Digestive Processes of the Small Intestine

1. Processes

   Nota:

   • Ingestion: Putting food into mouth Propusoon: Moves food through alimentary canal, includes swallowing and peristalsis Mechanical Digestion: Physical process of preparing food for chemical digestion and involves chewing, mixing churning and segmentation Chemical Digestion: Complex food molecules are broken down to chemical building blocks by enzymes Absorption: Passage fromt eh lumen thru mucosal cells into blood or lymph Defecation: Elimination of indigestible substances from body via the anus.
2. Chemical Digestion

   Nota:

   • Catabolic process whereby large food molecules are broken down to chemical monomers to be absorbed by the GI tract. Carbohydrates to disaccharides to monosaccharides proteins to peptides to aminoacids Lipids to diglycerides to monoglycerides and fatty acids.
   1. Carbohydrates

      Nota:

      • Digestible Polysaccharide found in diet is starch. Chemical digestions begin in mouth. Salivary amylase breaks large polysaccharides into smaller fragments (i.e glucose, galactose or fructose, maltose, lactose and sucrose.) Further digestion in small intestines by pancreatic amylase and brush border disaccharidesase
   2. Proteins

      Nota:

      • Pepsin, secreted by chief cells, begins the chemical digestion of proteins in stomach. Pancreatic enzymes such as trypsin a nd chymo trypsin to break down. brush border enzymes carboxypeptidase, amino peptidase and dipeptidase are the ones breaking down stuff in small intestine.
   3. Lipids

      Nota:

      • pancreas secretes lipase's and digest fat after they emulsified with bile.
3. Digestive Enzymes

Nota:

• Exstends form the pyloric sphincter to the ileocecal valve to the large intestines. Subdivided into 3 parts Duodenum, jejenum and the ileum. Highly adapted for absorption with 3 microscopic modifications. plicae circulares, villi and microvilli. Intestinal crypts secretes intestinal juices to serve carrier fluids 

1. Villus

   Nota:

   • Structured for nutrient absorption. Contained absorptiive vasculature and lined by enterocytes. And it maximises absorptive surfaces

Nota:

• Released by the pancreas into the duodenum alongside liver secretions and gallbladder products via the sphincter of oddi

1. Composition

   Nota:

   • Watery alkaline secretion rich in HCo3. Secreted by duct epithelial cells. To neutralise acidic stomach contents. Digestive Enzymes: Secreted by acinar cells. Secreted as inactive enzymes or zymogens, trypsinogen, chymotrypsinogen, carboxypeptidase and elactase, amylase, lipase.......... Those things are activated in small intestines by the enterokinase
2. Pancreatic HCO3- Secretion

   Nota:

   • 1. H20 diffuse thru cell membrane, Co2 also formed as a byproduct of cellular metabolism. 2. Carbonic anhydrase changes them into HCo3 and H. 3. H leaves cell via Na/H exchanger. 4. Hco3 leaves via Cl/HCO3 exchanger. 5. Outwards Cl- channnels in apical membrane return Cl- into lumen. 6. Na/K ATPase removes accumulating Na
   1. Control

      Nota:

      • Control is via Secretin: Released by stomach, increases H2o and bicarbonate secretions by the ducts. Cholecystokinin (CCK) Released when fatty acids and amino acids enter duodenum.

Nota:

• Peristalsis: Coordinated contraction of circa and longitudinal muscle to propel food. Segmentation: Contraction of smooth muscle to mix food without propelling food. MMC (migrating motility complex)  What...