Intercellular chemical messengers

target cells

paracrines

histamine

neurotransmitters

acetylcholine

hormones

T₃ and T₄

neurohormones

GnRH

General principles

specificity of communication depends on specialization of target-cell receptors

complementarity of endocrine and nervous systems

type of chemical messenger

distance of action of chemical messenger

means of specificity

anatomic arrangement

“wired” vs. “wireless”

major functions

regulation of organic metabolism, water and electrolyte balance

inducing adaptive changes to stress

promoting smooth, sequential growth and development

controlling reproduction

regulating red blood cell production

along with ANS, controlling and integrating circulation, digestion

speed of response

fast vs. slow

duration of action

Hormones

Hormonal types

peptides

amines

derived from the amino acid tyrosine

catecholamines

thyroid hormones

steroids

behavior

hydrophilic vs. hydrophobic

lipophobic vs. lipophilic

mechanisms of synthesis

peptide hormones

steroid hormones

cholesterol

amines

transport

Modes of action

postreceptor events

hydrophilic hormones

intracellular second messenger

cAMP

adenylate cyclase

lipophilic hormones

gene activation

hormone levels are regulated by changes in secretion rate

negative feedback

output of a system opposes a change in input

neuroendocrine reflexes

diurnal or circadian rhythms

response of target cell can be regulated by altering number of receptors

abnormal

testicular feminization syndrome

normal

down regulation

permissiveness

one hormone enhances responsiveness to another

synergism

FSH + testosterone

antagonism

progesterone and estrogen during pregnancy