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Chapter 45 ~ Chemical Signals in Animals Endocrine system ~Hormones growth hormones Regulatory systems • • • • • Hormone: chemical signal secreted into body fluids (blood) communicating regulatory messages Target cells: body cells that respond to hormones Endocrine system/glands: hormone secreting system/glands (ductless); exocrine glands secrete chemicals (sweat, mucus, enzymes) through ducts Neurosecretory cells: actual cells that secrete hormones Feedback mechanisms : negative and positive Local regulators: cells adjacent to or near point of secretion • Growth factors proteins for cell proliferation • Nitric oxide (NO) neurotransmitter and a local regulator • If oxygen in blood falls, endothelial cells in blood vessels make and release NO • NO activates enzyme, relaxes smooth muscle cells cause vasodilation • Viagra: prolonged activity of NO pathway Prostaglandins • In semen it stimulates smooth muscle in female uterus to contract and help sperm reach egg • secreted by cells in placenta to cause contraction in childbirth • Immune system: promote fever, inflammation, &pain ( Ibuprofin and aspirin inhibit) • Blood: regulate aggregation of platelets involved in blood clotting • Help protect the lining of the stomach Regulation • Why are hormones needed? – chemical messages from one body part to another – communication needed to coordinate whole body – daily homeostasis & regulation of large scale changes • solute levels in blood – glucose, Ca++, salts, etc. • • • • • metabolism growth development maturation reproduction growth hormones Regulation & Communication • Animals rely on 2 systems for regulation – endocrine system (paracrine and autocrine) • system of ductless glands – – – – secrete chemical signals directly into blood chemical travels to target tissue target cells have receptor proteins slow, long-lasting response – nervous system • system of neurons – transmits “electrical” signal & release neurotransmitters to target tissue – fast, short-lasting response Regulation by chemical messengers • Neurotransmitters released by neurons • Hormones release by endocrine glands • Neurohormones specialized neuron secretory cells endocrine gland neurotransmitter axon hormone carried by blood receptor proteins receptor proteins target cell Lock & Key system Classes of Hormones: water or lipid soluble • Protein-based hormones – polypeptides • small proteins: insulin, ADH insulin – glycoproteins • large proteins + carbohydrate: FSH, LH – amines • modified amino acids: epinephrine, melatonin Water soluble secreted by exocytosis travel freely in blood stream, bind to cell-surface receptors, induce changes in cytoplasmic molecules to alter gene transcription Classes of Hormones Cont. • Lipid-based hormones – steroids • modified cholesterol: sex hormones, aldosterone • Diffuse into target cells • Bind to intracellular signal receptors • Can cross the plasma membrane and nuclear membrane • Trigger changes in gene transcription Mode of Action: Chemical Signaling • 1- Plasma membrane reception signal-transduction pathways (neurotransmitters, growth factors, most hormones) • 2- Cell nucleus reception steroid hormones, thyroid hormones, some local regulators • • Action of lipid (steroid) hormones steroid hormone target cell S S cytoplasm blood 1 S protein carrier cross cell membrane 2 binds to receptor protein becomes transcription factor 5 S 3 mRNA read by ribosome plasma membrane DNA 4 mRNA nucleus 6 protein 7 protein secreted ex: secreted protein = growth factor (hair, bone, muscle, gametes) signal-transduction pathway Action of protein hormones 1 protein hormone signal P binds to receptor protein plasma membrane activates G-protein activates enzyme cAMP receptor protein activates cytoplasmic signal cytoplasm target cell GTP acts as 2° messenger transduction ATP ATP activates enzyme 2 secondary messenger system activates enzyme produces an action 3 response Benefits of a 2° messenger system signal 1 Activated adenylyl cyclase receptor protein 2 Not yet activated amplification 4 3 GTP amplification cAMP amplification 5 G protein protein kinase 6 Amplification! amplification enzyme Cascade multiplier! FAST response! 