3. Principles of Hormone Action Flashcards
what are HORMONES
- one type of FIRST (or PRIMARY) MESSENGER
- molecules that have an effect on specific organs
- called TARGET ORGANS
- only cells with SPECIFIC RECEPTORS for the hormone will respond to the
hormone - called TARGET CELLS
- organs, tissues or cells lacking the specific receptors do not respond to
the stimulating effects
what are the 4 CLASSIFICATIONS of HORMONES
- Lipid-Derived Hormones (Lipid-soluble)
- Amino acid derivative hormones
- Peptide hormones (hydrophilic)
- Chemical messengers derived from fatty acids (eicosanoids)
what is the primary class of LIPID HORMONES
STEROID HORMONES
most LIPID HORMONES are DERIVED from…
CHOLESTEROL
- thus have a similar structure to it
examples of LIPID HORMONES
- SEX-HORMONES
(androgens, estrogens and progesterone) - Hormones produced in ADRENAL GLANDS
(Glucocorticoids and mineralocorticoids)
FUNCTIONS of LIPID HORMONES include (3):
- WATER BALANCE
- SEXUAL DEVELOPMENT
- STRESS RESPONSE
AMINO ACID DERIVATIVE HORMONES are SMALL molecules commonly DERIVED from.. (2)
TYROSINE &
TRYPTOPHAN
examples of AMINO ACID DERIVATIVE HORMONES (2)
- THYROID hormone (lipid-soluble)
- CATECHOLAMINES (water-soluble)
eg noradrenalin, adrenalin
FUNCTIONS of AMINO ACID DERIVATIVE HORMONES include:
- Thyroid hormone regulates the development of organs
and metabolism. - Noradrenaline and adrenaline (catecholamines) increase
heart rate, dilate blood vessels and cause the release of glucose during times of stress
PEPTIDE HORMONES (hydrophilic) are…
CHAINS OF AMINO ACIDS (short or long)
most HORMONES are..
PEPTIDE HORMONES
examples of PEPTIDE HORMONES
FSH (small)
INSULIN (large)
PROLACTIN
GROWTH HORMONE
VASOPRESSIN
(pituitary)
ANP (which is produced by the heart -regulates homeostasis of the circulatory
system; released in response to high blood pressure and dilation of the atrium.)
CHEMICAL MESENGERS derived from FATTY ACIDS
- EICOSANOIDS
are synthesised from..
ARACHIDONIC ACID
- 20-CARBON AMINO ACID
CHEMICAL MESENGERS derived from FATTY ACIDS
- EICOSANOIDS…
- DEGRADE very EASILY
- do NOT GO FAR from production site
unique characteristic of CHEMICAL MESENGERS derived from FATTY ACIDS
- EICOSANOIDS
they are produced and secreted by
NEARLY EVERY CELL in the body instead of just one gland.
example of a CHEMICAL MESENGERS derived from FATTY ACIDS
- EICOSANOIDS
PROSTAGLANDIN
- Prostaglandins have a wide variety of functions ranging from
uterine contractions to
bronchodilation, inflammation and fever
(Aspirin acts on prostaglandins to reduce pain and fever)
various roles of EICOSANOIDS include
inflammation,
blood pressure
blood clotting
Endocrine, paracrine and autocrine
-paracrine signalling is
when NEIGHBOURING CELLS signal to each other
- Autocrine signalling is
when a cell sends signals to ITSELF - endocrine signalling uses the CIRCULATORY SYSTEM to transport ligands
Binding of a ligand to a receptor changes…
changes its SHAPE or ACTIVITY
- allowing it to transmit a SIGNAL or directly
produce a CHANGE inside of the cell
RECEPTORS can be divided into 2 categories:
- INTRACELLULAR RECEPTORS
(inside of the cell - in the cytoplasm or
nucleus) - CELL SURFACE RECEPTORS
(embedded in the plasma membrane)
What type of molecules reach INTRACELLULAR RECEPTORS
HYDROPHOBIC signalling molecules (ligands)
- DIFFUSE through plasma membrane
RECEPTORS function as..
ligand-dependent TRANSCRIPTION FACTORS
how do RECEPTORS function as ligand-dependent TRANSCRIPTION FACTORS?
