Endocrine System Lecture Outline PDF

Chapter 17: Endocrine System Lecture Outline ============================================ [Chapter 17 Lecture Learning Outcomes] - Describe in detail how body function is controlled via the endocrine system versus the nervous system. - Describe the categories of hormones, hormone transpor...

Chapter 17: Endocrine System Lecture Outline ============================================ [Chapter 17 Lecture Learning Outcomes] - Describe in detail how body function is controlled via the endocrine system versus the nervous system. - Describe the categories of hormones, hormone transport in the blood, and how hormones interact with body cells. - Describe in the detail the components of the endocrine system and the methods by which it controls the body systems and maintains homeostasis. [17.1a Overview of the Endocrine System] **Endocrine system** - Composed of ductless glands that synthesize and secrete **hormones** - Hormones are released into the blood and transported throughout the body - **Target cells** have the specific receptors for a hormone - They bind hormone and respond - Hormone transport to target cells: - - - - [17.1b Comparison of the Two Control Systems] - Endocrine and nervous systems are the two control systems of the body - Both the endocrine and nervous system - Release **ligands---**chemical messengers - Ligands bind to cellular receptor on particular target cells - Unlike the nervous system, the endocrine system - Transmits hormones through the blood - Targets any cells in the body with correct receptors - Can be very widespread - Exhibits longer reaction times - Has longer-lasting effects (minutes to days and weeks) - **Nervous and Endocrine System Communication Methods (Figure 17.1)** [17.1c General Functions of the Endocrine System] - **Regulating development, growth, and metabolism** - Hormones help regulate embryonic cell division and differentiation - Hormones regulate metabolism (both anabolism and catabolism) - **Maintaining homeostasis of blood composition and volume** - Hormones regulate blood solute concentrations (for example, glucose, ions) - Hormones regulate blood volume, cellular concentration, and platelet number - **Controlling digestive processes** - Hormones influence secretory processes and movement of materials in digestive tract - **Controlling reproductive activities** - Hormones affect development and function of reproductive systems and the expression of sexual behaviors [17.2a Location of the Major Endocrine Glands] - **Endocrine glands** contain epithelial tissue that makes and releases hormones within a connective tissue framework - Some glands are **endocrine organs** with solely endocrine function - Include: pituitary, pineal, thyroid, parathyroid, and adrenal glands - Some endocrine cells are found in clusters in organs with another function - Examples in: hypothalamus, skin, thymus, heart, liver, stomach, pancreas, small intestine, adipose connective tissue, kidneys, and gonads - **Location of the Major Endocrine Glands, Organs, and Tissues Containing** **Endocrine Cells (Figure 17.2)** [17.2b Stimulation of Hormone Synthesis and Release] - Hormone release is regulated by **endocrine reflexes** - Hormonal, humoral, or nervous stimuli can initiate hormone release - **Hormonal stimulation** - A gland cell releases its hormone when some other hormone binds to it - **Humoral stimulation** - A gland cell releases its hormone when there is a certain change in levels of a nutrient or ion in the blood - **Nervous system stimulation** - A gland cell releases its hormone when a neuron stimulates it - **Types of Endocrine Stimulation (Figure 17.3)** [17.3a Circulating Hormones ] - **Steroids (Figure 17.4a)** - Lipid-soluble molecules synthesized from cholesterol - Includes gonadal steroids (for example, estrogen) - Includes steroid synthesized by adrenal cortex (for example, cortisol) - Calcitriol sometimes classified in this group, but more accurately called a *sterol* - **Biogenic amines (*monoamines*) (Figure 17.4b)** - Modified amino acids - Includes: catecholamines, thyroid hormone, melatonin - Water-soluble except for thyroid hormone (TH) - TH is nonpolar (made from a pair of tyrosines) and lipid soluble - **Proteins (Figure 17.4c)** - Most hormones are in this category - Water-soluble chains of amino acids [17.3b Local Hormones] - **Local hormones** - Signaling molecules that don't circulate in blood - They bind to the cells that release them (**autocrine stimulation**) or neighboring cells (**paracrine stimulation**) - **Eicosanoids:** a type of local hormone formed from fatty acids within phospholipid bilayer of membrane - Synthesized through an enzymatic cascade - **Eicosanoid Formation (Figure 17.5)** - **Prostaglandins** are eicosanoids - Stimulate pain and inflammatory responses - Aspirin and other nonsteroidal anti-inflammatory drugs block prostaglandin formation [17.5a Lipid-Soluble Hormones] - **Lipid-soluble hormones** can diffuse across target cell membrane - Such hormones are small, nonpolar, and **lipophilic** - Their receptors are *inside* the cytosol or nucleus - Once hormone enters cell it binds to *intracellular receptor* and forms **hormone-receptor complex** - Results in synthesis of a new protein - **Lipid-Soluble Hormones and Intracellular Receptors (Figure 17.6)** [17.5b Water-Soluble Hormones] - **Water-soluble hormones** use *extracellular* membrane receptors - Such hormones are polar and can't diffuse through membrane - **Initiate series of biochemical events, signal transduction pathway** - initiated by the hormone, the **first messenger** - - termed **second messenger (e.g., cAMP)** - modifies some cellular activity - Multiple results possible with different signal transduction pathways - Activation or inhibition of enzymatic pathways - Growth through cellular division - Release of cellular secretions - Changes in membrane permeability - Muscle contraction or relaxation [17.6b Hormone Interactions on a Target Cell] - Different hormones can simultaneously bind to a cell, and their effects may interact - **Synergistic** interactions - One hormone reinforces activity of another hormone - For example, estrogen and progesterone effects on a target cell - **Permissive** interactions - One hormone requires activity of another hormone - For example, oxytocin's milk ejection effect requires prolactin's milk generating effect - **Antagonistic** interactions - One hormone opposes activity of another hormone - For example, glucagon increases blood glucose while insulin lowers it - **Hormone Interactions (Figure 17.9b)** [17.7a Anatomic Relationship of the Hypothalamus and the Pituitary Gland] - Hypothalamus controls pituitary, which controls several other endocrine organs: - **Pituitary gland** (*hypophysis*) - - - - - **Posterior pituitary** (*neurohypophysis*) - Smaller, neural part of pituitary gland - Hypothalamic neurons project through infundibulum and release hormones in posterior pituitary - Somas in **supraoptic nucleus** and **paraventricular nucleus** - Axons in **hypothalmo-hypophyseal tract** of infundibulum - Synaptic knobs within posterior pituitary - **Hypothalamo-Hypophyseal Tract (Figure 17.11a)** - **Anterior pituitary** - **Hypothalamo-hypophyseal portal system** of blood vessels connects hypothalamus to anterior pituitary - **Primary plexus** - Porous capillary network associated with - **Secondary plexus** -- Capillary network associated with anterior - **Hypophyseal portal veins** - Drain primary plexus and transport to secondary plexus - **Hypothalamo-Hypophyseal Portal System (Figure 17.11b)** [17.7b Interactions Between the Hypothalamus and the Posterior Pituitary Gland] - Posterior pituitary is storage and release site for **antidiuretic hormone ADH** & **oxytocin OT** - ADH and OT are hormones made in hypothalamus by **neurosecretory cells** - - - **Antidiuretic hormone** (*vasopressin*) - Made in supraoptic nucleus - Functions: decrease urine production, stimulate thirst, constrict blood vessels - **Oxytocin** - Made in paraventricular nucleus - Functions: uterine contraction, milk ejection, emotional bonding [17.7c Interactions Between the Hypothalamus and the Anterior Pituitary Gland] - Hypothalamus hormonally stimulates anterior pituitary to release its hormones - Hypothalamus secretes **regulatory hormones** - Travel via portal blood vessels to pituitary - Anterior pituitary secretes hormones into general circulation - **Hormones of the hypothalamus** - **Releasing