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Glandular epithelium

A gland is a structure made up of one or more cells modified to synthesize and secrete chemical substances. Most glands consist of groups of epithelial cells. A gland can be classified as an endocrine gland    , a ductless gland that releases secretions directly into surrounding tissues and fluids (endo- = “inside”), or an exocrine gland    whose secretions leave through a duct that opens directly, or indirectly, to the external environment (exo- = “outside”).

Endocrine glands

The secretions of endocrine glands are called hormones. Hormones are released into the interstitial fluid, diffused into the bloodstream, and delivered to targets, in other words, cells that have receptors to bind the hormones. The endocrine system is part of a major regulatory system coordinating the regulation and integration of body responses. A few examples of endocrine glands include the anterior pituitary, thymus, adrenal cortex, and gonads.

Exocrine glands

Exocrine glands release their contents through a duct that leads to the epithelial surface. Mucous, sweat, saliva, and breast milk are all examples of secretions from exocrine glands. They are all discharged through tubular ducts. Secretions into the lumen of the gastrointestinal tract, technically outside of the body, are of the exocrine category.

Glandular structure

Exocrine glands are classified as either unicellular or multicellular. The unicellular glands are scattered single cells, such as goblet cells, found in the mucous membranes of the small and large intestine.

The multicellular exocrine glands known as serous glands develop from simple epithelium to form a secretory surface that secretes directly into an inner cavity. These glands line the internal cavities of the abdomen and chest and release their secretions directly into the cavities. Other multicellular exocrine glands release their contents through a tubular duct. The duct is single in a simple gland but in compound glands is divided into one or more branches ( [link] ). In tubular glands, the ducts can be straight or coiled, whereas tubes that form pockets are alveolar (acinar), such as the exocrine portion of the pancreas. Combinations of tubes and pockets are known as tubuloalveolar (tubuloacinar) compound glands. In a branched gland, a duct is connected to more than one secretory group of cells.

Types of exocrine glands

This table shows the different types of exocrine glands: alveolar (acinar) versus tubular and those with simple ducts versus compound ducts. Each diagram shows a single layer of columnar epithelial cells with a line of cells travelling along the surface of a tissue (surface epithelium) and then dipping into a hole in the tissue. The cells travel down the right side of the hole until they reach the bottom, then curve around the bottom of the hole and then travel up the left side. Finally, the cells emerge back onto the surface of the tissue. The surface epithelial cells are those that are on the surface of the tissue; the duct cells are those that line both walls of the hole. The gland cells are those that line the bottom of the hole. The shape of the hole differs in each gland. In the simple alvelolar (acinar) gland, the duct and gland cells are bulb shaped with the gland cells being the larger end of the bulb. Simple alveolar glands are not found in adults, as these represent an early developmental stage of simple, branched glands. In simple tubular glands, the duct and gland cells are U shaped. Simple tubular glands are found in the intestinal glands. In simple branched alveolar glands, the gland cells form three bulbs at the end of the duct, similar in appearance to a clover leaf. The sebaceous (oil) glands are examples of simple branched alveolar glands. In simple coiled tubular glands, the duct and gland cells form a U, however, the bottom of the U, which is all gland cells, is curved up to the right. Merocrine sweat glands are examples of simple coiled tubular glands. In simple branched tubular glands, the duct is very short and the gland cells divide into three lobes, similar in appearance to a bird’s foot. The gastric glands of the stomach and mucous glands of the esophagus, tongue and duodenum are examples of simple branched tubular glands. Among the glands with compound ducts, compound alveolar (acinar) glands have three sets of clover leaf bulbs, for a total of six bulbs. Two of the clover leaf shaped structures extend parallel to the surface epithelium in opposite directions to each other. The third clover leaf extends down into the tissue, perpendicular to the surface. The duct is cross-shaped. The mammary glands are an example of compound alveolar glands. Compound tubular glands have a similar structure to compound alveolar glands. However, instead of three cloverleaf shaped bulbs, the compound tubular gland has three bird’s foot shaped bulbs. The duct is also cross-shaped in the compound tubular gland. The mucous glands of the mouth and the bulbourethral glands of the male reproductive system are examples of compound tubular glands, which are also found in the seminiferous tubules of the testis. Compound tubuloalveolar glands are a hybrid between the compound alveolar gland and the compound tubular gland. The two sets of bulbs that run parallel to the surface are bird-foot shaped; however, the set of bulbs that runs perpendicularly below the surface is cloverleaf shaped. The salivary glands, glands of the respiratory passages and glands of the pancreas are all compound tubuloalveolar glands.
Exocrine glands are classified by their structure.

