Chapter 18: Digestive System

Digestive system

A system of organs responsible for breaking down food, absorbing nutrients, and eliminating waste.

Ingestion

The process of taking food into the mouth.

Digestion

The mechanical and chemical breakdown of food into smaller molecules.

Absorption

The process by which nutrients pass from the digestive tract into the bloodstream or lymph.

Elimination

The removal of indigestible substances and waste as feces.

Alimentary canal

The continuous tube from mouth to anus through which food passes; also called the gastrointestinal (GI) tract.

Accessory digestive organs

Organs that assist in digestion but are not part of the GI tract (e.g., liver, pancreas, gallbladder).

Mouth (oral cavity)

The entry point of the digestive tract where mechanical digestion begins.

Teeth

Structures in the mouth used to mechanically break down food by chewing.

Tongue

A muscular organ in the mouth that aids in chewing, swallowing, and tasting.

Salivary glands

Glands that secrete saliva to moisten food and begin starch digestion.

Saliva

A fluid containing enzymes that starts the breakdown of carbohydrates.

Pharynx (throat)

A muscular passageway for food and air; connects the mouth to the esophagus.

Esophagus

A muscular tube that transports food from the pharynx to the stomach.

Peristalsis

Rhythmic muscular contractions that move food through the digestive tract.

Stomach

A muscular organ that mixes food with gastric juices and begins protein digestion.

Gastric juice

A mixture of hydrochloric acid and enzymes secreted by the stomach.

Pepsin

A stomach enzyme that begins the digestion of proteins.

Chyme

The semi-liquid mixture of partially digested food and gastric juices.

Small intestine

The main site of nutrient absorption; consists of the duodenum, jejunum, and ileum.

Villi

Finger-like projections in the small intestine that increase surface area for absorption.

Large intestine (colon)

Absorbs water and forms feces; includes the cecum, colon, rectum, and anal canal.

Rectum

The final section of the large intestine that stores feces before elimination.

Anus

The opening at the end of the digestive tract through which feces are expelled.

Liver

A large organ that produces bile, stores nutrients, and detoxifies substances.

Bile

A substance produced by the liver that emulsifies fats.

Gallbladder

A small organ that stores and releases bile into the small intestine.

Pancreas

An organ that secretes digestive enzymes and bicarbonate into the small intestine and hormones into the blood.

Pancreatic enzymes

Enzymes from the pancreas that digest carbohydrates, proteins, and fats.

Amylase

An enzyme that breaks down starch into sugars.

Lipase

An enzyme that breaks down fats into fatty acids and glycerol.

Protease

An enzyme that breaks down proteins into amino acids.

Appendix

A small pouch attached to the cecum with no known essential digestive function.

Digestion time

The average time it takes food to travel through the digestive tract—about 24 to 72 hours.

Constipation

A condition in which bowel movements are infrequent or difficult.

Diarrhea

Frequent, watery bowel movements usually caused by infection or irritation.

Heartburn

A burning sensation in the chest caused by acid reflux into the esophagus.

Gastroesophageal reflux disease (GERD)

A chronic condition where stomach acid frequently flows into the esophagus.

Ulcer

A sore that forms in the lining of the stomach or small intestine, often due to H. pylori bacteria.

Cirrhosis

Chronic liver damage from various causes leading to scarring and impaired function.

Hepatitis

Inflammation of the liver, commonly caused by viruses.

Gallstones

Hardened deposits that form in the gallbladder and may block bile flow.

Appendicitis

Inflammation of the appendix, often requiring surgical removal.

Colonoscopy

A procedure to examine the inner lining of the large intestine using a camera.

segmented movement

single segments of the intestine alternate between relaxing and contracting to push food through

mucosa

innermost lining of alimentary canal

submucosa

second layer of GI tract where absorption takes place

muscularis

third layer of digestive system consisting of smooth and skeletal muscle

serosa/peritoneum

fourth, serous layer of the digestive system that secretes mucus

peritontitus

inflammation of peritoneum

mesentery

peritoneum layer that lines posterior portion of abdominal cavity

greater omentum

double fold of peritoneum that protects stomach

buccal cavity

oral cavity

lingual frenulum

thing that connects tongue to base of mouth