Chapter 25: Digestive System Practice Flashcards

This set explores the anatomy and physiology of the human digestive system, including organ functions, enzymatic processes, and the movement of residue through the gastrointestinal tract.

Digestive system

An organ system that processes food, extracts nutrients, and eliminates residue.

Ingestion

The selective intake of food into the digestive system.

Digestion

The mechanical and chemical breakdown of food into forms usable by the body.

Absorption

The uptake of nutrient molecules into the epithelial cells of the digestive tract and then into the blood and lymph.

Compaction

The process of absorbing water and consolidating indigestible residue into feces.

Defecation

The elimination of feces from the body.

Mechanical digestion

The physical breakdown of food into smaller particles through actions like chewing and churning.

Chemical digestion

A series of hydrolysis reactions that breaks dietary macromolecules into their monomers.

Digestive enzymes

Proteins produced by salivary glands, stomach, pancreas, and small intestine to carry out chemical digestion.

Digestive tract

A muscular tube extending from the mouth to the anus, also known as the alimentary canal.

Gastrointestinal (GI) tract

The portion of the digestive system consisting of the stomach and intestines.

Accessory organs

Organs including the teeth, tongue, salivary glands, liver, gallbladder, and pancreas that assist in digestion.

Mucosa

The innermost layer of the digestive tract that lines the lumen and secretes mucus, enzymes, and hormones.

Submucosa

The layer of the digestive tract wall containing blood and lymphatic vessels and elastic tissue.

Muscularis externa

The muscular layer of the digestive tract wall consisting of inner circular and outer longitudinal layers.

Serosa

The outer layer of the digestive tract wall composed of areolar tissue and simple squamous mesothelium.

Inner circular layer

A layer of the muscularis externa that can form sphincters to regulate the passage of material.

Oral cavity

Also known as the mouth or buccal cavity; the site of ingestion and the start of mechanical digestion.

Mastication

The process of chewing; breaks food into smaller pieces to expose more surface area to enzymes.

Saliva

A fluid that is $99.5\%$ water and contains mucus, electrolytes, lysozymes, antibodies, and salivary amylase.

Bolus

A soft mass of food mixed with saliva that is swallowed.

Salivary amylase

An enzyme in saliva that begins the chemical breakdown of starches.

Intrinsic salivary glands

Small glands scattered throughout the oral cavity that secrete saliva at a constant rate.

Extrinsic salivary glands

Three pairs of glands connected to the oral cavity by ducts that secrete $1-1.5\,L$ of saliva per day.

Parotid glands

A pair of extrinsic salivary glands located near the ears.

Submandibular glands

A pair of extrinsic salivary glands located under the jawline.

Sublingual glands

A pair of extrinsic salivary glands located under the tongue.

Pharynx

A muscular funnel that allows the passage of food, fluids, and air, lined with mucus-producing glands.

Esophagus

A muscular tube that conducts the bolus from the pharynx to the stomach.

Peristalsis

Waves of involuntary contractions that move the bolus through the esophagus.

Heartburn

A burning sensation caused by stomach acid regurgitating into the esophagus.

Stomach

A J-shaped organ that primarily functions as a food storage organ and begins chemical digestion of proteins and fats.

Chyme

An acidic, soupy mixture of semi-digested food that passes from the stomach to the small intestine.

Intrinsic factor

A substance secreted by the stomach essential for the absorption of vitamin $B_{12}$.

Cardiac part

The topmost region of the stomach that connects to the esophagus.

Cardiac sphincter

A ring of smooth muscle that regulates the passage of the bolus from the esophagus into the stomach.

Fundus

The superior dome-shaped region of the stomach.

Body of stomach

The large midportion of the stomach.

Pyloric part

The narrower pouch at the inferior end of the stomach.

Pyloric sphincter

A ring of smooth muscle that regulates the passage of chyme from the stomach to the duodenum.

Gastric pits

Depressions in the gastric mucosa that lead to tubular glands.

Tubular (gastric) glands

Glands in the stomach wall that produce gastric juice.

Mucous cells

Cells in the stomach that secrete mucus to protect the lining.

Regenerative (stem) cells

Cells found in the base of gastric pits that divide rapidly to replace dead stomach cells.

Parietal cells

Cells in the stomach that secrete hydrochloric acid ($HCl$), intrinsic factor, and ghrelin.

Ghrelin

A hunger hormone secreted by the parietal cells of the stomach.

Chief cells

Cells in the stomach that secrete gastric lipase and pepsinogen.

Pepsinogen

The inactive precursor to pepsin secreted by chief cells.

Enteroendocrine (G) cells

Cells in the stomach that secrete hormones like gastrin.

Gastric juice

A mixture of water, hydrochloric acid, and pepsin; $2$ to $3\,L$ are produced per day.

