Chapter 15: Digestive Tract
What is composed by the oral cavity, esophagus, stomach, small and large intestines, and anus?
What are the eight functions of the digestive tract?
- ingestion of food and liquid
- mastication divides solid food
- motility moves materials through the tract
- secretion of mucus, enzymes, and fluids
- hormone release for local control
- chemical digestion or enzymatic degradation
- absorption of the small molecules and water
- elimination of indigestible components
What are the four main layers of the GI tract?
What are the three layers of the mucosa of the GI tract?
- epithelial lining
- lamina propria
- muscularis mucosae
What plexus of autonomic nerves is located in the submucosa of the GI tract?
submucosal (Meissner) plexus
What are the two layers of the muscularis of the GI tract based on the orientation of the smooth muscle fibers?
- inner circular layer
- outer longitudinal layer
What plexus of autonomic nerves is located in the muscularis of the GI tract?
myenteric (Auerbach) plexus
What do the submucosal plexus and myenteric plexus of the GI tract together comprise?
enteric nervous system
What is the simple squamous epithelium covering the serosa of the GI tract called?
What large fold of adipose connective tissue suspends the intestines and is continuous with the peritoneum?
What thick layer of connective tissue surrounds the esophagus instead of the serosa?
What do the numerous free immune cells and lymphoid nodules in the mucosa and submucosa comprise?
mucosa-associated lymphoid tissue (MALT)
What disease is caused by congenital absence of the plexuses of the enteric nervous system?
What disease is caused by infection with the protozoan Trypanosoma cruzi, resulting in injury to the plexuses of the enteric nervous system?
What vesicular or ulcerating lesions of the oral mucosa are caused by HSV-1?
Where is keratinized squamous epithelium found in the oral cavity?
In the masticatory mucosa on the gingiva (gum) and hard palate.
Where is nonkeratinized squamous epithelium found in the oral cavity?
In the lining mucosa over the soft palate, cheeks, the floor of the mouth, and the pharynx.
What is the transitional zone between internal mucous surface and the outer skin surface of the lip?
What is the V-shaped groove separating the anterior papillary and posterior tonsillar areas of the tongue?
What are the four types of lingual papillae?
Which lingual papillae are very numerous, have an elongated conical shape, and are heavily keratinized?
Which lingual papillae are less numerous, lightly keratinized, and interspersed?
Which lingual papillae consist of several parallel ridges on each side of the tongue?
Which lingual papillae are the largest, normally aligned just in front of the terminal sulcus?
What small, serous glands empty into the deep, moatlike groove surrounding each vallate papilla?
salivary (von Ebner) glands
What ovoid structures within the stratified epithelium on the tongue’s surface sample the general chemical composition of ingested material?
What three cell types comprise a taste bud?
- gustatory (taste) cells
- supportive cells
- stem cells
What is the small opening at the apical ends of the gustatory cells of a taste bud?
How many permanent teeth are found in the normal adult dentition?
How many deciduous teeth are found in the normal primary dentition?
What is the portion of the tooth exposed above the gingiva called?
What is the portion of the tooth that fits into the bony dental alveolus called?
What is the very hard, acellular tissue covering the crown of the tooth?
What is the bone-like tissue covering the root of the tooth?
What is the calcified material, surrounding the pulp cavity of the tooth?
What is the highly vascular and well-innervated tissue in the pumlp cavity and tooth roots?
What is the narrow extension of the pulp cavity into each tooth root?
What is the opening at the tip of each root where blood vessels, lymphatics, and nerves enter the pulp cavity?
What are the fibrous bundles of collagen fibers inserted into both the cementum and the alveolar bone?
What is the composition of dentin?
It consists of 70% hydroxyapatite, and an organic matrix containing type I collagen and proteoglycans.
Which cells lining the pulp cavity secrete predentin that is mineralized into dentin?
What are the spaces through which odontoblasts extend their long apical processes?
What bacterial infection is a frequent cause of pharyngitis and tonsillitis?
What viral infection is a frequent cause of leukoplakia on the sides of the tongue?
What fungal infection causes a white exudate on the tongue’s dorsal surface, oral thrush?
What is the composition of enamel?
It consists of 96% hydroxyapatite with little organic material including few proteins and no collagen.
What are the uniform, interlocking columns that comprise enamel?
Which cells secrete the matrix for the enamel rods in a developing tooth bud?