hormone-receptor complex binds to…
- the hormone-receptor complex BINDS to PROMOTER REGIONS of responsive GENES and STIMULATE/INHIBIT TRANSCRIPTION
- SELECTIVELY affecting TRANSCRIPTION of genes
- CONCENTRATIONS of respective PROTEINS ALTERED
-CHANGE IN PHENOTYPE OF CELL
3 main components of CELL-SURFACE RECEPTORS
- An external ligand binding domain- extracellular domain
- A hydrophobic membrane spanning region
- Intracellular domain inside the cell
3 types of CELL-SURFACE RECEPTORS
- G PROTEIN-LINKED
- ENZYME-LINKED
- ION CHANNEL-LINKED
What happens when a ligand binds to a G-PROTEIN COUPLED RECEPTOR
- G-PROTEIN IS ACTIVATED (membrane protein)
eg used by Catecholamines
what does an INACTIVE G-PROTEIN have on its ALPHA subunit
GDP
What happens when a G-Protein is activated
- ALPHA SUBUNIT swaps GDP for GTP
ALPHA subunit dissociates from the BETA and GAMMA subunits and triggers a cellular response
What does the GTP-BOUND ALPHA SUBUNIT do after dissociating from other G-protein subunits
- BINDS to and ACTIVATES ADENYLATE CYCLASE
- activated adenylate cyclase catalyses CONVERSION of ATP to CAMP and PYROPHOSPHATE
- cAMP ACTIVATES PROTEIN KINASE A (secondary messenger) which PHOSPHORYLATES and activates other proteins and triggers further responses
how does the alpha-subunit return to its original place on inactivated G-protein
GTP HYDROLYSED to GDP
- signalling molecule comes off the receptor
Alpha subunit comes back together with the receptor and beta and gamma subunits
What are ENZYME-LINKED RECEPTORS
Cell-surface receptors with intracellular
domains that are associated with an
ENZYME
- Normally have large extracellular and
intracellular domains - When a ligand binds to the extracellular
domain, a signal is transferred that
ACTIVATES THE ENZYME component of the
receptor which leads to a response
eg. Insulin binding to tyrosine-kinase receptor
what happens when a ligand binds to an ION-CHANNEL LINKED RECEPTOR
CONFORMATIONAL CHANGE in the STRUCTURE
- allows IONS to PASS THROUGH
eg. neurons
what happens when Ions pass through ION CHANNEL- LINKED RECEPTOR
Change the ACTIVTY of ION-BINDING ENZYMES and VOLTAGE-SENSITIVE CHANNELS
- to produce a response
multiple hormones can…
utilize the same second messenger system
a single hormone can…
utilize more than one second messenger system
what do we get in DOWN-REGULATION of RECEPTORS
LINGAND-INDUCED DESENSITIZATION
or INTERNALIZATION of receptor
How do you get DOWN-REGULATION of RECEPTORS
Receptors CHRONICALLY EXPOSED to an EXCESSIVE AMOUNT of a LIGAND
(endogenous mediators or from exogenous drugs)
what is UP-REGULATION of RECEPTORS
SUPER-SENSITIZED CELLS
- cell makes extra receptors on the surface (so any small amount of that ligand can bind)
how do you get UP-REGULATION of RECEPTORS
- REPEATED EXPOSURE to an
ANTAGONISTIC DRUG
or - PROLONGED ABSENCE of the
LIGAND
What do RECEPTOR AGONISTS cause
DOWN-REGULATION of their respective receptor
What do RECEPTOR ANTAGONISTS cause
UP-REGULATION of their respective receptor
may also damage receptors faster than they upregulate
(internalization of receptors due to antagonism)
How are hormones secreted (pattern)
Hormone secretion often follows a
RHYTHM or is PULSATILE
secreted in a burst-like or episodic
manner rather than constantly.
how is melatonin secretion (pattern)
Melatonin secretion is related to the
length of the NIGHT
Also melatonin profiles show a SEASONAL pattern (increased production in winter)
example of DIRECT and INDIRECT EFFECTS of hormones
eg growth hormone
DIRECT EFFECTS:
growth hormone binds to GH Receptors on Fat Cells, stimulating break down of triglycerides
INDIRECT EFFECTS:
Insulin-like Growth Factor-I (IGF-I) secreted in response to GH. The majority of the growth promoting effects of
GH are actually due to IGF-I acting on its
target cells.
