Introduction to the Endocrine System

Vocabulary flashcards covering key endocrine system terms from the lecture notes.

Endocrine system

A network of ductless glands that secrete hormones into the bloodstream to regulate body functions.

Hormone

A chemical messenger released by endocrine glands that binds to receptors on target cells to produce a response.

Endocrine gland

A gland that produces hormones and releases them into the bloodstream without ducts.

Endocrine tissue (organ)

Tissue within an organ that contains hormone-secreting cells or clusters of such cells.

Target cell

A cell with specific receptors for a hormone, allowing a response when the hormone binds.

Lipid-soluble hormone

Nonpolar, fat-soluble hormone that diffuses across membranes and binds intracellular receptors.

Water-soluble hormone

Polar hormone that cannot cross membranes and binds membrane receptors to trigger signaling.

Carrier protein

Blood protein that binds lipid-soluble hormones to improve solubility and extend their life.

Bound hormone

The portion of lipid-soluble hormone attached to carrier proteins in blood.

Free hormone

The unbound hormone fraction capable of exiting blood and acting on target cells.

Receptor

A protein that binds a hormone to initiate a cellular response.

Intracellular receptor

A receptor located in the cytosol or nucleus that mediates lipid-soluble hormone action.

Membrane receptor

A receptor on the cell surface that mediates signaling for water-soluble hormones.

Hormone-receptor complex

The bound form that activates downstream processes; can regulate gene expression.

Hormone-response element (HRE)

DNA sequence bound by the hormone-receptor complex to regulate transcription.

Second messenger

Intracellular signaling molecule produced after receptor activation (e.g., cAMP, DAG, IP3).

cAMP

Cyclic adenosine monophosphate; a second messenger produced by adenylyl cyclase.

DAG

Diacylglycerol; a second messenger that activates protein kinase C.

IP3

Inositol triphosphate; a second messenger that increases cytosolic Ca2+.

G protein

Membrane-bound protein that transmits signals from receptor to an effector enzyme.

Gs

G protein that stimulates adenylate cyclase to raise cAMP levels.

Gi

G protein that inhibits adenylate cyclase, lowering cAMP levels.

Gq

G protein that activates phospholipase C.

Adenylate cyclase

Membrane enzyme that converts ATP to cAMP when activated by Gs.

Phospholipase C

Membrane enzyme that cleaves PIP2 into DAG and IP3 upon activation by Gq.

Eicosanoids

Local hormones derived from fatty acids; include prostaglandins; do not circulate widely.

Prostaglandins

Eicosanoids that promote pain and inflammatory responses; blocked by NSAIDs.

Autocrine signaling

Local signaling where a cell responds to hormones it secretes.

Paracrine signaling

Local signaling where hormones act on neighboring cells.

Local hormones

Signaling molecules that do not circulate in blood but act locally.

Steroid hormones

Lipid-soluble hormones derived from cholesterol; bind intracellular receptors to regulate gene transcription.

Biogenic amines (monoamines)

Hormones derived from amino acids; include catecholamines and thyroid hormone; TH is lipid-soluble.

Protein (peptide) hormones

Most hormones; hydrophilic polypeptides that act via membrane receptors.

Circulating hormones

Hormones that travel in blood; lipid-soluble often bound to carriers; water-soluble travel freely.

Half-life

Time required for a hormone's blood concentration to fall to half; varies by type.

Upregulation

Increase in the number of receptors on a target cell, increasing sensitivity.

Downregulation

Decrease in receptor number on a target cell, reducing sensitivity.

Synergistic interaction

Two hormones enhance each other’s effects on a target cell.

Permissive interaction

One hormone enables another hormone to exert its full effect.

Antagonistic interaction

One hormone opposes the action of another hormone.

Aging and the endocrine system

Secretory activity declines with age, reducing hormone levels and system efficiency.