Pregnenolone, conversion into progesteron

An important transformation in steroid biochemistry is the conversion of pregnenolone into progesterone. Progesterone is a female sex hormone, a progestogen, but this reaction is also involved in the production of corticosteroids such as hydrocortisone and aldosterone. The reaction also occurs in plants, and features in the formation of cardioactive glycosides, such as digitoxin in foxglove. 

NAD A 3fi-hydroxysteroid dehydrogenase (3fi-HSD) The conversion of pregnenolone into progesterone involves two steps. The first reaction is the... 

To achieve the synthesis of cortisol, and possibly to a lesser extent corticosterone, it seems probable that the fetus and newborn infant can utilize a pathway which bypasses progesterone. The low activity of ZjS-HSD in the fetus and in infancy which has already been mentioned in Section 4 would be expected to cause an inhibition in the normal pathway of cortisol synthesis at the stage of conversion of pregnenolone into progesterone. Increased use of secondary pathways for corticoid synthesis via 21-OH-pregnenolone or 17a-OH-pregnenolone would then occur, with... 

Describe the synthesis of pregnenolone from cholesterol, the conversion of pregnenolone into progesterone, and the subsequent reactions leading to cortisol and aldosterone. 

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