hormones** - Increase secretion of anterior pituitary hormones - Thyrotropin-releasing hormone (TRH) - Prolactin-releasing hormone (PRH) - Gonadotropin-releasing hormone (GnRH) - Corticotropin-releasing hormone (CRH) - Growth hormone-releasing hormone (GHRH) - **Inhibiting hormones** - Decrease secretion of anterior pituitary hormones - Prolactin-inhibiting hormone (PIH) - Growth-inhibiting hormone (GIH) - **Hormones of the anterior pituitary** - **Thyroid-stimulating hormone (TSH**; *thyrotropin***)** - Release triggered by TRH from hypothalamus - Causes release of thyroid hormone (TH) from thyroid gland - **Prolactin (PRL)** - Release triggered by PRH, inhibited by PIH from hypothalamus - Causes milk production, mammary gland growth in females - **Adrenocorticotropic hormone (ACTH;** *corticotropin***)** - Release triggered by CRH from hypothalamus - Causes release of corticosteroids by adrenal cortex - - Release triggered by GnRH from hypothalamus - - In male: sperm development and secretion of testosterone - **Growth hormone (GH;** *somatotropin***)** - Causes liver to secrete **insulin-like growth factors 1** and **2** - GH and IGFs function synergistically to stimulate cell growth and division - **Anterior Pituitary Hormones (Figure 17.12)** [17.7d Growth Hormone: Its Regulation and Effects ] - Regulation of growth hormone release - Release controlled through hormonal stimulation (GHRH and GHIH) from - - - Amount of GHRH released from hypothalamus impacted by: - A person's age, time of day, nutrient levels, stress and exercise - Effects of growth hormone - Stimulates release of IGFs from liver - Similar functions as GH but longer half-life - All cells have receptors for GH, IGFs, or both - Hormone stimulates increased protein synthesis, cell division, cell - Also stimulates release of nutrients from storage - **Glycogenolysis** (breakdown of glycogen into glucose) stimulated - **Gluconeogenesis** (conversion of nutrients to glucose) stimulated - **Glycogenesis** (synthesis of glycogen) inhibited - **Lipolysis** (breakdown of triglycerides) stimulated - **Lipogenesis** (formation of triglycerides) inhibited - **Regulation and Action of Growth Hormone (Figure 17.13)** - **Variables That Influence Growth Hormone Levels (Figure 17.14)** [17.8a Anatomy of the Thyroid Gland] - Inferior to thyroid cartilage of larynx, anterior to trachea - **Left** and **right lobes** - Connected at midline by narrow **isthmus** - Rich vascularization gives it reddish color - Composed of microscopic follicles - **Follicular cells---**cuboidal epithelial cells that surround a central lumen, synthesize **thyroglobulin (TGB)** - Produce and release **thyroid hormone (TH)** - Follicle lumen houses **colloid---**a viscous, protein-rich fluid - **Parafollicular cells---**cells between follicles, make **calcitonin** - Hormone that decreases blood calcium levels - **Thyroid Gland, Anterior View (Figure 17.15a)** - **Microscopic View of Thyroid Gland (Figure 17.15b)** - **Thyroid Hormone: Synthesis, Storage, and Release (Figure 17.16)** [17.8b Thyroid Hormone: Its Regulation and Effects ] - Regulation of thyroid hormone release - **Hypothalamic-pituitary-thyroid axis** - Cold temperature, pregnancy, high altitude, hypoglycemia, or low TH - TRH causes anterior pituitary to release TSH - TSH binds receptors of follicular cells, triggers release of TH - Follicular cells release two forms of TH to blood: T~3~, T~4~ - T~3~ = triiodothyronine; T~4~ = tetraiodothyronine - T~3~ and T~4~ are transported within blood by carrier molecules - **Regulation and Action of Thyroid Hormone (Figure 17.17)** - Effects of Thyroid Hormone - Cellular transport brings TH into target cells, binds receptor - T~3~ versus T~4~ - Thyroid gland produces more T~4~ but T~3~ is more active form - Most target cells convert T~4~ to T~3~ - TH increases metabolic rate and protein synthesis in targets - Stimulates synthesis of sodium-potassium pumps in neurons - **Calorigenic:** generates heat, raises temperature - Stimulates increased amino acid and glucose uptake - Fosters energy (ATP) production - Hepatocytes stimulated to increase blood glucose - TH causes increases in glycogenolysis and gluconeogenesis, and a decrease in glycogenesis - Adipose