Methods and types of secretion

Exocrine glands can be classified by their mode of secretion and the nature of the substances released, as well as by the structure of the glands and shape of ducts ( [link] ). Merocrine secretion is the most common type of exocrine secretion. The secretions are enclosed in vesicles that move to the apical surface of the cell where the contents are released by exocytosis. For example, watery mucous containing the glycoprotein mucin, a lubricant that offers some pathogen protection is a merocrine secretion. The eccrine glands that produce and secrete sweat are another example.

Questions & Answers

Osuji Reply
why study anatomy?
esther Reply
to know the detailed functioning of the internay body organs
we study anatomy to know about the structure of the organs which in turn help to study physiology which is the knowledge related to function of the vital organ,and when we know the normal functionality we can understand the abnormalities in that organ,and the study of disease is called pathology
why is it so hard to know the spelling and words
they were made so that only the best and thr brightest would understand.
thank you
to know the internal structure of the human body and how it function
whats antonmy
Jaan Reply
the study of structure and function of internal body parts
is a branch of biology which describes the structures of the body and relationship from one part to another
what is anatomy and physiology
mwitwa Reply
Anatomy is the study of structures of the body
Physiology the study functions of the body
anatomy is study of structure of body nd physiology is study of function of body.
anatomy is the study of internal body structures and physiology is the functioning of these structures in the body
what is lungs
Shipon Reply
it an organ found in our thoracic cavity
lungs are spongy organs where our respiration takesplace
Lungs is a spongy organs located in the chest , is an a primary organs of respiration in human body and other Animals
lungs thorex me present hote hai ye organ hai and gas exchange (o2,co2 exchange)inka inka function hai.
lungs ka function hai
pls am a student I don't know
main function is respiration
respiration is the taking ing of oxygen by the body tissues and the removal of carbondioxide from the body tissues
what is heart beat,?
Naqeeb Reply
heart beat is the process briting
what functions of heart
Muthu Reply
To circulate the blood
it pump blood to the lungs
very twiest
what should be the nature of cell
Kashish Reply
Cells die and reproduce
knuckle of the middle finger
James Reply
because of the gases (nitrogen, oxygen)
what is ketone bodies
why the heart is protected with that sac
Joshua Reply
To prevent collision with the lungs, lubricates the heart, protects the heart from infection in the event a peripheral organ is effected, and stabilizes the heart within the mediastinum.
This app should be updated too much as there is very little information for some topics.I hope you will consider my information....
aman Reply
adenohypophysis is made up of what type of cells and what is the name of those cells?
Mannu Reply
armstrong Reply
motor root of the trigeminal nerve
what is the nervous system about
what passes through foramen ovale?
Farah Reply
what are the organelles of a cell
Amina Reply
muscular system
nucleus ribosome Golgi body call membrane cytoplasm
these are the cellular components that functions to provide energy,remove waste and cell division
Organelles of the cell are: Mitochondria,Ribosome,golgi apparatus, nucleus, secretory granules, nuclear e t c
what are local hormones
Local hormones are hormones that effect the cell that released them or cells near the releasing cell and they do not circulate within the blood stream.
the trachea bifurcated into how many branches on the right lung
three lobes
Explain the normal flow of blood.

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Source:  OpenStax, Anatomy & Physiology. OpenStax CNX. Feb 04, 2016 Download for free at http://legacy.cnx.org/content/col11496/1.8
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