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Transcript
The Endocrine System A. Overview • Second messenger system of the body (first is nervous) • Uses chemical messages (hormones) that are released into blood • Hormones control several major processes – Reproduction – Growth and development – Mobilization of body defenses against stress – Maintenance of much of homeostasis – Regulation of metabolism B. Hormones • Produced by specialized cells in glands • Cells secrete hormones into extracellular fluids • Blood transfers hormones to target sites or effectors • Hormones regulate activity of other cells in effector • Three chemical classifications of hormones –Amino acid-based hormones • Proteins • Peptides • Amines –Steroids – made from cholesterol –Prostaglandins – made from highly active lipids C. Hormones in Action • Affect only target tissues/organs via receptors – (that’s why heart muscle won’t produce sperm – no receptors for that action) • Once hormone binds to receptor, alters cellular activity – Increases or decreases normal metabolic process • Binding of receptor causes up to four changes – Changes in plasma membrane permeability or electrical state (chemicals in/out) – Synthesis of proteins, such as enzymes (digestion) – Activation or inactivation of enzymes – Stimulation of mitosis (growth) • If steroid hormone: – Hormones diffuse through the plasma membrane of target cells (steroids are lipidbased) – Enters the nucleus – Bind to a specific protein within the nucleus – Hormone-protein complex binds to specific sites on the cell’s DNA – Activate genes that result in transcription & translation to synthesize new proteins Steroid Hormone Action Figure 9.1a • If non-steroid hormone (amino-acid or prostaglandins) … – Hormone binds to a membrane receptor (can’t pass through membrane itself) – 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 (either cAMP, Ca2+, or protein) – Messenger molecule oversees additional intracellular changes to promote a specific response Non-steroid Hormone Action Figure 9.1b D. Control of Hormone Release • Most hormone levels in blood are maintained by negative feedback • External (5 senses) or internal stimulus or low hormone levels in blood triggers release of more hormone • Hormone release stops once appropriate level in blood is reached – Three stimuli types: 1. Hormonal Stimuli • Endocrine glands are activated by other hormones Figure 9.2a 2. Humoral Stimuli • Changing blood levels of certain ions or nutrients stimulate hormone release – Blood chemistry Figure 9.2b 3. Neural Stimuli • Nerve impulses stimulate hormone release • Most are under control of the sympathetic nervous system – “flight or fight” Figure 9.2c E. Major Endocrine Organs Figure 9.3 1. Pituitary Gland • Size of a grape • Hangs by a stalk from the hypothalamus • Protected by the sphenoid bone area called “Turk’s saddle” • Has two functional lobes – Anterior pituitary – glandular tissue – Posterior pituitary – nervous tissue • Six anterior pituitary hormones – Two affect non-endocrine targets • Growth hormone (GH) – overall growth (synthesizing protein), breaks down fats • Prolactin – stimulates breast milk production (lactation) – Four stimulate other endocrine glands (tropic hormones) • Thyroid stimulating hormone (TSH)- thyroid gland • Adrenocorticotropic hormone (ACTH) - cortex of adrenal gland • Follicle stimulating hormone (FSH) – follicles in ovaries and sperm in testes • (women) Luteinizing hormone (LH) – ovulation of egg • (men) Interstitial cell-stimulating hormone (ICSH) – testosterone production in testes • Characteristics of all anterior pituitary hormones – Proteins (or peptides) – Act through second-messenger systems – Regulated by hormonal stimuli, mostly negative feedback • Posterior pituitary is not strictly an endocrine gland so it doesn’t MAKE hormones • Posterior pituitary releases two hormones made by hypothalamus: – Oxytocin • Stimulates contractions of uterus during labor • Causes milk ejection triggered by suckling – Antidiuretic hormone (ADH) • inhibits urine production • In large amounts, causes vasoconstriction leading to increased blood pressure (as a result sometimes called vasopressin) Hormones of the Posterior Pituitary Figure 9.5 2. Hypothalamus • produces the two hormones that are transported to neurosecretory cells of the posterior pituitary (ADH & oxytocin) 3. Thyroid Gland • Found at base of throat • Consists of two lobes and a connecting isthmus • Produces two hormones: – Thyroid hormone (TH) Combines with iodine at thyroid gland to produce thyroxine. • Thyroxine (T4) – TH + 4I controls rate of body’s metabolism +I • Triiodothyronine (T3) – TH + 3I conversion of T4 at target tissues – Calcitonin - Decreases blood calcium