Ch 1: Endocrine System

Comprehensive vocabulary flashcards covering basic endocrine anatomy, mechanisms of hormone action, feedback systems, and associated metabolic disorders based on the lecture notes.

Endocrine system

Body system composed of ductless endocrine glands that synthesize and secrete hormones directly into the blood to travel throughout the body.

Nervous system

Body system that regulates activity of muscles and glands through electrochemical impulses delivered by neurons with millisecond response times.

Hormones

Chemical messengers released by endocrine cells that travel through the blood to target cells.

Ligands

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

Endocrine system vs. nervous system

The endocrine system uses hormones transported through blood, can have widespread effects, has slower

reaction times, and effects can last minutes, days, or weeks.

• The nervous system uses neurons to deliver electrochemical impulses, targets specific muscles and glands,

responds within milliseconds, and generally produces much faster effects.

General functions of the endocrine system

Regulates development, growth, and metabolism.

• Maintains blood composition and volume.

• Controls digestive processes.

• Controls reproductive activities.

Pituitary gland

Pea-sized gland located inferior to the hypothalamus in the sella turcica of the sphenoid bone, connected to the hypothalamus by the infundibulum.

Pineal gland

Small, unpaired structure located in the epithalamus of the diencephalon that secretes melatonin.

Thyroid gland

Gland located inferior to the thyroid cartilage of the larynx and anterior to the trachea, consisting of left and right lobes connected by an isthmus.

Parathyroid glands

Small glands, usually four in number, located on the posterior surface of the thyroid gland.

Adrenal glands

Glands located retroperitoneally on the superior surface of each kidney, embedded in fat and fascia.

Pancreas

Organ located posterior to the stomach, between the duodenum and spleen, containing both exocrine acinar cells and endocrine islets.

Thymus

Structure located anterior to the top of the heart that grows during childhood, shrinks during adulthood, and serves as the site for T-lymphocyte maturation.

Other organs/tissues containing endocrine cells

Hypothalamus, skin, thymus, heart, liver, stomach, pancreas, small intestine, adipose connective tissue,

kidneys, and gonads.

Endocrine reflex

A regulatory mechanism through which hormone release is initiated by hormonal, humoral, or nervous stimuli.

Hormonal stimulation

Hormone release mechanism where a gland cell releases its hormone in response to another hormone binding to it.

Humoral stimulation

Hormone release mechanism where a gland cell releases a hormone in response to changing blood levels of a nutrient or ion.

Nervous system stimulation

Hormone release mechanism where a gland cell releases a hormone when directly stimulated by a neuron.

Steroid hormones

Lipid-soluble chemical messengers synthesized from cholesterol, such as estrogen, cortisol, and calcitriol.

Biogenic amines

Hormones formed from modified amino acids, which are mostly water-soluble (e.g., catecholamines, melatonin) except for thyroid hormone.

Protein hormones

Water-soluble chains of amino acids; the category into which most body hormones fall.

Lipid-soluble hormones

Hormones that can cross the plasma membrane, require carrier proteins in the blood, and bind to intracellular receptors.

Water-soluble hormones

Hormones that travel freely through the blood without carrier proteins and bind to cell-surface receptors on target cells.

Local hormones

Signaling molecules that do not circulate in the blood, acting instead on the cell that released them or on neighboring cells.

Autocrine

Local signaling mechanism where a chemical messenger binds to and affects the exact same cell that released it.

Paracrine

Local signaling mechanism where a chemical messenger affects neighboring cells rather than circulating in the blood.

Eicosanoids

Local hormones synthesized through an enzymatic cascade from fatty acids within the membrane phospholipid bilayer.

Prostaglandins

Eicosanoids that stimulate pain and inflammatory responses, whose formation is blocked by aspirin and other NSAIDs.

Lipid-soluble hormone mechanism

Lipid-soluble hormones diffuse across the target cell membrane and bind intracellular receptors in the cytosol

or nucleus.

• The hormone-receptor complex binds DNA at a hormone-response element, causing transcription of mRNA

and protein production, which produces the cellular effect.

Intercellular receptor

A receptor located inside the target cell, either in the cytosol or nucleus.

Hormone-receptor complex

Structure formed inside a target cell when a lipid-soluble hormone binds to its intracellular receptor in the cytosol or nucleus.

Hormone-response element (HRE)

A specific DNA region to which a hormone-receptor complex binds to cause mRNA transcription and protein synthesis.

