Question

MCAT Tutorial: The Endocrine System

Answer 1

\({\bf{The~Basics:}}\)
- based on the production of hormones by the endocrine glands into the circulatory system via exocytosis/diffusion
- amino acid hormones: water soluble, derived from amino acids/polypeptides
- steroid hormones: not water soluble, derived from cholesterol, do not bind to the membrane, must be bound to other proteins to transport across cytosol
- prostaglandins: lipid-soluble derived from fatty acids; secreted by tissues into adjacent tissues, often used for vasodilation
- growth factors: stimulate growth, ex. erythropoietin (EPO, increases the # of red blood cells) and vascular endothelial growth factor (VEGF, increases blood flow to tumors)
- pheromones: signals a response from another organism

\({\bf{The~Hypothalamus:}}\)
- part of the brain
- combines communication signals from the endocrine and the nervous system
- regulates autonomic nervous system and secretes several peptide hormones
- made of neurosecretory cells, which respond to nerve impulses and release hormones
> two subtypes, parvocellular (contain releasing factors in vesicles --> exit into the hypophyseal portal system --> hypothalamus capillaries --> anterior lobe )
> and magnocellular (release hormones into the posterior pituitary lobe)

\({\bf{The~Thyroid~Gland:}}\)
- three hormones, T3, T4, and calcitonin
- T3 and T4 have same function (regulating metabolism and protein synthesis, T3 is more active)
- calcitonin: lowers blood calcium concentration, increases the amount of Ca2+ deposited into bone

\({\bf{The~Parathyroid~Glands:}}\)
- on the dorsal surface of thyroid
- also regulates blood calcium
- secretes PTH (parathyroid hormone) which has opposite effect of calcitonin

Answer 2

\({\bf{The~Pancreas:}}\) regulates blood sugar levels
- insulin (beta cells): lowers blood sugar, triggers carbohydrate metabolism, conversion of sugar into glycogen
- glucagon (alpha cells): raises blood sugar, conversion of glycogen to glucose, fat + protein metabolism
- gluconeogenesis: synthesis of glucose from non carbohydrates
- gastrin and CCK: increase glucagon production

\({\bf{The~Adrenal~Gland:}}\) regulates fight or flight response
- cortex:
> three zones of the cortex: zona glumerulosa, zona fasciculata, zona reticularis
-zona glumerulosa: produces mineralocorticoids, ex. aldosterone (regulates Na+ and K+)
-zona fasciculata: produce glucocorticoids (regulate glucose concentrations and metabolism)
-zona reticularis: produces sex hormones

- adrenal medulla:
> extension of the sympathetic nervous system
> converts tyrosine to epinephrine/norepinephrine

\({\bf{Gonads:}}\)
- testes: secrete testosterone in response to lutenizing hormone (LH), sexual differentiation and development of secondary sex characteristics in males
- ovaries: produce estrogen and progesterone, development of female secondary sex characteristics and plays a role in pregnancy/labor

Answer 3

Anyway, that's the end of my tutorial, I hope it was a helpful resource. Source material is the 2nd Edition Barron's Prep book for the new MCAT