The Endocrine System

Introduction Second messenger system of the body Hormones control several major processes Reproduction Growth and development Mobilization of body defenses Maintenance of much of homeostasis Regulation of metabolism

Hormones Cells secrete hormones into extracellular fluids Blood transfers hormones to target sites These hormones regulate the activity of other cells Steroid Hormones- derived from cholesterol, sex hormones, adrenal cortex hormones Ex. Estrogen, testosterone. Cortisol. Nonsteroid Hormones- amines, proteins, peptides, glycoproteins, most hormones Ex. OT, FSH, TSH

Steroid Hormone Action Diffuse through the plasma membrane of target cells Enter the nucleus Bind to a specific protein within the nucleus Bind to specific sites on the cell’s DNA Activate genes that result in synthesis of new proteins

Nonsteroid Hormones Hormone binds to a membrane receptor Hormone does not enter the cell Sets off a series of reactions that activates an enzyme Catalyzes a reaction that produces a second messenger molecule Oversees additional intracellular changes to promote a specific response

How are they Released

Major Glands

Pituitary Gland Size of a grape Hangs by a stalk from the hypothalamus Protected by the sphenoid bone Has two functional lobes Anterior pituitary – glandular tissue Posterior pituitary – nervous tissue

Anterior Pituitary Hormones Growth Hormone (GH)- stimulates increase in size and rate of body cells, enhances movement of amino acids through membranes, promotes growth of long bones, secretion inhibited by somatostatin, secretion stimulated by growth hormone-releasing hormone Prolactin (PRL)- sustains milk production after birth, amplifies effect of LH in males, Thyroid Stimulating Hormone (TSH)- controls secretions of hormones from the thyroid gland,

Cont…….. Adrenocorticotropic Hormone- controls secretions of some hormones of adrenal cortex, Follicle-Stimulating Hormone (FSH)- stimulates development of egg-containing follicles in ovaries, stimulates follicular cells to secrete estrogen, stimulates production of sperm cells, controlled by gonadotropin-releasing hormone Luteinizing Hormone (LH)- promotes secretions of sex hormones, stimulates release of egg from ovary, promotes growth of long bones, controlled by gonadotropin-releasing

Posterior Pituitary Hormones Antidiuretic Hormone (ADH)- causes kidneys to reduce water excretion, in high concentration, raises blood pressure, controlled by hypothalamus in response to changes in blood water concentration and blood volume Oxytocin (OT)- stimulates uterine contractions, stimulates mammary glands to release milk, controlled by hypothalamus in response to stretch in uterine and vaginal walls and stimulation of breasts

Overview

Thyroid Hormones Thyroxine (T4) and Triiodothyronine (T3)- increases rate of energy release from carbohydrates, increases rate of protein synthesis, accelerates growth, stimulates activity in the nervous system, controlled by TSH Calcitonin- lowers blood calcium and phosphate ion concentrations by inhibiting release of calcium and phosphate from bones, increases rate at which calcium and phosphate are deposited in bones

Thyroid Disorders General Hyperthyroidism high metabolic rate, hyperactivity, weight loss, protruding eyes Cretinism- hypothyroidism in infants, leads to small stature and mental retardation Myxedema- adult hypothyroidism, low metabolic rate, sluggishness

Parathyroid Hormone PTH- increases blood calcium levels, decreases blood phosphate levels, stimulates bone resorption by osteoclasts, inhibits osteoblasts, stimulates kidneys to retain calcium and excrete phosphate, promotes calcium absorption into intestine Disorders: Hyperparathyroidism- caused by tumor, fatigue, muscular weakness, altered mental functions, bone weakening. Hypoparathyroidism- caused by injury or removal of gland, muscle cramps, seizures, low blood calcium levels

Adrenal Hormones Epinephrine and Norepinephrine- come from the medulla of the adrenal gland release controlled by sympathetic nervous system, increases heart rate and blood pressure, dilates respiratory airways, promotes breakdown of glycogen, activates reticular formation, increases metabolic rates Cortex Hormomes: Aldosterone-increases blood volume and pressure by promoting conservation of sodium ions and water. Cortisol- decreases protein synthesis, increases fatty acid release, stimulates glucose synthesis from noncarbohydrates. Adrenal androgens- supplement sex hormones from the gonads, may be converted to estrogen

Pancreatic Hormones Glucagon- stimulates liver to break down glycogen, stimulates liver to convert noncarbohydrates into glucose, stimulates break down of fats, controlled by blood glucose concentrations Somatostatin- helps regulate carbohydrates Insulin- promotes formation of glycogen from glucose, inhibits conversion of noncarbohydrates into glucose, enhances movement of glucose into adipose and muscle cells, decreases blood glucose concentrations, promotes transport of amino acids, enhances synthesis of proteins and fats, controlled by blood glucose concentrations

Others Pineal Gland- secretes melatonin, regulates circadian rhythms, may control onset of puberty, helps regulate female reproductive Thymus Gland- secretes thymosins, promotes development of certain lymphocytes Reproductive Glands- ovaries secrete estrogen and progesterone, testes secrete testosterone, placenta secretes estrogen, progesterone, and gonadotropins

Life’s little Curves endocrine glands shrink GH levels even out, muscular strength decreases ADH levels increase due to slow break down calcitonin levels decrease PTH increases, osteoporosis risk increases insulin resistance may develop changes in melatonin secretion affect the body clock thymosin production declines increasing risk of infections

References Jack Brown M.S. Biology Shier,David, Jackie Butler, Ricki Lewis: Hole’s Human Anatomy and Physiology 10th edition: 2004: McGraw-Hill Marieb, Elaine: Essentials of Human Anatomy and Physiology 7th edition. 2003: Pearson Education Inc: Benjamin Cummings pub. Microsoft Encarta Encyclopedia 2004