Chapter 17 The Endocrine System Flashcards

Vocabulary practice flashcards covering terms, definitions, and major concepts from Chapter 17 (The Endocrine System).

Gap junctions

Structures that join single-unit smooth muscle, cardiac muscle, epithelial, and other cells, allowing passage of nutrients, electrolytes, and signaling molecules directly via cytoplasm.

Neurotransmitters

Chemical messengers released by neurons that diffuse across the synaptic cleft and bind to receptors of target cells.

Paracrines

Chemical signals secreted by one cell that diffuse to nearby cells of the same tissue to stimulate them; also called local hormones.

Hormones

Chemical messengers transported by the bloodstream that stimulate physiological responses of cells of another tissue or organ.

Endocrinology

The study of the endocrine system and the diagnosis and treatment of its disorders.

Exocrine glands

Glands that secrete their products by way of a duct onto an epithelial surface, producing extracellular effects.

Endocrine glands

Ductless glands that release internal secretions directly into the bloodstream to alter cell metabolism.

Fenestrated capillaries

A highly permeable type of blood capillary found in high density in endocrine glands, featuring patches of large pores in their walls.

Infundibulum

The stalk that connects the pituitary gland to the floor of the hypothalamus.

Sella turcica

A depression of the sphenoid bone that houses the pituitary gland.

Adenohypophysis

The anterior lobe of the pituitary gland, constituting about three-quarters of the gland and linked to the hypothalamus by the hypophyseal portal system.

Hypophyseal portal system

A vascular network consisting of primary capillaries in the hypothalamus, portal venules down the stalk, and secondary capillaries in the anterior pituitary.

Neurohypophysis

The posterior lobe of the pituitary gland, composed of nervous tissue and the hypothalamo-hypophyseal tract.

Hypothalamo-hypophyseal tract

A bundle of nerve fibers arising from hypothalamic cell bodies that pass down the infundibulum to end in the posterior pituitary.

Releasing hormones

Hypothalamic hormones that stimulate anterior pituitary cells to secrete their own hormones.

Inhibiting hormones

Hypothalamic hormones that suppress hormone secretion by the pituitary gland.

Follicle-stimulating hormone (FSH)

An anterior pituitary hormone secreted by gonadotropes that stimulates ovarian follicle development and sex hormone secretion in females, and sperm production in males.

Luteinizing hormone (LH)

An anterior pituitary hormone secreted by gonadotropes that stimulates ovulation, progesterone secretion by the corpus luteum, and testosterone secretion in males.

Thyroid-stimulating hormone (TSH)

An anterior pituitary hormone (thyrotropin) secreted by thyrotropes that stimulates growth of the thyroid gland and secretion of thyroid hormone.

Adrenocorticotropic hormone (ACTH)

An anterior pituitary hormone (corticotropin) secreted by corticotropes that stimulates the adrenal cortex to release glucocorticoids.

Prolactin (PRL)

An anterior pituitary hormone secreted by lactotropes that stimulates the mammary glands to synthesize milk after childbirth.

Growth hormone (GH)

An anterior pituitary hormone (somatotropin) secreted by somatotropes that promotes tissue growth by stimulating mitosis and cellular differentiation.

Antidiuretic hormone (ADH)

A hypothalamic hormone stored in the posterior pituitary that increases water retention by the kidneys, reduces urine volume, and helps prevent dehydration.

Oxytocin (OT)

A hypothalamic hormone stored in the posterior pituitary that functions in labor contractions, milk release, sexual arousal, and emotional bonding.

Neuroendocrine reflexes

Reflex mechanisms where hormone release from the posterior pituitary is triggered in response to nerve signals.

Osmoreceptors

Hypothalamic neurons that detect increases in blood osmolarity and trigger the release of antidiuretic hormone.

Negative feedback inhibition

A regulatory mechanism in which a hormone inhibits its own further secretion by binding to receptors on the pituitary or hypothalamus.

Insulin-like growth factors (IGFs)

Hormones (somatomedins) produced by the liver and other tissues upon stimulation by $GH$ that prolong growth hormone action and stimulate target cells.

Protein-sparing effect

The phenomenon where $GH$-stimulated fat catabolism provides fatty acids and glycerol for fuel, eliminating the need for cells to consume their own proteins.

Glucose-sparing effect

The reduction of cellular glucose consumption caused by $GH$-mobilized fatty acids, keeping glucose available for the brain.

Pineal gland

An endocrine gland attached to the roof of the third ventricle that synthesizes melatonin from serotonin during the night and undergoes involution after age $7$.

Involution

The developmental regression or reduction in size of an organ or tissue over time.

Melatonin

A monoamine hormone synthesized from serotonin by the pineal gland at night, implicated in circadian rhythms and seasonal physiological changes.

Thymus

A bilobed gland in the mediastinum superior to the heart that produces hormones like thymosin and serves as the site for $T$\,cell maturation.

Thyroid follicles

Sac-like histological structures in the thyroid lined with simple cuboidal follicular cells and filled with protein-rich colloid.

Calorigenic effect

An increase in cellular heat production caused by thyroid hormone elevating the body's metabolic rate and oxygen consumption.

Parafollicular cells

Nests of clear cells ($C$\,cells) in the thyroid gland that secrete calcitonin in response to elevated blood calcium levels.

Parathyroid hormone (PTH)

A hormone secreted by the parathyroid glands in response to low blood calcium levels.

