Endocrine glands are also known as ductless glands of the endocrine system. Its product hormone is secreted directly into the blood. The major glands of an endocrine system are the pineal gland, pituitary gland, pancreas, ovaries, testes, thyroid gland, parathyroid gland, hypothalamus, and adrenal gland.
Two types of hormones are released by the hypothalamus i.e. releasing hormones and inhibiting hormones. One of the hypothalamus hormones commonly known as gonadotropin-releasing hormones stimulates the total synthesis and release of gonadotropins. The other hormone-like somatostatin which is released from the hypothalamus inhibits the release of growth hormone from the pituitary gland.
The pituitary gland is present in the bony cavity known as Sella turcica and gets attached to the hypothalamus with the help of a stalk. It is divided into two parts: adenohypophysis and neurohypophysis. Pars distalis and pars intermedia are the parts of the adenohypophysis. The pars distalis is commonly known as the anterior pituitary which produces the growth hormones prolactin, thyroid-stimulating hormone, adrenocorticotropic hormone, luteinizing hormone, and follicle-stimulating hormone. The pass intermedia releases only one hormone which is known as a melanocyte-stimulating hormone. In human beings neurohypophysis is called the posterior pituitary which releases two hormones namely; oxytocin and vasopressin.
The pineal gland is placed in the dorsal part of the forebrain. It secretes and regulates the production of the hormone melatonin. Melatonin regulates the 24-hour rhythm of our body. It maintains our wake and sleep cycle and body temperature. Is also responsible for pigmentation, menstruation cycle and defense capability.
The thyroid gland consists of two lobes which are located on the side of the trachea. Both the loads are connected with a flap-like structure of connective tissue known as the isthmus. The thyroid gland is made up of follicle and stromal tissue. It releases hormones like Tetraiodothyronine or thyroxine (T4) and triiodothyronine(T3). Deficiency of iodine results in hypothyroidism which is commonly known as goiter. If goiter develops during pregnancy, it can cause abnormal development of the baby which can lead to cretinism, mental retardation, abnormal skin, etc. Thyroid glands also produce a protein hormone called thyroid calcitonin which helps to regulate the blood calcium level in the body.
The parathyroid gland is present behind the thyroid gland. In humans, 4 thyroid glands are present. It secretes a peptide hormone called the parathyroid hormone which is regulated by the level of calcium iron. This hormone is responsible for the calcium level in the blood. Parathyroid gland increases the blood calcium level and also helps to stimulate the absorption of calcium by renal tubules.
The thymus is present between the lungs and the backside of the sternum. This lobular structure plays a major role in the growth of the immune system. It's equipped with a hormone called thymosin which helps in the development of T lymphocytes. You must have noticed that the immune system of old people becomes weak. It happens because in older individuals thymus is degenerated which results in the decreased production of thymosin.
The adrenal gland is present in the anterior part of the kidney. It is composed of two types of tissue commonly known as the adrenal medulla and adrenal cortex. The hormones released are known as adrenaline or epinephrine and noradrenaline or norepinephrine. These two hormones are also known as catecholamines. Adrenaline and noradrenaline are known as emergency hormones or hormones of flight. The donor cortex is divided into three layers zona reticularis, zona fasciculata, and zona glomerulosa. The adrenal cortex releases the hormone which is known as corticoids.
Pancreas act as both exocrine and endocrine gland. The endocrine pancreas is made in Iceland of Langerhans. There are nearly 12 2 million isolates of Langerhans in the human pancreas. The two types of a cell present in Iceland are Langerhans which are known as Alpha cell and Beta cells. The Alpha cells secrete a hormone which is known as glucagon and beta cells secrete insulin.
Glucagon is commonly known as a peptide hormone that helps to maintain the normal blood glucose level in the body. Glucagon acts on a living cell which results in increased blood sugar levels called hyperglycemia. Insulin is another peptide hormone which helps in decreasing blood glucose level which is known as hypoglycemia. Insulin also converts glucose to glycogen which is known as the glycogenesis process. If a person has a loss of glucose through urine and a formation of ketone bodies then the person suffers from the disease called diabetes mellitus. This is cured by insulin therapy.
The testis is the part of the male reproductive system and is present as a pair in the scrotal sac. It is a primary sex organ in males and also acts as an endocrine gland. It is made up of seminiferous tubules and interstitial tissues. This gland will have a hormone called androgen and testosterone. Androgen helps in maturation of male accessory sex organs, growth of facial hair, low pitch of voice.
Females have a pair of ovaries which are located in the lower abdomen. The ovary is a female sex organ that produces ovum during each mensuration cycle. Ovaries produce the hormones estrogen and progesterone. It is made up of ovarian follicles and stromal tissue. Estrogen helps in the growth and activities of female secondary sex organs, the appearance of female secondary sex characteristics, development of mammary gland, etc. Progesterone helps in pregnancy. This hormone acts on the mammary gland and leads to the formation of alveoli and milk secretion.