What specialized area of epithelium in the tooth bud are the ameloblasts part of?
What are the apical extensions from each ameloblast contains numerous secretory granules?
ameloblast (or Tomes) process
What structural protein of developing enamel guides growth of each elongating enamel rod?
What type of disease is caused by inflammation of the gums or tissue surrounding the tooth?
What comprises the structures responsible for maintaining the teeth in the maxilla and mandible?
What four components comprise the periodontium?
- periodontal ligament
- alveolar bone
- associated gingiva
What large, elongated cells function to secrete the bone-like cementum covering the tooth root?
What are former cementoblasts residing in lacunae in the cementum around the tooth root tip called?
What is the a groove between the enamel and the gingival epithelium surrounding the neck of the tooth?
What specialized epithelium is bound to the tooth enamel by means of a cuticle?
What is the muscular tube which transports swallowed material from the pharynx to the stomach?
What small mucus-secreting glands in the submucosa of the esophagus lubricate and protect the mucosa?
What groups of glands in the mucosa of the esophagus near the stomach secrete additional mucus?
esophageal cardiac glands
What condition is caused by reflux of acid from the stomach into the esophagus?
reflux esophagitis (heartburn)
What disease is caused by erosion of the esophageal mucosa due to incompetency of the inferior esophageal sphincter?
gastroesophageal reflux disease (GERD)
What condition can result from metaplastic changes in the stratified squamous epithelium of the esophageal mucosa due to untreated GERD?
How is it that swallowing begins with voluntary muscle action but finishes with involuntary peristalsis?
- In the upper third of the esophagus, the muscularis is exclusively skeletal muscle.
- The middle third of the esophagus has a combination of skeletal and smooth muscle.
- In the lower third of the esophagus, the muscularis is exclusively smooth muscle.
What is the viscous mass of ingested food and acidic fluid produced in the stomach?
What enzyme is secreted by the stomach to promote the initial digestion of proteins?
What autoimmune disease is caused by deficiency of intrinsic factor, leading to inadequate absorption of vitamin B12, and reduced proliferation of erythroblasts?
What four regions make up the stomach?
What is the narrow transitional zone between the esophagus and the stomach?
What is the funnel-shaped region of the stomach that opens into the small intestine?
What are the longitudinal folds in the mucosa and submucosa of the stomach that allow for expansion?
What bacterial infection can cause painful erosive lesions of the mucosa in the stomach and intestine?
What are the invaginations on the mucosal surface of the stomach opening to the stomach lumen?
What cells the stomach lumen and gastric pits secrete a viscous mucous layer that protects the mucosa?
surface mucous cells
What cells are found in a narrow segment (isthmus) between each gastric pit and the gastric glands?
What four important cell types are found lining gastric pits and their associated glands?
- mucous neck cells
- parietal cells
- chief (zymogenic) cells
- enteroendocrine cells
What cells are found in the necks of gastric glands secreting an acidic fluid containing mucin?
mucous neck cells
What cells, found in the necks and deeper parts of the gastric glands, secrete hydrochloric acid (HCl)?
parietal (oxyntic) cells
What is the deep, circular invagination of the apical plasma membrane on parietal cells called?
What enzyme, contained in parietal cells, catalyzes the conversion of water and CO2 into HCO3 – and H+?
Describe HCl synthesis by parietal cells in four steps.
- carbonic anhydrase catalyzes the conversion of H2O and CO2 into HCO3 – and H+
- H+ is pumped into the lumen of the gastric gland in exchange for K+
- HCO3 – is exchanged by antiport at the basal cell domain for Cl–
- Cl– diffuses into the lumen of the gastric gland and combines with H+ to form HCl
What glycoprotein secreted by parietal cells is required for uptake of vitamin B12 in the small intestine?
What polypeptide secreted by enteroendocrine cells stimulates parietal cell secretory activity?
What cells in the lower regions of the gastric glands have granules containing inactive enzyme pepsinogens?
chief (zymogenic) cells
What are pepsinogens converted to in the acid environment of the stomach, which initiate the hydrolysis of ingested protein in the stomach?
What enzyme secreted by chief cells of the gastric glands digests many lipids?
What epithelial cells with endocrine or paracrine functions are scattered throughout the gastric mucosa?
What hormone is secreted enteroendocrine cells in the gastric glands of the fundus?
What peptid is secreted enteroendocrine cells in the gastric glands of the pylorus?
