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Transcript
PT-RN-Human Biology Endocrine System: Overview • Endocrine system – the body’s second great controlling system which influences metabolic activities of cells by means of hormones • Endocrine glands – pituitary, thyroid, parathyroid, adrenal, pineal, and thymus glands Basic Concepts of Endocrine System • The pancreas and gonads produce both hormones and exocrine products Dr. C.H. Lai • The hypothalamus has both neural functions and releases hormones 28-01-10 Endocrinology • The study of hormones • Other tissues and organs that produce hormones – adipose cells, pockets of cells in the walls of the small intestine, stomach, kidneys, and heart Hormones Hormones may be defined as • Chemical substances that are secreted by living cells • Released in small quantities into the blood, and upon delivery by the circulation to a specific site of action • Act to regulate reactions that elicit a typical response Hormones Hormones • This is endocrine action • Other modes of action include paracrine (acting on adjacent cells) and neurocrine (secreted at nerve endings) Chemical Natures of Hormones Mechanisms of Hormone Actions • Proteins and peptides (e.g. insulin, posterior pituitary hormones, hypothalamic releasing hormones, and GI hormones) • Amines (e.g. adrenaline, thyroxine) • Alter plasma membrane permeability • Steroids (e.g. adrenal corticosteroids, androgens, estrogen) • Activate or deactivate enzyme systems Hormones produce one or more of the following cellular changes: • Stimulate protein synthesis • Induce secretory activity • Stimulate mitosis Location of the Major Endocrine Glands • The major endocrine glands include: • Pineal gland, hypothalamus, and pituitary Pituitary Gland Pituitary (hypophysis) – attached to the hypothalamus by infundibulum • Anterior (adenohypophysis) • Posterior (neurohypophysis) • Thyroid, parathyroid, and thymus • Adrenal glands and pancreas • Gonads – male testes and female ovaries The Anterior Pituitary Hormones • Many of the hormones secreted are trophic hormones that control the secretion of other endocrine glands. • Excess trophic hormone can cause hypertrophy of target gland. • Insufficient amounts can cause atrophy of target gland The Anterior Pituitary Hormones • The six hormones of the anterior pituitary gland : • Growth hormone (GH) • Thyroid-stimulating Hormone (TSH) • Adrenocorticotropic Hormone (ACTH) • Luteinizing Hormone (LH) • Follicle-stimulating Hormone (FSH) • Prolactin (PRL) • Regulate the activity of other endocrine glands The Anterior Pituitary Hormones • GH – promotes movement of amino acid into cells. • TSH – stimulates thyroid to secrete T4. • ACTH – stimulates adrenal cortex to secrete glucocorticoids. • FSH – stimulates growth of follicles or production of sperm. • LH – stimulates ovulation and growth of corpus luteum or secretion of testosterone. The Anterior Pituitary Hormones Growth hormone (GH) • Stimulates bone growth • Increases protein synthesis • Stimulates gluconeogenesis, decreases utilization and uptake of glucose • Increase lipolysis (breakdown of fat) GH • PRL – stimulates milk production & … Endocrine Disturbances of Growth and Development Dwarfism Giantism Enlarged hand of the same patient in comparison with the hand of an adult male with a height of 6'1". Twelve-year-old boy with pituitary gigantism measuring 6'5" with his mother. Note the coarse facial features and prominent jaw. Endocrine Disturbances of Growth and Development Acromegaly (adult) The Anterior Pituitary Hormones Thyroid-stimulating Hormone (TSH) • TSH stimulates the synthesis and secretion of thyroid hormones from the thyroid The Anterior Pituitary Hormones Adrenocorticotropic Hormone (ACTH) • ACTH stimulates the synthesis and secretion of cortisol from the adrenal cortex The Anterior Pituitary Hormones The Anterior Pituitary Hormones Gonadotrophins Gonadotrophins: FSH Luteinizing Hormone (LH) Follicle-stimulating Hormone (FSH) In female: • Promotes the development of the follicles in the ovary In male: • Stimulates the formation and maturation of sperms in the testis The Anterior Pituitary Hormones Gonadotrophins: LH In female: • Involved in the maturation of follicles in the ovary • Stimulates the secretion of estrogens The Anterior Pituitary Hormones Prolactin (PRL) • It stimulates and maintains lactation after estrogen and progesterone priming and reduces the responsiveness of the gonads to gonadotrophins • Stimulates the secretion of progesterone from the corpus luteum In male: • Stimulates the secretion of testosterone from the Leydig cells of the testis The Anterior Pituitary Hormones Hypothalamus / Pituitary Gland The hypothalamic releasing hormones regulate the synthesis and release of anterior pituitary hormones. Hypothalamus / Pituitary Gland Hypothalamus / Pituitary Gland • Anterior pituitary control is regulated by negative feedback by two methods: • The target gland hormone can act on the hypothalamus and inhibit secretion of releasing hormones. • The target gland hormone can act on the anterior pituitary and inhibit response to the releasing hormone. GHIH PIH, dopamine Hypothalamus / Pituitary Gland Posterior Pituitary Hormones Posterior Pituitary Hormones • Oxytoxin and vasopressin are synthesized in the hypothalamus and transported down the axons to the posterior pituitary via axons of the hypothalamohypophyseal tract Posterior Pituitary Hormones Antidiuretic hormone (ADH, vasopressin). • Antidiuretic action, increases water reabsorption in the distal tubules and collecting ducts in the kidney • Pressor action, increases blood pressure by vasoconstriction Posterior Pituitary Hormones PT-RN-Human Biology Oxytocin • Effect on milk ejection - Causes contraction of the myoepithelium of the breast • Effect on the uterus Thyroid & Parathyroid Glands - Causes contraction in parturition Dr. C.H. Lai Thyroid Glands Thyroid Glands • Consists of 2 lateral lobes joined by a thin isthmus, on either side of the trachea Thyroid Glands • Composed of follicles with colloid (thyroglobulin) in the lumen Thyroid Hormone (Thyroxine) Physiological Effects Colloid (1) ↑ Basal metabolic rate and growth (2) Carbohydrate metabolism • ↑ Peripheral utilization of glucose (glycolysis) • ↑ Glycogen breakdown • ↑ Gluconeogenesis (amino acids, glycerol or lactate to glucose/glycogen) • ↑ GI glucose absorption Thyroid Hormone (Thyroxine) (3) Heart contraction Thyroid Hormone (Thyroxine) (5) Temperature regulation (4) Central nervous system • ↑ Heat production (↑ Cellular activities) • Essential for the normal development within the critical period (first year of life). • Important for response to cold • Hyperthyroidism → hyper-excitability, irritability, restlessness • Hypothyroidism → listlessness, lack of energy, decrease sensory capacity Diseases of the Thyroid Diseases of the Thyroid • Hypothyroid – too little hormone secreted • Goiter – caused by lack of iodine TSH is a trophic hormone, it stimulates not only T3/T4 secretion but also protein synthesis in follicular cells. Therefore, ↑ exposure in thyroid ↑ size Diseases of the Thyroid Hyperthyroid – too much hormone secreted. • Graves’ disease – Diseases of the Thyroid Hyperthyroid – Graves’ disease • Autoantibodies that mimic TSH overstimulate thyroid. • Produces high BMR, irritability, weight loss, exophthalmos. Thyroid Glands Calcitonin – • Secreted by the parafollicular cells (C-cells) of the thyroid gland • Blocks osteoclast activity • Decrease the formation of 1,25 (OH)2 Vit. D (in kidney) Swelling within the orbital cavities and enlargement of the perorbital muscles behind the eyes Thyroid Glands : Calcitonin Calcitonin – • Acts as an antagonist to parathyroid hormone (PTH) Parathyroid Glands Parathyroid Glands Parathyroid glands – embedded in posterior surface of thyroid • Secretes parathyroid hormone (PTH). • Increases serum calcium levels by: − Stimulating osteoclasts to resorb bone − Reabsorption of Ca++ by kidneys − Blocks