Digestive System Notes
Alimentary Canal (Gastrointestinal Tract)
The continuous tube through which food passes, allowing digestion and absorption of nutrients.
Organs Included:
1. Mouth:
• Entry point for food.
• Mechanical digestion via chewing (teeth).
• Chemical digestion begins with saliva containing amylase.
2. Pharynx:
• Passageway for food, fluids, and air.
3. Esophagus:
• Propels food to the stomach using peristalsis.
4. Stomach:
• Function: Temporary storage tank for food.
• Mixes food with gastric juices for breakdown into chyme.
• Secretes pepsin (breaks down proteins).
5. Small Intestine:
• Divisions:
• Duodenum.
• Jejunum.
• Ileum.
• Primary site of nutrient absorption.
• Receives bile (from liver) and pancreatic juices (from pancreas) to aid digestion.
6. Large Intestine:
• Divisions:
• Cecum, appendix, colon (ascending, transverse, descending, sigmoid), rectum, anal canal.
• Functions:
• Absorbs water.
• Houses bacterial flora for vitamin synthesis.
• Forms and eliminates feces.
7. Rectum and Anal Canal:
• Stores feces for elimination.
Accessory Digestive Organs
These organs assist the alimentary canal by producing or storing substances necessary for digestion.
Organs Included:
1. Teeth:
• Primary Teeth: 20 deciduous teeth erupt between 6 and 24 months.
• Permanent Teeth: 32 permanent teeth appear between 6 and 12 years.
• Classifications:
• Incisors: For cutting and nipping.
• Canines: Fang-like for tearing and piercing.
• Premolars (Bicuspids) and Molars: Broad crowns for grinding and crushing.
2. Tongue:
• Mostly skeletal muscle.
• Functions:
• Contains taste buds to analyze nutrient content of food.
• Mixes food with saliva to form a bolus.
• Aids in swallowing.
3. Salivary Glands:
• Function: Produce and secrete saliva (water-based liquid containing amylase) for chemical digestion.
• Types:
• Parotid glands.
• Submandibular glands.
• Sublingual glands.
• Fun Fact: Mumps infect the parotid glands.
4. Liver:
• Secretion: Produces bile, a greenish liquid (pH 7.6–8.6) essential for fat digestion.
• Functions of Hepatocytes:
• Produce bile.
• Process nutrients from blood.
• Store fat-soluble vitamins.
• Detoxify harmful substances.
5. Gallbladder:
• Thin-walled muscular sac on the liver’s ventral surface.
• Functions:
• Stores and concentrates bile.
• Releases bile into the duodenum to emulsify fats.
• Disorders:
• Gallstones causing blockages and pain.
• Extreme cases can result in gallbladder rupture.
6. Pancreas:
• Exocrine Function:
• Produces pancreatic juice containing enzymes for digesting carbohydrates, proteins, and lipids.
• Endocrine Function:
• Secretes insulin to regulate blood glucose levels.
• Disorders: Malfunction can cause diabetes.
Important Notes About Digestive System Processes
1. Ingestion: Intake of food through the mouth.
2. Propulsion:
• Swallowing.
• Peristalsis (waves of muscle contractions moving food through the tract).
3. Mechanical Digestion:
• Chewing (mouth).
• Churning (stomach).
• Segmentation (small intestine).
4. Chemical Digestion:
• Breakdown of food molecules by enzymes.
5. Absorption:
• Movement of nutrients into blood or lymph via small intestine.
6. Defecation:
• Elimination of indigestible substances and waste products as feces.
Note 
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