Glands are the secretory organs in human anatomy. They are sac-like structures consisting of secretory tissue.
There are two main types of glands as the
- Exocrine glands: Salivary, mucous, lachrymal, pancreatic, ceruminous glands i.e sweat glands, and mammary glands.
- Endocrine glands: Pituitary, thyroid, parathyroid, adrenal, pineal gland, thymus gland, etc.
These glands play a vital role in the physiology and homeostasis of the body. Hence, they are situated in safe and prominent locations of the body.
They can also be differentiated based on their structure, location, and secretions too.
These glands essentially secrete enzymes, hormones, and other essential fluids.
Different Types of Glands in the human body:
These glands secrete their contents into a particular region of the body. The secretion from the core of the gland is carried through a duct and released at the site of action.
This secretion mostly contains enzymes and other substances. The examples of exocrine glands include
These are the glance located in the mouth. They secrete saliva which consists of the enzyme salivary amylase. This salivary amylase helps in the digestion of carbohydrates in the mouth. This also consists of lysosomal enzymes. Check the functions of saliva for more details.
Mucous is a protective layer in the gastrointestinal tract. It helps to absorb the wear and tear during the digestion of food. There are numerous mucous glands 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 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 which 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 are glands that do not have any branches in their anatomy. These types of glands include mucous secreting glands in the large intestine.
Compound exocrine glands
These glands have numerous branches in their internal anatomy. All these branches collect the secretion to pour out into the main branch. Examples of this type of gland include salivary glands.
These glands do not release their secretion outside of their body. But the blood flowing through them carries away the secretion. These secretions, then act at a quite distant part of the body from their source. They are ductless glands and their secretions are called hormones.
The entire set of endocrine glands are categorized separately as the endocrine system under 12 body systems.
Major Endocrine glands include
Pituitary Gland (of 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 gland 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 Present behind the front part of the pituitary as shown in the diagram above.
- Vasopressin (antidiuretic hormone) controls water loss from 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 name 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.
One of the hormones insulin, released enhances glucose uptake in the tissues and glycogen formation in the liver. While 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 located each on the top of a kidney. As shown in the image above, it basically is a dual gland.
a) Adrenal cortex b) 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 as 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 in the development of cell-mediated immunity.
This is secreted by the testes. 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.
Reference: Principles of Anatomy and Physiology by Gerard J. Tortora
All the glands are located in distinct locations in the human body. They regulate physiology to a large extent by receiving stimuli from the brain.
So we can notice that those glands present in the brain secrete hormones that go outside the brain and act on other glands distributed in different parts of the body. They travel through the blood to the target organs after being released.
Without their secretions, there can arise enzyme and hormone deficiency diseases.
Besides the glands, individual cells also have the ability of secretion. For example, sperms produce the Hyaluronidase enzyme. By this, they can swim in the uterine tissue to reach the ova. The other application of this enzyme is to help the drug reach the innermost tissues of the body.