Mechanical and chemical digestion of foods rich in protein/fat/carbs and accessory organs involved

mechanical digestion (protein)

Begins in the mouth through chewing (mastication). This reduced the physical size of food particles which will later make it easier for enzymes to break down. Saliva which is secreted from the salivary glands in the mouth is secreted during chewing and moistens/lubricated the food which aids in swallowing and movement into the esophagus. The esophagus utilizes peristalsis (wave like contractions) to push the food into the stomach. The stomach muscles contract churning the food with gastric juices which breaks down the food further and increases the surface area for enzymatic digestion.

Chemical digestion (protein)

begins in the stomach where gastric acid is released. gastric acid contains hydrochloric acid which has a low ph and therefore gastric acid denatures(unfolds) the protein molecules which makes the easier for digestive enzymes to break down. The stomach lining creates pepsinogen which is activated by stomach acid and becomes its active form pepsin (protease enzyme) which will further break down the protein molecules (shorter AA chains). The chyme (partially digested food) then enters the small intestine. The pancreas secretes digestive enzymes into the duodenum (trypsin, chymotrypsin, carboxypeptidase). These proteases break down the peptide chains even further. Trypsin and chymotrypsin cleave the protein peptides at specific points while Carboxypeptidase removes individual amino acids from the carboxyl end of the peptide chain. The pancreas also produces bicarbonate which neutralizes acidic chyme and provides optimal pH for enzyme activity. Lastly, at the brush border of the small intestine, enzymes (aminopeptidase) break down the smaller peptides into individual amino acids by cleaving the AA from the N-terminal end of the peptide chain. Once they are broken down all the way they are absorbed by the enterocytes in the small intestine where they are transported into blood circulation and carried to liver/tissues.

accessory organs

salivary glands

pancreas

liver and gallbladder: liver produces bile (stored in the gallbladder) which is released into the small intestine. This aids in fat digestion which can promote overall absorption of fat-soluble vitamins necessary for overall digestive function.

Mechanical digestion (fats)

begins in the mouth with chewing and saliva (same as protein) and stomach churned with gastric juices to form chyme (same as protein). The churning action of the stomach helps to breakdown fat globules into smaller droplets, but no significant breakdown. The majority occurs in the small intestine when bile is secreted from the liver (stored in the gallbladder) into the duodenum (the first part of the small intestine).

Chemical digestion (fats)

begins with emulsification in the small intestine. Bile is secreted from the liver (stored in the gallbladder) into the duodenum (the first part of the small intestine). The bile contains bile salts which emulsify large fat globules into smaller droplets which increases the surface area for the enzymes to act upon. The pancreas then secretes pancreatic lipase and colipase into the small intestine. pancreatic lipase breaks down triglycerides into fatty acids and monoglycerides. Colipase binds to the fat droplets and assists pancreatic lipase in breaking down triglycerides in the presence of bile salts (enzymatic breakdown). The fatty acids and monoglycerides combine with bile salts to form micelles (tiny water-soluble complexes) which can easily move through the aqueous small intestine to the enterocytes (surface of intestinal cell). The fatty acids, monoglycerides and bile salts are absorbed by the enterocytes and then reassembled into triglycerides which are packaged into chylomicrons (lipoprotein particles that transport fat throughout the body). Chylomicrons are too large to enter the blood capillaries so the enter. the lymphatic vessels which drain into the bloodstream.

Mechanical digestion (carbs)

mainly focused in the mouth. when food is chewed by teeth, salivary glands within the mouth produce saliva which aids in chewing, swallowing, and making it easier for digestive enzymes to function on the food later on in the digestive process. When the food is chewed its surface area is increased foe enzymes to act upon as well.

Chemical digestion (carbs)

begins in the mouth. saliva which is released from the salivary glands contains salivary amylase which begins the process of hydrolyzing (breaking down) the starch molecules into shorter chains of sugars such as maltose or dextrins. The chewed food then moves to the stomach where it is churned with gastric acid (gastric juices and hydrochloric acid) to create a semi liquid substance called chyme. The chyme then moves into the small intestine where the pancreas releases pancreatic amylase into the duodenum. pancreatic amylase continues the breakdown of starches into maltose and other small sugar units. the epithelial cells that line the small intestine release enzymes called disaccharides at the brush border (microvilli) of the the small intestine which breaks down disaccharides into monosaccharides. For example, maltase splits maltose into two glucose. The monosaccharides are absorbed into the epithelial cells of the small intestine through facilitated diffusion or active transport. Once in the enterocytes (intestinal cells) the monosaccharides are transported into the bloodstream via glucose transporter proteins and then to the liver where fructose and galactose are converted to glucose and then enter the bloodstream. stored as glycogen or maintaining blood sugar.