Endocrine System Overview Flashcards
endocrine system
glands and tissues which secrete hormones
endocrine glands
specialized groups of cells that release hormones internally within the body
where do endocrine glands typically release hormones?
into interstitial space/ extracellular fluid for entry into the bloodstream
what are hormones?
chemical messengers
what do hormones do?
signal information between cells/organs to affect the actions and functions of distant organ systems
define molecular endocrinology
study of the molecular basis for the synthesis, actions and regulations of hormones and their receptors
how do hormones act?
are chemicals that act as signaling molecules to traffic specific info from one cell to another
hormones travel through ____ such as the ____
a medium, extracellular fluid or the bloodstream
a single hormone might…
regulate multiple physiological processes ( and have distinct effects in different target cells)
physiological processes might be regulated by _____ hormones
multiple different
general actions of hormones
- fetal development
- cell growth (and cancer)
- digestion
- metabolism of carbs, lipids, proteins/amino acids, nucleic acids
- ion and water balance
- renal function
- cardiovascular function and circulatory system
- respiration
- skeletal function
- reproductive function
- immune system function
- CNS function
- stress responses
what does dysfunction or dysregulation of hormone levels cause?
pathological chances like an endocrine disease or disorder
T/F: hormone levels in circulation must be tightly regulated
true
how is hormone regulation accomplished by?
- by controlling hormone production/release
- controlling ability of hormones to access target cells
- through hormone removal (degradation)
hormones can regulate…
their own production and release as well as that for other hormones
define juxtacrine
contact dependent signaling between neighboring cells
how does juxtacrine signaling work?
via gap junctions, or between a membrane ligand of one cell and cell surface receptor of adjacent cell
what is an example of juxtacrine signaling?
notch signaling
autocrine
ligand is released by the signaling cell, then acts on the same cell that produced it
paracrine
ligand is released by the signaling cell, then acts on a nearby cell
endocrine
ligand is transported by the circulatory system
what cells (distant, nearby, same) does endocrine act on?
distant cells
where do hormones secrete from? (15 places)
Pineal gland
Hypothalamus
Pituitary gland
Thyroid and parathyroid glands
Thymus
Adrenal
Pancreas
Ovaries/ Testis
Placenta (during pregnancy)
**Kidneys
**Heart
**GI tract
**Adipose
**Liver
**Bone
“_______” endocrine organs contain ______ that release hormones into EC space, where they eventually access circulating plasma
classic, ductless glandular structures
“_______” endocrine glands also secrete major hormones
non traditional
the endocrine system works in tandem with the ______, particularly via the ______ that is a ________
nervous system, hypothalamus, a primary link between the two systems
how does the nervous system communicate between cells?
via chemical messengers (ligands and receptors)
T/F: chemical messengers can be both NT’s and hormones
true, depends on where secreted and act on.
-> example is norepinephrine
what is the key difference between the endocrine and nervous sytem?
the NS uses electrical action potentials along neurons, and NTs across small distances
signaling in the nervous system
- signals are transmitted (electrically) much faster (response times in seconds)
- more specifically targeted
- generally shorter lived
signaling in endocrine system
- wider range of signal distribution
- tends to have higher affinity receptors (therefore can respond to lower concentrations of ligand)
- takes longer for signals to spread (min to hrs)
how do hormones act without entering circulation?
in autocrine or paracrine fashion
direct
endocrine glands innervated by nerves of NS
example of direct
nerves that innervate pancreas and cause release of hormones (eg insulin)
indirect
NS produces neurotransmitter or neurohormone that acts on cells of ES
cytokines
small proteins with cell signaling functions (similar to many peptide hormone functions)
cytokines have a _______ in the immune system
fundamental role
immune system
maintain homeostasis, prevent/fight infection, recognize own self vs pathology
cytokines are typically…
short lived, act locally
- autocrine, paracrine, juxtacrine signaling but NOT endocrine
a specific cytokine may often be ______
produced by multiple cell types
-> ES has more specific cell types produce specific hormones
cytokines are “______”
hormone like, they bind specific receptors eg MHC and toll-like receptors
MHC and toll-like receptors
have similar structure/functions to peptide hormone receptors
what are the three ways of cross talk btwn ES and IS?
