• What is Endocrinology? Study of endocrine glands, hormones and their effects is called endocrinology. • Endocrine gland - Secretes hormones- Chemical messenger- stimulates or inhibits the physiological process of body or particular organ. - Hormones are proteins, peptides, steroids or amines. - Without duct, directly poured in to venous blood. • Exocrine glands - With duct, salivary, gastric , intestinal, sebaceous glands.
The pituitary gland, together with the hypothalamus forms the most important endocrine system of the body. The pituitary secretes at least nine hormones some of which are called tropic hormones, because they stimulates the secretions of other endocrine glands. • Pituitary Gland – “Master” gland – Most of the pituitary hormones control other endocrine glands – It is lodged in depression of sphenoid bone of skull – Pituitary is connected with brain by a stalk called infundibulam. Pituitary Anatomy • Symmetrical bean shaped – Brownish red • 13 mm transverse • 9 mm Anterio-Posterior • 6 mm height (Dorso-ventraly) • Adult – Average weight in adult 0.4-0.9 grams. The weight varies with age, sex and physiological stage. – Larger in women – Larger in multiparous women (women having at least one previous birth) – During pregnancy increases to 0.9- 1 grams • The pituitary is a complex organ and it ismade up of… Adenohypophysis = Anterior lobe or Pars Distalis + Intermediate lobe or Pars Intermedia.
Neurohypophysis = Posterior lobe or Pars Nervosa.
• The blood supply to the adenohypophysis comes solely from the hypophysial portal system. The hypophysial arteries and internal carotid arteries forms a network of capillaries supplying blood to the median eminence. The portal veins finally opens into the adenohypophysis.
• The pituitary gland is under hypothalamic control, the adenohypophysis is influenced by hormones which comes from the hypothalamus via the Hypothalamo-Hypophysial portal system. Neurohypophysis receives two hormones directly from certain hypothalamic nuclei for storage in the neurohypophysis. Hypothalamic releasing hormones Hypothalamic releasing hormone Effect on pituitary
Adrenocorticotropin releasing Stimulates Corticotrophs for hormone (ACTH-RH) ACTH secretion Thyrotropin releasing hormone Stimulates Thyrotrophs forTSH (TSH-RH) secretion Growth hormone releasing hormone Stimulates Somatotrophs for GH (GH-RH) or (STH-RH) secretion Somatostatin Inhibits GH (and other hormone) secretion Gonadotropin releasing hormone Stimulates Gonadotrophs for LH (Gn-RH) and FSH secretion Prolactin releasing hormone (LTH- Stimulates Lactotrophs for PRL RH) secretion Prolactin inhibiting hormone Inhibits PRL secretion (dopamine) MSH-RH Stimulates Melanotrophs for MSH Pituitary Histology • Anterior lobe – 80% of gland, peripheral cells are Basophils, Central cells Acidophils and Scattered cells Neutrophils. – Anterior lobe is Brown color – It is Connected to hypothalamus by hypophysial portal system. • Posterior lobe – It is Gray/brown color – Two neurohypophysial hormones are stored in the pars nervosa i. e. Vasopressin and Oxytocin. Pituitary Gland Microscopic • Pars distalis – Pink coloured cells are acidophils • Somatotrophs (Growth hormone) • Lactotrophs (Prolactin) – Dark purple are basophils • Corticotrophs (ACTH) • Thyrotrophs (TSH) • Gonadotrophs (FSH) • Gonadotrophs(LH) Anterior pituitary: adenohypophysis
• Anterior pituitary: connected to the hypothalamus by the superior hypophyseal artery. • The antererior pituitary is an amalgam of hormone producing glandular cells. • The anterior pituitary produces six peptide hormones: prolactin, growth hormone (GH), thyroid stimulating hormone (TSH), adrenocorticotropic hormone (ACTH), follicle- stimulating hormone (FSH), and luteinizing hormone (LH). Anterior pituitary Hypothalamic Pituitary Target Hormone product product organ product
CRH ACTH Adrenal Cortisol cortex
TRH TSH Thyroid T4, T3
GHRH (+) GH Liver; IGF-I (systemic) SRIH (-) Tissues IGF-I (local)
PRIH PRL Breast [Lactation] (dopamine)
GnRH LH, Gonad Sex hormones (LHRH) FSH Anterior Pituitary Hormones Growth Hormone (GH, Somatotropin): It is a protein with molecular wt. 45000. It contain 188 amino acids. It has direct action on cellular metabolism and activity, especially on muscles, adipose tissue, bones, cartilage and connective tissues. primary hormone responsible for regulating body growth, and is important in cellular metabolism, Promote Protein biosynthesis by increasing DNA, RNA and ribosome activity, Increase mitotic activity. Enhances the uptake of Amino acids and synthesis of Mucopolysaccharides. Retention of Blood Sugar level, retention of Na, Ca, Mg ions. Hyposecretion- Hypofunction during the early age (up to puberty) results in stunted skeletal development. They are not mentally retarded but they may be sexually immature Dwarfism/stunted skeletal development. Hypersecretion- Gigantism (Up to puberty) and Acromegaly – Overgrowth of the bones of hands, feet and particularly jaws and face. Thick face, lips, nose and eyelids (Gorilla face)(it is due to Continued Secretion after puberty) Thyroid-stimulating Hormone (TSH): It has α-chain of 96 amino acods and a β-chain of 113 amino acids stimulates secretion of thyroid hormone & growth of thyroid gland, Increase the absorption of inorganic iodine. Increases the Cyclic AMP. It controls the release of thyroid hormone from intrafollicular thyroglobulin.
