Fig. 43.7). StAR protein is short-lived and rapidly activated posttranslationally (phosphorylation) and transcriptionally by pituitary tropic hormones. In patients with inactivating mutations in StAR protein, cells of the zona fasciculata become excessively laden with lipid (“lipoid”) because cholesterol cannot be accessed by CYP11A1 within the mitochondria and used for cortisol •Fig. 43.6 Someoftheindividualactionsofcatecholaminesthatcontributetotheintegratedsympa-thoadrenalresponsetoexercise.(ModifiedfromWhiteBA,PorterfieldSP.Endocrine and Reproductive Physiology. 4thed.Philadelphia:Mosby;2013.)Bronchiole (˜2) Dilation ° Exchange of O2 and CO2 ° Cardiac output ° Venous return GI and urinary tracts (˜2) ˝ Motility ˝ Energy usage ° Blood glucose ° Blood ketones ° Blood FFAs ° Blood lactate ° Blood glycerol Adipose (˜2, ˜3) ° Lipolysis ˝ Glucose uptake Liver (˜2) ° Glycogenolysis ° Gluconeogenesis ° Ketogenesis Hormonal reinforcement Skeletal muscle (˜2) ° Glycogenolysis ˝ Glucose uptake ˜ Cells (˙2) ˝ Insulin secretion ˙ Cells (˜2) ° Glucagon secretion ° Blood glucagon/insulin ratio ° Nutrient supply to muscle and adequate supply of oxygen and glucose to brain ˝ Blood flow to GI tract ° Blood flow to skeletal muscle Splanchnic arterioles (˙) Vasoconstriction Skeletal muscle arterioles (˜2) Vasodilation Veins and lymphatics (˙) Vasoconstriction Heart (˜1) (+)ˆve Inotropic (+)ˆve Chronotropic (+)ˆve Lusitropic •Fig. 43.7 Eventsinvolvedinthefirsttworeactionsinthesteroidogenicpathway:conversionofcholesteroltopregnenolone;conversionofpregnenolone(P5)toprogesterone(P4)inzonafasciculatacells.ACAT,acylCoA:cholesterolacyltransferase;3β HSD,3β hydroxysteroiddehydrogenase;CE,cholesterolesters;CYP11A1alsocalledP450 side-chain cleavage enzyme; FC,freecholesterol;HSL,hormone-sensitivelipase;LAL,lysosomalacidhydrolase;LDL,low-densitylipoprotein;LDLR,low-densitylipoproteinreceptor;P5,pregnenolone;StAR,steroidogenicacuteregulatoryprotein.(ModifiedfromWhiteBA,PorterfieldSP.Endocrine and Reproductive Physiology. 4thed.Philadelphia:Mosby;2013.) •Fig. 43.8 Summaryofthesteroidogenicpathwaysforeachofthethreezonesoftheadrenalcortex.Theenzymaticreactionsarecolorcodedacrosszones.sER,smoothendoplasmicreticulum.(ModifiedfromWhiteBA,PorterfieldSP.Endocrine and Reproductive Physiology. 4thed.Philadelphia:Mosby;2013.) synthesis. Moreover, these individuals cannot synthesize gonadal steroid hormones. The placenta does not express StAR, so these individuals have normal placental steroid production in utero.