The Endocrine System

Home , Adrenal medulla, Chromophobe cell, Gonad, Parafollicular cell, Parathyroid gland, Zona glomerulosa

PowerPoint® Lecture Slides The Endocrine System: An Overview prepared by Leslie Hendon University of Alabama, Birmingham • A system of ductless glands • Secrete messenger molecules called hormones C H A P T E R 17 • Interacts closely with the nervous system Part 1 • Endocrinology The Endocrine • Study of hormones and endocrine glands System

Endocrine Organs Location of the Major Endocrine Glands

Pineal gland • Scattered throughout the body Hypothalamus Pituitary gland • Pure endocrine organs are the … Thyroid gland • Pituitary, pineal, thyroid, parathyroid, and adrenal Parathyroid glands glands (on dorsal aspect of thyroid gland) • Organs containing endocrine cells include: Thymus • Pancreas, thymus, gonads, and the hypothalamus Adrenal glands • Plus other organs secrete hormones (eg., kidney, stomach, intestine) Pancreas • Hypothalamus is a neuroendocrine organ • Produces hormones and has nervous functions Ovary (female)

• Endocrine cells are of epithelial origin Testis (male)

Hormones Control of Hormones Secretion • Classes of hormones • Amino acid–based hormones • Secretion triggered by three major types of • Steroids—derived from cholesterol stimuli: • Basic hormone action • Humoral—simplest of endocrine control mechanisms • Circulate throughout the body in blood vessels • Secretion in direct response to changing • Influences only specific tissues— those with ion or nutrient levels in the blood target cells that have receptor molecules for that hormone • Example: Parathyroid monitors calcium • A hormone can have different effects on • Responds to decline by secreting different target cells (depends on the hormone to reverse decline receptor)

1 Control of Hormones Secretion Types of Endocrine Gland Stimuli

(a) Humoral stimulus (b) Neural stimulus (c) Hormonal stimulus • Secretion triggered by three major types of stimuli 1 Capillary blood contains 1 Preganglionic sympathetic fibers 1 The hypothalamus secretes low concentration of Ca2+, stimulate adrenal medulla cells… hormones that… (continued) which stimulates… CNS (spinal cord) Hypothalamus • Neural Capillary (low Ca2+ • Sympathetic nerve fibers stimulate cells in the in blood) 2 …stimulate the anterior Thyroid gland adrenal medulla pituitary gland (posterior view) Parathyroid to secrete • Induces release of epinephrine and norepinephrine glands hormones Pituitary that… gland • Hormonal Preganglionic sympathetic • Stimuli received from other glands fibers

• Certain hormones signal secretion of other Thyroid Adrenal Gonad gland cortex (Testis) hormones Medulla of Parathyroid adrenal gland • Example: Hypothalamus secretes hormones  glands stimulates pituitary  stimulates other glands PTH Capillary

2 …secretion of parathyroid hormone 2 …to secrete catecholamines 3 …stimulate other endocrine glands (PTH) by parathyroid glands. PTH acts to (epinephrine and norepinephrine) to secrete hormones increase blood Ca2+.

Control of Hormone Secretion The Pituitary Gland

• Always controlled by feedback loops • Secretes nine major hormones • Blood concentration declines below a • Attached to the hypothalamus by the infundibulum minimum --> More hormone is secreted • Two basic divisions of the pituitary gland • Adenohypophysis (anterior lobe) • Blood concentration exceeds maximum • Has three major divisions --> Hormone production is halted • Pars distalis, pars intermedia, and pars tuberalis • Neurohypophysis (posterior lobe) —has two major divisions • Pars nervosa and infundibular

The Pituitary Gland The Anterior Lobe

Corpus callosum Thalamus • The pars distalis—largest division of the Pineal anterior lobe Hypothalamus Mammillary body • Contains five different endocrine cell groups Brain stem Pituitary (hypophysis) • Makes and secretes seven different hormones (b) Acidophil Basophil Chromophobe cell (a) • Tropic hormones regulate hormone secretion by other glands Optic chiasma Mammillary Median eminence body of hypothalamus Tuber cinereum • Include: TSH, ACTH, FSH, LH Anterior lobe Pars tuberalis Posterior lobe Pars intermedia Infundibulum • GH, PRL, and MSH Pars distalis Pars nervosa • Act directly on non-endocrine target tissues

Capillary with Spherical cluster red blood cells of cells (c) (d)

2 The Anterior Lobe The Anterior Lobe

• Growth hormone, GH (somatotropic • Thyroid-stimulating hormone, TSH hormone) • Produced by thyrotropic cells • Produced by somatotropic cells • Signals thyroid gland to secrete thyroid • Stimulates body growth by stimulating hormone increased protein production and growth of • Adrenocorticotropic hormone, ACTH epiphyseal plates • Stimulates the adrenal cortex to secrete • Stimulates growth directly and indirectly by hormones that help cope with stress the liver’s secretion of insulin-like growth factor-1.

