Anatomy & Physiology (Digestive System)

Ingestion

The process of taking food, drink, or another substance into the body by swallowing or absorbing it.

Digestion

The mechanical and chemical breakdown of food into molecules small enough for absorption.

Absorption

The process by which nutrient molecules pass through the wall of the digestive system into the blood.

Elimination

The removal of indigestible wastes and undigested food from the body.

Assimilation

The usage of absorbed nutrient molecules by body cells for energy, growth, and repair.

Alimentary Canal

The continuous muscular tube of the digestive system stretching from the mouth to the anus.

Accessory Organs

Digestive organs that assist in breakdown but are not part of the continuous alimentary canal.

Mechanical Digestion

The physical breakdown of large food pieces into smaller ones without altering chemical composition.

Chemical Digestion

The enzymatic breakdown of complex food molecules into their simpler chemical building blocks.

Peristalsis

Alternating waves of smooth muscle contraction and relaxation that propel food through the tract.

Mastication

The mechanical process of chewing food in the mouth to prepare it for swallowing.

Deglutition

The physiological process of swallowing food.

Deciduous Teeth

The first set of temporary teeth in humans, numbering 20 in total.

Permanent Teeth

The second and final set of human teeth, numbering 32 in total.

Cusps

The raised, pointed projections on the chewing surfaces of premolar and molar teeth.

Enamel

The extremely hard, calcified substance covering and protecting the crown of a tooth.

Dentin

The hard, bone-like tissue making up the bulk of a tooth beneath the enamel.

Gingiva

The soft tissue lining the mouth that surrounds the teeth, commonly called the gum.

Cementum

A specialized calcified substance covering the outer surface of the root of a tooth.

Periodontal Ligament

The fibrous connective tissue structure that anchors the tooth root into the alveolar bone.

Apical Foramen

The opening at the tip of a tooth root through which nerves and blood vessels enter.

Serous Saliva

Watery saliva containing digestive enzymes, primarily amylase, for chemical breakdown.

Mucous Saliva

Thick, viscous saliva that acts primarily as a lubricant for swallowing.

Parotid Glands

The largest pair of salivary glands, located in front of and below each ear.

Submandibular Glands

Salivary glands located along the medial surface of the mandible in the floor of the mouth.

Sublingual Glands

The smallest pair of salivary glands, located directly beneath the tongue.

Epiglottis

The elastic cartilage flap that covers the laryngeal inlet during swallowing to prevent choking.

Esophagus

A muscular tube about 25 cm long connecting the pharynx to the stomach.

Rugae

The large folds in the mucous membrane lining of the stomach that allow for expansion.

Assimilation

The process where cells absorb and use molecules from digested food.

Alimentary Canal vs. Accessory Organs

Alimentary canal forms the continuous food tube; accessory organs assist digestion externally.

Mechanical vs. Chemical Digestion

Mechanical physically breaks food down; chemical uses enzymes to break covalent bonds.

Peristalsis vs. Segmental Contraction

Peristalsis propels food forward; segmental contractions mix food with digestive juices.

Deciduous vs. Permanent Teeth

Humans have 20 temporary deciduous teeth and 32 permanent adult teeth.

Serous vs. Mucous Saliva

Serous saliva contains digestive enzymes; mucous saliva acts primarily as a lubricant.

Hard Palate vs. Soft Palate

Hard palate is the bony anterior roof; soft palate is the muscular posterior roof.

Epiglottis Function

Prevents choking by folding over the larynx during swallowing to block food.

Stomach Mucosa Protection

Mucous cells secrete alkaline mucus to prevent self-digestion by hydrochloric acid.

Pepsinogen Activation

Hydrochloric acid (HCl) converts inactive pepsinogen from chief cells into active pepsin.

Vagus Nerve (CN X) in Digestion

Provides parasympathetic innervation to initiate stomach secretions and motility.

Duodenum, Jejunum, and Ileum Lengths

Duodenum is 25 cm; jejunum is 2.5 m; ileum is 3.5 m.

Small Intestine Gradient Changes

Diameter, wall thickness, circular folds, and villi count decrease from duodenum to ileum.

Peyer's Patches Location

Lymphoid tissue aggregates located exclusively in the mucosa of the ileum.

Endocrine vs. Exocrine Pancreas

Endocrine secretes hormones (insulin/glucagon); exocrine secretes digestive enzymes via acinar cells.

Bicarbonate Secretion Function

Neutralizes acidic stomach chyme in the duodenum, protecting mucosa and activating pancreatic enzymes.

Bile Production vs. Storage

The liver produces bile; the gallbladder stores and concentrates it.

Bile Salts Function

Emulsify large fat globules into smaller droplets to increase lipase efficiency.

Large Intestine vs. Small Intestine Dimensions

Large intestine is shorter (~5 feet vs 20 feet) but wider in diameter.

Teniae Coli

Three longitudinal bands of smooth muscle that bunch the large intestine into haustra.

Visceral vs. Parietal Peritoneum

Visceral covers the abdominal organs; parietal lines the abdominal cavity wall.

Gastric vs. Duodenal Ulcers

Gastric ulcers occur in the stomach; duodenal ulcers occur in the first part of small intestine.

Squamous Cell Carcinoma vs. Adenocarcinoma (Esophagus)

Squamous arises from epithelial lining; adenocarcinoma arises from glandular cells, often due to GERD.

Lactose Intolerance Mechanism

Deficiency of lactase prevents breakdown of lactose into glucose and galactose.

Hepatitis B vs. Hepatitis C Transmission

Hep B spreads via bodily fluids/sex/needles; Hep C spreads primarily via contaminated blood.

