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Health Sciences
HSCI 100
Nienke Van Houten

Chapter 10 – the endocrine system Functions: - Produces hormones - Helps coordinate organ systems - Responds to stress - Helps regulate fluid/pH balance - Help regulate metabolism System: - Comprised of glands that contain secretory cells that release products (hormones) into extracellular fluid where they diffuse into bloodstream - Hormone = type of chem messenger in body - Results in slow (prolonged) response - Regulates development, metabolism, behavior SIGNAL TYPES 1. Endocrine 2. Paracrine 3. Neuronal 4. Contact-dependent 5. Pheromone signaling – organism to organism Maintaining homeostasis - Hypothalamus bridges regulatory functions of nervous and endocrine o Nervous system respond to change in ext enviro o Info may result in rapid or prolonged responses Exocrine vs endocrine glands - Exocrine: secrete products into ducts that carry products to other organs/outside body - Endocrine: secrete products directly into blood stream (hormones) Hormones – chemical signals promoting communication btwn cells, body parts, individuals - Prostaglandins: local hormones affect neighboring cells and are not carried in bloodstream (paracrine) - Pheromones: chem signals influence behavior of other individuals - Peptide hormones: bind to receptor in plasma membrane - Steroid hormones: lipids that enter cell and affect gene activity (= protein synthesis) - FUNCTIONS & MECHANISMS: o Target cells have receptors which protein molecules recognize & bind o Mechanism by which hormone influences target cells depends on chem makeup of hormone o Two main types: lipid soluble (steroid)/water-soluble (protein/peptide soluble) STEROID HORMONES 1. Steroid hormone diffuses through plasma membrane of target cell 2. Steroid hormone binds to receptor in cytoplasm 3. Hormone receptor complex enters nucleus 4. Hormone receptor complex binds to DNA 5. Certain genes activated 6. Proteins (enzymes) synthesized 7. Enzymes alter activity of cell WATER-SOLUABLE HORMONE 1. Water soluble hormone (first messenger) binds to receptor on surface of plasma membrane 2. Binding activates enzyme response for producing cAMP (2 messenger) from ATP 3. cAMP initiates an enzyme cascade 4. enzyme 3 stimulates the breakdown of glycogen to glucose - can’t pass through lipid bilayer and cannot enter target cells themselves ENDOCRINE SYSTEM - HYPOTHALAMUS o Release & inhibit hormones: regulate anterior pituitary - PITUITARY GLAND o Posterior pituitary  Antidiuretic (ADH) – water reabsorption by kidneys  Oxytocin – stimulates uterine contraction/milk letdown o Anterior pituitary  Thyroid stimulating (TSH) – stimulates thyroid  Adrenocorticotropic (ACTH) – stimulates adrenal cortex  Gonadotropic (LSH, LH) – egg &sperm production, sex hormone prod  Prolactin (PL) – milk production  Growth (GH) – bone growth, protein synthesis, cell division - THYROID o Thyroid hormones (TH) - Thyroxine (T4) & triiodthyronine (T3) – increase metabolic rate, reg growth + dev. iodine needed for production  undersecretion of TH during infancy = cretinism. dwarfism/delayed mental+sex dev  undesecretion of TH in adulthood = myxedema, fluid accumulates in facial tissue  oversecretion of TH = graves’ disease. autoimmune. increased metabolic rate, weight loss, sweating, protruding eyes o Calcitonin (CT) – lowers blood calcium levels secreted by parafollicular cells - ADRENAL GLAND o ADRENAL CORTEX  Glucocorticoids (cortisol) – raise blood glucose level, stimulates breakdown of protein  Mineralocorticoids (aldosterone) – reabsorption of sodium + excretion of potassium  Sex hormones – reproductive organs/bring about sex characteristics o ADRENAL MEDULLA  Epinephrine & norepinephrine – active in emergency sits raise blood glucose levels - PARATHYROIDS o Parathyroid hormone (PTH) – raises blood calcium level  1. bone destroying cells called osteoclasts that raise calcium from bone into blood  2. kidneys to reabsorb more calcium from the filtrate - THYMUS o thymopoietin/Thymosins – production/maturation of T lymphocytes - PANCREAS o Insulin + Glucagon – lower blood glucose level, formation of glycogen - GONADS o TESTES  Androgens (testosterone) – male sex characteristics o OVARIES  Estrogen & progesterone – female sex characteristics - PINEAL GLAND o secretory cells produce melatonin o influence daily rhythms – sleep, seasonal changes == too much melatonin = SAD, lethargy, craving for carbs FUNCTIONS & MECHANISMS OF HORMONES - Interaction between hormones o Antagonistic – effector of 1 hormone opposes that of another hormone o Synergistic – response of a tissue to a combo of hormones is much greater than its response to either individual hormone o Permissive – one hormone must be present for another hormone to exert its effects Contractions at childbirth 1. head of baby stretches cervix of uterus 2. response to stretching = nerve impulses sent to hypothalamus 3. hypothalamus signals posterior pituitary to release OT 4. posterior pituitary releases OT, travels into blood to muscles of uterus 5. uterus responds to OT by contracting more vigorously 6. a) positive feedback == uterine contractions increase dilation of cervix which further releases OT = more frequent and vigorous contractions b) @ birth, stretching lessens positive feedback cycle broken GLANDS OF THE ENDOCRINE HYPOTHALAMUS - Regulates internal
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