anatomy Anatomy () is the branch of biology concerned with the study of the structure of organisms and their parts. Anatomy is a branch of natural science that deals with the structural organization of living things. It is an old science, having its ...

and

physiology Physiology (; ) is the scientific study of functions and mechanisms in a living system. As a sub-discipline of biology, physiology focuses on how organisms, organ systems, individual organs, cells, and biomolecules carry out the chemical ...

, a duct is a circumscribed channel leading from an

exocrine gland Exocrine glands are glands that secrete substances on to an epithelial surface by way of a duct. Examples of exocrine glands include sweat, salivary, mammary, ceruminous, lacrimal, sebaceous, prostate and mucous. Exocrine glands are one of two ...

or organ.

Types of ducts

Examples include:

Duct system

As ducts travel from the

acinus An acinus (; plural, acini; adjective, acinar or acinous) refers to any cluster of cells that resembles a many-lobed "berry," such as a raspberry ('' acinus'' is Latin for "berry"). The berry-shaped termination of an exocrine gland, where the ...

which generates the fluid to the target, the ducts become larger and the epithelium becomes thicker. The parts of the system are classified as follows: Some sources consider "lobar" ducts to be the same as "interlobar ducts", while others consider lobar ducts to be larger and more distal from the acinus. For sources that make the distinction, the interlobar ducts are more likely to classified with

simple columnar epithelium Simple columnar epithelium is a single layer of columnar epithelial cells which are tall and slender with oval-shaped nuclei located in the basal region, attached to the basement membrane. In humans, simple columnar epithelium lines most organ ...

(or

pseudostratified epithelium A pseudostratified epithelium is a type of epithelium that, though comprising only a single layer of cells, has its cell nuclei positioned in a manner suggestive of stratified epithelia. As it rarely occurs as squamous or cuboidal epithelia ...

), reserving the stratified columnar for the lobar ducts. File:Gray1025.png, Section of

submaxillary gland The paired submandibular glands (historically known as submaxillary glands) are major salivary glands located beneath the floor of the mouth. They each weigh about 15 grams and contribute some 60–67% of unstimulated saliva secretion; on stimula ...

kitten A kitten is a juvenile cat. After being born, kittens display primary altriciality and are totally dependent on their mothers for survival. They normally do not open their eyes for seven to ten days. After about two weeks, kittens develop qu ...

. Duct semidiagrammatic. X 200. File:Gray1173.png, Section of portion of

mamma Mama(s) or Mamma or Momma may refer to: Roles *Mother, a female parent *Mama-san, in Japan and East Asia, a woman in a position of authority *Mamas, a name for female associates of the Hells Angels Places *Mama, Russia, an urban-type settlement ...

Intercalated duct

The intercalated duct, also called intercalary duct (ducts of Boll), is the portion of an

leading directly from the

to a

striated duct In anatomy and physiology, a duct is a circumscribed channel leading from an exocrine gland or organ. Types of ducts Examples include: Duct system As ducts travel from the acinus which generates the fluid to the target, the ducts become larg ...

. The intercalated duct forms part of the

intralobular duct In anatomy and physiology, a duct is a circumscribed channel leading from an exocrine gland or organ. Types of ducts Examples include: Duct system As ducts travel from the acinus which generates the fluid to the target, the ducts become larger ...

. This duct has the thinnest epithelium of any part of the duct system, and the epithelium is usually classified as "low"

simple cuboidal Simple cuboidal epithelium is a type of epithelium that consists of a single layer of cuboidal (cube-like) cells which have large, spherical and central nuclei. Simple cuboidal epithelium is found on the surface of ovaries, the lining of nephro ...

. They are found in both the

pancreas The pancreas is an organ of the digestive system and endocrine system of vertebrates. In humans, it is located in the abdomen behind the stomach and functions as a gland. The pancreas is a mixed or heterocrine gland, i.e. it has both an end ...

and in

salivary gland The salivary glands in mammals are exocrine glands that produce saliva through a system of ducts. Humans have three paired major salivary glands (parotid, submandibular, and sublingual), as well as hundreds of minor salivary glands. Salivary gla ...

Striated duct

A striated duct (Pflüger's ducts ) is a

gland In animals, a gland is a group of cells in an animal's body that synthesizes substances (such as hormones) for release into the bloodstream (endocrine gland) or into cavities inside the body or its outer surface (exocrine gland). Structure De ...

duct which connects an

intercalated duct In anatomy and physiology, a duct is a circumscribed channel leading from an exocrine gland or organ. Types of ducts Examples include: Duct system As ducts travel from the acinus which generates the fluid to the target, the ducts become larg ...

to an interlobular duct. It is characterized by the basal infoldings of its plasma membrane, characteristic of ion-pumping activity by the numerous mitochondria. Along with the intercalated ducts, they function to modify salivary fluid by secreting HCO₃⁻ and K⁺ and reabsorbing Na⁺ and Cl⁻ using the Na-K pump and the Cl-HCO₃ pump, making the saliva hypotonic. Their

epithelium Epithelium or epithelial tissue is one of the four basic types of animal tissue, along with connective tissue, muscle tissue and nervous tissue. It is a thin, continuous, protective layer of compactly packed cells with a little intercellul ...

can be

or simple columnar. Striated ducts are part of the

s. They are found in the

submandibular gland The paired submandibular glands (historically known as submaxillary glands) are major salivary glands located beneath the floor of the mouth. They each weigh about 15 grams and contribute some 60–67% of unstimulated saliva secretion; on stimula ...

sublingual duct The excretory ducts of the sublingual gland are from eight to twenty in number. Of the smaller sublingual ducts (ducts of Rivinus), some join the submandibular duct; others open separately into the mouth, on the elevated crest of mucous membrane (p ...

, and the

parotid gland The parotid gland is a major salivary gland in many animals. In humans, the two parotid glands are present on either side of the mouth and in front of both ears. They are the largest of the salivary glands. Each parotid is wrapped around the man ...

, but are more developed in the parotid gland. They are not present in

Intralobular duct

An intralobular duct is the portion of an

inside a

lobule In anatomy, a lobe is a clear anatomical division or extension of an organ (as seen for example in the brain, lung, liver, or kidney) that can be determined without the use of a microscope at the gross anatomy level. This is in contrast to the m ...

, leading directly from

to an interlobular duct (between lobules). It is composed of two subdivisions, the

and the

. In the human mammary gland, the intralobular duct is a part of the glandular system that resides within the lobules. Lobules contain clusters of ducts whose secretory alveolies are drained by the intralobular duct. The intralobular ducts are usually lined with simple cuboidal epithelial cells that are lined by myoepithelial cells as well. The intralobular ducts of the lobules drain into the interlobular ducts between lobules. They can be seen in: *

salivary glands The salivary glands in mammals are exocrine glands that produce saliva through a system of ducts. Humans have three paired major salivary glands (parotid, submandibular, and sublingual), as well as hundreds of minor salivary glands. Salivary gla ...

References

External links

Overview at uwa.edu.au

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