Renal medulla

Last updated
Renal medulla
Illu kidney.jpg
Details
System Urinary system
Identifiers
Latin medulla renalis
MeSH D007679
TA98 A08.1.01.020
TA2 3369
FMA 74268
Anatomical terminology

The renal medulla (Latin: medulla renis 'marrow of the kidney') is the innermost part of the kidney. The renal medulla is split up into a number of sections, known as the renal pyramids. Blood enters into the kidney via the renal artery, which then splits up to form the segmental arteries which then branch to form interlobar arteries. The interlobar arteries each in turn branch into arcuate arteries, which in turn branch to form interlobular arteries, and these finally reach the glomeruli. At the glomerulus the blood reaches a highly disfavourable pressure gradient and a large exchange surface area, which forces the serum portion of the blood out of the vessel and into the renal tubules. Flow continues through the renal tubules, including the proximal tubule, the loop of Henle, through the distal tubule and finally leaves the kidney by means of the collecting duct, leading to the renal pelvis, the dilated portion of the ureter.

Contents

The renal medulla contains the structures of the nephrons responsible for maintaining the salt and water balance of the blood. These structures include the vasa rectae (both spuria and vera), the venulae rectae, the medullary capillary plexus, the loop of Henle, and the collecting tubule. [1] The renal medulla is hypertonic to the filtrate in the nephron and aids in the reabsorption of water.

Blood is filtered in the glomerulus by solute size. Ions such as sodium, chloride, potassium, and calcium are easily filtered, as is glucose. Proteins are not passed through the glomerular filter because of their large size, and do not appear in the filtrate or urine unless a disease process has affected the glomerular capsule or the proximal and distal convoluted tubules of the nephron.

Though the renal medulla only receives a small percentage of the renal blood flow, the oxygen extraction is very high, causing a low oxygen tension and more importantly, a critical sensitivity to hypotension, hypoxia, and blood flow. [2] The renal medulla extracts oxygen at a ratio of ~80% making it exquisitely sensitive to small changes in renal blood flow. The mechanisms of many perioperative renal insults are based on the disruption of adequate blood flow (and therefore oxygen delivery) to the renal medulla. [2]

Interstitium

The medullary interstitium is the tissue surrounding the loop of Henle in the medulla. It functions in renal water reabsorption by building up a high hypertonicity, which draws water out of the thin descending limb of the loop of Henle and the collecting duct system. Hypertonicity, in turn, is created by an efflux of urea from the inner medullary collecting duct. [3]

Pyramids

Renal pyramids
Kidney PioM.png
Details
System Urinary system
Identifiers
Latin pyramides renales
MeSH D007679
TA98 A08.1.01.020
TA2 3369
FMA 74268
Anatomical terminology

Renal pyramids (or malpighian pyramids or Malpighi's pyramids named after Marcello Malpighi, a seventeenth-century anatomist) are cone-shaped tissues of the kidney. In humans, the renal medulla is made up of 10 to 18 of these conical subdivisions. [4] The broad base of each pyramid faces the renal cortex, and its apex, or papilla, points internally towards the pelvis. The pyramids appear striped because they are formed by straight parallel segments of nephrons' Loops of Henle and collecting ducts. The base of each pyramid originates at the corticomedullary border and the apex terminates in a papilla, which lies within a minor calyx, made of parallel bundles of urine collecting tubules.

Papilla

The renal papilla is the location where the renal pyramids in the medulla empty urine into the minor calyx in the kidney. Histologically it is marked by medullary collecting ducts converging to form a papillary duct to channel the fluid. Transitional epithelium begins to be seen.

Clinical significance

Some chemicals toxic to the kidney, called nephrotoxins, damage the renal papillae. Damage to the renal papillae may result in death to cells in this region of the kidney, called renal papillary necrosis. The most common toxic causes of renal papillary necrosis are NSAIDs [ dubious – discuss ], such as ibuprofen, acetylsalicylic acid, and phenylbutazone, in combination with dehydration. Perturbed renal papillary development has also been shown to be associated with onset of functional obstruction and renal fibrosis. [5] [6] [7]

Renal papillary damage has also been associated with nephrolithiasis and can be quantified according to the papillary grading score, which accounts for contour, pitting, plugging and randall plaque. [8]

See also

Related Research Articles

<span class="mw-page-title-main">Kidney</span> Organ that filters blood and produces urine in humans

In humans, the kidneys are two reddish-brown bean-shaped blood-filtering organs that are a multilobar, multipapillary form of mammalian kidneys, usually without signs of external lobulation. They are located on the left and right in the retroperitoneal space, and in adult humans are about 12 centimetres in length. They receive blood from the paired renal arteries; blood exits into the paired renal veins. Each kidney is attached to a ureter, a tube that carries excreted urine to the bladder.

