renal corpuscles
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A renal corpuscle (also called malpighian body) is the blood-filtering component 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 ...
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 ...
. It consists of a glomerulus - a tuft of
capillaries A capillary is a small blood vessel from 5 to 10 micrometres (μm) in diameter. Capillaries are composed of only the tunica intima, consisting of a thin wall of simple squamous endothelial cells. They are the smallest blood vessels in the body: ...
composed of
endothelial cells The endothelium is a single layer of squamous endothelial cells that line the interior surface of blood vessels and lymphatic vessels. The endothelium forms an interface between circulating blood or lymph in the lumen and the rest of the vessel ...
, and a glomerular capsule known as
Bowman's capsule Bowman's capsule (or the Bowman capsule, capsula glomeruli, or glomerular capsule) is a cup-like sac at the beginning of the tubular component of a nephron in the mammalian kidney that performs the first step in the filtration of blood to form u ...
.


Structure

The renal corpuscle is composed of two structures, the glomerulus and the Bowman's capsule. The glomerulus is a small tuft of
capillaries A capillary is a small blood vessel from 5 to 10 micrometres (μm) in diameter. Capillaries are composed of only the tunica intima, consisting of a thin wall of simple squamous endothelial cells. They are the smallest blood vessels in the body: ...
containing two cell types. Endothelial cells, which have large
fenestrae A fenestra (fenestration; plural fenestrae or fenestrations) is any small opening or pore, commonly used as a term in the biological sciences. It is the Latin word for "window", and is used in various fields to describe a pore in an anatomical st ...
, are not covered by diaphragms.
Mesangial cell Mesangial cells are specialised cells in the kidney that make up the mesangium of the glomerulus. Together with the mesangial matrix, they form the vascular pole of the renal corpuscle. The mesangial cell population accounts for approximately 30 ...
s are modified smooth muscle cells that lie between the capillaries. They regulate blood flow by their contractile activity and secrete
extracellular matrix In biology, the extracellular matrix (ECM), also called intercellular matrix, is a three-dimensional network consisting of extracellular macromolecules and minerals, such as collagen, enzymes, glycoproteins and hydroxyapatite that provide s ...
,
prostaglandins The prostaglandins (PG) are a group of physiologically active lipid compounds called eicosanoids having diverse hormone-like effects in animals. Prostaglandins have been found in almost every tissue in humans and other animals. They are deri ...
, and
cytokines Cytokines are a broad and loose category of small proteins (~5–25 kDa) important in cell signaling. Cytokines are peptides and cannot cross the lipid bilayer of cells to enter the cytoplasm. Cytokines have been shown to be involved in autocrin ...
. Mesangial cells also have phagocytic activity, removing proteins and other molecules trapped in the
glomerular basement membrane The glomerular basement membrane of the kidney is the basal lamina layer of the glomerulus. The glomerular endothelial cells, the glomerular basement membrane, and the filtration slits between the podocytes perform the filtration function of ...
or filtration barrier. The Bowman's capsule has an outer parietal layer composed of simple squamous epithelium. The visceral layer, composed of modified simple squamous epithelium, is lined by
podocyte Podocytes are cells in Bowman's capsule in the kidneys that wrap around capillaries of the glomerulus. Podocytes make up the epithelial lining of Bowman's capsule, the third layer through which filtration of blood takes place. Bowman's capsule ...
s. Podocytes have foot processes, pedicels, that wrap around glomerular capillaries. These pedicels interdigitate with pedicels of adjacent podocytes forming filtration slits. There are two poles in the renal corpuscle, a vascular pole and a tubular pole. The vascular pole is a location of the glomerulus. At the vascular pole, the
afferent arterioles The afferent arterioles are a group of blood vessels that supply the nephrons in many excretory systems. They play an important role in the regulation of blood pressure as a part of the tubuloglomerular feedback mechanism. The afferent arterio ...
and
efferent arterioles The efferent arterioles are blood vessels that are part of the urinary tract of organisms. Efferent (from Latin ex + ferre) means "outgoing", in this case meaning carrying blood out away from the glomerulus. The efferent arterioles form a conv ...
enter and leave the glomerulus in the Bowman's capsule. The tubular pole is at the other end opposite to the vascular pole. At the tubular pole, the
proximal convoluted 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 straig ...
arises.


Function

The renal corpuscle acts to filter blood. Fluid from blood in the glomerulus is collected in the Bowman's capsule to form "glomerular filtrate", which is then further processed along the nephron to form
urine Urine is a liquid by-product of metabolism in humans and in many other animals. Urine flows from the kidneys through the ureters to the urinary bladder. Urination results in urine being excreted from the body through the urethra. Cellul ...
. It does this via a filtration barrier. The renal corpuscle filtration barrier is composed of: the fenestrated endothelium of glomerular capillaries, the fused basal lamina of endothelial cells and podocytes, and the filtration slits of the podocytes. This barrier permits passage of water, ions, and small molecules from the bloodstream into Bowman's space (the space between the visceral and parietal layers). Large and/or negatively charged proteins are prevented from passing into Bowman's space, thus retaining these proteins in the circulation. The basal lamina is composed of 3 layers: lamina rara externa, lamina densa, and lamina rara interna. The lamina rara externa is adjacent to the podocyte processes. The lamina densa is the central layer consisting of type IV collagen and laminin. This layer acts as a selective macromolecular filter, preventing the passage of large protein molecules into Bowman's space. The lamina rara interna is adjacent to endothelial cells. This layer contains
heparan sulfate Heparan sulfate (HS) is a linear polysaccharide found in all animal tissues. It occurs as a proteoglycan (HSPG, i.e. Heparan Sulfate ProteoGlycan) in which two or three HS chains are attached in close proximity to cell surface or extracellular ma ...
, a negatively charged
glycosaminoglycan Glycosaminoglycans (GAGs) or mucopolysaccharides are long, linear polysaccharides consisting of repeating disaccharide units (i.e. two-sugar units). The repeating two-sugar unit consists of a uronic sugar and an amino sugar, except in the case ...
that contributes to the electrostatic barrier of the glomerular filter.


Eponym

A renal corpuscle is also known as a ''Malpighian corpuscle'',
named after A namesake is a person, geographic location, or other entity bearing the name of another. History The word is first attested around 1635, and probably comes from the phrase "for one's name's sake", which originates in English Bible translations ...
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 ...
(1628–1694), an Italian
physician A physician (American English), medical practitioner (Commonwealth English), medical doctor, or simply doctor, is a health professional who practices medicine, which is concerned with promoting, maintaining or restoring health through th ...
and
biologist A biologist is a scientist who conducts research in biology. Biologists are interested in studying life on Earth, whether it is an individual cell, a multicellular organism, or a community of interacting populations. They usually specialize ...
. This name is no longer widely used, probably to avoid confusion with a Malpighian corpuscle in the
spleen The spleen is an organ found in almost all vertebrates. Similar in structure to a large lymph node, it acts primarily as a blood filter. The word spleen comes .
.


Additional images

File:Gray1130.svg, Image showing the main components of the renal corpusle. Glomerulus is red;
Bowman's capsule Bowman's capsule (or the Bowman capsule, capsula glomeruli, or glomerular capsule) is a cup-like sac at the beginning of the tubular component of a nephron in the mammalian kidney that performs the first step in the filtration of blood to form u ...
is pink. File:Glomerular Physiology.png, Outline of function of renal corpuscle


References


External links

* * {{DEFAULTSORT:Renal Corpuscle Kidney anatomy