• Histology: Nonkeratinized stratified squamous, minor glands, Mucosal immune cells.
• Anomalies: Cleft lip/palate, macroglossia, branchial cleft cysts.

• Aphthous Ulcers (Canker Sores): 40% pop. Shallow, erythematous rim. Cells: Mononuclear early -> Neutrophils (if infected). Triggers: stress, fever. Assoc: Celiac, Inflammatory Bowel Disease (IBD), Behcet. Self-limiting.
• Herpetic Stomatitis: HSV-1 > HSV-2. Dormant in trigeminal ganglia. Vesicles -> clear fluid -> shallow ulcers. Dx: Tzanck test shows intranuclear inclusions & multinucleated giant cells.
• Candidiasis (Thrush): Normal flora (50%). Assoc: DM, anemia, steroids/antibiotics. Signs: White, cheese-like pseudomembrane, easily scraped off, red base. Dx: Pseudohyphae positive on PAS stain.
• AIDS Lesions: Kaposi’s Sarcoma (HSV-8, 25%). Hairy Leukoplakia (EBV, white patches lateral tongue, CANNOT be scraped off, hyperkeratosis/acanthosis, NOT precancerous).

• Leukoplakia: White patch, epidermal thickening (hyperkeratosis). CANNOT be scraped off. Risk: tobacco, friction, alcohol, HPV. All are precancerous (3-6% SCC risk). Biopsy mandatory.
• Erythroplakia: Red velvety area. Intense subepithelial inflammation & vascular congestion. High atypia. 50% SCC risk.
• Squamous Cell Carcinoma (SCC): 90% of oral cancers. Sites: Lip > ant. floor > tongue > palate. Spread: submandibular, high jugular LNs. Mortality: 50% at 5 years.

• Sjogren’s Syndrome: Autoimmune. Causes Xerostomia (dry mouth) & Keratoconjunctivitis sicca (dry eyes). 90% females. 50% bilateral parotid. M/E: Lymphocytic infiltration & fibrosis. Dx: anti-SS-A & SS-B. High lymphoma risk.
• Sialolithiasis: Stones (Staph aureus, Strep viridans). Ductal obstruction by impacted food debris. Unilateral, major glands (Submandibular).
• Mucocele (Ranula): Most common. Ruptured duct -> mucin leakage. Lower lip fluctuant blue swelling (changes with meals). Pseudocyst (no epithelium, granulation tissue).
• Salivary Tumors (80% Parotid):
  • Pleomorphic Adenoma: Most common benign (65-80%). Mixed tumor. Penetrates capsule. 15-40% malignancy risk.
  • Warthin’s Tumor: Benign. Male smokers (Parotid). Cystic spaces + abundant lymphoid tissue. Arises from branchial cleft remnants.
  • Mucoepidermoid Carcinoma: Most common malignant (15%). Squamous + mucous cells. Lacks capsule.
  • Adenoid Cystic Carcinoma: Most aggressive, locally invasive.

• Symptoms: Dysphagia (swallowing difficulty), Heartburn (reflux), Hematemesis (vomiting blood), Melena (blood in stool).
• Atresia: No lumen (thin cord). Assoc: Tracheoesophageal fistula (aspiration pneumonia).

• Hiatal Hernia: Stomach sac above diaphragm. Sliding (95%) vs. Paraesophageal (rolling, strangulation risk). Assoc with GERD.
• Achalasia: Failure of Lower Esophageal Sphincter (LES) to relax.
  Triad: Aperistalsis, Partial LES relaxation, Increased LES basal tone.
  Cause: Absent myenteric ganglia. Secondary: Chagas disease (Trypanosoma cruzi). Risk: 5% develop SCC.
• Mallory-Weiss Syndrome: Longitudinal mucosal tears at GE junction. Due to severe vomiting in alcoholics. Heals completely.

• Esophageal Varices: Tortuous dilated veins due to Portal Hypertension (Liver Cirrhosis). Asymptomatic until rupture -> Massive hematemesis. 40% mortality.
• Esophagitis:
  1. GERD: Most common. M/E: Basal zone hyperplasia + intra-epithelial eosinophils/neutrophils.
  2. Candida: Gray-white pseudomembranes.
  3. Viral: HSV/CMV -> Intranuclear inclusions.

• Barrett’s Esophagus: GERD complication. Squamous replaced by Intestinal/Gastric Glandular Metaplasia (goblet cells) in distal esophagus. Pre-malignant -> ONLY precursor to Adenocarcinoma (30-40X risk).
• Squamous Cell Carcinoma (SCC) (80%): Middle 1/3. Risks: Smoking, alcohol, nitrites, Achalasia, Plummer-Vinson.
• Adenocarcinoma: Lower 1/3. Arises exclusively from Barrett's.

• Diaphragmatic Hernia: Abdominal contents in thorax -> Embryonic pulmonary hypoplasia (fatal).
• Pyloric Stenosis: Circular muscle hypertrophy. 2nd-3rd week of life. Projectile non-bilious vomiting, visible left-right peristalsis, firm ovoid mass. Rx: Pyloromyotomy.

• Definitions: Gastritis (Neutrophils present). Gastropathy (No inflammatory cells).
• Acute Gastritis: Transient. H+ back-diffusion. Causes: NSAIDs/Aspirin (25%), alcohol, burns, shock. Shows shallow blood-suffused erosions.
• Chronic H. pylori Gastritis (Type B): Most common. Antrum. Normal gastrin. M/E: Lymphocytes, Crypt abscesses, Intestinal metaplasia. Dx: Biopsy (Methylene blue), Urea breath. Complications: Ulcer, Cancer, MALToma.
• Chronic Autoimmune Gastritis (Type A): Body & Fundus. Autoantibodies against Parietal Cells. Result: Achlorhydria -> Hypergastrinemia. Lack of Intrinsic Factor -> Pernicious Anemia. 2-4% Carcinoma risk.
• Hypertrophic Gastritis: Enlarged rugae. Menetrier’s (protein-losing), Zollinger-Ellison (gastrinoma). Mimics cancer.

