L13 Intro to Endocrine Flashcards
What is the main function of the endocrine system?
Maintain the internal environment of the organism
When an endocrine gland releases a hormone, where does it release it to?
Directly into the bloodstream
What does it mean if a hormone has a “trophic” effect?
It regulates hormone secretion by another gland
Or it regulates the growth and integrity of the endocrine gland
What does it mean if a hormone is “pleiotropic?”
It means it has more than one effect once it binds to its target cell
What does it mean if a hormone has a “paracrine” effect?
It means that it targets cells right next to it
What does it mean if a hormone has an “autocrine” effect
It gets released and then acts back on the same cell that released it
What is an “intracrine” hormone?
One that regulates processes inside the cell that made it without ever being secreted
What is a neurocrine hormone?
Hormone that is released from a neuron
Can end up in synaptic cleft or in the bloodstream
What are the examples of “novel” endocrine glands he talked about?
Heart (epicardial fat)
Adipose tissue
Skeleetal muscle
What are the 3 classification systems of hormones?
Chemical structure
Signal transduction pathways
Solubility in plasma
What are the 3 classifications of chemical structure for hormone?
Peptide hormones
Amine hormones
Steroid hormones
How are peptide hormones produced?
Produced from a gene that is transcribed into mRNA
Normal way of making proteins duh
What are amine hormones derived from?
Tyrosine
What are steroid hormones derived from?
Cholesterol
The majority of hormones are (steroid/peptide/amine) hormones
Peptide
Thyroid hormones are (steroid/amine/peptide) hormones
Amine
Catecholamines are (steroid/peptide/amine) hormones
Amine
CatecholAMINE
Glycoproteins are a subsection of (peptide/steroid/amine) hormones
Peptide
What makes glycoproteins different from the rest of the peptide hormones?
They have a carbohydrate moiety
Peptide hormones and catecholamines are (hydrophilic/hydrophobic)
Hydrophilic
Travel easily- dissolved in the blood stream
Thyroid hormones and steroid hormones are (hydrophobic/hydrophilic)
Hydrophobic
How are hydrophobic hormones transported?
Bound to binding proteins
99% of a hydrophobic hormone is (free/bound to proteins) when it travels through the bloodstream
Bound to proteins
Less than 1% is free
Are protein-bound hormones active?
No
How do binding proteins affect the half-life of hormones?
Increases
What are the 4 benefits of hormone binding proteins?
- Provides a reserve that can replenish the free pool
- Keeps the hormone in an inactive state
- Increases hormone half-life
- Involved in hormone turnover
What is hormone turnover?
How much hormone is entering and leaving the bloodstream
How do the liver and kidney affect hormone turnover?
They degrade the hormone into a product that is water soluble and is easily excreted
(Done via glucuronidation and sulfate conjugation)
What regulates the secretion of a hormone
Rate of production
Feedback mechanisms
What regulates the delivery of a hormone to its target tissues?
Blood flow
Where are steroid hormones synthesized in the cell?
Cytosine
ER
Mitochondria
Are steroid hormones stored inside the cell once they are synthesized?
No, they are released as soon as they’re made
Where are amines synthesized?
Catecholamines- made enzymatically in the cytosol
T3 and T4- made in the follicular cell AND the colloid of the thyroid (intra and extracellular)
Are amine hormones stored once they are made?
Yes
T3 and T4: inside follicular cells
Catecholamines: in granules
Where are peptide hormones made inside the cell?
Ribosomes
ER
Golgi
Are peptide hormones stored once they are made?
Yes. In granules
What is the step by step process of the synthesis of peptide hormones?
- Gene is transcribed into mRNA
- mRNA in the ER binds amino acids into a peptide chain called a preprohormone (ex: preproinsulin)
- In the ER, the preprohormone is cleaved to a prohormone
- In the Golgi, the prohormone is cleaved to a hormone
- Hormone (and some “pro” fragments) are stored in secretory vesicles
- Hormone is secreted
What is meant by peripheral conversion?
Steroid and amine hormones are converted in the tissues to their much more active form
What is a prohormone with regard to steroid and amine hormones?
I thought that was just peptide hormones!
It is the original hormone that gets released and then peripherally converted into an active form
Ex: Thyroxine (T4) gets converted into Triiodothyronine (T3) to become active.
T4 is the prohormone
Vitamin D3 is released from the skin and converted by ________ into ______________
Converted by liver and kidney
1,25- dihydroxyvitamin D3 (active vitamin D)
Why is testosterone considered a prohormone?
Because it gets converted into more active forms: dihydrotestosterone (DHT) and Estradiol (E2)
Where is T4 converted into T3?
Most tissues
What is humoral regulation of hormone secretion?
Secretion of the hormone is based on the level of a substrate in the blood (aka “humor”)
Ex: calcium levels are low= PTH is released to raise calcium
What is neural regulation of hormone secretion?
The CNS tells the endocrine gland to secrete the hormone
Ex: Fight/flight response causes release of epinephrine
What is hormonal regulation of hormone secretion?
Hormones regulate the secretion of hormones
Ex: hypothalamic TRH stimulates pituitary to release TSH which stimulates the thyroid to secrete thyroid hormone (T4/T3)
Which is more common in hormone regulation: negative feedback or positive feedback?
Negative feedback
Hormone action inhibits further secretion of the hormone
What are the only 2 examples of positive feedback regulation?
Estrogen
Oxytocin
How do peptides and catecholamines (hydrophilic) act on their target cells?
They bind to a receptor on the cell surface
How do steroid and thyroid hormones act on their target cell?
They diffuse right through the lipid bilateral and bind to a nuclear receptor
What is the “threshold”
The hormone concentration required to achieve a response from a target cell
What is a “sensitivity”
The hormone concentration required to produce 50% of the maximum response from the target cell
What is a “maximal response”
The response from the target cell when it is saturated in the hormone
A decrease in maximal response is caused by?
Aka increasing the amount of hormone does not increase the max response
Decrease in target cells
Decreased signal transduction mechanisms and enzyme activity inside the cell
What is meant by a decrease in sensitivity?
More hormone is required to produce 50% of the max response
Which direction does the curve shift when sensitivity decreases?
Right —->
What causes a decrease in sensitivity?
Decrease in receptor number
Decreased affinity for the hormone
What causes a hormone to have a decreased maximal response and a decreased sensitivity?
Hormone levels are too high and the body is trying to reduce the physiologic response to the hormone
(Ex: type II diabetes)
What is synergism?
Hormones have low effect alone, but when combined, the overall effect is greater than the sum of their separate effects
Ex: growth spurts in teens
What is permissiveness?
A hormone cannot exert its full effect without another hormone being present.
Hormone X must be present to exert the full effect of hormone Y
Ex: cortisol must be present for catecholamines to affect blood pressure
What is antagonism?
One hormone has the opposite effect of another hormone
What is autologous up or downregulation?
A hormone regulates the number/affinity of its own receptor
What is heterologous up or down regulation?
A hormone regulates the number/affinity of ANOTHER hormone’s receptor
