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

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 Regulation 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 axon endocrine gland receptor proteins target cell Neurotransmitters released by neurons Hormones release by endocrine glands Neurohormones specialized neuron secretory cells receptor proteins hormone carried by blood neurotransmitter Lock & Key system

Classes of Hormones : water or lipid soluble Protein-based hormones – polypeptides small proteins: insulin, ADH – 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 insulin

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

nucleus target cell DNA mRNA protein blood protein carrier S S S S Action of lipid (steroid) hormones binds to receptor protein cytoplasm becomes transcription factor ex: secreted protein = growth factor (hair, bone, muscle, gametes) cross cell membrane 1 steroid hormone mRNA read by ribosome 5 plasma membrane protein secreted 7 3

Action of protein hormones activates enzyme activates enzyme activates enzyme ATP produces an action P cytoplasm receptor protein response signal secondary messenger system signal-transduction pathway acts as 2° messenger target cell plasma membrane binds to receptor protein protein hormone ATP activates cytoplasmic signal cAMP GTP activates G-protein transduction

Benefits of a 2° messenger system Amplification! signal receptor protein Activated adenylyl cyclase amplification GTPG protein product enzyme protein kinase cAMP Not yet activated FAST response! amplification Cascade multiplier!

Maintaining homeostasis high low hormone 1 lowers body condition hormone 2 gland specific body condition raises body condition gland 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 pituitary posterior anterior

Thyroid gland hypothalamus anterior pituitary gonadotropic hormones: follicle- stimulating hormone (FSH) & luteinizing hormone (LH) Mammary glands in mammals Muscles of uterus Kidney tubules posterior pituitary thyroid-stimulating hormone (TSH) antidiuretic hormone (ADH) Adrenal cortex Bone and muscle Testes Ovaries Melanocyte in amphibian adrenocorticotropic hormone (ACTH) melanocyte-stimulating hormone (MSH) oxytocin prolactin (PRL) growth hormone (GH) tropic hormones = target endocrine glands

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

Regulation of Blood Calcium blood calcium level (10 mg/100mL) calcitonin parathyroid hormone (PTH)  Ca ++ uptake in intestines high low Feedback Endocrine System Control  kidney reabsorption of Ca ++ bones release Ca ++  kidney reabsorption of Ca ++ Ca ++ deposited in bones activated Vitamin D thyroid parathyroid

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)

liver pancreas liver Regulation of Blood Sugar blood sugar level (90mg/100ml) insulin body cells take up sugar from blood liver stores glycogen reduces appetite glucagon pancreas liver releases glucose triggers hunger high low Feedback Endocrine System Control islets of Langerhans beta islet cells islets of Langerhans alpha islet cells

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