Endocrine System Endo crine System inside secrete Odd

Endocrine System

Endo crine System “inside” “secrete” • Odd organ system – Compared to nervous sys. & digestive sys. • Endocrine glands usually not connected – Considered a “system” because of functional similarity • Secrete chemical messages called hormones to target cells “to excite” Also skin, heart, GI tract, placenta, kidneys, adipose tissue

Principal functions of the endocrine system • Maintenance of the internal environment in the body (maintaining the optimum biochemical environment). • Integration and regulation of growth and development. • Control, maintenance and instigation of sexual reproduction and development. Glands with a sensing and signaling system which regulates the duration and magnitude of hormone release via feedback from the target cell.

Control of Endocrine Activity The concentration of hormone as seen by target cells is determined by three factors: • Rate of production • Rate of delivery • Permissiveness/Synergism/Antagonism • Upregulation (insipidus)/downregulation (Type II, melitus) • Rate of degradation and elimination What is a feedback loop?

Components of an automatic control system Variable characteristic of the internal environment that is controlled by this mechanism (internal temp in this example) Sensor (receptor) detects changes in variable and feeds that information back to the integrator (control center) (thermometer in this example) Integrator (control center) integrates (puts together) data from sensor and stored "setpoint" data (thermostat in this example) Setpoint "ideal" or "normal" value of the variable that is previously "set" or "stored" in memory Effector mechanism (furnace in this example) that has an "effect" on the variable (internal temperature in this example)

Types of hormones • Hormones are categorized into four structural groups, with members of each group having many properties in common: – – Peptides and proteins (polypeptides) Amino acid derivatives Steroids (cholesterol based) Fatty acid derivatives - Eicosanoids (mostly paracrines, i. e. leukotrines, prostaglandins)

Types of hormones: Proteins Peptides • Water soluble • Largest # of hormones – Hypothalamus – Pituitary (Ant. & Post. ) – Islets of Langerhans – Parathyroid hormone – Digestive system hormones

Types of hormones • Amino Acid Based – Tyrosine derivatives • Thyroid hormones – Thyroxine (T 4) – Triiodothyronine (T 3) • Catecholamines/Adrenal medulla – Epinephrine – Norepinephrine » Both neurohormones & neurotransmitter – Tryptophan derivatives (precursor to serotonin and the pineal hormone melatonin) – Glutamic acid (converted to histamine)

Types of hormones: Lipids • Steroids – Derivatives of cholesterol differing in side chains – Lipid soluble (freely diffuse, not stored, not packaged) • Examples – Glucocorticoids (cortisol major representative in mammals) – Mineralocorticoids (aldosterone most prominent) – Androgens (i. e. testosterone) – Estrogens (i. e. estradiol and estrone) – Progestogens (i. e. progestins) • Eicosanoids – derived from polyunsaturated fatty acids. – The principal groups of hormones of this class are prostaglandins, prostacyclins, leukotrienes (inflammation) and thromboxanes (platelet aggregation).

Mechanisms of Hormone Action • Lipid-soluble steroids & thyroid hormones • Peptides & water-soluble amines – Diffuse through plasma membrane – Enter nucleus – Forms “hormone-receptor complex”, binds as TFs to chromosome to activate/ inactivate gene(s) Signal Transduction Pathway Animation Transduction Pathway Epinephrine – Hormone (A) binds to receptor on cell surface – Activates G- protein – Activates adenylate cyclase • Converts ATP to c. AMP – c. AMP activates protein kinases, which produce final effect.

Hormone Targets • A cell is a target because is has a specific receptor for the hormone • Most hormones circulate in blood, coming into contact with essentially all cells. However, a given hormone usually affects only a limited number of cells, which are called target cells. • A target cell responds to a hormone because it bears receptors for the hormone.

Which diagram represents… Steroid hormones? Lipid hormones? Peptide hormones?

Target cell concept Receptor Target cell Hormone

Target cell concept Not all hormones find their target How are chemical signals sent to cells?

