Chapter 45: Hormones and Endocrine System

• Concentration of the hormone in the body

• Presence of the hormone receptor in a cell

• Response of the cell when the receptor binds the hormone

What variables shape a hormone’s effect on an animal’s body and behavior?

Endocrine System: Stimulus

Affects an endocrine cell

Endocrine System: Signal

Chemical signal called a hormone; signal travels in the blood to everywhere

Endocrine System: Target

Any cell with a receptor for that hormone (target cell)

Endocrine System: Response

Slow, long-lasting response

Nervous system: Stimulus

Affects the cell body of a neuron

Nervous System: Signal

Nerve impulse or action potential; signal travels down the axon of a neuron

Nervous system: Target

The cell on the other end of the axon (another neuron, muscle cell, etc)

Nervous System: Response

Fast response, does not last very long

Hormone

a molecule (a chemical signal) secreted into extracellular fluid by an endocrine cell that circulates through the body and stimulates specific target cells

• Hormones can reach all parts of the body, but only target cells have receptors for that hormone; effects of hormones and other signaling molecules depend on target receptors

Communication between animal cells through secreted signals can be classified by two criteria:

1. The type of secreting cell

2. The route taken by the signal in reaching its target

Endocrine signaling

hormones secreted into extracellular fluids by endocrine cells reach their target cells via the bloodstream

Functions of endocrine signaling

• Maintains homeostasis

• Mediates responses to stimuli

• Regulates growth and development

• Triggers physical and behavioral changes underlying sexual maturity and reproduction

Local Regulators

molecules that act over short distances, reaching cells solely by diffusion

Paracrine and Autocrine signaling both play a role in…

blood pressure regulation, nervous system function, and reproduction

Paracrine Signaling

targets cells near the secreting cells

Autocrine Signaling

the target cell is also the secreting cell

Synapse

junction between neuron and another cell

Synaptic signaling

at the synapse, secreted molecules called neurotransmitters diffuse short distances and bind to receptors on the target cells.

Neuroendocrine signaling

specialized neurosecretory cells secrete neurohormones; diffuse from the nerve endings into the bloodstream.

Pheromones

chemical signals used to communicate with other individuals of the same species (action occurs outside the body)

polypeptides, steroids, and amines

What three major classes do hormones fall into?

Insulin

• Water-soluble (hydrophilic)

• Polypeptide

Epinephrine

• Water-soluble (hydrophilic)

• Amine

Cortisol

• Lipid-soluble (hydrophobic)

• Steroid

Thyroxine

• Lipid-soluble (hydrophobic)

• Amine

Water-soluble hormones

• secreted via exocytosis

• travel freely in bloodstream

• bind to cell surface receptors

Lipid-soluble hormones

• diffuse across membranes of endocrine cells

• bind to endocrine transport proteins that keep them soluble in bloodstream

• diffuse into target cells from bloodstream and bind to intracellular signal receptors

hormone binds to its receptor on membrane

What initiates a signal transduction pathway?