First messenger

The hormone itself, which initiates intracellular signaling events by binding to a cell-surface receptor.

G-protein

An internal membrane protein bound to a guanine nucleotide that is activated when GTP replaces GDP following hormone binding.

Adenylate cyclase

A plasma membrane enzyme activated by a G-protein that assists in producing a second messenger.

Phospholipase C

A plasma membrane enzyme activated by a G-protein that triggers a second-messenger signaling pathway.

Second messenger

An intracellular chemical that modifies cellular activity after a water-soluble hormone binds to its membrane receptor.

Effects of water soluble hormones

Can cause activation or inhibition of enzymatic pathways, cell division, cellular secretions, changes in

membrane permeability, and muscle contraction or relaxation.

Target cell

A cell possessing specific cellular receptors for a particular hormone, enabling it to respond to that signal.

Up-regulation

An increase in target cell receptor number that heightens cellular sensitivity to a hormone, typically occurring when hormone levels are low.

Down-regulation

A decrease in target cell receptor number that reduces cellular sensitivity to a hormone, typically occurring when hormone levels are high.

Factors affecting receptor number

Blood hormone levels, development, cell cycle, and cell activity.

Synergism

Hormone interaction where one hormone reinforces the activity of another, producing an amplified effect.

Permissiveness

Hormone interaction where one hormone requires the activity of another hormone in order to exert its full effect.

Antagonism

Hormone interaction where one hormone opposes the activity of another hormone.

ex: cortisol

Hypothalamus

Controls the pituitary gland, which in turn controls several other endocrine organs.

Infundibulum

Stalk-like structure that connects the hypothalamus to the pituitary gland.

Posterior pituitary (Neurohypophysis)

Neural portion of the pituitary gland that stores and releases ADH and oxytocin delivered via the hypothalamo-hypophyseal tract.

Anterior pituitary (Adenohypophysis)

Glandular portion of the pituitary gland controlled by hypothalamic regulatory hormones via the hypothalamo-hypophyseal portal system.

Hypothalamo-hypophyseal portal system

Vascular network comprising a primary plexus, hypophyseal portal veins, and a secondary plexus that connects the hypothalamus to the anterior pituitary.

Antidiuretic hormone (ADH)

Hormone synthesized in the supraoptic nucleus of the hypothalamus (also called vasopressin) that decreases urine production, stimulates thirst, and constricts blood vessels.

Oxytocin (OT)

Hormone synthesized in the paraventricular nucleus of the hypothalamus that induces uterine contractions, milk ejection, and emotional bonding.

Tropic hormone

A hormone whose main function is to stimulate another endocrine gland to synthesize and release its hormones.

Thyroid-stimulating hormone (TSH)

Anterior pituitary hormone that stimulates the thyroid gland to release thyroid hormone.

Prolactin (PRL)

Anterior pituitary non-tropic hormone that stimulates milk production and mammary gland growth.

Adrenocorticotropic hormone (ACTH)

Anterior pituitary hormone triggered by CRH that stimulates the adrenal cortex to release corticosteroids.

Follicle-stimulating hormone (FSH)

Anterior pituitary hormone that stimulates ovarian follicle maturation in females and sperm development in males.

Luteinizing hormone (LH)

Anterior pituitary hormone that triggers ovulation and estrogen/progesterone release in females, and testosterone synthesis in males.

Growth hormone (GH)

Anterior pituitary hormone that stimulates liver release of IGF-1 and IGF-2, promoting skeletal growth, cell division, lipolysis, and elevated blood glucose.

Thyroid follicle

Microscopic structural unit of the thyroid gland consisting of simple cuboidal follicular cells surrounding a central colloid lumen.

Follicular cells

Cuboidal epithelial cells surrounding the thyroid follicle lumen that synthesize thyroglobulin and produce thyroid hormone.

Colloid

Viscous, protein-rich fluid contained within the lumen of a thyroid follicle.

Parafollicular cells

Cells located between thyroid follicles that synthesize and secrete calcitonin.

Thyroid hormone (TH)

Metabolic hormone existing as T3 and T4 that increases metabolic rate, protein synthesis, and body temperature.

T3

Triiodothyronine.

• More biologically active than T4.

• Most target cells convert T4 into T3.

T4

Tetraiodothyronine.

• The thyroid gland produces more T4 than T3.

• Most target cells convert T4 into the more active T3.

Effects of thyroid hormone

Increases metabolic rate and protein synthesis and generates heat (calorigenic effect).

