Overview Flashcards
Protein hormones are made where?
Hypothalamus
Pituitary gland
Thyroid/parathyroid glands
In the synthesis of protein hormones, hormones enter the golgi complex as ______ and leave as _____.
pro hormones
active hormones
The release of protein hormones from secretory vesicles depends on what?
Calcium
Steroid hormones are produced by:
Adrenal Cortex
Genitals
Kidney, liver, skin (Vitamin D)
What are the three fates of cholesterol?
- Vitamin D (skin)
- Bile Acids (Liver, most)
- Pregnenolone
What is the sequence of conversions that cholesterol undergoes in steroid secreting cells?
- Desmolase converts cholesterol to pregnenolone
- Pregnenolone becomes progesterone
- Progesterone becomes:
a. Glucocorticoids (i.e. cortisol)
b. Mineralocorticoids (aldosterone)
c. Androgens (testosterone)
Androgens -> estrogens
How are steroids stored?
Cholesterol is stored as cholesterol esters in vacuoles; rapidly accessible upon stimulation
Steroid hormones are NOT stored in large amounts
Which 2 factors control secretion of steroids and thyroid hormones (amines), and how long does it take?
- Amount of substrate (cholesterol ester for steroids, iodine for thyroid hormones)
- Availability of enzymes/transporters (StAR for steroids)
Slow (hours to days)
Amines are produced by:
- Adrenal medulla (catecholamines)
2. Thyroid (thyroid hormones)
Catecholamines are derivatives of which amino acid?
Tyrosine
Within the adrenal medulla, where specifically are catecholamines made?
Cytosol of chromaffin cells
What are the two catecholamines and which is more abundant?
- Epinephrine (main)
2. Norepinephrine
Where are catecholamines stored and what stimulates their release?
Stored in secretory vesicles
Release stimulated by calcium (sympathetic system)
Within the thyroid, where specifically are thyroid hormones produced?
Follicular cells
What are the steps in thyroid hormone synthesis?
- TG-T3-T4 in colloid enters follicular cell via endocytosis
- Endocytic vesicle fuzes w/ lysosomes
- Molecules diffuse into cytosol and through cell’s plasma membrane into blood vessel
What are the steps in regulating the endocytosis of TG-T3-T4 into the follicular cells?
- TSH (from blood vessel) binds TSH receptor (on follicular cell)
- ATP -> cAMP
- cAMP activates Protein Kinase
- Protein kinase activates protein P, triggering endocytosis
Where are thyroid hormones stored?
Colloid/follicular lumen
*Note that the follicular cells surround this lumen, but the thyroid hormones are not stored within the follicular cells themselves
Which hormones are hydrophilic and mostly unbound to plasma proteins?
Peptides
Catecholamines (may be loosely bound to albumin)
Which hormones are hydrophobic and travel bound to albumin?
Iodothyronines (also bind thyroid hormone-binding globulin/TBG)
Steroids
Hormone receptors have high _____ but low _____ for hormones.
High affinity (small Kd) Low specificity
Which type of hormone activates transmembrane receptors and which types of reactions do transmembrane receptors induce?
- Hydrophilic (peptides/catecholamines) activate transmembrane receptors
- Transmembrane receptors induce GPCR and protein tyrosine kinases
Which type of receptors do hydrophobic hormones activate?
Intracellular receptors
Where are steroid receptors? Thyroid hormone receptors?
Steroids - cytoplasm
Thyroid hormone - nucleus
How are protein hormones removed?
- Degraded by proteases in circulation
- Degraded in lysosomes on cellular receptors
- SMALL proteins filtered by kidney
