WordNet

a continuous tube formed by a row of elongated cells lacking intervening end walls
an enclosed conduit for a fluid
a bodily passage or tube lined with epithelial cells and conveying a secretion or other substance; "the tear duct was obstructed"; "the alimentary canal"; "poison is released through a channel in the snakes fangs" (同)epithelial duct, canal, channel

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certificate of deposit / (また『C.D.』)Civil Defense民間防衛
送水管;(建物・船などの)通気管;(地下ケーブルなどの)ダクト / (体液を運ぶ)導管,(植物が水・空気を運ぶ)導管

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出典(authority):フリー百科事典『ウィキペディア（Wikipedia）』「2014/12/05 04:07:36」(JST)

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The collecting duct system of the kidney consists of a series of tubules and ducts that connect the nephrons to the ureter. It participates in electrolyte and fluid balance through reabsorption and excretion, processes regulated by the hormones aldosterone and antidiuretic hormone.

There are several components of the collecting duct system, including the connecting tubules, cortical collecting ducts, and medullary collecting ducts.

1 Structure
- 1.1 Connecting tubule
- 1.2 Initial collecting tubule
- 1.3 Cortical collecting duct
- 1.4 Medullary collecting duct
  - 1.4.1 Outer segment
  - 1.4.2 Inner segment
- 1.5 Papillary duct
- 1.6 Cell types
  - 1.6.1 Principal cells
  - 1.6.2 Intercalated cells
2 Function
3 References
4 External links

Structure

Simple cuboidal epithelium in the collecting ducts of the pig kidney. The surfaces of the large and small collecting tubes (a and b), the circular structures, are surrounded by the simple cuboidal epithelium.

The segments of the system are as follows:

Segment	Description
connecting tubule
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 corpuscle, 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 nephrons 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.

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 medulla 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 borders with the thin ascending limb of loop of Henle^[1]^:837

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 papilla and empty into a minor 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 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 channels located on the cell's apical membrane. Aldosterone determines expression of sodium channels with increased aldosterone causing increased expression of luminal sodium channels^[2]^{[verification needed]}. Aldosterone increases the number of Na⁺/K⁺-ATPase pumps ^[3]^:949 that allow increased sodium reabsorption and potassium secretion.^[3]^:336 Vasopressin determines the expression of aquaporin channels on the cell surface.^[4] Together, aldosterone and vasopressin let the principal cell control the quantity of water that is reabsorbed.

Intercalated cells

Image depicting intercalated cells

Intercalated cells come in α and β varieties and participate in acid-base homeostasis.

Type of cell	Secretes	Reabsorbs
α-intercalated cells	acid (via an apical H⁺-ATPase and H⁺/K⁺ exchanger) in the form of hydrogen ions	bicarbonate (via band 3, a basolateral Cl^-/HCO₃^- exchanger)^[5]
β-intercalated cells	bicarbonate (via pendrin a specialised apical Cl^-/HCO₃^-)	acid (via a basal H⁺-ATPase)

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)(reference).

Function

Diagram outlining movement of ions in nephron, with the collecting ducts on the right.

The collecting duct system is the final component of the kidney to influence the body's electrolyte 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).

In the absence of ADH, water in the renal filtrate is left alone to enter the urine, promoting diuresis.
When ADH is present, aquaporins allow for the reabsorption of this water, thereby inhibiting diuresis.

The collecting duct system participates in the regulation of other electrolytes, including chloride, potassium, hydrogen ions, and bicarbonate.

References

^ Boron, Walter F. (2005). Medical Physiology: A Cellular and Molecular Approach (updated ed.). Philadelphia: Elsevier/Saunders. ISBN 1-4160-2328-3.
^ Physiology at MCG 7/7ch03/7ch03p19 – "The Nephron: Collecting Duct"
^ ^a ^b Guyton, Arthur C.; John E. Hall (2006). Textbook of Medical Physiology (11 ed.). Philadelphia: Elsevier Saunders. ISBN 0-7216-0240-1.
^ Schlatter, Eberhard; Schafer, James A. (1987). "Electrophysiological studies in principal cells of rat cortical collecting tubules ADH increases the apical membrane Na+-conductance". Pflügers Archiv European Journal of Physiology 409: 81. doi:10.1007/BF00584753.
^ Physiology at MCG 7/7ch07/7ch07p17 – "Intercalated Cells"

External links

Histology at KUMC epithel-epith04 "Collecting Duct (Kidney)"
Histology image: 15803loa - Histology Learning System at Boston University – "Urinary System: kidney, medulla, collecting duct and ascending tubule"
Histology image: 16013loa - Histology Learning System at Boston University – "Urinary System: kidney, H&E, collecting duct and ascending tubule"

UpToDate Contents

全文を閲覧するには購読必要です。 To read the full text you will need to subscribe.

