Bowman's capsule
Encyclopedia
The Bowman's 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 urine. A glomerulus is enclosed in the sac. Fluids from blood in the glomerulus are collected in the Bowman's capsule (i.e., glomerular filtrate) and further processed along the nephron to form urine
. This process is known as ultrafiltration
.
Inside the capsule, the layers are as follows, from outside to inside:
|->
B - Proximal tubule
C - Distal convoluted tubule
D - Juxtaglomerular apparatus
1. Basement membrane (Basal lamina)
2. Bowman's capsule - parietal layer
3. Bowman's capsule - visceral layer
3a. Pedicels (podocytes)
3b. Podocyte or sometimes called Bowman's cells
4. Bowman's space (urinary space)
5a. Mesangium - Intraglomerular cell
5b. Mesangium - Extraglomerular cell
6. Granular cells (Juxtaglomerular cells)
7. Macula densa
8. Myocytes (smooth muscle)
9. Afferent arteriole
10. Glomerulus Capillaries
11. Efferent arteriole
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(or glomerular filtration), and the normal rate of filtration is 125 ml/min, equivalent to 36 times the daily blood volume.
Any proteins under roughly 30 kilodaltons can pass freely through the membrane, although there is some extra hindrance for negatively charged molecules due to the negative charge of the basement membrane and the podocytes.
Any small molecules such as water
, glucose
, salt
(NaCl), amino acid
s, and urea
pass freely into Bowman's space, but cell
s, platelets and large proteins do not.
As a result, the filtrate leaving the Bowman's capsule is very similar to blood plasma
in composition as it passes into the proximal convoluted tubule.
A decreased GFR may be a sign of renal failure
.
A number of diseases can result in various problems within the glomerulus. Examples include acute proliferative (endocapillary) glomerulonephritis, mesangioproliferative glomerulonephritis, mesangiocapillary (membranoproliferative) glomerulonephritis, acute crescentic glomerulonephritis, focal segmental glomerulonephritis, and diabetic glomerulosclerosis.
Bowmans capsule.
Sir William Bowman (1816-1892), a British surgeon
and anatomist.
Together with the glomerulus it is known as a renal corpuscle
, or a Malpighian corpuscle, named after
Marcello Malpighi
(1628-1694), an Italian physician
and biologist
. This name is not used widely anymore, probably to avoid confusion with Malpighian bodies of the spleen
.
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....
in the mammalian 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...
that performs the first step in the filtration of blood to form urine. A glomerulus is enclosed in the sac. Fluids from blood in the glomerulus are collected in the Bowman's capsule (i.e., glomerular filtrate) and further processed along the nephron to form urine
Urine
Urine is a typically sterile liquid by-product of the body that is secreted by the kidneys through a process called urination and excreted through the urethra. Cellular metabolism generates numerous by-products, many rich in nitrogen, that require elimination from the bloodstream...
. This process is known as ultrafiltration
Ultrafiltration (renal)
In biological terms, ultrafiltration occurs at the barrier between the blood and the filtrate in the renal corpuscle or Bowman's capsule in the kidneys. The Bowman's capsule contains a dense capillary network called the glomerulus. Blood flows into these capillaries through a wide afferent...
.
Anatomy
Outside the capsule, there are two "poles":- The vascular poleVascular poleThe vascular pole is a location of the glomerulus. At the vascular pole, the afferent arterioles and efferent arterioles enter the Bowman's capsule.The urinary pole is at the other end....
is the side with the afferent arteriole and efferent arterioleEfferent arterioleThe efferent arterioles are blood vessels that are part of the urinary tract of organisms. The efferent arterioles form from a convergence of the capillaries of the glomerulus...
. - the urinary poleUrinary poleThe urinary pole is a location on the renal corpuscle opposite to the vascular pole. At the urinary pole, the proximal convoluted tubules arises....
is the side with the proximal convoluted tubule.
Inside the capsule, the layers are as follows, from outside to inside:
- parietal layer -- A single layer of simple squamous epitheliumSimple squamous epitheliumA simple squamous epithelium is a single layer of flat cells in contact with the basal lamina of the epithelium. This type of epithelium is often permeable and occurs where small molecules pass quickly through membranes via filtration or diffusion...
. Does not function in filtration. - Bowman's space (or "urinary space", or "capsular space") -- Between the visceral and parietal layers, into which the filtrate enters after passing through the Funny bob filtration slitsFiltration slitsFoot processes of podocytes interdigitate with one another forming filtration slits that, in contrast to those in the glomerular endothelium, are spanned by slit diaphragms.-Structure:...
. - visceral layer -- Lies just above the thickened glomerular basement membraneGlomerular basement membraneThe glomerular basement membrane is the basal laminal portion of the glomerulus. The Glomerular capillary endothelial cells, the GBM and the filtration slits between the podocytes perform the filtration function of the glomerulus, separating the blood in the capillaries from the filtrate that...
and is made of podocytePodocytePodocytes are cells in the Bowman's capsule in the kidneys that wrap around the capillaries of the glomerulus...
s. Beneath the visceral layer lie the glomerular capillaries. - Filtration Barrier -- The filtration barrier is composed of the fenestrated endothelium of the glomerular capillaries, the fused basal lamina of the endothelial cells and podocytes, and the filtration slits of the podocytes. The barrier permits the passage of water, ions, and small molecules from the bloodstream into the Bowman's space. The barrier prevents the passage of large and/or negatively charged proteins (such as albumin). The basal lamina of the filtration barrier is composed of three layers. The first layer is the lamina rara externa, adjacent to the podocyte processes. The second layer is the lamina rara interna, adjacent to the endothelial cells. The final layer is the lamina densa which is a darker central zone of the basal lamina. It consists of the meshwork of type IV collagen and laminin which act as a selective macromolecular filter.
