Youtor
Bile Acid Synthesis
>> YOUR LINK HERE: ___ http://youtube.com/watch?v=-TMNV5vEtC0
In this video I have explained the details about bile acid synthesis from cholesterol in the liver. • My video link for fates of cholesterol is as below. • • Fates of Cholesterol in the Liver • My video link on lipid digestion • • Lipid digestion • • Theory about bile acids: from Wikipedia. • Bile acids are steroid acids found predominantly in the bile of mammals and other vertebrates. Different molecular forms of bile acids can be synthesized in the liver by different species.[1] Bile acids are conjugated with taurine or glycine in the liver, and the sodium and potassium salts of these conjugated bile acids are called bile salts. • Primary bile acids are those synthesized by the liver. Secondary bile acids result from bacterial actions in the colon. In humans, taurocholic acid and glycocholic acid (derivatives of cholic acid) and taurochenodeoxycholic acid and glycochenodeoxycholic acid(derivatives of chenodeoxycholic acid) are the major bile salts in bile and are roughly equal in concentration. The conjugated salts of their 7-alpha-dehydroxylated derivatives, deoxycholic acid and lithocholic acid, are also found, with derivatives of cholic, chenodeoxycholic and deoxycholic acids accounting for over 90% of human biliary bile acids. • Bile acids are about 80% of the organic compounds in bile (others are phospholipids and cholesterol). An increased secretion of bile acids produces an increase in bile flow. The main function of bile acids is to allow digestion of dietary fats and oils by acting as a surfactant that emulsifies them into micelles, allowing them to be colloidally suspended in the chyme before further processing. They also have hormonalactions throughout the body, particularly through the farnesoid X receptor and GPBAR1 (also known as TGR5). • • Bile acid synthesis occurs in liver cells which synthesize primary bile acids (cholic acid and chenodeoxycholic acid in humans) via cytochrome P450-mediated oxidation of cholesterol in a multi-step process. Approximately 600 mg of bile salts are synthesized daily to replace bile acids lost in the feces, although, as described below, much larger amounts are secreted, reabsorbed in the gut and recycled. The rate-limiting step in synthesis is the addition of a hydroxyl group on position 7 of the steroid nucleus by the enzyme cholesterol 7 alpha-hydroxylase. This enzyme is down-regulated by cholic acid, up-regulated by cholesterol and is inhibited by the actions of the ileal hormoneFGF15/19. • Prior to secreting any of the bile acids (primary or secondary, see below), liver cells conjugate them with one of two amino acids, glycine or taurine, to form a total of 8 possible conjugated bile acids. These conjugated bile acids are often referred to as bile salts because of their physiologically-important acid-base properties. The pKa of the unconjugated bile acids are between 5 and 6.5, and the pH of the duodenum ranges between 3 and 5, so when unconjugated bile acids are in the duodenum, they are almost always protonated (HA form), which makes them relatively insoluble in water. Conjugating bile acids with amino acids lowers the pKa of the bile-acid/amino-acid conjugate to between 1 and 4. Thus conjugated bile acids are almost always in their deprotonated (A-) form in the duodenum, which makes them much more water-soluble and much more able to fulfil their physiologic function of emulsifying fats. • When these bile salts are secreted into the lumen of the intestine, bacterial partial dehydroxylation and removal of the glycine and taurine groups forms the secondary bile acids, deoxycholic acid and lithocholic acid. Cholic acid is converted into deoxycholic acid and chenodeoxycholic acid into lithocholic acid. All four of these bile acids can be taken back up into the blood stream, return to the liver, and be re-secreted in a process known as enterohepatic circulation. • • For REGULAR UPDATES you can consider SUBSCRIBING to this channel: https://goo.gl/eMs6rw • For short write up of theory on USMLE Biochemistry and other topics on food and nutrition, obesity, weight loss tips you may visit my site: • http://www.drmungli.com/ • You can follow my Facebook page Biochemistry Made Easy: https://goo.gl/23S9Y7 • checkout other awesome channels to learn biochemistry and other subjects from: • ThePenguineProf: https://goo.gl/ySNURB • Osmosis: https://goo.gl/d1zBs1 • Armando: https://goo.gl/jcYwwR • Khan Academy: https://goo.gl/7YmIf9 • Nucleus Medical Media: https://goo.gl/xdlqsr • Trending medical youtube channels: https://goo.gl/nUuJOL • 20 useful sites for medical students: https://goo.gl/aPnc19 • Biochemistry single line questions site: https://goo.gl/PFCewk
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