BIOL 2402 Chapter 16 - Endocrine System Part 1

Vocabulary flashcards covering overview concepts, chemical categories, mechanisms of action, regulation mechanisms, and specific hypothalamic and pituitary hormones from BIOL 2402 Chapter 16 Part 1.

Endocrinology

The scientific study of hormones and endocrine organs.

Hormones

Long-distance chemical signals that travel in blood or lymph throughout the body to regulate cellular metabolic activities.

Autocrines

Local chemical messengers that exert their effects on the same cells that secrete them.

Paracrines

Local chemical messengers that act locally and affect target cell types other than those that secrete them.

Exocrine Glands

Glands that produce non-hormonal substances (such as sweat and saliva) and have ducts to carry their secretions to a membrane surface.

Endocrine Glands

Ductless glands that produce hormones directly into the surrounding tissue fluid and vascular system.

Target Cells

Tissues containing specific receptors that bind to a given hormone to produce cellular responses.

Water-Soluble Hormones

All amino acid-based hormones except thyroid hormone; they act on plasma membrane receptors via G protein second messengers and cannot enter the cell.

Lipid-Soluble Hormones

Steroid and thyroid hormones that can enter the cell and act on intracellular receptors to directly activate gene transcription.

Cyclic AMP (cAMP)

An intracellular second messenger produced from ATP by adenylate cyclase that activates protein kinases inside the cell.

Direct Gene Activation

Mechanism used by lipid-soluble hormones where the receptor-hormone complex enters the nucleus, binds specific DNA regions, and initiates mRNA transcription.

Humoral Stimulus

Hormone release caused by changing blood levels of critical ions or nutrients (e.g., low blood $\text{Ca}^{2+}$ triggering parathyroid hormone release).

Neural Stimulus

Hormone release caused by direct impulse from nerve fibers (e.g., sympathetic nervous system fibers stimulating the adrenal medulla).

Hormonal Stimulus

Hormone release caused by tropic hormones released by other endocrine glands (e.g., hypothalamic hormones triggering anterior pituitary secretion).

Up-Regulation

A cellular response where target cells form more receptors in response to persistently low hormone levels to increase sensitivity.

Down-Regulation

A cellular response where target cells lose receptors in response to persistently high hormone levels to desensitize the cell.

Half-Life

The length of time required for the level of a hormone in the blood to decrease by half.

Permissiveness

A hormonal interaction where one hormone cannot exert its full effects on a target cell without another hormone being present.

Synergism

A hormonal interaction where more than one hormone produces the same effect on a target cell, resulting in an amplified response.

Antagonism

A hormonal interaction where one or more hormones oppose the action of another hormone (e.g., insulin and glucagon).

Infundibulum

The funnel-shaped stalk of tissue that connects the pituitary gland to the superiorly located hypothalamus.

Posterior Pituitary (Neurohypophysis)

The neural lobe of the pituitary gland that stores and releases neurohormones (oxytocin and ADH) synthesized in the hypothalamus.

Anterior Pituitary (Adenohypophysis)

The glandular portion of the pituitary gland that synthesizes and secretes six major peptide/protein hormones under hypothalamic control.

Hypothalamic-Hypophyseal Tract

A neural tract running through the infundibulum that transports neurohormones made in the supraoptic and paraventricular nuclei to the posterior pituitary.

Hypophyseal Portal System

A vascular connection between the hypothalamus and anterior pituitary consisting of primary and secondary capillary plexuses linked by portal veins.

Oxytocin (OXT)

A posterior pituitary peptide hormone that stimulates uterine contractions during labor and triggers milk ejection via the letdown reflex.

Antidiuretic Hormone (ADH)

A posterior pituitary peptide hormone that stimulates kidney tubules to reabsorb water to prevent urine formation when blood solute concentration is high.

Tropic Hormones

Hormones that regulate the secretory activity of other endocrine glands; includes TSH, ACTH, FSH, and LH.

Growth Hormone (GH)

An anterior pituitary protein hormone that exerts direct metabolic actions (glucose-sparing, glycogenolysis) and indirect growth-promoting actions via IGFs.

Gigantism

A homeostatic imbalance in children caused by hypersecretion of Growth Hormone (GH), leading to excessive height that can reach 8 feet.

Acromegaly

A homeostatic imbalance in adults caused by hypersecretion of Growth Hormone (GH), characterized by overgrowth of the hands, feet, and face.

Pituitary Dwarfism

A homeostatic imbalance in children caused by hyposecretion of Growth Hormone (GH), resulting in maximum heights of around 4 feet.

Thyroid-Stimulating Hormone (TSH)

A tropic glycoprotein hormone secreted by anterior pituitary thyrotropic cells that stimulates development and secretion of the thyroid gland.

Adrenocorticotropic Hormone (ACTH)

A tropic peptide hormone secreted by anterior pituitary corticotropic cells that stimulates the adrenal cortex to release corticosteroids.

Follicle-Stimulating Hormone (FSH)

A tropic glycoprotein gonadotropin secreted by the anterior pituitary that stimulates gamete (egg or sperm) production.

Luteinizing Hormone (LH)

A tropic glycoprotein gonadotropin that triggers ovulation and gonadal steroid synthesis in females, and testosterone production in males.

Prolactin (PRL)

An anterior pituitary protein hormone that stimulates milk production in breast secretory tissue in females.

Prolactin-Inhibiting Hormone (PIH)

Dopamine secreted by the hypothalamus that continuously inhibits prolactin release until lactation is required.