What part of the endocrine system are enteroendocrine cells considered to be part of?
diffuse neuroendocrine system (DNES)
What are serotonin-secreting tumors of enteroendocrine EC cells called?
What are the coiled portions of the tubular glands in the cardia and pylorus which secrete mucus?
cardiac or pyloric glands
What are the three layers of the muscularis of the stomach based on the orientation of the smooth muscle fibers?
- outer longitudinal layer
- middle circular layer
- innermost oblique layer
What is the thickening of the middle muscularis layer at the pylorus of the stomach?
Where is the site where the digestive processes are completed and where the nutrients are absorbed?
The small intestine is approximately 5 m. What are the three segments of the small intestine?
What tumors of smooth muscle cells are the most common tumor of the stomach and small intestine?
What are the circular or semilunar folds in the mucosa and submucosa of the small intestine?
What are the short outgrowths projecting from the mucosa into the lumen of the small intestine?
What is the central lymphatic extending into the core of loose connective tissue of each villus called?
What disease, characterized by an immune reaction to gluten, causes malabsorption and can lead to damage or destruction of the villi?
celiac disease (sprue)
What are the short tubular glands located between the villi of the small intestine?
intestinal glands or crypts (of Lieberkühn)
What are the four main cell types in the mucosa of the small intestine?
- goblet cells
- paneth cells
- enteroendocrine cells
What are the columnar epithelial cells lining the villi which function in absorption?
What is the prominent ordered region of microvilli located at the the apical end of each enterocyte?
striated (or brush) border
Describe the absorption of lipids by enterocytes. (5)
- Ingested fats are emulsified by bile acids to form a suspension of lipid droplets.
- Lipids are digested by lipases to produce glycerol, fatty acids, and monoglycerides.
- The products diffuse across the membranes and resynthesized as triglyceride.
- These triglycerides are packaged in vesicles containing chylomicrons.
- Chylomicrons are into the extracellular space, where most enter the lacteals.
What are the mucin-secreting cells interspersed among the absorptive enterocytes in the small intestine?
What are the secretory located in the basal portion of the intestinal crypts below the stem cells?
What hydrophobic peptides secreted by paneth cells break down membranes of microorganisms?
What specialized epithelial cells, located in the ileum overlying the lymphoid follicles of Peyer patches, play an important part in mucosal immunity?
M (microfold) cells
What is the nerve plexus located in the submucosa of the small intestine?
submucosal (Meissner) nerve plexus
What are the branched tubular glands in the proximal part of the duodenum, which secrete alkaline mucus to neutralize chyme entering from the pylorus?
duodenal (or Brunner) glands,
What are the large lymphoid nodule aggregates, located primarily in the ilium, underlying M cells?
What is the nerve plexus located between the layers of the muscularis of the small intestine?
myenteric (Auerbach) nerve plexus
What chronic inflammatory bowel disease occurs most commonly in the ileum or colon, effecting any or all layers of the tract wall?
What portion of the GI tract absorbs water and electrolytes and forms indigestible material into feces?
large intestine (bowel)
What are the five regions of the large intestine?
- ascending colon
- transverse colon
- descending colon
What structure in the cecum separates the ileum from the large intestine?
What is the blind projection of the cecum containing large aggregates of lymphoid tissue?
What are large sacs arranged in series, making up the walls of the colon?
What are the tubular glands lined by goblet and absorptive cells in the large intestine?
What are the columnar absorptive cells lining the intestinal glands of the large intestine?
What are the three longitudinal bands of smooth muscle within the muscularis of the large intestine?
What adenocarcinoma develops from benign polyps in the mucosal epithelium of the rectum or colon?
What are three screening tests for colorectal cancer?
- fecal occult blood
What painful disorder is caused by swollen blood vessels in the mucosa or submucosa of the anal canal?
What is the 3-4 cm long canal located at the distal end of the GI tract?
What is the transition area where the simple columnar mucosal lining of the rectum is replaced by stratified squamous epithelium of the anal canal?
What are the longitudinal fold in the mucosa and submucosa of the anal canal ?
What is formed by the circular layer of the muscularis of the anal canal at the entrance to the anus?
internal anal sphincter
What is formed by voluntary skeletal muscle surrounding the anus?
external anal sphincter
What are bulges formed by herniation of the mucosa of the colon between teniae coli?
What is local inflammation of diverticula due to impaction of fecal material?
See summary table.