endocrine
hormones: are chemical messengers that are made in one place (origin) and transported via blood? to reach specific cells in other tissues (target)
types of hormones
neurocrine: a hormone communicating between cells in nervous system or from neurons to a vascular bed for transport to a distal site
paracrine: a hormone is secreted to act at a local site targeting neighboring cells of a different type (ex: gastrin)
endocrine: a hormone secreted into a capillary bed for transport to a distal site
autocrine: a hormone that is produced by a cell to act on that same cell or via gap junctions to neighboring identical cells
structure of hormones
protein and polypeptides
steroids
derivatives of the amino acid tyrosine
ex: insulin, glucagon, parathyroid hormone
receptor: on the plasma membrane
ex: cortisol, aldosterone, estrogen, and testosterone
receptor: intracellular receptor
ex: thyroxine (T4), epinephrine, norepinephrine
receptor: nucleus membrane receptor
tyrosine kinase receptors: nerve growth factor, growth factor, and insulin receptors all have a tyrosine kinase portion
hormone transportation
hydrophobic hormones: circulate in the blood bound to plasma proteins (mainly albumin) (ex: steroids, thyroid hormones)
water-soluble hormones: dissolved in the plasma and travel to their target tissues (ex: proteins, catecholamine = NE, dopamine, epinephrine)
effects of hormones
stimulate synthesis of proteins or regulatory molecules within the cell
activate or deactivate enzymes
alter plasma membrane permeability, potential, or both
induce secretory activity
stimulate mitosis