Types of cell-to-cell signaling • Classic endocrine hormones travel via bloodstream to target cells • Neurohormones are released via synapses and travel via the bloostream • Paracrine hormones act on adjacent cells • Autocrine hormones are released and act on the cell that secreted them • Intracrine hormones act within the cell that produces them

Response vs. distance traveled Endocrine action: the hormone is distributed in blood and binds to distant target cells. Paracrine action: the hormone acts locally by diffusing from its source to target cells in the neighborhood. Autocrine action: the hormone acts on the same cell that produced it.

Ways of influencing target cells Within beside/near self close to

Create a Venn diagram comparing the nervous & endocrine systems

Endocrine vs. Nervous System • Major communication systems in the body • Integrate stimuli and responses to changes in external and internal environment • Both are crucial to coordinated functions of highly differentiated cells, tissues and organs • Unlike the nervous system, the endocrine system is anatomically discontinuous.

Nervous Sys. vs Endocrine Sys. • The nervous system exerts point-topoint control through nerves, similar to sending messages by conventional telephone. Nervous control is electrical in nature and fast. • The endocrine system broadcasts its hormonal messages to essentially all cells by secretion into blood and extracellular fluid. Like a radio broadcast, it requires a receiver to get the message - in the case of endocrine messages, cells must bear a receptor for the hormone being broadcast in order to respond.

Regulation of hormone secretion • Sensing and signaling: a biological need is sensed, the endocrine system sends out a signal to a target cell whose action addresses the biological need. Key features of this stimulus response system are: · receipt of stimulus · synthesis and secretion of hormone · delivery of hormone to target cell · evoking target cell response · degradation of hormone

Receipt of Stimulus • Humoral in response to changing blood levels • i. e. PTH regulation of Ca 2+ via parathyroid • Neural in response to nerve fibers • i. e. catecholamines (norepinephrine & epinephrine) from adrenal medulla • Hormonal in response to other hormones • i. e. GHRH secreted by hypothalamus which regulates GH secretion by anterior pituitary

Inputs to endocrine cells

Feedback Control of Hormone Production • Feedback loops are used extensively to regulate secretion of hormones • Negative feedback occurs when a change in a physiological variable triggers a response that counteracts the initial fluctuation

Negative Feedback • Neurons in the hypothalamus secrete thyroid releasing hormone (TRH), which stimulates cells in the anterior pituitary to secrete thyroid-stimulating hormone (TSH) • TSH binds to receptors on epithelial cells in the thyroid gland, stimulating synthesis and secretion of thyroid hormones, which affect probably all cells in the body • When blood concentrations of thyroid hormones increase above a certain threshold, TRH-secreting neurons in the hypothalamus are inhibited and stop secreting TRH.

Feedback control • Negative feedback is most common: for example, LH from pituitary stimulates the testis to produce testosterone which in turn feeds back and inhibits LH secretion • Positive feedback is less common: examples include LH stimulation of estrogen which stimulates LH surge at ovulation Positive & Negative Feedback

• A steroid hormone affects target cells by directly binding with: – A. c. AMP – B. nuclear receptors which activate genes – C. protein receptors on the target cell’s surface – D. The RER – E. The second messenger

Endocrine Glands • Hypothalamus • Pituitary – Anterior lobe – Posterior lobe • Thyroid gland • Parathyroid glands • Adrenal Glands – Cortex – Medulla Hormonal Communication • Islets of Langerhans • Gonads – Ovaries – Testes • Pineal gland • Thymus • others

Hypothalamus • Part of brain – Regulates ANS, emotions, feeding/satiety, thirst, body temperature, etc. – Hormones related to these functions • “Releasing hormones” • Axonal transport to posterior lobe

Anterior Pituitary • “Releasing” hormones regulate AP aka adeno hypo physis “glands” “under” “growth” • All proteins – TSH (thryoid stimulating hormone/thyrotropin) – ACTH (adrenocorticotropic hormone) – FSH (gonadotropin) – LH (gonadotropin) • Tropins/tropic hormones – GH (growth hormone) – Prolactin-releasing H Hypothalamic Pituitary Axis Animation : IP Web

