The endocrine system

 

Endocrine system is a system that consists of all the endocrine glands and their secretions which are called hormones. The study of this endocrine system and associated diseases is known as endocrinology.

Let’s see what are endocrine glands.

Endocrine glands are the ductless glands that release their secretions (hormones) directly into the blood. Each hormone has got a specific job. The actions they produce in our body account for major physiological processes to happen for e.g. a hormone called thyroxin, plays vital role in metabolism. 

Endocrine glands and their secretions 

There are different types of endocrine glands which are involved in many different activities through their secretions. 

Hypothalamus is one of the main endocrine organs that is located below the thalamus and just above the pituitary gland and releases hormones which control the functioning of pituitary gland.

Pituitary gland is the master gland that controls and regulates other endocrine glands. It is located at the base of the brain.

Anterior pituitary gland releases the following hormones in the blood that regulate the secretions of other hormones such as;

• Growth hormone which is regulated by hypothalamus and proteinous in nature. It stimulates bone growth and enhances metabolism.
• Thyroid stimulating hormone (TSH) is regulated by hypothalamic hormone and thyroxine in blood. It is a glycoprotein and stimulates thyroid gland which in turn releases thyroxine in the blood.
• Adrenocorticotropic hormone (ACTH) is a peptide and regulated by hypothalamic hormones and stimulates adrenal cortex that secretes glucocorticoids. 
• Follicle stimulating hormone (FSH) is a glycoprotein and regulated by hypothalamic hormone and stimulates production of ovum and sperms.
• Luteinizing hormone (LH) is another glycoprotein hormone that is regulated by hypothalamic hormone and stimulates ovaries and testes.

Posterior pituitary gland releases some hormones in the blood that perform different functions.

• Oxytocin that is regulated by our nervous system. It is peptide in nature and controls the contraction of uterus and mammary glands.
• Antidiuretic hormone which is also known as vasopressin, is regulated by our water and salt content. It belongs to peptide class and helps kidneys to regulate water retention.

Thyroid gland is a very important gland that is regulated by TSH of anterior pituitary gland. It is located above the larynx. It releases two important hormones.

• T3 (Triiodothyronine) and T4 (Thyroxine) hormones that stimulate and maintain metabolism.
• Calcitonin is regulated by calcium level in the blood. It is basically peptide in nature and lowers the blood calcium level.

Parathyroid gland is another important gland, it is located behind the thyroid gland and releases parathyroid hormone (PTH). It raises calcium level in blood and is regulated by blood calcium level.

Pineal gland is located at epithalamus and releases melatonin in blood that adjusts sleep pattern.

Pancreas is another important gland and is located behind the stomach and releases two peptide hormones.

• Insulin that lowers blood glucose level
• Glucagon which raises sugar level in the blood.

Both of these hormones are regulated by the blood glucose.

Adrenal glands are located on top of the kidneys. 

Adrenal medulla releases two essential hormones. 

• Epinephrine and norepinephrine which are regulated by nervous system. It raises glucose level and causes constriction in blood vessels. 

Adrenal cortex releases two other hormones. 

• Glucocorticoid is steroidal in nature and raises blood glucose level under the regulation of ACTH.
• Mineralocorticoid is also steroidal in nature and regulated by level of potassium in the blood. It enhances sodium reabsorption and excretes potassium ions.

Gonads refer to male and female reproductive organs that control male and female characteristics. 

Testes is the male gonad. It is located behind the penis in the scrotum and releases 

• androgen (testosterone) which is steroidal in nature and promotes secondary sexual characteristics in male (like appearance of moustaches, change of voice etc). It releases sperms. 

Ovary is the female gonad and is located on both sides of the uterus. It secretes two important steroidal hormones.

• Estrogen is a very important hormone that is regulated by FSH and LH. It promotes secondary sexual characteristics in female. It also stimulates uterine lining growth.
• Progesterone is regulated by FSH and LH in blood. It also promotes uterine lining growth.