7 amplification product Maintaining homeostasis hormone 1 lowers body condition gland high specific body condition low raises body condition gland hormone 2 Negative Feedback Model Vertebrate Endocrine System • • • • • • • • • • Tropic hormones : a hormone that has another endocrine gland as a target Hypothalamus: pituitary Pituitary gland Pineal gland Thyroid gland Parathyroid glands Thymus Adrenal glands Pancreas Gonads (ovary, testis) Nervous & Endocrine systems linked • Hypothalamus = “master nerve control center” – nervous system – receives information from nerves around body about internal conditions – releasing hormones: regulates release of hormones from pituitary • Pituitary gland = “master gland” – endocrine system – secretes broad range of “tropic” hormones regulating other glands in body hypothalamus posterior pituitary anterior tropic hormones = target endocrine glands hypothalamus thyroid-stimulating hormone (TSH) Thyroid gland posterior pituitary anterior pituitary antidiuretic hormone (ADH) Kidney tubules Muscles of uterus Adrenal cortex gonadotropic hormones: folliclestimulating hormone (FSH) & luteinizing hormone (LH) Melanocyte in amphibian Bone and muscle Testes Ovaries Mammary glands in mammals The hypothalamus & pituitary, I • • • • • • • • • • Releasing and inhibiting hormones Anterior pituitary: Growth (GH):bones √gigantism/dwarfism √acromegaly Prolactin (PRL):mammary glands; milk production Follicle-stimulating (FSH) & Luteinizing (LH):ovaries/testes Thyroid-stimulating (TSH): thyroid Adrenocorticotropic (ACTH): adrenal cortex Melanocyte-stimulating (MSH) Endorphins~natural ‘opiates’; brain pain receptors The pituitary, II • The posterior pituitary: • Oxytocin uterine and mammary gland cell contraction • Antidiuretic (ADH) retention of water by kidneys The pineal, thyroid, & parathyroid • Melatonin pineal gland; biological rhythms • Thyroid hormones: Calcitonin lowers blood calcium Thyroxine metabolic processes • Parathyroid (PTH) raises blood calcium Endocrine System Control Regulation of Blood Calcium Feedback calcitonin kidney reabsorption of Ca++ thyroid Ca++ deposited in bones high blood calcium level Ca++ uptake in intestines (10 mg/100mL) low activated Vitamin D bones release Ca++ kidney reabsorption of Ca++ parathyroid parathyroid hormone (PTH) Regulating metabolism • Hypothalamus – TRH = TSH-releasing hormone • Anterior Pituitary – TSH = thyroid stimulating hormone • Thyroid – produces thyroxine hormones – metabolism & development • • • • • • • bone growth mental development metabolic use of energy blood pressure & heart rate muscle tone digestion reproduction tyrosine + iodine thyroxines The pancreas • Islets of Langerhans • Alpha cells: glucagon • raises blood glucose levels by promoting the release of glucose from the liver (glycogen) • Beta cells: insulin • lowers blood glucose levels by triggering uptake of glucose from blood into body cells • Type I diabetes mellitus (insulin-dependent; autoimmune disorder) • Type II diabetes mellitus (non-insulin-dependent; reduced responsiveness in insulin targets) Endocrine System Control Feedback Regulation of Blood Sugar islets of Langerhans insulin beta islet cells liver stores glycogen body cells take up sugar from blood pancreas liver high blood sugar level (90mg/100ml) low triggers hunger liver releases glucose liver pancreas glucagon islets of Langerhans alpha islet cells reduces appetite The adrenal glands • Adrenal medulla (catecholamines): •epinephrine & norepinephrine~ increase basal metabolic rate (blood glucose and pressure) • Adrenal cortex (corticosteroids): •glucocorticoids (cortisol)~ raise blood glucose •mineralocorticoids (aldosterone)~ reabsorption of Na+ and K+ The gonads • Steroid hormones: precursor is cholesterol • androgens (testosterone)~ sperm formation; male secondary sex characteristics; gonadotropin • estrogens (estradiol)~uterine lining growth; female secondary sex characteristics; gonadotropin • progestins (progesterone)~uterine lining growth QuickTime™ and a Cinepak decompressor are needed to see this picture.
