Il Colesterolo

Il Colesterolo

Il Colesterolo

Il colesterolo è una molecola lipidica della classe degli steroli che riveste un ruolo particolarmente importante nella fisiologia degli animali, uomo incluso, è un costituente insostituibile delle membrane cellulari animali ed è il precursore degli ormoni steroidei, della vitamina D e degli acidi biliari.

E’ indispensabile per la vita animale, mentre è assente nelle piante, le quali contengono però sostanze lipidiche strutturalmente simili.

Le più importanti funzioni svolte dal colesterolo sono:
– Funzioni strutturali:
• E’ un componente insostituibile delle membrane di tutte le cellule animali, permette la permeabilità a piccole molecole idrosolubili
• E’ un costituente della guaina mielinica dei nervi.
• E’ essenziale nella crescita e nella divisione cellulare, soprattutto nei tessuti ad alto turnover (es. epidermide, epiteli).
• E’ essenziale per lo sviluppo embrionale: le malformazioni di neonati dopo la somministrazione di Contergan alle madri erano causate da un disturbo nella biosintesi di colesterolo.

– Funzioni metaboliche:
• Il colesterolo è la sostanza base per la sintesi degli ormoni steroidei delle ghiandole surrenali (aldosterone, cortisolo) e delle gonadi (testosterone, estradiolo, ecc.).
• E’ essenziale per la sintesi della vitamina D operata dall’azione dei raggi ultravioletti sulla cute.
• E’ prodotto nel fegato viene impiegato in buona parte per la produzione degli acidi biliari della bile, una sostanza secreta nel duodeno che serve a emulsionare i lipidi alimentari per renderli assorbibili dall’intestino tenue.

Il contenuto di colesterolo dell’organismo umano è di circa 150 g;

l’encefalo da solo ne contiene 30 g e il plasma circa 8 g.

L’uomo produce per biosintesi autonoma la maggior parte del colesterolo necessario (pool endogeno), solo una piccola parte, in media 0,1-0,3 g (massimo 0,5 g), viene assunta giornalmente con l’alimentazione (pool esogeno); entrambi i pools sono soggetti a meccanismi regolatori, in modo tale che, in condizioni di equilibrio.

Tutte le cellule dell’organismo sono capaci di sintetizzarlo a partire dall’acetil-coenzima A, ma l’organo centrale del metabolismo del colesterolo è il fegato.
L’ormone che stimola la produzione è l’insulina.

…tratto dal libro biochimica degli alimenti.

Quale cibo stimola la produzione di insulina?

About the author

Talarico Domenico

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