Theme 1: Endocrine Control, Hormones & Receptors

Endocrine system

Uses hormones released into blood; responses are generally slower and longer-lasting than neural responses.

Nervous system

Uses electrical signals and neurotransmitters; responses are usually rapid and brief.

Endocrine gland

Ductless gland that releases hormones into interstitial fluid and then blood.

Exocrine gland

Gland that releases its products through ducts onto a surface or into a cavity.

Hormone target cell

Cell with the specific receptor that recognizes a hormone.

Why is endocrine signaling less spatially specific than neural signaling?

Hormones travel through the bloodstream throughout the body, while neural signals follow defined pathways.

How do hormones achieve cellular target specificity?

Only cells with the appropriate receptors respond to a given hormone.

Peptide hormone solubility

Water-soluble; generally binds receptors on the outer plasma membrane.

Steroid hormone precursor

Cholesterol.

Steroid hormone solubility

Lipid-soluble; can cross the plasma membrane and bind intracellular receptors.

Amino acid derivatives

Hormones derived from amino acids such as tyrosine or tryptophan; solubility varies by hormone.

Thyroid hormone solubility

Lipid-soluble despite being an amino acid derivative; travels in blood largely bound to carrier proteins.

Water-soluble hormone mechanism

Binds a cell-surface receptor and activates intracellular signaling pathways.

Lipid-soluble hormone mechanism

Crosses the plasma membrane and binds an intracellular receptor, often changing gene expression.

Intracellular steroid/thyroid hormone receptors

Located in the cytoplasm or nucleus.

Hormone carried in blood

Lipid-soluble hormones commonly travel bound to carrier proteins; water-soluble hormones usually circulate dissolved in plasma.

Permissive hormone interaction

One hormone enables another hormone to exert its full effect.

Synergistic hormone interaction

Two or more hormones produce a combined effect greater than either produces alone.

Antagonistic hormone interaction

One hormone opposes or blocks the effect of another hormone.

Hormone receptor binding

Binding changes target-cell activity; receptor number and responsiveness influence the strength of the response.