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An elderly male patient with stomach cancer ((Food passes from mouth into…
An elderly male patient with stomach cancer
Organs of the digestive system fall into two groups:
Alimentary canal (gastrointestinal (GI) tract or gut)
Continuous muscular tube that runs from the mouth to anus
Digests food: breaks down into smaller fragments
Absorbs fragments through lining into blood
Organs: mouth, pharynx, esophagus, stomach, small & large intestine, anus
Accessory digestive organs
Teeth, tongue, and gallbladder
Digestive glands: produce secretions that help break down foodstuffs
Salivary glands, liver, and pancreas
The mouth (1) ingests, (2) begins mechanical breakdown by chewing, (3) initiates propulsion by swallowing, and (4) starts the digestion of polysaccharides
Also called the oral (buccal) cavity
Bounded by lips anteriorly, cheeks laterally, palate superiorly, and tongue inferiorly
Palate forms the roof of the mouth and has two distinct parts
Hard palate: formed by palatine bones and palatine processes of maxillae
Mucosa is slightly corrugated to help create friction against tongue
Soft palate: formed by mostly skeletal muscle; closes off nasopharynx during swallowing with help of downward projecting uvula
Tongue composed of interlacing bundles of skeletal muscle
Functions include gripping, repositioning, and mixing of food during chewing
Forms bolus – compact mixture of food and saliva
Initiates swallowing and aids in speech and sense of taste
Superior surface bears papillae, peglike projections of underlying mucosa
Filiform papillae: gives tongue roughness to provide friction; only one that does not contain taste buds; gives tongue a whitish appearance
Food passes from mouth into oropharynx and then into laryngopharynx
Allows passage of food, fluids, and air
Stratified squamous epithelium lining with mucus-producing glands
External muscle layers consists of two skeletal muscle layers
Inner layer of muscles runs longitudinally
Outer pharyngeal constrictors encircle wall of pharynx
The esophagus is a flat muscular tube that runs from laryngopharynx to stomach
Is collapsed when not involved in food propulsion
Pierces diaphragm and joins stomach at cardial orifice
Gastroesophageal (cardiac) sphincter surrounds cardial orifice
Keeps orifice closed when food is not being swallowed
Unlike mouth and pharynx, has all four previously discussed layers
Esophageal mucosa contains stratified squamous epithelium
Changes to simple columnar at stomach
Submucosa has mucus-secreting esophageal glands that aid in food passage
Muscularis: skeletal superiorly; mixed in middle; smooth inferiorly
Has adventitia instead of serosa
Empty stomach has ~50 ml volume but can expand to 4 L
When empty, stomach mucosa forms folds called rugae, which allow distension
Major regions include
Cardial region (cardia): surrounds cardial orifice
Fundus: dome-shaped region beneath diaphragm
Body: the midportion
Pyloric region: terminates in pylorus, which is continuous with duodenum through pyloric valve (sphincter controlling stomach emptying)
Greater curvature: convex lateral surface of stomach
Lesser curvature: concave medial surface of stomach
Liver, gallbladder, and pancreas are accessory organs associated with small intestine
Liver: digestive function is production of bile (fat emulsifier)
Gallbladder: chief function is storage of bile
Pancreas: supplies most of enzymes needed to digest chyme, as well as bicarbonate to neutralize stomach acid
Small intestine is the major organ of digestion and absorption
7–13 ft from pyloric sphincter to ileocecal valve, point at which it joins large intestine
Subdivisions
Duodenum: mostly retroperitoneal; ~10.0 in long; curves around head of pancreas; has the most features of interest
Jejunum: ~8 ft long; attached posteriorly by mesentery
Ileum: ~12 ft long; attached posteriorly by mesentery; joins large intestine at ileocecal valve
Only monosaccharides can be absorbed
Starch and disaccharides are broken down to oligosaccharides and disaccharides
Begins in mouth with salivary amylase
Further broken down into lactose, maltose, and sucrose
Final breakdown into monosaccarides (glucose, fructose, galactose)
Steps of starch digestion in intestine
Pancreatic amylase breaks down starch or glycogen that escaped salivary amylase into oligosaccharides and disaccharides
Brush border enzymes further break these into lactose, maltose, and sucrose; and then into monosaccharides (glucose, fructose, galactose)
Steps of protein digestion in intestine
Pancreatic proteases cleave protein into smaller peptides,
Brush border enzymes break oligopeptides and dipeptides into amino acids
Processing of food involves six essential activities:
Ingestion: eating
Propulsion: movement of food through the alimentary canal, which includes:
Swallowing
Peristalsis: major means of propulsion of food that involves alternating waves of contraction and relaxation
Mechanical breakdown: mechanical processes that include chewing, mixing food with saliva by the tongue, churning food in stomach, and segmentation
Segmentation: rhythmic local constrictions of the small intestine that mixes food with digestive juices; also make absorption more efficient
Digestion: series of catabolic steps that involves enzymes that break down complex food molecules into chemical building blocks
Absorption: passage of digested end products (plus vitamins, minerals, and water) from lumen of GI tract into blood or lymph
Defecation: elimination of indigestible substances via anus in form of feces
They would need to add enzymes to the food so it can get adequately absorbed
What processes are bypassed
Propulsion: movement of food through the alimentary canal, which includes:
Swallowing
Peristalsis: major means of propulsion of food that involves alternating waves of contraction and relaxation
Mechanical breakdown: mechanical processes that include chewing, mixing food with saliva by the tongue, churning food in stomach, and segmentation
Segmentation: rhythmic local constrictions of the small intestine that mixes food with digestive juices; also make absorption more efficient
Digestion: series of catabolic steps that involves enzymes that break down complex food molecules into chemical building blocks
feeding tube inserted into his alimentary
canal to bypass the esophagus, stomach, and duodenum