Digestive System Functions and Processes

Digestive System Functions

• Breaks down large food molecules into smaller ones.
• Absorbs smaller molecules into the circulatory system for distribution to the body.

Human Digestive System Types

• Complete: Gastrointestinal tract with accessory organs.
• Simple: Opening and gastrovascular cavity.

Main Steps in Digestion

• Ingestion: Taking in nutrients.
• Digestion: Mechanical and chemical breakdown of nutrients.
• Absorption: Transfer of nutrients to the bloodstream.
• Egestion: Removal of waste.

Mechanical Digestion

• Physical breakdown of food.
• Increases surface area for better nutrient absorption.
• Occurs in the mouth, esophagus, and stomach.

Chemical Digestion

• Chemical breakdown of food.
• Breaks down macronutrients into smaller components.
• Glands release hormones that control enzymes (speed up chemical reactions).
• Occurs in the mouth, stomach, and small intestine.

Mouth

• Receives food, initiates digestion.
• Incisors and Canines cut food; Premolars and Molars grind food.
• Saliva, released by salivary glands (triggered by sight, smell, or presence of food), moistens and binds food into a bolus.
• Saliva contains amylase (digests starch to disaccharides) and mucus (lubricant).

Swallowing

• Tongue pushes bolus to the back of the mouth (voluntary).
• Food moves to the pharynx.
• Soft palate prevents food from entering the nasal passage.
• Epiglottis covers the airway.
• Pharyngeal muscles contract to force bolus into the esophagus (involuntary).

Esophagus

• Carries food from pharynx to stomach.
• Peristalsis (wave-like muscular contractions) moves food down.
• Gastroesophageal sphincter (circular muscle) regulates food entry to the stomach.
• Prevents acid reflux (heartburn).

Stomach

• J-shaped, muscular organ, stores up to 2 liters of food.
• Four layers: mucosa, submucosa, muscularis, serosa.
• Mucosa: Folds, secretes gastric juice (cells replaced every three days).
• Submucosa: Connective tissue, nerves, blood vessels.
• Muscularis: Smooth muscle, churns food with gastric juice to create chyme.
• Serosa: Outermost layer, holds stomach in place, lubricates.

Stomach: Chemical Digestion

• Gastrin hormone released to stimulate gastric juice secretion.
• Gastric juice contains enzymes, acid, mucus, and intrinsic factor.
• HCl kills pathogens, activates pepsinogen to pepsin, and begins protein breakdown.
• Mucus protects stomach lining from digestion.
• Intrinsic factor is needed for B12 absorption.

Stomach: Mechanical Digestion

• Food stimulates muscular contractions to mix with gastric juices.

Stomach: Absorption

• Small amounts of water, glucose, ions, and alcohol absorbed.

Stomach Ulcers

• H. pylori bacteria neutralize stomach acid and burrow into the mucosa.
• Reduced mucus production exposes the stomach lining to acid, causing ulcers.
• Treated with antibiotics.

Small Intestine

• ~20 feet long, 1 inch in diameter.
• Main site of chemical digestion and nutrient absorption.
• Three sections: duodenum (digestion), jejunum (digestion and absorption), ileum (absorption).
• Villi and microvilli greatly increase surface area, maximizing absorption.
• Capillaries absorb all nutrients except fats, which are absorbed by lacteals.

Duodenum

• Chyme enters from the stomach.
• Peristalsis moves chyme.
• Bile and pancreatic juice are added.

Bile

• Produced in liver, stored in gallbladder.
• Enters the small intestine through the common bile duct.
• Aids in fat digestion and absorption.

Pancreatic Juice

• Pancreas produces, released through pancreatic duct.
• Contains amylase (starch digestion), trypsin (protein digestion), and lipase (fat digestion).
• Bicarbonate ions neutralize stomach acid.

Jejunum and Ileum

• Digestion and absorption of nutrients continue.
• Intestinal glands secrete enzymes (carbohydrases, peptidases) for further digestion.

Liver and Gallbladder

• Liver removes sugar (glucose) excess stored as glycogen
• Removes amino acids and produces bile (bile salts aid digestion).
• Blood from intestines passes through liver before returning to the heart.

Pancreas

• Secretes enzymes for digestion.
• Secretes hormones that regulate glucose levels.

Large Intestine

• ~1.5 meters long, 7.6 cm diameter.
• Water reabsorbed, waste remains, forms feces
• Houses gut bacteria (beneficial).
• 4 segments (ascending, transverse, descending, sigmoid).
• Rectum stores feces.

Egestion

• Indigestible components keep you full, retain water to aid elimination.

Anus

• Two sphincter muscles (internal - involuntary, external - voluntary).

Explore the key functions and types of the digestive system in this quiz. Understand the steps involved in digestion, including ingestion, digestion, absorption, and egestion. Test your knowledge on both mechanical and chemical digestion.