In biology, a tubule is a general term referring to small tube or similar type of structure. Specifically, tubule can refer to: * a small tube or fistular structure * a minute tube lined with glandular epithelium * any hollow cylindrical body structure * a minute canal found in various structures or organs of the body * a slender elongated anatomical channel * a minute tube, especially as an anatomical structure.

Examples of tubules

* Collecting tubules: terminal channels of the

nephrons The nephron is the minute or microscopic structural and functional unit of the kidney. It is composed of a renal corpuscle and a Nephron#Renal tubule, renal tubule. The renal corpuscle consists of a tuft of capillary, capillaries called a glomer ...

* Cuvierian tubules: clusters of sticky tubules located at the base of the respiratory tree, which may be discharged by some

sea cucumbers Sea cucumbers are echinoderms from the class Holothuroidea ( ). They are benthic marine animals found on the sea floor worldwide, and the number of known holothuroid species worldwide is about 1,786, with the greatest number being in the Asi ...

( holothurians) when mechanically stimulated (i.e. being threatened by a predator) * Dentinal tubules or

dental canaliculi Dental may refer to: * Dental consonant, in phonetics * Dental Records, an independent UK record label * Dentistry Dentistry, also known as dental medicine and oral medicine, is the branch of medicine focused on the Human tooth, teeth, gums ...

: minute channels in the dentine of a

tooth A tooth (: teeth) is a hard, calcified structure found in the jaws (or mouths) of many vertebrates and used to break down food. Some animals, particularly carnivores and omnivores, also use teeth to help with capturing or wounding prey, tea ...

that extend from the pulp cavity to the cementum or the enamel *

Distal convoluted tubule The distal convoluted tubule (DCT) is a portion of kidney nephron between the loop of Henle and the collecting tubule. Physiology It is partly responsible for the regulation of potassium, sodium, calcium, and pH. On its apical surface (lum ...

: the convoluted portion of the vertebrate

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 structu ...

that lies between the loop of Henle and the nonsecretory part of the

and that is concerned especially with the concentration of

urine Urine is a liquid by-product of metabolism in humans and many other animals. In placental mammals, urine flows from the Kidney (vertebrates), kidneys through the ureters to the urinary bladder and exits the urethra through the penile meatus (mal ...

* Galactophorous tubule or

lactiferous ducts Lactiferous ducts are ducts that converge and form a branched system connecting the nipple to the lobules of the mammary gland. When lactogenesis occurs, under the influence of hormones, the milk is moved to the nipple by the action of smooth mu ...

: small channels for the passage of milk from the secreting cells in the

mammary gland A mammary gland is an exocrine gland that produces milk in humans and other mammals. Mammals get their name from the Latin word ''mamma'', "breast". The mammary glands are arranged in organs such as the breasts in primates (for example, human ...

to the

nipple The nipple is a raised region of tissue on the surface of the breast from which, in lactating females, breast milk, milk from the mammary gland leaves the body through the lactiferous ducts to Breastfeeding, nurse an infant. The milk can flow th ...

Loop of Henle In the kidney, the loop of Henle () (or Henle's loop, Henle loop, nephron loop or its Latin counterpart ''ansa nephroni'') is the portion of a nephron that leads from the proximal convoluted tubule to the distal convoluted tubule. Named after it ...

: the long U-shaped part of the renal tubule, extending through the medulla from the end of the

proximal convoluted tubule The proximal tubule is the segment of the nephron in kidneys which begins from the renal (tubular) pole of the Bowman's capsule to the beginning of loop of Henle. At this location, the glomerular parietal epithelial cells (PECs) lining bowman’s ...

. It begins with a descending limb (comprising the proximal straight tubule and the thin tubule ), followed by the ascending limb (the distal straight tubule ), and ending at the

distal convoluted tubule The distal convoluted tubule (DCT) is a portion of kidney nephron between the loop of Henle and the collecting tubule. Physiology It is partly responsible for the regulation of potassium, sodium, calcium, and pH. On its apical surface (lum ...

* Malpighian tubule: any of the excretory organs in

insects Insects (from Latin ') are hexapod invertebrates of the class Insecta. They are the largest group within the arthropod phylum. Insects have a chitinous exoskeleton, a three-part body (head, thorax and abdomen), three pairs of jointed ...

that lie in the abdominal body cavity and empty into the junction between the

midgut The midgut is the portion of the human embryo from which almost all of the small intestine and approximately half of the large intestine develop. After it bends around the superior mesenteric artery, it is called the "midgut loop". It comprises ...

and

hindgut The hindgut (or epigaster) is the posterior ( caudal) part of the alimentary canal. In mammals, it includes the distal one third of the transverse colon and the splenic flexure, the descending colon, sigmoid colon and up to the ano-rectal junct ...

Mesonephric tubule The mesonephros () is one of three excretory organs that develop in vertebrates. It serves as the main excretory organ of aquatic vertebrates and as a temporary kidney in reptiles, birds, and mammals. The mesonephros is included in the Wolffian b ...

: tubules comprising the mesonephros or temporary

kidney In humans, the kidneys are two reddish-brown bean-shaped blood-filtering organ (anatomy), organs that are a multilobar, multipapillary form of mammalian kidneys, usually without signs of external lobulation. They are located on the left and rig ...

of amniotes * Metanephric tubule: tubules comprising the permanent

of amniotes *

Microtubule Microtubules are polymers of tubulin that form part of the cytoskeleton and provide structure and shape to eukaryotic cells. Microtubules can be as long as 50 micrometres, as wide as 23 to 27 nanometer, nm and have an inner diameter bet ...

: a microscopically small tubule *

Proximal convoluted tubule The proximal tubule is the segment of the nephron in kidneys which begins from the renal (tubular) pole of the Bowman's capsule to the beginning of loop of Henle. At this location, the glomerular parietal epithelial cells (PECs) lining bowman’s ...

