Introduction to Endocrine Physiology Flashcards
What are the methods of controlling body functioning?
Nervous
Hormonal
How can hormones be classified according to nature?
Local Hormones
General Hormones
Specific Hormones
Characteristics of Local Hormones
Act locally
E.g. acetylcholine
Characteristics of General Hormones
Act on all body cells
E.g. thyroid hormone
Characteristics of Specific Hormones
Act on specific target tissues
E.g. adrenocorticotropic hormone (ACTH) acts on adrenal cortex
How can hormones be classified according to their chemical structure?
Protein and Polypeptide Hormones: E.g. anterior and posterior pituitary hormones
Steroid hormones: Have a steroid nucleus and derived from cholesterol, e.g. cortisol, aldosterone, testosterone, estrogen
Amino acids derivatives: E.g. T3, T4, Epinephrine, Norepinephrine
How are protein hormones formed and stored?
Preprohormones are formed by the rough ER
Cleaved into smaller protein called prohormone in ER
Cleaved into active hormone in Golgi Apparatus
In golgi apparatus they are packed as secretary vesicle and stored
Specific signal cause the secretion
How are steroid hormones formed and stored?
Stored in small quantities on specific signal enzymes
Act on precursor molecules to synthesize hormones
How are thyroid hormones formed and stored?
Formed as a part of large protein thyroglobulin
Stored in follicle of thyroid gland
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What are cyclical hormonal variations?
Periodic variations in hormone release
How are peptide hormones transported?
Dissolved in plasma
How are steroid and thyroid hormones transported?
Circulate in blood bound to plasma proteins
Bound proteins are physiologically inactive since they cannot diffuse across the capillaries
What factors affect hormone concentrations?
Hormone secretion
Metabolic clearance rate
What are the types of hormone receptors?
Membrane receptors: Peptide hormone receptors
Cytoplasmic receptors: Steroid hormone
Nucleus receptors: T3 and T4
What are the methods by which hormone binding affects cells?
Activating receptors
Activating intracellular enzymes
Activating genes
How does hormone binding cause receptor activation?
Binds to receptors and causes conformational change
How does hormone binding cause activation of intracellular enzymes?
Activates adenylyl cyclase forming cAMP from ATP
cAMP acts as a second messenger causing intracellular changes
How does hormone binding cause gene activation?
Some steroid and thyroid hormones bind to receptors inside the cells
Activates portion of DNA
What are the types of second messengers?
Cyclic AMP (cAMP)
Calcium-Calmodulin
Phospholipid
How does cAMP act as a second messenger?
It activates a cascade of enzymes
Initiates biological actions (e.g. secretion + muscle contraction and relaxation)
Describe the Calcium-Calmodulin second messenger system
Calcium channels open allowing Ca to bind to calmodulin
Four Ca++ ions can bind to calmodulin
Calmodulin activates other enzymes
Describe the formation of IP3 and DAG in phospholipid second messenger systems
Phospholipase C activated by hormone binding
Phospholipase C causes breaks down phosphatidylinositol biphosphate (PIP2) forming inositol triphosphate (IP3) and diacylglycerol (DAG)
How do IP3 and DAG act as second messengers?
IP3 causes mobilization of Ca
DAG activates protein kinase C and cause cell division and proliferation
This action is enhanced by Ca that have been released by IP3
Eg. Angiotensin II, TRH, Oxytocin etc
