Digestive System Overview

Study Notes

The digestive system, also known as the alimentary canal or gastrointestinal (GI) tract, is a muscular tube that runs from the mouth to the anus.
It is responsible for the breakdown of food into smaller molecules that can be absorbed into the bloodstream.
The accessory digestive organs include the teeth, tongue, salivary glands, liver, gallbladder, and pancreas.
The digestive system is vital for providing the body with the nutrients it needs to function.

Mouth: The first part of the digestive system, where food is ingested and mechanically broken down by chewing.
Pharynx: A muscular tube that acts as a passageway for food and air.
Esophagus: A muscular tube that connects the pharynx to the stomach.
Stomach: A muscular sac that mixes and churns food with gastric juices.
Small Intestine (Small Bowel): The longest part of the digestive system, where most nutrient absorption occurs.
Large Intestine (Large Bowel): The final part of the digestive system, where water absorption and the formation of feces take place.
Anus: The terminal opening of the digestive system, where feces are eliminated from the body.

Ingestion: The process of taking food into the mouth.
Propulsion: The movement of food through the digestive tract.
Mechanical Digestion: The physical breakdown of food into smaller pieces.
Chemical Digestion: The chemical breakdown of food molecules into smaller molecules.
Absorption: The passage of digested nutrients from the digestive tract into the bloodstream.
Defecation: The elimination of undigested food residues from the body as feces.

Mucosa: The innermost layer of the digestive tract, composed of epithelium, lamina propria, and muscularis mucosae.
Submucosa: A layer of connective tissue that contains blood vessels, lymphatics, and nerves.
Muscularis Externa: A layer of smooth muscle that propels food through the digestive tract.
Serosa/Adventitia: The outermost layer of the digestive tract, which provides support and protection.

Teeth: Hard structures in the mouth that mechanically break down food.
Tongue: A muscular organ that helps to manipulate food in the mouth.
Salivary Glands: Secrete saliva, which moistens food and contains enzymes that begin the breakdown of carbohydrates.
Liver: Produces bile, which helps to emulsify fats, and performs numerous metabolic functions.
Gallbladder: Stores and concentrates bile.
Pancreas: Produces digestive enzymes and hormones that regulate blood sugar levels.

Peritoneum: A serous membrane that lines the abdominal cavity.
Visceral Peritoneum: Covers the external surfaces of most digestive organs.
Parietal Peritoneum: Lines the body wall.
Peritoneal Cavity: A potential space between the visceral and parietal peritoneum, filled with lubricating fluid.
Mesenteries: Double layers of peritoneum that hold digestive organs in place, store fat, and provide routes for blood vessels and nerves.

The digestive organs in the abdomen and pelvis can be classified as intraperitoneal (completely surrounded by peritoneum) or secondarily retroperitoneal (originally intraperitoneal but moved to lie against the posterior abdominal wall).