Endocrine System Part 1

Important terms and concepts to know about the Endocrine System

Hormone

steroid or amino acid based molecules released to the blood that act as long distance chemical messengers to regulate specific body functions

Peptide

short chain of amino acids; usually water soluble

Proteins

long chain amino acids; usually water soluble

Steroids

a class of lipids derived from cholesterol; act as hormones and as constituents of phospholipid bilayer membranes

Circulatory hormones

hormones that travel in blood and act on distant target cells

Local hormones

hormones that act locally without first entering the blood stream (nerve and gland cells)

Paracrines

short distance chemical signals that act locally within the same tissue; not a hormone

Autocrines

short distance chemical signals that exert their effects on the same cells that secrete them; not a hormone

Target cell

tissue with receptor for specific hormone

Negative Feedback

a change in a given direction causes change in the oppostie direction

controls blood levels of hormones

Hormonal stimuli

hormones stimulate other endocrine organs to release hormones

Ex. hypothalamus → anterior pituitary gland

Humoral stimuli

hormone release stimulated by altered levels of certain critical ions or nutrients; response to body fluid

Neural stimuli

nerve fibers stimulate hormone release

Hypothalamus

area in brain that produces hormones that controls body temperature, heart rate, hunger, mood etc.

main link between endocrine system and nervous system

keeps body in homeostasis

Tropic Hormone

hormone targets endocrine gland to produce another hormone

Ex. anterior pituitary

Target Cell Activation

1. blood levels of hormones
2. relative number of receptors on or in target cell
3. affinity of binding between receptor and hormone

Up-regulation

target cells form more receptors in response to low hormone levels

Down-regulation

target cells lose receptors in response to high hormone levels

Permissiveness

one hormone cannot exert its effects without another hormone being present

Ex. Prolactin and Oxytocin -- need both or no effect

Synergism

more than 1 hormone produces same effects on target cell (amplification; 1 + 1 = 5)

Ex. Epinephrine and Glucagon -- both raise blood sugar

Antagonism

one or more hormones oppose(s) action of another hormone (1 + (-1) = 0)

Ex. Insulin and Glucagon -- Glucagon raises blood sugar but Insulin brings down blood sugar