• Pathogenesis: Excess Gastric acid (HCl) & Pepsin. Linked to H. pylori, NSAIDs, smoking.
• Duodenal Ulcer (DU): M:F 3:1. H. pylori in 100%. High acid. Pain 1.5-3h post-meal, relieved by food. NO cancer risk.
• Gastric Ulcer (GU): H. pylori in 70%. Normal/low acid (low mucosal resistance). Pain 30m post-meal, NOT relieved by food. Associated with cancer (MUST biopsy all GUs).
• Ulcer Histology (4 Zones): Necrotic debris -> Active inflammation (neutrophils) -> Granulation -> Scar.
• Stress Ulcers: Curling’s (Burns). Cushing’s (High ICP/Brain trauma, vagal stim). Multiple, shallow, no chronic gastritis.

• Hyperplastic (Inflammatory): Most common (85%). NO malignant transformation.
• Adenomas (Neoplastic): 5%. Dysplastic. 50% cancer risk if >2 cm.

• 95% of gastric cancers. Early stage: Confined to mucosa/submucosa (regardless of LN status). Advanced: Beyond submucosa.
• Intestinal Type: From intestinal metaplasia. Exophytic/polypoid well-formed glands. Risks: H. pylori, Nitrites, smoked foods. Decreasing frequency. >50 yrs, M>F.
• Diffuse Type: Arises de novo. Signet-ring cells (mucin pushes nucleus). Diffuse infiltration creates Linitis Plastica (thick leathery stomach). Risks: E-cadherin mutation. Increasing frequency. Younger age (<50), M=F.
• Metastasis: Virchow’s Node (supraclavicular).

• MALToma: B-cell type (CD20+). Stomach is most common extranodal site.
• Pathogenesis: Driven by H. pylori antigenic stimulation (polyclonal -> monoclonal). Later becomes HP-independent via t(11;18) API2-MLT fusion.
• Diagnosis: Lymphoepithelial lesions. Good prognosis. Rx: Antibiotics.

• Meckel’s Diverticulum: Most common benign. Remnant of omphalomesenteric duct. Ileum. Heterotopic gastric mucosa causes bleeding/pain mimicking appendicitis.
• Hirschsprung’s Disease (Congenital Megacolon): Arrested neural crest migration -> Lack of Meissner's/Auerbach's ganglia in distal colon. Distal functional obstruction -> massive dilatation of normal proximal segment. Dx: Full-thickness biopsy of the NARROW (aganglionic) segment.

• Diarrhea Types: Secretory (toxins), Osmotic (lactose), Exudative (IBD/ulcers).
• Celiac Sprue (Gluten-Sensitive): Allergy to gliadin. HLA-DQ. CD4+ T-cells -> IFN-γ -> activates Intraepithelial Lymphocytes (IELs).
  M/E: Villous flattening/atrophy, Crypt elongation, IELs increase.
  Abs: Anti-tTG, Anti-endomysial. High risk: T-cell lymphoma.
• Tropical Sprue: Infectious. Follows diarrhea. Folic acid deficiency (Megaloblastic anemia). Rx: Tetracycline.
• Whipple’s Disease: Systemic (gut, CNS, joints). M/E: Lamina propria packed with PAS+ Macrophages containing Tropheryma whippelii.

• Ischemic Bowel Disease: Perfusion <50%. Target: Watershed areas (Splenic flexure & rectosigmoid).
  1. Transmural: Occlusive (SMA thrombus). Gangrene, perforation, 90% mortality.
  2. Mural/Mucosal: Non-occlusive (shock/heart failure). Inner layers only, intact serosa.
• Angiodysplasia: Tortuous submucosal vessels. Cecum/Right colon. Elderly. Major cause of lower GI bleed. NOT precancerous.
• Hemorrhoids (Piles): Varices from Portal HTN, constipation, pregnancy. Internal (above dentate line), External (below).

Crohn’s Disease (Regional Enteritis):

• Site: Any part of GIT (Terminal ileum classic).
• Gross: Skip lesions (patchy), Cobblestone appearance, Deep linear fissures/ulcers. String sign on X-ray (early stenosis). Fistulas common.
• Microscopic: Transmural inflammation, Non-caseating Granulomas (40-60%).
• Cancer Risk: Increased, but LESS than UC.

Ulcerative Colitis (UC):

• Site: Limited to Colon. Starts at Rectum -> extends Continuously.
• Gross: Superficial broad ulcers, Pseudopolyps. Loss of haustra. Thin wall.
• Microscopic: Inflammation Mucosa & Submucosa ONLY. Crypt abscesses (neutrophils). NO granulomas.
• Complications: Toxic Megacolon (life-threatening dilatation). Significantly High risk of Dysplasia & Adenocarcinoma (highest in pan-colitis & long duration).

• Diverticulosis: Acquired blind outpouching of mucosa & submucosa through muscle. Associated with low-fiber diet -> constipation -> high intraluminal pressure.
• Location: Sigmoid colon (95%).
• Pathology: Thin-walled sacs. Prominent taeniae coli due to hypertrophy.
• Complication: Diverticulitis (inflammation of diverticulum, fever, LLQ pain).