cells stimulated to increase blood glycerol and fatty acids - TH causes increase in lipolysis and decrease in lipogenesis - This saves glucose for the brain (**glucose-sparing effect**) - TH increases respiration rate - To meet additional oxygen demand - TH increases heart rate and force of contraction - Increased blood flow to deliver more nutrients and oxygen - Causes heart to increase receptors for epinephrine and *[Clinical View: Disorders of Thyroid Hormone Secretion ]* - **Hyperthyroidism** - Results from excessive production of TH - Increased metabolic rate, weight loss, hyperactivity, heat intolerance - Caused by T~4~ ingestion, excessive stimulation by pituitary, or loss of feedback control in thyroid (**Graves disease**) - Treated by removing the thyroid (then giving hormone supplements) - **Hypothyroidism** - Results from decreased production of TH - Low metabolic rate, lethargy, cold intolerance, weight gain - Caused by decreased iodine intake, loss of pituitary stimulation of thyroid, postsurgical, or immune system destruction of thyroid (**Hashimoto thyroiditis**) - Treated with thyroid hormone replacement - **Goiter** - Enlargement of thyroid - Typically due to insufficient dietary iodine - Lack of dietary iodine preventing thyroid from producing thyroid hormone - Once relatively common in United States, but no longer now that iodine added to table salt [17.8c Calcitonin: Its Regulation and Effects] - **Calcitonin** - Synthesized and released from parafollicular cells of thyroid gland - Stimulus for release is high blood calcium or stress from exercise - Acts to decrease blood calcium levels by - Inhibiting osteoclast activity - Stimulate kidneys to increase excretion of calcium in urine [17.9a Anatomy of the Adrenal Glands] - Located on superior surface of each kidney - Retroperitoneal; embedded in fat and fascia - Two regions: - **Adrenal medulla** - Forms inner core of each adrenal gland - Red-brown color due to extensive blood vessels - Releases **epinephrine** and **norepinephrine** with sympathetic stimulation - **Adrenal cortex** - Synthesizes more than 25 corticosteroids - Yellow color due to lipids within cells - Three regions producing different steroid hormones: zona glomerulosa, zona fasciculata, and the inner zona reticularis - **Adrenal Gland Location (Figure 17.18a)** - **Adrenal Gland Sectional Anatomy and Histology (Figure 17.18b)** - Hormones of the Adrenal Cortex - **Mineralocorticoids:** hormones that regulate electrolyte levels - Made in **zona glomerulosa:** thin, outer cortical layer - **Aldosterone** fosters Na^+^ retention and K^+^ secretion - **Glucocorticoids:** hormones that regulate blood sugar - Made in **zona fasciculata:** larger, middle cortical layer - **Cortisol** increases blood sugar - **Gonadocorticoids:** sex hormones - Made in **zona reticularis:** thin, inner cortical layer - **Androgens** are male sex hormones made by adrenals - Converted to estrogen in females - Amount of produced by adrenals is less than amount from testes [17.9b Cortisol: Its Regulation and Effects ] - Regulation of cortisol release - **Cortisol** and **corticosterone** increase nutrient levels in blood - To resist stress and repair injured tissue - Release regulated by **hypothalamic-pituitary-adrenal axis** - Stress, late stages of sleep, and low levels of cortisol stimulate hypothalamus to release CRH - CRH stimulates anterior pituitary to release ACTH - ACTH stimulates adrenal cortex to release cortisol and corticosterone - Cortisol travels through blood attached to carrier proteins - Small amounts of cortisol dissociate from carrier and leave bloodstream - Cortisol levels are regulated by negative feedback - Cortisol inhibits release of CRH from hypothalamus and ACTH from anterior pituitary - **Regulation and Action of Cortisol Hormone (Figure 17.19)** - **Variables That Influence Blood Levels of Cortisol (Figure 17.20)** - Effects of Cortisol - Cortisol causes target cells to increase blood nutrient levels - Liver cells increase glycogenolysis and gluconeogenesis; decrease glycogenesis - Adipose cells increase lipolysis and decrease lipogenesis - Many body cells break down proteins to amino acids - Liver cells use the amino acids for gluconeogenesis - Most cells