Collecting duct system
Encyclopedia
The collecting duct system of the kidney
consists of a series of tubules and ducts that connect the nephron
s to the ureter
. It participates in electrolyte
and fluid balance through reabsorption and excretion, processes regulated by the hormone
s aldosterone
and antidiuretic hormone.
There are several components of the collecting duct system, including the connecting tubules, cortical collecting ducts, and medullary collecting ducts.
and fluid balance. In humans, the system accounts for 4-5% of the kidney's reabsorption of sodium
and 5% of the kidney's reabsorption of water. At times of extreme dehydration, over 24% of the filtered water may be reabsorbed in the collecting duct system.
The wide variation in water reabsorption levels for the collecting duct system reflects its dependence on hormonal activation. The collecting ducts, in particular, the outer medullary and cortical collecting ducts, are largely impermeable to water without the presence of antidiuretic hormone (ADH, or vasopressin).
The collecting duct system participates in the regulation of other electrolyte
s, including chloride
, potassium
, hydrogen ion
s, and bicarbonate
.
, the "connecting tubule" is the most proximal part of the collecting duct system. It is adjacent to the distal convoluted tubule
, the most distal segment of the renal tubule. Connecting tubules from several adjacent nephrons merge to form cortical collecting tubules, and these may join to form cortical collecting ducts. Connecting tubules of some juxtamedullary nephron
s may arch upward, forming an arcade.
The connecting tubule derives from the metanephric blastema
, but the rest of the system derives from the ureteric bud
. Because of this, some sources group the connecting tubule as part of the nephron
, rather than grouping it with the collecting duct system.
The initial collecting tubule is a segment with a constitution similar as the collecting duct, but before the convergence with other tubules.
to form medullary collecting ducts.
"Medullary collecting ducts" are divided into outer and inner segments, the latter reaching more deeply into the medulla. The variable reabsorption of water and, depending on fluid balances and hormonal influences, the reabsorption or secretion of sodium, potassium, hydrogen and bicarbonate ion continues here. Urea passively transports out of duct here and creates 500mOsm gradient.
The outer segment of the medullary collecting duct follows the cortical collecting duct. It reaches the level of the renal medulla where the thick ascending limb of loop of Henle
borders with the thin ascending limb of loop of Henle
The inner segment is the part of the collecting duct system between the outer segment and the papillary ducts.
and empty into a minor calyx
. It is also called duct of Bellini.
s located on the cell's apical membrane. Aldosterone
determines expression of sodium channels with increased aldosterone causing increased expression of luminal sodium channels. Aldosterone increases the number of Na⁺/K⁺-ATPase pumps that allow increased sodium reabsorption and potassium secretion. and vasopressin
determines the expression of aquaporin
channels on the cell surface. Together, aldosterone
and vasopressin
let the principal cell control the quantity of water that is reabsorbed.
.
For their contribution to acid-base homeostasis, the intercalated cells play important roles in the kidney's response to acidosis
and alkalosis
. Damage to the α-intercalated cell's ability to secrete acid can result in distal renal tubular acidosis
(RTA type I, classical RTA).
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...
consists of a series of tubules and ducts that connect the nephron
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....
s to the ureter
Ureter
In human anatomy, the ureters are muscular tubes that propel urine from the kidneys to the urinary bladder. In the adult, the ureters are usually long and ~3-4 mm in diameter....
. It participates in electrolyte
Electrolyte
In chemistry, an electrolyte is any substance containing free ions that make the substance electrically conductive. The most typical electrolyte is an ionic solution, but molten electrolytes and solid electrolytes are also possible....
and fluid balance through reabsorption and excretion, processes regulated by the hormone
Hormone
A hormone is a chemical released by a cell or a gland in one part of the body that sends out messages that affect cells in other parts of the organism. Only a small amount of hormone is required to alter cell metabolism. In essence, it is a chemical messenger that transports a signal from one...
s aldosterone
Aldosterone
Aldosterone is a hormone that increases the reabsorption of sodium ions and water and the release of potassium in the collecting ducts and distal convoluted tubule of the kidneys' functional unit, the nephron. This increases blood volume and, therefore, increases blood pressure. Drugs that...
and antidiuretic hormone.
