secretion (% compared to filtered amount)					60
reabsorption (mmoles Mole (unit) The mole is a unit of measurement used in chemistry to express amounts of a chemical substance, defined as an amount of a substance that contains as many elementary entities as there are atoms in 12 grams of pure carbon-12 , the isotope of carbon with atomic weight 12. This corresponds to a value... /day)
Concentration
electrical driving force Membrane potential Membrane potential is the difference in electrical potential between the interior and exterior of a biological cell. All animal cells are surrounded by a plasma membrane composed of a lipid bilayer with a variety of types of proteins embedded in it...  (mV Volt The volt is the SI derived unit for electric potential, electric potential difference, and electromotive force. The volt is named in honor of the Italian physicist Alessandro Volta , who invented the voltaic pile, possibly the first chemical battery.- Definition :A single volt is defined as the... )	-3		+3			+15	-5 to +5			-40
chemical driving force Chemical potential Chemical potential, symbolized by μ, is a measure first described by the American engineer, chemist and mathematical physicist Josiah Willard Gibbs. It is the potential that a substance has to produce in order to alter a system...  (mV Volt The volt is the SI derived unit for electric potential, electric potential difference, and electromotive force. The volt is named in honor of the Italian physicist Alessandro Volta , who invented the voltaic pile, possibly the first chemical battery.- Definition :A single volt is defined as the... )
electrochemical driving force (mV Volt The volt is the SI derived unit for electric potential, electric potential difference, and electromotive force. The volt is named in honor of the Italian physicist Alessandro Volta , who invented the voltaic pile, possibly the first chemical battery.- Definition :A single volt is defined as the... )
apical transport proteins	solvent drag Solvent drag Solvent drag, also known as bulk transport, is a phenomenon primarily in renal physiology, but it also occurs in gastrointestinal physiology... unknown transporter			Urea transporter 2?	unknown transporter						urea transporter 1
basolateral  transport proteins	unknown transporter			Urea transporter 2?	unknown transporter						urea transporter 4
Other reabsorption features