Hormone overview Flashcards
1
Q
signaling mechanisms
A
- nervous (most important system for signaling)
- endocrine (second most important system for signaling)
- neuroendocrine
- paracrine (uses a hormone or signaling mechanism for cel nearby)
- autocrine (substance acts on cell that secreted it)
2
Q
Nervous vs. endocrine signaling
A
- in NS, you have to have contact at synapse and signaling is through NT
- in endo, target is at distance and signal is mediated through molecule released into blood
3
Q
hormones
A
- signaling molecule (chemical) released by signaling cell that stimulates some target (usually glandular) and the target exists at a distance
- can be: steroids, derivatives of tyrosine (i.e. thyroxine aka T4 - two tyrosines together with attached iodines, epinephrine), or proteins or peptides (less than 100 = peptide, over 100 = protein; peptide hormone = oxytocin and ADH)
4
Q
steroid hormones
A
- i.e. progesteron
- all steroids have same 4 carbon ring structure
- structure makes it nonpolar and easy to move through cell membranes
5
Q
Production and release of hormones
A
- protein hormones formed in rough endo reticulum –> released via exocytosis
- steroid hormones not really stored, made on demand, cholesterol is stored and can be converted quickly. Once hormone appears in cytoplasm, diffuses into extracellular fluid
- tyrosine derivative hormones are also not stored. Once thyroid hormones appear in cytoplasm, they diffuse out. Epi and Norepi are different in that they are stored until secretion
6
Q
Control of hormone secretion
A
- most often controlled by negative feedback
- ***It is not the amount secreted, but the activity of the hormone that matters
7
Q
How do hormones cause an effect in the cell
A
- hormone cascades amplify signal
- ACTS THROUGH A RECEPTOR
- locations of receptors differ: cell membrane for proteins and catcholamins, within cell in cytoplasm or nucleus for steroid and thyroid hormones
- receptors are usually specific for a single hormone
- effects are direct (intracellular enzymes), or indirect (second messenger systems)
8
Q
example of cAMP signaling
A
- renal tubule
- cAMP phosphorylates other molecules and enzymes within the tubular cell
9
Q
hormone actions - gene effects
A
- steroid and thyroid hormones
- receptor in cytoplasm or nucleus
- formation of protein complex acting as a transcription factor –> alters production of RNA
- once bound, thyroid hormone is active for up to weeks
10
Q
transcription factor
A
multi subunit polymer of protein subunits
11
Q
signaling by second messenger systems
A
- MAJOR SYSTEM –> MOST PREVALENT
- based on adenyl cyclase activity forming cAMP
- specific actions of cAMP depend on specific cell chemistry
- in general, it phosphorylates things
12
Q
calcium/calmodulin role in signaling
A
- calcium enters with permeability change
- calmodulin enzyme is activated
- intracellular effects vary
13
Q
Phospholipase C
A
- intracellular surface of receptor
- membrane components split
- products lead to various cascades
- inositol triphosphate causes Ca release
- Diacyclglycerol activates protein kinase C
- arachidonic acid is prostaglandin precursor
14
Q
measuring hormones
A
- hormones are maintained at very low levels which can make it difficult to measure - usually in picograms
- small amount makes it difficult
- competitive binding models with radioactive markers used (radioimmuno assay)
15
Q
clearance of hormones
A
- hormone levels effected by secretion and clearance - every molecule in our body is affected by rate of clearance
- metabolic clearance = ml blood cleared/min –> to calculate, (removal from blood/hormone in plasma)
- infusion of hormone at steady rate to find where levels stabilize
- Hormones can be cleared by: metabolic destruction, binding with tissues, excretion by liver, excretion in urine
