Gastrointestinal System

Digestive System

• The stomach serves as a temporary food storage and secretes proteases and acid that facilitate digestion.
• The small intestine is the primary site for nutrient absorption.
• The kidneys reabsorb fluids and electrolytes but do not absorb nutrients.
• The pancreas secretes digestive enzymes and bicarbonate to neutralize gastric acid.
• The gallbladder stores bile between meals.
• The liver initiates fat and carbohydrate metabolism.
• The esophagus is a conduit to the stomach.
• The salivary glands add secretions to the hollow organs of the gastrointestinal tract.
• The mouth mechanically breaks down and lubricates food.
• The pharynx propels food into the oesophagus.

Carbohydrate Digestion and Absorption

• The process of enzymatic conversion of complex dietary substances to a form that can be absorbed is called digestion.
• Fiber is NOT a major group of carbohydrates.
• Monosaccharides can be directly absorbed by the small intestine.
• Glycogen is the storage form of carbohydrate in animals.
• The step of carbohydrate digestion that involves the hydrolysis of starch to oligosaccharides is called maltase.
• The SGLT1 membrane protein is responsible for glucose and galactose uptake at the apical membrane.
• There are 4 brush border oligosaccharidases present in the small intestine.

Protein Digestion and Absorption

• The process of protein digestion-absorption that does not occur is the uptake of whole proteins into the bloodstream.
• Proteases are secreted as proenzymes for protein hydrolysis.
• There are 9 essential amino acids out of the 20 amino acids.
• The process of protein uptake by the gut epithelial cells occurs during the neonatal period, but largely ceases after six months of age.
• The main form in which proteins are absorbed by adults is amino acids.
• Dipeptides, tripeptides, and tetrapeptides are absorbed by the small intestine through a peptide transport system.
• There are 7 distinct amino acid transport systems present at the apical membrane of the villous epithelial cell.
• The direction of movement of amino acids across the basolateral membrane of the villous epithelial cell is out of the cell.
• There are 4 amino acid transporters present in the basolateral membrane of the villous epithelial cell.
• The processes that mediate amino acid exit from the cell into the blood on the basolateral membrane of the villous epithelial cell are facilitated diffusion and active transport.
• Amino acids move across the apical membrane of enterocytes through a secondary active transport system.

Lipid Digestion and Absorption

• Lipids are preferentially soluble in non-polar solvents compared to water.
• The recommended intake of fat in a typical adult Western diet is 20-35% of total energy.
• In adults, proteins are absorbed as amino acids, not as whole proteins.
• During the neonatal period, proteins are absorbed as whole proteins.
• The role of whole protein uptake in adults is negligible.
• Amino acids enter the blood after absorption through the hepatic portal vein.
• There are 7 distinct transport systems present at the apical membrane for amino acid absorption.
• The direction of movement of amino acids across the basolateral membrane is out of the cell.
• There are 4 amino acid transporters present in the basolateral membrane.
• Lipids are preferentially soluble in non-polar solvents compared to water.
• The typical fat intake in adult Western diets is 20-35% of total energy.
• The biological fate of lipids is dependent on their absorption, transport, and metabolism.