Key Terms
Endocrine
Hormone secreted into bloodstream; travels far; affects distant target cells.
Paracrine
Chemical affects neighboring cells only. Example: histamine released in the lungs causes smooth muscle to constrict airw
Autocrine
Chemical affects the same cell that secreted it. Example: interleukin-1 (IL-1) in inflammatory response.
Examples using cAMP
Calcitonin, glucagon, TSH
DOWNREGULATION
Too much hormone chronically present; cell DECREASES receptor number; becomes less sensitive.
UPREGULATION
Too little hormone chronically present; cell INCREASES receptor number; becomes more sensitive.
Permissive
Hormone A must be present for hormone B to work. Thyroid hormones enable certain reproductive hormones to function.
Synergistic
Two hormones together produce a bigger effect than either alone. FSH + estrogens are both required for egg maturation.
Antagonistic
Two hormones oppose each other. Insulin lowers blood glucose; glucagon raises it.
NEGATIVE FEEDBACK
Most common. Rising hormone levels signal the gland to stop producing more.
POSITIVE FEEDBACK
Less common. Rising hormone triggers MORE release.
Example
Oxytocin during labor. Cervical stretch triggers more oxytocin; contractions intensify; more stretch; loop continues unt
Humoral
Change in blood chemistry (ions, nutrients). High blood glucose triggers insulin.
Hormonal
One hormone triggers another. Hypothalamus releases TRH; TRH triggers TSH; TSH triggers thyroid hormones.
Neural
Nerve impulse triggers hormone release. Sympathetic nervous system signals adrenal medulla to release epinephrine/norepi