Digestive System Flashcards

Overview of the Digestive System

• Nomenclature and Length: The digestive system is referred to as the alimentary canal, digestive tract, or gastrointestinal (GI) tract.

  • It extends from the mouth to the anus.

  • The total length of the tract is approximately $9\,meters$ ($29\,feet$).

• Primary Functions: The system is involved in three major processes:

  • Digestion of nutrients.

  • Absorption of nutrients.

  • Metabolism of nutrients.

• Organ Classification:

  • Main Organs: Mouth, pharynx, esophagus, stomach, small intestine, large intestine, rectum, and anal canal.

  • Accessory Organs: Teeth, tongue, salivary glands, liver, gallbladder, pancreas, and vermiform appendix.

Anatomy of the Digestive Tract Wall

• The Four Layers: The wall of the digestive tract consists of four distinct tissue layers:

  • Mucosa (Mucous Membrane): The innermost layer, which may contain various folds and glands.

  • Submucosa: A connective tissue layer containing blood vessels, nerves (nerve plexus), glands, and ducts.

  • Muscularis: The muscle layer responsible for motility, consisting of two sub-layers:

    • Circular muscle layer.

    • Longitudinal muscle layer.

  • Serosa: The outermost layer composed of connective tissue and visceral peritoneum. It is continuous with the mesentery.

• Key Landmarks:

  • Mesentery: A fold of peritoneal tissue that anchors the digestive organs and carries nerves and blood vessels.

  • Lymphoid Tissue: The wall includes solitary lymphoid nodules and aggregated lymphoid nodules for immune defense.

The Mouth (Oral Cavity)

• General Structure: A hollow chamber defined by a roof, a floor, and walls.

• The Roof of the Mouth:

  • Hard Palate: Formed by the maxillary and palatine bones.

  • Soft Palate: An arch-shaped muscle that separates the mouth from the pharynx.

  • Uvula: A downward projection of the soft palate. Together with the soft palate, it prevents food and liquid from entering the nasal cavities during swallowing. It also assists in speech and swallowing (deglutition).

• The Floor of the Mouth:

  • Tongue: Formed by muscle tissue.

  • Lingual Frenulum: A fold of mucous membrane that anchors the tongue to the floor of the mouth.

  • Papillae: Small elevations on the mucosa of the tongue.

  • Taste Buds: Sensory structures found within many of the papillae.

• Teeth:

  • Types: Incisors, cuspids (canines), bicuspids (premolars), and tricuspids (molars).

  • Deciduous Teeth (Baby or Primary Teeth):

    • Total set: $20$ teeth.

    • The first tooth typically erupts at about $6\,months$ of age.

    • The complete set is usually in place by age $2\,years$.

  • Permanent Teeth:

    • Total set: $32$ teeth in most adults (though $28$ is a normal variation for some).

    • First permanent tooth erupts at approximately $6\,years$ of age.

    • The set is completed between the ages of $17$ and $24\,years$.

  • Tooth Anatomy:

    • Crown: The visible, exposed part. It is made of bony dentin and covered by hard enamel. The biting surface features elevations called cusps.

    • Neck: The narrow portion surrounded by pink gingiva (gum) tissue. It is covered in cementum.

    • Root: Fits into the jaw socket and is supported by the fibrous periodontal membrane and periodontal ligament.

    • Pulp Cavity: Contains nerves and blood vessels within the center of the tooth, extending into the root canal.

Salivary Glands

• General Characteristics: There are three pairs of salivary glands located outside the GI tract that convey secretions via ducts into the lumen.

  • They secrete approximately $1\,dm^3$ of saliva per day.

  • Saliva Components: Contains salivary amylase, which initiates the chemical digestion of carbohydrates.

• Specific Glands:

  • Parotid Glands: The largest pair, located in front of the ear at the angle of the jaw. The ducts open into the mouth opposite the second molars. These glands become inflamed during mumps.

  • Submandibular Glands: Ducts open on either side of the lingual frenulum.

  • Sublingual Glands: The ducts open directly into the floor of the mouth.

Clinical Conditions of the Mouth and Teeth

• Oral Infections and Cancer:

  • Leukoplakia: A precancerous condition involving white patches in the mouth tissue.

  • Snuff Dipper’s Pouch: A condition caused by chronic use of chewing tobacco.

  • Squamous Cell Carcinoma: The most common form of mouth cancer.

• Tooth and Gum Diseases:

  • Dental Caries: Tooth decay resulting in a "cavity." Infections can spread to the blood or adjacent tissues. Damaged teeth are replaced by implants or dentures.

  • Gingivitis: Inflammation/infection of the gums, often due to poor hygiene, but can be a complication of pregnancy, diabetes, or vitamin deficiency.

  • Thrush (Oral Candidiasis): Caused by the yeastlike fungus $Candida\,albicans$. It presents as "cheesy" looking exudate that itches and bleeds. It is common in immunosuppressed individuals (e.g., those with AIDS) or following antibiotic therapy.

