Glands:Pituitary and thyroid gland

Glands are the groups of specialized cells that produce some chemical substance needed in Metabolic processes of the body. 

TYPES OF GLANDS: 

1)EXOCRINE GLAND: 

The glands whose secretion are carried by ducts into the site of action is known as exocrine gland.They are present near the site of action of their secretions. They produce enzyme. Eg:Pancreas,Salivary gland 2)ENDOCRINE GLAND: The ductless glands whose secretion are directly poured into the blood is known as endocrine gland.They are present at sites distant from sites of action of their secretion.They produce hormones.Eg:Pituitary gland,Thyroid gland etc. The main function of endocrine system is to maintain homeostasis withe the help of autonomic nervous system. 

ENDOCRINOLOGY: 

The study of endocrine glands and its secretion is known as endocrinology. THOMAS EDDISON is regarded as Father of Endocrinology. HORMONES: Hormones are the chemical messengers secreted by endocrine glands that are circulated in blood and act on specific target cells to bring about the biological effect. 

TYPES OF HORMONES: 

1)AUTOCRINE HORMONE: 

Hormones that act on the cells secreting it is called autocrine hormone. Eg:Platelet activating factor 2)PARACRINE HORMONE: Hormones that act on the cell adjacent to the cell secreting it is called paracrine hormone; also called local hormones. Eg:gastrin,secreted by G cells act on the parietal cell of the stomach to secrete HCl. 

CHEMICAL CLASSIFICATION OF HORMONE: 

1)AMINE HORMONES: Derived from amino acid tryosine.Eg:Thyroid hormone, epinephrine, norephinephrine,dopamine 

2)STEROID HORMONE: Derived from cholesterol.Eg:Sex hormone and adrenal cortex hormones 3)PEPTIDE HORMONE: Eg:pancreatic hormone,pituitary hormone,parathyroid hormone,calcitonin

TYPES OF ENDOCRINE HORMONE: 

1)PITUITARY GLAND/HYPOPHYSIS: Pituitary gland is a small pea shaped,reddish grey endocrine gland that lies at the base of the brain below hypothalamus.It is also known as master gland as it controls activities of almost all endocrine gland and effect metabolism of somatic gland.Pituitary gland is connected to the base of hypothalamus by a small stalk called pituitary infundibulum.Pituitary gland along with hypothalamus is known as hypophysis as it lie in hypophoseal fossa of sphenoid bone.It consists of three parts: 

a)ANTERIOR LOBE: It is important part of Pituitary gland which secrete eight different hormone that stimulate the glands.

HORMONES SECRETED BY ANTERIOR LOBE: 

i)FOLLICLE STIMULATING HORMONE(FSH): FSH stimulate the development and maturation of ovarian follicles which produce egg in female and promote spermatogenisis in male. 

ii)LEUTINIZING HORMONE(LH): LH stimulate ovulation,formation of corpus luteum and production of secondary growth hormonei.e progesterone and oestrogene. In male,LH is known as interstitial cell stimulating hormone(ICSH).It stimulate interstitial cell of testis and produce testerone.

iii)PROLACTIN HORMONE(PH): It stimulates lactation(milk production) in female. iv)ADRENOCORTICOTROPHIN HORMONE(ACTH): It stimulate adrenal cortex and produce adrenocorticosteroid hormone. 

v)THYROOXINE OR THYROID STIMULATING HORMONE(TSH): It stimulate thyroid gland. vi)GROWTH STIMULATING HORMONE OR SOMATROPHINE: It stimulate growth hormone.Deficiency of it causes Dwarfism in child and hypersecretion leads to gigantism in child and Acromegaly in adult. 

b)INTERMEDIATE LOBE: It arises from connective tissue.

 i)MELANOCYTE STIMULATING HORMONE: It stimulate pigmentation of skin. 

C)POSTERIOR LOBE: It is down growth of nervous tissue of hypothalamus.It collects the hormone secreted by neurosecretory cells of hypothalamus. i)OXYTOCIN: It causes contraction of smooth muscle during child birth.It also stimulate milk from mammary gland. ii)VASOPRESSION/ANTIDEURETIC HORMONE(ADH): Stimulate water reabsorption by kidney which also cause blood pressure by constructing arterioles.Hyposecretion of ADH leads to Diabetis insipidus characterized by frequent urination. 

NOTE: Hyposecretion of GH along with LH and FSH cause Frohlich Syndrome. 

2)THYROID GLAND: Thyroid gland is the largest endocrine gland of human body located below thyroid cartilage and on the lateral side of larynx at the level of 5th,6th,7th cervical vertebrae and 1st thoracic vertebrae. It is butterfly shaped or bow tie in shape. The two lobes are joint at the center of trachea by thin stipes of connective tissue called Isthmus. Each lobe is 5cm long and 3 cm in wide and covers externally by fibrous capsule. It received blood supply from superior and inferior thyroid artery which are the branches of subclavian artery and superior artery whereas the blood is carried away by thyroid vein which open into internal jugular vein. It weighs about 25-40 gm. The Transverse section of thyroid gland shows that it is made up of follicles of different shape, sizes and number. Follicles are formed due to inward invagination of inter lobular connective tissue. Each follicles are lined by single layer of cuboidal epithelium or follicular cells. Follicle stores thyroglobuline i.e combination of thyroid hormones and proteins. In between the follicles,group of special cell known as parafollicular or C-cell are present.These cell secrete the hormone calcitonine.Calcitonine along with parathormone(PTH) maintains phosphate and calcium level of blood.This two hormone acts opposite to each other.Calcitonin decrease the blood calcium level whereas parathormone increase the blood calcium level. The secretion of thyroid hormone begins from the 3rd month of pregnancy(12 weeks)and increases during puberty whereas rest of life it remains constant.The secretion of thyroid hormone is under the control of negative feed back mechanism.Iodine is essential for the formation of thyroid hormone as well as non essential amino acid such as thyroxine. HORMONES OF THYROID GLAND: The follicular cell of thyroid gland secrete two important hormone i.e T3 and T4.The function of both the hormones are same. 

FUNCTION: a)It regulates the Basal metabolic rate(BMR). b)It also regulate normal mechanism of carbohydrate,protein and fat. c)It promote gluconeogenesis. d)it also control tissue differentiation. e)It is responsible for normal functioning of cardio vascular and nervous system. f)in frog ,it controls metamorphosis. g)it regulates heat production. h)It increases mental agility. i)It also increases the permeability of renal tube for the absorption of amino acid and iodine. j)It also increases the absorption of iodine from gastro intestinal tract. 

HYPERSECRETION: A)EXOLPTHALMIC GOITRE'S OR GRAVE'S DISEASES: Due to excessive metabolism as a result of hypersecretion,the fats are deposited in adipose tissue behind the eye ball i.e in eye socket.The eye balls are protruded outside.In extreme cases,it is very difficult for patient to close the eyelid completely.As a result the conjuctiva of eye dries out and the eyes are prove to secondary eye infection. 

HYPOSECRETION: A)CRETINISM: In young or children,hypothyroidism causes retardation of physical,mental and sexual development.This condition is known as cretenism. B)MYXOEDEMA: it is characterised by pecular thickening and puffiness of the skin along with the thickening of sub cutaneous tissue,particularly on the face and at the extremities. C)SIMPLE GOITRE: This is the enlargement of thyroid gland.This enlargement results in the swelling of the neck which is called simple goitre.It is caused by the difficiency of iodine. D)AMENARRHOE: Human suffering from hypothyroidism also suffer from cessation of menstruation or scanty menstruation.This is called amenorrhoe disease.hypothyroidism in animals often lead to infertility.