Digestive System

The process of changing complex solid foods into simpler soluble forms for absorption by body cells, aided by digestive juices containing enzymes

Digestion

 Includes the alimentary canal and accessory digestive organs.

Digestive System

 Approximately 20–25 feet long, consisting of the mouth, pharynx, esophagus, stomach, small intestine, large intestine (colon), and anus.

Alimentary Canal

Includes the tongue, teeth, salivary glands, pancreas, liver, and gallbladder.

Accessory Organs

Path of Digestive system

Mouth → Pharynx → Esophagus → Stomach → Small Intestine → Large Intestine → Rectum → Anus 

Take food into the mouth for mechanical and chemical breakdown. | Functions of the Digestive System

Ingestion

Use peristalsis and segmented movement to push food through the digestive tract. | Functions of the Digestive System

Movement

Use mechanical (teeth) and chemical (enzymes) mechanisms to break down food. | Functions of the Digestive System

Digestion

Absorb nutrients into blood capillaries and lacteals of the small intestine. | Functions of the Digestive System

Absorption

Eliminate waste products from the body. | Functions of the Digestive System

Elimination

Made of epithelial cells, responsible for secretion and absorption.| Tunics (Layers) of the Digestive System

Mucosa (Innermost Layer)

Secretes mucus for lubrication and protection.| Tunics (Layers) of the Digestive System

Mucosa (Innermost Layer)

Secretes enzymes and mucus in specific regions (e.g., stomach, small intestine). | Tunics (Layers) of the Digestive System

Mucosa (Innermost Layer)

Absorbs nutrients in the small intestine.| Tunics (Layers) of the Digestive System

Mucosa (Innermost Layer)

Connective tissue layer with blood vessels, lymphatics, and nerves to support mucosa.| Tunics (Layers) of the Digestive System

Submucosa

Contains nerve endings (submucosal plexus) to regulate digestive processes.| Tunics (Layers) of the Digestive System

Submucosa

Muscular layer that helps move food through the digestive tract.| Tunics (Layers) of the Digestive System

Muscularis Externa

Skeletal Muscle - Found in mouth, pharynx, and upper/middle esophagus, enables voluntary swallowing.| Tunics (Layers) of the Digestive System

Muscularis Externa

Smooth Muscle - Found in the rest of the digestive tract, responsible for peristalsis (involuntary muscle contractions that move food).| Tunics (Layers) of the Digestive System

Muscularis Externa

Outermost layer; serosa (visceral peritoneum) for intraperitoneal organs, adventitia for retroperitoneal organs (e.g., esophagus).| Tunics (Layers) of the Digestive System

Serosa/Adventitia (Outer Layer)

Provides structural support and protection for the digestive organs..| Tunics (Layers) of the Digestive System

Serosa/Adventitia (Outer Layer)

Begins mechanical breakdown (teeth) and chemical digestion (salivary amylase).

Mouth (1)

 Shared passageway for food and air; initiates swallowing to esophagus.

Pharynx (2)

Transports food to the stomach via peristalsis.

Esophagus (3)

Mechanical churning and chemical digestion (pepsin, HCl) form chyme.

Stomach (4)

Final digestion (pancreatic enzymes, bile) and nutrient absorption via villi.

Small Intestine (5)

 Absorbs water, forms feces from undigested material.

Large Intestine (6)

 Eliminates waste.

Anus (7)

Entry point for food; includes lips, mucous membrane, hard and soft palates, and uvula.

Mouth

Assists in swallowing, helps close nasopharynx to reduce food entry into nasal cavity.| Mouth

Attached to mouth floor; aids chewing, swallowing; contains taste buds..| Mouth

Connects tongue to mouth floor, influences tongue mobility..| Mouth

 Secrete saliva with salivary amylase to initiate carbohydrate digestion..| Mouth

Salivary Glands

 Secrete amylase-rich saliva; may inflame during mumps. | Salivary Glands| Mouth

Parotid Glands

 Facilitate mastication (chewing).| Mouth

Teeth

Gums; support and protect teeth.| Mouth

Gingivae

Comprises crown, neck, root; includes pulp cavity, dentin, enamel.| Mouth

Tooth Structure

 Throat; conducts food and air; initiates swallowing to esophagus.

Pharynx

Muscular tube from pharynx to stomach; uses peristalsis for food transport.

Esophagus

Upper abdominal cavity; divided into fundus, body, pylorus

Stomach

 Controls esophagus-to-stomach opening.| Stomach

Cardiac Sphincter

Regulates chyme entry into duodenum. | Stomach

Pyloric Sphincter

 Innermost; secretes gastric juice (pepsin, HCl), has rugae for expansion, mucus for protection.| Stomach Wall Layers

Mucosa

Connective tissue; supports mucosa with blood vessels, lymphatics, nerves.| Stomach Wall Layers

Submucosa

Thick smooth muscle (oblique, circular, longitudinal); churns, mixes, moves chyme.| Stomach Wall Layers

Outermost; thin peritoneum layer, protects, reduces friction. | Stomach Wall Layers

Serosa

Secreted by mucosa; contain gastrin, HCl, pepsinogen, mucus.

Gastric Juices

Coiled tube for digestion and absorption; has folds, villi, microvilli for maximum absorption.