  • Periodontitis: Inflammation of the periodontal membrane; often a progression of untreated gingivitis and the leading cause of adult tooth loss.

• Congenital Defects:

  • Cleft Lip and Cleft Palate: The most common congenital mouth defects, caused by the failure of structures to fuse during embryonic development. They can occur independently or together.

The Pharynx and Esophagus

• Pharynx (Throat):

  • A muscular tube lined with mucous membrane.

  • Serves both the respiratory and digestive systems.

  • Segments: Nasopharynx, Oropharynx, and Laryngopharynx.

  • Tonsils: Includes the pharyngeal tonsil (adenoids), palatine tonsil, and lingual tonsil.

• Esophagus:

  • A muscular, mucus-lined tube measuring approximately $25\,cm$ ($10\,inches$) in length.

  • Connects the pharynx to the stomach.

  • Sphincters:

    • Upper Esophageal Sphincter (UES).

    • Lower Esophageal Sphincter (LES): Also known as the cardiac sphincter, it prevents backflow from the stomach.

• Esophageal Disorders:

  • Gastroesophageal Reflux Disease (GERD): Backflow of acidic stomach contents causing heartburn and indigestion. Severe GERD can cause asthma, chest pain, or bleeding.

  • Barrett Esophagus: A precancerous condition resulting from chronic, untreated GERD irritation.

  • Hiatal Hernia: A condition where a portion of the stomach protrudes through the diaphragm, often causing GERD symptoms.

The Stomach

• Anatomy and Physical Properties:

  • Located in the upper abdominal cavity under the diaphragm.

  • Size is roughly that of a large sausage when empty; it expands significantly after meals.

  • Divisions: Fundus (top portion), Body (central part), and Pylorus (lower narrow section).

  • Rugae: Folds in the mucous membrane lining that appear when the stomach is empty.

  • Sphincters: The pyloric sphincter closes the opening to the small intestine to retain food for digestion.

• Function: Muscular walls contract to mix food with gastric juice and hydrochloric acid ($HCl$), turning it into a semi-solid mixture called chyme.

• Gastroenterology and Clinical Signs:

  • Gastroenterology: The study of the stomach and intestines.

  • Common Symptoms: Gastritis (inflammation), anorexia (loss of appetite), nausea (upset stomach), and emesis (vomiting).

• Specific Stomach Conditions:

  • Pylorospasm: Abnormal spasms of the pyloric sphincter, common in infants.

  • Pyloric Stenosis: An obstructive narrowing of the pyloric opening.

  • Ulcers: Open wounds caused by gastric acid. They are often associated with $Helicobacter\,pylori$ infection and the use of Nonsteroidal Anti-inflammatory Drugs (NSAIDs). Treatment typically involves "triple therapy."

  • Stomach Cancer: Linked to $H.\,pylori$ infection, excessive alcohol consumption, preserved foods, and chewing tobacco.

The Small Intestine

• Anatomy:

  • Sections: Duodenum, Jejunum, and Ileum.

  • Lining Structures:

    • Plicae: Circular folds in the mucous membrane.

    • Villi: Microscopic finger-shaped projections that increase surface area. They contain blood capillaries and lymph capillaries called lacteals.

    • Microvilli: A "brush border" of even smaller projections on epithelial cells.

• Disorders:

  • Enteritis: Inflammation of the intestine.

  • Gastroenteritis: Inflammation affecting both the stomach and intestines.

  • Malabsorption Syndrome: Failure to absorb nutrients, leading to symptoms like abdominal bloating, cramps, anemia, and weight loss.

  • Maldigestion: A deficit in bile salts or digestive enzymes that hinders nutrient breakdown.

The Liver and Gallbladder

• Liver Properties:

  • The body's largest gland.

  • Occupies the upper right section of the abdominal cavity.

  • Classified as an exocrine gland because it secretes bile.

• Biliary Duct System:

  • Hepatic Ducts: Drain bile from the liver.

  • Cystic Duct: Carries bile into and out of the gallbladder.

  • Common Bile Duct: Formed by the union of the hepatic and cystic ducts; it empties into the duodenum.

• Gallbladder:

  • Located on the undersurface of the liver.

  • Functions: Concentrates and stores bile.

• Conditions:

  • Gallstones (Calculi): Made of crystallized bile pigments and calcium salts.

  • Cholelithiasis: The condition of having gallstones.

  • Cholecystitis: Inflammation of the gallbladder.

  • Jaundice: Skin yellowing caused by bile duct obstruction.

  • Hepatitis: Liver inflammation characterized by jaundice, liver enlargement, and dark urine. Causes include toxins, bacteria, parasites, and viruses (Hepatitis A, B, and C).

  • Cirrhosis: Degeneration of liver tissue where healthy tissue is replaced by fibrous and fatty tissue.

