(LE 3) Endocrine Glands Flashcards
What types of chemical messengers does the endocrine system use?
Hormones: secreted by endocrine glands. travel to specific cell receptors
Neurohormones: secreted by specialized neurons. affect the metabolism of targets (e.g. epi and norepi)
What are amine hormones?
derived from tyrosine or tryptophan
e.g. Norepi, epi, thyroxine, melatonin
What are peptide hormones?
polypeptide and protein hormones are chains of amino acids
(e.g. ADH, GH, insulin, glucagon, oxytocin, ACTH, PTH)
glycoproteins: LH, FSH, TSH
What are steroid hormones?
Derived from cholesterol
e.g. testosterone, estradiol, progesterone, cortisol
Compare and contrast Endocrine system and nervous system physiology
- Both use chemical messengers with specific target receptors
- hormones transport in blood with diversity of effects
- some chemicals are used as hormones and NTs
What is permissive effect?
if a hormone enhances responsiveness of a target organ to 2nd hormone
What is physiological range?
Hormone’s normal concentration in the body
What is pharmacological dose in hormones?
abnormally high concentrations of hormones. Can have adverse effects if used chronically
What determines whether or not a cell will respond to the presence of the hormone?
- presence of specific receptors
- hormone concentration
- receptor density
- receptor sensitivity
What is priming effect?
upregulation; occurs when hormone induces more of its own receptors in target cells.
- results in greater response in target cell
What is desensitization?
downregulation; occurs after long exposure to high levels of hormone.
- produces lesser response
What is pulsatile secretion?
hormones secreted in spurts rather than continuously to prevent desensitization
What is low capacity when talking about hormone receptors?
possibility of saturating receptors with hormone molecules because of the limited number of receptors per target cell
What is genomic action?
target is nucleus where they affect transcription. effects take at least 30 mins
What is nongenomic action?
Do not cause gene expression/make protein. act through 2nd messengers; effects are quick
Describe the mechanism of steroid hormone action
- Steroid hormone travels in blood attached to carrier protein to target cell
- Hormone enters cell and binds to ligand-binding site of nuclear hormone receptors where they function as transcription factors
- DNA-binding domain of Nuclear hormone receptor bind to the Hormone-response element of the target gene. Each HRE contains two half-sites where receptors bind to and requires two of them.
- When two receptors bind to HRE, they undergo dimerization to initiate transcription of target gene
How do thyroid hormones act on its target cell?
T4 (Thyroxine) converted to T3 (Triiodothyronine) in the target cell. T3 hormone-receptor complex binds to DNA sequence on one half site of HRE. Other half site binds to 9-cis-retinoic acid. They form heterodimer and stimulate genetic transcription
Describe Adenylate cyclase pathway
- Hormone binds to receptor. G-protein unit dissociates
- G-protein binds to and activates adenylate cyclase to convert ATP to cAMP
- cAMP attaches to inhibitory subunit of protein kinase
- Inhibitory subunit dissociates activating protein kinase to phosphorylate enzymes to produce hormone’s effects
- cAMP inactivated by phosphodiesterase
Describe phospholipase-C pathway
- Hormone binds to surface receptor and activates G-protein to activate phospholipase C
- Phospholipase C splits membrane phospholipid into 2nd messengers IP3 and DAG
- IP3 diffuses through cytoplasm to ER. Ca2+ channels open
- Ca2+ diffuses into cytoplasm and binds to and activates calmodulin
- Ca2+ Calmodulin activates protein kinases to phosphorylate enzymes to produce hormone’s effect
Describe how Epinephrine can act via two second messenger systems. What is the effect of each pathway?
can have beta-adrenergic effect effect when cAMP is used or can have alpha-adrenergic effect when calmodulin is used. both allow for release of free glucose
Describe how insulin uses tyrosine kinase second messenger system to uptake glucose from the bloodstream
- insulin binds to receptor, tyrosine kinase
- Two halves dimerize
- receptors phosphorylated. tyrosine kinase now active
- tyrosine kinase phosphorylates signaling molecules causing cascade of effects leading to glucose uptake
