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endo system consists of:
"ductless" endo glands scattered thru out body
target cells have:
what are hormones imp for?
- receptors for binding c/ specific hormone
- regulating or directing particular function
endo system regulates activities that require _____ rather than _____.
where do endo glands act in relation to where they are secreted?
located a long distance from the endocrine gland
how do cells most commonly communicate with one another?
indirectly thru extracellular chemical messengers or signal molecules
4 types of chemical messengers or signal molecules?
rapidly inactivated, diffuses to local cell area (ex histamine)
describe neurotransmitter secretion:
short term chemical messengers in response to electrical activity
describe hormone secretion:
Long range chemical messengers travel via blood to specific target cell
Endocrine hormone molecules are secreted directly into:
the bloodstream, typically into fenestrated capillaries
describe neurohormone secretion:
neurohormone goes into the blood and acts on a distant target cell (ex vasopressin (ADH))
signal transduction functions like a:
occurs when an:
- extracellular signaling molecule activates a receptor
what are protein kinases?
enzymes that transfer a phosphate group from ATP to a particular intracellular protein
what does this phosphorylation do?
alters protein shape and function and it becomes “activated”
Protein kinase is activated on binding of the signal molecule to the surface receptor in one of two ways:
- The Tyrosine Kinase Pathway
- The Second Messenger Pathway
describe how receptor becomes activated in the tyrosine kinase pathway:
- the simplest of the 2 pathways
- the receptor itself functions as an enzyme aka " receptor enzyme"
- An enzyme site on the cytoplasmic side of a receptor enzyme is activated when an extracellular messenger binds to the side facing outside the cell
- The activated receptor bound enzyme ultimately leads to the cellular response
what occurs upon activation in the tyrosine kinase pathway
- 2 extracellular messengers bind with2 receptors & receptors pair, activating receptor's protein kinase site
- protein kinase sire self-phosphorylates receptors tyrosines
- inactive designated protein binds to receptor, which phos's it- activating it
- active designated protein brings about desired response
Most extracellular chemical messengers activate second messenger pathways via:
describe what occurs upon binding and activation of the G protein:
- -Activated G protein serves as a membrane bound intermediary that shuttles along the membrane to alter the activity of a nearby membrane protein called the effector protein
- -Once altered, the effector protein leads to an increased concentration of an intracellular messenger, known as the second messenger
what does the second messenger do?
- •Second messenger via cascade of reactions activates designated proteins which accomplish the cellular response dictated by the first messenger
- •Most commonly, the second messenger activates an intracellular protein kinase, which leads to Phosphorylation and thereby altered function of designated proteins
what are G proteins?
- also known as guanosine nucleotide-binding proteins,
- are a family of proteins involved in transmitting signals from a variety of different stimuli outside a cell into the inside of the cell
what do G proteins do?
- •G protein-coupled receptor and G proteins working together, transmit signals from many hormones, neurotransmitters, and other signaling factors
- •G proteins regulate metabolic enzymes, ion channels, transporter, and other parts of the cell machinery, controlling transcription, motility, contractility, and secretion, which in turn regulate diverse system functions
About half of all drugs prescribed today act on:
G protein coupled receptors
- Drugs used to
- –Reduce high blood pressure
- –Treat congestive heart failure
- –Suppress stomach acid
- –Open airways in asthmatics
- –Ease symptoms of enlarged prostate
- –Block histamine induced allergic responses–Relieve pain
- –Treat hormone dependent cancers
The effects of protein kinases in the tyrosine kinase and second messenger signal transduction pathways are reversed by:
- protein phosphatases
- (signal transduction reversal)
describe activation of protein phosphatases:
- most are continuously active in cells
- Continual phosphate group removal of designated proteins occur
First messenger once released from the target cell can be:
- –Degraded by the liver and/or excreted in the urine
- –By receptor mediated endocytosis (ex insulin)
molecules that function as hormones must exhibit 2 basic characteristics:
- 1.Must be sufficiently complex to convey regulatory information to their target cells
- 2.Must be adequately stable to resist destruction before reaching their target cells
what are 3 chemical classes that meet the "molecules functioning as hormones" requirements?
- 1. Peptides and proteins
- -Glycoproteins (most abundant chemical category)
- 2. Amino acid derivatives
- -Catecholamines (tyrosine derivative)
- -Thyroid hormones (iodinated tyrosine derivative)
- -Melatonin (indole-amines)
- 3. Steroids
- -Sex steroids (cholesterol derivative)
- -Corticosteroids (cholesterol derivative)
hormones can also be categorized based on:
- Lipophilic (nonpolar)= fat-soluble
- Hydrophilic (polar)= water soluble
which hormones are lipophilic?
where do they bind?
what do they do?
- –Steroid hormones and thyroid hormones
- –Bind to intracellular receptors
- –Ultimately, regulate gene expression to produce desired effect
which hormones are hydrophilic?
where do they bind?
what do they do?
- –All other hormones
- –Bind to extracellular receptors
- –Ultimately, alters the activity of preexisting intracellular proteins, usually enzymes, to produce desired effect
how are hydrophilic hormones processed?
- 1.Large preprohormones, are synthesized by ribosome's on the RER
- 2.Preprohormones are pruned to active hormones via ER/GA
- 3.Golgi finishes off hormones into secretory vesicles (stored in cytoplasm)
- 4.On stimulation, the secretory vesicles undergo exocytosis
how are lipophilic hormones processed?
- 1.Cholesterol is the precursor for all steroid hormones
- 2.Unlike peptide hormones, they are not stored. Once formed, they immediately diffuse to enter the blood.
- 3.Accordingly, the rate of steroid hormone secretion is controlled entirely by the rate of hormone synthesis
lipophilic hormones include:
- –Steroid hormones (derived from cholesterol)
- –Thyroid hormones (tyrosine + iodine)
- –As well as the retinoids, or vitamin A
Lipophilic hormones circulate in blood bound to:
pass thru the cell membrane and bind to:
hormone-receptor complex binds to:
what do they do?
- transport proteins
- an intracellular receptor, either in the cytoplasm or the nucleus
- hormone response elements in DNA
- regulate gene expression
Hydrophilic hormones include:
hormones bind to:
what do they initiate:
- the peptide, protein and catecholamine hormone (too large or polar to cross cell membrane)
- extracellular receptors
- signal transduction pathways (The tyrosine kinase pathway & the second messenger pathway)
•There are 2 major second messenger pathways (both G protein type) that use the following as their second messenger:
- 1.Cyclic adenosine monophosphate