Digestive System: Anatomy and Function of Organs

Posted on May 4, 2024 in Biology

ITEM 6: Digestive System

The Digestive Tract

The digestive tract is a series of interconnected organs responsible for the breakdown and absorption of food. It includes the following parts:

  • Mouth
  • Pharynx
  • Esophagus
  • Stomach
  • Small intestine (duodenum, jejunum, ileum)
  • Large intestine (cecum, colon, rectum)

Accessory Digestive Organs

Several glands play crucial roles in digestion by secreting enzymes and other substances:

  • Salivary glands
  • Liver
  • Pancreas

Organs Within the Mouth

The mouth contains various structures involved in the initial stages of digestion:

  • Gums
  • Teeth
  • Tongue
  • Palate (hard and soft)
  • Uvula
  • Pillars
  • Tonsils
  • Fauces

Tonsils

Tonsils are almond-shaped lymphoid organs located between the anterior and posterior pillars of the fauces. They play a role in the immune system.

Functions of the Tongue

The tongue is essential for chewing, swallowing, and speech.

Parts of a Tooth

A tooth consists of three main parts:

  • Crown: The visible part above the gum line.
  • Root: The part embedded in the jawbone.
  • Neck: The area connecting the crown and root.

Dental Pulp

The dental pulp is the soft tissue within a tooth containing nerves, blood vessels, and connective tissue.

Functions of the Pharynx

The pharynx connects the mouth and nasal cavity to the esophagus and larynx. It serves both digestive and respiratory functions:

  • Digestive: Passage of food (bolus) to the esophagus.
  • Respiratory: Passage of air to the trachea.

Esophagus

The esophagus is a muscular tube about 24-28 cm long that connects the pharynx to the stomach.

Stomach

Parts of the Stomach

  • Body: The main central region.
  • Lesser curvature: The shorter, concave inner border.
  • Greater curvature: The longer, convex outer border.
  • Fundus: The upper portion.
  • Cardia: The opening where the esophagus connects to the stomach.
  • Pylorus: The opening where the stomach connects to the duodenum.

Small Intestine

Parts of the Small Intestine

  • Duodenum: The first part, about 12 cm long, where most chemical digestion occurs.
  • Jejunum and Ileum: The remaining sections responsible for further digestion and absorption of nutrients.

Functions of the Stomach and Small Intestine

  • Mechanical digestion: Peristalsis (muscular contractions) moves food through the digestive tract.
  • Chemical digestion: Enzymes break down food into smaller molecules for absorption.

Microscopic Anatomy of the Stomach and Small Intestine

Both organs have similar layers, including the mucosa, submucosa, muscularis, and serosa. The small intestine also has villi and microvilli, which increase the surface area for absorption.

Gastric Glands

Gastric glands in the stomach secrete gastric juice, which contains enzymes and hydrochloric acid for digestion.

Lieberkühn Glands

Lieberkühn glands in the small intestine secrete intestinal juice, which further aids in digestion.

Large Intestine

Location and Anatomy

The large intestine frames the small intestine and consists of the cecum, colon, and rectum. It absorbs water and electrolytes and forms feces.

Parts of the Large Intestine

  • Cecum: The pouch-like beginning of the large intestine.
  • Colon: The longest part, divided into ascending, transverse, descending, and sigmoid sections.
  • Rectum: The final portion leading to the anus.

External Features of the Large Intestine

  • Haustra: Sacculations that give the colon its segmented appearance.
  • Epiploic appendages: Small pouches of fat attached to the colon.
  • Taeniae coli: Three longitudinal muscle bands.

Cecum and Appendix

The cecum is the first part of the large intestine. The appendix is a small, finger-like projection attached to the cecum.

Ileocecal Valve

The ileocecal valve controls the passage of material from the small intestine to the large intestine, preventing backflow.

Colon

The colon consists of four sections: ascending, transverse, descending, and sigmoid. Each section plays a role in the movement and processing of fecal matter.

Rectum

The rectum is the final portion of the large intestine, ending at the anus.

Accessory Digestive Glands

Functions

Salivary glands, liver, and pancreas secrete fluids that aid in digestion:

  • Salivary glands: Produce saliva, which contains enzymes for carbohydrate digestion.
  • Liver: Produces bile, which helps digest fats.
  • Pancreas: Produces pancreatic juice, which contains enzymes for digesting carbohydrates, proteins, and fats.

Salivary Glands

Three pairs of salivary glands are located in the head and neck region:

  • Parotid glands
  • Submandibular glands
  • Sublingual glands

Liver

The liver is a large organ located in the upper right abdomen. It performs numerous functions, including bile production, glycogen storage, and protein synthesis.

Pancreas

The pancreas is located behind the stomach and has both exocrine and endocrine functions:

  • Exocrine: Produces pancreatic juice for digestion.
  • Endocrine: Produces hormones like insulin and glucagon, which regulate blood sugar levels.