THE DIGESTIVE SYSTEM

EDILBERTO A. RAYNES, MD

ORGANS OF THE DIGESTIVE SYSTEM

• MAIN ORGAN

• ACCESSORY ORGAN

MAIN ORGAN

• MOUTH

• PHARYNX (THROAT)

• ESOPHAGUS (FOODPIPE)

• STOMACH

• SMALL INTESTINE (DUODENUM, JEJUNUM, ILEUM)

• LARGE INTESTINE (CECUM; COLON: ASCENDING, TRANSVERSE, DESCENDING, SIGMOID; RECTUM; ANAL CANAL)

ACCESSORY ORGAN

• TEETH AND TONGUE• SALIVARY GLANDS (PAROTID,

SUBMANDIBULAR, SUBLINGUAL)• LIVER• GALLBLADDER• PANCREAS• VERMIFORM APPENDIX

FUNCTIONS OF DIGESTIVE SYSTEM

• INGESTION

• DIGESTION

• ABSORPTION

• DEFECATION

PERITONEUM

• ENVELOPS THE ENTIRE ABDOMINAL WALL

• LARGEST SEROUS MEMBRANE IN THE BODY

• THE FREE SURFACE IS LUBRICATED WITH A SEROUS FLUID THAT ALLOWS THE DIGESTIVE STRUCTURES AND OTHER VISCERAL ORGANS TO GLIDE EASILY AGAINST THE ABDOMINAL WALL WITHOUT FRICTION

PERITONEUM

• CONTAINS BLOOD VESSELS, LYMPH VESSELS AND NERVES

• INCLUDES MESENTERIES, PARIETAL AND VISECERAL PERITONEUM, GREATER AND LESSER OMENTUM

WALL OF DIGESTIVE TRACT: FOUR LAYERS

1. MUCOSA OR MUCOUS MEMBRANES-MUCOUS EPITHELIUM

2. SUBMUCOSA- CONNECTIVE TISSUE LAYER; BLOOD VESSELS AND NERVES

3. MUSCULARIS: 2 OR 3 LAYERS OF SMOOTH MUSCLE; PERISTALSIS

4. SEROSA-OUTERMOST COVERING; VISCERAL EPITHELIUM; ATTACHES THE DIGESTIVE TRACT TO THE WALL OF THE ABDOMINOPELVIC CAVITY BY FORMING FOLDS CALLED MESENTERIES

MOUTH OR ORAL CAVITY

ROOF• FORMED BY THE HARD AND SOFT

PALATES• HARD PALATE: PARTS OF MAXILLARY

AND PALATINE BONES• SOFT PALATE: ARCH-SHAPED MUSCLE

SEPARATING MOUTH FROM PHARYNX• UVULA: DOWNWARD PROJECTION OF THE

SOFT PALATE

MOUTH OR ORAL CAVITY

FLOOR• FORMED BY TONGUE AND ITS MUSCLES

•SKELETAL MUSCLE

•FRENULUM: ATTACHES THE TONGUE TO

FLOOR

•PAPILLAE: SMALL ELEVATIONS

-VALLATE: LARGEST

-TASTE BUDS: SENSORY RECEPTORS

TEETH

TYPES:

1. INCISORS: MASTICATION OR CHEWING

2. CANINES (CUSPIDS): PIERCING OR TEARING

3. PREMOLARS OR BICUSPIDS

4. MOLARS OR TRICUSPIDS

TEETH

• AT AGE 2, 20 TEETH IN TEMPORARY SET

• AT AGE BETWEEN 17 AND 24, 32 PERMANENT TEETH

• TYPICAL TOOTH

1. CROWN

2. NECK

3. ROOT

SALIVARY GLANDS

1. PAROTID GLAND: LARGEST; LIE BELOW AND IN FRONT OF EACH EAR AT THE ANGLE OF THE JAW; DUCT OPENS AT THE OPPOSITE THE 2ND MOLAR TOOTH ON EITHER SIDE OF THE UPPER JAW

2. SUBMANDIBULAR: ON EITHER SIDE OF THE LINGUAL FRENULUM

3. SUBLINGUAL

*SALIVA CONTAINS MUCUS AND A DIGESTIVE ENZYME THAT IS CALLED SALIVARY AMYLASE

PHARYNX

• MUSCULAR TUBE THAT FUNCTIONS AS PART OF THE RESPIRTORY AND DIGESTIVE SYSTEMS

ESOPHAGUS

• MUCUS LINED TUBE BETWEEN PHARYNX AND STOMACH

*HIATAL HERNIA: THE STOMACH PUSHES THROUGH THE GAP IN THE DIAPHRAGM THAT ALLOWS THE ESOPHAGUS BECOMES ENLARGED, ALLOWING ACIDIC STOMACH CONTENTS TO BYPASS A VALVELIKE SPHINCTER MUSCLE AND FLOW UPWARD INTO THE ESOPHAGUS

