Exocrine glands are

gland A gland is a Cell (biology), cell or an Organ (biology), organ in an animal's body that produces and secretes different substances that the organism needs, either into the bloodstream or into a body cavity or outer surface. A gland may also funct ...

s that secrete substances onto an

epithelial 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 ...

surface by way of a duct. Examples of exocrine glands include

sweat Perspiration, also known as sweat, is the fluid secreted by sweat glands in the skin of mammals. Two types of sweat glands can be found in humans: eccrine glands and Apocrine sweat gland, apocrine glands. The eccrine sweat glands are distribu ...

, salivary, mammary, ceruminous, lacrimal, sebaceous,

prostate The prostate is an male accessory gland, accessory gland of the male reproductive system and a muscle-driven mechanical switch between urination and ejaculation. It is found in all male mammals. It differs between species anatomically, chemica ...

and mucous. Exocrine glands are one of two types of glands in the human body, the other being

endocrine gland The endocrine system is a network of glands and organs located throughout the body. Along with the nervous system, it makes the neuroendocrine system, which controls and regulates many of the body's functions. Endocrine glands are ductless gland ...

s, which secrete their products directly into the bloodstream. The

liver The liver is a major metabolic organ (anatomy), organ exclusively found in vertebrates, which performs many essential biological Function (biology), functions such as detoxification of the organism, and the Protein biosynthesis, synthesis of var ...

and

pancreas The pancreas (plural pancreases, or pancreata) is an Organ (anatomy), organ of the Digestion, digestive system and endocrine system of vertebrates. In humans, it is located in the abdominal cavity, abdomen behind the stomach and functions as a ...

are both exocrine and endocrine glands; they are exocrine glands because they secrete products—

bile Bile (from Latin ''bilis''), also known as gall, is a yellow-green/misty green fluid produced by the liver of most vertebrates that aids the digestion of lipids in the small intestine. In humans, bile is primarily composed of water, is pro ...

and

pancreatic juice Pancreatic juice is a liquid secreted by the pancreas, which contains a number of digestive enzymes, including trypsinogen, chymotrypsinogen, elastase, carboxypeptidase, pancreatic lipase, nucleases and amylase. The pancreas is located in th ...

—into the

gastrointestinal tract The gastrointestinal tract (GI tract, digestive tract, alimentary canal) is the tract or passageway of the Digestion, digestive system that leads from the mouth to the anus. The tract is the largest of the body's systems, after the cardiovascula ...

through a series of ducts, and endocrine because they secrete other substances directly into the bloodstream. Exocrine sweat glands are part of the integumentary system; they have eccrine and apocrine types.

Classification

Structure

Exocrine glands contain a glandular portion and a duct portion, the structures of which can be used to classify the gland. * The duct portion may be branched (called compound) or unbranched (called simple). * The glandular portion may be tubular or acinar, or may be a mix of the two (called tubuloacinar). If the glandular portion branches, then the gland is called a branched gland.

Method of secretion

Depending on how their products are secreted, exocrine glands are categorized as merocrine, apocrine, or holocrine. * Merocrine – the cells of the gland excrete their substances by

exocytosis Exocytosis is a term for the active transport process that transports large molecules from cell to the extracellular area. Hormones, proteins and neurotransmitters are examples of large molecules that can be transported out of the cell. Exocytosis ...

into a duct; for example, pancreatic acinar cells, eccrine sweat glands,

salivary gland The salivary glands in many vertebrates including 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 min ...

goblet cell Goblet cells are simple columnar epithelial cells that secrete gel-forming mucins, like mucin 2 in the lower gastrointestinal tract, and mucin 5AC in the respiratory tract. The goblet cells mainly use the merocrine method of secretion, secre ...

intestinal gland In histology, an intestinal gland (also Crypt (anatomy), crypt of Johann Nathanael Lieberkühn, Lieberkühn and intestinal crypt) is a gland found in between Intestinal villus, villi in the intestinal epithelium, intestinal epithelial lining of th ...

s, tear glands, etc. * Apocrine – the apical portion of the

cytoplasm The cytoplasm describes all the material within a eukaryotic or prokaryotic cell, enclosed by the cell membrane, including the organelles and excluding the nucleus in eukaryotic cells. The material inside the nucleus of a eukaryotic cell a ...

in 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 ...