The Anterior Lobe The Anterior Lobe

• Melanocyte-stimulating hormone, MSH • Prolactin—produced by prolactin cells • In humans, MSH functions in appetite • Targets milk-producing glands in the breast— supression stimulates milk production • Gonadotropins— are produced by • Endocrine cells of the pars distalis gonadotropic cells and affect the gonads • Clustered in spheres and branching cords • Follicle-stimulating hormone, FSH, and luteinizing hormone, LH

The Anterior Lobe The Anterior Lobe

3 Hypothalamic Control of Hormone Secretion Hypothalamic Control of Hormone Secretion from the Anterior Lobe from the Anterior Lobe • The hypothalamus • Releasing hormones • Controls secretion of anterior lobe hormones • Are secreted like neurotransmitters • Exerts control by secreting: • Enter a primary capillary plexus • Releasing hormones—prompt anterior • Travel in hypophyseal portal veins to a lobe to release hormones secondary capillary plexus • Inhibiting hormones—turn off secretion of (hypothalamohypophyseal portal system) anterior lobe hormones • From the secondary capillary plexus, hormones secreted by the anterior lobe enter general circulation and travel to target organs

The Anterior Lobe The Posterior Lobe

• Is structurally part of the brain • Its axons make up the hypothalamic– Hypothalamic neuron Hypothalamus 1 When appropriately cell bodies stimulated, hypothalamic hypophyseal tract Superior hypophyseal neurons secrete releasing artery and inhibiting hormones into Hypophyseal the primary capillary plexus. • Arises from neuronal cell bodies in the portal system Primary capillary hypothalamus 2 Hypothalamic hormones plexus travel through the portal Hypophyseal veins to the anterior pituitary • Supraoptic nucleus portal veins where they stimulate or Secondary inhibit release of hormones Paraventricular nucleus capillary from the anterior lobe. • plexus Anterior lobe 3 Anterior pituitary of pituitary hormones are secreted into the secondary capillary TSH, FSH, LH, plexus. ACTH, GH, PRL (a) Relationship between the anterior pituitary and the hypothalamus

The Posterior Lobe Relationship Between the Posterior Pituitary and Hypothalamus • Does not make hormones 1 Hypothalamic neurons synthesize oxytocin and • Stores and releases hormones made in the ADH. hypothalamus Paraventricular nucleus Hypothalamus • Releases two peptide hormones Supraoptic nucleus 2 Oxytocin and ADH are Optic chiasma transported along the • Antidiuretic hormone (ADH) [aka, vasopressin] hypothalamic- Infundibulum (connecting stalk) hypophyseal tract to the • Oxytocin (OT) Hypothalamic- Inferior posterior lobe. hypophyseal hypophyseal tract artery 3 Oxytocin and ADH are stored in axon terminals Axon in the posterior pituitary. terminals Posterior 4 Oxytocin and ADH are lobe of Oxytocin released into the blood pituitary ADH when hypothalamic neurons fire. (b) Relationship between the posterior pituitary and the hypothalamus

4 The Posterior Lobe

• ADH (vasopressin) • Made in supraoptic nucleus • Targets kidneys to reabsorb water • Oxytocin • Produced in the paraventricular nucleus • Induces smooth muscle contraction of reproductive organs, ejects milk during breast feeding, and signals contraction of the uterus during childbirth

The Thyroid Gland The Thyroid Gland Hyoid bone Thyroid cartilage Epiglottis • Located in the anterior neck External carotid artery • Largest pure endocrine gland Superior thyroid Common carotid artery • Composed of follicles and areolar connective artery Inferior thyroid Isthmus of artery tissue thyroid gland • Produces two hormones

• Thyroid hormone (TH) Right Left subclavian subclavian artery artery • Calcitonin Left lateral Trachea lobe of thyroid gland Aorta

(a) Gross anatomy of the thyroid gland, anterior view

The Thyroid Gland The Parathyroid Glands Colloid-filled Follicular cells follicles (secrete thyroid hormone) • Lie on the posterior surface of the thyroid gland • Contain two types of endocrine cells • Chief cells • Produce parathyroid hormone (PTH) • Increases blood concentration of Ca2+ • Oxyphil cells • Function unknown