<span class="mw-page-title-main">Urinary system</span> Human anatomical system consisting of the kidneys, ureters, urinary bladder, and the urethra

The urinary system, also known as the urinary tract or renal system, consists of the kidneys, ureters, bladder, and the urethra. The purpose of the urinary system is to eliminate waste from the body, regulate blood volume and blood pressure, control levels of electrolytes and metabolites, and regulate blood pH. The urinary tract is the body's drainage system for the eventual removal of urine. The kidneys have an extensive blood supply via the renal arteries which leave the kidneys via the renal vein. Each kidney consists of functional units called nephrons. Following filtration of blood and further processing, wastes exit the kidney via the ureters, tubes made of smooth muscle fibres that propel urine towards the urinary bladder, where it is stored and subsequently expelled from the body by urination. The female and male urinary system are very similar, differing only in the length of the urethra.

<span class="mw-page-title-main">Nephron</span> Microscopic structural and functional unit of the kidney

The nephron is the minute or microscopic structural and functional unit of the kidney. It is composed of a renal corpuscle and a renal tubule. The renal corpuscle consists of a tuft of capillaries called a glomerulus and a cup-shaped structure called Bowman's capsule. The renal tubule extends from the capsule. The capsule and tubule are connected and are composed of epithelial cells with a lumen. A healthy adult has 1 to 1.5 million nephrons in each kidney. Blood is filtered as it passes through three layers: the endothelial cells of the capillary wall, its basement membrane, and between the foot processes of the podocytes of the lining of the capsule. The tubule has adjacent peritubular capillaries that run between the descending and ascending portions of the tubule. As the fluid from the capsule flows down into the tubule, it is processed by the epithelial cells lining the tubule: water is reabsorbed and substances are exchanged ; first with the interstitial fluid outside the tubules, and then into the plasma in the adjacent peritubular capillaries through the endothelial cells lining that capillary. This process regulates the volume of body fluid as well as levels of many body substances. At the end of the tubule, the remaining fluid—urine—exits: it is composed of water, metabolic waste, and toxins.

<span class="mw-page-title-main">Collecting duct system</span> Kidney system

The collecting duct system of the kidney consists of a series of tubules and ducts that physically connect nephrons to a minor calyx or directly to the renal pelvis. The collecting duct participates in electrolyte and fluid balance through reabsorption and excretion, processes regulated by the hormones aldosterone and vasopressin.

<span class="mw-page-title-main">Distal convoluted tubule</span> Feature of kidney anatomy

The distal convoluted tubule (DCT) is a portion of kidney nephron between the loop of Henle and the collecting tubule.

<span class="mw-page-title-main">Renal physiology</span> Study of the physiology of the kidney

Renal physiology is the study of the physiology of the kidney. This encompasses all functions of the kidney, including maintenance of acid-base balance; regulation of fluid balance; regulation of sodium, potassium, and other electrolytes; clearance of toxins; absorption of glucose, amino acids, and other small molecules; regulation of blood pressure; production of various hormones, such as erythropoietin; and activation of vitamin D.

<span class="mw-page-title-main">Proximal tubule</span> Segment of nephron in kidneys

The proximal tubule is the segment of the nephron in kidneys which begins from the renal pole of the Bowman's capsule to the beginning of loop of Henle. At this location, the glomerular parietal epithelial cells (PECs) lining bowman’s capsule abruptly transition to proximal tubule epithelial cells (PTECs). The proximal tubule can be further classified into the proximal convoluted tubule (PCT) and the proximal straight tubule (PST).

<span class="mw-page-title-main">Loop of Henle</span> Part of kidney tissue

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, the German anatomist Friedrich Gustav Jakob Henle, the loop of Henle's main function is to create a concentration gradient in the medulla of the kidney.

<span class="mw-page-title-main">Glomerulus (kidney)</span> Functional unit of nephron

The glomerulus is a network of small blood vessels (capillaries) known as a tuft, located at the beginning of a nephron in the kidney. Each of the two kidneys contains about one million nephrons. The tuft is structurally supported by the mesangium, composed of intraglomerular mesangial cells. The blood is filtered across the capillary walls of this tuft through the glomerular filtration barrier, which yields its filtrate of water and soluble substances to a cup-like sac known as Bowman's capsule. The filtrate then enters the renal tubule of the nephron.

<span class="mw-page-title-main">Macula densa</span> A region of juxtaglomerular apparatus in nephron of kidney

In the kidney, the macula densa is an area of closely packed specialized cells lining the wall of the distal tubule where it touches the glomerulus. Specifically, the macula densa is found in the terminal portion of the distal straight tubule, after which the distal convoluted tubule begins.

An osmotic diuretic is a type of diuretic that inhibits reabsorption of water and sodium (Na). They are pharmacologically inert substances that are given intravenously. They increase the osmolarity of blood and renal filtrate. This fluid eventually becomes urine.

<span class="mw-page-title-main">Renal circulation</span>

The renal circulation supplies the blood to the kidneys via the renal arteries, left and right, which branch directly from the abdominal aorta. Despite their relatively small size, the kidneys receive approximately 20% of the cardiac output.

<span class="mw-page-title-main">Vasa recta (kidney)</span>

The vasa recta of the kidney, are the straight arterioles, and the straight venules of the kidney, – a series of blood vessels in the blood supply of the kidney that enter the medulla as the straight arterioles, and leave the medulla to ascend to the cortex as the straight venules.. They lie parallel to the loop of Henle.