, which contains the excretion, buds off. Examples are sweat glands of arm pits, pubic region, skin around anus, lips and nipples;

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 ...

s, etc. * Holocrine – the entire cell disintegrates to excrete its substance; for example, sebaceous glands of the

skin Skin is the layer of usually soft, flexible outer tissue covering the body of a vertebrate animal, with three main functions: protection, regulation, and sensation. Other animal coverings, such as the arthropod exoskeleton, have different ...

and nose, meibomian gland, zeis gland, etc. File:405 Modes of Secretion by Glands Merocine.png, Merocrine secretion File:405 Modes of Secretion by Glands Apocrine.png, Apocrine secretion File:405 Modes of Secretion by Glands Holocrine.png, Holocrine secretion

Product secreted

* Serous cells secrete

protein Proteins are large biomolecules and macromolecules that comprise one or more long chains of amino acid residue (biochemistry), residues. Proteins perform a vast array of functions within organisms, including Enzyme catalysis, catalysing metab ...

s, often

enzyme An enzyme () is a protein that acts as a biological catalyst by accelerating chemical reactions. The molecules upon which enzymes may act are called substrate (chemistry), substrates, and the enzyme converts the substrates into different mol ...

s. Examples include

gastric chief cell A gastric chief cell, peptic cell, or gastric zymogenic cell is a type of gastric gland cell that releases pepsinogen and gastric lipase. It is the cell responsible for secretion of chymosin (rennin) in ruminant animals and some other animals. ...

s and Paneth cells * Mucous cells secrete

mucus Mucus (, ) is a slippery aqueous secretion produced by, and covering, mucous membranes. It is typically produced from cells found in mucous glands, although it may also originate from mixed glands, which contain both Serous fluid, serous and muc ...

. Examples include

Brunner's gland Brunner's glands (or duodenal glands) are compound tubuloalveolar submucosal glands found in that portion of the duodenum proximal to the hepatopancreatic sphincter (i.e sphincter of Oddi). For decades, it was believed that the main function o ...

s, esophageal glands, and pyloric glands * Seromucous glands (mixed) secrete both protein and mucus. Examples include the

s: although 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 m ...

(saliva secretion 25%) is predominantly serous, the

sublingual gland The sublingual gland (''glandula sublingualis'') is a seromucous polystomatic exocrine gland. Located underneath the oral diaphragm (''diaphragma oris''), the sublingual gland is the smallest and most diffuse of the three major salivary glands of ...

(saliva secretion 5%) mainly mucous gland, and the submandibular gland (saliva secretion 70%) is a mixed, mainly serous gland. *

Sebaceous gland A sebaceous gland or oil gland is a microscopic exocrine gland in the skin that opens into a hair follicle to secrete an oily or waxy matter, called sebum, which lubricates the hair and skin of mammals. In humans, sebaceous glands occur in ...

s secrete

sebum A sebaceous gland or oil gland is a microscopic exocrine gland in the skin that opens into a hair follicle to secrete an oily or waxy matter, called sebum, which lubricates the hair and skin of mammals. In humans, sebaceous glands occur ...

, a lipid product. These glands are also known as oil glands, e.g. Fordyce spots and

Meibomian glands Meibomian glands (also called tarsal glands, palpebral glands, and tarsoconjunctival glands) are sebaceous glands along the rims of the eyelid inside the tarsal plate. They produce meibum, an oily substance that prevents evaporation of the ey ...

Additional images

File:Gray1033.png, Section of the human

esophagus The esophagus (American English), oesophagus (British English), or œsophagus (Œ, archaic spelling) (American and British English spelling differences#ae and oe, see spelling difference) all ; : ((o)e)(œ)sophagi or ((o)e)(œ)sophaguses), c ...

. File:Gray1172.png, Dissection of a lactating breast.

References

External links

Diagram at mhhe.com
{{Authority control Exocrine system