Understanding the Digestive System: Functions and Anatomy

The Digestive System: Functions and Anatomy

The digestive system is responsible for several key functions:

• Food intake: Consuming food.
• Nutrient preparation: Breaking down nutrients through mechanical and chemical digestion.
• Absorption: Absorbing nutrients into surrounding tissues.
• Elimination: Eliminating undigested waste.

Components of the Digestive System

The digestive system consists of the following organs:

• Mouth
• Pharynx
• Esophagus
• Stomach
• Intestines:
  • Duodenum
  • Jejunum
  • Ileum
  • Large Intestine (Cecum, Appendix, Ascending Colon, Transverse Colon, Descending Colon, Sigmoid Colon, Rectum, Anal Canal, Anus)

The entire system is lined with the peritoneum, a serous membrane.

Accessory Glands

Several accessory glands aid in digestion:

• Minor and major salivary glands (parotid, submandibular, and sublingual)
• Pancreas
• Liver
• Bile ducts

Detailed Anatomy

Mouth

Adults have 32 teeth.

Pharynx

The pharynx consists of intrinsic constrictor muscles (superior, middle, and inferior) and the stylopharyngeus muscle.

Sections of the Pharynx

• Nasopharynx: Contains the pharyngeal opening of the auditory tube.
• Oropharynx: The second portion of the pharynx.
• Laryngopharynx

Esophagus

The esophagus connects the pharynx to the stomach. The lower esophageal sphincter (LES) separates the esophagus from the stomach at the cardia.

Stomach

The stomach has several regions: the fundus, cardia, body, antrum, pyloric orifice, and pyloric sphincter.

Small Intestine

Duodenum

The duodenum is a segmented tube where exocrine pancreatic secretions and bile enter.

Jejunum

The jejunum is approximately 2 meters long.

Ileum

The ileum is about 3.5 meters long and is responsible for intestinal absorption of nutrients.

Large Intestine

The large intestine includes the ileocecal valve, cecum, appendix, ascending colon, transverse colon, descending colon, sigmoid colon, rectum, and anal canal.

The colon has a fiber layer forming haustra. In the sigmoid colon, there are only two layers. Epiploic appendages, clusters of fat, are present.

Haustra: Visible indentations on the surface of the large intestine.

Cecum

The cecum is adjacent to the ileocecal valve.

Vermiform Appendix

The appendix is a worm-like structure.

Rectum

The rectum has two portions: the pelvic and perineal portions.

Anal Canal

The anal canal contains the internal anal sphincter (smooth muscle) and the external anal sphincter (striated muscle).

Liver

The liver is a large gland with over 500 functions and regenerative capabilities.

Surfaces of the Liver

• Diaphragmatic surface: Features the falciform ligament.
• Visceral surface: Contains the inferior vena cava and gallbladder.

Grooves

• Anteroposterior left groove: Contains the round ligament and venous ligament.
• Transverse groove: Hepatic hilum.

Hepatic Hilum

The hepatic hilum contains the hepatic ducts (right and left), portal vein (posterior), hepatic artery, hepatic vein, nerves, and lymphatics.

Lobes of the Liver

The liver has right, left, caudate, and quadrate lobes.

Bile Ducts

Bile, containing biliverdin and bilirubin, is produced in the liver. Bile salts aid in fat emulsification and are stored in the gallbladder before being transported to the duodenum.

Pancreas

The pancreas has both endocrine and exocrine functions. The exocrine pancreas releases enzymes such as amylase and pancreatic lipase, which aid in the digestion of fats and carbohydrates.

Salivary Glands

Submandibular Glands

Located in the mandibular fossa, these glands secrete saliva into the sublingual compartment.

Sublingual Glands

Located in the sublingual fossa, these glands secrete into the sublingual frenulum through the sublingual ducts.

Parotid Glands

Located in the parotid region near the ear, these glands secrete into the oral cavity via the Stensen's duct.

Muscles of Mastication

These muscles facilitate opening and closing of the mouth, as well as lateral movements.

• Masseter
• Medial pterygoid
• Temporalis (anterior and medial)
• Mylohyoid
• Geniohyoid
• Digastric
• Lateral pterygoid (protraction and retraction of the mandible)
• Temporalis