Human Digestive System Flashcards

Human Digestive System

Overview

The human digestive system is responsible for the physical and chemical breakdown of food, enabling absorption into the bloodstream for use by body cells and tissues. It comprises the alimentary canal and accessory organs.

Alimentary Canal

Mouth (Buccal Cavity)

  • Receives food.

  • Food is tasted and physically broken down by teeth.

Teeth

  • Special structures that physically break down food through chewing and grinding (mastication).

Tongue

  • Muscular organ.

  • Contains taste buds for sweet, salty, sour, and bitter sensations.

  • Aids in chewing and swallowing food.

Hard Palate

  • Bony structure forming the roof of the mouth.

  • Separates the mouth from the nasal cavity.

Soft Palate

  • Located behind the hard palate.

  • Separates the mouth from the nasopharynx.

Salivary Glands

  • Produce saliva, which lubricates the mouth during speech and chewing.

  • Moistens food for easy swallowing.

  • Saliva contains salivary amylase, an enzyme that begins the chemical breakdown of carbohydrates (starches) into sugars.

  • Types: sublingual, submandibular, parotid glands.

Pharynx (Throat)

  • Carries both air and food.

  • Air goes to the trachea; food goes to the esophagus.

  • The epiglottis closes over the larynx during swallowing to prevent food from entering the respiratory tract.

Esophagus

  • Muscular tube dorsal to the trachea.

  • Receives food from the pharynx and carries it to the stomach.

  • Peristalsis: rhythmic, wavelike, involuntary muscle movements that move food forward.

Stomach

  • Receives food from the esophagus.

  • Rugae: folds in the mucous membrane lining of the stomach that disappear as the stomach fills.

  • Cardiac Sphincter: circular muscle between the esophagus and stomach that closes after food enters to prevent reflux.

  • Pyloric Sphincter: circular muscle between the stomach and small intestine that keeps food in the stomach until it is ready to enter the small intestine.

  • Food remains in the stomach for 1-4 hours, during which it is converted into a semifluid material called chyme by gastric juices.

  • Gastric Juices:

    • Contain hydrochloric acid (HCl) and enzymes.

    • Hydrochloric Acid:

      • Kills bacteria.

      • Facilitates iron absorption.

      • Activates pepsin.

    • Enzymes:

      • Lipase: starts the chemical breakdown of fats.

      • Pepsin: starts the chemical breakdown of proteins.

      • Rennin: aids in the digestion of milk (found in infants only).

Small Intestine

  • Receives food (chyme) from the stomach.

  • Approximately 20 feet long and 1 inch in diameter.

    • Duodenum: first 9-12 inches; bile (from the gallbladder and liver) and pancreatic juices enter here.

    • Jejunum: middle 8 feet; absorption takes place here.

    • Ileum: final 12 feet; some absorption occurs here; connects with the large intestine at the cecum.

Processes in the Small Intestine

  • Digestion is completed.

  • Products of digestion are absorbed into the bloodstream for use by body cells.

  • Intestinal juices contain enzymes to break down sugars, fats, and proteins.

  • Villi: fingerlike projections lining the walls of the small intestine.

    • Contain blood capillaries and lacteals.

    • Blood capillaries absorb digested nutrients and carry them to the liver, where they are stored or released into general circulation.

    • Lacteals absorb most of the digested fats.

  • Remaining materials: wastes, indigestible materials, and excess water.

Large Intestine

  • 5 feet long, 2 inches in diameter.

  • Absorbs water and any remaining nutrients.

  • Stores indigestible materials before elimination.

  • Synthesizes and absorbs some B and K vitamins via bacteria.

  • Transports waste products out of the alimentary canal.

  • Sections: cecum (with appendix) → colon (ascending, transverse, descending, sigmoid) → rectum → anus.

Rectum

  • 6-8 inches long.

  • Storage area for indigestibles and waste.

Anus

  • End of the anal canal, right after the rectum.

  • Opening through which fecal material/stool is expelled.

Accessory Organs

Liver

  • Located under the diaphragm, in the right upper quadrant (RUQ) of the abdomen.

  • Secretes bile to emulsify fats in the digestive tract (making them water-soluble for absorption).

  • Stores iron and some vitamins.