5 The Parathyroid Glands The Adrenal (Suprarenal) Glands

• Pyramid-shaped glands located on the superior surface of each kidney

Pharynx • Supplied by about 60 suprarenal arteries (posterior aspect) • Nerve supply is almost exclusively Parathyroid cells sympathetic fibers Thyroid (secrete parathyroid gland Parathyroid hormone) glands Esophagus Oxyphil cells Trachea Capillary

(a) Location of parathyroid (b) Photomicrograph of glands, posterior view parathyroid gland tissue (360×)

The Adrenal (Suprarenal) Glands The Adrenal Medulla

• Two endocrine glands in one • Chromaffin cells • Adrenal medulla—a cluster of neurons • Are modified ganglionic sympathetic neurons • Derived from neural crest • Secrete amine hormones epinephrine and • Part of the sympathetic nervous system norepinephrine • Adrenal cortex—forms the bulk of the gland • Enhance “fight-or-flight” response • Derived from somatic mesoderm • Hormones are stored in secretory vesicles • All adrenal hormones help one cope with • Are arranged in spherical clusters and some danger, terror, or stress branching cords

The Adrenal Cortex The Adrenal Cortex

• Secretes lipid-based steroid hormones • Hormones are corticosteroids • Cortex is composed of three layers (zones) • Adrenal corticosteroids are of two main • Zona glomerulosa—cells arranged in classes spherical clusters • Mineralocorticoids • Zona fasciculata—cells arranged in parallel • Glucocorticoids cords; contains lipid droplets • Also secretes androgens • Zona reticularis—cells arranged in a branching network

6 Mineralocorticoids Glucocorticoids

• Aldosterone—secreted by the zona • Cortisol is the main type glomerulosa • Secreted by zona fasciculata and zona • Secreted in response to decline in blood reticularis volume or blood pressure • Helps the body deal with stressful situations • Is the terminal hormone of the renin- angiotensin mechanism

The Adrenal Gland–Gross and Microscopic Stress and the Adrenal Gland

Short-term stress More prolonged stress

Stress

Hormones Nerve impulses Hypothalamus Capsule secreted Zona Aldosterone glomerulosa CRH (corticotropin- releasing hormone)

Zona Spinal cord fasciculata

Adrenal gland Medulla Cortisol Corticotroph cells Cortex and of anterior pituitary Cortex Preganglionic androgens To target in blood sympathetic fibers Zona Adrenal cortex reticularis Adrenal medulla (secretes steroid Kidney (secretes amino acid– hormones) based hormones) ACTH

Catecholamines Mineralocorticoids Glucocorticoids (epinephrine and Adrenal Epinephrine norepinephrine) medulla and Short-term stress response Long-term stress response

Medulla norepinephrine 1.Increased heart rate 1.Retention of sodium 1.Proteins and fats converted 2.Increased blood pressure and water by kidneys to glucose or broken down 3.Liver converts glycogen to glucose and releases 2.Increased blood volume for energy (a)Drawing of the histology of the (b) Photomicrograph (140X) glucose to blood and blood pressure 2.Increased blood glucose adrenal cortex and a portion of 4.Dilation of bronchioles 3.Suppression of immune the adrenal medulla 5.Changes in blood flow patterns leading to decreased system digestive system activity and reduced urine output 6.Increased metabolic rate

The Pineal Gland The Pancreas

• Located on the roof of the diencephalon • Located in the posterior abdominal wall • Shaped like a pine cone • Contains endocrine and exocrine cells • “Pineal sand” is radiopaque • Exocrine cells • Used as a landmark to identify other brain • Acinar cells —secrete digestive enzymes structures in X rays • Endocrine cells • Pinealocytes secrete melatonin • Pancreatic islet cells —islets of Langerhans • A hormone that regulates circadian rhythms • About one million islets—scattered throughout the pancreas

7 The Pancreas The Pancreas

• Main endocrine cell types • Pancreatic islets contain two rare cell types • Alpha cells (α cells)—secrete glucagon • Delta (∂) cells • Signals liver to release glucose from glycogen • Secrete somatostatin Raises blood sugar • • Inhibits secretion of insulin and glucagon • Beta cells (β cells)—secrete insulin • F (PP) cells • Signals most body cells to take up glucose from the blood • Secrete pancreatic polypeptide • Promotes storage of glucose as glycogen in • May inhibit exocrine activity of the liver pancreas • Lowers blood sugar

The Thymus The Gonads

• Located in the lower neck and anterior thorax • Main sources of sex hormones • Important immune organ • Testes and ovaries • Site at which T-lymphocytes arise from • Male precursor cells • Interstitial cells secrete androgens • Primarily testosterone • Promotes the formation of sperm • Maintains secondary sex characteristics

