Lecture 1 - Introduction to Endocrinology Flashcards
3 groups of hormones:
Proteins/polypeptides Steroid Miscellaneous
Synthesis of protein hormones - ACTH Adenocorticotrophic hormone
DNA codes for mRNA of POMC mRNA makes POMC using a.a. from blood POMC modified in Golgi Exported in vesicles where enzymes cut off the ‘pro’ bit ACTH vesicles accumulate under surface Wait for signal ACTH is then exocytosed into blood
Where is ACTH produced?
Anterior Pituitary
Synthesis of steroid hormones - cortisol
Cholesterol delivered to cell as LDLs Then stored as Fatty Acid Esters Esterase breaks down the FAE Cholesterol enters the mitochondria via StAR proteins Enzymes in mitochondria catalyse the steps to convert cholesterol into steroid cortisol is then secreted into cytoplasm and then into blood
What is the precursor molecule to all steroids?
Cholesterol
Where are most steroid hormones produced?
In the adrenal glands or gonads
Where are steroids synthesised in the cell?
Mitochondria
What is the rate limiting step for cholesterol synthesis?
Cholesterol entry into mitochondria via StAR
Differences between polypeptide and steroid hormone secretion
PH stored in vesicles in the cell, waiting for signal SH secreted into blood stream as soon as produced
How do protein hormones travel around the body?
Secreted into blood
Travel unbound - so sensitive to enzymatic breakdown Very short half lives - usually matter of minutes Stored in production tissues
How do steroid hormones travel around the body?
Stored in blood Bind to plasma proteins - Albumin (mops up large amount but non-specific interaction) Each steroid has specific plasma proteins eg: Coricosteroid Binding Globulin (Cortisol) Vast majority of SH bound to plasma proteins in blood SMALL AMOUNT free - which can move into tissues
What is the equilibrium equation in the blood for protein hormones?
Hormone + Plasma proteins <=> Protein Bound Hormone
To maintain equilibrium of SH in blood, how does the equilibrium react when decrease of SH occurs?
Less unbound SH Equilibrium shifts to left, releasing more bound hormone *Endocrine cells are stimulated to produce more SH* (Occurs with any shift in equilibrium)
What is the mechanism of action of protein hormones to cause an effect on the cell?
ACTH binds to G-protein coupled receptor Activates Adenylate Cyclase - Causes ATP -> cAMP Increase of cAMP activates Protein Kinase A (PKA) PKA phosphorylates esterase, releasing cholesterol from LDLs StAR is phosphorylated, hence activated StAR allows cholesterol to enter the mitochondrion Stimulating SH production
What is the mechanism of action of steroid hormones to cause a reaction?
Free SH enter cells via diffusion SH binds into intracellular receptors Complex translocates to nucleus Affects DNA transcription, translocation CHANGE PROTEIN MACHINERY WITHIN CELL