Chromaffin cells

Neuroendocrine cells in the adrenal medulla that lack axons and dendrites and release epinephrine, norepinephrine, and dopamine directly into the bloodstream.

Zona glomerulosa

The thin, outer layer of the adrenal cortex that secretes mineralocorticoids such as aldosterone.

Zona fasciculata

The thick middle layer of the adrenal cortex containing spongiocytes that secretes glucocorticoids and androgens.

Zona reticularis

The narrow, innermost layer of the adrenal cortex adjacent to the adrenal medulla that secretes glucocorticoids and androgens.

Aldosterone

The principal mineralocorticoid produced by the zona glomerulosa that stimulates the kidneys to retain sodium and excrete potassium.

Cortisol

The most potent glucocorticoid secreted by the adrenal cortex that stimulates fat and protein catabolism, gluconeogenesis, and anti-inflammatory responses.

Dehydroepiandrosterone (DHEA)

The principal adrenal androgen, which is converted in peripheral tissues into more potent forms such as testosterone and dihydrotestosterone.

Pancreatic islets

Clusters of endocrine cells (islets of Langerhans) scattered throughout the exocrine tissue of the pancreas that regulate blood glucose concentration.

Alpha cells

Pancreatic islet cells that secrete glucagon between meals when blood glucose levels decrease.

Beta cells

Pancreatic islet cells that secrete insulin during and immediately following meals when blood nutrient levels rise.

Delta cells

Pancreatic islet cells that secrete somatostatin concurrently with insulin to inhibit stomach acid secretion.

Hyperglycemic hormone

Any hormone, such as glucagon or epinephrine, that acts to raise blood glucose concentrations.

Hypoglycemic hormone

Any hormone, specifically insulin, that acts to lower blood glucose concentrations.

Cytogenic glands

Glands such as the testes and ovaries whose exocrine products are whole cells (sperm and eggs).

Hepcidin

A liver hormone involved in iron homeostasis that promotes intestinal iron absorption and iron mobilization for hemoglobin synthesis.

Erythropoietin (EPO)

A hormone secreted mainly by the kidneys ($85\%$) and liver ($15\%$) that stimulates red blood cell production in the bone marrow.

Calcitriol

The fully active, calcium-regulating form of vitamin $D_3$ produced by the sequential actions of the skin, liver, and kidneys.

Leptin

A hormone secreted by fat cells (adipocytes) that acts on the hypothalamus to regulate long-term appetite and signal fat storage levels.

Osteocalcin

A hormone secreted by osteoblasts that increases pancreatic beta cell number, insulin output, and insulin sensitivity.

Steroid hormones

A chemical class of lipophilic hormones derived from cholesterol, including sex steroids and corticosteroids.

Monoamines

A chemical class of hormones made from amino acids retaining an amino group, including catecholamines, melatonin, and thyroid hormone.

Peptide hormones

A chemical class of hormones consisting of chains of $3$ to $200$ or more amino acids, including oligopeptides and glycoproteins.

Thyroglobulin

A large protein synthesized by thyroid follicular cells containing $123$ tyrosines, serving as the precursor matrix for thyroid hormone assembly.

Bound hormone

A hormone that is attached to a hydrophilic transport protein while circulating in the blood.

Unbound hormone

A free hormone not attached to a transport protein, which is able to exit blood capillaries and act on target cells.

Signal amplification

The mechanism by which a single hormone molecule binding to a receptor triggers the synthesis or activation of a vast number of downstream enzyme molecules.

Up-regulation

The process by which a target cell increases its number of receptors to become more sensitive to a hormone.

Down-regulation

The process by which a target cell reduces its number of receptors to become less sensitive to a hormone.

Synergistic effects

Interactive hormone effects in which two or more hormones act together to produce a response greater than the sum of their separate effects.

Permissive effects

Interactive hormone effects in which one hormone enhances the target organ's responsiveness to a second hormone administered later.

Antagonistic effects

Interactive hormone effects in which one hormone opposes the action of another.

Metabolic clearance rate (MCR)

The rate at which a hormone is cleared and removed from the blood by the liver and kidneys.

General adaptation syndrome (GAS)

The body's physiological response to stress, occurring in three stages: alarm reaction, stage of resistance, and stage of exhaustion.

Eicosanoids

A family of $20$-carbon paracrine signaling molecules synthesized from arachidonic acid.

Leukotrienes

Eicosanoids formed via the lipoxygenase pathway that mediate allergic and inflammatory reactions.

Prostaglandins

A diverse group of eicosanoids containing a five-sided ring structure, produced via the cyclooxygenase pathway.

Acromegaly

A condition caused by hypersecretion of growth hormone in adults, characterized by thickening of bones and soft tissues.

Myxedema

A condition associated with severe or prolonged adult hypothyroidism.

Endemic goiter

Pathological enlargement of the thyroid gland resulting from a dietary deficiency of iodine required for thyroid hormone synthesis.

Cushing syndrome

A disorder caused by excess cortisol secretion, characterized by hyperglycemia, muscle wasting, hypertension, edema, and abnormal fat deposition.

Adrenogenital syndrome (AGS)

A disorder resulting from hypersecretion of adrenal androgens, causing masculinization of females and premature puberty in children.

Diabetes mellitus

A metabolic disease characterized by disrupted carbohydrate, fat, and protein metabolism resulting from insulin hyposecretion or unresponsiveness.

Kussmaul respiration

Deep, gasping breathing typical of terminal diabetes caused by ketoacidosis.