The Endocrine System
Chapter 9
Intro to Endocrine System
Endocrine works with nervous system to control body (homeostasis).
Endocrine acts slower than nervous though.
Endocrine system uses hormones – chemical messengers (transported through bloodstream). Endocrine System & Hormone Function
Endocrine organs are very small compared to other organs in the body. THE CHEMISTRY OF HORMONES: Hormones are chemical substances that regulate the metabolic activity of other cells in the body. Amino Acid-based hormones vs. Steroids
AA-based: proteins, peptides, and amines
Steroids: cholesterol; sex hormones (gonads) & hormones in adrenal cortex
Prostaglandins: lipids in cell membrane
Endocrine System & Hormone Function
MECHANISMS OF HORMONE ACTION:
Target cells/organs – responds to hormones Must have specific protein receptors on cell membrane where hormone can attach
Hormones act to increase or decrease the rate of normal metabolic activities within the cell.
Endocrine System & Hormone Function
MECHANISMS OF HORMONE ACTION: What happens when the hormone binds to the cell membrane? 1. Changes in plasma membrane permeability or electrical state. 2. Synthesis of proteins or certain regulatory molecules (enzymes) in the cell. 3. Activation or inactivation of enzymes. 4. Stimulation of mitosis (cell division). Endocrine System & Hormone Function
2 Main Mechanisms for Hormone Action:
Steroid Hormone Action 1. Steroid hormones diffuse across plasma membrane (lipid-soluble). 2. Steroid hormones enter nucleus. 3. Steroid hormones bind to specific receptor protein. 4. Hormone-receptor complex binds to DNA. 5. Activates transcription & translation (makes protein). Endocrine System & Hormone Function
Nonsteroid Hormone Action:
1. Hormone binds to membrane receptor (cannot go through membrane on its own). 2. Starts a series of reactions that activate enzyme. 3. Enzyme catalyzes rxn to make a 2nd messenger molecule. 4. 2nd messenger molecule oversees other intracellular changes. Endocrine System & Hormone Function
CONTROL OF HORMONE RELEASE:
Negative Feedback Mechanisms – hormone secretion is triggered by some stimulus, and when hormone levels reach a certain level, hormone release is inhibited.
Endocrine System & Hormone Function 3 Categories for
Endocrine Gland Stimuli:
1) HORMONAL – most common; Hypothalamus secretes hormones that stimulate the anterior pituitary gland to secrete hormones that stimulate other endocrine glands to secrete hormones.
Hierarchal control system with the hypothalamus in control Endocrine System & Hormone Function
3 Categories for Ex. Decrease blood Ca Endocrine Gland release of PTH to Stimuli: increase Ca 2) HUMORAL – Increase Ca release monitoring levels of of calcitonin to various substances in decrease Ca body fluids such as blood Changing blood level concentrations release hormone
Endocrine System & Hormone Function
3 Categories for Endocrine Gland Stimuli: 3) NEURAL – Nerve fibers stimulate hormone secretion Ex. Sympathetic NS stimulates adrenal medulla cells to secrete catecholamines (epinephrine and norepinephrine) during times of stress
Major Endocrine Organs - 10
Organs can be endocrine only (anterior pituitary, thyroid, adrenals, & parathyroids) OR
Endocrine & Exocrine (pancreas & gonads)
Endocrine glands are ductless (hormones release into blood or lymph)
Exocrine glands have ducts to release to body surface or cavities – Ex sweat glands
Major Endocrine Organs
Hypothalamus Pituitary gland Thyroid gland Parathyroid glands Adrenal gland Pineal gland Thymus gland Pancreas Gonads – Ovaries and Testes
Pituitary Gland
About the size of a grape Hangs from inferior surface of hypothalamus Surrounded by “turk’s saddle” of sphenoid bone 2 Lobes: Anterior pituitary (glandular tissue) & Posterior pituitary (nervous tissue) Tropic hormones – stimulate target organs, which are also endocrine glands, to secrete their hormones (HORMONAL) Pituitary Gland Hormones
ANTERIOR PITUITARY: All are proteins, act through 2nd messenger system, and regulated by hormonal stimuli Growth Hormone (GH) - stimulates growth of bones and muscles; metabolism; regulated by hypothalamus releasing and inhibiting hormones Prolactin (PRL) – stimulates milk production targets human breasts; regulated by hypothalamic hormones Follicle-stimulating hormone (FSH) – stimulates production of ova & sperm; regulated by hypothalamic hormones Pituitary Gland Hormones ANTERIOR PITUITARY: Luteinizing hormone (LH) – stimulates ovulation of egg and causes ruptured follicle to become corpus luteum produce progesterone and some estrogen; in men (also interstitial cell-stimulating hormone (ICSH)) stimulates interstitial cells of testes to produce testosterone; regulated by hypothalamic hormones Thyrotropic hormone (TSH) – Thyroid-stimulating hormone – stimulates thyroid; regulated by thyroxine in blood and hypothalamic hormones Adrenocorticotropic hormone (ACTH) – stimulates adrenal cortex to secrete glucocorticoids; regulated by glucocorticoids and hypothalamic hormones Pituitary Gland Hormones
POSTERIOR PITUITARY:
Storage area
Oxytocin – made by hypothalamus; released during childbirth to increase contractions, released during sex, released when breast-feeding; oxytocin drugs are used to induce labor; oxytocics are used to stop postpartum bleeding and stimulate milk ejection reflex Pituitary Gland Hormones
POSTERIOR PITUITARY:
