Exocrine glands are glands that secrete substances on to an epithelial surface by way of a duct. Examples of exocrine glands include

sweat Perspiration, also known as sweating, is the production of fluids secreted by the sweat glands in the skin of mammals. Two types of sweat glands can be found in humans: eccrine glands and apocrine glands. The eccrine sweat glands are distrib ...

salivary 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 glan ...

mammary A mammary gland is an exocrine gland in humans and other mammals that produces milk to feed young offspring. Mammals get their name from the Latin word ''mamma'', "breast". The mammary glands are arranged in organs such as the breasts in prima ...

, ceruminous, lacrimal, sebaceous,

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

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

endocrine gland Endocrine glands are ductless glands of the endocrine system that secrete their products, hormones, directly into the blood. The major glands of the endocrine system include the pineal gland, pituitary gland, pancreas, ovaries, testes, ...

s, which secrete their products directly into the

bloodstream The blood circulatory system is a system of organs that includes the heart, blood vessels, and blood which is circulated throughout the entire body of a human or other vertebrate. It includes the cardiovascular system, or vascular system, tha ...

. The

liver The liver is a major organ only found in vertebrates which performs many essential biological functions such as detoxification of the organism, and the synthesis of proteins and biochemicals necessary for digestion and growth. In humans, it ...

and

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 en ...

are both exocrine and endocrine glands; they are exocrine glands because they secrete products— bile and pancreatic juice—into the gastrointestinal tract 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

Exocrine glands are named apocrine glands, holocrine glands, or merocrine glands based on how their products are secreted. *

Merocrine Merocrine (or eccrine) is a term used to classify exocrine glands and their secretions in the study of histology. A cell is classified as merocrine if the secretions of that cell are excreted via exocytosis from secretory cells into an epithelia ...

secretion – cells excrete their substances by exocytosis into a duct; for example, pancreatic acinar cells, maximum

sweat glands Sweat glands, also known as sudoriferous or sudoriparous glands, , are small tubular structures of the skin that produce sweat. Sweat glands are a type of exocrine gland, which are glands that produce and secrete substances onto an epithelial sur ...

of humans,

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 gl ...

, goblet cells, intestinal glands, tear glands, etc. *

Apocrine Apocrine () glands are a type of exocrine gland, which are themselves a type of gland, i.e. a group of cells specialized for the release of secretions. Exocrine glands secrete by one of three means: holocrine, merocrine and apocrine. In apocri ...

secretion – apical portion of the

cytoplasm In cell biology, the cytoplasm is all of the material within a eukaryotic cell, enclosed by the cell membrane, except for the cell nucleus. The material inside the nucleus and contained within the nuclear membrane is termed the nucleoplasm. ...

in the

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

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

Holocrine Holocrine (from Ancient Greek ὅλος; ''hólos'', “whole, entire” + κρῑ́νω; ''krī́nō'', “to separate”) is a term used to classify the mode of secretion in exocrine glands in the study of histology. Holocrine secretions are p ...

secretion – 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 de ...

and nose, meibomian gland, zeis gland, etc.

Product secreted

* Serous cells secrete

protein Proteins are large biomolecules and macromolecules that comprise one or more long chains of amino acid residues. Proteins perform a vast array of functions within organisms, including catalysing metabolic reactions, DNA replication, res ...

s, often

enzyme Enzymes () are proteins that act as biological catalysts by accelerating chemical reactions. The molecules upon which enzymes may act are called substrates, and the enzyme converts the substrates into different molecules known as products ...

s. Examples include

gastric chief cell A gastric chief cell (or 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 in ruminant animals. The cell stains basophilic upo ...

s and Paneth cells *

Mucous cell Mucous gland, also known as muciparous glands, are found in several different parts of the body, and they typically stain lighter than serous glands during standard histological preparation. Most are multicellular, but goblet cells are single-cel ...

s 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 and mucous cells. It ...

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

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 ...

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 ma ...

(saliva secretion 25%) is predominantly serous, the sublingual gland (saliva secretion 5%) mainly mucous gland, and the submandibular gland (saliva secretion 70%) is a mixed, mainly serous gland. *

Sebaceous gland A sebaceous 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 the greatest nu ...

s secrete sebum, 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 eye' ...

Additional images

File:Gray1033.png, Section of the human

esophagus The esophagus ( American English) or oesophagus (British English; both ), non-technically known also as the food pipe or gullet, is an organ in vertebrates through which food passes, aided by peristaltic contractions, from the pharynx to ...

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

References

External links

Diagram at mhhe.com
{{Authority control Exocrine system