levels by causing it to be deposited on bone Thyroxine Control 4. Parathyroid Glands • Tiny masses on posterior of thyroid • Secrete parathyroid hormone or parathormone (PTH) – Stimulate osteoclasts to remove calcium from bone when levels in blood are too low – Stimulate kidneys & intestine to absorb more calcium – Raise calcium levels in the blood (opposite calcitonin) Calcitonin vs PTH Figure 9.9 5. Adrenal Glands • Two glands that sit on top of kidneys • Divided into two areas: – Cortex – outer glandular region in three layers – Medulla – inner neural tissue region • Cortex produces three major groups of steroid hormones collectively called corticosteroids • Produce over 50 different hormones themselves • CORTICOSTEROIDS: – Mineralocorticoids (mainly aldosterone) • Produced in outer adrenal cortex • Regulate mineral content in blood, water, and electrolyte balance (target organ is kidney) • Production stimulated by renin (produced in kidneys) and aldosterone • Production inhibited by atrial natriuretic peptide (produced by heart) – Glucocorticoids (including cortisone and cortisol) • • • • Produced in middle layer of adrenal cortex Promote normal cell metabolism Help resist long-term stressors (work, family, health stress) Released in response to increased blood levels of ACTH – Sex hormones • Produced in inner layer of adrenal cortex • Androgens (male) and some estrogen (female) Hormones of the Adrenal Cortex Figure 9.10 • Two hormones produced by medulla called catecholamines which are triggered by sympathetic nervous system – Epinephrine (adrenaline) – Norepinephrine (noradrenaline) • prepare the body to deal with short-term stress as in fight-or-flight scenarios Adrenal Glands in Stress Response Figure 9.12 6. Pancreas (Pancreatic Islets) • pancreas is a mixed gland • Islets of Langerhans in pancreas produce hormones – Insulin (from beta cells) – allows glucose to cross plasma membranes into cells • Blood glucose now delivered to cells for energy – Glucagon (from alpha cells) – allows glucose to enter blood • Converts stored glucose (glycogen) back into glucose – these hormones are antagonists that maintain blood sugar homeostasis Pancreatic Islets Figure 9.13 Blood Sugar Hormones Figure 9.14 Glucose ($) blood Glycogen ($100) liver Fats/protein (£) 7. Pineal Gland • Found on third ventricle of brain • Secretes melatonin – Helps establish body’s wake/sleep cycles – May have other asyet-unsubstantiated functions 8. Thymus • Located posterior to sternum • Largest in infants and children • Produces thymosin that – Matures & activates lymphocytes (WBC) in infants & children (other organs produce WBC during adulthood) in immune system 9. Ovaries • Produce estrogens – Produced by Graafian follicles in ovaries or placenta – Stimulates development of secondary female characteristics – Matures female reproductive organs – Helps prepare uterus to receive a fertilized egg – Helps maintain pregnancy – Prepares breasts to produce milk • Also produce progesterone – Produced by corpus luteum – Acts with estrogen to bring about menstrual cycle – Helps in implantation of an embryo in uterus 10.Testes • Interstitial cells of testes are hormone-producing • Produce several androgens • Testosterone is the most important androgen – Responsible for adult male secondary sex characteristics – Promotes growth and maturation of male reproductive system – Required for sperm cell production 11.Placenta • Produces hormones that maintain pregnancy • Some hormones play a part in baby delivery • Produces human chorionic gonadotropin (hCG) in addition to estrogen, progesterone, and other hormones • Home pregnancy tests check for presence of hCG 12.Others • Duodenum (first part) of small intestine – Gastrin – delivered to stomach to inhibit HCl – Secretin – stimulates pancreas to release high pH juice; stimulates release of bile from liver – Cholecystokinin (CCK) – stimulates pancreas to release enzymes; gallbladder to release stored bile • Stomach – Gastrin – stimulates stomach glands to release HCl • Adipose tissue – Leptin – stimulates brain to suppress appetite & increase energy usage • Complete hormone table as shown below. There are 35 hormones in your notes – yes, really. Hormone Producing Agent Growth hormone (GH) Anterior pituitary Function Overall growth; synthesize proteins; breakdown fats Gastrin Duodenum & stomach Control HCl production in stomach Thyroxine (T4) Thyroid Type of iodine-containing thyroid hormone secreted by thyroid follicles F. Diseases/Disorders • Long-term imbalance of particular hormones leads to diseases or disorders of endocrine system –Acromegaly (gigantism) –Goiter –Addison’s disease –Diabetes mellitus (Type I & Type II) –Sterility (male & female) –PCOS Acromegaly Sandy