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Structure and Function of the Digestive SystemChapter 38

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Gastrointestinal Tract Mouth Esophagus Stomach Small intestine Large intestine Rectum Anus

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Gastrointestinal Tract

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Gastrointestinal Tract Ingestion of food Propulsion of food and wastes from the mouth

to the anus Secretion of mucus, water, and enzymes Mechanical digestion of food particles Chemical digestion of food particles Absorption of digested food Elimination of waste products by defecation

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Gastrointestinal Tract Histology

Mucosa Submucosa Muscularis Serosa or adventitia

Enteric plexus Submucosal plexus Myenteric plexus Subserosal plexus

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Gastrointestinal Tract

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Mouth Reservoir for chewing and mixing of food

with saliva Taste buds

Salty, sour, bitter, and sweet Olfactory nerves Teeth

32 permanent teeth

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Salivary Glands Three pairs

Submandibular Sublingual Parotid

Saliva Water with mucus, sodium, bicarbonate, chloride,

potassium, and salivary α-amylase (carbohydrate digestion)

Controlled by sympathetic and parasympathetic fibers

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Swallowing Esophagus Peristalsis

Primary and secondary Upper esophageal sphincter Lower esophageal sphincter Phases

Oral and pharyngeal phases Esophageal phase

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Stomach The stomach is a hollow, muscular organ that

stores food, secretes digestive juices, mixes food with the juices, and propels partially digested food (chyme)

Muscle layers Longitudinal Circular Oblique

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Stomach Boundaries

Cardiac orifice Pyloric sphincter Pylorus

Functional areas Fundus Body Antrum

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Stomach

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Gastric Motility Swallowing Gastrin Cholecystokinin Motilin Secretin Gastric emptying

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Gastric Secretion The stomach secretes large volumes of gastric

juices Mucus Acid Enzymes Hormones Intrinsic factor Gastroferrin

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Gastric Secretion Gastric pits Gastric glands

Parietal cells Hydrochloric acid and intrinsic factor

Chief cells Pepsinogen

G cells Gastrin

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Gastric Secretion Gastric glands

Enterochromaffin-like cells Histamine

D cells Somatostatin

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Gastric Pits and Gastric Glands

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Gastric Secretion Phases of gastric secretion

Cephalic phase Gastric phase Intestinal phase

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Small Intestine 5 to 6 meters long Three segments

Duodenum Jejunum Ileum

Ileocecal valve

Peritoneum Peritoneal cavity

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Small Intestine Muscle layers

Outer—longitudinal Inner—circular

Mucosal folds (plica) Villi Microvilli

Brush border Lamina propria Lacteal

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Small Intestine

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Intestinal Digestion and Absorption Hydrochloric acid Pepsin Pancreatic enzymes Intestinal enzymes Bile salts

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Intestinal Digestion and Absorption Carbohydrates Proteins Fats Water Electrolytes

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Intestinal Digestion and Absorption

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Intestinal Digestion and Absorption

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Intestinal Digestion and Absorption

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Intestinal Motility The movements of the small intestine

facilitate both digestion and absorption Segmentation Peristalsis Ileogastric reflex Intestinointestinal reflex Gastroileal reflex

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Large Intestine Cecum Appendix Colon

Ascending Transverse Descending Sigmoid

Rectum Anus

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Large Intestine

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Large Intestine Ileocecal valve O’Beirne sphincter Internal anal sphincter External anal sphincter Taenia coli Haustra

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Gastrointestinal Absorption

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Intestinal Bacteria The environment of the stomach is relatively sterile

because of secreted stomach acid Bile acid secretion, motility, and antibody

production keeps bacterial numbers in the duodenum to a minimum

There is a low concentration of aerobes in the jejunum

Anaerobic bacteria are distal to the ileocecal valve Anaerobes are 95% of the fecal flora in the colon

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Accessory Organs of Digestion

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Accessory Organs of Digestion Liver

Lobes Separated and attached to the anterior abdominal wall

by the falciform ligament Right lobe

Caudate and quadrate lobes

Left lobe

Glisson capsule

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Liver

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Hepatic Portal Circulation

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Liver Liver lobules

Hepatocytes Lipocytes Sinusoids Bile canaliculi Common bile duct Major duodenal papilla (sphincter of Oddi)

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Liver Lobules

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Liver Kupffer cells Stellate cells Pit cells Disse space

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Secretion of Bile Bile is an alkaline, bitter-tasting, yellowish

green fluid that contains bile salts, cholesterol, bilirubin, electrolytes, and water

Bile is formed by hepatocytes and secreted into the bile canaliculi

Enterohepatic circulation Recycling of bile salts

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Enterohepatic Circulation

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Metabolism of Bilirubin Bilirubin is a by-product of the destruction of

aged red blood cells Bilirubin gives bile a greenish black color and

produces the yellow tinge of jaundice Unconjugated bilirubin Conjugated bilirubin Urobilinogen

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Metabolism of Bilirubin

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Vascular and Hematologic Liver Functions Blood storage Bacterial and foreign particle removal Synthesizes clotting factors Produces bile to absorb fat-soluble vitamins Metabolizes fats

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Vascular and Hematologic Liver Functions Metabolizes proteins Metabolizes carbohydrates Metabolic detoxification Storage of minerals and vitamins

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Gallbladder The gallbladder is a saclike organ that lies on

the inferior surface of the liver The function of the gallbladder is to store and

concentrate bile between meals The gallbladder holds about 90 mL of bile

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Exocrine Pancreas The exocrine pancreas is composed of acini

and networks of ducts that secrete enzymes and alkaline fluids to assist in digestion

Pancreatic duct Ampulla of Vater

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Exocrine Pancreas

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Exocrine Pancreas Secretions

Potassium, sodium, bicarbonate, magnesium, calcium, and chloride

Enzymes Trypsinogen, chymotrypsinogen, and

procarboxypeptidase Trypsin inhibitor Pancreatic α-amylase Pancreatic lipase

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Aging and the Digestive Function Tooth enamel and dentin wear down Teeth are lost Periodontal disease Gum recession Osteoporotic bone changes

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Aging and the Digestive Function Number of taste buds decline Sense of smell diminishes Salivary secretion decreases Decreased esophageal and gastric motility