A countercurrent mechanism system is a mechanism that expends energy to create a concentration gradient.

<span class="mw-page-title-main">Interlobular arteries</span>

Cortical radial arteries, formerly known as interlobular arteries, are renal blood vessels given off at right angles from the side of the arcuate arteries looking toward the cortical substance. The interlobular arteries pass directly outward between the medullary rays to reach the fibrous tunic, where they end in the capillary network of this part.

<span class="mw-page-title-main">Descending limb of loop of Henle</span>

Within the nephron of the kidney, the descending limb of loop of Henle is the portion of the renal tubule constituting the first part of the loop of Henle.

<span class="mw-page-title-main">Ascending limb of loop of Henle</span>

Within the nephron of the kidney, the ascending limb of the loop of Henle is a segment of the heterogenous loop of Henle downstream of the descending limb, after the sharp bend of the loop. This part of the renal tubule is divided into a thin and thick ascending limb; the thick portion is also known as the distal straight tubule, in contrast with the distal convoluted tubule downstream.

The rock dove, Columbia livia, has a number of special adaptations for regulating water uptake and loss.

The kidneys are a pair of organs of the excretory system in vertebrates, which maintains the balance of water and electrolytes in the body (osmoregulation), filters the blood, removes metabolic waste products, and in many vertebrates also produces hormones and maintains blood pressure. In healthy vertebrates, the kidneys maintain homeostasis of extracellular fluid in the body. When the blood is being filtered, the kidneys form urine, which consists of water and excess or unnecessary substances, the urine is then excreted from the body through other organs, which in vertebrates, depending on the species, may include the ureter, urinary bladder, cloaca, and urethra.

<span class="mw-page-title-main">Mammalian kidney</span> Paired organ in the urinary system of mammals

The mammalian kidneys are a pair of excretory organs of the urinary system of mammals, being functioning kidneys in postnatal-to-adult individuals. The kidneys in mammals are usually bean-shaped or externally lobulated. They are located behind the peritoneum (retroperitoneally) on the back (dorsal) wall of the body. Each kidney consists of a renal capsule, peripheral cortex, internal medulla, which can be split up into renal pyramids forming papillae with their innermost parts, calices, and renal pelvis, although the calices or renal pelvis may be absent in some species. Generally, urine produced by the cortex and medulla drains from the papillae into the calices, and then into the renal pelvis, from which urine exits the kidney through the ureter. Nitrogen-containing waste products are excreted by the kidneys in mammals mainly in the form of urea.

References

PD-icon.svgThis article incorporates text in the public domain from page 1221 of the 20th edition of Gray's Anatomy (1918)

  1. ↑ Kelly CR, Landman J (March 2012). The Netter Collection of Medical Illustrations: Urinary System. Elsevier Health Sciences. plate 337
  2. 1 2 Pardo M, ed. (2022). Miller's Basics of Anesthesia (8th ed.). Elsevier. pp. 553–554. ISBN   978-0-323-79677-4.
  3. ↑ Boron WG (2003). Medical Physiology: A Cellular And Molecular Approaoch. Elsevier/Saunders. p. 1300. ISBN   1-4160-2328-3. Page 837
  4. ↑ Young B, O'Dowd G, Woodford P (2014). Wheater's Functional Histology (6 ed.). Philadelphia, PA: Elsevier. p. 293. ISBN   978-0-7020-4747-3.
  5. ↑ Wilkinson L, Kurniawan ND, Phua YL, Nguyen MJ, Li J, Galloway GJ, et al. (August 2012). "Association between congenital defects in papillary outgrowth and functional obstruction in Crim1 mutant mice" (PDF). The Journal of Pathology. 227 (4): 499–510. doi:10.1002/path.4036. PMID   22488641. S2CID   2777257.
  6. ↑ Phua YL, Gilbert T, Combes A, Wilkinson L, Little MH (April 2016). "Neonatal vascularization and oxygen tension regulate appropriate perinatal renal medulla/papilla maturation". The Journal of Pathology. 238 (5): 665–676. doi:10.1002/path.4690. hdl: 11343/291071 . PMID   26800422. S2CID   13482413.
  7. ↑ Phua YL, Martel N, Pennisi DJ, Little MH, Wilkinson L (April 2013). "Distinct sites of renal fibrosis in Crim1 mutant mice arise from multiple cellular origins". The Journal of Pathology. 229 (5): 685–696. doi:10.1002/path.4155. PMID   23224993. S2CID   22837861.
  8. ↑ Cohen AJ, Borofsky MS, Anderson BB, Dauw CA, Gillen DL, Gerber GS, et al. (January 2017). "Endoscopic Evidence That Randall's Plaque is Associated with Surface Erosion of the Renal Papilla". Journal of Endourology. 31 (1): 85–90. doi:10.1089/end.2016.0537. PMC   5220550 . PMID   27824271.
This page is based on this Wikipedia article
Text is available under the CC BY-SA 4.0 license; additional terms may apply.
Images, videos and audio are available under their respective licenses.