Hormones and the Endocrine System

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Local regulators are divided into two types:

Paracrine signals act on cells near the secreting cell.

Autocrine signals act on the secreting cell itself.

Slide 9

Intercellular communication by secreted molecules

Blood

vessel

Response

Response

Response

(a) Endocrine signaling

(b) Paracrine signaling

(c) Autocrine signaling

Slide 10

Neurotransmitters and Neurohormones

Neurons (nerve cells) contact target cells at synapses.

At synapses, neurons often secrete chemical signals called neurotransmitters that diffuse a short distance to bind to receptors on the target cell. Neurotransmitters play a role in sensation, memory, cognition, and movement.

Neurohormones are a class of hormones that originate from neurons in the brain and diffuse through the bloodstream.

Slide 11

Intercellular communication by secreted molecules

Response

(d) Synaptic signaling - neurotransmitters

Neuron

Neurosecretory

cell

(e) Neuroendocrine signaling

Blood

vessel

Synapse

Response

Slide 12

Pheromones

Pheromones are chemical signals that are released from the body and used to communicate with other individuals in the species.

Pheromones mark trails to food sources, warn of predators, and attract potential mates.

Slide 13

Chemical Classes of Hormones

Three major classes of molecules function as hormones in vertebrates:

Polypeptides (proteins and peptides)

Amines derived from amino acids

Steroid hormones

Polypeptides and amines are water-soluble.

Steroids are lipid-soluble.

Slide 14

Lipid-soluble hormones (steroid hormones) pass easily through cell membranes.

Water-soluble hormones (polypeptides and amines) do not pass through the cell membrane.

The solubility of a hormone correlates with the location of receptors inside or on the surface of target cells.

Slide 15

Hormones differ in form and solubility

Water-soluble

Lipid-soluble

Steroid:

Cortisol

Polypeptide:

Insulin

Amine:

Epinephrine

Amine:

Thyroxine

0.8 nm

Slide 16

Cellular Response Pathways

Water and lipid soluble hormones differ in their paths through a body.