There are several components of the collecting duct system, including the connecting tubules, cortical collecting ducts, and medullary collecting ducts.
Function
The collecting duct system is the final component of the kidney to influence the body's electrolyteElectrolyte
In chemistry, an electrolyte is any substance containing free ions that make the substance electrically conductive. The most typical electrolyte is an ionic solution, but molten electrolytes and solid electrolytes are also possible....
and fluid balance. In humans, the system accounts for 4-5% of the kidney's reabsorption of sodium
Sodium
Sodium is a chemical element with the symbol Na and atomic number 11. It is a soft, silvery-white, highly reactive metal and is a member of the alkali metals; its only stable isotope is 23Na. It is an abundant element that exists in numerous minerals, most commonly as sodium chloride...
and 5% of the kidney's reabsorption of water. At times of extreme dehydration, over 24% of the filtered water may be reabsorbed in the collecting duct system.
The wide variation in water reabsorption levels for the collecting duct system reflects its dependence on hormonal activation. The collecting ducts, in particular, the outer medullary and cortical collecting ducts, are largely impermeable to water without the presence of antidiuretic hormone (ADH, or vasopressin).
- In the absence of ADH, water in the renal filtrate is left alone to enter the urine, promoting diuresisDiuresisDiuresis may refer to:* Urine production, as an aspect of fluid balance* Excessive urine production - see polyuria* Immersion diuresis...
. - When ADH is present, aquaporinAquaporinAquaporins are proteins embedded in the cell membrane that regulate the flow of water.Aquaporins are integral membrane proteins from a larger family of major intrinsic proteins that form pores in the membrane of biological cells....
s allow for the reabsorption of this water, thereby inhibiting diuresis.
The collecting duct system participates in the regulation of other electrolyte
Electrolyte
In chemistry, an electrolyte is any substance containing free ions that make the substance electrically conductive. The most typical electrolyte is an ionic solution, but molten electrolytes and solid electrolytes are also possible....
s, including chloride
Chloride
The chloride ion is formed when the element chlorine, a halogen, picks up one electron to form an anion Cl−. The salts of hydrochloric acid HCl contain chloride ions and can also be called chlorides. The chloride ion, and its salts such as sodium chloride, are very soluble in water...
, potassium
Potassium
Potassium is the chemical element with the symbol K and atomic number 19. Elemental potassium is a soft silvery-white alkali metal that oxidizes rapidly in air and is very reactive with water, generating sufficient heat to ignite the hydrogen emitted in the reaction.Potassium and sodium are...
, hydrogen ion
Hydrogen ion
Hydrogen ion is recommended by IUPAC as a general term for all ions of hydrogen and its isotopes.Depending on the charge of the ion, two different classes can be distinguished: positively charged ions and negatively charged ions....
s, and bicarbonate
Bicarbonate
In inorganic chemistry, bicarbonate is an intermediate form in the deprotonation of carbonic acid...
.
Anatomy
The segments of the system are as follows:| Segment | Description |
|---|---|
| connecting tubule Connecting tubule In the kidney, the collecting tubule is a tubular segment of the renal collecting duct system that connects the distal convoluted tubule to the cortical collecting duct.-Classification:... |
|
| initial collecting tubule | Before convergence of nephrons |
| cortical collecting ducts | |
| medullary collecting ducts | |
| papillary ducts, also known as duct of Bellini |
Connecting tubule
With respect to the renal corpuscleRenal 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...
, the "connecting tubule" is the most proximal part of the collecting duct system. It is adjacent to the distal convoluted tubule
Distal convoluted tubule
The distal convoluted tubule is a portion of kidney nephron between the loop of Henle and the collecting duct system.- Physiology :It is partly responsible for the regulation of potassium, sodium, calcium, and pH...
