Lecture 16 - Hormones Flashcards
Endocrine system
Regulates other organ systems using chemical messengers called hormones
Primary endocrine organs
Secrete hormones as their main functions or only function
Examples: pituitary gland, thyroid gland, adrenal gland, pineal gland
Secondary endocrine organs
Secrete hormones in addition to carrying out their own primary functions
Examples: heart, thymus, digestive tract, kidneys, gonads
What is a hormone and what are their 3 criteria?
Chemical messenger molecule that travels through the blood to reach its target organ(s)
- Be produced (synthesized) by one cell
- Bind to and trigger activation of protein receptors located on or in another cell
- Travel in the circulatory system to reach its target cell
3 classes of hormones
Class 1: amino acid derivative
Class 2: peptide hormone
Class 3: lipid derivative
How is epinephrine synthesized? What class?
Modification of amino acids - phenylalanine and tyrosine
Occurs in the adrenal medulla of the adrenal gland using chromaffin cells
Class 1
How is epinephrine stored and when are they released?
Stored in vesicles that are released when intracellular calcium levels rise
How are peptide hormones synthesized? What class?
Synthesized by ribosomes and RER and then activated through enzymatic cleavage
Peptide hormones are gene products synthesized with extra amino acid sequences - preprohormone
Class 2
How are peptide hormones stored and when are they released?
Stored in large vesicles and released via exocytosis when calcium levels rise
How are steroid hormones synthesized? What class?
They are synthesized by modifications of cholesterol and by enzymes in the smooth ER and in the mitochondria
Class 3
How are steroid hormones transported?
Since steroid hormones are lipid soluble, they are synthesized on demand and must be transported by carrier proteins.
How are thyroid hormones synthesized? What class?
Modification of individual amino acids on a large protein. Specifically, it is formed by adding iodine to a large protein called thyroglobulin, not from free amino acids.
Class 1
How are thyroid hormones stored?
They are stored as part of the thyroglobulin protein (contains T3 and T4) then diffuse through the cell membrane once they are cleaved.
T3 and T4 go through free diffusion and then transport in blood on carrier proteins b/c they’re lipid soluble
How do lipid soluble (hydrophobic) hormones bind to receptors?
They act through intracellular receptors (located within the cytosol) and alter gene expression
How do hydrophilic hormones bind to their receptors?
Act through membrane bound (extracellular) receptors of various types:
- G-protein coupled receptors (GPCRs)
- enzyme-linked receptors (usually kinases which activate other proteins, but some create second messengers directly)
These metabotropic receptors signal through soluble, mobile, second messenger molecules