Allen 7’7 ¼” • Hypersecretion (excess) of pituitary growth hormone (GH) even after long bones have grown results in acromegaly or gigantism. – Facial bones, hands and feet enlarge tremendously – Height can reach between 8 – 9 feet! – Results from tumor on pituitary gland that secretes GH too. Goiter • Enlargement of thyroid gland as a result of deficiency of iodine – Iodine is needed to make thyroxine – When TSH stimulates thyroxine production, it’s produced, but it’s disfunctional – TSH continues to stimulate thryoid, so in turn, it grows to meet demands (although demands are never met) • Iodine only found naturally in seafood, so USA added iodine to salt – Other land-locked areas continue to produce goiters Addison’s Disease • Hyposecretion (deficiency) of all adrenal hormones results in Addison’s disease, and a bronzing of skin is the effect (melanocytestimulating hormone overactive). – Low aldosterone leads to water & electrolyte loss – Low glucocorticoids leads to hypoglycemia (too little glucose in blood), and suppression of immune system • No glucocorticoids would mean death Diabetes Mellitus • Hyperglycemia or excess glucose (sugar) in blood – Literally from Latin “something sweet is being siphoned from body” • Normal fasting blood glucose 80 – 120 mg/100 mL blood – Diabetes is higher than 126 mg (121-125 is borderline) – Autoimmune disorder where beta cells are attacked, so pancreas does not produce insulin (Type I) or cells’ receptors don’t recognize it (Type II) • No glucose means no fast energy – Body must then break down proteins or fats for energy, blood becomes acidic • Acidosis or ketosis results which can lead to coma or death • Three main signs of diabetes: – Polyuria = excessive urination to rid body of glucose/ketones – Polydipsia = excess thirst from lack of water – Polyphagia = hunger since cells don’t receive glucose energy “Juvenile Diabetes” No insulin produced “Adult-Onset Diabetes” Insulin produced, receptors weaker • Long-term effects of uncontrolled diabetes (I or II): – Cardiovascular disease • Excess glucose in blood makes it more viscous, causes heart to beat faster (hypertension/high blood pressure), circulate slower leading to tissue damage (possible gangrene), eventually heart attack – Chronic renal (kidney) failure • Kidneys have to filter so much glucose, eventually shut down from overwork – Blindness (retinal damage) • Blood vessels in retina get damaged & retina can’t process image Sterility • Hormonal imbalances (too much or too little) leads to sterility in both males and females – Males • Less FSH – little/no sperm production • Less LH – less testosterone • Less testosterone – little/no sperm production – Females • • • • Excess prolactin – no ovulation Less FSH and/or LH – no ovulation Less estrogen – less FSH/LH – no ovulation Less progesterone - miscarriage Polycystic Ovary Syndrome (PCOS) • PCOS occurs when ovaries grow many small cysts causing a chain reaction of hormone imbalance • Cysts make excess male androgens which then leads to hormone imbalance. • Inhibits further growth and release of mature eggs. • First noticed in teen years affecting 1 out of 15 women • There is a high genetic component. PCOS • Symptoms of PCOS • No ovulation • Irregular periods (too little, too much) • Weight gain • Excess acne • Facial & body hair • Thinning hair • Results in • Infertility • Insulin resistance (leading to diabetes II) • Depression • High cholesterol • Heart disease G. Development • In utero – Up to 11 weeks pregnant, both males & female fetuses have same genital makeup – At 12 weeks, Y chromosome triggers testosterone to form male genitals; absence of Y chromosome triggers estrogen to form female genitals – If hormone levels are off, can result in intersex (formerly hermaphrodite) Embryo at 11 weeks individual • Chromosomes show male or female but genitalia something in between • 46 XY Intersex – Male chromosomes, external genitals incomplete or female-like • 46 XX Intersex – Female chromosomes, ovaries, male-like external genitalia • Gonadal Intersex – Both ovarian and testicular tissue – May be either XY or XX • Complex/Undetermined Intersex – XO, XXX, XXY, XYY • Puberty – Increase in hormone production by ovaries or testes to initiate secondary sex characteristics and be able to reproduce – Girls: begins at 10-11 and complete by 15-17 – Boys: begins at 12-13 and complete by 16-18 • Adulthood – Most endocrine organs operate smoothly until old age • Late Adulthood – Menopause in women is brought about by lack of efficiency of the ovaries • Problems associated with reduced estrogen are common (hot flashes, insomnia, moodiness) – Growth hormone production declines with age – Many endocrine glands decrease output with age including testes