Digestion of Proteins (Nursing)

00:01 Now let's look at the digestion of proteins.

00:06 Note, the source of proteins is not only dietary but also includes digestive enzymes as well as proteins from the breakdown of mucosal cells.

00:18 Proteins are going to be broken into large polypeptides, small polypeptides, and small peptides.

00:27 And finally, into their monomeric unit of amino acids with some dipeptides and tripeptides as well.

00:36 Digestion of proteins begins in the stomach when pepsinogen is converted to pepsin at a very low pH of about 1.5 to 2.5.

00:48 It becomes inactive when it hits the high pH of the duodenum.

00:56 Pancreatic protease has trypsin and chymotrypsin are then going to cleave the protein into smaller peptides while carboxy peptidase is going to take off one of the amino acids at a time from the ends of these polypeptides.

01:15 Brush border enzymes also known as amino peptidases, carboxypeptidases and dipeptidases are going to break these polypeptides down into smaller units and eventually into amino acids.

01:32 It is the amino acids that will then be co-transported across the apical membrane of our absorptive epithelial cells via secondary active transport with either sodium ions or H+ ions.

01:48 Then after crossing through the cell, the amino acids will exit across the basolateral membrane by way of facilitated diffusion.

02:00 So to recap these steps using a diagram.

02:03 Recall that the breakdown of protein actually starts in the stomach, but once it leaves the stomach it's going to be further broken down through pancreatic proteases.

02:17 Further at the brush border.

02:19 There are going to be brush border enzymes that are going to break these now polypeptides or oligopeptides down into amino acids.

02:29 These amino acids will then be transported across the apical membrane by way of active transport with either sodium or H+ ions.

02:39 It will then travel through the cell and exit through the basolateral membrane into the bloodstream into hepatic portal circulation.

02:50 So to summarize the digestion of proteins.

02:54 1. protein digestion is going to begin in the stomach where the acidic environment is going to activate the protease pepsin.

03:04 Once in the small intestine pancreatic enzymes, trypsin, chymotrypsin and carboxypeptidase as well as the brush border enzymes will then break down these proteins into amino acids.

03:19 The amino acids are then absorbed into the blood and transported to the liver by way of the hepatic portal vein.