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Hormonal Stimuli

Endocrine glands are activated by other hormones

Humoral Stimuli

Changing blood levels of certain ions or nutrients stimulate hormone release

Blood chemistry

Neural Stimuli

Nerve impulses stimulate hormone release

Most are under control of the sympathetic nervous system – “flight or fight”

Hormone Action

Endocrine cells secrete hormones into extracellular fluids

Blood transfers hormones to target cells (a.k.a., effectors)

Hormones regulate activity of effector organs

Binding of receptor causes changes in the target cell

Changes in plasma membrane permeability or electrical state → chemicals in/out

Activation of genes → production of proteins

cytoplasmic changes cause changes to the cell’s function

Two classes of hormones act on cells differently: steroid hormones and non-steroid hormones

If steroid hormone:

Hormones diffuse through the plasma membrane of target cells (steroids are lipid-based)

Enters the nucleus

Bind to a specific protein within the nucleus

Hormone-protein complex binds to specific sites on the cell’s DNA

Activate genes that result in transcription & translation to synthesize new proteins

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If non-steroid hormone (amino-acid or prostaglandins) …

Hormones binds to membrane receptors (can’t pass through membrane itself)

Membrane receptors produce secondary messenger molecules like cAMP

Secondary messenger molecules set off a chain reaction that activates a series of enzymes in the cytoplasm

This results in changes to the cell’s function