A&P Chapter 17

Functional organization of the endocrine system

endocrine system

consists of glands that secrete chemical messengers (hormones) into the cirulatory system

hormones

transplanted in blood, acts on target tissues, regulates the activities of body structures

hypothalamus

site of nervous and endocrine interaction

axons

nervous system mode of transport

blood

endocrine mode of transport

instant/milliseconds

nervous system speed of response

delayed/seconds

endocrine system speed of response

milliseconds/seconds

nervous system duration of response

minutes/days

endocrine duration of response

frequency

nervous system modulation/regulation of systems

amplitude

endocrine system modulation/regulation of systems

lipid soluble hormones

prolonged effects that travel through plasma and remain at a constant rate through time

water soluble hormones

rapid onset with a short duration that does not bind to plasma and they are quickly broken down or taken up by tissues. They do not remain in the bloodstream. Includes proteins, epinephrine, norepinephrine

chronic regulation

relatively stable and almost always running. Hormone is maintained in the circulating blood for a long period of time (ex: thyroid hormone T3 & T4)

Acute regulation

hormone rapidly increases in concentration in the blood for a short time in response to a stimulus (ex: epinephrine)

Episodic (cylcic) regulation

hormone is stimulated cyclically so it increases and decreases in the blood at a relatively constant time (ex: female reproductive hormones - estrogen, progesterone)

negative feedback system

maintains homeostasis and controls the secretion of most hormones

1. Changes in extracllular concentration of non-hormone substance

2. Stimulation of nervous system

3. Stimulation by a hormone from another endocrine tissue

Name 3 ways hormones are regulated by the endocrine tissue

humoral stimuli

Fluid in the body where changes in the extracellular concentration of a non-hormone substance can cause hormones to be released

Calcium levels are low and PTH is released

Name an example of a humoral stimulus

neural stimuli

Neuron causes secretion of stimulatory or inhibitory of a neurotransmitter, the endocrine cell secretes or is unable to secrete its hormone.

Hormonal stimuli

Releasing hormones stimulate release of tropic hormones which then causes another hormone to be stimulated. One hormone stimulates the next or can inhibit the next.

lipid soluble hormone

hormone goes to intracellular or nuclear receptors to activate genes (synthesize mRNA) and then synthesize new proteins or enzymes. Slower process think making lasagna.

water soluble hormones

hormone goes to membrane bound proteins, recepters alter activity of G proteins causing the opening and closing of ion channels and activate existing enzymes. More rapid process, think hot pocket.

binding site

portion of the molecule that the hormone attatches to. Receptors are specific for a particular hormones and the purpose is to elicit a response by the target cell

Membrane bound receptors

span the plasma membrane. Interact with hormones that cannot pass through the plasma membrane. Typically bind to water soluble or large molecular weight hormones

Intracellular (nuclear) receptors

located in the cytoplasm or nucleus and they bind to lipid-soluble hormones or small molecules

Alpha, beta, gamma

3 G protein subunits

inactive state

GDP bound to alpha subunit, not bound to a receptor

active state

GTP bound to alpha subunit and the hormone is bound