is a mediator molecule that is released in one part of the body but regulates the activity of cells in other parts of the body
secrete their products into ducts that carry the secretions into body cavities, into the lumen of organs or to the outer surface of the body. they include sudoriferous (sweat) glands, sebaceous (oil), mucous and digestive glands
secrete their products into the interstitial fluid surrounding the secretory cells rather than into ducts. They secrete hormones
only the target cells for a given hormone have these that bind and recognize that hormone.
are constantly being broken down and synthesized.
if a hormone is present in excess the number of traget cell receptors may decrease. It makes a target cell less sensitive to a hormone
when a hormone is deficient, the number of receptors may increase. This makes a target cell more sensitive to a hormone.
most endocrine hormones are these. They pass from the secretory cells that make them into interstitial fluid and then into the blood
act locally on neighbouring cells or on the same cell that secrete them without first entering the blood stream
local hormones that act on neighbouring cells
local hormones that act on the same cell that secreted them
include steroids, thyroid hormones, and nitric oxide
are derived from cholesterol and are lipid soluble.
two types T3 and T4. They are lipid soluble.
nitric oxide (NO)
the gas is both a hormone and a neurotransmitter. It is lipid soluble.
water soluble hormones
these hormones are soluble in water and include amine hormones, peptide hormones, protein hormones and eicosanoid hormones
these include epinephrine, norepinephrin, and dopamine, histamine, serotonin and melatonin. they are water soluble
peptide hormones and protein hormones
are amino acid polymers ex are oxytocins and proteins include human growth hormone and insulin.
the two major types are prostaglandins and leukotrines. They are important local hormones and may act as circulatory hormones.
most lipid soluble hormones are bound to these so they can travel in the blood. They make them temporarily water soluble. They slow the passage of small hormone molecules through the kidneys thus slowing the rate of hormone loss in urine. They provide a ready reserve of hormones already present in the bloodstream.
some lipid-soluble hormoes are not attached to a transport protein. The diffuse out of capillaries, bind to receptors and trigger responses
when a water soluble hormone binds to its receptor at the outer surface of the plasma membrane
the first one causes the creation of a second one inside the cell where specific hormone-stimulated responses take place.
Cyclic AMP (cAMP)
a second messenger
target cell responsiveness
depends on 1)hormone concentration 2)the abundance of target cell receptors 3) the influence exerted by other hormones