, the most distal segment of the renal tubule. Connecting tubules from several adjacent nephrons merge to form cortical collecting tubules, and these may join to form cortical collecting ducts. Connecting tubules of some juxtamedullary nephron
Juxtamedullary nephron
A juxtamedullary nephron is a type of nephron, found only in birds and mammals and not in other vertebrates. The "medullary" is referring to the renal medulla, while the "juxta", , refers to the relative position of the renal corpuscle, which in these nephrons is near the medulla...
s may arch upward, forming an arcade.
The connecting tubule derives from the metanephric blastema
Metanephric blastema
The metanephrogenic blastema or metanephric blastema is one of the two embryological structures that give rise to the kidney...
, but the rest of the system derives from the ureteric bud
Ureteric bud
The ureteric bud is a protrusion from the mesonephric duct during the development of the urinary and reproductive organs. It later develops into the adult kidney, except for the nephrons, which, in contrast, originate from the metanephric blastema....
. Because of this, some sources group the connecting tubule as part of the nephron
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....
, rather than grouping it with the collecting duct system.
Initial collecting tubule
The initial collecting tubule is a segment with a constitution similar as the collecting duct, but before the convergence with other tubules.
Cortical collecting duct
The "cortical collecting ducts" receive filtrate from multiple initial collecting tubules and descend into the renal medullaRenal medulla
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 arcuate arterioles. The arcuate arterioles each in turn branch into...
to form medullary collecting ducts.
Medullary collecting duct
"Medullary collecting ducts" are divided into outer and inner segments, the latter reaching more deeply into the medulla. The variable reabsorption of water and, depending on fluid balances and hormonal influences, the reabsorption or secretion of sodium, potassium, hydrogen and bicarbonate ion continues here. Urea passively transports out of duct here and creates 500mOsm gradient.
Outer segment
The outer segment of the medullary collecting duct follows the cortical collecting duct. It reaches the level of the renal medulla where the thick ascending limb of loop of Henle
Thick ascending limb of loop of Henle
The thick ascending limb of loop of Henle also known as distal straight tubule, is a segment of the nephron in the kidney. It can be divided into two parts: that in the renal medulla, and that in the renal cortex.-Medullary thick ascending limb:...
borders with the thin ascending limb of loop of Henle
Inner segment
The inner segment is the part of the collecting duct system between the outer segment and the papillary ducts.
Papillary duct
The terminal portions of the medullary collecting ducts are the "papillary ducts", which end at the renal papillaRenal papilla
In the kidney, the renal papilla is the location where the medullary pyramids empty urine into the minor calyx. Histologically it is marked by medullary collecting ducts converging to form a duct of Bellini to channel the fluid. Transitional epithelium begins to be seen.-Role in disease:Some...
and empty into a minor calyx
Minor calyx
The minor calyx, in the kidney, surrounds the apex of the renal pyramids. Urine formed in the kidney passes through a papilla at the apex into the minor calyx then into the major calyx....
. It is also called duct of Bellini.
Cell types
Each component of the collecting duct system contains two cell types, intercalated cells and a segment-specific cell type:- For the connecting tubules, this specific cell type is the connecting tubule cell
- For the collecting ducts, it is the principal cell. The inner medullary collecting ducts contain an additional cell type, called the inner medullary collecting duct cell.
Principal cells
The principal cell mediates the collecting duct's influence on sodium and potassium balance via sodium channels and potassium channelPotassium channel
In the field of cell biology, potassium channels are the most widely distributed type of ion channel and are found in virtually all living organisms. They form potassium-selective pores that span cell membranes...
s located on the cell's apical membrane. Aldosterone
Aldosterone
Aldosterone is a hormone that increases the reabsorption of sodium ions and water and the release of potassium in the collecting ducts and distal convoluted tubule of the kidneys' functional unit, the nephron. This increases blood volume and, therefore, increases blood pressure. Drugs that...
determines expression of sodium channels with increased aldosterone causing increased expression of luminal sodium channels. Aldosterone increases the number of Na⁺/K⁺-ATPase pumps that allow increased sodium reabsorption and potassium secretion. and vasopressin
Vasopressin
Arginine vasopressin , also known as vasopressin, argipressin or antidiuretic hormone , is a neurohypophysial hormone found in most mammals, including humans. Vasopressin is a peptide hormone that controls the reabsorption of molecules in the tubules of the kidneys by affecting the tissue's...