STOMACH

• LIES IN THE UPPER PART OF THE ABDOMINAL CAVITY JUST UNDER THE DIAPHRAGM

• LOWER ESOPHAGEAL OR CARDIAC SPHINCTER KEEPS THE FOOD FROM REENTERING THE ESOPHAGUS WHEN THE STOMACH CONTRACTS

• CONTRACTION OF THE STOMACH’S MUSCULAR WALLS MIXES THE FOOD THOROUGHLY WITH THE GASTRIC JUICE AND BREAKS IT DOWN INTO A SESAMOID MIXTURE CALLED CHYME.

STOMACH

• MUSCLE CONTRACTION RESULTS IN PERISTALSIS THAT PROPELS FOOD DOWN THE DIGESTIVE TRACT TOGETHER WITH THE GASTRIC JUICE AND HYDROCHOLORIC ACID INTO THE STOMACH

• PARTS: FUNDUS, BODY, PYLORUS• LESSER CURVATURE: UPPER RIGHT BORDER • GREATER CURVATURE: LOWER LEFT

BORDER

STOMACH

• THE GASTRIC MUCOSA CONTAINS ENDOCRINE AND EXOCRINE CELLS.

• G CELLS: ENDOCRINE CELLS THAT SECRETE HORMONE GASTRIN, WHICH INITIATES THE PRODUCTION AND SECRETION OF GASTRIC JUICE AND STIMULATES BILE AND PANCREATIC ENZYMES INTO THE SMALL INTESTINE

STOMACH

• 2 TYPES OF EXOCRINE CELLS: PARIETAL AND CHIEF CELLS

• PARIETAL CELLS: PRODUCE (1) INTRINSIC FACTOR, A SUBSTANCE REQUIRED FOR THE ABSORPTION OF VITAMIN B12 FROM THE SMALL INTESTINE TO THE BLOODSTREAM; (2) HYDROCHOLORIC ACID, WHICH BREAKS DOWN PROTEIN AND ACTIVATES MANY GASTRIC ENZYMES

STOMACH

• CHIEF CELLS: PRODUCE GASTRIC ENZYME, PEPSINOGEN, A PRECURSOR TO PEPSIN. PEPSIN IS SECRETED IN AN INACTIVE FORM TO PREVENT THE GASTRIC LINING FROM ERODING FROM PEPSIN’S PROTEIN DIGESTION. PEPSINOGEN CONVERTS TO PEPSIN WHEN IT COMES IN CONTACT WITH HCL AND BEGINS THE CHEMICAL DIGESTION OF PROTEINS BY CONVERTING THEM INTO PEPTIDES

STOMACH

• CHYMOSIN OR RENNIN, AN ENZYME PRESENT IN THE GASTRIC JUICES OF INFANTS, IS USED TO AID IN MILK CURDLING AND IS USED COMMERCIALLY TO PRODUCE CHEESE.

SMALL INTESTINE

• DIVISIONS: DUODENUM, JEJUNUM, ILEUM• WALL CONTAINS SMOOTH MUSCLE FIBERS

THAT CONTRACT TO PRODUCE PERISTALSIS• LINED BY MUCOUS MEMBRANES• INTESTINAL GLANDS: INTESTINAL JUICE• VILLI: FINGER-SHAPED PROJECTIONS THAT

CONTAIN BLOOD AND LYMPH CAPILLARIES THAT ABSORB THE PRODUCTS OF CARBOHYDRATE AND PROTEIN DIGESTION

LIVER

• LARGEST GLAND• SECRETE BILE• HEPATIC DUCTS: DRAINS BILE FROM

LIVER• CYSTIC DUCT: BILE ENTERS AND LEAVES

GALLBLADDER• COMMON BILE DUCT: UNION OF HEPATIC

AND CYSTIC DUCT; DRAINS BILE FROM HEPATIC OR CYSTIC DUCTS INTO DUODENUM

BILE

• MECHANICALLY BREAKS UP OR EMULSIFIES FATS

• WHEN CHYME CONTAINING LIPID OR FAT ENTERS THE DUODENUM, IT INITIATES A MECHANISM THAT CONTRACTS THE GALLBLADDER AND FORCES THE BILE INTO THE SMALL INTESTINE

