hormones
signaling molecules secreted into the extracellular fluid that bind to specific receptors in the body
3 main chemical classes of hormones: polypeptides, steroids, and amines
target cells
cells with a receptor matching a specific hormones
nervous system
major communication and control system of the body, signals transmitted by neurons
endocrine system
body system for communication and regulation facilitated by hormones
endocrine signaling
secreted molecules diffuse into the bloodstream and trigger responses in target cells anywhere in the body
paracrine signaling
secreted molecules diffuse locally and trigger a response in neighboring cells
target cells lie near the secreting cell
autocrine signaling
secreted molecules diffuse locally and trigger a response in the cells that secrete them
secreting cells themselves are the target cells
local regulators
molecules that act over short distances and reach their target cells solely by diffusion, once secreted act w/in seconds or milliseconds
ex: cytokines, growth factors
prostaglandins
group of modified fatty acids, local regulators that mediate signaling
synaptic signaling
neurons form specialized junctions (synapses) with target cells
neurotransmitters
secreted by neurons, diffuse a very short distance and bind to receptors on the target cells
neuroendocrine signaling
specialized neurons (neurosecretory cells) secrete neurohormones
neurohormones
diffuse from nerve cell endings into the bloodstream
pheromones
chemicals that are produced by the body and released into the external environment
nitric oxide (NO)
gas, functions in the body as both a local regulator and neurotransmitter
O2 level in blood decreases, endothelial cells in blood vessel walls synthesize and release NO which activates an enzymes that relaxes cells resulting in vasodilation
polypeptide
class of hormones, chains of amino acids, water soluble
ex: insulin
steroid
class of hormones, lipids that contain four fused carbon rings, lipid soluble
ex: cortisol
amines
class of hormones, synthesized from a single amino acid, usually water soluble
ex: epinephrine
water-soluble hormones
secreted by exocytosis and travel freely in bloodstream, can't diffuse through plasma membrane of target cells, to to cell-surface receptors
lipid-soluble hormones
diffuse out across the cell membranes of endocrine cells, outside cell bind to transport proteins that keep them soluble in aq solution then diffuse into target cell
exert different effects on different target cells
signal transduction
series of changes in cellular proteins that converts the extracellular chemical signal to a specific intracellular response
epinephrine
hormone secreted by adrenal glands, aka adrenaline
increases blood flow to major skeletal muscles and decreases blood flow to digestive tract
simple endocrine pathway
- endocrine cells respond directly to an internal or environmental stimulus by secreting a particular hormone
- hormone travels in bloodstream to target cells where it interacts with specific receptors.
- signal transduction w/in target cells causes physiological change
simple neuroendocrine pathway
- stimulus received by sensory neuron
- sensory neuron stimulates neurosecretory cell which secretes a neurohormone
- neurohormone diffuses into the bloodstream and travels to target cells
oxytocin
neurohormone, from posterior pituitary gland, stimulates mammary glands to secrete milk
negative feedback
response reduces the initial stimulus
(helps restore a preexisting state)
positive feedback
reinforces a stimulus, leads to a greater response
(amplifies both the stimulus and the response)
pituitary gland
gland located at the base of the hypothalamus, comprised of two fused glands that preform different functions, receives signals from the hypothalamus
posterior pituitary
extension of hypothalamus, neurohormones produced by hypothalamus secreted here
anterior pituitary
endocrine gland that synthesizes and secretes hormones in response to hormones from the hypothalmus