Hepatitis D Requirement

Cannot replicate or cause infection without the presence of active Hepatitis B.

Diverticulosis vs. Diverticulitis

Diverticulosis is the presence of asymptomatic pouches; diverticulitis is the painful inflammation of those pouches.

Crohn's Disease vs. Ulcerative Colitis

Crohn's affects any part of the GI tract transmurally; colitis is restricted to colon mucosa.

Celiac Disease Mucosal Pathology

Autoimmune reaction to gluten leads to flattening and destruction of villi and microvilli.

Assimilation

The usage of absorbed nutrient molecules by body cells for energy and growth.

Peristalsis

Gravity-independent, wave-like smooth muscle contractions that propel food along the digestive tract.

Mastication

The mechanical process of chewing food to increase its surface area in the mouth.

Deglutition

The physiological process of swallowing food to move it into the esophagus.

Airway Protection During Swallowing

The soft palate elevates to block the nasal cavity while the epiglottis seals the larynx.

Pepsin Activation Mechanism

Inactive pepsinogen secreted by chief cells is converted into active pepsin by hydrochloric acid.

Gastric Acid Production

Parietal cells in the stomach mucosa synthesize and secrete hydrochloric acid (HCl).

Vagus Nerve (CN X) Role in Digestion

Triggers the neurological initiation of gastric secretions and motility in the stomach.

Segmental Contractions

Non-propulsive, localized contractions in the small intestine that mix chyme with digestive enzymes.

Bile Emulsification Mechanism

Bile salts break large fat droplets into smaller micelles, increasing surface area for lipase.

Pancreatic Neutralization Process

Hydrogen carbonate ions secreted by the pancreas neutralize acidic chyme entering the duodenum.

Large Intestine Water Absorption

Osmotic gradient shifts pull water and salts from indigestible residue back into the bloodstream.

H. pylori Ulcer Pathogenesis

Bacteria degrade the protective mucus lining, exposing underlying gastric cells to corrosive stomach acid.

NSAID-Induced Ulcer Mechanism

NSAIDs inhibit prostaglandin synthesis, reducing protective mucus and bicarbonate secretion in the stomach.

Lactose Intolerance Biochemical Mechanism

Lacking lactase, undigested lactose undergoes bacterial fermentation in the colon, producing gas and acids.

Hepatitis B Progression

Chronic viral inflammation leads to hepatocyte death, which is replaced by non-functional scar tissue (cirrhosis).

Appendicitis Diagnostic Test

Applying and releasing pressure at McBurney's point triggers rebound tenderness, indicating localized peritonitis.

Diverticulitis Fistula Formation

Severe inflammation erodes diverticula walls, creating abnormal passages between the colon and bladder or vagina.

GERD Pathophysiology

The lower esophageal sphincter (LES) fails to close tightly, allowing gastric acid to reflux upward.

Crohn's Disease Autoimmune Attack

The immune system mistakenly attacks the GI tract wall, causing deep, transmural inflammation.

Celiac Disease Villous Atrophy

Gluten ingestion triggers an autoimmune reaction that flattens and destroys small intestinal villi.

Colorectal Cancer Metastasis Path

Cancer cells break into the venous system, traveling via the portal vein to seed the liver.

Diarrhea Defense Mechanism

The gut accelerates motility to rapidly flush out pathogens and toxins before absorption occurs.

Bile Concentration Process

The gallbladder actively absorbs water and electrolytes from stored bile to increase its potency.

Incisors vs. Molars Function

Incisors cut food with sharp edges; molars grind food with broad, flat crowns.

Serous vs. Mucous Saliva

Serous saliva provides enzymatic breakdown (amylase); mucous saliva provides lubrication for swallowing.

Stomach Volume Expansion

Rugae folds flatten out, allowing the stomach wall to expand without increasing internal pressure.

Small Intestine Surface Area Enhancement

Circular folds, villi, and microvilli work together to maximize the area available for absorption.

Fecal-Oral Transmission Route

Pathogens from infected feces contaminate food or water, which is then ingested by another host.

Gravity-Independent Transport (Example)

The ability to swallow food and have it reach the stomach even when hanging upside down.

Mastication (Application)

The mechanical process of chewing food to increase its surface area for chemical digestion.

Choking Mechanism (Clinical)

Occurs when the epiglottis fails to cover the trachea, allowing food or liquid into the airway.

Stomach Volume Expansion (Mechanism)

Rugae folds flatten out, allowing the stomach to stretch and accommodate a large meal.

Pepsin Activation (Process)

Inactive pepsinogen is converted to active pepsin by the highly acidic HCl in the stomach.

Mucous Cells (Protective Function)

Prevent the stomach from digesting itself by secreting a thick, alkaline mucus barrier.

Vagus Nerve Stimulation (Digestive Response)

Triggers the brain to initiate gastric secretions and motility before food even enters the stomach.

Segmental Contractions (Function)

Non-propulsive mixing movements in the small intestine that slosh chyme back and forth to maximize absorption.

Bile Emulsification (Action)

Bile salts break down large fat globules into tiny droplets, increasing surface area for lipase.

Pancreatic Hydrogen Carbonate (Role)

Neutralizes highly acidic chyme entering the duodenum, protecting the mucosa and optimizing enzyme function.

Appendix (Modern Bacterial Reservoir)

Repopulates the large intestine with beneficial gut bacteria after a diarrheal illness.

H. pylori Ulcer Mechanism

Bacteria degrade the protective mucus lining of the stomach, exposing cells to corrosive gastric acid.

NSAID-Induced Ulcers (Cause)

Inhibition of prostaglandins, which normally promote mucus production and blood flow in the stomach wall.