The Endocrine System

The Endocrine System collection of glands that produce hormones that regulate metabolism, growth and development, tissue function, sexual function, reproduction, sleep, and mood and other functions secrete hormones (chemical messages) directly into the circulatory system to be carried towards distant target organs coordinates whole body to maintain homeostasis accessory organs: (secondary endocrine functions) kidney, liver, heart and gonads

Regulation and Communication Animals rely on two systems for regulation endocrine system 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 widely dispersed fast, short-lasting response

Regulation by Chemical Messengers Neurotransmitters released by neurons Hormones release by endocrine glands hormone carrier By blood neurotransmitter Target cell Pheromones Hormones Local Regulators Chemical signal from 1 individual to another individual Chemical signal from endocrine gland through blood to target cell Chemical signal from one cell to an adjacent cell Eg. ant trail; sex phermones Eg. peptide, steroid hormones Eg. cytokines, growth factors, nitric oxide (NO)

Classes of Hormones Protein-based hormones polypeptides small proteins: insulin, ADH glycoproteins large proteins + carbohydrate: FSH, LH amines modified amino acids: epinephrine, melatonin Lipid-based hormones steroids modified cholesterol: sex hormones, aldosterone

Hormones Action on Target Cells Protein-based hormones (Peptide) Water-soluble Bind to receptors on plasma membrane & triggers signal transduction pathway Affects protein activity already present in cell Rapid response Short-lived Eg. oxytocin, insulin, epinephrine Lipid-based hormones (steroid) Lipid-soluble Enters cell & binds to intracellular receptors Causes change in gene expression (protein synthesis) Slower response Longer life Eg. androgens (testosterone), estrogen, progesterone, cortisol animation

Action of Lipid (Steroid) Hormones

Action of Protein Hormones Uses Signal Transduction Pathway o Secondary Messenger System

Action of Epinephrine (adrenaline) Liver cells break down glycogen and release glucose Blood vessels to skeletal muscles dilate Blood vessels to intestines constrict

Benefits of a Secondary Messenger

Hormones and Homeostasis Negative feedback “more gets you less” stimulus triggers control mechanism that inhibits further change body temperature sugar metabolism Positive feedback “more gets you more” stimulus triggers control mechanism that amplifies effect lactation labor contractions

Negative Feedback Stimulus & Response in opposite directions Thyroid hormones Blood Ca2+ levels Blood glucose levels

Positive Feedback Stimulus and response in same direction Pressure on uterus  oxytocin released causing more pressure

Nervous System Control of Body Temperature

Endocrine Control Regulation of Blood Sugar (Insulin and Blucagon)

Diabetes Mellitus Type I diabetes (10%):deficiency of insulin Insulin-dependent Autoimmune disorder  beta cells of pancreas destroyed Type II diabetes (90%): failure of target cells to respond to insulin Non-insulin dependent Insulin produced  cells don’t respond (defect in insulin receptor or response pathway) Risk factors: obesity, lack of exercise

Endocrine Control of Blood Osmolarity Maintaining Water Balance Low blood osmolarity level/low BP Juxtaglomerular apparatus (JGA) releases renin in kidney Renin converts angiotnesinogen to angiotensin Angiotensin causes arterioles to constrict increases blood pressure Angiotensin triggers release of aldosterone from adrenal gland Increases reabsorption of NACl and H2O in kidneys puts more water and salts back in blood

Regulating Blood Osmolarity If amount of dissolved material in blood is too high, body needs to dilute blood

Endocrine Control Regulation of Blood Calcium

Female Reproductive Cycle hormones from the hypothalamus and anterior pituitary control the ovarian cycle ovarian cycle is hormonally regulated in two phases estrogen secreted before ovulation; progesterone secreted after ovulation.

Nervous and Endocrine Systems Linked Hypothalamus “master nerve control center” nervous system Receives info from nerves and brain Regulates release of hormones from pituitary Pituitary gland “master gland” endocrine system secretes broad range of “tropic” hormones regulating other glands in body

Endocrine Glands Pituitary Growth hormone Stimulates growth Oxytocin Childbirth; lactation attachment Tropic hormones Travel to other glands (ex: TSH, ACTH, FSH) ADH (Anti-Diuretic Hormone) Retain water

Endocrine Glands Thyroid Thyroxine Regulates metabolism Calcitonin Uptake of Ca in blood animation

Thyroid Disorders Goiter due to iodine deficiency Thyroid enlarges as it tries to produce thyroxine Graves’ Disease: autoimmune disorder antibodies bind to TSH receptor hyperthyroidism high temp, sweating, weight loss, high BP

Endocrine Glands Adrenal Epinephrine Fight-or-flight response Release of glucose for more ATP animation Parathyroid Parathyroid hormone Regulates calcium levels (adds Ca to blood)

Adrenal Gland: Effect of Stress

Endocrine Organs Pancreas (Pancreatic islets) Insulin Removes glucose from blood Glucagon Release glucose from glycogen (add to blood) Testes Testosterone Stimulated sperm production Maintains male sex characteristics

Tropins (tropic hormones) stimulate growth in target organs/cells (tropic means nourishment) when the target organ is another gland, tropic hormones cause them to produce & release their own hormones

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 Hypothalamus TRH Anterior pituitary TSH Thyroid T3 T4

Homology in Hormones This list suggests that prolactin is an ancient hormone whose functions have diversified during the evolution of the various vertebrate groups. Growth hormone (GH) is so similar structurally to prolactin that scientists hypothesize that the genes directing their production evolved from the same ancestral gene. Gene duplication.

Homology in Hormones

Hormonal Regulation in Insect Development