Adrenocorticotropic Hormone (ACTH): stimulates cortisol secretion by the adrenal cortex & promotes growth of adrenal cortex, Increase the Cyclic AMP. ACTH increases adenyl cyclase activity. Hypersecretion resuted in Cushing’s Disease (Obesity of Trunk, Face, Hands and Feet, High boold pressure, mood disorders, Hump, No erect posture) Gonadotrophic hormones or Gonadotrophins Follicle-stimulating Hormone (FSH): Females: stimulates growth & development of ovarian follicles, promotes secretion of estrogen by ovaries. Males: required for growth of testis and sperm production by spermatogenesis Luteinizing Hormone (LH): Females: responsible for development of ovarian follicle, ovulation (by combine action of FSH and LH), Regulation of Menstrual cycle, formation of corpus luteum in the ovary, and regulation of ovarian secretion of female sex hormones. Males: It is called ICSH (Interstitial cells Stimulating Hormone) stimulates the Leydig’s cells in the testes to secrete testosterone. Prolactin: Females: Estrogen and Progesterone stimulates breast development by the proliferation of mammary gland cells during pregnancy - Prolactin is responsible for lactation (milk production) with the help of thyroid hormone. -Lactation does not occur normally and even during pregnancy. It is because prolactin secretion is Inhibited by Prolactin Inhibiting Hormone (PrIH). - After parturition (labour pain and expusion of placenta) stimulates the prolactin secretion and Suckling of baby lifts the inhibition form hypothalamus. Suckling also stimulates the secretion of Oxytocin. Pars Intermedia hormone: • Pars intermedia is a part of adenohypophysis. In,human parsintermedia form only 2% of the hypophysis. It secretes Melanocyte Stimulating Hormone (MSH). • There are two chains of MSH. α-chainis of 13 amino acids. While β-chain has 22 amino acids. • MSH is responsible for synthesis of melanin pigments. In vertebrtaes it affects upon the dispersion of melanin pigments in chromatophores and darkning of skin (colour Change) of the skin takes place. • Corticosteroids inhibits the secretion ofMSH. Epinephrine and nor-epinephrine inhibits the actionof MSH. Posterior Pituitary: neurohypophysis
• Posterior pituitary: an outgrowth of the hypothalamus composed of neural tissue. • Hypothalamic neurons pass through the neural stalk and end in the posterior pituitary. • The upper portion of the neural stalk extends into the hypothalamus and is called the median eminence. The Posterior Pituitary Secretion of Posterior Pituitary Hormones: Oxytocin • Is synthesized as the precursor hormone:prepro-oxyphysin. • Acts primarily on the mammary gland and uterus. It causes dilation of smooth muscle of the uterus and vagina for parturition. i.e. expulsion of foetus and placenta. • Oxytocin secreted as labour pain starts (Inhibits the placental progesteron secretion). • It is also called Milk Ejection Hormone because it causes contraction of myoepithelial cells of the mammary glands. Prolactin secretion starts after parturition since the prolactin inhibitary harmone secretion of hypothalamus stoped. Suckling of the baby generates afferent impulses which stimulate the prolactin secretion. Vasopressin (ADH) Is also known as Antiduretic Hormone (ADH) Participates in body water regulation (Water is lost from lungs, sweat, feces and urine on a daily basis). Plasma osmolality is monitored by osmoreceptors in the hypothalamus Increases in plasma osmotic pressure stimulates secretion of vasopressin. It increases the reabsorption of water form renal tubules. It increases blood pressure, constriction of coronary vessels, effect on the muscles of urinary bladder andureter. Feedback Regulation of Anterior pituitary hormones
TSHRH
TSH Thyroxin hormone
Thyroid gland Feedback Regulation of Oxytocin Feedback Regulation Of ADH
ADH
Osmatic pressure