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 anusEpithelium lines the lumenBarrier to invadersSubmucosal layerMuscularis

Taste and smell

Peristalsis

Muscular contractions that move food along throughout GI tract

The Mouth

Mastication: chewing

SalivaEnzymes to help breakdown simple sugarsMucus to lubricate the food for easier

swallowingLysozyme to kill bacteria

TongueTaste receptors: sweet, sour, salty,

bitter, savoryEnzymes to help break down fatty acids

SwallowingBolus 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 sphincterStorage capacity of ~4 cupsSecretion of acid, enzymes, and intrinsic factorHolds food for 2-4 hoursFormation of chymeMucus layer protects stomach from digestionVery 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 hereAbout 10 feet longDuodenum (10 inches)Jejunum (4 feet) Ileum (5 feet)

Folded walls with villi projectionsAbsorptive cells are located on the villiIncreases intestinal surface area 600x Rapid cell turnover

The Small Intestine

Nutrient AbsorptionPassive 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 circulationLiver detoxifies and repackages

The Large Intestine

~3 1/2 feet in lengthNo villi or enzymes presentLittle digestion occursIndigestible food stuff Absorption of water, some minerals, vitaminsContains bacteria which break down fiber; produce Vitamin KFormation of feces for elimination

Rectum

Stool remains

Stimulates elimination

Muscle contraction

Anal sphinctersVoluntary controlOpens 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

UlcersHelicobacter pylori Excessive use of aspirinExcessive acid production StressStomach loses its mucus protectionS/S: pain in ~2 hrs after eatingRx: 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 functionPossibly caused by altered intestinal peristalsis and decreased pain thresholdRx: 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