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Endocrine System
What are the 4 principles that cells communicate with each other?
Cells communicate with each other through (1) gap Junctions, which join single-unit smooth
muscle, cardiac muscle, epithelial and other cells to each other. They let cells pass
nutrients, electrolytes, and signaling molecules directly from the cytoplasm of one cell to the
cytoplasm of the NXT thru pores in their plasma membrane.
(2) Neurotransmitters help cells communicate with ea. other by letting go neurons, the
neurons spread across a narrow synaptic cleft, & bind to receptors on the surface of the
next cells.
(3) Paracrine are sometime called local hormones, they are secreted by one cell and
spread to other cells close by in the same tissue, & stimulate their physiology.
(4) Hormones are chemical messengers that secrete cells into the blood stream.
Vocab:
1. Endocrine sys: compromised by glands, tissues, & cells that secrete hormones
2. Endocrinology: study of the treatment / diagnosis of its disorder
What are the differences b/w the endocrine and exocrine glands?
1) Exocrine Glands
a) Secrete their products thru DUCTS onto an epithelial surface like the skin or the mucosa
of the digestive tract.
b) they have EXTRACELLULAR EFFECTS such as digestion of food
2) Endocrine Glands
a) DUCTLESS release their secretion into the BLOODSTREAM
b) INTRACELLULAR EFFECTS- change cell metabolism
What are the differences b/w nervous and endocrine system?
What are the functions of hormones?
, Hormones help regulate the chemical structure/ volume of its internal environment
(interstitial fluid), metabolism and energy balance, contraction of smooth muscle and
cardiac muscle fibers.
Glandular secretions and some immune system activities.
Controls growth/development
Regulate operation of reproductive systems
Helps establish circadian (Sleep) rhythms
Why is the is the target-cell concept essential for understanding hormone function?
Only target cells and organs respond to certain hormones that are sent thru the blood
stream b/c they have receptors that will bind to it. W/o these receptors the hormones will
not bind, and no effect will be made to the body.
What is down-regulation?
When a hormone is present in excess the # of target- cell- receptors may decrease.
What is up-regulation?
When a hormone is lacking the # of receptors may increase. This makes the target cell
more Sensitive.
What are the hormone receptors?
Protein or glycoprotein molecules (on plasma membrane, in the cytoplasm, or nucleus)
Act like switches turning the metabolic pathways when hormones bind to them
Receptor- hormone interactions show specificity & saturation
Specific receptors for ea. Hormone
Saturated when all receptor molecules are taken by a hormone molecule
2
,Signal Amplification
Hormones are
extremely potent
chemicals.
One hormone
molecule can cause
the synthesis of many
enzyme molecules.
Small stimulus=large
effects
Circulating
concentrations are
very low (circulating
hormones go
everywhere the blood
goes)
Circulating hormones are carried through the bloodstream to act on distant target cells.
Paracrine act on neighboring cells, and autocrine act on the same cells that produced them.
How does signal amplification work?
Peptides and catecholamines (Epinephrine and norepinephrine; secreted by the adrenal
medulla) are hydrophilic (Water loving) & cnt penetrate a target cell
- Binds to receptors on the surface of the cell, which activates a 2nd- messenger system.
- Best known 2nd messenger system = Cyclic adenosine monophosphate (cAMP)
- cAMP leads to the activation of enzymes
- SOMATOSTAIN inhibits(prevents) cAMP synthesis.
- 2nd messenger systems don’t stay in the cells for long. cAMP is broken down by
the enzyme phosphodiesterase, the hormonal effect is short lived
3
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