Kidney

The kidney is a generally even body located in the Abdomen, behind of the peritoneum, between the 11th dorsal vertebra and the 3rd lumbar one (for the left kidney) and 12th and spaces it between 3rd and the 4th lumbar one (for the right kidney). The kidney is thus retro-péritonéal. It ensures, by filtration and Excrétion of Urine, the balance hydroelectrolytic (homeostasis) of the Sang and the organization in general. Only one kidney (5% of the individuals) is necessary to live and in this case it is generally about the right kidney, better vascularized contrary to the left and the presence of the quadrilateral of Rogié which supports the venous damning up and has repercussions at the left genital level.

They are flattened bodies, ovoid. Their height is of 12 cm, their width is of 6 cm, their thickness is of 3 cm. These dimensions are important to know because a badly functioning kidney will be atrophied, which facilitates the clinical examination and thus the diagnosis.

The external face of the kidneys is convex. The kidney is vascularized by the arteries and renal veins and it is by a notch in the concave face that these vessels penetrate in the kidney.

In the kidney, one can note the presence of a cavity (the renal sine) where ramifies the renal artery. This artery then will ramify in the kidney itself. The veins also ramify in the renal sine. The hile is the zone of transit of the arteries, the veins, the ways excrétrices. It should be noted that the renal parenchyma is surrounded by a hard capsule, very resistant which protects it. The peripheral part of the parenchyma is the cortex whereas the central part is the médula. This médula is not continuous: it is stopped by prolongations of the cortex which goes until the renal sine. The urine is secreted on the level of papillae which are themselves the top of the pyramids.

The kidney has also an endocrine function (érythropoïétine, system Rénine - Angiotensine - Aldostérone).

The kidneys are covered by small glands which one calls suprarenals. Those consist of a cortex (cortico-suprarenal), secreting primarily Corticostéroïde S and of a medullary part (adrenal medullas), secreting Adrénaline.

In the popular speech, one often names kidneys the lumbar Muscles. It is of an abuse language and an error.

An animation in 3D on the physiology of the kidney is visible in the medical encyclopedia Vulgaris:

Néphron

A néphron is the structural and functional unit basic kidney.

It is a consistent thin tubule in a cluster of capillaries called gloméruli ( glomérulus in the singular), surrounded by a hollow bulb, the Capsule of Bowman. The capsule of Bowman brings to a length tubule twisted in 2 sections: the Tubule proximal, the Handle of Henle, the distal Tubule, and the collecting Tube. The collecting tubes flow in the chalices via the papillae, the chalices are thrown in the small basin (also called pyélon), which is connected to the Uretère. Each human kidney counts approximately a million will néphrons. The number of will néphrons, fixed at the birth, is of a great variability. It depends on multiple factors of which the age gestationnel, the intra-uterine delay of growth, the maternal nutritional state.

Capsule of Bowman

It is about the beginning of the Néphron. It is a blind bag reinflated out of bulb with double-layer which corresponds to the urinary part of the corpuscle of Malpighi. It receives the Ultrafiltrat plasma filtered by the wall of the Glomérule. The liquid contained in this capsule of bowman constitutes the primitive urine. Its composition will be modified in the remainder of the néphron.

Tubule proximal

It is located after the capsule of Bowman and before the handle of Henle; it takes part in the reabsorption of certain substances.

The tubular reabsorption

The tubular reabsorption has two mechanisms of transport through the membrane:
  • a passive transport: osmosis and the diffusion (example: water is transferred by osmosis).
  • an active transport: need for a cellular work (example: glucose, sodium).
The wall of the tubule has conveyers who recover certain molecules to return them in the interior medium (blood). It is the case for example glucose: it is filtered completely by the cluster to find itself in the primitive urine on the level of the capsule of Bowman. Under normal conditions, it is completely reabsorbed by specific conveyers and is completely absent from final urine The goal of the tubular reabsorption is the development of the final urine.

There exist two kinds of reabsorption:

  • the obligatory reabsorption, which is done in the tube circumvented proximal and the purpose of which is to work out almost the totality of the glomerular filtrate (99%). It takes place for water and sodium (the active reabsorption of sodium associates a passive reabsorption of water according to a phenomenon of osmosis).

  • the optional reabsorption, it is controlled by two hormones:
A.D.H: antidiuretic hormone of the posthypophyse. It increases the permeability of the distal circumvented tube and the collecting tube and supports the reabsorption of water thanks to the membrane protein opening called aquaporine. Consequently, the ADH influences the concentration of the secreted urine and influences blood volume and the blood pressure.
  • Aldosterone: secreted by the corticosuprarenal ones. It supports the active reabsorption of sodium in the distal circumvented tube and thus a passive reabsorption of water. The purpose of it is to adjust the composition of the urine to meet the needs for the organization by maintaining homeostasis. This mechanism starts in the event of hypotension related to the hypo-volemy, in the event of dehydration…

    Tubular secretion

    Beside this tubular reabsorption there exists a tubular secretion which allows the passage of molecules of the blood of the perish-tubular capillaries towards the filtrate through the cell of the tube. The purpose of it is to allow elimination in the urine of the undesirable substances or in excesses which (or insufficiently) were not filtered by the cluster. The mechanisms are comparable with those of the tubular reabsorption.

    Handle of Henle

    The handle of Henle is the section of the Néphron leading tubule proximal to the distal tubule. It owes its name with F.G.J. Henle which described it. It has a diameter of 12 micrometers. The handle goes up towards the cortex, with an elbow with 180°.

    Downward branch

    The downward part (hail) is completely permeable with water and impermeable with sodium. =>Augmentation of the osmolarity.

