Chapter 17 Lecture Outline: Endocrine System

Flashcards on Endocrine System Anatomy & Physiology

Endocrine System

Composed of ductless glands that synthesize and secrete hormones, released into the blood and transported throughout the body.

Hormones

Chemical messengers released into the blood, affecting target cells with specific receptors.

Ligands

Chemical messengers released by both the endocrine and nervous systems that bind to cellular receptors on target cells.

Endocrine System vs Nervous System

Endocrine system transmits hormones through the blood, targets any cells in the body with correct receptors, exhibits longer reaction times and has longer-lasting effects. Nervous system uses electrical signals for quick, direct responses.

Hormones Regulate Development, Growth, and Metabolism

They help regulate embryonic cell division and differentiation, as well as metabolism (both anabolism and catabolism).

Hormones Maintain Homeostasis

They regulate blood solute concentrations (e.g., glucose, ions), blood volume, cellular concentration, and platelet number.

Hormones Control Digestive Processes

They influence secretory processes and movement of materials in the digestive tract.

Hormones Control Reproductive Activities

They affect development and function of reproductive systems and the expression of sexual behaviors.

Endocrine Glands

Epithelial tissue that makes and releases hormones within a connective tissue framework; includes pituitary, pineal, thyroid, parathyroid, and adrenal glands.

Hormonal Stimulation

A gland cell releases its hormone when another 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.

Steroids

Lipid-soluble molecules synthesized from cholesterol, including gonadal steroids (e.g., estrogen) and steroids synthesized by the adrenal cortex (e.g., cortisol).

Biogenic Amines (Monoamines)

Modified amino acids, including catecholamines, thyroid hormone, and melatonin; mostly water-soluble except for thyroid hormone (TH).

Proteins (as Hormones)

Water-soluble chains of amino acids; most hormones are in this category.

Local Hormones

Signaling molecules that don’t circulate in blood, binding to the cells that release them (autocrine stimulation) or neighboring cells (paracrine stimulation).

Eicosanoids

A type of local hormone formed from fatty acids within the phospholipid bilayer of the membrane; prostaglandins are eicosanoids that stimulate pain and inflammatory responses.

Prostaglandins

Eicosanoids that stimulate pain and inflammatory responses.

Lipid-Soluble Hormone Transport

Requires a carrier protein because they do not dissolve readily in blood; carriers are water-soluble proteins made by the liver.

Water-Soluble Hormone Transport

Travel freely through the blood; a few use carrier proteins to prolong their life.

Hormone Elimination

Occurs through enzymatic degradation in liver cells, removal from blood via kidney excretion or target cell uptake.

Half-Life (Hormones)

Time necessary to reduce a hormone’s concentration to half of its original level; steroid hormones generally have longer half-lives due to carrier proteins.

Lipid-Soluble Hormone Action

Diffuse across target cell membrane, bind to receptors in the cytosol or nucleus, form a hormone-receptor complex that binds to DNA, resulting in transcription of mRNA and synthesis of new proteins.

Water-Soluble Hormone Action

Use membrane receptors, initiating a signal transduction pathway involving a G-protein and second messengers (e.g., cAMP, IP3).

Signal Transduction Pathway

The process involving a hormone (first messenger) binding to a receptor, activating a G-protein, and triggering the formation of a second messenger to modify cellular activity.

Up-Regulation

Increases number of receptors, increasing sensitivity to hormone; can occur when blood levels of hormone are low or with changes in development.

Down-Regulation

Decreases number of receptors, decreasing sensitivity to hormone; can occur when blood levels of hormone are high or with changes in development.

Synergistic Interactions (Hormones)

One hormone reinforces the activity of another hormone (e.g., estrogen and progesterone effects on a target cell).

Permissive Interactions (Hormones)

One hormone requires the activity of another hormone (e.g., oxytocin's milk ejection effect requires prolactin's milk generating effect).

Antagonistic Interactions (Hormones)

One hormone opposes the activity of another hormone (e.g., glucagon increases blood glucose while insulin lowers it).

Pituitary Gland (Hypophysis)

Lies inferior to the hypothalamus in the sella turcica of the sphenoid bone, connected to the hypothalamus by the infundibulum, and partitioned into anterior and posterior pituitary.

Posterior Pituitary (Neurohypophysis)

Smaller, neural part of the pituitary gland; hypothalamic neurons project through the infundibulum and release hormones in the posterior pituitary.

