Digestion and absorption

Digestion Break-down of large foodstuff All components of food Carbohydrates Proteins Fats Monomer level Process Mechanical Chemical

Absorption Amount of absorption Site of absorption Ingestion (1.5 L) plus secretion (7 L) 83 % absorbed in the small intestine Site of absorption Stomach Very poor No absorptive villi/membrane Large intestine Proximal half Water and electrolytes

Small intestine Increased surface size Folding (3 X) Villi (10 X) Brush border (20 X)

Villus Adaptation for increased nutrient absorption Vasculature Lymph vessel Constant movement of microvilli

Hydrolysis Universal process Break down of large molecules by addition of water Break of the polymers into smaller fragments Break bonds Process Different enzymes based on the macromolecule

Digestion of Carbohydrates Starches Maltose + 3-9 glucose polymers Maltase + -dextinase Glucose Galactose Lactose Sucrose Lactase Fructose Sucrase - amylase (saliva) pancreatic amylase

Location of digestion Mouth Stomach Small intestine 5 % of all starches Stomach Inhibition of amylase activity (too acidic) 30-40 % of starch converted to maltose Small intestine Amylase from pancreas Enzymes on the enterocytes of villi

Absorption of carbohydrates Glucose 80 % of carbohydrates being absorbed Secondary active transport Sodium-glucose co-transporter Use of sodium concentration gradient as an energy Concentration gradient generated by removal of sodium from intestinal epithelium to the blood

Other monosaccharides Absorbed as they are Converted to glucose

Digestion of proteins (Stomach) (Duodenum and jejunum) (Enterocytes)

Absorption of proteins Individual amino acids 99 % of final products of protein digestion Transported via sodium-AA co-transporter The same mechanism as glucose transport Multiple transporter proteins to accommodate different amino acids Some amino acids Transported without co-transporters

Fat digestion Dietary fats Site of digestion and absorption Triglycerides Majority Phospholipids Cholesterol Site of digestion and absorption Small intestine

Process Emulsification Starts in the stomach Majority takes place in the duodenum Combination with bile products Fragmentation of large molecules Increased surface area

Cholesterol and phospholipids Transport Micelle Cholesterol and phospholipids Cholesterol esterase and phospholipase A2

Absorption of fats Monoglycerides and free fatty acids Diffuse out of the micelle when contact with epithelial membrane Enters SER and forms new triglycerides Released into the central lacteal Transported to the thoracic duct to enter the circulation Short chain fatty acids Directly into the circulation

Absorption of other materials Water Osmosis Active transport Calcium Iron Other ions

Sodium ions Active transport Diffusion Increased by aldosterone Epithelium to paracellular spaces Diffusion From intestinal lumen to the epithelium Increased by aldosterone

Effects of sodium absorption Increased chloride ion absorption Increased osmosis Secretion of hydrogen ions Counter-transport Formation of carbonic acid CO2 (dissolve in blood) Water (excreted/reabsorved)

Absorption at the large intestine Proximal half Absorption Sodium Chloride Water Secretion Bicarbonate ions Counter-transport with chloride ions

Feces Dead bacteria (30 %) Fat (10-20 %) Inorganic matter (10-20 %) Undigested plant matter (30 %) Proteins (2-3 %) Metabolic waste (bilirubin metabolites)

Abnormalities Esophagus Swallowing problem Entrance of food materials into the respiratory system Closure of glottis Entrance of food materials into the nasal cavity Failure of lower sphincter to relax Achalasia

Stomach Inflammation of gastric mucosa (gastritis) Bacterial infection Irritant substances Damage to tight epithelial junction Gastric ulcer

Gastric atrophy Triggered by chronic gastritis Loss of HCL secretion Achlorohydria Hypochlorohydria Diminished secretion Loss of pepsin function

Peptic ulcer Imbalance between gastric secretion and gastric protection Loss of mucosal barrier Reduced acid neutralization Excess gastric secretion Causes Chronic bacterial infections Chemicals that increase gastric secretion and breakdown of mucosa

Small intestine Loss of digestion Pancreatitus Blockage of ducts Excessive alcohol consumption Blockage of ducts Gallstone Digestion of pancreas Loss of pancreatic functions

Malabsorption of nutrients Spruce Idiopathic Gluten enteropathy Inflammation caused by infection Malabsorption Lipids Vitamin K, folic acid, and B12 Calcium

Large intestine Constipation Obstruction of intestinal passage Irregular bowel habits Spasm of a small segment within the sigmoid colon Insufficient ganglions Megacolon

Diarrhea Enteritis Psychogenic Inflammation caused by infection Irritation of mucosa Excess secretion Psychogenic Excessive parasympathetic stimulation Motility Secretion

Vomiting Removal of materials from upper GI tract Sensory information Excessive irritation Overdistention Overexcitation Sensory information Pharynx Esophagus Stomach Upper small intestine

Nausea Irritation impulse from the GI tract Impulse from the lower brain associated with motion sickness Impulse from the cerebral cortex to initiate vomiting Excitation of medulla near the vomiting center