Glands are the secretory organs located at specific sites in the body. They contain secretory tissue and secrete hormones, enzymes and other secretions that are vital for the regulation of body physiology.
There are two types of glands as
- Salivary glands
- Mucous glands
- Lachrymal glands
- Pancreatic gland
- Ceruminous glands (sweat glands and mammary glands).
- Pituitary gland
- Thyroid gland
- Parathyroid gland
- Adrenal gland
- Pineal gland
- Thymus gland
Exocrine glands secrete enzymes that act as biocatalysts to speed up the biochemical reactions.
While the endocrine glands secrete hormones that act as chemical messengers and are involved in the homeostasis of the body.
Scientifically, these glands can be differentiated based on their structures, location, and secretions.
- These glands secrete their contents into a particular region of the body.
- The secretion located in the core of the gland is carried through a duct and released at the site of action.
This secretion mostly has enzymes and other substances.
Examples of exocrine glands include
- These are the glance located in the walls of the mouth. They secrete saliva and have the enzyme salivary amylase.
- This amylase helps in the digestion of carbohydrates in the mouth.
- Saliva also consists of lysosomal enzymes.
For more details, check out the article on the functions of saliva.
- Mucous is a protective layer in the gastrointestinal tract. It helps to absorb the wear and tear during the digestion of food.
- Numerous mucous glands are present in the mucosa layer throughout the digestive tract. These glands secrete mucus.
The pancreas is a gland located near the digestive tract.
- Its exocrine portion secretes enzymes with pancreatic juice into the duodenum of the small intestine.
This pancreatic juice consists of digestive enzymes like pancreatic amylase, trypsin, and lipase. These enzymes digest carbohydrates, proteins, and fats, respectively.
These are the glands present near the eye.
They secrete tears that have the lysosomal enzyme, salts, immunoglobulins, and water.
The lysosome enzyme helps to destroy microbes entering the eye.
- These are modified sweat glands present in the outer ear.
- They secrete sticky material called cerumen, which is sticky (ear wax).
- This ear wax contains lysosomal enzymes and immunoglobulins.
This helps to prevent the entry of insects and microbes into the ear.
- Mammary glands are modified sweat glands present in the female reproductive system.
- These glands produce milk to nourish the newborn baby.
Types of Exocrine Glands
Exocrine glands can be divided into
- Simple and
- Compound glands
Simple exocrine glands
These glands have a simplified structure without any branches in their anatomy.
Mucous-secreting glands of the large intestine are an example.
Compound exocrine glands
As seen in the image above, these glands have numerous branches in their anatomical structure.
All these branches collect the secretion and pour it out into the main branch. Examples of this type of gland include salivary glands.
These glands, unlike exocrine’s, do not have ducts to release their secretion.
Instead, the blood flowing through the glandular tissue carries away the secretion.
These secretions are called hormones and are meant to act at a quite distant part away from their origin source.
The entire set of endocrine glands is categorized separately as the endocrine system under 12 body systems.
Major Endocrine glands include
This is a neuroendocrine gland, but some do not consider it a gland.
Its secretion is meant to regulate the function of the pituitary gland, as listed in the table below.
|1||Growth hormone releasing|
hormone release inhibitory
|Restricts the release of growth hormone.|
|Stimulates release of gonadotrophic hormones.|
|4||Prolactin release inhibitory|
|Stimulates release of the thyrotrophic hormone.|
Pituitary Gland (below the hypothalamus)
This is a gland located below the hypothalamus in the brain.
For more about its anatomy, refer to the pituitary structure.
The gland is differentiated as anterior and posterior glands and has definite secretions for each type i.e.
i) Anterior pituitary gland
Located in the front part of the pituitary
- Prolactin: Stimulates milk production in mothers.
- Somatotropin: A hormone that regulates the growth of the body and tissues.
- Luteinizing hormone: Stimulates ovulation (egg formation) in females and testosterone production in males.
- Thyroid-stimulating hormone: Stimulates the thyroid gland to produce T3 & T4 hormones.
- Adrenocorticotrophic hormone: Stimulates secretion of glucocorticoids and mineralocorticoid hormones.
- Follicle-stimulating hormone signals the formation of estrogen and progesterone by the female reproductive system.
ii. Posterior pituitary
It is present behind the front part of the pituitary, as shown in the diagram above.
- Vasopressin (antidiuretic hormone) controls water loss in the kidneys. So minimizes urine formation and saves water in the body.
- Oxytocin signals the uterus for delivery in pregnant women after the period of gestation. It also stimulates milk secretion in mothers.
This endocrine gland is situated in the throat region, as shown in the picture. It has a butterfly-like appearance.
It specifically produces two thyroid hormones named Tri-iodothyronine (T3) and thyroxine (T4).
These glands are present near the thyroid gland. They produce the hormone parathormone. This parathormone is involved in calcium regulation.
Both thyroid and parathyroid glands are examples of types of glands in the neck.
The pancreas has both exocrine and endocrine functions. Its endocrine portion has islets of Langerhans cells. These islets secrete hormones that regulate the body’s glucose metabolism.
The hormone insulin released enhances glucose uptake in the tissues and glycogen formation in the liver.
At the same time, glucagon enhances the release of glucose from the liver into the blood.
The hormone somatostatin inhibits the secretion of both insulin and glucagon hormones.
A pair of glands are located on the top of each kidney.
As shown in the image above, it basically has two regions like.
- Adrenal cortex
- Adrenal medulla
The adrenal cortex portion secretes glucocorticoids and mineralocorticoids.
The adrenal medulla portion secretes nor-adrenalin. This is one of the neurotransmitters and is called a flight or fight hormone.
This is another gland located inside the brain. It secretes the hormone melatonin, a sleep hormone. It regulates sleep patterns and hence is called a natural body clock.
One can see jet lag effects due to its secretions.
You may also read-> Hormones in the human body.
This gland secretes the hormone thymosin, which is in the development of cell-mediated immunity.
The testes secrete this. It is produced in males to a large extent and to a minimum extent in women. It signals male characters like the beard, heavy muscles, hoarse voice, etc.
Produce Estrogen, progesterone. Secreted only in women and regulate the reproduction cycle.
All the glands are located in distinct locations in the human body. They regulate physiology to a large extent upon receiving the stimuli from the brain to do so.
Without their secretions, there can arise enzyme and hormone deficiency diseases.
Besides the glands, individual cells also have the ability to secrete.
For example, sperms produce the Hyaluronidase enzyme. By this, sperm can swim in the uterine tissue to reach the ova.
Frequently asked questions and answers.
1. What gland has both endocrine and exocrine functions
Pancreas is the gland that has both functions.
The endocrine portion secretes hormones like glucagon and insulin hormones.
Through the exocrine portion, it secretes digestive enzymes like pancreatic lipase, trypsin, chymotrypsin, lipase, and nucleases.
2. How to remember endocrine glands and hormones
Endocrine glands and their hormones can be remembered from their location, shape, and role in physiology.
- Principles of Anatomy and Physiology by Gerard J. Tortora