decrease their glucose uptake, sparing it for brain - Therapeutic doses of Corticosterone - Corticosterone is used as a treatment for inflammation - It inhibits inflammatory agents and suppresses immune system - At high doses it has side effects - Increases risk of infections, cancer - Increases retention of sodium and water - Inhibits connective tissue repair *[Clinical View: Disorders in Adrenal Cortex Hormone Secretion ]* - **Cushing syndrome** - Chronic exposure to excessive glucocorticoid hormones in people taking corticosteroids for therapy - Some cases when adrenal gland produces too much hormone - Obesity, hypertension, **hirsuitism** (excess male-pattern hair growth), kidney stones, and menstrual irregularities - **Addison disease** - Form of adrenal insufficiency - Develops when adrenal glands fail - Chronic shortage of glucocorticoids and sometimes mineralocorticoids - May develop from lack of ACTH or lack of response to ACTH - Weight loss, fatigue and weakness, hypotension, and skin darkening - Therapy of oral corticosteroids - **Adrenogenital syndrome (congenital adrenal hyperplasia)** - Begins in embryo or fetus - Inability to synthesize corticosteroids leads to overproduction of ACTH - High ACTH causes increased size of adrenal gland and production of hormones with testosterone-like effects - Masculinizes newborn *[Clinical View: Stress Response]* - Stressors elicit a **stress response** - Hypothalamus initiates neuroendocrine response - Three stages - **Alarm reaction** - Initial response involving sympathetic nervous system activation, epinephrine, norepinephrine - **Stage of resistance** - After depletion of glycogen stores, adrenal secretes cortisol to raise blood sugar and help meet energy demands - **Stage of exhaustion** - After weeks or months, depletion of fat stores results in protein breakdown for energy leading to weakening of the body and illness [17.10a Anatomy of the Pancreas] - Located posterior to stomach, between duodenum and spleen - Pancreas has endocrine and exocrine functions - **Acinar cells** generate exocrine secretions for digestion - They make up vast majority of pancreas as saclike **acini** - **Pancreatic islets** (of Langerhans) contain clusters of endocrine cells - **Alpha cells** secrete **glucagon** - **Beta cells** secrete **insulin** - Delta cells (secrete somatostatin) and F cells (secrete pancreatic polypeptide) also present - **Pancreas (Figure 17.21)** [17.10b Pancreatic Hormones ] - Pancreatic hormones help maintain blood glucose - Normal range is 70 to 110 mg of glucose/deciliter - High levels damage blood vessels and kidneys - Low levels cause lethargy, mental and physical impairment, death - **Lowering high blood glucose levels with insulin** - After food intake, beta cells detect rise in blood glucose and respond by secreting insulin - Insulin travels through blood and randomly leaves bloodstream to encounter target cells - Insulin binds to receptors and initiates 2^nd^ messenger systems - Once blood glucose falls, beta cells stop secreting insulin - **Lowering high blood glucose levels with insulin** (*continued*) - Hepatocytes remove glucose from blood; store it as glycogen - Glycogenesis stimulated; glycogenolysis and gluconeogenesis inhibited - Adipose cells decrease fatty acid levels in blood; store fat - Lipogenesis stimulated and lipolysis inhibited - Most body cells increase nutrient uptake in response to insulin - Increased amino acid uptake, protein synthesis (especially in muscle) - Increased glucose uptake by incorporating more glucose transport proteins into plasma membrane - With less alternate fuels available (for example, less fatty acids) more body cells use glucose - Some cells do not require insulin to take in glucose - Including: neurons, kidney cells, hepatocytes, red blood cells - **Regulation and Action of Insulin (Figure 17.22)** *[Clinical View: Conditions Resulting in Abnormal Glucose Levels ]* - **Diabetes mellitus** - Inadequate uptake of glucose from blood - Chronically elevated glucose, blood vessels damaged - Leading cause of retinal blindness, kidney failure, and nontraumatic amputations in the United States - Associated with increased heart disease and stroke - **Type 1 diabetes** - Absent or diminished