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

1. endocrine cells respond directly to an internal or environmental stimulus by secreting a particular hormone
2. hormone travels in bloodstream to target cells where it interacts with specific receptors.
3. signal transduction w/in target cells causes physiological change

simple neuroendocrine pathway

1. stimulus received by sensory neuron
2. sensory neuron stimulates neurosecretory cell which secretes a neurohormone
3. 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