Fat Metabolism
Fat digestion is a critical process that allows the body to break down dietary fats (lipids) into smaller molecules that can be absorbed and utilized for energy, cell structure, and various physiological functions.
1. Mouth
Process: Fat digestion begins minimally in the mouth. Some lipases (enzymes that break down fats) are present in saliva, but their role in fat digestion at this stage is limited.
2. Stomach
Process:
In the stomach, fats are mixed with gastric juices, leading to emulsification (the breaking down of fat into smaller droplets). Gastric lipase, an enzyme produced by the stomach, begins the digestion of fats into diglycerides and free fatty acids, but this process is relatively minor compared to what occurs in the small intestine.
3. Small Intestine
The majority of fat digestion occurs in the small intestine, where bile acids and enzymes play crucial roles.
Bile:
Produced by the liver and stored in the gallbladder, bile is released into the duodenum (the first part of the small intestine) in response to the presence of fat. Bile contains bile salts, which emulsify fats, breaking them down into tiny droplets in a process that greatly increases the surface area available for enzymatic action.
Pancreatic Lipase:
The pancreas secretes pancreatic juice, which contains pancreatic lipase, into the small intestine. Pancreatic lipase is the primary enzyme responsible for the digestion of fats. It breaks down the emulsified fat droplets into monoglycerides and free fatty acids.
Mechanism
The products of fat digestion, mainly monoglycerides and free fatty acids, are then incorporated into micelles small transport carriers formed from bile salts. These micelles ferry the digested fats to the intestinal cells (enterocytes), where they are absorbed
Absorption & Transport
Inside the enterocytes, monoglycerides and free fatty acids are reassembled into triglycerides and then packaged with proteins into particles called chylomicrons.
Chylomicrons are released into the lymphatic system and eventually enter the bloodstream. Once in the blood, the fats can be transported to various tissues, where they are used for energy, stored, or incorporated into cell membranes.
4. Large Intestine
Minimal amounts of fats that are not digested and absorbed in the small intestine pass into the large intestine.
In the large intestine, some fats can be metabolized by bacteria, but most undigested fats are excreted in the feces.
Protein Digestion
Protein digestion is the process by which proteins in the food are broken down into their basic building blocks, amino acids,
Amino acids are used in our body for various functions, including tissue repair, muscle growth, and as a source of energy.
1. Mouth
Protein digestion in the mouth, only refers to breaking down the food into smaller pieces, making it easier for enzymes to work on them later in the digestive process.
However, there are no enzymes in the saliva that significantly break down proteins.
2. Stomach
The stomach plays a significant role in protein digestion. When protein-rich foods enter the stomach, they trigger the release of gastrin, a hormone that stimulates the secretion of gastric juice.
Gastric Juice:
This acidic fluid contains hydrochloric acid (HCl) and the enzyme pepsin.
Hydrochloric Acid: HCl lowers the pH of the stomach contents, unfolding the proteins (denaturation), which makes them more accessible to enzymatic digestion.
Pepsin:
An enzyme that starts the chemical digestion of proteins by breaking them down into smaller peptides. Pepsin is unique because it works best in the acidic environment of the stomach.
3. Small Intestine
The majority of protein digestion and absorption occurs in the small intestine. As the partially digested proteins enter the duodenum (the first part of the small intestine), they stimulate the secretion of hormones that trigger the pancreas to release pancreatic juice.
Pancreatic Enzymes:
Pancreatic juice contains several enzymes crucial for protein digestion, including trypsin, chymotrypsin, and carboxypeptidase. These enzymes further break down peptides into shorter peptides and individual amino acids.
Intestinal Enzymes:
The epithelial cells lining the small intestine also secrete enzymes, such as aminopeptidases and dipeptidases, which break down peptides into free amino acids directly at the intestinal wall.
Absorption
Once inside the enterocytes (intestinal cells), amino acids are transported into the bloodstream, where they can be circulated to various tissues throughout the body.
The absorbed amino acids are used for protein synthesis, energy production, or converted into other compounds as needed by the body.
4. Large Intestine
Very little protein reaches the large intestine under normal conditions, as most proteins are digested and absorbed by the time the chyme reaches this part of the digestive tract.
Any remaining peptides can be further broken down by gut bacteria, but this is a minor part of protein digestion