• Increases amino acid and glucose uptake, cellular respiration enzymes, ATP production, glucose release by

the liver, lipolysis, respiration rate, heart rate, and force of contraction.

• Increases heart receptors for epinephrine and norepinephrine.

Calcitonin

Hormone secreted by parafollicular cells in response to high blood calcium that inhibits osteoclasts and promotes renal calcium excretion.

Thyroid peroxidase

Enzyme that attaches iodine molecules to tyrosine residues within thyroglobulin inside the thyroid colloid.

Monoiodotyrosine (MIT)

Intermediate molecule formed when one iodine atom attaches to a tyrosine residue on thyroglobulin.

Diiodotyrosine (DIT)

Intermediate molecule formed when two iodine atoms attach to a tyrosine residue on thyroglobulin.

Parathyroid hormone (PTH)

Hormone produced by chief cells of the parathyroid glands that increases blood calcium levels by targeting bone, kidneys, and calcitriol pathways.

Calcitriol

Active sterol hormone converted in the kidneys that increases blood calcium levels by enhancing intestinal calcium absorption and decreasing urinary loss.

Adrenal cortex

Outer lipid-rich region of the adrenal gland that secretes over 25 different corticosteroids across three structural zones.

Adrenal medulla

Inner red-brown core of the adrenal gland that secretes epinephrine and norepinephrine under sympathetic stimulation.

Zona glomerulosa

Outermost layer of the adrenal cortex that synthesizes mineralocorticoids, primarily aldosterone.

Aldosterone

Mineralocorticoid that promotes renal sodium and water reabsorption while enhancing potassium excretion to maintain blood pressure and volume.

Zona fasciculata

Middle layer of the adrenal cortex composed of linear cell cords that produce glucocorticoids.

Cortisol

Primary glucocorticoid that increases blood nutrient levels via gluconeogenesis, glycogenolysis, lipolysis, and protein catabolism while suppressing inflammation.

Zona reticularis

Innermost layer of the adrenal cortex featuring a net-like cell arrangement that secretes adrenal androgens.

Alarm reaction

Initial stage of the stress response governed by sympathetic nervous stimulation and epinephrine/norepinephrine release.

Stage of resistance

Second stage of the stress response where cortisol is secreted by the adrenal cortex to maintain elevated blood nutrient levels after glycogen depletion.

Stage of exhaustion

Final stage of chronic stress response characterized by fat store depletion, structural protein breakdown, and systemic bodily weakening.

Alpha cells

Endocrine cells of the pancreatic islets that synthesize and secrete glucagon.

Beta cells

Endocrine cells of the pancreatic islets that synthesize and secrete insulin.

Delta cells

Endocrine cells of the pancreatic islets that synthesize and secrete somatostatin.

F cells

Endocrine cells of the pancreatic islets that synthesize and secrete pancreatic polypeptide.

Insulin

Pancreatic hormone released by beta cells in response to elevated blood glucose that stimulates glycogenesis, lipogenesis, and cellular nutrient uptake.

Glucagon

Pancreatic hormone released by alpha cells in response to low blood glucose that stimulates glycogenolysis, gluconeogenesis, and lipolysis.

Melatonin

Pineal gland hormone secreted at night that induces drowsiness, regulates circadian rhythms, and influences GnRH secretion.

Leptin

Adipose tissue hormone that regulates appetite by binding to hypothalamic neurons relative to body fat content.

Atrial natriuretic peptide (ANP)

Hormone secreted by heart atrial walls in response to high blood pressure that induces vasodilation and urinary fluid excretion.

Erythropoietin (EPO)

Renal hormone released in response to low blood oxygen levels that stimulates red blood cell production in bone marrow.

Gastrin

Stomach hormone that enhances digestive tract motility and stomach acid secretions.

Angiotensinogen

Inactive precursor protein produced by the liver that is converted to active angiotensin II to raise blood pressure.

Secretin

Small intestine hormone that stimulates the secretion of bile and pancreatic digestive juice.

Cholecystokinin (CCK)

Small intestine hormone that stimulates the gallbladder to contract and release stored bile.

Osteocalcin

Hormone secreted by osteoblasts that enhances glucose handling, promotes pancreatic beta cell division, and restricts adipocyte fat storage.

Hyposecretion

Underproduction or inadequate release of a specific hormone by an endocrine gland.

Hypersecretion

Overproduction or excessive release of a specific hormone by an endocrine gland.