Anterior Pituitary

Connected to the hypothalamus by the hypothalamo-hypophyseal portal system of blood vessels.

Antidiuretic Hormone (ADH) /Vasopressin

Made in supraoptic nucleus of the hypothalamus; functions to decrease urine production, stimulate thirst, and constrict blood vessels.

Oxytocin

Made in paraventricular nucleus of the hypothalamus; functions in uterine contraction, milk ejection, and emotional bonding.

Releasing Hormones

Hormones secreted by the hypothalamus that increase secretion of anterior pituitary hormones.

Inhibiting Hormones

Hormones secreted by the hypothalamus that decrease secretion of anterior pituitary hormones.

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 and mammary gland growth in females.

Adrenocorticotropic Hormone (ACTH/Corticotropin)

Release triggered by CRH from hypothalamus; causes release of corticosteroids by adrenal cortex.

Follicle-Stimulating and Luteinizing Hormone

Release triggered by GnRH from hypothalamus; regulate ovarian development, estrogen and progesterone secretion in females, and sperm development and testosterone secretion in males.

Growth Hormone (GH/Somatotropin)

Causes liver to secrete insulin-like growth factors 1 and 2 (IGFs); GH and IGFs function synergistically to stimulate cell growth and division.

Growth Hormone Deficiency (Pituitary Dwarfism)

Inadequate growth hormone production due to hypothalamic or pituitary problem; results in short stature and low blood sugar (hypoglycemia).

Pituitary Gigantism

Too much growth hormone results in excessive growth, increased blood sugar, enormous internal organs, and early death if untreated.

Acromegaly

Excessive growth hormone production in adults; enlargement of bones of face, hands, and feet, increased release of glucose, and increased size of internal organs.

Thyroid Gland Anatomy

Inferior to the thyroid cartilage of the larynx; composed of follicles with follicular cells that produce thyroid hormone (TH), and parafollicular cells that make calcitonin.

Follicular Cells

Cuboidal epithelial cells that surround a central lumen, synthesize thyroglobulin (TGB) that produce and release thyroid hormone (TH).

Parafollicular cells

Cells between follicles, make calcitonin, a hormone that decreases blood calcium levels

Hypothalamic-Pituitary-Thyroid Axis

Cold temperature, pregnancy, high altitude, hypoglycemia, or low TH cause hypothalamus to release TRH. TRH causes anterior pituitary to release TSH, which binds receptors of follicular cells, triggering release of TH.

T3 (Triiodothyronine)

One form of thyroid hormone, is more active form.

T4 (Tetraiodothyronine)

One form of thyroid hormone is produced More.

Hyperthyroidism

Excessive production of TH, resulting in increased metabolic rate, weight loss, hyperactivity, and heat intolerance.

Hypothyroidism

Decreased production of TH, resulting in low metabolic rate, lethargy, cold intolerance, and weight gain.

Goiter

Enlargement of thyroid, typically due to insufficient dietary iodine.

Calcitonin

Synthesized and released from parafollicular cells of thyroid gland; acts to decrease blood calcium levels by inhibiting osteoclast activity and stimulating kidneys to increase excretion of calcium in urine.

Adrenal Glands

Located on superior surface of each kidney; consist of an adrenal medulla (inner core) and adrenal cortex (outer layer).

Adrenal Medulla

Forms inner core of each adrenal gland; releases epinephrine and norepinephrine with sympathetic stimulation.

Adrenal Cortex

Synthesizes more than 25 corticosteroids; three regions (zona glomerulosa, zona fasciculata, zona reticularis) producing different steroid hormones.

Mineralocorticoids

Hormones that regulate electrolyte levels; made in zona glomerulosa; aldosterone fosters Na+ retention and K+ secretion.

Glucocorticoids

Hormones that regulate blood sugar; made in zona fasciculata; cortisol increases blood sugar.

Gonadocorticoids

Sex hormones; made in zona reticularis; androgens are male sex hormones made by adrenals and converted to estrogen in females.

Cortisol

Increases nutrient levels in blood; release regulated by hypothalamic-pituitary-adrenal axis.

Cushing Syndrome

Chronic exposure to excessive glucocorticoid hormones; results in obesity, hypertension, hirsuitism, kidney stones, and menstrual irregularities.

Addison Disease

Form of adrenal insufficiency; develops when adrenal glands fail; results in chronic shortage of glucocorticoids and mineralocorticoids.

