The Endocrine System Introduction o o Second messenger

The Endocrine System

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

Introduction o Endocrine glands are “ductless”. They release hormones directly into the blood or lymph

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

Major Glands

Pituitary Gland Size of a grape o Hangs by a stalk from the hypothalamus o Protected by the sphenoid bone o Has two functional lobes n Anterior pituitary – glandular tissue n Posterior pituitary – nervous tissue o Technically not an endocrine gland but a storage area for hormones produced by the hypothalamus

Anterior Pituitary Hormones o o o Growth Hormone (GH)- stimulates increase in size and rate of body cells, enhances movement of amino acids through membranes, promotes growth of long bones, 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,

Anterior Pituitary Hormones Cont… o o o Adrenocorticotropic Hormone (ACTH)- 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 Luteinizing Hormone (LH)- promotes secretions of sex hormones in both testes and ovaries; stimulates release of egg from ovary, promotes growth of long bones

Anterior Pituitary Hormones Cont… o Melanocyte-Stimulating Hormone (MSH)-stimulates the melanocytes in the skin to produce the pigment melanin

Posterior Pituitary Hormones o o Antidiuretic Hormone (ADH)- decreases water lost in urine by returning water to the blood, raises blood pressure, controlled by and produced in the 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 and produced in the hypothalamus in response to stretch in uterine and vaginal walls and stimulation of breasts

Overview

Thyroid Hormones o Thyroxine (T 4) and Triiodothyronine (T 3)- increases metabolism and basal metabolic rate (BMR), controlled by TSH o Calcitonin- decreases blood calcium and phosphate ion concentrations by inhibiting osteoclasts

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

Parathyroid Hormone o Parathyroid Hormone PTH- increases blood calcium levels

Parathyroid Disorders o 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 o o 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 Hormones: 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 o o Glucagon- stimulates liver to break down glycogen, stimulates liver to convert noncarbohydrates into glucose, stimulates break down of fats, controlled by blood glucose concentrations 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 o o o Pineal Gland- secretes melatonin, regulates circadian rhythms, may control onset of puberty, helps regulate female reproductive cycles Thymus Gland- secretes thymosins, promotes development of certain lymphocytes (T-cells) Reproductive Glands- ovaries secrete estrogen and progesterone develops and maintains female secondary sex characteristics and uterine lining growth, testes secrete testosterone develops and maintains male secondary sex characteristics and sperm formation, placenta secretes estrogen, progesterone, and gonadotropins

Life’s little Curves o o o o 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

Mechanisms of hormone release (a) Humoral: in response to changing levels of ions or nutrients in the blood (b) Neural: stimulation by nerves (c) Hormonal: stimulation received from other hormones 2 2

How are they Released

FEEDBACK SYSTEM. Figure 6 -26: Negative and positive feedback

NEGATIVE FEEDBACK REFLEXES : LONG , SHORT & ULTRASHORT LOOP. Figure 7 -14: Negative feedback loops in the hypothalamicanterior pituitary pathway

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