1. 腎細胞癌の疫学、病理、および病因 epidemiology pathology and pathogenesis of renal cell carcinoma
2. 非淡明細胞型腎癌に対する治療アプローチ the treatment approach to non clear cell renal carcinoma
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4. 腎細胞癌患者における予後因子 prognostic factors in patients with renal cell carcinoma
5. 腎細胞癌の臨床症状、評価、および病期分類 clinical manifestations evaluation and staging of renal cell carcinoma

English Journal

Aldosterone regulates Na(+), K(+) ATPase activity in human renal proximal tubule cells through mineralocorticoid receptor.

Salyer SA, Parks J, Barati MT, Lederer ED, Clark BJ, Klein JD, Khundmiri SJ.SourceDepartment of Medicine, Kidney Disease Program, University of Louisville, Louisville, KY, USA; Department of Physiology, University of Louisville, Louisville, KY, USA.
Biochimica et biophysica acta.Biochim Biophys Acta.2013 Oct;1833(10):2143-52. doi: 10.1016/j.bbamcr.2013.05.009. Epub 2013 May 16.
The mechanisms by which aldosterone increases Na(+), K(+) ATPase and sodium channel activity in cortical collecting duct and distal nephron have been extensively studied. Recent investigations demonstrate that aldosterone increases Na-H exchanger-3 (NHE-3) activity, bicarbonate transport, and H(+) A
PMID 23684706

WNK4 inhibits Ca(2+)-activated big-conductance potassium channels (BK) via mitogen-activated protein kinase-dependent pathway.

Yue P, Zhang C, Lin DH, Sun P, Wang WH.SourceDepartment of Pharmacology, New York Medical College, Valhalla, NY 10595, USA.
Biochimica et biophysica acta.Biochim Biophys Acta.2013 Oct;1833(10):2101-10. doi: 10.1016/j.bbamcr.2013.05.004. Epub 2013 May 12.
We used the perforated whole-cell recording technique to examine the effect of with-no-lysine kinase 4 (WNK4) on the Ca(2+) activated big-conductance K channels (BK) in HEK293T cells transfected with BK-α subunit (BK-α). Expression of WNK4 inhibited BK channels and decreased the outward K currents
PMID 23673010

New insights into regulated aquaporin-2 function.

Fenton RA, Pedersen CN, Moeller HB.SourceDepartment of Biomedicine, Aarhus University and Center for Interactions of Proteins in Epithelial Transport (InterPrET), Aarhus University, Aarhus, Denmark.
Current opinion in nephrology and hypertension.Curr Opin Nephrol Hypertens.2013 Sep;22(5):551-8. doi: 10.1097/MNH.0b013e328364000d.
PURPOSE OF REVIEW: Aquaporin-2 (AQP2) water channels in principal cells of the kidney collecting duct are essential for urine concentration. Due to application of modern technologies, progress in our understanding of AQP2 has accelerated in recent years. In this article, we highlight some of the new
PMID 23852332

Japanese Journal

腎嚢胞から発生した集合管癌の1例

南方良仁,藤井令央奈,西澤哲 [他]
泌尿器科紀要 = Acta urologica Japonica 59(1), 11-15, 2013-01-00
NAID 40019562134

高カルシウム血症を呈した若年性ベリニ管癌の1例

上村吉穂,清川岳彦,増田憲彦 [他],宇都宮紀明,六車光英,川喜田睦司
泌尿器科紀要 58(2), 83-86, 2012-02-00
… Laparoscopic radical nephrectomy was performed and diagnosis of Bellini collecting duct carcinoma was made pathologically. …
NAID 40019169007

Distinct Cytoplasmic Expression of KL-6 Mucin in Chromophobe Renal Cell Carcinoma: A Comparative Immunohistochemical Study with Other Renal Epithelial Cell Tumors

Fukushima Mana,Higuchi Kayoko,Shimojo Hisashi,Uehara Takeshi,Ota Hiroyoshi
ACTA HISTOCHEMICA ET CYTOCHEMICA 45(5), 301-308, 2012
… Cytoplasmic expression of KL-6 and sialyl MUC1 was distinctive in the chromophobe RCC and renal oncocytoma cells, and in the intercalated cells in collecting duct epithelia. … Apical-surface staining of these sialyl glycoproteins was predominantly observed in clear RCC, in the epithelia of the distal tubule and collecting duct, and in the neonatal renal proximal tubule, but not in those of the adult renal proximal tubule. …
NAID 130001854260

Related Pictures

★リンクテーブル★

リンク元	「集合管」「CD」「collecting kidney tubule」
拡張検索	「kidney collecting duct」
関連記事	「duct」

「集合管」

Collecting duct system
	Scheme of renal tubule and its vascular supply.
Details
Latin	tubulus renalis colligens
Identifiers
Gray's	p.1223
MeSH	Kidney+Collecting+Ducts
Dorlands; /Elsevier	12830107
	Anatomical terminology