Antidiuretic hormone (ADH) – produced by hypothalamus; inhibits urine production causes kidneys to reabsorb more water urine volume decreases & blood volume increases; can increase blood pressure (vasopressin)
Drinking alcohol and caffeine inhibits ADH urinate more Homeostatic Imbalance
Too much or too little GROWTH HORMONE: Hyposecretion pituitary dwarfism Hypersecretion pituitary gigantism
If hypersecretion after long-bone growth has ended acromegaly (malformed facial features) READ pg. 286 Closer Look box Homeostatic Imbalance
Too little (hyposecretion) of FSH or LH sterility in males & females
Drugs that promote fertility stimulate gonadotropic hormones (multiple births may occur)
Hyposecretion of ADH excessive urine (DIABETES INSIPIDUS) Pituitary-Hypothalamus Relationship
Anterior pituitary gland is sometimes called the “master endocrine gland”
However the hypothalamus produces releasing & inhibiting hormones (sent into the portal circulation)
Hypothalamus makes OXYTOCIN & ANTIDIURETIC HORMONE (sent to posterior pituitary for storage by the axons of neurosecretory cells) Thyroid Gland
Located at base of throat, inferior to Adam’s apple
2 lobes joined by a central mass called the isthmus
Follicles inside thyroid gland store colloidal material hormones
Thyroid hormone – major metabolic
hormone; made in follicles; Thyroxine (T4) and Triiodothyroxine (T3) Thyroid Gland
T4 is major hormone secreted by thyroid follicles
T3 is formed at target tissues by converting T4 Thyroid hormone – controls rate of glucose burning into energy; every cell is targeted; controls growth and development in reproductive & nervous systems; regulated by TSH Thyroid Gland
Calcitonin – decreases blood calcium levels calcium is deposited into bones; it does opposite of parathyroid hormone; made by C cells in connective tissue between follicles; released when blood calcium is too high; calcitonin production decreases in elderly; regulated by calcium in blood Homeostatic Imbalance
Goiters – enlargement of thyroid gland caused by deficient amount of iodine in diet; TSH keeps calling for thyroxine and thyroid gland tries to put it out (enlarges); not common in US (salt has iodine in it) Cretinism – occurs in early childhood as a result of hyposecretion of thyroxine lack of TH stimulation (dwarfism) Myxedema – hypothyroidism in adults; physical and mental sluggishness, puffiness in face, fatigue, poor muscle tone, low body temp. Treat with oral thyroxine Parathyroid Glands
Found on posterior surface of thyroid gland Normally 2 glands per lobe = 4 (but 8 have been reported before) Parathyroid hormone (PTH) – regulates blood calcium levels; low blood Ca2+ release PTH stimulates osteoclasts to break down bone and release calcium; regulated by calcium in blood **PTH is hypercalcemic hormone & Calcitonin is hypocalcemic hormone Homeostatic Imbalance
Hypoparathyroidsim: Blood calcium is too low neurons become overactive TETANY (uncontrollable spasms) Severe hyperparathyroidism massive bone destruction bones are fragile Adrenal Glands
2 bean-shaped glands that curve over kidneys Parts are medulla region & adrenal cortex Adrenal Cortex Hormones
Produces corticosteroids mineralcorticoids, glucocorticoids, and sex hormones MINERALCORTICOIDS:
Aldosterone – regulate mineral content of blood; mainly Na & K; Blood levels of aldosterone rises kidney tubules keep Na and allow K to leave in the urine keeps water in body; regulated by changes in bv or bp & K/Na levels in blood
RENIN – enzyme that kidneys release when bp drops that causes aldosterone to be released retains Na in blood retains water bv increases bp increases Adrenal Cortex Hormones
GLUCOCORTICOIDS: Cortisone & Cortisol – promote normal cell metabolism; help resist long-term stressors (increase blood glucose); Glucocorticoids are high in blood fats & proteins broken down for glucose (hyperglycemic hormones); they also decrease edema (inflammation) and inhibit prostoglandins (cause pain) Given to patients to suppress inflammation Regulated by blood levels of ACTH (released when ACTH is high) Adrenal Cortex Hormones
SEX HORMONES: Produced in small amounts Androgens – male hormone; support sperm formation and development of male characteristics; regulated by FSH and LH Estrogens – female hormone; stimulate uterine lining growth and help with development of female characteristics; regulated by FSH and LH Homeostatic Imbalances
Addison’s disease – caused by hyposecretion of all adrenal cortex hormones; bronze tone of skin; sodium and water are lost from body (water and electrolyte imbalance); muscles weaken and shock may occur Homeostatic Imbalance
Cushing’s syndrome – tumor in middle of cortex area in adrenal gland; too much of the glucocorticoids are released moon face & buffalo hump on back
High blood pressure
Possible diabetes
Weakened bones Homeostatic Imbalances
Masculinization – caused by oversecretion of sex hormones Dramatic in women beard, body hair, voice Hormones of the Adrenal Medulla
Developed from nervous tissue – stimulated by sympathetic nervous tissue Epinephrine (adrenaline) & Norepinephrine (noradrenaline) = Catecholamines Released for “fight or flight” response Increase HR, BP, and blood glucose levels, and dilate small passageways of lungs Catecholamines are for short-term stressors, whereas Glucocorticoids are for prolonged stressors. Hormones of the Adrenal Medulla
HOMEOSTATIC IMBALANCE:
Hypersecretion of catecholamines leads to excessive sympathetic nervous system activity.
