Lecture 45: Introduction to the Endocrine System Flashcards
Protein Peptide Hormones
- stored in secretory vesicles until needed
> 100 AA = PROTEINS, < 100 AA = peptides
- water-soluble
- normally target membrane receptors
Steroid Hormones and Amines
SH: from cholesterol, lipid-soluble, not stored
Amine: from tyrosine
- normally target intra/extracellular receptors
Protein/Peptide Hormone Synthesis and Secretion
- synthed as non-functional preprohormone
- modified in ER = prohormone
- packed into vesicles (proteolytic enzymes cleave to form functional hormone)
Nucleus –> ribosome –> ER –> Golgi Apparatus
- endocrine cell stimulus = RELEASE (inc. intracellular calcium or inc. cAMP/PKA activation)
Steroid Hormone Synthesis and Secretion
- derivatives of CHOLESTEROL (modified by addition/removal or side chains, hydroxylation, aromatization of steroid nucleus)
- synth/secretion by: adrenal cortex, gonads, corpus luteum, placenta
Amine Hormone Synthesis (Catecholamines and Thyroid Hormones)
C: synthed in cytosol and secretory granules
- act via cell membrane-associated receptors
T: synthed by thyroid gland and stored as thyroglobulin (follicles w/in gland)
- cross cell membrane, act through nuclear receptor
Protein Binding and correlation to Plasma Half-Life and Metabolic Clearance
Increased Protein Binding = INC. Half-Life and DEC. metabolic clearance
Neural Regulation of Hormone Secretion
- neuronal input to endocrine cell inc/dec hormonal secretion
EX: sympathetic preganglionic innervation of adrenal medulla
Feedback Mechanisms of Hormone Secretion
- more common than neuronal regulation
- some elements feedback (directly or indirectly) on endocrine gland to change secretion rate (Positive vs Negative)
Positive Endocrine Feedback and examples
- some elements cause addition secretion of hormone
- uncommon in biologic systems, but usually EXPLOSIVE if they do occur
EX: ovulation and labor contraction (estadiol) in females
Negative Endocrine Feedback and examples
- predominant mode of feedback loop (some features inhibit secretion of the hormone)
- confer stability by keeping physiological parameter within a normal range (blood glucose levels)
EX: Testosterone in males
Long-loop, Short-loop, Ultra Short-loop Feedback
Long: hormone from 3rd tier (periphery) feeds back to 2nd tier (pituitary) and 1st tier (hypothalamus)
Short: hormone from 2nd tier feeds back to 1st tier
Ultra Short: gland inhibits its own secretion
3 major inputs on Hypothalamus Regulation
- Suprachiasmatic Nucleus (SCN)
- impose circadian rhythm on hypothalamic secretions
- Pineal Gland
- releases melatonin (day/night feedback to SCN)
- Physiological Stress
2 ways to affect responsiveness of receptors to hormones
- changing the number of available receptors
2. changing the affinity of the receptors for the hormone
Adenylyl Cyclase signal transduction pathway (5)
hormones: ACTH, LH, FSH, TSH, glucagon
- adenyly cyclase activated by alpha subunit = ATP –> cAMP (5-AMP)
- cAMP activates Protein Kinase A (PKA)
Phospholipase C signal transduction pathway (3)
hormones: GnRH, TRH, oxytocin
- phospholipase C activated by alpha-subunit = PIP2
- PIP2 –> IP3 (release intracellular Ca), DAG, Ca
- secondary affector: PKC or calmodulin
