ecdysteriod
- A steroid hormone, secreted by the prothoracic glands, that triggers molting in arthropods.
- Communicate w/ other hormones to regulate the timing of metamorphosis.
endocrine signaling
Secreted molecules diffuse into the bloodstream and trigger responses in target cells anywhere in the body.
local regulators
Molecules that act over short distances and reach their target cells solely by diffusion.
paracrine signaling
- Target cells lie near the secreting cell.
- Secreted molecules diffuse locally and trigger a response in the neighboring target cells.
autocrine signaling
- The target cell is the secreting cell itself.
- Secreted molecules diffuse locally and trigger a response in the cells that secrete them.
synaptic signaling
- Neurons form specialized junctions called synapses w/ target cells, such as other neurons and muscle cells.
- At synapses, neurons secrete molecules called neurotransmitters that diffuse a very short distance to bind to receptors on the target cells.
neuroendocrine signaling
- Specialized neurons called neurosecretory cells secrete molecules that diffuse from nerve cell endings into the bloodstream.
- These molecules, which travel thru the bloodstream to target cells, are a class of hormone called neurohormones.
pheromone
In animals and fungi, a small molecule released into the environment that functions in communication between members of the same species. In animals, it acts much like a hormone in influencing physiology and behavior.
endocrine glands
A ductless gland that secretes hormones directly into the interstitial fluid, from which they diffuse into the bloodstream.
exocrine glands
- Have ducts that carry secreted substances onto body surfaces or into body cavities.
- Ex: salivary glands.
polypeptide hormone
- Water-soluble; not soluble in lipids
- Can’t pass through the plasma membranes of cells; instead, they bind to cell-surface receptors that relay information to the nucleus thru intracellular pathways
- Ex: insulin, formed by cleavage of 1 long polypeptide chain.
3 major chemical classes of hormones:
polypeptides (proteins and peptides), steroids, amines
amine hormone
- Each synthesized from a single amino acid, either tryptophan or tyrosine
- Ex: epinephrine and thyroxine
- Can’t pass through the plasma membranes of cells; instead, they bind to cell-surface receptors that relay information to the nucleus thru intracellular pathways
steroid hormone
- 4 fused carbon rings
- All derived from the steroid cholesterol
- Lipid-soluble, can pass thru cell membranes readily
- Receptors for them reside in the cytoplasm or nucleus
growth factor
- Polypeptide local regulator.
- Stimulates cell proliferation and differentiation. Many types of cells grow, divide, and develop normally only when growth factors are present in their extracellular environment.
nitric oxide (NO)
- Functions as both a neurotransmitter and a local regulator.
- When blood oxygen level falls, endothelial cells in blood vessel walls synthesize and release NO. NO activates an enzyme that relaxes the surrounding smooth muscle cells, resulting vasodilation, which improves blood flow to tissues.
- Highly reactive and potentially toxic, NO usually triggers changes in a target within a few seconds of contact and then breaks down.
prostaglandin
- Group of local regulators; modified fatty acids
- So named b/c they were first discovered in prostate gland secretions that contribute to semen. In semen that reaches a female’s reproductive tract, prostaglandins stimulate the smooth muscles of the female’s uterine wall to contract, helping sperm reach an egg. At the onset of childbirth, prostaglandin-secreting cells of the placenta cause the nearby muscles of the uterus to become more excitable, helping to induce labor.
- In the immune system, prostaglandins promote fever and inflammation and intensify the sensation of pain. The anti-inflammatory and pain-relieving effects of aspirin and ibuprofen are due to the inhibition of prostaglandin synthesis by these drugs.
- Help to regulate the aggregation of platelets, one step in the formation of blood clots. B/c blood clots can cause a heart attack, some physicians recommend that people at risk take aspirin; however, b/c prostaglandins help maintain a protective lining in the stomach, aspirin therapy can cause debilitating stomach irritation.
