Digestive System: Mouth, Esophagus, and Stomach

• Five main parts of the digestive system include the mouth, esophagus, stomach, small intestine, and large intestine.

Mouth

• Functions in chemical digestion via enzymes present in the mouth
• Salivary glands produce saliva
• Saliva lubricates food, mixes it into a bolus, and neutralizes acids
• Tongue enhances the eating experience, mixes food with saliva, and helps move food to the back of the mouth for swallowing
• Teeth break food into smaller pieces

Esophagus

• It's a muscular tube connecting the mouth to the stomach
• Peristalsis, a wave-like muscle contraction, transports food
• Food becomes small particles referred to as bolus after the mouth

Before the Esophagus

• Pharynx, also known as the throat, is first.
• Larynx, or trachea, leads down to the lungs
• The epiglottis is a cartilage that opens and closes to allow for air and food
• Sphincters are positioned from the esophagus down to the stomach

Stomach

• It's a muscular organ that secretes acids and enzymes
• Does not regulate insulin and glucagon, this is the role of the pancreas
• Three acid juices in the stomach aid in digestion
• Gastric juices help digest foods
• Enzymes, originating from the pancreas, digest proteins
• Mucus protects the stomach lining from its own acids
• Hydrochloric acid, with a pH of 2, kills bacteria and pathogens

Key Parts of the Stomach

• Gastric glands produce gastric juices, including pepsin, which breaks down proteins
• Pyloric sphincter regulates the passage of food from the stomach to the small intestine
• Rugae, folds inside the stomach, aid mechanical digestion and allow stomach expansion

Small Intestine

• Serves as the primary organ for digestion and absorption

Three Sections of the Small Intestine

• Duodenum is where chemical digestion occurs, involving digestive enzymes, fats, and cholesterol
• It receives bile from the liver and gallbladder and digestive enzymes from the pancreas
• Jejunum is responsible for nutrient absorption
• Lined with villi- projections that increase surface area and aid movement.
• Ileum is the last and largest part of the small intestine
• Microvilli are finger-like projections that increase the surface area for absorption
• Bile regulates fats

Large Intestine

• Absorbs water and electrolytes

Four Sections of the Large Intestine

• Cecum connects to the ileum and receives undigested food
• Colon absorbs water and salt
• Rectum stores feces
• Anus is the opening for waste elimination
• Anal sphincters control the release of feces

Two Anal Sphincters

• Internal sphincter (involuntary)
• External sphincter (voluntary)

Accessory Organs

• Liver produces bile and detoxifies harmful substances
• Gallbladder stores bile which is connected to the liver via the bile duct
• Pancreas secretes enzymes and regulates blood sugar
• Pancreatic juice neutralizes acid from the chyme
• Chyme refers to digested food
• Stool or feces is the waste product of digestion