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Chemical Signaling Endocrine System Hormones Chemical signal secreted into body fluid for communication Secreted by neurosecretory cells Received by target cells Slow Long duration Often “talks” with nervous system Endocrine System Local regulators: influence nearby cells Growth factors: peptides & proteins that stimulate cell growth, division, & development Prostaglandins (PGs): modified fatty acids act as local regulators, esp. in reproductive & defense systems Endocrine System Two pathways 1) Hormone binds to receptor on target cell signal transduction pathway response Response depends on target cell type Endocrine System 2) Hormone enters target cell & nucleus signal transduction pathway (acting as transcription factor) response (change in gene expression through protein synthesis) Steroids, thyroid hormones Vertebrate Endocrine System Overview of hormones, including tropic hormones Have other endocrine organs as target Vertebrate Endocrine System Hypothalamus Lower brain Receives info from nerves & brain Sends appropriate hormone response based on environmental conditions Have two sets of neurosecretory cells Secretions stored in or regulate activity of pituitary gland Vertebrate Endocrine System Pituitary gland Two discrete parts 1) Anterior pituitary (adenohypophysis) Secretes directly into blood “On” if releasing hormones were secreted from hypothalamus “Off” if inhibitory hormones were secreted Vertebrate Endocrine System Tropic hormones include: Thyroid-stimulating hormone (TSH) Follicle-stimulating hormone (FSH)** Leutinizing hormone (LH)** Adrenocorticotropic hormone – stimulates adrenal cortex Vertebrate Endocrine System **gonadotropins – stimulate gonad activity Other hormones Growth hormone (GH) – protein; stimulates liver to produce insulinlike growth factors (IGF), which stimulates bone & cartilage growth Prolactin (PRL) – protein; mammary growth & milk production in mammals (different in other species) Vertebrate Endocrine System Melanocyte-stimulating hormone (MSH) – regulates skin pigment & fat metabolism Endorphins – inhibit pain perception Vertebrate Endocrine System 2) Posterior pituitary (neurohypophysis) Extension of the brain Hormones include: Antidiuretic hormone (ADH) – regulates osmolarity of blood If osmolarity increases, osmoreceptors in hypothalamus shrink & send impulse to release ADH Signal-transduction pathway in kidney tubules to increase water permeability, which will stop ADH release (neg feedback) Vertebrate Endocrine System Oxytocin – acts on uterus to contract during birth & mammary glands to eject milk during nursing Vertebrate Endocrine System Pineal gland Center of brain Secretes melatonin (amino acid) Regulates function (mostly reproductive) based on changes in day length Secreted at night Has light-sensitive cells or connections from eyes Vertebrate Endocrine System Thyroid gland Two lobes on ventral surface of trachea Hormones: Triiodothyronine (T3) – 3 I atoms Thyroxine (T4) – 4 I atoms – predominant secretion – converted to T3 Calcitonin – lowers Ca2+ in blood Vertebrate Endocrine System Embryonic brain development Vertebrate development & maturation Homeostasis Bp, hr, muscle tone, digestion, reproduction Metabolism Vertebrate Endocrine System Malfunctions Hyperthyroidism Hypothyroidism Cretinism (in infants – muscular & skeletal retardation) Goiter Enlarged thyroid Iodine deficiency Vertebrate Endocrine System Parathyroid 4 Embedded in thyroid Homeostasis of Ca2+ ions Hormones: Parathyroid hormone (PTH) Raises blood levels of Ca2+ Vertebrate Endocrine System Induces osteoclasts to decompose bone minerals and put into blood, increases kidney 7 intestine absorption of calcium Malfunctions Tetany – convulsive contraction of skeletal muscles due to lack of PTH Vertebrate Endocrine System Pancreas Islets of Langerhans – endocrine cell clusters Secrete glucagon (through alpha cells) & insulin (through beta cells) Regulate glucose in blood (negative feedback) Insulin lowers blood sugar, slows glycogen breakdown in liver, inhibits a.a. & glycerol conversion to sugar Liver is extremely sensitive to glucagon Vertebrate Endocrine System Malfunctions Diabetes melliuts High blood sugar Excessive thirst, frequent urination, sugar in urine Use fat breakdown for cell respiration instead of sugar – can lower blood pH Two types Vertebrate Endocrine System Type I (insulin-dependent) Immune system attacks pancreas Childhood Destroys ability to make insulin Insulin injections Type II (insulin-independent) Deficiency of insulin or reduced responsiveness in target cell (change in receptors) Vertebrate Endocrine System Adulthood More than 90% of diabetics Managed by diet & exercise Adrenal glands Sit on top of both kidneys Two glands Vertebrate Endocrine System Adrenal medulla (central portion) Works with nervous system Cells derived from neural crest Hormones: Epinephrine (adrenaline) Norepinephrine (noradrenaline) Both known as catecholamines, from a.a tyrosine Vertebrate Endocrine System Secreted in response to + & stress Inc. availability of energy sources Boost metabolic rate Work with circ. & resp. systems to inc. O2 flow & divert blood to heart, brain, & muscles Works with sympathetic portion of the autonomic nervous system When nerves stimulated, release acetylcholine in medulla, which causes release of epinephrine Vertebrate Endocrine System Norepinephrine works to sustain blood pressure Adrenal cortex (outer portion) Reacts to stress, but responds to endocrine rather than nervous system Hypothalamus secretes anterior pituitary releases ACTH adrenal cortex secretes corticosteroids (glucocorticoids, such as cortisol, & mineralocorticoids, such as aldosterone) Vertebrate Endocrine System Glucocorticoids – work on bioenergetics, specifically glucose metabolism They promote synthesis of glucose from noncarbohydrate sources like muscle proteins High doses suppress immune system, but are used to fight inflammation Vertebrate Endocrine System Mineralocorticoids – salt & water balance They stimulate kidney cells to reabsorb sodium & water Vertebrate Endocrine System Gonads Hormones affect growth, development, reproductive regulation, sexual behavior Secrete 3 types of steroids (testes of males, ovaries of females) Androgens Primary steroid of testes (testosterone) In embryo, development of male organs Secondary sex characteristics of male Vertebrate Endocrine System Estrogens Estradiol Female development & secondary sex characterstics Progestins Progesterone Prepare & maintain uterus Controlled by gonadotropins, FSH, LH, GnRH of hypothalamus