PITUITARY GLAND AND HORMONES:
Hormones are non- nutrient chemicals which are produced in trace amounts and act as intercellular messengers. These are responsible for regulating the biological processes in the body. First hormone was discovered by Williams M. Bayliss and Earnest H. Starling in 1903.
Properties of Hormones:
· Hormones are secreted by endocrine glands (biogenic in origin).
· Secretion of hormones is released directly into the blood. (Except local hormones i.e. gastrin).
· These are carried to distantly locate specific organs called target organ.
· Hormones have specific physiological actions (excitatory or inhibitory). These co-ordinate different physical, mental and metabolic activities and they also help in maintaining homeostasis.
· The hormones have low molecular weight, for example ADH has 600-2000 Dalton. They perform their function in very low concentration.
· Hormones are non- antigenic.
· Hormones are short lived in nature.
· Some hormones are quick acting i.e. they perform their action faster.
· Some hormones are secreted in inactive form called Pro-hormones. Eg: Pro-insulin
· Hormones are specific. They are carriers of specific information to their specific target organ. Only those target cells respond to a particular hormone.
There are following glands which are present in human body. We will discuss about pituitary gland.
· They also known as hypohysis cerebri. Its name was given by Vesaline.
· It is known as the master gland of the body which controls all other endocrine gland of the body.
· It is a sac like gland situated on the ventral side of the brain (diencephalon region).
· It is the smallest endocrine gland which plays an important role in the human endocrine system.
· It originates from the ectoderm of the embryo.
· The pituitary gland consists of three parts: Anterior, intermediate and posterior lobe.
Location and Structure:
It is reddish grey in colour and roughly oval in shape. It is about a size of pea seed. The pituitary gland is located in a small bony cavity of the brain called sella tursica.
Anatomically pituitary gland is divided into three lobes:
It is the glandular anterior portion of the pituitary gland. It further consists of two parts i.e. Pars Distalis and Pars intermedia. These two parts expressed the anterior and intermediate lobes of pituitary.
a) Pars Distalis: Also called as anterior pituitary, it produces following hormones:
i. Growth Hormone: It stimulates the somatotroph cells of anterior lobes of pituitary gland to release its growth hormone or Somatotropin which helps in stimulating the body growth, protein, fat and carbohydrate metabolism.
ii. Prolactin (PRL): It stimulates lactotroph cells of the anterior lobe of pituitary gland to secrete its prolactin. PRL regulates the growth of mammary glands and formation of milk in them.
iii. Thymus Stimulating Hormone (TSH): TSH stimulates thyrotroph cells of the anterior lobe of the pituitary gland to secrete its TSH or thyrotropic which stimulates the synthesis and secretion of thyroid hormone from the thyroid gland.
iv. ACTH (Adreno-corticotrophic Hormone): It is secreted when Adrenocorticotropin Releasing Hormone (ACRH) stimulates the synthesis and secretion of steroid hormone called glucocorticoids from the adrenal cortex.
v. Gonadotrophin Hormone: It is the gonadotroph cells of anterior lobe of the pituitary gland which secretes LH (Luteinizing Hormone) and FSH (Follicle Stimulating Hormone), both stimulates the gonadal activity hence called Gonadotrophin.
· LH in males, stimulating the synthesis and secretion of hormone called androgens from testies while in females it induce ovulation of fully mature follicle called Graffian follicle and also help in maintaining the corpus luteum formed from the remnants of the graffian follicles after ovulation. LH also known as ICSH (Interstitial Cell Stimulating Hormone) in males as it affects the interstitial cells or leydig’s cells of testes.
· FSH in males, the FSH and androgens together regulate spermatogenesis. In females, these hormones stimulate the growth and development of ovarian foliicle.
b) Pars Distalis or Intermediate lobe: It secretes only one hormone.
I. MSH (Melanin Simulating Hormone): MSH stimulates the intermediate lobe of the pituitary gland to secrete its melanocyte stimulating hormone. MSH acts on melanocytes (melanin containing cells) and regulates the pigmentation of the skin. Like MSH, MIH (Melanin Inhibiting Hormone) also secreted which inhibits the secretion of MSH.
It is a collection of axonal projections from the hypothalamus, which is terminated behind the anterior lobe of the pituitary gland. It is pars nervosa of the neurohypophysis that forms the posterior lobe of the pituitary gland which store and release two hormones.
a) Oxytocin: It is also known as Pitocin. It is a short peptide which is composed of 49 amino acid long chain. It acts on the smooth muscles of our body and stimulates a vigorous contraction of the uterus at the time of child birth. It also plays an important role in ejection of milk from the mammary gland in females.
b) Vasopressin: It is also known as Pitressin or ADH (Anti Diuretic Hormone). It acts mainly on the kidney and stimulating the re-absorption of water and electrolysis by the dorsal tubules. They reduce the loss of water through the urine which is known as diuresis.
During Parturition in mother, the secretion of oxytocin hormone is about its maximum. It is the only hormone which is responsible for causing labour pain at the time of birth of a child. So, this is also known as Birth hormone and milk ejecting hormone.
Endocrine glands are ductless glands and their secretions are known as Hormones. They are chemical messengers which are secreted in trace amounts and affects the target organ of the body.
Thyroid glands are located in our neck region and secretes thyroxine, TCT and calcitonin hormone. On the other hand Parathyroid gland is located on the posterior side of thyroid gland and release PTH.
Adrenal glands are supra-renal glands which consists of two parts; cortex and medulla which releases certain hormones to regulate the process of human body.
Gonads,testes in male and ovary in female are the reproductive glands which secretes hormones that helps in the reproduction of male and female. Testes secrete androgen, inhibin,AMF and ovary release estrogen and progesterone.
Pancreas is a composite gland which function as both exocrine and endocrine gland. The endocrine pancreas consists of islets of langerhans. Alpha cells of pancreas secretes glucagon and beta cells release insulin.
Thymus gland is a lymphoid organ that secretes the peptide hormone thymosin. Thymus gland promotes the development of specific cell of the immune system called as T- lymphocytes.
Pineal gland is an endocrine gland found in the cerrebral ventricle in the brain midline. Pineal gland release melatonin hormone which controls circadian rhythm of the body.
Hypothalamus is the basal part of the brain which contain neuro-secretory cells called nuclei These nuclei produce hormones which regulate the functioning of pituitary hormones.