- endocrine tissues are affected by immune modulators, such as cytokines
- autoimmune diseases that affect endocrine tissues
- the immune system is highly receptive to endocrine signals
endocrine tissues are affected by immune modulators such as cytokines, why?
Possibly because receptors are functionally similar – cytokine could interact with a receptor for a peptide hormone
-> E.g. immune cytokines can cause release of hormones such as ACTH, prolactin, GnRH if their receptors are present
how is the immune system highly receptive to endocrine signals?
many immune cells have receptor for hormones, so hormones can cause signaling effects within immune cells
-> Eg. Differential susceptibility to autoimmune diseases and infections between men and women – more prevalent in women
—> Influenced by sex hormones – differences in levels of estradiol and
androgens
classically hormones are named after…
the effect they cause
-> eg follicle stimulating hormones, growth hormone
problem with classically naming hormones?
A hormone may exert many effects, or different effects depending on cell types, or effects may depend on whether acutely or chronically elevated, etc
-> E.g. FSH has different effects on female and male ES
ways to classify hormones aside from their function:
- By where they’re produced/secreted (and in response to what stimuli)
- By their chemical structure
- By their solubility
- By their receptor location (cell surface vs. cytosolic/nuclear)
- By their receptor sub-type (Cell surface receptors vs Cytosolic or nuclear receptors)
- By whether they act as receptor agonists or receptor antagonists
- By key intracellular messengers (e.g., cAMP, cGMP, inositol trisphosphate (IP3), Ca2+) & effector mechanisms in their signal transducMon pathway
cell surface receptors
G-protein-coupled receptors, Receptor tyrosine kinases (growth factor receptors), Cytokine receptors, Guanylyl cyclase receptors
cytosolic or nuclear receptors
intracellular receptors
chemical structure
protein, peptide, amino acid derivative, monoamine, steroid, or fatty acid derivative
Hormone biological activity depends on
interactions with specific receptors – ligand
binding to specific receptor causes signal transduction responses (effector systems) in target
cell
What modifications might proteins and peptides undergo for full biological activity?
might be modified and/or dimerized or cleaved for full biological activity.
proteins & peptides: are encoded by
cellular genes; increased gene expression is often a key part of biosynthesis. regulation of gene expression is necessary
What processes are often required to generate biologically active mature forms of proteins and peptides?
Precursor processing, post-translational modification, assembly/dimerization/cleavage are often required for the generation of biologically active mature forms.
proteins & peptides: hydrophilic or hydrophobic?
hydrophilic
Where are proteins and peptides often stored in endocrine cells?
in secretory vesicles/granules in endocrine cells for later release.
What happens to proteins and peptides once they are released from secretory vesicles?
Once released from vesicles, proteins and peptides can be easily transported through circulation.
How do proteins and peptides act on target cells?
via cell surface receptors and cannot enter the cell.
What role do amino acid derivatives and monoamines play in biosynthesis?
are a key part of biosynthesis, involving the sequestering of precursors and increased activity of enzymes needed for hormone production through the modification of amino acid precursors.
What processes are often required to generate active mature forms of amino acid derivatives and monoamines?
Precursor processing, post-translational modification, and assembly are often required to generate active mature forms of these hormones.
Are monoamines hydrophilic or hydrophobic?
hydrophilic
are thyroid hormones hydrophilic or hydrophobic?
hydrophobic
How do monoamines, such as norepinephrine and epinephrine, act on target cells?
via cell surface receptors
How do thyroid hormones act on target cells?
nuclear receptors
What is the primary source from which steroids are derived?
cholesterol
What is a key step in the biosynthesis of steroids?
The translocation of cholesterol to mitochondria and the activation of enzymes needed for hormone production.
are steroids hydrophilic or hydrophobic?
hydrophobic
How do steroids pass through cellular membranes?
lipid membranes
Are steroids stored in secretory vesicles, and how are they synthesized?
no ; they are synthesized on demand.
What is often required for the circulation of steroids in the bloodstream?
blood binding proteins
How do steroids typically act on target cells, and what receptors do they engage?