B - Proximal tubule
C - Distal convoluted tubule
D - Juxtaglomerular apparatus
1. Basement membrane (Basal lamina)
2. Bowman's capsule - parietal layer
3. Bowman's capsule - visceral layer
3a. Pedicels (podocytes)
3b. Podocyte or sometimes called Bowman's cells
4. Bowman's space (urinary space)
5a. Mesangium - Intraglomerular cell
5b. Mesangium - Extraglomerular cell
6. Granular cells (Juxtaglomerular cells)
7. Macula densa
8. Myocytes (smooth muscle)
9. Afferent arteriole
10. Glomerulus Capillaries
11. Efferent arteriole
>-
Physiology
The process of filtration of the blood in the Bowman's capsule is ultrafiltrationUltrafiltration (renal)
In biological terms, ultrafiltration occurs at the barrier between the blood and the filtrate in the renal corpuscle or Bowman's capsule in the kidneys. The Bowman's capsule contains a dense capillary network called the glomerulus. Blood flows into these capillaries through a wide afferent...
(or glomerular filtration), and the normal rate of filtration is 125 ml/min, equivalent to 36 times the daily blood volume.
Any proteins under roughly 30 kilodaltons can pass freely through the membrane, although there is some extra hindrance for negatively charged molecules due to the negative charge of the basement membrane and the podocytes.
Any small molecules such as water
Water
Water is a chemical substance with the chemical formula H2O. A water molecule contains one oxygen and two hydrogen atoms connected by covalent bonds. Water is a liquid at ambient conditions, but it often co-exists on Earth with its solid state, ice, and gaseous state . Water also exists in a...
, glucose
Glucose
Glucose is a simple sugar and an important carbohydrate in biology. Cells use it as the primary source of energy and a metabolic intermediate...
, salt
Salt
In chemistry, salts are ionic compounds that result from the neutralization reaction of an acid and a base. They are composed of cations and anions so that the product is electrically neutral...
(NaCl), amino acid
Amino acid
Amino acids are molecules containing an amine group, a carboxylic acid group and a side-chain that varies between different amino acids. The key elements of an amino acid are carbon, hydrogen, oxygen, and nitrogen...
s, and 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....
pass freely into Bowman's space, but cell
Cell (biology)
The cell is the basic structural and functional unit of all known living organisms. It is the smallest unit of life that is classified as a living thing, and is often called the building block of life. The Alberts text discusses how the "cellular building blocks" move to shape developing embryos....
s, platelets and large proteins do not.
As a result, the filtrate leaving the Bowman's capsule is very similar to 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...
in composition as it passes into the proximal convoluted tubule.
Clinical significance
Measuring the glomerular filtration rate (GFR) is a diagnostic test of kidney function.A decreased GFR may be a sign of renal failure
Renal failure
Renal failure or kidney failure describes a medical condition in which the kidneys fail to adequately filter toxins and waste products from the blood...
.
A number of diseases can result in various problems within the glomerulus. Examples include acute proliferative (endocapillary) glomerulonephritis, mesangioproliferative glomerulonephritis, mesangiocapillary (membranoproliferative) glomerulonephritis, acute crescentic glomerulonephritis, focal segmental glomerulonephritis, and diabetic glomerulosclerosis.
Bowmans capsule.
Eponym
Bowman's capsule is named afterEponym
An eponym is the name of a person or thing, whether real or fictitious, after which a particular place, tribe, era, discovery, or other item is named or thought to be named...
Sir William Bowman (1816-1892), a British surgeon
Surgery
Surgery is an ancient medical specialty that uses operative manual and instrumental techniques on a patient to investigate and/or treat a pathological condition such as disease or injury, or to help improve bodily function or appearance.An act of performing surgery may be called a surgical...
and anatomist.
Together with the glomerulus it is known as a renal corpuscle
Renal corpuscle
In the kidney, a renal corpuscle is the initial blood-filtering component of a nephron. It consists of two structures: a glomerulus and a Bowman's capsule. The glomerulus is a small tuft of capillaries containing two cell types. Endothelial cells, which have large fenestrae, are not covered by...
, or a Malpighian corpuscle, named after
Eponym
An eponym is the name of a person or thing, whether real or fictitious, after which a particular place, tribe, era, discovery, or other item is named or thought to be named...
Marcello Malpighi
Marcello Malpighi
Marcello Malpighi was an Italian doctor, who gave his name to several physiological features, like the Malpighian tubule system.-Early years:...
(1628-1694), an Italian physician
Physician
A physician is a health care provider who practices the profession of medicine, which is concerned with promoting, maintaining or restoring human health through the study, diagnosis, and treatment of disease, injury and other physical and mental impairments...
and biologist
Biologist
A biologist is a scientist devoted to and producing results in biology through the study of life. Typically biologists study organisms and their relationship to their environment. Biologists involved in basic research attempt to discover underlying mechanisms that govern how organisms work...
. This name is not used widely anymore, probably to avoid confusion with Malpighian bodies of the spleen
Splenic lymphoid nodules
White pulp is a histological region of the spleen. The altered coat of the arterioles, consisting of adenoid tissue, presents here and there thickenings of a spheroidal shape, the white pulp .These bodies vary in size from about 0.25 mm. to 1 mm...
.
