Chapter 17 - Endocrine System
Terms
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- Endocrine
- derived from greek words "endo" and "crino", meaning to separate within
- Endocrine System
- body's communication organ system; composed of glands that secrete chemical signals into the circulatory system
- Hormones
-
secretory products of endocrine glands; means "to set into motion"; a chemical signal that
1)is produced in minute amounts by collections of cells
2)is secreted into the interstitial places
3)enters the circulatory system, where it is transported some distance, and
4)acts on specific tissues at another site in the body to influence the activity of those tissues in a specific fashion - Amplitude-modulated signals
- signals that impact target tissues mainly by increases or decreases in the conc. of hormones in the body fluid; most endocrine hormones are this
- Frequency-modulated signals
- signals that vary in frequency but not in amplitude; exert their effect based on frequency of stimulus; common among neuronal signals
- Neurohoromone
-
chemical signals that are secreted into the circulatory system by neurons;
function like hormones - Intercellular chemical signals
- allow one cell to communicate with other cells
- Autocrine chemical signals
- type of intercellular chemical signal released by cells and have a local effect on the same cell type from which the chemical signals are released
- Paracrine chemical signals
- type of intercellular chemical signal released by cells and affect other cell types locally without being transported in the blood
- Pheromones
- specialized chemical signals that are secreted into the environment and modify the behavior and the physiology of other individuals
- Biological half-life
- the length of time it takes for half a dose of a substance to be eliminated from the circulatory system
- Factors by which the half-life of hormones is shortened
-
1)Excretion
2)Metabolism
3)Active Transport
4)Conjugation - Factors by which the half-life of hormones is lengthened
-
1)bind reversibly with plasma proteins
2)some hormones are protected by their structure (i.e., carbohydrate complexes of glycoprotein hormones - Conjugation
- accomplished when cells in the liver attach water-soluble molecules to the hormone, usually sulfate or glucuronic acid; "mark" molecules for excretion by the kidney and liver at a greater rate
- Receptor site
- the portion of each protein or glycoprotein molecule where a chemical signal binds on a receptor molecule
- Specificity
- the tendency for each type of chemical signal to bind to a specific type of receptor site, and not to others
- Down-regulation
-
a phenomenon in which the number of receptors on a cell surface can rapidly decrease after exposure to certain chemical signals;
in general, tissues that exhibit this are adapted to respond to short-term increases in hormone conc. and tissues that respond to hormones maintained at constant levels normally do not exhibit this - Up-regulation
-
periodic increases in the sensitivity of some cells to certain hormones;
results from an increase in the rate of receptor molecule synthesis - Membrane-bound receptors
-
hormone molecule receptors that extend across the plasma membrane and have their receptor sites exposed to the outer surface of the plasma membrane;
initiates a response inside the cell - Intracellular receptors
- receptors in the cytoplasm or in the nucleus of the cell; usually interact with lipid-soluble hormones
- G-protein
- complex receptor proteins of the plasma membrane that produce intracellular response through the action of a second-messenger; consists of three subunits: alpha, beta, and gamma
- Intracellular mediators
- ions or molecules that either enter the cell, or are synthesized in the cell, and regulate enzyme activities inside of the cell
- Adenylate cyclase
- an enzyme activated by G proteins; converts ATP to cAMP
- Protein kinases
- enzymes that regulate the activity of other enzymes by attaching phosphates to them; activated by cAMP
- Phosphorylation
-
regulation of cellular activity by the attachment of phosphate ions;
increases or decreases the activity of the enzyme, depending on the specifc enzyme - Cyclic guanine monophosphate (cGMP)
-
an intracellular mediator molecule that is synthesized in response to a chemical signal binding with a membrane-bound receptor;
combine with specific enzymes in the cytoplasm of the cell and activates them, producing a response - Guanylate cyclase
- an enzyme located at the inner surface of the plasma membrane that converts GTP to cGMP and two phosphates
- Cascade effect
- an amplification system that facilitates rapid hormonal response within a cell; results when a few mediator molecules activate several enzymes and each of the activated enzymes in turn activates several other enzymes that produce the final response