determines the expression of aquaporin
Aquaporin
Aquaporins are proteins embedded in the cell membrane that regulate the flow of water.Aquaporins are integral membrane proteins from a larger family of major intrinsic proteins that form pores in the membrane of biological cells....
channels on the cell surface. Together, aldosterone
Aldosterone
Aldosterone is a hormone that increases the reabsorption of sodium ions and water and the release of potassium in the collecting ducts and distal convoluted tubule of the kidneys' functional unit, the nephron. This increases blood volume and, therefore, increases blood pressure. Drugs that...
and vasopressin
Vasopressin
Arginine vasopressin , also known as vasopressin, argipressin or antidiuretic hormone , is a neurohypophysial hormone found in most mammals, including humans. Vasopressin is a peptide hormone that controls the reabsorption of molecules in the tubules of the kidneys by affecting the tissue's...
let the principal cell control the quantity of water that is reabsorbed.
Intercalated cells
Intercalated cells come in α and β varieties and participate in acid-base homeostasisAcid-base homeostasis
Acid–base homeostasis is the part of human homeostasis concerning the proper balance between acids and bases, in other words, the pH. The body is very sensitive to its pH level, so strong mechanisms exist to maintain it...
.
| Type of cell | Secretes | Reabsorbs >- | α-intercalated cells |
acid Acid An acid is a substance which reacts with a base. Commonly, acids can be identified as tasting sour, reacting with metals such as calcium, and bases like sodium carbonate. Aqueous acids have a pH of less than 7, where an acid of lower pH is typically stronger, and turn blue litmus paper red... (via an apical H+-ATPase Proton pump A proton pump is an integral membrane protein that is capable of moving protons across a cell membrane, mitochondrion, or other organelle. Mechanisms are based on conformational changes of the protein structure or on the Q cycle.-Function:... and H+/K+ exchanger) in the form of hydrogen ion Hydrogen ion Hydrogen ion is recommended by IUPAC as a general term for all ions of hydrogen and its isotopes.Depending on the charge of the ion, two different classes can be distinguished: positively charged ions and negatively charged ions.... s |
bicarbonate Bicarbonate In inorganic chemistry, bicarbonate is an intermediate form in the deprotonation of carbonic acid... (via band 3 Band 3 Anion Exchanger 1 or Band 3 is a phylogenetically preserved transport protein responsible for mediating the exchange of chloride for bicarbonate across a plasma membrane. Functionally similar members of the AE clade are AE2 and AE3.It is ubiquitous throughout the vertebrates... , a basolateral Cl-/HCO3- exchanger) >- | β-intercalated cells |
bicarbonate (via pendrin Pendrin Pendrin also known as sodium-independent chloride/iodide transporter is a protein that in humans is encoded by the SLC26A4 gene .- Function :Pendrin is an ion exchanger found in the cortical collecting duct.... a specialised apical Cl-/HCO3-) |
acid (via a basal H+-ATPase Proton pump A proton pump is an integral membrane protein that is capable of moving protons across a cell membrane, mitochondrion, or other organelle. Mechanisms are based on conformational changes of the protein structure or on the Q cycle.-Function:... ) |
For their contribution to acid-base homeostasis, the intercalated cells play important roles in the kidney's response to acidosis
Acidosis
Acidosis is an increased acidity in the blood and other body tissue . If not further qualified, it usually refers to acidity of the blood plasma....
and alkalosis
Alkalosis
Alkalosis refers to a condition reducing hydrogen ion concentration of arterial blood plasma . Generally, alkalosis is said to occur when pH of the blood exceeds 7.45. The opposite condition is acidosis .-Causes:...
. Damage to the α-intercalated cell's ability to secrete acid can result in distal renal tubular acidosis
Renal tubular acidosis
Renal tubular acidosis is a medical condition that involves an accumulation of acid in the body due to a failure of the kidneys to appropriately acidify the urine. When blood is filtered by the kidney, the filtrate passes through the tubules of the nephron, allowing for exchange of salts, acid...
(RTA type I, classical RTA).