: the portion of the

immediately after the

glomerulus ''Glomerulus'' (; : glomeruli) is a common term used in anatomy to describe globular structures of entwined vessels, fibers, or neurons. ''Glomerulus'' is the diminutive of the Latin ''glomus'', meaning "ball of yarn". ''Glomerulus'' may refer to ...

Renal tubule 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 ...

: the minute canals made up of

basement membrane The basement membrane, also known as base membrane, is a thin, pliable sheet-like type of extracellular matrix that provides cell and tissue support and acts as a platform for complex signalling. The basement membrane sits between epithelial tis ...

and lined with

epithelium Epithelium or epithelial tissue is a thin, continuous, protective layer of cells with little extracellular matrix. An example is the epidermis, the outermost layer of the skin. Epithelial ( mesothelial) tissues line the outer surfaces of man ...

, composing the substance of the

and secreting, reabsorbing, collecting and conducting the

. Include proximal convoluted, the nephron loop (containing the proximal straight tubule, descending and ascending thin, and the distal straight tubules) and the distal convoluted tubules *

Seminiferous tubules Seminiferous tubules are located within the testicles, and are the specific location of meiosis, and the subsequent creation of male gametes, namely spermatozoa. Structure The epithelium of the tubule consists of a type of sustentacular cells ...

: any of the numerous long convoluted tubules in the

testis A testicle or testis ( testes) is the gonad in all male bilaterians, including humans, and is Homology (biology), homologous to the ovary in females. Its primary functions are the production of sperm and the secretion of Androgen, androgens, p ...

which are the sites where

spermatozoa A spermatozoon (; also spelled spermatozoön; : spermatozoa; ) is a motile sperm cell (biology), cell produced by male animals relying on internal fertilization. A spermatozoon is a moving form of the ploidy, haploid cell (biology), cell that is ...

mature * T tubule: transverse

intracellular This glossary of biology terms is a list of definitions of fundamental terms and concepts used in biology, the study of life and of living organisms. It is intended as introductory material for novices; for more specific and technical definitions ...

tubules invaginating from the

cell membrane The cell membrane (also known as the plasma membrane or cytoplasmic membrane, and historically referred to as the plasmalemma) is a biological membrane that separates and protects the interior of a cell from the outside environment (the extr ...

and surrounding the

myofibrils A myofibril (also known as a muscle fibril or sarcostyle) is a basic rod-like organelle of a muscle cell. Skeletal muscles are composed of long, tubular cells known as muscle fibers, and these cells contain many chains of myofibrils. Each myofibr ...

of the T system of skeletal and cardiac muscle, serving as a pathway for the spread of electrical excitation within a

muscle cell A muscle cell, also known as a myocyte, is a mature contractile Cell (biology), cell in the muscle of an animal. In humans and other vertebrates there are three types: skeletal muscle, skeletal, smooth muscle, smooth, and Cardiac muscle, cardiac ...

Trachea The trachea (: tracheae or tracheas), also known as the windpipe, is a cartilaginous tube that connects the larynx to the bronchi of the lungs, allowing the passage of air, and so is present in almost all animals' lungs. The trachea extends from ...

: tubules forming the

respiratory system The respiratory system (also respiratory apparatus, ventilatory system) is a biological system consisting of specific organs and structures used for gas exchange in animals and plants. The anatomy and physiology that make this happen varies grea ...

of most

and many

arachnids Arachnids are arthropods in the class Arachnida () of the subphylum Chelicerata. Arachnida includes, among others, spiders, scorpions, ticks, mites, pseudoscorpions, harvestmen, camel spiders, whip spiders and vinegaroons. Adult arachnids ...

* Uriniferous tubules: any of the small tubules that are the excretory units of the vertebrate

* Uveoscleral pathway: a tubule that drains excess

aqueous humor The aqueous humour is a transparent water-like fluid similar to blood plasma, but containing low protein concentrations. It is secreted from the ciliary body, a structure supporting the lens of the eyeball. It fills both the anterior and the po ...

* Vasa efferentia: convoluted tubules that lead from the

rete testis The rete testis ( ; : retia testes) is an anastomosis, anastomosing network of delicate tubules located in the hilum of the testicle (mediastinum testis) that carries spermatozoon, sperm from the seminiferous tubules to the efferent ducts. It is t ...

to the

vas deferens The vas deferens (: vasa deferentia), ductus deferens (: ductūs deferentes), or sperm duct is part of the male reproductive system of many vertebrates. In mammals, spermatozoa are produced in the seminiferous tubules and flow into the epididyma ...

and form the head of the

epididymis The epididymis (; : epididymides or ) is an elongated tubular genital organ attached to the posterior side of each one of the two male reproductive glands, the testicles. It is a single, narrow, tightly coiled tube in adult humans, in length; ...

Vesicular-tubular clusters The endoplasmic-reticulum–Golgi intermediate compartment (ERGIC) is an organelle in eukaryotic cells. This compartment mediates transport between the endoplasmic reticulum (ER) and Golgi complex, facilitating the sorting of cargo. The cluster wa ...

between the

golgi apparatus The Golgi apparatus (), also known as the Golgi complex, Golgi body, or simply the Golgi, is an organelle found in most eukaryotic Cell (biology), cells. Part of the endomembrane system in the cytoplasm, it protein targeting, packages proteins ...

and

endoplasmic reticulum The endoplasmic reticulum (ER) is a part of a transportation system of the eukaryote, eukaryotic cell, and has many other important functions such as protein folding. The word endoplasmic means "within the cytoplasm", and reticulum is Latin for ...

which assist in transport.

References

{{Reflist Histology