Anterior Pituitary

Parathyroid Glands • Four small glands embedded in posterior of thyroid – Parathyroid hormone (PTH) – Stimulates osteoclasts to free Ca 2+ from bone – Stimulates Ca 2+ uptake from intestine by stimulating conversion of vitamin D to calcitrol – Stimulates Ca 2+ reuptake from kidney Hormonal Regulation of Calcium

Feedback Loop • Negative feedback in calcium homeostasis. A rise in blood Ca 2+ causes release of calcitonin from the thyroid gland, promoting Ca 2+ deposition in bone and reducing reabsorption in kidneys. • A drop in blood Ca 2+ causes the parathyroid gland to produce parathyroid hormone (PTH), stimulating the release of Ca 2+ from bone. • PTH also promotes reabsorption of Ca 2+ in kidneys and uptake of Ca 2+ in intestines.

Pancreas • Consists of two major types of secretory tissues which reflects its dual function – Exocrine gland • secretes digestive juice • localized in the acinar cells – Endocrine gland • releases hormones • localized in the islet cells (islets of Langerhans)

Pancreatic Islets • “About a million” embedded in pancreas • Control centers for blood glucose – Insulin from beta cells – Glucagon from alpha cells

Regulation of Blood Glucose Mc. Graw-Hill Online Learning Center Test Insulin Glucagon

Islets of Langerhans • Insulin stimulates glucose uptake, glycogenesis • Glucagon stimulates glycogenolysis, glucose release from liver (vs gluconeogenesis)

Feedback Loop • A rise in blood glucose causes release of insulin from beta cells the pancreas, promoting glucose uptake in cells and storage as glycogen in the liver. • A fall in blood glucose stimulates alpha cells in the pancreas to secrete glucagon, which causes the liver to break down glycogen and release glucose.

Pancreas Homeostatic Imbalances Diabetes “siphon” mellitus mel= “honey” Symptoms: • Polyuria • Polydipsia • Polyphagia Blood Level Regulation in Diabetics

Non-Endocrine Gland Hormones • Stomach (gastrin) • Small intestine (duodenum intesetinal gastrin, secretin, cholecystokinin) • Heart (atrial natriuretic peptide) • Kidneys (erythropoietin, active vitamin D 3) • Adipose tissue (leptid, resistin) • Skin • Placenta (human chorionic gonadotropin, human placental lactogen, relaxin)

Functions regulated by the Endocrine System • • Growth Healing Water balance & Blood Pressure Calcium Metabolism Energy Metabolism Stress Regulation of other Endocrine Organs

1. Juvenile diabetes mellitis (type 1) is: a. insulin dependent b. Non-insulin dependent c. Diabetes insipidus d. Goiter associated e. Caused by thyroid deficiency 2. Which of the following processes is not regulated by adrenal cortical hormones: a. Adaptatoin to stress b. Blood pressure c. Glucose utilization d. Labor and delivery e. Sodium/potassium balance

Essential knowledge 3. D. 2: Cells communicate with each other through direct contact with other cells or from a distance via chemical signaling. a. Cells communicate by cell-to-cell contact. b. Cells communicate over short distances by using local regulators that target cells in the vicinity of the emitting cell. c. Signals released by one cell type can travel long distances to target cells of another cell type. – 1. Endocrine signals are produced by endocrine cells that release signaling molecules, which are specific

Resources • • • • • Endocrinology Questions: Endocrinology Quiz: Pathophysiology of the Endocrine System: Endocrine Surgery: Dr. Ross BIO 218 A&P: Mc. Graw Hill Tutorial: http: //www. mhhe. com/biosci/esp/2002_general/Esp/default. htm Lion Den: http: //www. lionden. com/ap. htm Medical Mneumonics: http: //www. medicalmnemonics. com/cgi-bin/browse. cfm Peptide Hormone Signal Transduction Animation: Pathophysiology of the Endocrine System: 106 Animated Tutorials: BIOMedia: http: //bio 1152. nicerweb. com/Locked/media/ Signal Transduction Pathway: Human Physiology U of Colorado: Textbook in Medical Physiology And Pathophysiology: Pituitary Tumors: Bozeman: Elements of a Feedback Loop