Valsalva Maneuver: Not applicable due to constantly open state.<br>- Important for patients to pay attention to constipation as they cannot use the Valsalva maneuver effectively, increasing the risk of difficulty in passing dry feces.
Basic Principle: Nutrients like carbohydrates, proteins, and nucleic acids must be broken down into their fundamental components to be absorbed (monosaccharides, amino acids, nucleotides).
Absorption Process:
Active Transport: Requires energy at the apical surface of enterocytes (cells lining small intestine).
Facilitated Diffusion: Nutrients exit through the basal surface into capillaries.
Carbohydrates:
Only three monosaccharides are absorbable: glucose, fructose, and galactose.
Breakdown begins in the mouth (salivary amylase), continues with pancreatic amylase in the duodenum, and final enzymes at the brush border.
Lactose intolerance example: Lacking lactase results in undigested lactose drawing water into the intestine, causing discomfort.
Initial Breakdown: Begins in the stomach (hydrochloric acid denatures proteins), followed by enzymes like pepsin (activated from pepsinogen).
Further Breakdown: Small intestine’s alkaline environment inactivates pepsin; further digestion depends on pancreatic enzymes.
Transport: Amino acids are transported via active transport across the apical membrane and exit through facilitated diffusion at the basal side.
Complex Nature: Lipids (fats) are nonpolar; thus, they cannot use the same absorption methods as carbohydrates and proteins.
Emulsification: Bile salts act as detergents to mix fat with water, enabling pancreatic lipases to access and break down fats.
Digestion Process:
Triglycerides broken down into monoglycerides and free fatty acids.
Lipids form micelles (with bile salts) for absorption through the brush border of the enterocyte.
Inside cells, lipids are reassembled into triglycerides, forming chylomicrons, which enter lymphatic vessels (lacteals) instead of blood capillaries.
Circulatory Entry: Chylomicrons eventually enter the bloodstream after passing through lymphatic vessels and nodes.
Final Breakdown: Chylomicrons must be re-broken down into free fatty acids and glycerol for cellular use.
Process: Breakdown of RNA and DNA into nucleotides, pentose sugars, and phosphate groups.
Enzymes cleave nucleic acids, allowing individual components to be absorbed into the bloodstream.