Digestive System – PCL LEVEL
1. Introduction
The digestive system is responsible for the mechanical and chemical breakdown of food, absorption of nutrients, and elimination of waste.
Components: Oral cavity, Pharynx, Esophagus, Stomach, Small intestine, Large intestine, Accessory organs (Salivary glands, Liver, Gallbladder, Pancreas)
Functions:
Ingestion – taking in food
Propulsion – swallowing and peristalsis
Mechanical digestion – chewing, churning
Chemical digestion – enzymatic breakdown
Absorption – nutrients into blood/lymph
Defecation – elimination of indigestible substances
2. Oral Cavity and Salivary Glands
2.1 Oral Cavity Anatomy
Lips, cheeks, tongue, palate, teeth
Tongue: intrinsic and extrinsic muscles, papillae
Teeth: 32 permanent teeth, 20 deciduous teeth
2.2 Salivary Glands
Parotid → Serous, amylase-rich
Submandibular → Mixed (serous + mucous)
Sublingual → Mucous
Saliva secretion: 1–1.5 L/day, contains amylase, mucins, lysozyme
Innervation: Parasympathetic (CN VII, IX), sympathetic stimulation modulates protein content
Clinical correlation:
Sialolithiasis → salivary stones
Xerostomia → dry mouth, impaired digestion
3. Pharynx and Esophagus
3.1 Pharynx
Nasopharynx, Oropharynx, Laryngopharynx
Muscles: constrictors aid in swallowing
3.2 Esophagus
Muscular tube, 25–30 cm, posterior mediastinum
Upper 1/3 skeletal, middle mixed, lower 1/3 smooth muscle
LES prevents reflux
Clinical correlation:
Achalasia → failure of LES relaxation
GERD → acid reflux
4. Stomach
Regions: Cardia, Fundus, Body, Pylorus
Curvatures: Greater and Lesser
Gastric folds: Rugae
Layers: Mucosa, Submucosa, Muscularis externa, Serosa
4.3 Physiology
Motility: Mixing waves, peristalsis
Secretion: HCl (parietal), Pepsinogen (chief), Mucus, Gastrin
Regulation: Neural (vagus), hormonal (gastrin, somatostatin), paracrine
Clinical correlation:
Peptic ulcer → excess acid or Helicobacter pylori
Pernicious anemia → lack of intrinsic factor
5. Small Intestine
5.1 Anatomy
Duodenum (25 cm), Jejunum (2.5 m), Ileum (3.5 m)
Villi and microvilli increase surface area (~200 m²)
·
5.2 Accessory Organs
Liver: Bile production, metabolism
Gallbladder: Stores and concentrates bile
Pancreas: Exocrine (enzymes), Endocrine (insulin, glucagon)
Absorption:
Carbs → glucose, galactose, fructose
Proteins → amino acids
Fats → chylomicrons → lymph
6. Large Intestine
6.1 Anatomy
Cecum, Appendix, Colon (ascending, transverse, descending, sigmoid), Rectum, Anal canal
Haustra: sacculations; taenia coli: longitudinal muscle bands
6.2 Physiology
Water and electrolyte absorption
Bacterial fermentation → Vit K, B vitamins
Storage and defecation
Clinical correlation:
Appendicitis → inflammation of appendix
Ulcerative colitis → mucosal inflammation
7. Digestive Physiology – Regulation
7.1 Neural Control
Enteric nervous system: Myenteric (motility), Submucosal (secretion)
Extrinsic: Parasympathetic (vagus), Sympathetic (inhibitory)
8. Clinical Correlations
9. High-Yield MCQs
Enzyme initiating starch digestion → Salivary amylase
Parietal cells secrete → HCl & intrinsic factor
Hormone stimulating pancreatic bicarbonate → Secretin
Vitamin B12 absorption site → Ileum
Bile is stored in → Gallbladder
Brush border enzyme for lactose → Lactase
Upper esophageal sphincter innervation → CN X
Most nutrient absorption occurs in → Jejunum
Liver's functional unit → Hepatic lobule
Hormone stimulating gallbladder contraction → CCK
Gastric parietal cell regulator → Gastrin
Condition with autoimmune parietal cell destruction → Pernicious anemia
Main site for iron absorption → Duodenum
Vitamin K production site → Colon
Stomach’s anatomical part at cardiac orifice → Cardia
You can add important points below.