BILE

• FATS IN CHYME TRIGGER THE SECRETION OF THE HORMONE CHOLECYSTOKININ (CCK) FROM THE INTESTINAL MUCOSA OF THE DUODENUM. CCK STIMULATES THE CONTRACTION OF THE GALLBLADDER AND BILE FLOWS INTO THE DUODENUM

GALLBLADDER

• LOCATED UNDER THE SURFACE OF THE LIVER

• CONCENTRATES AND STORES BILE PRODUCED IN THE LIVER

PANCREAS

• BEHIND THE STOMACH• FUNCTIONS: 1. PANCREATIC CELLS SECRETE

PANCREATIC JUICE INTO PANCREATIC DUCTS; MAIN DUCTS EMPTIES INTO DUODENUM

2. PANCREATIC ISLETS OF LANGERHANS: CELLS NOT CONNECTED WITH PANCREATIC DUCTS; SECRETE HORMONES GLUCAGON AND INSULIN INTO THE BLOOD

LARGE INTESTINE

• DIVISIONS: CECUM; COLON (ASCENDING, TRANSVERSE, DESCENDING AND SIGMOID); RECTUM

• WALL: SMOOTH MUSCLE FIBERS THAT CONTRACT TO PRODUCE CHURNING, PERISTALSIS AND DEFECATION

FUNCTIONS OF LARGE INTESTINE

1. ABSORPTION OF WATER AND CERTAIN ELECTROLYTES

2. SYNTHESIS OF CERTAIN VITAMINS BY THE INTESTINAL BACTERIA (ESPECIALLY VITAMIN K AND CERTAIN B VITAMINS)

3. TEMPORARY STORAGE SITE OF WASTE (FECES)

4. ELIMINATION OF WASTE FROM THE BODY (DEFECATION)

APPENDIX

• BLIND TUBE OFF CECUM

• NO IMPORTANT DIGESTIVE FUNCTION IN HUMANS

PROCESSING OF FOOD

1. DIGESTION

2. ABSORPTION

3. METABOLISM

DIGESTION

• CHANGING FOODS SO THAT THEY CAN BE ABSORBED AND USED BY CELLS

• TYPES: MECHANICAL, CHEMICAL, CARBOHYDRATE, PROTEIN, FAT DIGESTION

MECHANICAL DIGESTION

• CHEWING, SWALLOWING AND PERISTALSIS BREAK FOOD INTO TINY PARTICLES

• MIX WELL WITH DIGESTIVE JUICES

• MOVE THEM ALONG THE DIGESTIVE TRACT

CHEMICAL DIGESTION

• BREAKS UP LARGE FOOD MOLECULES INTO COMPOUNDS HAVING SMALLER MOLECULES

• BROUGHT ABOUT BY DIGESTIVE ENZYMES

CARBOHYDRATE DIGESTION

• MAINLY IN SMALL INTESTINE• PANCREATIC AMYLASE: CHANGES

STARCHES TO MALTOSE• INTESTINAL JUICE ENZYMES 1. MALTASE: CHANGES MALTOSE TO

GLUCOSE 2. SUCRASE: SUCROSE TO GLUCOSE 3. LACTASE: LACTOSE TO GLUCOSE

PROTEIN DIGESTION

• STARTS IN STOMACH; COMPLETED IN SMALL INTESTINE

• GASTRIC JUICE ENZYMES, RENNIN AND PEPSIN: PARTIALLY DIGEST PROTEINS

• PANCREATIC ENZYME, TRYPSIN: COMPLETES DIGESTION OF PROTEINS TO AMINO ACIDS

• INTESTINAL ENZYMES, PEPTIDASES: COMPLETE DIGESTION OF PARTIALLY DIGESTED PROTEINS TO AMINO ACIDS

FAT DIGESTION

• BILE CONTAINS NO ENZYMES BUT EMULSIFIES FATS (BREAKS FAT DROPLETS INTO VERY SMALL DROPPLETS)

• PANCREATIC LIPASE: CHANGES EMULSIFIED FATS TO FATTY ACIDS AND GLYCEROL IN SMALL INTESTINE

ABSORPTION

• DIGESTED FOOD MOVES FROM INTESTINE INTO BLOOD OR LYMPH

• FOODS AND MOST WATER FROM SMALL INTESTINE

• WATER FROM LARGE INTESTINE