Revision sheet: Digestive System Anatomy

📋 Course Outline

1. Digestive Tract Organization
2. Oral Cavity and Palate
3. Teeth and Their Structure
4. Tongue and Salivary Glands
5. Pharynx and Waldeyer Ring
6. Esophagus and Stomach
7. Small Intestine
8. Large Intestine
9. Liver and Biliary System
10. Pancreas

📖 1. Digestive Tract Organization

🔑 Key Concepts & Definitions

• Digestive system : A tube extending from the mouth to the anus and measuring approximately 9 m.

★ Must-know

• The digestive tract comprises the oral cavity, pharynx, esophagus, stomach, small intestine, and large intestine.

📌 The upper digestive tract is lined mainly by tough stratified squamous epithelium, whereas the lower tract is lined mainly by delicate glandular columnar epithelium.

Further detail

• Associated digestive organs include the liver, pancreas, salivary glands, teeth, and gallbladder.

💡 Memory Hook

Mouth → pharynx → esophagus → stomach → intestines

📖 2. Oral Cavity and Palate

🔑 Key Concepts & Definitions

• Oral cavity : The initial part of the digestive system, extending from the lips to the pharynx and divided into the oral vestibule and the proper oral cavity.
• Oral vestibule : A horseshoe-shaped space outside the dental arches, bounded externally by the lips and cheeks and connected to the proper oral cavity through spaces between the teeth and the retrodental space.

★ Must-know

📌 The hard palate forms the anterior two-thirds of the oral roof, whereas the soft palate forms the posterior one-third.

• During swallowing, the levator and tensor veli palatini elevate and tense the soft palate to close the upper nasopharynx and prevent food from entering it.

Further detail

• The parotid duct opens into the oral vestibule on the papilla of the parotid duct opposite the second upper molar.

💡 Memory Hook

Hard palate supports; soft palate moves

📖 3. Teeth and Their Structure

🔑 Key Concepts & Definitions

• Tooth regions : Each tooth consists of a root embedded in an alveolus, a narrowed neck, and a free crown projecting into the oral cavity.

★ Must-know

• Humans first develop 20 deciduous teeth and later have 32 permanent teeth.

• The four groups of permanent teeth are incisors, canines, premolars, and molars.

📐 Formula — The formula for one half of the permanent dentition is $\frac{I2\ C1\ P2\ M3}{I2\ C1\ P2\ M3}$.

Further detail

📐 Formula — The formula for one half of the deciduous dentition is $\frac{i2\ c1\ m2}{i2\ c1\ m2}$.

• Deciduous teeth begin erupting at about 7 months, finish during the first two years, and are replaced by permanent teeth between 7 and 12 years.

💡 Memory Hook

Root → neck → crown

📖 4. Tongue and Salivary Glands

🔑 Key Concepts & Definitions

• Tongue : A highly mobile muscular organ involved in speech, chewing, swallowing, and taste sensation.

★ Must-know

• The four types of lingual papillae are filiform, fungiform, foliate, and vallate papillae.

📌 Filiform papillae lack taste buds and have a mechanical function, whereas fungiform, foliate, and vallate papillae contain taste buds.

• The extrinsic tongue muscles are genioglossus, hyoglossus, and styloglossus, while the intrinsic muscles form longitudinal, vertical, and transverse systems; all tongue muscles are innervated by the hypoglossal nerve.

• The major salivary glands are the parotid, submandibular, and sublingual glands, while minor glands occur in the lips, cheeks, palate, and tongue.

Further detail

• The tongue has a root, body, and apex, separated by the V-shaped terminal sulcus; its upper surface also has a median sulcus, dorsum, and margins.

💡 Memory Hook

Filiform papillae feel; other papillae taste

📖 5. Pharynx and Waldeyer Ring

🔑 Key Concepts & Definitions

• Pharynx : A shared digestive and respiratory organ extending from the skull base to the sixth cervical vertebra and serving as a passage for food and air and as a speech resonator.

📝 Essential Points

• The pharynx consists of the nasopharynx, oropharynx, and laryngopharynx.

📌 The nasopharynx conducts air only, whereas the oropharynx conducts both air and food.

• The three pharyngeal constrictors narrow the pharyngeal lumen during swallowing, while the stylopharyngeus, palatopharyngeus, and salpingopharyngeus elevate the pharynx.

• Waldeyer’s lymphatic ring consists of the lingual, palatine, tubal, and pharyngeal tonsils and protects the body at the entrance to the pharynx.

