Human Anatomy and Physiology: Endocrine System

Vocabulary practice flashcards covering endocrine gland anatomy, hormone classifications, mechanisms of action, and physiological stress responses.

Exocrine Glands

Glands that secrete their products through tubes or ducts to external body surfaces, such as those releasing stomach acid and sweat.

Endocrine Glands

Glands that release substances into the extracellular spaces surrounding endocrine cells, allowing hormones to travel through the bloodstream to specific target cells.

Autocrine Hormones

Short-distance chemical signals that exert their physiological effects directly on the same cells that secrete them, such as certain prostaglandins released by smooth muscle cells.

Paracrine Hormones

Short-distance chemical signals that regulate neighboring cells rather than the secreting cell itself, such as somatostatin inhibiting insulin release from adjacent pancreatic cells.

Upregulation

An increase in the total number of receptors on a target cell in response to a decrease in hormone level.

Downregulation

A decrease in the total number of receptors on a target cell due to an increase in hormone level.

Steroid Hormones

Lipid-based hormones derived from cholesterol that are insoluble in water, soluble in lipids, contain complex rings of carbon and hydrogen, and diffuse through target cell membranes to bind nuclear receptors.

Nonsteroid Hormones

Water-soluble hormones—including amines, peptides, proteins, and glycoproteins—that cannot cross the plasma membrane and instead act as first messengers by binding membrane receptors.

Cyclic AMP (cAMP)

A secondary messenger generated from ATP by adenylate cyclase that initiates a cascade of cellular changes, including altering membrane permeability, activating enzymes, and promoting protein synthesis.

Tropic Hormones

Hormones that act directly on other endocrine glands to regulate their hormone secretion.

Neurosecretory Cells

Specialized neurons whose secretions are released into the bloodstream to act as hormones rather than functioning as neurotransmitters across synapses.

Growth Hormone (GH)

An anterior pituitary hormone that stimulates bone and muscle growth, enhances amino acid movement across cell membranes, and increases the rate of protein synthesis.

Prolactin (PRL)

An anterior pituitary hormone that stimulates milk production in females and is thought to help maintain normal sperm count in males.

Thyroid Secreting Hormone (TSH)

An anterior pituitary hormone that controls the secretion of hormones from the thyroid gland.

Adrenocorticotropic Hormone (ACTH)

An anterior pituitary hormone that regulates the secretion of specific hormones produced in the adrenal cortex.

Follicle-Stimulating Hormone (FSH)

An anterior pituitary hormone that stimulates egg-containing follicle development and estrogen release in females, as well as sperm cell production in males.

Luteinizing Hormone (LH)

An anterior pituitary hormone that promotes the secretion of sex hormones in males and females and triggers the release of an egg from the ovary.

Antidiuretic Hormone (ADH)

A hormone produced in the hypothalamus and released by the posterior pituitary that maintains constant blood volume by stimulating water reabsorption in the kidneys.

Oxytocin (OT)

A hormone synthesized in the hypothalamus and released by the posterior pituitary that stimulates uterine contractions and milk ejection from mammary glands.

Triiodothyronine (T3)

A thyroid hormone that shares the metabolic functions of thyroxine ($T_4$) but is $5\text{X}$ more potent, increasing carbohydrate energy release, protein synthesis, growth rate, and nervous system activity.

Calcitonin

A thyroid hormone that lowers blood calcium and phosphate concentrations by inhibiting their release from bone and increasing their rate of deposition into bone.

Parathyroid Hormone (PTH)

A hormone from the parathyroid glands that increases blood calcium and decreases phosphate by stimulating osteoclasts, inhibiting osteoblasts, retaining calcium in the kidneys, and promoting dietary absorption.

Adrenal Medulla

The inner portion of the adrenal gland, regulated by the sympathetic nervous system, that secretes $80\%$ epinephrine and $20\%$ norepinephrine during acute stress.

Adrenal Cortex

The outer layer of the adrenal gland that synthesizes and secretes more than $30$ different steroid hormones essential to survival across three distinct functional zones.

Aldosterone

A mineralocorticoid secreted by the zona glomerulosa that increases blood volume and blood pressure by promoting sodium retention, eliminating potassium, and conserving water through osmosis.

Cortisol

A glucocorticoid secreted by the zona fasciculata that maintains normal blood glucose between meals, decreases protein synthesis, releases fatty acids from adipose tissue, and stimulates gluconeogenesis.

Adrenal Androgens

Steroid hormones produced by the adrenal cortex that supplement sex hormones from the gonads in males and can be converted into estrogen by skin, liver, and adipose tissues in females.

Zona Glomerulosa

The outer zone of the adrenal cortex responsible for synthesizing aldosterone and other mineralocorticoids that promote sodium reabsorption.

Zona Fasciculata

The middle zone of the adrenal cortex responsible for producing cortisol and other glucocorticoids that provide anti-inflammatory effects and metabolic support.

Zona Reticularis

The inner zone of the adrenal cortex that produces male sex hormones (adrenal androgens).

Pancreatic Islets

Specialized clusters of endocrine cells arranged around blood vessels in the pancreas, containing alpha, beta, and delta cells.

Glucagon

A hormone produced by pancreatic alpha cells that triggers the breakdown of glycogen into glucose when blood sugar is low or extra energy is needed.

Insulin

A hormone produced by pancreatic beta cells that promotes glycogen synthesis, inhibits glucose production from noncarbohydrates, and enhances glucose uptake into muscle and adipose cells.

Somatostatin

A pancreatic delta cell hormone that helps regulate glucose metabolism by inhibiting the secretion of both insulin and glucagon.

Melatonin

A pineal gland hormone that maintains the internal clock and sleep-wake rhythms, with production stimulated by darkness and suppressed by light.

Thymosin

A hormone secreted by the thymus gland that facilitates the development and differentiation of specialized lymphocytes known as T-cells.

Stressor

Any stimulus that directly or indirectly triggers the hypothalamus to initiate coordinated short-term or long-term stress-compensating responses.