    Thin ascending branch

    This branch is impermeable with water and permeable with sodium.

    => Diminution in the osmolarity.

    Medullary thick ascending branch

    This branch is impermeable with water and permeable with sodium.

    => Diminution in the osmolarity.

    Cortical thick ascending branch

    This branch is impermeable with water and permeable with sodium.

    > Reduction in the osmolarity.

    Distal Tubule

    Its circumvented part is in contact with the small artery related of sound néphron with the level of a structure called the apparatus juxtaglomérulaire. It is on this level that is made the secretion of Rénine, hormone headlight of the control of the blood-pressure by the kidney. The tubule distal participle with the development of the final urine. It allows in particular if necessary the reabsorption of Na+ which is accompanied by a Cl reabsorption, therefore overall an additional NaCl reabsorption. In addition there is of all small water reabsorption because the permeability of the distal tubule is still very low, in other words, the urine which leaves the distal tubule is a urine always little concentrated (approximately 100 mosmols/L). The distal tubule allows moreover a controlled Ca reabsorption, under the effect of 2 hormones which are the Parathormone (PTH) and the Calcitonine (CT), under the influence in particular of the Vitamine D. The PTH increases the controlled Ca reabsorption while the CT decreases this reabsorption. Following the distal circumvented tube one finds the tube collecting cortical.

    Tube collecting

    The collecting tube has a cortical part and a medullary part.

    Tube collecting cortical

    Under the effect of hormones there will be modification of the permeability of the plasmic membrane. There are three hormones which control this permeability.
    • the Aldosterone (secreted on the level of the corticosuprarenal ones) on the one hand, which allows an increase in the reabsorption of Na+, and consequently of water, which involves an increase in blood volume (volemy) and thus an increase in the blood-pressure.
    • the ANP (secreted on the level of the cardiac auricle), which inhibits the reabsorption of Na+, therefore supports the water elimination.
    This involves a reduction in the volemy and thus in the blood-pressure. It is this urine which will penetrate in the collecting tube in its medullary part.
    • vasopressine (ADH: Antidiurétique hormone) which will increase the transport of water, by inducing the synthesis of channels.

    Tube collecting medullary

    Channels of Bellini

    Have sodic channels allowing the excretion final of the sodic ions.

    Anatomy of the Kidney

    Outside towards the interior:

    Cortical zone

    It comprises the clusters, the circumvented tubes proximaux and distal and the collecting tubes.

    Medullary zone

    • renal Pyramids or of Malpighi; the point turned towards the interior, the papillae on which come ventouser the small chalices form. They comprise the proximaux and distal right tubes as well as the handle of Henle, and the channels of Bellini.
    • Columns of Bertin, in spaces between the pyramids.

    A pyramid and its columns form a lobule of the kidney.

    Chalice

    Tube brought together with the point of the renal pyramid, and which while meeting forms it:

    Small basin S

    Tube in the shape of funnel which is thrown in the Uretère. It is also called pyélon. It is the place where will pass the urine to its exit of the néphron via the collecting tube. The small basins just like the chalices have a muscular fabric smoothes which contracts and propels the urine by peristalsis.

    Blood irrigation of the néphron

    The blood irrigation passes by several Veine S and Artère S. While going there in the order:

    Development and embryonic and fetal function of the kidney

    The kidney is resulting from the metamerisation (segmentation then formation of tubules) of the mésoblaste intra-embryonic intermediary (fabric of the embryonic disc) in cord nephrogene during the 4th week of development. This cord is divided into 3 distinct areas in time and space (according to a céphalo-caudal axis) which will evolve/move successively: - the cord pronephrogene (most cephalic) which métamérise in pronéphros . This first kidney do not function and degenerates at the end of the 4th week of development; - the cord mesonephrogene which métamérise after the degeneration of the pronéphros in mésonéphros . This kidney functions as of the end of the 4th week of development, but it will also degenerate; - the cord metanephrogene (most caudal) which gives the métanéphros , functional kidney, which is the kidney primitive. It with the characteristic of not métamériser.

    Statistics

    In an adult, one estimates that plasma is filtered 100 times by the kidneys per day, that is to say a capacity for treatment of approximately 180 liters! The primitive urine undergoes by the various segments of the renal tubule of the modifications, primarily of the phenomena of reabsorption. The normal daily diuresis is from 1 to 1,5 L depend on the hydrous contributions. More than 99% of water and filtered salts are reabsorbed.

    The flow of glomerular filtration normal is of 120 mL/min is 173 liters/j. An impaired renal function starts to be noted when the flow or rate of glomerular filtration is in lower parts of 50 mL/min. It is about a light impaired renal function. The moderate and severe impaired renal functions are noted when the rates respectively reach 30 and 10 mL/min. When one is returned to 10 mL/min and less, the final impaired renal function requires the assistance of a kidney machine, that is to say by the Dialyze péritonéale or even by the hemodialysis.

    Kidney machine

    to see Dialysis

    Clerc's Office of kidney

    • the first carried out in France took place in Paris on the young person Marius Renard in 1952, by the team of the doctor Louis Michon with the Hôpital Necker; the nephrologic continuations were ensured by the professor Jean Hamburger, but the young man is quickly deceased.

    • It is carried out nearly 2700 Clerc's Offices of kidneys per annum in France.

    Function of the Kidney

    See too

    External bond

    • renaloo, of dialysis to transplantation
    • interactive Portail dialyzes, transplantation, kidney and health
    • Physiologie of the handle of Henle
    • the Community on line for dialyzed by dialyzed

    Internal bonds

    • Diurétiques of the handle
    • Néphron

    Fiu-vro: Rauh Simple: Kidney

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