What are glands? Describe different types of glands and their function in the human body?

Glands:

Glands are an organ that synthesizes and release some substances/chemicals directly in the blood (endocrine) and inside body, into cavities (exocrine) that perform a specific function in the body. Glands are located throughout the body.

Based on the type of secretion, glands are divided into two categories-

1.       Exocrine glands

2.      Endocrine glands

1.      Exocrine glands:

Exocrine glands release their product into a duct. e.g., the salivary gland release saliva into the salivary duct. They release into an area of the body by a duct and their secretions are called enzymes (Generally though some are non-enzymes).

·         Type of exocrine glands

It includes:

·      Salivary gland:  Secrete saliva in the buccal cavity of the mouth. This saliva has many functions such as its actions about taste, chewing, bolus formation, enzymatic breakdown, and swallowing.

·    Pancreas: It secretes enzyme lipase, trypsin & amylase. These enzymes digest proteins, fats & carbohydrates individually.

·        Testes: Testes produce sperm and sperms produce an enzyme known as Hyaluronidase, which helps the sperm to swim in the uterine tissue to reach ova.

·         Sweat glands: It secretes sweat which controls body temperature and excretion.

·     Sebaceous gland: It is an oil secreting gland in the body. This is also known as oil glands. The function of this gland is to secrete sebum (a mixture of fatty substances).

·       Lachrymal glands: This is a paired exocrine gland. It secretes a layer of tear film to moisturize the eye.

2.     Endocrine glands:

Endocrine glands are the glands that release their products directly into the bloodstream. There are no ducts present in the endocrine system. The endocrine system regulates the body functions including metabolism & growth by secreting hormones. When glands release an inappropriate amount of hormones, it causes endocrine ailments. Endocrine glands are also known as ductless glands and their secretions are known as hormones. These hormones act as a messenger between body organs and nervous system. The nervous system controls the operation of the endocrine system.

·         Type of endocrine glands: -

The endocrine glands present in the body are the hypothalamus gland, thyroid gland, parathyroid gland, pituitary gland, thymus, pineal gland, pancreas, testes, ovaries and adrenal gland.

Details of some major endocrine glands are mentioned below: -

1.    Hypothalamus: This gland is located in the brain and produces releasing & inhibitory hormones. It regulates the secretion of hormones from pituitary glands.

2.   Pituitary Gland: This gland is situated just below the hypothalamus in the brain and releases different hormones. The gland is distinguished as anterior & posterior gland and both have certain secretions i.e.

a.   Anterior pituitary gland: This is located in the front portion of the pituitary gland. It releases several hormones i.e.-

·     Prolactin: It causes the breast to grow and develop and stimulates milk production in mothers.

·   Somatotropin (Growth hormone): This hormone regulates the growth of the body and all tissues, including bones.

·   Luteinising hormone (LH): Produced by gonadotropic cells in the anterior pituitary and stimulates ovulation (egg formation) & development of corpus luteum in females and testosterone production in males.

·         Follicle-stimulating hormone (FSH): It is also secreted by gonadotropic cells of the anterior pituitary gland and regulates growth, development, pubertal maturation & reproductive process of the body. It also signals the development of estrogen and progesterone by the female reproductive system.

·   Thyroid-stimulating hormone (TSH): This is also known as a thyrotrophic hormone, thyrotropin. This hormone stimulates the thyroid gland to produce T3 & T4 hormones. The function of this hormone is to control, the metabolism rate of proteins, fats and carbohydrates.

·    Adrenocorticotrophic hormone (ACTH): This is produced and secreted by the anterior pituitary gland. It stimulates the adrenal cortex & secretion of glucocorticoids & mineralocorticoid hormones.

b.        Posterior pituitary gland:

Posterior pituitary gland functionally connected to the hypothalamus by a small tube called a pituitary stalk. This gland produces two types of hormones i.e. vasopressin and oxytocin. These both hormones released when hypothalamus send signals to the pituitary gland by the nerve cell.

·        Vasopressin: It is also known as Antidiuretic hormone (ADH).  It controls water loss from kidneys to maintain osmolality and maintain water volume in the extracellular fluid (ECF.

·         Oxytocin: It stimulates the uterine muscle to contract which signals uterus for delivery in pregnant women. It also stimulates milk secretion in mother. It also releases when peoples snuggle or bond socially so, it is also known as the love hormone.

3.      Thyroid gland: This is a butterfly-shaped organ located on the neck base. The thyroid gland is attached to the windpipe and produces thyroid hormones T3 & T4. These hormone control metabolism rates.

4.      Parathyroid gland: This is situated on behind of thyroid gland. It is four small glands of the endocrine system and regulates & monitor blood calcium level in our body. It makes a parathyroid hormone (Parathormone) which helps in the regulation of calcium in the blood.

5.      Adrenal gland: This is also known as a suprarenal gland. Adrenal glands are situated at the top of the two kidneys. It consists of an outer cortex and inner medulla regions. This gland secretes a variety of adrenal hormones that regulate breathing rate, heart rate, blood pressure, blood pressure (BP) and carbohydrate metabolism. These hormones are secreted in large quantity when a person is excited or frightened so, this gland is also known as a gland of emergency.

Cortex part of the adrenal gland secretes glucocorticoids and mineralocorticoids whereas Medulla secretes adrenaline & noradrenaline. This is a neurotransmitter also called flight or fight hormone.

6.    Pancreas: This is present just below the stomach. The pancreas has both exocrine and endocrine functions. It secretes numerous hormones that control body glucose metabolism. Its endocrine function release secretions like insulin, glucagon, somatostatin.

7.      Kidneys: These are two bean-shaped organs in the renal system. They help to filter the blood before sending it back to the heart. They also help the body to pass waste product and maintain overall fluid balance. They also produce Renin-angiotensin enzyme which controls blood pressure.

8.   Pineal gland: It is a small pea-shaped gland located inside the brain and also known as the body natural clock. It regulates and produces melatonin (Sleep hormone) hormone which regulates sleep patterns.

9.  Testes: It is a pair of sperm-producing organs that maintain the male reproductive system. The hormone secreted by testes is testosterone. This hormone is secreted by Leydig cells present at adjacent to seminiferous tubules in the testicle. Testosterone produced in males to the large amount and very small amount in women.

10.  Ovaries: ovaries are the main female reproductive system. It produces estrogen and progesterone. These hormones are secreted only in women and regulate reproduction cycle. They also promote the development of female sex characteristics during puberty and confirms fertility.

All the glands are situated in different locations in the human body. They control the physiology to a large degree by getting stimulus from the brain. Glands present in the brain, secrete hormones which go outside the brain and function on other glands that are distributed in diverse parts of the body. They also travel through the blood and reach to target organs after being released.