Overview: Digestive System
- The digestive system consists of the oral region, alimentary canal, and extrinsic glands.
- Digestive system is the organ system that takes in food, breaks it down, absorbs useful molecules, and removes indigestible material.
- Oral region is the entrance area of the digestive system and includes structures for chewing, tasting, swallowing preparation, and immune defense.
- Alimentary canal is the continuous hollow tube that carries food from the esophagus through the intestines.
- Extrinsic glands are digestive glands outside the tube that send secretions into it, such as salivary glands, pancreas, liver, and gallbladder-related ducts.
- The esophagus carries swallowed food from the pharynx to the stomach.
- Stomach stores and churns food while adding acid, mucus, enzymes, and hormones.
- Small intestine completes much digestion and absorbs most nutrients.
- Large intestine absorbs fluid, electrolytes, and gases while compacting feces.
- Hollow tube organization means the alimentary canal has a lumen surrounded by layered tissue walls.
- The lumen is the open space inside the digestive tube where food, chyme, or feces travels.
- Oral cavity modification means the mouth has specialized teeth, tongue, glands, and mucosa rather than a simple tube wall.
- Variable diameter lets different digestive regions store, mix, propel, or absorb material differently.
- The mucosa is the innermost layer facing the lumen.
- The submucosa is the connective-tissue layer beneath the mucosa and often carries vessels, nerves, and glands.
- Muscularis externa is the main smooth-muscle layer that moves material along the digestive tract.
- Serosa is a slippery outer covering made of mesothelium and connective tissue where the organ is intraperitoneal.
- Mesothelium is a simple squamous epithelial lining that makes a smooth, low-friction surface for organs that move inside body cavities.
- Intraperitoneal digestive organs are covered by visceral peritoneum, so their outer layer is called serosa rather than adventitia.
- Adventitia is an outer connective-tissue attachment layer where the organ is fixed to surrounding structures.
- Enzymes are proteins that speed chemical digestion of food molecules.
- Hormones are chemical messengers that coordinate secretion, motility, hunger, and satiety.
- Ingestion means taking food and fluid into the mouth.
- Digestion means breaking large food molecules into smaller absorbable units.
- Absorption means moving digested products from the lumen into blood or lymph.
- Elimination means expelling indigestible residue as feces.
- Regional specialization is the major histology pattern because each digestive region modifies the same basic wall plan for a different job.
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