Adrenogenital Syndrome (Congenital Adrenal Hyperplasia)

Begins in embryo or fetus; inability to synthesize corticosteroids leads to overproduction of ACTH, causing masculinization.

Pancreas

Located posterior to stomach, between duodenum and spleen; has endocrine (pancreatic islets) and exocrine (acinar cells) functions.

Pancreatic Islets (of Langerhans)

Clusters of endocrine cells in the pancreas; alpha cells secrete glucagon, beta cells secrete insulin.

Insulin

Lowers high blood glucose levels; stimulates hepatocytes to remove glucose from blood and store it as glycogen.

Glucagon

Raises low blood glucose levels; stimulates hepatocytes to release glucose.

Diabetes Mellitus

Inadequate uptake of glucose from blood; chronically elevated glucose damages blood vessels; includes Type 1, Type 2, and Gestational diabetes.

Hypoglycemia

Glucose levels below 60 mg/DL; symptoms include hunger, dizziness, confusion, sweating, and sleepiness.

Pineal Gland

Small unpaired body in the epithalamus of the diencephalon; secretes melatonin at night.

Melatonin

Causes drowsiness, regulates circadian rhythm, and has effects on mood.

Parathyroid Glands

Small structures on the posterior surface of the thyroid gland; contain chief cells that make parathyroid hormone (PTH).

Parathyroid Hormone (PTH)

Increases blood calcium by liberating it from bone, decreasing its loss in urine, and activating calcitriol hormone.

Atrial Natriuretic Peptide (ANP)

Hormone secreted by endocrine tissue in heart atria; lowers blood pressure by increasing urine output and dilating blood vessels.

Erythropoietin (EPO)

Hormone released by kidney endocrine cells in response to low blood oxygen; causes increased red blood cell production.

Leptin

Secreted by adipose connective tissue; controls appetite by binding to neurons in hypothalamus.

Endocrine System

Composed of ductless glands that synthesize and secrete hormones, released into the blood and transported throughout the body.

Hormones

Chemical messengers released into the blood, affecting target cells with specific receptors.

Ligands

Chemical messengers released by both the endocrine and nervous systems that bind to cellular receptors on target cells.

Endocrine System vs Nervous System

Endocrine system transmits hormones through the blood, targets any cells in the body with correct receptors, exhibits longer reaction times and has longer-lasting effects. Nervous system uses electrical signals for quick, direct responses.

Hormones Regulate Development, Growth, and Metabolism

They help regulate embryonic cell division and differentiation, as well as metabolism (both anabolism and catabolism).

Hormones Maintain Homeostasis

They regulate blood solute concentrations (e.g., glucose, ions), blood volume, cellular concentration, and platelet number.

Hormones Control Digestive Processes

They influence secretory processes and movement of materials in the digestive tract.

Hormones Control Reproductive Activities

They affect development and function of reproductive systems and the expression of sexual behaviors.

Endocrine Glands

Epithelial tissue that makes and releases hormones within a connective tissue framework; includes pituitary, pineal, thyroid, parathyroid, and adrenal glands.

Hormonal Stimulation

A gland cell releases its hormone when another 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.

Steroids

Lipid-soluble molecules synthesized from cholesterol, including gonadal steroids (e.g., estrogen) and steroids synthesized by the adrenal cortex (e.g., cortisol).

Biogenic Amines (Monoamines)

Modified amino acids, including catecholamines, thyroid hormone, and melatonin; mostly water-soluble except for thyroid hormone (TH).

Proteins (as Hormones)

Water-soluble chains of amino acids; most hormones are in this category.

Local Hormones

Signaling molecules that don’t circulate in blood, binding to the cells that release them (autocrine stimulation) or neighboring cells (paracrine stimulation).

Eicosanoids

A type of local hormone formed from fatty acids within the phospholipid bilayer of the membrane; prostaglandins are eicosanoids that stimulate pain and inflammatory responses.

Prostaglandins

Eicosanoids that stimulate pain and inflammatory responses.

Lipid-Soluble Hormone Transport

Requires a carrier protein because they do not dissolve readily in blood; carriers are water-soluble proteins made by the liver.

Water-Soluble Hormone Transport

Travel freely through the blood; a few use carrier proteins to prolong their life.

Hormone Elimination

Occurs through enzymatic degradation in liver cells, removal from blood via kidney excretion or target cell uptake.

Half-Life (Hormones)

Time necessary to reduce a hormone’s concentration to half of its original level; steroid hormones generally have longer half-lives due to carrier proteins.