  • Portal Hypertension: High blood pressure in hepatic portal veins due to liver obstruction; can lead to systemic varicosities.

The Pancreas

• Location and Dual Function:

  • Located behind the stomach.

  • Exocrine Function: Secretes pancreatic juice (containing enzymes) into ducts that empty into the duodenum.

  • Endocrine Function: Pancreatic islets (of Langerhans) secrete the hormones glucagon and insulin directly into the blood.

• Conditions:

  • Pancreatitis: Inflammation; acute cases occur when blocked ducts cause pancreatic enzymes to digest the gland itself.

  • Cystic Fibrosis: Thick secretions block the flow of pancreatic juice.

  • Pancreatic Cancer: A very serious condition that is fatal in most cases.

The Large Intestine and Appendix

• Dimensions and Sections:

  • Total length is approximately $1.5\,meters$.

  • Divisions: Cecum, Colon (Ascending, Transverse, Descending, Sigmoid), Rectum, and Anal Canal.

  • Anus: The external opening.

• The Vermiform Appendix:

  • A blind tube attached to the cecum with no known digestive function in humans.

  • Appendicitis: Inflammation or infection of the appendix. It is the most common acute abdominal condition requiring surgery, affecting $7\%$ to $12\%$ of people under $30\,years$ old. Rupture can spread infection (peritonitis).

• Conditions of the Large Intestine:

  • Motility Disorders: Diarrhea (increased motility; risk of dehydration) and Constipation (decreased motility).

  • Diverticulitis: Inflammation of abnormal outpouchings called diverticula.

  • Colitis: General term for inflammatory conditions of the large intestine.

  • Colorectal Cancer: A common malignancy linked to colonic polyps, age, high-fat/low-fiber diets, and genetics.

The Peritoneum and Its Extensions

• Structure: A large serous membrane sheet.

  • Parietal Layer: Lines the abdominal cavity.

  • Visceral Layer: Covers the abdominal organs.

  • Peritoneal Space: The fluid-filled space between the two layers.

  • Retroperitoneal Space: Contains organs like the pancreas, duodenum, and rectum which are outside the peritoneum.

• Extensions:

  • Mesentery: Attaches most of the small intestine to the posterior abdominal wall.

  • Greater Omentum: Known as the "lace apron," it hangs from the stomach and transverse colon over the intestines.

• Conditions:

  • Peritonitis: Inflammation resulting from infection or irritants (e.g., from a ruptured appendix).

  • Ascites: Abnormal fluid accumulation in the peritoneal space causing abdominal bloating.

Mechanisms of Digestion and Absorption

• Mechanical Digestion: Includes chewing (mastication), swallowing (deglutition), and peristalsis. These processes break food into particles, mix them with juices, and move them forward.

• Chemical Digestion: The breakdown of large molecules into smaller ones via digestive enzymes through the process of hydrolysis (adding water to break bonds).

• Carbohydrate Digestion:

  • Begins with salivary amylase in the mouth.

  • Pancreatic Amylase: Breaks starches into maltose in the small intestine.

  • Intestinal Enzymes: Maltase (maltose to glucose), Sucrase (sucrose to glucose), and Lactase (lactose to glucose).

• Protein Digestion:

  • Begins in the stomach with Pepsin.

  • Trypsin: A pancreatic enzyme that continues breakdown in the small intestine.

  • Peptidases: Intestinal enzymes that finish breaking proteins into amino acids.

• Fat Digestion:

  • Bile: Emulsifies fats (mechanical breakdown into tiny droplets; contains no enzymes).

  • Pancreatic Lipase: Chemically breaks emulsified fats into fatty acids and glycerol.

• Absorption:

  • The movement of digested food from the intestine into the blood or lymph.

  • The small intestine's lining uses Fractal Geometry (surfaces with complex, repeating bumps) to create a nearly limitless surface area for absorption.

List of Clinical and Pathological Sources Mentioned

• Regezi JA, Sciubba JJ, Pogrel MA: Atlas of Oral and Maxillofacial Pathology.

• Callen JP, Paller AS, Greer KE: Color Atlas of Dermatology.

• Grundy JR, Jones JG: A Color Atlas of Clinical Operative Dentistry.

• Emond RTD, Welsby PD, Rowland HAK: Colour Atlas of Infectious Diseases.

• Wilson SF, Giddens JF: Health Assessment for Nursing Practice.

• Greig JD, Garden OJ: Color Atlas of Surgical Diagnosis.

• Kumar V, Abbas AK, Fausto N: Robbins and Cotran Pathologic Basis of Disease.

• Heuman DM, Mills AS, McGuire HH: Gastroenterology.

• Zitelli BJ, Davis HW: Atlas of Pediatric Physical Diagnosis.

• Thompson JM, Wilson SF: Health Assessment for Nursing Practice.

• Swartz MH: Textbook of Physical Diagnosis.