endocrine system Flashcards
allow cells to communicate with each other to regulate body activities
-most are produced by a specific collection of cells or gland
chemical messenger
organ consisting of epithelial cells that specialized in secretion
gland
controlled release of chemicals from a cell
secretion
– secreted in a local area
-stimulates the cell that originally secreted it
autocrine
act locally on nearby cells
-secreted by one cell type in ECF and affect surrounding cells
paracrine
– secreted by neurons
- activate an adjacent cell, whether neuron, muscle cell or glandular cell
- secreted into synaptic cleft
- can be considered paracrine agents
neurotransmitters
– secreted into the bloodstream by certain glands and cells
-affect cells distant from source
endocrine
composed of – endocrine glands + endocrine cells (throughout the body)
endocrine system
– chemical messengers secreted into bloodstream, not into a duct
hormones
types of hormones
– nonpolar
-steroid, thyroid, fatty acid derivative (e.g. eicosanoids)
Lipid-soluble hormones
type of hormone
– polar
-protein, peptide, most amino acid derivative
water soluble hormones
• Circulate as free hormones (dissolve directly into blood and delivered to target tissue w/o attaching to binding proteins) because they can dissolve in blood
water soluble hormones
• Tend to diffuse from the walls of the capillaries more slowly (because they are big)
water soluble hormones
• Capillaries regulated by these hormones are usually fenestrated or very porous
water soluble hormones particularly protein
type of hormone that • Have short half-lives
water soluble
• Travel in the bloodstream attached to binding proteins (because they are small and low solubility in aqueous fluids, this prevents them from being degraded or eliminated)
lipid soluble hormones
hormones from the anterior pituitary gland
tropic hormones
type of control of hormonal release
• These hormones are sensitive to blood levels of a particular substance
occurs when there are bloodborne molecules that can directly stimulate the release of some hormones
Humoral stimuli
type of control of hormonal release
occurs when neurons release a neurotransmitter into the synapse with the cells that produce the hormone
control by neural stimuli
– hormones that are secreted by neurons directly into the blood when they are stimulated
neuropeptides
– neuropeptides that stimulate hormone secretion from other endocrine cells
-usually for hormones from hypothalamus
releasing hormones
occurs when a hormone is secreted and in turn stimulates the secretion of other hormones
control by hormonal stimuli
type of regulation of hormones
– regulates most hormones
-hormone’s secretion is inhibited by the hormone itself once blood levels have reached a certain point and there is adequate hormone to activate the target cell (self-limiting system)
negative feedback
type of regulation of hormones
some hormones, when stimulated by a tropic hormone, promote the synthesis and secretion of the tropic hormone in addition to stimulating their target cell (self-propagation system)
positive feedback
proteins where hormones bind to exert their actions
receptors
portion of each receptor molecule where a hormone binds
receptor site
tendency for each type of hormone to bind to one type of receptor
specificity
class of receptor where lipid soluble hormones bind (because they are small and can diffuse into the plasma membrane) -found in cell nucleus or in the cytoplasm (but move to nucleus when activated) -hormone-receptor complex interacts with DNA in the nucleus or w/ cellular enzymes to regulate the transcription of particular genes in the target tissue
nuclear
class of receptor
where water soluble hormones bind (because they are big and cannot diffuse into PM)
-proteins that extend across the plasma membrane’s outer surface
-hormone-receptor complex initiates a response inside the cell
membrane-bound
MBR activate responses in 2 ways:
- Altering the activity of G proteins at the inner surface of PM
- Directly altering the activity of intracellular enzymes
chemical produced inside a cell once a hormone or another chemical messenger binds to certain MBR, which then activates specific cellular processes
- some are second messengers
- second-messenger system
intracellular mediator
happens wheneach receptor produces thousands of second messengers
-a single hormone activates many second messengers, each of which activates enzymes that produce an enormous amout of final product
signal amplification
