Structure and Function of the Digestive System PDF

# Structure and Function of the Digestive System ## Nursing 302 ## Functions of the GI Tract 1. Ingestion of food 2. Propulsion of food and wastes from the mouth to the anus 3. Secretion of mucus, water, and enzymes 4. Mechanical digestion of food particles 5. Chemical digestion of food particles...

# Structure and Function of the Digestive System ## Nursing 302 ## Functions of the GI Tract 1. Ingestion of food 2. Propulsion of food and wastes from the mouth to the anus 3. Secretion of mucus, water, and enzymes 4. Mechanical digestion of food particles 5. Chemical digestion of food particles 6. Absorption of digested food 7. Elimination of waste products by defecation 8. Immune and microbial protection agains infection ## The Gastrointestinal Tract - **Mouth:** reservoir for chewing and mixing food with saliva. - **Saliva:** water with mucus, sodium, bicarbonate, chloride, potassium and salivary a-amylase (carbohydrate enzyme) - **Tongue:** covered in taste buds (salty, sour, bitter, sweet, and savory (umami)) - **Esophagus:** food formed into a bolus and enters the esophagus where peristalsis occurs to move food down to the lower esophageal sphincter to the stomach - **Stomach:** A hollow, smooth muscle organ that stores food, secretes digestive juices, mixes food with the juices, and propels partially digested food (chyme) ## The Gastrointestinal Tract - **Small intestine:** 5-6 m long; split into three segments (duodenum, jejunum, ileum); the ileocecal valve controls the flow of material into the large intestine; absorption is done through the villi & microvilli - **Large intestine:** begins at the cecum, a pouch that receives chyme from the ileum; then moves through the ascending, transverse, descending and sigmoid colon to the rectum and anus. - **Peritoneum:** membrane surrounding the organs of the abdomen and pelvic cavity; comparable to pericardium of the heart and pleura of the lungs.Visceral peritoneum lies against the organs, and the parietal peritoneum lies against the wall of the body cavity; the space between the two is known as the peritoneal cavity ## Intestinal Microbiome - Numbers of bacteria increase from proximal to distal GI tract - Highest in the colon - Multiple factors affect normal composition of bacterial flora - Genetics, diet, environmental, medications - Alert immune system to protect agains infection - Intestinal tract - Sterile at birth but colonized within a few hours - Number and diversity of bacteria decrease with aging - Bacteria in the stomach are relatively sparse - Acid kills ingested pathogens and inhibits bacterial growth. ## Intestinal Digestion and Absorption - Initiated in the stomach - Actions of gastric hydrochloric acid and pepsin - Continues in the proximal portion of the smal intestine - Action of pancreatic enzymes, intestinal enzymes, and bile salts - Carbohydrate breakdown - Proteins degraded - Fats emulsified - Nutrients absorbed by active transport, diffusion, or facilitated diffusion ## Accessory Organs of Digestion - **Liver:** split into lobules; hepatocytes are the functional cells of the liver; common bile duct - **Gallbladder:** sac-like organ that lies on the inferior surface of the liver; function is to store and concentrate bile between meals; begins to contract 30 minutes after eating under the influence of the vagus nerve and cholecystokinin - **Pancreas (EXOCRINE FUNCTION):** composed of acinar cells that secrete enzymes and networks of ducts that secrete alkaline fluids to assist in digestion ## The Gallbladder - **Anterior view** - Aorta, falciform ligament, left triangular ligament, porta hepatis, caudate lobe, left lobe, right lobe, proper hepatic artery, teres ligament, gallbladder, common bile duct, quadrate lobe, inferior vena cava - **Posterior view** - Coronary ligament, right hepatic duct, left hepatic duct, cystic duct, common hepatic duct, bile duct - **Gallbladder** - Gallbladder, duodenum ## Bile - Bile is an alkaline, bitter-tasting, yellowish green fluid that contains bile salts, cholesterol & bilirubin - Helps with absorption of fats. - Formed by hepatocytes in the liver and stored in the gallbladder. - **Bile** - Made in the Liver - Stored in the gallbladder - **Helps with** - Digestion - Absorption of fats - Excreation - **Composition** - Bile salts - Phospholipids - Cholesterol - Bile pigments (bilirubin) ## Liver Functions - Stores blood - Hemostatic functions - Synthesizes clotting factors (vitamin K) - Metabolism of nutrients - Fats - Proteins - Carbohydrates - Metabolic detoxification - Storage of minerals and vitamins ## Aging and the GI System ### Oral Cavity and Esophagus - Deterioration of tooth enamel; cavities more likely - Taste buds decline in number. - Sense of smell diminishes - Salivary secretion decreases - Dysphagia is more common. - Eating is less pleasurable, appetite is reduced, and food in not sufficiently chewed or lubricated, therefore swallowing is difficult. ### Stomach - Gastric motility, blood flow, and volume and acidic content of gastric juice may be reduced, particularly with gastric atrophy, gastric emptying is delayed. - Protective mucosal barrier decreases - higher risk for ulcer formation. ### Liver - Decreased hepatic regeneration; size and weight of liver decreases. - Ability to detoxify medications decreases. - Blood flow decreases, influencing the efficiency of medication metabolism. ### Intestines - Change in composition of intestinal microbiota; therefore increased risk susceptibility to disease. - Mucosal immunity decline; increased risk for infection and inflammation - Brain-gut axis may be disrupted, changes in GI motility, secretion, and absorption, as will as the person's appetite and nutritional status. - Villi become shorter and more convoluted; not able to repair themselves. - Absorption, motility and blood flow decrease. - Rectal muscle mass decreases and anal sphincter weakens - Constipation, fecal impaction, and incontinence may develop and are related to immobility and low-fibre diet. ### Pancreas and Gallbladder - Fibrosis, fatty acid deposits, and pancreatic atrophy. - Secretion of digestive enzymes decrease. - Increased prevalence of gallstones and cholecystitis.