That is “Protein Digestion and Absorption”, part 6.3 from the guide An Introduction to Diet (v. 1.0). For particulars on it (together with licensing), click on right here.
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6.3 Protein Digestion and Absorption
How do the proteins from meals, denatured or not, get processed into amino acids that cells can use to make new proteins? If you eat meals the physique’s digestive system breaks down the protein into the person amino acids, that are absorbed and utilized by cells to construct different proteins and some different macromolecules, akin to DNA. We mentioned the method of meals digestion in depth in Chapter 3 “Nutrition and the Human Body”, however now let’s comply with the particular path that proteins take down the gastrointestinal tract and into the circulatory system. Eggs are a great dietary supply of protein and can be used as our instance to explain the trail of proteins within the processes of digestion and absorption. One egg, whether or not uncooked, hard-boiled, scrambled, or fried, provides about six grams of protein.
From the Mouth to the Abdomen
Until you might be consuming it uncooked, step one in egg digestion (or some other protein meals) includes chewing. The enamel start the mechanical breakdown of the big egg items into smaller items that may be swallowed. The salivary glands present some saliva to help swallowing and the passage of the partially mashed egg by way of the esophagus. The mashed egg items enter the abdomen by way of the esophageal sphincter. The abdomen releases gastric juices containing hydrochloric acidSecreted by abdomen cells; aids within the chemical breakdown of proteins. and the enzyme, pepsinAn enzyme secreted by abdomen cells. It breaks the peptide bonds between amino acids, producing a lot shorter protein fragments., which provoke the breakdown of the protein. The acidity of the abdomen facilitates the unfolding of the proteins that also retain a part of their three-dimensional construction after cooking and helps break down the protein aggregates shaped throughout cooking. Pepsin, which is secreted by the cells that line the abdomen, dismantles the protein chains into smaller and smaller fragments. Egg proteins are massive globular molecules and their chemical breakdown requires time and mixing. The highly effective mechanical abdomen contractions churn the partially digested protein right into a extra uniform combination, which, you could recall from Chapter 3 “Nutrition and the Human Body”, is known as chyme. Protein digestion within the abdomen takes an extended time than carbohydrate digestion, however a shorter time than fats digestion. Consuming a high-protein meal will increase the period of time required to sufficiently break down the meal within the abdomen. Meals stays within the abdomen longer, making you are feeling full longer.
From the Abdomen to the Small Gut
The abdomen empties the chyme containing the damaged down egg items into the small gut, the place the vast majority of protein digestion happens. The pancreas secretes digestive juice that accommodates extra enzymes that additional break down the protein fragments. The 2 main pancreatic enzymes that digest proteins are chymotrypsin and trypsin. The cells that line the small gut launch further enzymes that lastly break aside the smaller protein fragments into the person amino acids. The muscle contractions of the small gut combine and propel the digested proteins to the absorption websites. Within the decrease elements of the small gut, the amino acids are transported from the intestinal lumen by way of the intestinal cells to the blood. This motion of particular person amino acids requires particular transport proteins and the mobile vitality molecule, adenosine triphosphate (ATP). As soon as the amino acids are within the blood, they’re transported to the liver. As with different macronutrients, the liver is the checkpoint for amino acid distribution and any additional breakdown of amino acids, which could be very minimal. Recall that amino acids comprise nitrogen, so additional catabolism of amino acids releases nitrogen-containing ammonia. As a result of ammonia is poisonous, the liver transforms it into urea, which is then transported to the kidney and excreted within the urine. Urea is a molecule that accommodates two nitrogens and is extremely soluble in water. This makes it a sensible choice for transporting extra nitrogen out of the physique. As a result of amino acids are constructing blocks that the physique reserves in an effort to synthesize different proteins, greater than 90 % of the protein ingested doesn’t get damaged down additional than the amino acid monomers.
Amino Acids Are Recycled
Simply as some plastics may be recycled to make new merchandise, amino acids are recycled to make new proteins. All cells within the physique regularly break down proteins and construct new ones, a course of known as protein turnoverThe processes of regularly breaking down proteins and constructing new ones.. Every single day over 250 grams of protein in your physique are dismantled and 250 grams of recent protein are constructed. To kind these new proteins, amino acids from meals and people from protein destruction are positioned right into a “pool.” Although it isn’t a literal pool, when an amino acid is required to construct one other protein it may be acquired from the extra amino acids that exist throughout the physique. Amino acids are used not solely to construct proteins, but in addition to construct different organic molecules containing nitrogen, akin to DNA and RNA, and to some extent to provide vitality. It’s important to take care of amino acid ranges inside this mobile pool by consuming high-quality proteins within the weight loss program, or the amino acids wanted for constructing new proteins can be obtained by growing protein destruction from different tissues throughout the physique, particularly muscle. This amino acid pool is lower than one % of whole body-protein content material. Thus, the physique doesn’t retailer protein because it does with carbohydrates (as glycogen within the muscle groups and liver) and lipids (as triglycerides in adipose tissue).
– “what happens to protein after food is swallowed”
“what happens to protein after food is swallowed”