  • Detoxifies substances like alcohol and pesticides.

  • Destroys bacteria taken into the blood from the intestines.

Gallbladder

  • Small muscular sac located under the liver, attached by connective tissue.

  • Stores and concentrates bile.

Pancreas

  • Glandular organ located behind the stomach.

  • Produces pancreatic juices containing enzymes to digest food.

  • Produces insulin, which is secreted into the bloodstream to regulate the metabolism of carbohydrates, converting glucose (sugar) to energy.

Appendix

  • Vestigial organ with uncertain function.

  • Theories:

    • Nature preserve for beneficial bacteria to "reboot" the digestive system after diarrheal illnesses.

    • Plays a role in the immune system, helping produce antibodies.

GI Diseases & Abnormal Conditions

Appendicitis

  • Acute inflammation of the appendix, usually from obstruction and infection.

  • Symptoms: abdominal pain in RUQ, nausea, vomiting, mild fever, elevated white blood cell count.

  • Ruptured Appendix: infectious material spills inside the body, leading to a very serious condition.

  • Treatment: appendectomy (with major antibiotics if ruptured).

Cholecystitis

  • Inflammation of the gallbladder.

  • Symptoms: indigestion, nausea, vomiting, pain starting under the ribcage radiating to the right shoulder (usually after eating fatty foods).

  • Treatment: low-fat diet, cholecystectomy.

Cirrhosis

  • Chronic destruction of liver cells with the formation of fibrous connective and scar tissue.

  • Causes: hepatitis, chemical toxins, malnutrition associated with alcoholism.

  • Symptoms: liver enlargement, anemia, nosebleeds, nausea, vomiting, indigestion, jaundice.

  • Treatment: prevent further damage to the liver (proper nutrition, vitamin supplements, avoiding alcohol).

  • Liver failure can lead to disorientation, hallucinations, coma, and death.

Colon Cancer

  • Cancerous cells grow in the colon; may metastasize.

  • Risk Factors: family history of colon cancer in a first-degree relative, polyps in the colon, 3 or more alcoholic drinks daily, smoking, overweight, sedentary lifestyle, high-fat and low-fiber diet.

  • Symptoms: blood in stool, changes in bowel habits (diarrhea, constipation), pain during bowel movements, continuous urges to defecate.

  • Treatment: surgical removal of the affected area, chemotherapy, radiation.

Constipation

  • Fecal material remains in the colon too long, causing excessive reabsorption of water, resulting in difficult-to-eliminate feces.

  • Causes: poor bowel habits, low-fiber diet, some digestive diseases, chronic laxative use.

  • Treatment: high-fiber diet, exercise, adequate fluids.

  • Frequent laxative use may be habit-forming and lead to chronic constipation.

Diabetes

  • Inability to manage glucose in the blood due to insufficient insulin production or insensitivity to insulin.

  • Risk factors: overweight, sedentary lifestyle, family history, hypertension (HTN).

  • Symptoms: increased urine output, excessive thirst, hunger, fatigue, slow-healing wounds, tingling/numbness in feet/toes.

  • Can lead to blindness and kidney failure (due to damage to small vessels); 7th leading cause of death in the US.

Diarrhea

  • Frequent watery stools.

  • Causes: infection, stress, diet, irritated colon, toxic substances.

  • Treatment: eliminate the cause, provide adequate fluid intake, modify diet.

  • Can be extremely dangerous in infants and small children due to excessive fluid loss.

Gastroenteritis

  • Inflammation of the mucous membrane lining the stomach and intestinal tract.

  • Causes: food poisoning, infections, toxins.

  • Symptoms: abdominal cramping, nausea, vomiting, fever, diarrhea.

  • Treatment: rest, increased fluid intake; severe cases may need antibiotics, IV fluids, medications to slow peristalsis.

Hemorrhoids

  • Painful, dilated/varicose veins of the rectum and/or anus.

  • Causes: straining to defecate, constipation, pressure during pregnancy, insufficient fluid intake, laxative abuse, prolonged sitting/standing.

  • Symptoms: pain, itching, bleeding.

  • Treatment: high-fiber diet, increased fluid intake, stool softeners, warm/moist compresses, surgery if necessary (hemorrhoidectomy).