PLAY Male Hormones

The Gonads Other Endocrine Structures

• Female • Endocrine cells occur within • Ovaries • The heart • Androgens secreted by the theca folliculi • Atria contain atrial natriuretic peptide • Converted to estrogen by follicular granulosa (ANP) cells • The GI tract • Estrogen • Enteroendocrine cells • Maintains secondary sex characteristics • The placenta • Progesterone • Sustains the fetus and secretes several • Prepares the uterus for pregnancy steroid protein hormones

8 Other Endocrine Structures Pituitary Disorders

• The kidneys • Gigantism • Cells of the juxtaglomerular apparatus • Hypersecretion of GH in children (JGA) secrete renin • Pituitary dwarfism • Endothelial cells and interstitial connective • Hyposecretion of GH tissue—secrete erythropoietin • Diabetes insipidus • The skin • Pars nervosa does not make enough ADH • Modified cholesterol molecules convert to a precursor of vitamin D

Disorders of the Pancreas: Diabetes Mellitus Diabetes Mellitus

• Caused by • Type 2 diabetes • Insufficient secretion of insulin • Adult onset • Resistance of body cells to the effects of • Usually occurs after age 40 insulin • Cells have lowered sensitivity to insulin • Type 1 diabetes • Controlled by dietary changes and regular • Develops suddenly, usually before age 15 exercise • T cell–mediated autoimmune response destroys beta cells

Disorders of the Thyroid Gland Disorders of the Thyroid Gland

• Grave’s disease • Myxedema • Most common type of hyperthyroidism • Adult hypothyroidism • Immune system makes abnormal antibodies • Antibodies attack and destroy thyroid tissue • Stimulates the oversecretion of TH by • Low metabolic rate and weight gain are follicle cells common symptoms • Leads to nervousness, weight loss, sweating, and rapid heart rate

9 Disorders of the Thyroid Gland Thyroid Disorders

• Endemic goiter • Due to lack of iodine in the diet • Cretinism • Hypothyroidism in children • Short, disproportionate body, thick tongue, and mental retardation

Disorders of the Adrenal Cortex Thyroid Disorders

• Cushing’s syndrome • Caused by hypersecretion of glucocorticoid hormones—usually a pituitary tumor • Addison’s disease • Hyposecretory disorder of the adrenal cortex • Deficiencies of both mineralocorticoids and glucocorticoids

The Endocrine System Throughout Life Embryological Origin of Selected Endocrine Organs • Thyroid gland • Pineal gland • Forms from a thickening of endoderm on the floor of the pharynx • Originates from ependymal cells • Parathyroids and the thymus gland • Pituitary gland—dual origin • From endoderm lining the pharyngeal • Adenohypophysis originates from the roof pouches of the mouth • Neurohypophysis grows inferiorly from the floor of the brain

10 Embryological Origin of Selected Endocrine Embryological Origin of Selected Endocrine Organs Organs

Hypophyseal pouch • Adrenal gland—dual origin gland Pharyngeal pouches • Adrenal medulla—from neural crest cells of Brain Future thymus Hypothalamus Future parathyroid glands nearby sympathetic trunk ganglia Neurohypophyseal (a) Week 5. Thyroid, thymus, bud Future thyroid and parathyroid glands form gland • Adrenal cortex—from mesoderm lining the from pharyngeal endoderm. Esophagus Hypophyseal pouch extends Lung bud coelom superiorly from ectoderm in the roof of the mouth. Future mouth

Hypophyseal pouch

(b) Week 6. Inferior extension Neurohypophyseal of the floor of the bud diencephalon forms the neurohypophyseal bud. Anterior Posterior

Embryological Origin of Selected Endocrine The Endocrine System Throughout Life Organs • Endocrine organs operate effectively until old age Hypophyseal pouch • Anterior pituitary Neurohypophyseal (c) Week 7. Hypophyseal bud • Increase in connective tissue and lipofuscin pouch pinches off the surface ectoderm and is • Decrease in vascularization and number of hormone- closely associated with the secreting cells neurohypophyseal bud. Third • Adrenal cortex ventricle • Normal rates of glucocorticoid secretion continue of brain • Adrenal medulla (d) Week 8. Hypophyseal pouch forms the Anterior lobe Posterior lobe • No age-related changes in catecholamines anterior lobe of pituitary; neurohypophyseal bud Pars tuberalis Infundibulum forms the posterior lobe. Pars distalis Pars nervosa Distinct portions of each differentiate. Pars intermedia

The Endocrine System Throughout Life

• Thyroid hormones • Decrease slightly with age • Parathyroid glands • Little change with aging • GH, DHEA, and the sex hormones • Marked drops in secretion with age