NURS 208: Digestion of Protein & Lipid

Examination of digestion processes focusing on protein and lipid metabolism within the gastrointestinal (GI) system.

Understand the two types of vitamins and their absorption mechanisms in the GI tract.
Comprehend the regulation of gastric acid secretion.
Describe the processes involved in lipid and protein metabolism.

Digestion in the small intestine involves enzymes, hormones, and digestive fluids from various organs (oral cavity, stomach, pancreas, gallbladder, small intestine).

Pepsin: An enzyme that breaks down proteins into smaller peptide chains.
- Activation: Hydrochloric acid (HCl) activates pepsinogen into pepsin in the stomach.
- Pepsin converts polypeptides into shorter chains of peptides and amino acids.
Peptidases: Enzymes from the small intestine that further digest peptides into amino acids.

Lipases: Enzymes responsible for breaking down lipids into monoglycerides and free fatty acids.
- Types: Lingual lipase, gastric lipase, pancreatic lipase, and lipase from the small intestine.

Amylases: Convert carbohydrates (starch) into disaccharides and further into monosaccharides.
- Examples: Salivary amylase, pancreatic amylase, maltase, sucrase, lactase.
End Products: Monosaccharides like glucose, galactose, and fructose.
- Only monosaccharides can be absorbed in the intestine.
- Digestion of cellulose cannot occur due to the lack of GI enzyme.

Mono- and disaccharides are absorbed in the small intestine:
- Glucose and galactose enter cells via SGLT and exit through GLUT2.
- Fructose enters through GLUT5.

Bile Salts: Facilitate fat digestion by emulsifying fat droplets, making them more accessible to lipases.
- Bile salts have an amphipathic nature, combining with lipids to form smaller emulsified particles.
- Co-lipase: A pancreatic secretion that assists lipase in accessing lipid droplets.
Micelles: Formed during fat digestion, moving fatty acids and monoglycerides to absorptive cells in the intestinal lumen.

Fatty acids and monoglycerides move to the smooth endoplasmic reticulum where they are reassembled into triglycerides.
Triglycerides combine with cholesterol and proteins to form chylomicrons.
- Chylomicrons are secreted into the lymphatic system through lacteals.

Types:
- Fat-soluble: Vitamins A, D, E, K (absorbed with lipids).
- Water-soluble: Vitamins B and C (absorbed with water).
Vitamin B12 absorption requires intrinsic factor from parietal cells and is dependent on gastric acidity for release from proteins.

Initiated by the cephalic and gastric phases:
- Cephalic phase triggers secretion in response to stimuli (sight, smell, taste).
- Gastric phase involves distension of the stomach, leading the enteric nervous system to release ACh, promoting gastric acid secretion.
Gastrin: Released in response to partially digested proteins, further stimulating acid production.
Somatostatin: Released by D cells to inhibit gastrin secretion when pH declines (negative feedback).

Initiation of the cephalic phase of digestion can be triggered by smell, sight, taste, thought, or swallowing food.
- Correct answer: a) Smell, sight, taste, thought, and swallowing of food.
Gastrin release is stimulated by:
- Correct answer: c) Partially digested proteins in chyme.
What structure is formed within the smooth endoplasmic reticulum by combining triglycerides with cholesterol and proteins?
- Correct answer: a) chylomicrons.
Carbohydrates absorbed in our intestines are in the form of:
- Correct answer: a) monosaccharides.