Bi 103 Notes: Chapter 33: Endocrine System

I. Background

            A. Types of glands

                        1. Endocrine

                                    a. release substances within body, via bloodstream

                        2. Exocrine

                                    a. release substances outside body via ducts (e.g. sweat)

            B. Target Cells: Respond to endocrine hormones

                        1. Response can be prolonged and irreversible (e.g. puberty)

                        2. Response can be transient, reversible

            C. General Classes of Hormones

                        1. Peptide hormones (polar)

                        2. Amino Acid-based hormones (polar)

                        3. Steroid Hormones (non-polar)

            D. Hormones (first messenger) bind to receptors in target cells

                        1. Second messenger system

                                    a. used by polar hormones

                                    b. bind to receptor in cell membrane of target cell

                                    c. receptor then activates second messenger in cell

                                    d. it activates biochemical reactions

                        2. Internal receptor system

                                    a. used by non-polar hormones

                                    b. hormone can pass through plasma membrane, bind to receptor in cell

                                    c. initiates response in cell

II. Major Endocrine Glands in Humans

            A. Pituitary

                        1. Anterior (production of these hormones regulated by releasing hormones and                            inhibiting hormones from hypothalamus)

                                    a. FSH: Regulates egg/sperm production

                                    b. LH: regulates sex hormone production

                                    c. TSH: Regulates hormones from thyroid

                                    d. ACTH: Regulates hormones from adrenal cortex

                                    e. Prolactin: stimulates mammary gland development

                                    f. MSH: Stimulates production of melanin

                                    g. Growth Hormone: regulates growth of body cells

                        2. Posterior (these hormones produced by neurosecretory cells with their cell bodies in the hypothalamus)

                                    a. ADH: Antidiuretic Hormone: Signals kidneys to retain water

                                    b. Oxytocin: Uterine contractions, milk letdown reflex, maternal behaviors

            B. Thyroid       

                        1. Thyroxine: (T4) (regulated in feedback loop with TSH...)

                                    a. increases metabolic rate, regulating growth and body temperature

                                    b. Iodine required for synthesis, iodine deficiency results in goiter

                        2. Calcitonin

                                    a. Regulates [Ca++] in blood (decreases [Ca++] in blood)

            C. Parathyroid

                        1. Parathormone

                                    a. Regulates [Ca++] in blood (increases [Ca++] in blood)

            D. Pancreas (see feedback loop diagram 33-8)

                        1. Insulin

                                    a. signals cells to take up glucose (decrease blood sugar)

                                    b. signals liver to convert glucoseŕ glycogen

                        2. Glucagon

                                    a. signals for increased blood sugar levels

                                    b. signals liver to break down glycogen ŕ glucose

            E. Sex Organs

            (signal for early development, and surge at puberty, to develop secondary sexual characteristics)

                        1. Ovaries

                                    a. Estrogen/Progesterone

                        2. Testes

                                    a. Testosterone

                        Release of these is regulated by LH and FSH from anterior pituitary

            F. Adrenal gland

                        1. Adrenal Medulla

                                    a. Epinephrine/Norepinephrine: Fight or flight situations

                                                1. Release regulated by CNS

                        2. Adrenal Cortex

                                    a. Glucocorticoids

                                                1. Released in longer term stress situations

                                                            a. Trauma, infection, emotional stress

                                                            b. release regulated by ACTH

                                                            c. influences glucose metabolism, immune system

                                    b.  Aldosterone (regulates [Na+], signals kidneys to retain [Na+]

                                    c. Testosterone (in males and females)

            G. Other sources in body

                        1.  Most cells in Body

                                    a. Prostaglandins (target nearby cells, many varied functions)

                                                1. Inflammation, uterine contraction, stomach acid regulation…

                        2. Pineal gland

                                    a. Melatonin (influences sleep/wake cycles, circadian rhythms)

                        3. Thymus      

                                    a. Thymosin: stimulates immune cell development

                        4. Adipose cells

                                    a. Leptin: Regulates body fat.