FUNDAMENTALS OF HUMAN NUTRITION
TOPIC: THE DIGESTION AND ABSORPTION OF FATS
Final Presentation [pic][pic]
Miss Mehmoona Khalid
• Introduction of Digestion
• Digestion of Triglycerides in GI Tract
• In Mouth
• In Oesophagus
• In Stomach
• In Small Intestine
• Lipids Absorption
• Lipids in the Body
Digestion of triglycerides (Fat) through the GI Tract:
The triglycerides are digested through the GI tract by the following route:
In the Mouth:
Fat digestion starts off slowly in the mouth, with some hard fats beginning to melt when they reach body temperature.
Role of Salivary Glands:
A salivary gland at the base of the tongue releases an enzyme called lingual lipase that plays:
• In Adults: A minor role in the digestion in adults.
• In Infants: An active role in infants. In infants, this enzyme efficiently digests the short-and medium- chain fatty acids found in milk.
This is a simple tube through the thorax, which connects the mouth to the rest of the gut. No digestion takes place in oesophagus. There is a thin epithelium, no villi, a few glands secreting mucus, and a thick muscle layer, which propels the food by peristalsis. This is a wave of circular muscle contraction, which passes down the oesophagus and is completely involuntary. The oesophagus is a soft tube that can be closed, unlike the trachea, which is a hard tube, held open by rings of cartilage.
In the Stomach:
In a quiet stomach, fat would float as a layer above the other components of swallowed food. But the strong muscle contractions of the stomach propel the stomach contents toward the pyloric spinchter. Some chime (chewed food) passes through the pyloric spinchter periodically, but the remaining partially digested food is propelled back into the body of the stomach. This churning grinds the solid pieces to finer particles, mixes the chime, and disperses the fat into smaller droplets. Then the gastric lipase enzyme performs best in the acidic environment of the stomach. Still, little fat digestion takes place in the stomach; most of the action occurs in the small intenstine.
In the Small Intestine:
Fat in the small intestine triggers the release of the hormone cholecystokinin (CCK), which signals the gallbladder to release its stores of bile. (liver makes bile, and the gallbladder stores it until it is needed.
Components of Bile:
Among bile’s many ingredients are bile acids, which are made in the liver from cholesterol and have a similar structure. In addition, they often pair up with an amino acid (a building block of protein).
Process of Emulsification:
The amino acid end is attracted to water, and the sterol end is attracted to fat. This structure improves bile’s ability to act as an emulsifier, drawing fat molecules into the surrounding watery fluids. There the fats are fully digested as they encounter lipase enzymes from the pancreas and small intestine. The process of emulsification is diagrammed below: -
Figure 1 Emulsification of Fat by Bile
Hydrolosis of Triglycerides
Most of the hydrolysis of triglycerides occurs in the small intestine. The major fat digesting enzymes are pancreatic lipases; some intestinal lipases are also active. These enzymes remove one, then the other, of each triglyceride’s outer fatty acids, leaving a monoglyceride. Occasionally, enzymes remove all three fatty acids, leaving a free molecule of glycerol....
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