Chapter 22 — The Digestive System

Mechanical digestion and chemical digestion.

In the oral cavity, where salivary enzymes begin chemical digestion of starch.

Mastication mechanically breaks food apart; saliva lubricates food, begins starch digestion, supports taste, and provides defense.

Chewing, or the mechanical breakdown of food in the mouth.

Swallowing; the movement of food from the mouth through the pharynx and esophagus.

It stores food, mixes it with gastric secretions, begins protein digestion, and releases chyme into the small intestine.

Through folds, rugae, plicae, villi, and microscopic projections such as microvilli.

Folds in the stomach lining that allow it to expand.

Circular folds of the small intestine that increase surface area.

Fingerlike projections of the small intestinal mucosa that increase absorptive surface area.

Glandular invaginations in the intestinal mucosa that contain secretory and renewing cells.

It acts as a temporary storage reservoir and regulates the delivery of chyme to the small intestine.

In the small intestine, especially the duodenum.

Mucosa, submucosa, muscularis externa, and serosa.

The innermost layer that faces the lumen and performs secretion, absorption, and protection.

A connective tissue layer containing blood vessels, lymph vessels, and the submucosal nerve plexus.

The smooth muscle layer responsible for mixing and propelling GI contents.

The outer covering of the GI tract, continuous with the peritoneal membrane.

Digestion, absorption, secretion, and motility.

Avoiding autodigestion, maintaining mass balance, and providing defense against pathogens and harmful substances.

Approximately 9 liters per day.

Fluid secreted by the body, such as saliva, gastric juice, bile, pancreatic juice, and intestinal secretions.

Fluid from food and drink that enters through the mouth.

Mixing digestive contents and propelling them along the tract.

Specialized pacemaker cells that generate slow waves and help coordinate GI smooth muscle activity.

Peristaltic contractions, segmentation contractions, and tonic contractions.

A coordinated wave of contraction that propels contents forward through the GI tract.

Localized rhythmic contractions that mix intestinal contents and increase contact with the absorptive surface.

Sustained contractions that maintain tension, such as in sphincters.

The enteric nervous system, often called the gut's "little brain."

Within the enteric nervous system in the wall of the GI tract.

In the central nervous system.

Regulating GI motility by controlling smooth muscle activity.

Regulating secretion, absorption, and local blood flow.

The anticipatory phase initiated by the sight, smell, thought, or taste of food, activating brain pathways that stimulate digestive activity.

The brain activates autonomic pathways that increase salivation, gastric secretion, and digestive activity before food reaches the stomach.

The tongue pushes food into the pharynx; sensory signals trigger a brainstem reflex that closes the airway and moves food into the esophagus.

Storage of food, mixing food into chyme, and initiating protein digestion.

The semifluid mixture of partially digested food and digestive secretions leaving the stomach.

A mucus-bicarbonate barrier, tight epithelial junctions, rapid epithelial replacement, and secretion of pepsin as inactive pepsinogen protect the stomach lining.

Glands in the stomach mucosa that secrete acid, enzymes, mucus, and regulatory substances.

The upper region of the stomach that can store food and gas.

The lower region of the stomach that helps grind and mix food and regulates gastric emptying.

A sphincter that regulates the movement of chyme from the stomach into the duodenum.

They absorb and transport dietary fats, especially chylomicrons, from the small intestine.

A venous system that carries nutrient-rich blood from the digestive organs to the liver before it enters general circulation.

Bile, pancreatic enzymes, pancreatic bicarbonate, intestinal secretions, and mucus.

Hormones such as insulin, glucagon, somatostatin, and pancreatic polypeptide.

Digestive enzymes and bicarbonate-rich fluid delivered into the duodenum.

It neutralizes acidic chyme entering the duodenum from the stomach.

Inactive enzyme precursors that must be activated before they can digest molecules.

Brush-border enteropeptidase converts trypsinogen into trypsin; trypsin then activates other pancreatic zymogens.

It activates trypsinogen to trypsin in the small intestine.

It activates other pancreatic digestive enzyme precursors.

Produces bile; processes and stores nutrients; regulates blood glucose; metabolizes toxins and drugs; synthesizes plasma proteins; and converts ammonia to urea.

A fluid produced by hepatocytes that contains bile salts, bile pigments, cholesterol, and other substances.

In the gallbladder.

The duodenum, through the common bile duct.

They emulsify large fat droplets and help form micelles, allowing lipid digestion and absorption.

Small aggregates of bile salts that carry fatty acids and monoglycerides to the intestinal surface for absorption.

Bile salts emulsify fats; pancreatic lipase and colipase produce fatty acids and monoglycerides; these enter intestinal cells, are reassembled into triglycerides, packaged into chylomicrons, and transported through lymph.

A lipoprotein particle that transports absorbed dietary fats from intestinal cells through lymph and into the blood.

Chylomicrons are too large to enter ordinary blood capillaries efficiently, so they enter intestinal lacteals.

Carbohydrates are digested into monosaccharides, which enter intestinal epithelial cells through specific transporters and then move into portal blood.

Maltose, sucrose, and lactose.

Glucose, galactose, and fructose.

Glucose plus glucose.

Glucose plus fructose.

Glucose plus galactose.

They have insufficient lactase activity, so lactose is not fully digested in the small intestine.

Bloating, gas, abdominal discomfort, and diarrhea due to undigested lactose in the intestine.

Proteins are digested into amino acids and small peptides, which enter intestinal epithelial cells through transporters and then pass into portal blood.

An enzyme that breaks peptide bonds within a protein chain.

An enzyme that removes amino acids from the ends of a peptide chain.

Endopeptidases cut internal peptide bonds; exopeptidases remove terminal amino acids.

A stomach hormone that stimulates gastric acid secretion and supports gastric motility.

A small-intestinal hormone that stimulates pancreatic enzyme secretion and gallbladder contraction and slows gastric emptying.

A small-intestinal hormone released in response to acidic chyme that stimulates bicarbonate secretion.

A hormone that helps regulate migrating motor complexes during fasting.

An intestinal hormone that promotes insulin release and helps reduce gastric activity.

An intestinal hormone that stimulates glucose-dependent insulin secretion, suppresses glucagon, slows gastric emptying, and promotes satiety.

Signals from the duodenum, including CCK and secretin, slow gastric emptying when acidic, fatty, or concentrated chyme enters the small intestine.

The first section of the small intestine, where chyme mixes with bile and pancreatic secretions.

The middle section of the small intestine and a major site of nutrient absorption.

The final section of the small intestine, which absorbs remaining nutrients including bile salts and vitamin B12.

Absorb water and electrolytes, house gut microbes, compact and store feces, and eliminate waste.

Gas passed from the digestive tract through the rectum and anus.

A passageway that carries swallowed food from the mouth toward the esophagus.

A muscular tube that moves food from the pharynx to the stomach by peristalsis.

Accessory digestive glands that produce saliva to lubricate food and begin starch digestion.

An accessory organ that releases digestive enzymes and bicarbonate into the intestine and hormones into the blood.

An organ that processes absorbed nutrients, produces bile, detoxifies substances, and performs important metabolic functions.

The hollow interior through which food and digestive contents pass.