Key Terms

absorption

passage of digested products from the intestinal lumen through mucosal cells and into the bloodstream or lacteals

accessory digestive organ

includes teeth, tongue, salivary glands, gallbladder, liver, and pancreas

accessory duct

(also, duct of Santorini) duct that runs from the pancreas into the duodenum

acinus

cluster of glandular epithelial cells in the pancreas that secretes pancreatic juice in the pancreas

alimentary canal

continuous muscular digestive tube that extends from the mouth to the anus

aminopeptidase

brush border enzyme that acts on proteins

anal canal

final segment of the large intestine

anal column

long fold of mucosa in the anal canal

anal sinus

recess between anal columns

appendix

(vermiform appendix) coiled tube attached to the cecum

ascending colon

first region of the colon

bacterial flora

bacteria in the large intestine

bile

alkaline solution produced by the liver and important for the emulsification of lipids

bile canaliculus

small duct between hepatocytes that collects bile

bilirubin

main bile pigment, which is responsible for the brown color of feces

body

mid-portion of the stomach

bolus

mass of chewed food

brush border

fuzzy appearance of the small intestinal mucosa created by microvilli

cardia

(also, cardiac region) part of the stomach surrounding the cardiac orifice (esophageal hiatus)

cecum

pouch forming the beginning of the large intestine

cementum

bone-like tissue covering the root of a tooth

central vein

vein that receives blood from hepatic sinusoids

cephalic phase

(also, reflex phase) initial phase of gastric secretion that occurs before food enters the stomach

chemical digestion

enzymatic breakdown of food

chief cell

gastric gland cell that secretes pepsinogen

chylomicron

large lipid-transport compound made up of triglycerides, phospholipids, cholesterol, and proteins

chyme

soupy liquid created when food is mixed with digestive juices

circular fold

(also, plica circulare) deep fold in the mucosa and submucosa of the small intestine

colon

part of the large intestine between the cecum and the rectum

common bile duct

structure formed by the union of the common hepatic duct and the gallbladder’s cystic duct

common hepatic duct

duct formed by the merger of the two hepatic ducts

crown

portion of tooth visible superior to the gum line

cuspid

(also, canine) pointed tooth used for tearing and shredding food

cystic duct

duct through which bile drains and enters the gallbladder

deciduous tooth

one of 20 “baby teeth”

defecation

elimination of undigested substances from the body in the form of feces

deglutition

three-stage process of swallowing

dens

tooth

dentin

bone-like tissue immediately deep to the enamel of the crown or cementum of the root of a tooth

dentition

set of teeth

deoxyribonuclease

pancreatic enzyme that digests DNA

descending colon

part of the colon between the transverse colon and the sigmoid colon

dipeptidase

brush border enzyme that acts on proteins

duodenal gland

(also, Brunner’s gland) mucous-secreting gland in the duodenal submucosa

duodenum

first part of the small intestine, which starts at the pyloric sphincter and ends at the jejunum

enamel

covering of the dentin of the crown of a tooth

enteroendocrine cell

gastric gland cell that releases hormones

enterohepatic circulation

recycling mechanism that conserves bile salts

enteropeptidase

intestinal brush-border enzyme that activates trypsinogen to trypsin

epiploic appendage

small sac of fat-filled visceral peritoneum attached to teniae coli

esophagus

muscular tube that runs from the pharynx to the stomach

external anal sphincter

voluntary skeletal muscle sphincter in the anal canal

fauces

opening between the oral cavity and the oropharynx

feces

semisolid waste product of digestion

flatus

gas in the intestine

fundus

dome-shaped region of the stomach above and to the left of the cardia

G cell

gastrin-secreting enteroendocrine cell

gallbladder

accessory digestive organ that stores and concentrates bile

gastric emptying

process by which mixing waves gradually cause the release of chyme into the duodenum

gastric gland

gland in the stomach mucosal epithelium that produces gastric juice

gastric phase

phase of gastric secretion that begins when food enters the stomach

gastric pit

narrow channel formed by the epithelial lining of the stomach mucosa

gastrin

peptide hormone that stimulates secretion of hydrochloric acid and gut motility

gastrocolic reflex

propulsive movement in the colon activated by the presence of food in the stomach

gastroileal reflex

long reflex that increases the strength of segmentation in the ileum

gingiva

gum

haustral contraction

slow segmentation in the large intestine

haustrum

small pouch in the colon created by tonic contractions of teniae coli

hepatic artery

artery that supplies oxygenated blood to the liver

hepatic lobule

hexagonal-shaped structure composed of hepatocytes that radiate outward from a central vein

