The renal medulla is the innermost part of the
kidney
The kidneys are two reddish-brown bean-shaped organs found in vertebrates. They are located on the left and right in the retroperitoneal space, and in adult humans are about in length. They receive blood from the paired renal arteries; blo ...
. 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
The arcuate arteries of the kidney, also known as arciform arteries, are vessels of the renal circulation. They are located at the border of the renal cortex and renal medulla.
They are named after the fact that they are shaped in arcs due to the ...
, which in turn branch to form
interlobular arteries
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 betw ...
, and these finally reach the
glomeruli
''Glomerulus'' () is a common term used in anatomy to describe globular structures of entwined vessels, fibers, or neurons. ''Glomerulus'' is the diminutive of the Latin ''glomus'', meaning "ball of yarn".
''Glomerulus'' may refer to:
* the filter ...
. 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 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. It can be further classified into the proximal convoluted tubule (PCT) and the proximal strai ...
, the
Loop of Henle
In the kidney, the loop of Henle () (or Henle's loop, Henle loop, nephron loop or its Latin counterpart ''ansa nephroni'') is the portion of a nephron that leads from the proximal convoluted tubule to the distal convoluted tubule. Named after its ...
, through the
distal tubule
The distal convoluted tubule (DCT) is a portion of kidney nephron between the loop of Henle and the collecting tubule.
Physiology
It is partly responsible for the regulation of potassium, sodium, calcium, and pH.
On its apical surface (lumen ...
and finally leaves the kidney by means of the
collecting duct
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 system is the last part of nephron and participates in elect ...
, leading to the renal pelvis, the dilated portion of the
ureter
The ureters are tubes made of smooth muscle that propel urine from the kidneys to the urinary bladder. In a human adult, the ureters are usually long and around in diameter. The ureter is lined by urothelial cells, a type of transitional epit ...
.
The renal medulla (Latin: ''medulla renis'' 'marrow of the kidney') contains the structures of the
nephron
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 ...
s responsible for maintaining the salt and water balance of the blood. These structures include the
vasa rectae
The vasa recta of the kidney, (vasa recta renis) 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 th ...
(both spuria and vera), the venulae rectae, the medullary capillary plexus, the loop of Henle, and the collecting tubule. 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.
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.
Interstitium
The medullary interstitium is the tissue surrounding the
loop of Henle
In the kidney, the loop of Henle () (or Henle's loop, Henle loop, nephron loop or its Latin counterpart ''ansa nephroni'') is the portion of a nephron that leads from the proximal convoluted tubule to the distal convoluted tubule. Named after its ...
in the medulla. It functions in renal water reabsorption by building up a high
hypertonicity
In chemical biology, tonicity is a measure of the effective osmotic pressure gradient; the water potential of two solutions separated by a partially-permeable cell membrane. Tonicity depends on the relative concentration of selective membrane- ...
, which draws water out of the
thin descending limb of the loop of Henle
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.
Physiology
The permeability is as follows:
Also, the medullary interstitium is highly c ...
and the
collecting duct system. Hypertonicity, in turn, is created by an efflux of
urea
Urea, also known as carbamide, is an organic compound with chemical formula . This amide has two amino groups (–) joined by a carbonyl functional group (–C(=O)–). It is thus the simplest amide of carbamic acid.
Urea serves an important ...
from the
inner medullary collecting duct
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 system is the last part of nephron and participates in ele ...
.
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Pyramids
Renal pyramids (or malpighian pyramids or Malpighi's pyramids named after
Marcello Malpighi
Marcello Malpighi (10 March 1628 – 30 November 1694) was an Italian biologist and physician, who is referred to as the "Founder of microscopical anatomy, histology & Father of physiology and embryology". Malpighi's name is borne by several ph ...
, a seventeenth-century anatomist) are cone-shaped
tissues of the
kidney
The kidneys are two reddish-brown bean-shaped organs found in vertebrates. They are located on the left and right in the retroperitoneal space, and in adult humans are about in length. They receive blood from the paired renal arteries; blo ...