release of insulin by pancreas - Tends to occur in children and younger individuals - May have autoimmune component - Requires daily injections of insulin - **Type 2 diabetes** - From decreased insulin release or insulin effectiveness - Obesity major cause in development - Tends to occur in older individuals, but can occur in young adults - Treatment with diet, exercise, and medications - **Gestational diabetes** - Seen in some pregnant women - If untreated, causes risk to fetus and increases delivery complications - Increases chance of later developing type 2 diabetes - **Hypoglycemia** - Glucose levels below 60 mg/DL - Numerous causes - Insulin overdose, prolonged exercise, alcohol use, liver or kidney dysfunction - Deficiency of glucocorticoids or growth hormone, genetics - Symptoms of hunger, dizziness, confusion, sweating, and sleepiness - Glucagon given if individual unconscious and unable to eat - **Raising low blood glucose levels with glucagon** - Alpha cells detect drop in blood glucose and release glucagon - Glucagon acts through membrane receptors and 2^nd^ messengers causing body cells to release stored nutrients into blood - Hepatocytes release glucose - Glycogenolysis and gluconeogenesis stimulated; glycogenesis inhibited - Adipose cells release fatty acids and glycerol - Lipolysis stimulated, while lipogenesis inhibited - Glucagon does not affect protein composition - Glucagon can be given by paramedics to unconscious individuals with low blood sugar - Once blood glucose rises, glucagon release is inhibited - **Regulation and Action of Glucagon (Figure 17.23)** [17.11a Pineal Gland] - **Pineal gland** is a small unpaired body in the epithalamus of the diencephalon - Pineal secretes **melatonin** at night - Causes drowsiness - Regulates circadian rhythm and has effects on mood - Melatonin influences GnRH secretion [17.11b Parathyroid Glands] - **Parathyroid glands** are small structures on the posterior surface of the thyroid gland - There are between 2 and 6 of them (usually 4) - Contain **chief cells** and oxyphil cells - Chief (principal) cells make **parathyroid hormone (PTH)** - PTH increases blood calcium - Liberates it from bone, decreases its loss in urine, activates calcitriol hormone [17.11c Structures with an Endocrine Function ] - **Thymus** epithelial cells secrete **thymic hormones** - Located anterior to top of heart - Grows during childhood but shrinks during adulthood - Maturation site for T-lymphocyte white blood cells - Endocrine tissue in **heart** atria secretes **atrial natriuretic peptide (ANP)** - ANP is a hormone that lowers blood pressure - Kidneys increase urine output and blood vessels dilate - **Kidney** endocrine cells release **erythropoietin (EPO)** - Secretion occurs in response to low blood oxygen - EPO causes increased red blood cell production - **Liver** secretions include insulin-like growth factors and the inactive hormone **angiotensinogen** - Angiotensinogen is converted to active **angiotensin II** by enzymes from the kidney and lung blood vessels - Angiotensin II helps raise blood pressure when it starts to fall - Causes vessel constriction, decreases urine output, stimulates thirst - **Stomach** secretes **gastrin** - Gastrin increases secretion and motility in stomach for digestion - **Small intestine** secretes **secretin** and **cholecystokinin (CCK)** into blood - Secretin stimulates secretion of bile and pancreatic juice - CCK stimulates release of bile from gall bladder - In **skin** cells, light converts modified cholesterol to **vitamin D~3~,** which is then released into blood - Vitamin D~3~ is converted to calcidiol by a liver enzyme - Calcidiol is converted to calcitriol by a kidney enzyme - **Calcitriol** is the active hormone that raises blood calcium - Stimulates Ca^2+^ from bone, decreases Ca^2+^ loss in urine, stimulates Ca^2+^ absorption in intestine - **Adipose connective tissue** secretes **leptin** - Leptin controls appetite by binding to neurons in hypothalamus - Lower body fat is associated with less leptin and this stimulates appetite - **Adipose has other endocrine effects** - Excess adipose raises risk of cancer - Excess adipose delays male puberty - Abnormally low adipose interferes with female menstrual cycle