hepatic portal vein

vein that supplies deoxygenated nutrient-rich blood to the liver

hepatic sinusoid

blood capillaries between rows of hepatocytes that receive blood from the hepatic portal vein and the branches of the hepatic artery

hepatic vein

vein that drains into the inferior vena cava

hepatocytes

major functional cells of the liver

hepatopancreatic ampulla

(also, ampulla of Vater) bulb-like point in the wall of the duodenum where the bile duct and main pancreatic duct unite

hepatopancreatic sphincter

(also, sphincter of Oddi) sphincter regulating the flow of bile and pancreatic juice into the duodenum

hydrochloric acid (HCl)

digestive acid secreted by parietal cells in the stomach

ileocecal sphincter

sphincter located where the small intestine joins with the large intestine

ileum

end of the small intestine between the jejunum and the large intestine

incisor

midline, chisel-shaped tooth used for cutting into food

ingestion

taking food into the GI tract through the mouth

internal anal sphincter

involuntary smooth muscle sphincter in the anal canal

intestinal gland

(also, crypt of Lieberkühn) gland in the small intestinal mucosa that secretes intestinal juice

intestinal juice

mixture of water and mucus that helps absorb nutrients from chyme

intestinal phase

phase of gastric secretion that begins when chyme enters the intestine

intrinsic factor

glycoprotein required for vitamin B₁₂ absorption in the small intestine

jejunum

middle part of the small intestine between the duodenum and the ileum

labial frenulum

midline mucous membrane fold that attaches the inner surface of the lips to the gums

labium

lip

lactase

brush border enzyme that breaks down lactose into glucose and galactose

lacteal

lymphatic capillary in the villi

large intestine

terminal portion of the alimentary canal

laryngopharynx

part of the pharynx that functions in respiration and digestion

left colic flexure

(also, splenic flexure) point where the transverse colon curves below the inferior end of the spleen

lingual frenulum

mucous membrane fold that attaches the bottom of the tongue to the floor of the mouth

lingual lipase

digestive enzyme from glands in the tongue that acts on triglycerides

lipoprotein lipase

enzyme that breaks down triglycerides in chylomicrons into fatty acids and monoglycerides

liver

largest gland in the body whose main digestive function is the production of bile

lower esophageal sphincter

smooth muscle sphincter that regulates food movement from the esophagus to the stomach

main pancreatic duct

(also, duct of Wirsung) duct through which pancreatic juice drains from the pancreas

major duodenal papilla

point at which the hepatopancreatic ampulla opens into the duodenum

maltase

brush border enzyme that breaks down maltose and maltotriose into two and three molecules of glucose, respectively

mass movement

long, slow, peristaltic wave in the large intestine

mastication

chewing

mechanical digestion

chewing, mixing, and segmentation that prepares food for chemical digestion

mesoappendix

mesentery of the appendix

micelle

tiny lipid-transport compound composed of bile salts and phospholipids with a fatty acid and monoacylglyceride core

microvillus

small projection of the plasma membrane of the absorptive cells of the small intestinal mucosa

migrating motility complex

form of peristalsis in the small intestine

mixing wave

unique type of peristalsis that occurs in the stomach

molar

tooth used for crushing and grinding food

motilin

hormone that initiates migrating motility complexes

motility

movement of food through the GI tract

mucosa

innermost lining of the alimentary canal

mucosal barrier

protective barrier that prevents gastric juice from destroying the stomach itself

mucous neck cell

gastric gland cell that secretes a uniquely acidic mucus

muscularis

muscle (skeletal or smooth) layer of the alimentary canal wall

myenteric plexus

(plexus of Auerbach) major nerve supply to alimentary canal wall; controls motility

nucleosidase

brush border enzyme that digests nucleotides

oral cavity

(also, buccal cavity) mouth

oral vestibule

part of the mouth bounded externally by the cheeks and lips, and internally by the gums and teeth

oropharynx

part of the pharynx continuous with the oral cavity that functions in respiration and digestion

palatoglossal arch

muscular fold that extends from the lateral side of the soft palate to the base of the tongue

palatopharyngeal arch

muscular fold that extends from the lateral side of the soft palate to the side of the pharynx