Corrected by surgically removing catecholamine-secreting cells. Pancreatic Islets
Pancreas = mixed gland Called islets of Langerhans Exocrine parts act in digestive system
Insulin – released from beta cells in response to high blood glucose; increases ability of body cells to transport glucose across their membranes glucose oxidized for energy or stored as glycogen (hypoglycemic – acts to lower glucose in blood) Homeostatic Imbalance Diabetes mellitus – no insulin causes blood glucose to rise over normal (80-120 mg / 100 mL blood) Glucose flows out through urine and takes water with it = dehydration Fats & Proteins are broken down for energy weaker, harder to fight infection Large amounts of fats used for energy blood becomes acidic (acidosis) ketones are in blood (can cause coma or death) Signs: 1) polyuria (excessive urination) 2) polydipsia (excessive thirst) 3) polyphagia (hunger) Treat with diet, insulin injections, and oral medications. Type I: juvenile (serious) and Type II: adult Pancreatic Islets
Glucagon – antagonist of insulin; released by alpha cells in response to low blood glucose; (hyperglycemic = acts to increase blood glucose); targets the liver to break down stored glycogen Pineal Gland
Also called Pineal Body; found in 3rd ventricle of brain
Melatonin – levels change for day and night; peak levels at night make you drowsy; lowest at noon; establishes day- night cycle; helps coordinate hormones of fertility and inhibits reproductive system
Thymus
In upper thorax, posterior to sternum
Large in infants and decreases in size throughout adulthood
Thymosin – programs “T cells”
Incubator for maturation of white blood cells = T lymphocytes Hormones of the Ovaries
Ovaries produce eggs and 2 steroid hormones Anterior pituitary gonadotropic hormones stimulate puberty Estrogens – estrone and estradiol are produced by Graafian follicles = stimulate development of secondary sex characteristics
Work with progesterone to prepare uterus (menstrual cycle)
Help maintain pregnancy and prepare breasts Hormones of the Ovaries
Progesterone – helps with menstrual cycle; helps to relax muscles of uterus when pregnant; produced by corpus luteum
Both hormones are released in a cycle by the anterior pituitary gonadotropic hormones Hyposecretion of either hormone can inhibit the ability to get pregnant Hormones of the Testes
Testes are suspended in scrotum (sac) outside pelvic cavity Testes produces sperm and androgens Androgens Testosterone – made by interstitial cells and causes development of adult male characteristics; needed for continuous production of sperm Hyposecretion sterile
Testosterone production is stimulated by LH Other Hormone-Producing Tissues & Organs
Hormone-producing cells are found in walls of small intestine, stomach, kidneys and heart. Placenta – temporary organ during pregnancy produces estrogen & progesterone Cancer cells – make excessive and uncontrollable amounts of normal hormones Placenta
Formed in uterus of pregnant women Respiratory, Excretory, and Nutrition-delivery for fetus Human chorionic gonadotropin (hCG) – produced by conceptus and then by fetal part of placenta; similar to LH stimulates corpus luteum of ovary to produce progesterone and estrogen (keep uterus wall in tact) Home pregnancy tests mainly for hCG in woman’s urine Placenta
3rd month: ovaries become inactive, so placenta must make progesterone and estrogen (to maintain lining of uterus & prepare breasts) Human placental lactogen (hPL) – works with estrogen and progesterone to prepare breasts for lactation Relaxin – causes mother’s pelvic ligaments and pubic symphysis to relax and become flexible for birth Developmental Aspects
Menopause – woman’s reproductive organs begin atrophy estrogen deficiency arteriosclerosis, osteoporosis, decreased skin elasticity, sympathetic nervous system (hot flashes), fatigue, nervousness, mood changes Anterior pituitary declines in old age muscle atrophy & target organs become less productive Older people have decline in insulin production diabetes