Anatomy Lecture Notes

Anatomy of the Digestive System

• The digestive system is crucial for:
  • Nutrient intake
  • Food digestion
  • Nutrient absorption into body tissues
  • Waste elimination
• Structures include:
  • Mouth (oral cavity)
  • Pharynx (throat)
  • Esophagus
  • Stomach
  • Liver
  • Gallbladder
  • Pancreas
  • Small intestine
  • Large intestine

Digestion Process

Mouth

• First site of digestion.
• Teeth break down food via chewing (mastication).
• Saliva contains amylase, a digestive enzyme that breaks down carbohydrates.
• The tongue aids mastication by pressing food against teeth.
• Chewed food is then swallowed.

Pharynx

• Also known as the throat.
• Serves as a passageway for food, water, and air.
• Food passes from the pharynx to the esophagus.

Esophagus

• A long tube connecting the pharynx to the stomach.
• Function: transports food.
• Lined with smooth muscle.
• Peristalsis (rhythmic smooth muscle contractions) propels food along.

Stomach

• Both ends close off upon food entry.
• Churns food to break it down manually.
• Stomach acids (e.g., hydrochloric acid, pepsin) further digest food.
• The pylorus (bottom of the stomach) opens to allow food to enter the small intestine.

Small Intestine

• Major site of nutrient absorption.
• Accessory organs (liver, gallbladder, pancreas) aid digestion.

Accessory Organs

Liver

• The heaviest internal organ.
• Mainly detoxifies blood by filtering harmful substances.
• Aids digestion by producing bile, which emulsifies fats.

Gallbladder

• Stores bile produced by the liver until needed.
• Empties bile into the small intestine through the bile duct, connected to the duodenum.

Pancreas

• Creates pancreatic juice to digest proteins, lipids, and carbohydrates.
• Empties substances into the small intestine through the bile duct.

Duodenum

• First section of the small intestine.
• The last section where food digestion takes place.
• Bile and pancreatic juice mix with food.
• Peristalsis moves food into the jejunum.

Jejunum

• Middle portion of the small intestine.
• The major site of nutrient absorption.

Ileum

• Final section of the small intestine.
• Final absorption occurs here.
• Food moves into the large intestine.

Large Intestine

• Two primary functions:
  • Water absorption
  • Waste elimination
• Water absorption occurs as feces move through; too much absorption leads to constipation, too little leads to diarrhea.
• Sections: ascending colon, transverse colon, descending colon, and sigmoid colon.
• Feces enter the rectum from the sigmoid colon, ready for elimination.