pancreas

accessory digestive organ that secretes pancreatic juice

pancreatic amylase

enzyme secreted by the pancreas that completes the chemical digestion of carbohydrates in the small intestine

pancreatic juice

secretion of the pancreas containing digestive enzymes and bicarbonate

pancreatic lipase

enzyme secreted by the pancreas that participates in lipid digestion

pancreatic nuclease

enzyme secreted by the pancreas that participates in nucleic acid digestion

parietal cell

gastric gland cell that secretes hydrochloric acid and intrinsic factor

parotid gland

one of a pair of major salivary glands located inferior and anterior to the ears

pectinate line

horizontal line that runs like a ring, perpendicular to the inferior margins of the anal sinuses

pepsinogen

inactive form of pepsin

peristalsis

muscular contractions and relaxations that propel food through the GI tract

permanent tooth

one of 32 adult teeth

pharynx

throat

phosphatase

brush border enzyme that digests nucleotides

porta hepatis

“gateway to the liver” where the hepatic artery and hepatic portal vein enter the liver

portal triad

bile duct, hepatic artery branch, and hepatic portal vein branch

premolar

(also, bicuspid) transitional tooth used for mastication, crushing, and grinding food

propulsion

voluntary process of swallowing and the involuntary process of peristalsis that moves food through the digestive tract

pulp cavity

deepest portion of a tooth, containing nerve endings and blood vessels

pyloric antrum

wider, more superior part of the pylorus

pyloric canal

narrow, more inferior part of the pylorus

pyloric sphincter

sphincter that controls stomach emptying

pylorus

lower, funnel-shaped part of the stomach that is continuous with the duodenum

rectal valve

one of three transverse folds in the rectum where feces is separated from flatus

rectum

part of the large intestine between the sigmoid colon and anal canal

reticuloendothelial cell

(also, Kupffer cell) phagocyte in hepatic sinusoids that filters out material from venous blood from the alimentary canal

retroperitoneal

located posterior to the peritoneum

ribonuclease

pancreatic enzyme that digests RNA

right colic flexure

(also, hepatic flexure) point, at the inferior surface of the liver, where the ascending colon turns abruptly to the left

root

portion of a tooth embedded in the alveolar processes beneath the gum line

ruga

fold of alimentary canal mucosa and submucosa in the empty stomach and other organs

saccharolytic fermentation

anaerobic decomposition of carbohydrates

saliva

aqueous solution of proteins and ions secreted into the mouth by the salivary glands

salivary amylase

digestive enzyme in saliva that acts on starch

salivary gland

an exocrine gland that secretes a digestive fluid called saliva

salivation

secretion of saliva

segmentation

alternating contractions and relaxations of non-adjacent segments of the intestine that move food forward and backward, breaking it apart and mixing it with digestive juices

serosa

outermost layer of the alimentary canal wall present in regions within the abdominal cavity

sigmoid colon

end portion of the colon, which terminates at the rectum

small intestine

section of the alimentary canal where most digestion and absorption occurs

soft palate

posterior region of the bottom portion of the nasal cavity that consists of skeletal muscle

stomach

alimentary canal organ that contributes to chemical and mechanical digestion of food from the esophagus before releasing it, as chyme, to the small intestine

sublingual gland

one of a pair of major salivary glands located beneath the tongue

submandibular gland

one of a pair of major salivary glands located in the floor of the mouth

submucosa

layer of dense connective tissue in the alimentary canal wall that binds the overlying mucosa to the underlying muscularis

submucosal plexus

(plexus of Meissner) nerve supply that regulates activity of glands and smooth muscle

sucrase

brush border enzyme that breaks down sucrose into glucose and fructose

tenia coli

one of three smooth muscle bands that make up the longitudinal muscle layer of the muscularis in all of the large intestine except the terminal end

tongue

accessory digestive organ of the mouth, the bulk of which is composed of skeletal muscle

transverse colon

part of the colon between the ascending colon and the descending colon

upper esophageal sphincter

skeletal muscle sphincter that regulates food movement from the pharynx to the esophagus

Valsalva’s maneuver

voluntary contraction of the diaphragm and abdominal wall muscles and closing of the glottis, which increases intra-abdominal pressure and facilitates defecation

villus

projection of the mucosa of the small intestine

voluntary phase

initial phase of deglutition, in which the bolus moves from the mouth to the oropharynx

α-dextrin

breakdown product of starch

α-dextrinase

brush border enzyme that acts on α-dextrins