Chapter 8: The Digestive System

Digestive System

A long canal (gastrointestinal tract) that processes food through digestion, absorption, and excretion.

GI Tract (Gastrointestinal Tract)

Another name for the digestive system; also called the alimentary canal.

Main Functions of the Digestive System

Digestion, absorption, and excretion of food.

Digestion

The breakdown of large molecules into smaller molecules.

Absorption

The movement of nutrients from the digestive tract into the bloodstream.

Excretion

The elimination of indigestible waste as feces.

Why Digestion is Necessary

Large molecules cannot cross cell membranes and must be broken into smaller molecules to be absorbed.

Main Organs of the Digestive System

Mouth, esophagus, stomach, small intestine, and large intestine.

Accessory Organs

Salivary glands, pancreas, liver, and gallbladder.

Accessory Organs Function

They release substances that help digest food, but food does not pass through them.

Peristalsis

Rhythmic contractions of smooth muscle that push food through the digestive tract.

Mechanical Digestion

Physical breakdown of food through chewing (mastication).

Chemical Digestion

Breakdown of food using digestive enzymes.

Bolus

The semi-solid mass of food formed after chewing and mixing with saliva.

Salivary Glands

Glands that produce saliva to aid digestion.

Parotid Glands

Salivary glands located near the ears.

Sublingual Glands

Salivary glands located under the tongue.

Submandibular Glands

Salivary glands located beneath the jaw.

Salivary Amylase

An enzyme that begins digestion of starch in the mouth.

Mucus

Lubricates food to make swallowing easier.

Lysozymes

Enzymes in saliva that destroy bacteria.

Epiglottis

A structure that closes the trachea during swallowing to prevent food from entering the airway.

Guardian of the Airways

Another name for the epiglottis because it protects the respiratory tract from food.

Trachea

The windpipe that carries air to the lungs.

Esophagus

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

Stomach

An organ that temporarily stores food and begins protein digestion.

Major Functions of the Stomach

Temporary storage of food, protein digestion, and regulation of food release into the small intestine.

Mucus Cells

Cells that produce mucus to protect the stomach lining.

Pepsinogen

An inactive enzyme released in the stomach that becomes pepsin.

Pepsin

An enzyme that begins protein digestion.

Hydrochloric Acid (HCl)

A strong acid in the stomach that activates pepsinogen into pepsin.

Parietal Cells

Cells in the stomach that produce hydrochloric acid.

Pancreas

An accessory organ that releases digestive enzymes into the small intestine.

Endocrine Function of Pancreas

Releases hormones such as insulin and glucagon.

Exocrine Function of Pancreas

Releases digestive enzymes into the small intestine.

Pancreatic Juice

A mixture of digestive enzymes produced by the pancreas.

Trypsinogen

An inactive enzyme that digests proteins once activated.

Chymotrypsinogen

An inactive enzyme involved in protein digestion.

Procarboxypeptidase

An inactive enzyme that participates in protein digestion.

Pancreatic Amylase

Enzyme that digests carbohydrates.

Pancreatic Lipase

Enzyme that digests lipids.

Bicarbonate

A substance released by the pancreas that neutralizes stomach acid in the small intestine.

Acinar Cells

Pancreatic cells that produce digestive enzymes.

Liver

The heaviest organ in the body that produces bile.

Gallbladder

An organ that stores bile produced by the liver.

Bile

A yellow-green substance that emulsifies fats.

Emulsification

The process of breaking large fat droplets into smaller droplets.

Micelles

Vesicles that package lipids for absorption.

Small Intestine

The primary site of digestion and absorption of nutrients.

Length of Small Intestine

Approximately 6 meters.

Three Sections of Small Intestine

Duodenum, jejunum, and ileum.

Duodenum

The first section of the small intestine where most digestion occurs.

Peptidase

Enzyme that breaks peptides into amino acids.

Maltase

Enzyme that breaks maltose into glucose.

Sucrase

Enzyme that breaks sucrose into glucose and fructose.

Lactase

Enzyme that breaks lactose into glucose and galactose.

Enterokinase

Enzyme that activates trypsinogen into trypsin.

Trypsin

Activated enzyme that activates other pancreatic enzymes.

Final Absorbed Carbohydrate

Glucose.

Final Absorbed Protein

Amino acids.

Final Absorbed Lipids

Fatty acids.

Fat-Soluble Vitamins

Vitamins A, D, E, and K that are absorbed with lipids.

Water-Soluble Vitamins

Vitamin B and Vitamin C absorbed by diffusion.

Vitamin B12

A vitamin that requires intrinsic factor for absorption.

Intrinsic Factor

A substance produced in the stomach required for vitamin B12 absorption.

Pernicious Anemia

A condition caused by vitamin B12 deficiency due to lack of intrinsic factor.

Large Intestine

The organ responsible for water absorption and formation of feces.

Functions of the Large Intestine

Water absorption, electrolyte absorption, and feces formation.

Intestinal Flora (Gut Microbiota)

Trillions of bacteria living in the large intestine.

Microflora

Another term for intestinal bacteria.

Functions of Gut Bacteria

Help digest fiber, produce vitamin K, produce vitamin B12, and produce fatty acids.

Belching

The release of gas caused by swallowed air.

Flatulence

Gas produced by bacterial metabolism in the digestive tract.

Heartburn

A burning sensation caused by stomach acid entering the esophagus.

Gastroesophageal Sphincter

A ring of smooth muscle that prevents stomach contents from moving into the esophagus.

GERD (Gastroesophageal Reflux Disease)

A chronic condition where acid reflux damages the esophagus.

Ulcer

A painful lesion in the stomach lining caused by bacterial infection.

Helicobacter pylori

Bacteria that cause stomach ulcers.

Celiac Disease

An immune reaction to gluten that damages the small intestine.

Gliadin

A protein in wheat that triggers celiac disease.

Gluten

A protein found in wheat, barley, and rye associated with celiac disease.

Crohn’s Disease

An inflammatory disease that commonly affects the ileum of the small intestine but may occur anywhere in the digestive tract.

Symptoms of Crohn’s Disease

Severe diarrhea, fever, fatigue, abdominal pain, reduced appetite, and weight loss.

Cause of Crohn’s Disease

Exact cause is unknown; diet and stress may aggravate symptoms but are not direct causes.

Ulcerative Colitis

Inflammation of the mucosal lining of the colon that can cause bloody stool.

Treatment of Ulcerative Colitis

Often treated with anti-inflammatory medications.

Gut Microbiome

The community of bacteria living in the digestive tract.

Importance of Healthy Gut Flora

Healthy bacteria release beneficial substances that support metabolism and cardiovascular health.