Hydrochloric acid (HCl)

Stomach acid with a pH of $1.5–3.5$ that activates pepsin and kills bacteria.

Pepsin

An enzyme formed from pepsinogen by $HCl$ that digests proteins.

Gastric lipases

Stomach enzymes that digest $10\%-15\%$ of dietary fats.

Bicarbonate ($HCO_3^-$)

An ion formed in parietal cells that leaves the cell while chloride enters during $HCl$ production.

Mucosal barrier

A protective layer in the stomach consisting of thick mucus, tight junctions, and rapid cell replacement.

Gastritis

Inflammation of the stomach caused by a breach in the mucosal barrier.

Peptic ulcers

Erosions in the stomach wall due to pepsin and $HCl$, often caused by Helicobacter pylori.

Helicobacter pylori

A bacterium responsible for causing most peptic ulcers.

Cephalic phase

The stage of gastric regulation where the stomach responds to the sight, smell, taste, or thought of food.

Gastric phase

The stage of gastric regulation where ingested food stimulates activity by stretching the stomach or increasing pH.

Intestinal phase

The stage of gastric regulation where the duodenum responds to arriving chyme and moderates gastric activity.

Vagus nerve

Nerve fibers that stimulate gastric secretion during the cephalic phase.

Gastrin

A hormone that triggers the release of $HCl$ in response to food or rising pH in the stomach.

Secretin

A hormone released by the duodenum in response to acidic chyme that inhibits gastric secretion.

Cholecystokinin (CCK)

A hormone released by the duodenum that inhibits gastric secretion and induces gallbladder contraction.

Liver

An accessory organ whose digestive function is the production of bile.

Gallbladder

A sac on the underside of the liver whose chief function is the storage and concentration of bile.

Bile

A yellow-green alkaline solution containing bile salts, bilirubin, cholesterol, and electrolytes.

Bile salts

Cholesterol derivatives that function in fat emulsification and absorption.

Bilirubin

A bile pigment formed from heme that is broken down by bacteria into stercobilin.

Stercobilin

A substance derived from bilirubin that gives feces its brown color.

Common hepatic duct

A duct formed by the merging of the right and left hepatic ducts.

Cystic duct

A duct coming from the gallbladder that joins the common hepatic duct.

Common bile duct

A duct formed by the union of the common hepatic and cystic ducts that empties into the duodenum.

Gallstones

Also called biliary calculi; hard masses in the gallbladder or bile ducts often caused by excess cholesterol.

Pancreas

An endocrine and exocrine gland that supplies digestive enzymes and bicarbonate to the small intestine.

Pancreatic islets

The endocrine portion of the pancreas that secretes insulin and glucagon.

Pancreatic juice

An alkaline mixture of water, enzymes, sodium bicarbonate, and electrolytes produced by the pancreas.

Hepatopancreatic sphincter

A muscular valve that controls the release of bile and pancreatic juice into the duodenum.

Sodium bicarbonate

A component of pancreatic juice that buffers and neutralizes $HCl$ from the stomach.

Pancreatic amylase

A pancreatic enzyme that digests starch in the small intestine.

Pancreatic lipase

A pancreatic enzyme that digests lipids in the small intestine.

Nucleases

Enzymes that break up DNA and RNA during chemical digestion.

Acetylcholine (ACh)

A neurotransmitter that stimulates the pancreas to secrete enzymes during the cephalic phase.

Small intestine

The major organ of chemical digestion and nutrient absorption, measuring $7-13\,ft$ in length.

Duodenum

The first $10\,in$ of the small intestine which receives chyme, bile, and pancreatic enzymes.

Jejunum

The middle portion of the small intestine where most digestion and absorption occurs.

Ileum

The longest and final portion of the small intestine, characterized by being less muscular and vascular than the jejunum.

Circular folds

Internal folds of the small intestine that force chyme to spiral slowly through the lumen.

Villi

Finger-like projections of the intestinal mucosa that contain capillaries and lacteals.

Lacteal

A lymphatic capillary within a villus responsible for lipid absorption.

Microvilli

Extensions of the plasma membrane of enterocytes that create a brush border to increase surface area.

Brush border enzymes

Enzymes secreted by microvilli that assist in the final stages of digestion.

Intestinal crypts

Pores between the bases of villi that lead to tubular glands on the floor of the small intestine.

Enterocytes

The primary epithelial cells of the small intestine that absorb nutrients and secrete intestinal juice.

Paneth cells

Cells deep in intestinal crypts that secrete antimicrobial proteins.

Segmentation

Stationary ring-like constrictions in the small intestine that knead and churn intestinal contents.

Large intestine

An organ approximately $5\,ft$ long and $2.5\,in$ in diameter that reduces meal residue to feces.

Cecum

The blind pouch that forms the first part of the large intestine.

Appendix

A blind tube attached to the cecum populated with lymphocytes and acting as a source of immune cells.