Endocrine systems

chemical messengers (hormones) released into bloodstream for distribution throughout body

Paracrine system

employ hormones that diffuse short distances and affect neighboring cells

Autocrine systems

employ hormones to influence own behavior

Neuroendocrine/synaptic chemical messenger systems

release neurotransmitter that diffuses a short distance to specific neighboring cell

Cytokines

chemical messengers that coordinate immune system response

can behave like endocrine, paracrine, or autocrine systems

peptide and catecholamine hormones

cannot cross cell membrane; bind to receptors on membrane, which activate second messenger systems that uptimately alter enzyme activity via phosphorylation or dephos.

steroid hormones, thyroid hormone, vitamin D

hydrophobic, can cross cell membranes easily

bind to receptors located in cytosol or nucleus, altering gene expression

synergistic response

2+ messengers together produce a response greater than either messenger alone

antagonistic response

2+ messengers acting together reduce response magnitude

permissive response

when presence of 1 hormone in greater than threshold conc is required for second hormone to express its effect

1st hormone is permissive for second hormone

trophic effects

hormone effects another endocrine gland, promoting its health and growth but not necessarily its release of hormones

mechanisms to terminate response of receptor+ligand system

1. local enzymes destroy ligand (neural)

2. receptor becomes desensitized, no longer activates 2nd messenger system

3. internalization of receptor+ligand complex and destruction of complex or ligand

Stimuli for hormone release

signal from other hormone, chemical stimulus (solute conc.), physical stimulus (stretch, temperature), neural signals

diurnal rhythm

serum concentration of a hormone varies over the course of a day

pulsatile rhythm

variation in hormone conc over the course of 1-2 hrs

negative feedback

presence of a substance inhibits production/release of a hormone

what removes chemical messengers from circulation?

liver and kidney

half lives range from minutes to days

cytokine family

interleukin family

interferons

tumor growth and necrosis factors

how cytokines differ from hormones

produced by variety of cells all over the body, not just in one specific endocrine organ

present in concentrations 3 orders of magnitude smaller than hormones

controlled

vs

regulated

controlled: physiological variable can be altered by some internal biological process

regulated: value held constant even when disturbances are present, accomplished by mechanisms which control contributing factors

ex: heart rate controlled, blood pressure regulated