reabsorption of phosphate by kidneys − Promotes production of 1, 25-dihydroxyvitamin D3 PTH (parathormone) PTH • Causes bone resorption through rapid formation of new osteoclasts and transient depression of osteoblasts •Osteoclasts are for bone resorption and osteoblasts are for bone formation) PTH Resorption of bone by osteoclasts PTH PT-RN-Human Biology • Increases kidney calcium reabsorption and decreases phosphate reabsorption Adrenal Gland Dr. C.H. Lai • Increases the formation of the active form of vitamin D to increase GI calcium and phosphate absorption Adrenal Gland • The adrenals (suprarenals, in human) lie above the kidneys Adrenal Gland Adrenal Cortex • The outer cortex is made up of 3 zones: zona glomerulosa (secretes aldosterone), z. fasciculata and z. reticularis (secrete cortisol & androgens) Adrenal Cortex Aldosterone Functions Adrenal Cortex: Aldosterone Functions • Increases the reabsorption of sodium in the distal tubules and hence excretion of potassium and hydrogen ions • Increase in sodium reabsorption results in increase in water reabsorption, hence increase in blood volume Cortisol Functions • Carbohydrate - ↑ gluconeogenesis (from amino acids) - ↓ glucose utilization & uptake - too much leads to ↑ blood glucose • Protein - ↓ protein synthesis (except liver), ↑ protein breakdown. • Fat (triglycerides) - ↑ lipolysis (permissive). Cortisol Functions Cortisol Metabolic effects of glucocorticoids • Response to stress – source of energy, synthesis of new proteins, maintenance of blood pressure • Anti-inflammatory action Cortisol Regulation of Secretion • CRH stimulates ACTH synthesis/ secretion, and ACTH stimulates cortisol synthesis/secretion • Negative feed-back – by free circulating cortisol • Stress stimulates • Diurnal rhythm – high in the morning, low in the evening. Adrenal Cortex: Hyper Secretion e.g. Cushing's Syndrome Adrenaline & Noradrenaline Adrenal Gland Adrenal medulla Hormones Actions • Adrenaline & noradrenaline (also from sympathetic nerve endings) (1) Heart contraction, vasoconstriction (alpha), vasodilation (beta 2) Receptors (2) Metabolism - glycogenolysis (liver/muscle), lipolysis • Adrenaline- equally on alpha & beta receptors (3) Contraction of smooth muscles • Noradrenaline- mainly on alpha, also on beta 1 (heart) Regulation of Secretion (1) Sympathetic nervous system (2) Stress PT-RN-Human Biology Pancreatic Hormones Insulin / Glucagon Pancreatic Hormones & Glucose Metabolism Dr. C.H. Lai • Both are peptide hormones secreted by the pancreas; insulin by beta cells and glucagon by alpha cells Pancreatic Hormones Pancreatic Hormones Insulin (1) Physiological effects • Increases the uptake of glucose by muscle, adipose tissue (transporters), and liver, increases glycolysis - Excess is converted to glycogen or fat Pancreatic Hormones Glucagon (1) Physiological effects • Increases blood glucose levels by increasing glycogenolysis and gluconeogensis • Increases lipolysis • Decreases gluconeogenesis (in liver) • Decreases blood glucose level • Increases lipogenesis in the liver and decreases lipolysis in the adipose tissue • Increases protein synthesis Regulation of Insulin and Glucagon Secretion Diseases of the Pancreas Diseases of the Pancreas Diabetes mellitus • Two types: insulin dependent or non-insulin dependent; due to lack of insulin secretion or response to insulin, leading to hyperglycaemia (increase in blood glucose) • Hyperglycemia – high plasma [glucose] • IDDM (type I) – β cells do not secrete insulin. May be an autoimmune disorder. Hyperglycemia and glycosuria occur. Requires insulin injections. • NIDDM (type II) – β cells decrease insulin output and/or cells become resistant to insulin (e.g. downregulate receptors). Hyperglycemia but not glycosuria (except severe cases). Treated with oral pancreatic stimulators and/or drugs that decrease insulin resistance Diabetes Mellitus (DM) Diseases of the Pancreas • Hypoglycemia - low plasma [glucose] • If plasma [glucose] drops too low, coma develops.