Small Intestine

Shortest (~25 cm); receives chyme, pancreatic juice, bile; neutralizes acid, begins digestion of carbohydrates, proteins, fats. | Small Intestine

Duodenum

Middle (~2.5 m); primary nutrient absorption site, enhanced by villi, microvilli.| Small Intestine

Jejunum

 Longest (~3.5 m); completes absorption of nutrients, bile salts, vitamin B12; passes chyme to large intestine via ileocecal valve.| Small Intestine

Ileum

 Regulates chyme flow from ileum to cecum.| Small Intestine

Ileocecal Valve

Behind stomach; exocrine (digestive) and endocrine (hormonal) functions. | Pancreas

Pancreas

 Produce pancreatic juice (amylase, protease, lipase) secreted into duodenum.| Pancreas

Acini Cells

 Carbohydrates - converted to glucose and transported to the liver| Pancreas | Acini Cells

Amylase

 Proteins - amino acids enter bloodstream| Acini Cells

Protease

 Fats - absorbed into lymphatic system as chylomicrons| Acini Cells

Lipase

 Largest internal organ; produces bile, stored in gallbladder; performs metabolic, detox, storage functions.

Liver

Stores, concentrates bile; secretes bile into duodenum for fat emulsification. | Liver

Gallbladder

Receives chyme via ileocecal valve; absorbs water, electrolytes, forms feces.

Large Intestine (Colon)

Pouch-like; connected to appendix; receives chyme. | Large Intestine (Colon)

Cecum

 Right side; absorbs water, electrolytes. | Large Intestine (Colon)

Ascending Colon

 Horizontal; continues water absorption, forms feces. | Large Intestine (Colon)

Transverse Colon

Left side; stores feces.| Large Intestine (Colon)

Descending Colon

 S-shaped; compacts feces, leads to rectum. | Large Intestine (Colon)

Sigmoid Colon

 Stores feces before elimination. | Large Intestine (Colon)

Rectum

Final segment; sphincters control defecation. | Large Intestine (Colon)

Anal Canal

Salivary amylase (mouth) and pancreatic amylase (small intestine) convert to glucose and are transported to the liver.| Enzyme Actions on Nutrients

Carbohydrates

 Pepsin (stomach) and pancreatic proteases (e.g., trypsin, small intestine) break down into amino acids, entering the bloodstream.| Enzyme Actions on Nutrients

proteins

Pancreatic lipase (small intestine), aided by bile (liver, emulsifies fats), breaks into fatty acids, glycerol; absorbed as chylomicrons into lymphatic system. | Enzyme Actions on Nutrients

fats

Wave-like muscular contractions move food through the GI tract.

Peristalsis Mechanism

Coordinated by the enteric nervous system (ENS), also known as the "second brain."

Peristalsis Mechanism

The ENS controls peristalsis and enzyme secretion without input from the brain or spinal cord.

Peristalsis Mechanism

The ENS regulates digestion through reflexes that control peristalsis and enzyme secretion.

Nervous Regulation

The vagus nerve stimulates gastric acid secretion and motility; also triggers pancreatic enzyme release.

Nervous Regulation

Parasympathetic signals enhance motility and secretion, while sympathetic signals slow them.

Nervous Regulation

Hormonal signals regulate digestion (see Digestive Hormones).

Endocrine Regulation

Stimulates gastric acid and pepsin secretion in the stomach; inhibited by high acid levels.| Digestive Hormones

Gastrin

 Stimulates bile release from gallbladder and pancreatic enzyme secretion.| Digestive Hormones

Cholecystokinin (CCK)

Stimulates pancreatic bicarbonate secretion to regulate pH.| Digestive Hormones

Secretin

 Secreted by stomach, stimulates hunger and gastric motility before meals.| Digestive Hormones

Ghrelin

Secreted by adipose tissue, signals satiety to reduce appetite.| Digestive Hormones

Leptin

Community of microorganisms (bacteria, viruses, fungi) in the digestive tract, primarily the colon.

Gut Microbiota

Ferments undigested carbohydrates, produces vitamins (K, B vitamins) and short-chain fatty acids

Gut Microbiota

Supports immune function, influences IBS, obesity, diabetes; enhanced by fiber, probiotics, altered by antibiotics.

Gut Microbiota

Nutrients are converted into energy within cells through metabolism.

Metabolism

Oxidizes nutrients (e.g., glucose) with oxygen to produce ATP. | Metabolism

Aerobic Metabolism

Breaks down glucose without oxygen, producing lactate or other byproducts. | Metabolism

Anaerobic Metabolism

Breaks down glucose without oxygen, producing lactate or other byproducts. | Metabolism

Anabolism

Breaks down complex molecules (e.g., glucose, fats) into simpler ones. | Metabolism

Catabolism

 Carbohydrates and proteins enter bloodstream via hepatic portal vein; fats enter lymphatic system as chylomicrons.  | Metabolism

Transport of Nutrients

 Essential for providing all necessary nutrients for body functions. | Health and Nutrition

Balanced Diet

 Supports digestion and promotes regular bowel movements.| Health and Nutrition

Fiber

Essential for nutrient absorption and maintaining digestive function.| Health and Nutrition

Hydration

 Support gut health by promoting beneficial bacteria.| Health and Nutrition

Probiotics and Prebiotics

Regular, balanced meals support digestive health; long gaps may cause discomfort or overeating.| Health and Nutrition

Meal Timing

 Excessive saturated fats may slow digestion or increase gallstone risk.| Health and Nutrition

High-Fat Diet

Diseases of the digestive system are responsible for the hospitalization of more people in the United States than any other group of diseases.

Common Digestive Disorders

 Inflammation of mouth tissues; symptoms include pain, sores.

Stomatitis

Gum disease from plaque; symptoms include swelling, bleeding.

Gingivitis