Digestion and Absorption

Digestion Breaks down Carbohydrates (starch and sugar) → single sugar molecules Proteins → amino acids Fats → fatty acids, glycerol

Enzymes Proteins that break bonds

The Digestive System Is a long tube from the mouth to the anus

Digestive System Mouth to anus Epithelium lines the lumen Barrier to invaders Submucosal layer Muscularis Taste and smell

Peristalsis Muscular contractions that move food along throughout GI tract

The Mouth Mastication: chewing Saliva Enzymes to help breakdown simple sugars Mucus to lubricate the food for easier swallowing Lysozyme to kill bacteria

Tongue Taste receptors: sweet, sour, salty, bitter, savory Enzymes to help break down fatty acids

Swallowing Bolus is the food swallowed at one time Epiglottis blocks windpipe, prevents choking

The Esophagus Long tube Connects pharynx to the stomach Peristalsis, muscle contraction Lower esophageal sphincter Heartburn

The Stomach Lower esophageal sphincter and pyloric sphincter Storage capacity of ~4 cups Secretion of acid, enzymes, and intrinsic factor Holds food for 2-4 hours Formation of chyme Mucus layer protects stomach from digestion Very little absorption of nutrients

Physiology of the Stomach

Stomach Acid Activates digestive enzymes Partially digests dietary protein Assists in calcium absorption Makes dietary minerals soluble for absorption

The Small Intestine Most digestion and absorption happens here About 10 feet long Duodenum (10 inches) Jejunum (4 feet) Ileum (5 feet) Folded walls with villi projections Absorptive cells are located on the villi Increases intestinal surface area 600x Rapid cell turnover

The Small Intestine

Nutrient Absorption Passive diffusion: driven by concentration; fats, water, some minerals Active absorption: uses energy; glucose and amino acids Phagocytosis and pinocytosis: absorptive cells engulf compounds, generally larger molecules, as in immune substances in breast milk

Nutrient Absorption

Site of Absorption

Absorption Digestion → small particles End products of digestion: Carbohydrates → monosaccharides Proteins → amino acids Fats → glycerol, fatty acids

Absorption Through small intestine walls Absorbed into Blood – water soluble nutrients Lymph – fat soluble nutrients Blood → liver → general circulation Liver detoxifies and repackages

The Large Intestine ~3 1/2 feet in length No villi or enzymes present Little digestion occurs Indigestible food stuff Absorption of water, some minerals, vitamins Contains bacteria which break down fiber; produce Vitamin K Formation of feces for elimination

Rectum Stool remains Stimulates elimination Muscle contraction Anal sphincters Voluntary control Opens for elimination

Accessory Organs Salivary glands Pancreas Gallbladder Liver

Salivary Glands Saliva Works in mouth Moistens Salivary amylase Digests starch

The Pancreas Produces glucagon and insulin (endocrine) Manufactures digestive enzymes→ small intestine Secretes pancreatic juices Bicarbonate needed to neutralize chyme when it enters small intestine

The Liver Produces bile (fat digestion) Enterohepatic circulation

The Gallbladder Stores bile Concentrates it Releases to small intestine when needed

The Urinary System Kidneys Ureter Bladder Urethra Removes waste products Regulates blood acid-base balance Proper function determined by cardiovascular system, fluid intake, and drug use

Exchange of Nutrients Insert Fig. 3-4

Nutrient Storage Capabilities System of maintaining reserves Adipose tissue Glucose Amino acids in the blood Vitamins and minerals in the liver Calcium in bones

Ulcers Helicobacter pylori Excessive use of aspirin Excessive acid production Stress Stomach loses its mucus protection S/S: pain in ~2 hrs after eating Rx: Antibiotics, antacid, refrain from smoking, limit use of aspirin and aspirin like meds.

Heartburn S/S: Gnawing pain in the upper chest Movement of acid from the stomach into the esophagus Gastroesophageal reflux disease (GERD) Rx: smaller, more frequent meals, low fat, wait 2 hours before lying down, refrain from smoking, low excess weight, limit spicy foods, medication

Constipation Difficult or infrequent bowel movement Caused by slow motility, medication, &/or supplements of calcium/iron Feces stay in the large intestine longer Ignore normal urges to defecate Rx: Eat plenty of dietary fiber, drink more fluids, regular physical activity

Laxatives Irritate the intestinal nerve to stimulate peristaltic muscles or Draws water into the intestine Regular use can decrease muscle action in the large intestine GI tract becomes dependent on laxatives

Hemorrhoids Swollen veins of the rectum and anus Intense pressure and straining S/S: pain, itching, bleeding Rx: eat plenty of fiber and fluid

Irritable Bowel Syndrome S/S: Cramps, gassiness, bloating, irregular bowel function Possibly caused by altered intestinal peristalsis and decreased pain threshold Rx: individualized, elimination diet, moderate caffeine, low fat, small meals, stress reduction

Diarrhea Increased fluidity, frequency, or amount of bowel movement Usually caused by an infection in the intestine Bacteria and viruses cause the intestinal cells to secrete fluid Rx: plenty of fluid