. In humans, the renal medulla is made up of 10 to 18 of these conical subdivisions. The broad ''base'' of each pyramid faces the
renal cortex
The renal cortex is the outer portion of the kidney between the renal capsule and the renal medulla. In the adult, it forms a continuous smooth outer zone with a number of projections (cortical columns) that extend down between the pyramids. It ...
, and its
apex
The apex is the highest point of something. The word may also refer to:
Arts and media Fictional entities
* Apex (comics), a teenaged super villainess in the Marvel Universe
* Ape-X, a super-intelligent ape in the Squadron Supreme universe
*Apex, ...
, or
papilla
Papilla (Latin, 'nipple') or papillae may refer to:
In animals
* Papilla (fish anatomy), in the mouth of fish
* Basilar papilla, a sensory organ of lizards, amphibians and fish
* Dental papilla, in a developing tooth
* Dermal papillae, part of ...
, points internally towards the pelvis. The pyramids appear striped because they are formed by straight parallel segments of
nephron
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 ...
s' 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
The renal medulla 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 whi ...
in the medulla empty urine into the
minor calyx in the
kidney
The kidneys are two reddish-brown bean-shaped organs found in vertebrates. They are located on the left and right in the retroperitoneal space, and in adult humans are about in length. They receive blood from the paired renal arteries; blo ...
. 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
nephrotoxin Nephrotoxicity is toxicity in the kidneys. It is a poisonous effect of some substances, both toxic chemicals and medications, on kidney function. There are various forms, and some drugs may affect kidney function in more than one way. Nephrotoxin ...
s, 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
Renal papillary necrosis is a form of nephropathy involving the necrosis of the renal papilla. Lesions that characterize renal papillary necrosis come from an impairment of the blood supply and from subsequent ischemic necrosis that is diffuse. ...
. The most common toxic causes of renal papillary necrosis are
NSAIDs, such as
ibuprofen,
acetylsalicylic acid
Aspirin, also known as acetylsalicylic acid (ASA), is a nonsteroidal anti-inflammatory drug (NSAID) used to reduce pain, fever, and/or inflammation, and as an antithrombotic. Specific inflammatory conditions which aspirin is used to treat ...
, and
phenylbutazone
Phenylbutazone, often referred to as "bute", is a nonsteroidal anti-inflammatory drug (NSAID) for the short-term treatment of pain and fever in animals.
In the United States and United Kingdom, it is no longer approved for human use (except in th ...
, in combination with
dehydration
In physiology, dehydration is a lack of total body water, with an accompanying disruption of metabolic processes. It occurs when free water loss exceeds free water intake, usually due to exercise, disease, or high environmental temperature. Mil ...
. Perturbed renal papillary development has also been shown to be associated with onset of functional obstruction and renal fibrosis.
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.
Additional Images
File:Slide4iii.JPG, Renal medulla
File:Slide21iii.JPG, Renal medulla
File:Slide5iii.JPG, Renal papilla
File:Illu kidney2.jpg, Frontal section through the kidney
File:Gray1127.png, Vertical section of kidney. (Label "medullary sub." visible near top.)
File:Blausen 0592 KidneyAnatomy 01.png, Kidney anatomy, with pyramids labeled at right
See also
*
Medullipin
*
Kokko and Rector Model, a theory to explain how a gradient is generated in the inner medulla
*
Renal sinus
The renal sinus is a cavity within the kidney which is occupied by the renal pelvis, renal calyces, blood vessels, nerves and fat. The renal hilum extends into a large cavity within the kidney occupied by the renal vessels, minor renal calyces, m ...
*
Medullary interstitium
*
Renal capsule
The renal capsule is a tough fibrous layer surrounding the kidney and covered in a layer of perirenal fat known as the adipose capsule of kidney. The adipose capsule is sometimes included in the structure of the renal capsule. It provides some p ...
References
External links
*
* - "Posterior Abdominal Wall: Internal Structure of a Kidney"
* - "Urinary System: neonatal kidney"
* ()
{{DEFAULTSORT:Renal Medulla
Kidney anatomy