Steroids typically act via nuclear receptors, although some can activate both cell surface and intracellular receptors.
-> ie. glucocorticoid and estrogen receptors can be present on both cell surfaces and within cells, and these receptors act in different ways.
What is the nature of fatty acid derivatives, and how are they synthesized?
are hydrophobic and synthesized on demand
Describe the half-life and range of action of fatty acid derivatives.
have a very short half-life and act in an autocrine or paracrine manner, not entering circulation or acting long-range throughout the body
Are fatty acid derivatives strictly hormones?
No, fatty acid derivatives are “hormone-like” but not strictly hormones.
What role do prostaglandins play in the body?
involved in mediating responses to injury and illness, controlling inflammation, blood flow, and other processes.
How do fatty acid derivatives, particularly prostaglandins, act on target cells?
cell surface receptors
receptor agonist
triggers the effector mechanisms and elicit a biological response
receptor antagonist
binds to the receptor but does not activate the effector mechanisms; blocks/dampens a biological response
example of receptor antagonist
by occupying the receptor/blocking access of an agonist
-> ligand or drug that fits in biochemical ‘pocket’ of receptor, but does not cause downstream effects
partial agonist-partial antagonist
limited ability to activate the effector mechanisms
- response less than half that caused by a full agonist
mixed agonist-antagonist
acts as agonist in some cases, antagonist in others
- depending on dose, cell type, receptor; what the downstream effect is
-> eg if it needs other components to cause the effect
- more pharmacological term - eg drugs that are designed to block specific receptors in some cases or in certian tissues
steroid hormone receptors
all act as transcription factors when activated
response element
specific sequence on DNA that TF binds to
additivity
effects of 2 or more hormones together is equivalent to the sum of their individual effects
- 1 + 1 = 2
- eg combined effect on increasing blood glucose levels of glucagon + epinephrine together
synergy
effects of 2 or more hormones together is greater than the sum of their individual effects
- 1 + 1 > 2
- eg combined effect on blood glucose of glucagon + epinephrine + cortisol together ( could be due to down stream effects, such as if one hormone increases the number of receptors for another)
hormone levels and actions must be tightly regulated, this is accomplished by…
- controlling hormone sythesis/precursor processing/release
- controlling ability of hormones to access target cells/receptors
- hormone metabolism
controlling hormone sythnesis/precursor processing/release
- natural important point of acute control for a hormone
- Synthesis (e.g., gene expression, precursor availability, enzyme activity)
- Processing (e.g., prohormone conversion/cleavage, modification or assembly)
- Secrection (controlled by signaling events triggered by exogenous regulators/2nd messengers)
controlling ability of hormones to access target cells/receptors
- Hormone transport (e.g., blood binding proteins)
- Changes to receptor expression or cellular localization
- Interations with other regulatory proteins/hormones (e.g., receptor antagonists)
hormone metabolism
- Conversions/structural changes that increase or decrease activity of hormone
- Degradation of ligand (and/or receptor) over time
negative feedback loops
response tends to return variable back to original levels (holding a set point to maintain homeostasis)
positive feedback loop
response changes further changes from a set point… amplifies change. specific threshold or separate input is needed to limit the positive feedback loop
tropic hormone
a hormone that cause the release of another hormone
hormones in plasma
either free form (=bio active form) or bound to other molecules, eg blood binding proteins
blood binding proteins affect…
the controlled release and stability of the pool of hormones
- increase hormone solubility (eg steroid hormones are hydrophobic - low solubility in aqueous solutions)
- provide reservoir of hormone (making hormone pool more stable - more uniform/disbituion, slowing hormone metabolism/breakdown)
interactions btwn hormones and their receptors depends on…
- number of receptors
- affinity of hormone for the receptor
- concentration of circulating hormone
regulation at the level of the receptors is also an important point of endocrine function control
- increasing or decreasing receptor synthesis
- internalization vs cell membrane localization of cell surface receptors
- desensitization of receptors (‘uncoupled’ from signal transduction pathway, due to such mechanisms as phosphorylation of the receptor)
dysregulation of hormone levels or dysfunction in cellular responses to hormones can…
cause pathological changes (ie endocrine dz or disorder)