💡 Memory Hook

Nasopharynx → oropharynx → laryngopharynx

📖 6. Esophagus and Stomach

🔑 Key Concepts & Definitions

• Esophagus : An approximately 25 cm hollow tube extending from the sixth cervical to the tenth or eleventh thoracic vertebra and conveying swallowed material to the stomach.

★ Must-know

• The stomach is a variable, expanded sac-like organ shaped approximately like a vertical hook or the letter J, with a cardia and a pylorus.

• The stomach consists of the body, fundus, and pyloric part, which includes the pyloric antrum and pyloric canal; the lesser curvature is concave and the greater curvature is convex.

Further detail

• The esophagus has cervical, thoracic, and abdominal parts, and its upper muscular layer is striated while its lower part contains smooth muscle fibers.

• The stomach muscularis has outer longitudinal, middle circular, and inner oblique smooth-muscle layers.

💡 Memory Hook

Cardia receives; pylorus releases

📖 7. Small Intestine

🔑 Key Concepts & Definitions

• Small intestine : An approximately 6 m long tube, with a reported range of 4.6–9 m, extending from the pylorus to the ileal opening into the large intestine.

★ Must-know

• The small intestine consists of the duodenum, jejunum, and ileum.

• The duodenum is approximately 25 cm long, C-shaped, and surrounds the head of the pancreas; its four parts are superior, descending, inferior or horizontal, and ascending.

• The hepatopancreatic ampulla is formed by the union of the common bile duct and the major pancreatic duct and opens at the major duodenal papilla.

• Circular folds and intestinal villi increase the small-intestinal mucosal surface six- to sevenfold, and aggregated lymphoid nodules called Peyer’s patches are characteristic of the ileum.

Further detail

• The jejunum occupies the upper two-fifths and the ileum the lower three-fifths of the approximately 6 m combined length of jejunum and ileum.

💡 Memory Hook

Duodenum → jejunum → ileum

📖 8. Large Intestine

🔑 Key Concepts & Definitions

• Large intestine : The terminal part of the digestive tract, extending from the ileal opening to the anus and measuring approximately 1.5–1.8 m.

★ Must-know

• The large intestine comprises the cecum with vermiform appendix, colon, and rectum.

• The colon consists of ascending, transverse, descending, and sigmoid parts; the transverse and sigmoid colons are mobile because they have mesenteries, whereas the ascending and descending colons are attached to the posterior abdominal wall.

• The cecum lies in the right iliac fossa, measures approximately 7–8 cm, and receives the ileum through an ileal valve that prevents reflux into the small intestine.

• The internal anal sphincter is smooth muscle, whereas the external anal sphincter is striated muscle under voluntary control during defecation.

Further detail

• The vermiform appendix is approximately 9 cm long, arises from the cecum, and projects to the McBurney point on the right spinoumbilical line.

💡 Memory Hook

Cecum → colon → rectum

📖 9. Liver and Biliary System

🔑 Key Concepts & Definitions

• Liver : The largest digestive gland, producing bile and processing blood containing substances absorbed from the digestive tract.
• Hepatic lobule : A hexagonal structural unit composed of radiating plates of hepatocytes around a central vein, with capillaries carrying blood toward that vein.

★ Must-know

• The liver has right, left, quadrate, and caudate lobes; the right lobe is considerably larger than the left lobe.

• The hepatic artery provides the nutritive circulation, while the portal vein provides the functional circulation by bringing blood from the digestive organs and spleen.

Further detail

• In adults, the liver weighs approximately 1200–1500 g and occupies the right hypochondriac and epigastric regions and part of the left hypochondriac region.

📖 10. Pancreas

🔑 Key Concepts & Definitions

• Gallbladder : A pear-shaped sac on the inferior surface of the liver that stores bile and consists of a fundus, body, and neck.
• Pancreas : A major digestive gland with a head in the concavity of the duodenum, a body extending leftward, and a tail reaching the splenic hilum.

📝 Essential Points

• The right and left hepatic ducts unite as the common hepatic duct, which joins the cystic duct to form the common bile duct opening at the major duodenal papilla.

📌 The exocrine pancreas consists of enzyme-secreting acini, whereas the endocrine pancreas consists of islets of Langerhans that secrete hormones.

• The pancreatic endocrine cells secrete insulin and glucagon, hormones essential for regulating blood glucose concentration.

💡 Memory Hook

Exocrine enzymes; endocrine hormones