Digestion, Absorption, Metabolism, and GI Disorders

Flashcards providing terminology and definitions covering human digestion, transport mechanisms, metabolic energy pathways, gut microbiota, and GI disorders.

Digestion

The process by which food is broken down into absorbable units (such as simple sugars, amino acids, and fatty acids).

Lumen

The hollow tube inside of the gastrointestinal (GI) tract where food digestion into nutrients takes place.

Mucosa

The inner layer of cells lining the GI tract lumen that is continuously replaced every $2\text{--}5$ days.

Mechanical Digestion

The physical disruption of food into smaller food particles, increasing surface area for chemical digestion.

Chemical Digestion

The enzymatic breakdown of chemical bonds between macronutrients occurring in the mouth, stomach, and intestines.

Mucus (GI Secretion)

A fluid secreted by mucosal cells lining the GI tract that moistens, lubricates, and protects the digestive tract.

Enzymes

Functional proteins made from amino acids that break down food into smaller compounds and are specific to each macromolecule.

Gastrointestinal Hormones

Signaling molecules released into the blood that regulate motility, digestive rate, and appetite.

Bolus

A mass of chewed food mixed with saliva in the mouth before swallowing.

Epiglottis

A flap of tissue that blocks the bolus from entering the trachea and lungs during swallowing, preventing choking and aspiration pneumonia.

Peristalsis

Rhythmic muscle contractions that propel food and chyme through the esophagus and GI tract.

Chyme

A semifuid mixture of food bolus and gastric juices formed by the churning action of the stomach.

Gastrin

A stomach hormone that stimulates the secretion of gastric juice and the release of chyme into the small intestine.

Cholecystokinin (CCK)

A hormone that prepares the intestines for nutrient digestion and triggers pancreatic enzyme release.

Small Intestine

The main site for digestion and absorption, approximately $20\text{ feet}$ long, featuring folds, villi, and microvilli.

Villi and Microvilli

Finger-like projections and cellular extensions lining the small intestine wall that drastically increase surface area for nutrient absorption.

Segmentation

Rhythmic constrictions of the small intestine that mix chyme with digestive secretions.

Absorption

The process by which digested nutrients pass through cells in the intestinal wall into circulation for body utilization.

Simple Diffusion

The passive movement of a substance across a membrane from high to low concentration without requiring ATP (e.g., fatty acids).

Osmosis

The passive diffusion of water across a membrane.

Facilitated Diffusion

Passive transport across a membrane moving down a concentration gradient that requires a carrier molecule (e.g., fructose).

Active Transport

Movement of nutrients across a membrane that requires cellular energy ($\text{ATP}$) and a carrier molecule (e.g., glucose, amino acids).

Capillaries (GI)

Microscopic blood vessels that absorb water-soluble nutrients from absorptive cells and route them to the liver via the hepatic portal vein.

Lacteals

Specialized lymphatic vessels in the small intestine that absorb fat-soluble nutrients into the lymphatic system.

Colon

The main part of the large intestine that absorbs water, ferments dietary fiber, forms feces, and harbors healthy vitamin-producing bacteria.

Liver

The master metabolic regulator that produces bile, synthesizes blood proteins and cholesterol, stores/utilizes nutrients, and detoxifies compounds.

Pancreas

An accessory organ with exocrine function (secreting bicarbonate, amylase, protease, and lipase) and endocrine function (secreting insulin and glucagon).

Peyer's Patches

Nodes of immune cells embedded in the GI mucosa that protect against invading pathogens.

Metabolism

The sum of chemical processes occurring within a living organism to maintain life.

Adenosine Triphosphate (ATP)

The high-energy phosphate compound that serves as the universal energy currency for cellular metabolism.

Mitochondria

The membrane-bound cellular organelle responsible for aerobic energy and ATP production.

Glycolysis

An anaerobic metabolic pathway in the cytosol that breaks down glucose to generate a small amount of ATP for short-term needs.

Citric Acid Cycle (TCA / Krebs Cycle)

An aerobic pathway in the mitochondria that oxidizes fatty acids and breakdown products of glucose and amino acids to yield high volumes of ATP.

Oxidative Phosphorylation

The mitochondrial process where oxygen drives the Electron Transport Chain (ETC) to produce major quantities of ATP.

Microorganisms (GI)

A population of helpful and harmful microbes (approx. 100 trillion) populating the GI tract, mostly in the colon.

Dysbiosis

A state of low diversity in gut microbiota leading to the overgrowth of unhealthy or pathogenic species.

Food Allergies

An immune system reaction to non-harmful protein antigens (allergens) in food.

Major Food Allergens

The nine food groups responsible for the majority of allergic reactions: milk, eggs, fish, crustacean shellfish, tree nuts, peanuts, wheat, soy, and sesame.

Antigen

A unique sequence of amino acids recognized as foreign by the immune system, inducing antibody production.

Celiac Disease

An inherited autoimmune disorder where exposure to gluten causes immune-mediated damage and destruction of small intestinal villi.

Gastroesophageal Reflux Disease (GERD)

A condition resulting from the failure of the lower esophageal sphincter to prevent stomach acid from flowing back into the esophagus.

Peptic Ulcers

Sores formed in the mucosal lining of the esophagus, stomach, or small intestine due to erosion by acid and pepsin, frequently caused by Helicobacter pylori or NSAIDs.

Diarrhea

Frequent, watery stools occurring when intestinal contents move too rapidly through the large intestine for adequate water absorption.

Constipation

Infrequent passage of hard, dry stools, commonly caused by dehydration, low fiber intake, inactivity, or medications.

Gallstones

Small calcified deposits of cholesterol and bile that accumulate in the gallbladder and can block the bile ducts.