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How do hormones influence their target cells?
by chemically binding to specific protein receptors.
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Only the target cells for a given hormone have _____ that bind and _____ that hormone.
receptors
recognize
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Are receptors constantly synthesized and broken down?
yes
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What is down-regulation?
If a hormone is present in excess, the number of target-cell receptors may decrease.
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Why does down regulating occur?
If there is excess hormone, the number of receptors need to decrease to maintain homeostasis.
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Down-regulation makes a target cell ___ _____ to a hormone.
less sensitive
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What is up regulation?
When a hormone is deficient, the number of receptors may increase and makes a target cell more sensitive to a hormone.
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Most endocrine hormones are ____ ____, they pass from the secretory cells that make them into interstitial fluid and then into the blood.
circulating hormones
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____ ____ act locally on neighboring cells or on the same cell that secreted them without first entering the bloodstream.
local hormones
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What are local hormones that act on neighboring cells called?
paracrines
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What are local hormones that act on the same cell that secreted them called?
autocrines
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Are local hormones quickly or slowly inactivated?
quickly
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How long do circulating hormones linger in the blood and exert their effects?
a few minutes or sometimes a few hours
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How are circulating hormones inactivated?
by the liver and excreted by the kidneys
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What are the 2 classes hormones can be divided into chemically?
those that are soluable in lipids and those soluable in water.
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What are the 3 lipid soluble hormones?
1. steroid hormones
2. thyroid hormones
3. nitric oxide
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These hormones are derived from cholesterol. They are unique due to the presence of different chemical groups attached at various sites on the 4 rings at the core of its structure. These differences allow for a lg diversity of functions.
steriod hormones
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These 2 hormones are synthesized by attaching iodine to the amino acid tyrosine. The benzene ring of tyrosine plus the attached iodines make these hormones very lipid soluble.
thyroid hormones (T3 & T4)
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This hormone is both a hormone and neurotransmitter.
Nitric oxide (NO)
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What is nitric oxide (NO) synthesis catalyzed by?
the enzyme nitric oxide synthase
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What are the water soluble hormones?
(3)
1. amine hormones
2. peptide and protein hormones
3. eicosanoid hormones
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How are amine hormones synthesized?
by decarboxylating (removing a molecule of CO2) and otherwise modifying certain amino acids
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Why are amine hormones called amines?
because they retain an amino group (--NH3+).
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What are the 3 catecholamines?
epinephrine
norepinephrine
dopamine
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How are the catecholamines synthesized?
by modifying the amino acid tyrosine
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How is histamine synthesized?
From the amino acid histidine by mas cells and platelets.
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What are serotomin and melatonin derived from?
tryptophan
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What hormones are amino acid polymers?
peptide hormones and protein hormones
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The smaller peptide hormones consist of chains of ___ to ___ amino acids.
3-49
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The larger protein hormones include __ to ___ amino acids.
50-200
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Name examples of peptide hormones
antidiuretic hormone and oxytocin
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name an example of protein hormones
human growth hormone and insulin
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Why are several proteing hormones like thyroid-stimulating hormone considered glycoprotein hormones?
Because they have attached carbohydrate groups
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What hormones are derived from arachidonic acid? (a 20 carbon fatty acid)
eicosanoid hormones
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What are the 2 major types of eicosanoids?
prostaglandins and leukotrienes
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What hormones are important local hormones, but may also act as circulating hormones?
eicosanoids
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What type of hormones are aldosterone, cortisol, and androgens and where are they located?
steroid hormones located in the adrenal cortex
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What type of hormone is calcitriol and where is it located?
Steroid hormone located in the kidneys
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What type of hormone is testosterone and where is it located?
Steroid hormone located in the testes.
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What type of hormone are estrogens and progesterone and where are they located?
Steroid hormones located in the ovaries.
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What type of hormones are the T3 (triiodothyronine) and T4 (throxine) and where are they located?
Thyroid hormones located in the thyroid.
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What type of hormone is nitric oxide (NO) and where is it located?
Gas located in the endothelial cells lining blood vessels.
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What type of hormones are epinephrine and norepinephrine and where are they located?
Amines located in the adrenal medulla
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What type of hormone is melatonin and where is it located?
amines located in the pineal gland.
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What type of hormone is histamine and where is it located?
Amines located in the mast cells in connective tissues.
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What type of hormone is serotonin and where is it located?
Amines located in the platelets in blood.
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What type of hormones are all hypothalamic releasing and inhibiting hormones and where are they located?
They are peptides and proteins and they are located in the hypothalamus.
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What type of hormones are oxytocin, antidiuretic hormone and where are they located?
Peptides and proteins located int he posterior pituitary
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What type of hormones are HGH, thyroid-stimulating hormone, adrenocorticotropic hormone, follicle-stimulating hormone, luteinizing hormone, prolactin, melanocyte-stimulating hormone and where are they located?
Peptides and proteins located in the anterior pituitary.
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What type of hormones are insulin, glucagon, somatostatin, pancreatic polypeptide and where are they located?
peptides and proteins located in the pancreas
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What type of hormone is the parathyroid hormone and where is it located?
Peptide and protein located in the parathyroid glands.
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What type of hormone is calcitronin and where is it located?
peptide/protein located in the thyroid gland (parafollicular cells)
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What type of hormones are gastrin, secretin, cholecystokinin, & GIP (glucose-dependent insulinotropic peptide) and where are they located?
peptide/protein located in the stomach and small intestine (enteroendocrine cells)
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What type of hormone is erythropoietin and where is it located?
peptide/protein located in the kidneys
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What type of hormone is leptin and where is it located?
peptide/protein located in the adipose tissue
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What type of hormones are prostaglandins and leukotrienes and where are they located?
eicosanoids located in all cells except red blood cells.
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How are most water soluble hormone molecules circulated?
In the watery blood plasma in a "free" form (not attached to other molecules)
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How are most lipid soluble hormone molecules circulated?
They are bound to transport proteins
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What are the 3 functions of the transport proteins?
1. They make lipid-soluble hormones temporarily water soluble, thus increasing their solubility in blood
2. They retard passage of small hormone molecules thru the filtering mechanism in the kidneys, thus slowing the rate of hormone loss in the urine.
3. They provide a ready reserve of hormone, already present in the bloodstream.
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How are transport proteins synthesized?
By cells in the liver
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.1-10% of the molecules of a lipid soluble hormone are not bound to a transport protein. What is this called?
free fraction
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What is the process of the free fraction?
1. diffuses out of capillaries
2. binds to receptors
3. triggers responses
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How is the free fraction replinished?
As free hormone molecules leave the blood and bind to their receptors, transport proteins release new ones.
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Why is insulin not a good oral medication?
because digestive enzymes destroy them by breaking their peptide bonds
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