beachy ch 21 digestive

What are the two broad components of the digestive system?

The digestive tract and the other organs that aid digestion (accessory organs).

What is another name for the digestive tract?

The alimentary canal or gastrointestinal (GI) tract.

How is the digestive tract organized?

As a hollow tube that is open at both ends and passes through the ventral cavities of the body.

Why is food in the lumen of the GI tract technically outside the body's internal environment?

The GI tract is continuous with the external environment through the mouth and anus.

List the major segments of the GI tract in order.

Mouth → oropharynx → esophagus → stomach → small intestine (duodenum, jejunum, ileum) → large intestine (cecum, colon, rectum) → anal canal.

Which structures are listed as accessory organs of digestion?

Salivary glands, tongue, teeth, liver, gallbladder, pancreas, and vermiform appendix.

What are the four layers of the GI tract wall, from innermost to outermost?

Mucosa → submucosa → muscularis → serosa.

What are the three components of the mucosa?

Mucous epithelium, lamina propria (loose connective tissue), and muscularis mucosae (thin smooth muscle).

What is the mucosa?

The innermost layer of the GI wall, facing the lumen.

What is the submucosa made of and what does it contain?

Connective tissue containing small glands, blood vessels, and parasympathetic nerves organized into the submucosal plexus.

What is the muscularis of the typical GI tract wall composed of?

An inner circular layer and an outer longitudinal layer of smooth muscle.

What nerve plexus is found in the muscularis?

The myenteric plexus.

What is the serosa?

The outermost layer of the GI wall; it is the visceral layer of the peritoneum.

What is the parietal peritoneum?

The layer of peritoneum lining the walls of the abdominopelvic cavity.

How can the epithelial lining of the GI tract vary along its length?

The upper esophagus has protective stratified squamous epithelium, while much of the remainder has simple columnar epithelium suited for absorption and secretion.

What structures form the boundaries of the oral cavity?

The lips form the anterior boundary, the cheeks form the lateral boundaries, and the hard and soft palates form the roof; the tongue and its muscle foundation form part of the cavity.

What are two functions of the lips described in the chapter?

They keep food in the mouth during chewing and help sense food temperature and texture; they also participate in speech.

What muscle forms much of the bulk of the cheeks?

The buccinator muscle.

What bones form the hard palate?

Portions of the two maxillae and two palatine bones.

What is the function of the soft palate?

It forms a partition between the mouth and the nasopharynx.

What is the uvula?

A small cone-shaped process suspended from the midpoint of the posterior border of the soft palate.

What is the tongue made of and what covers it?

A solid mass of skeletal muscle covered by mucous membrane.

What are the three parts of the tongue?

The blunt root, tip, and central body.

What are papillae and what sensory structures do they possess?

Papillae are rough elevations on the dorsal surface of the tongue that possess taste buds.

What is the lingual frenulum?

A midline fold of mucous membrane on the ventral surface of the tongue that helps anchor it to the floor of the mouth.

What are the tongue's roles in digestion-related activity?

It moves food during mastication and deglutition and also helps form speech sounds.

Why can some soluble drugs be absorbed rapidly when placed under the tongue?

The floor of the mouth and ventral tongue have many superficial blood vessels covered by a thin mucosa.

Where are the salivary glands located relative to the alimentary canal?

Outside the alimentary canal; their exocrine secretions enter the tract through ducts.

What are the three paired major salivary glands?

Parotid, submandibular, and sublingual glands.

About how much saliva do the three major pairs of salivary glands produce each day, according to the chapter?

About 1 liter.

Where are the parotid glands located?

Between the skin and masseter muscle, in front of and below the external ear.

What type of saliva do the parotid glands produce?

Watery, serous saliva containing enzymes but not mucus.

Where do the parotid ducts open?

Into the mouth opposite the upper second molars.

Where are the submandibular glands located?

Just below the angle of the mandible.

What type of secretion do the submandibular glands produce?

A mixture from enzyme-producing and mucus-producing elements.

Where do the submandibular ducts open?

On either side of the lingual frenulum.

Where are the sublingual glands located?

Under the mucous membrane covering the floor of the mouth, in front of the submandibular glands.

What type of saliva do the sublingual glands produce?

Mucous saliva.

How do the sublingual glands drain into the mouth?

Each gland is drained by approximately 8 to 20 ducts opening into the floor of the mouth.

What are the main functions of teeth in digestion?

To cut, tear, and grind food so it can mix with saliva before swallowing.

What are the three main parts of a typical tooth?

Crown, neck, and root.

What is the crown of a tooth?

The exposed portion of the tooth, covered by enamel.

What is enamel?

The hard, chemically stable tissue covering the crown; the chapter identifies it as the hardest tissue in the body.

What is the neck of a tooth?

The section connecting the crown with the root.

Where does the root of a tooth fit?

Into the socket of the alveolar process of the upper or lower jaw.

What holds the tooth root in its socket?

The fibrous periodontal membrane suspends it in the socket.

What is dentin and where is it located?

The tissue making up most of the tooth shell; it is covered by enamel in the crown and cementum in the root area.

What is cementum?

Dental tissue covering the dentin in the root area.

What does the pulp cavity contain?

Connective tissue, blood and lymphatic vessels, and sensory nerves.

How many deciduous and permanent teeth are there?

There are 20 deciduous teeth and 32 permanent teeth.

What does dentition refer to?

The type, number, and arrangement of teeth in the jaws.

At about what age does the first deciduous tooth usually erupt?

About 6 months of age.

During what age range are deciduous teeth generally shed?

Between 6 and 13 years of age.

When do third molars (wisdom teeth) usually erupt?

Usually sometime after 17 years of age.

What is a bolus?

A rounded mass of food being swallowed.

Through which part of the pharynx does a swallowed food bolus pass after leaving the mouth?

The oropharynx.

Describe the esophagus.

A collapsible, muscular, mucosa-lined tube about 25 cm (10 inches) long that extends from the pharynx to the stomach.

What is the function of the esophagus?

It serves as a muscular passageway that pushes food toward the stomach.

Where is the esophagus located relative to the trachea and heart?

Posterior to the trachea and heart.

How does the muscle type change along the esophagus?

The upper third is striated, the middle third is mixed striated and smooth, and the lower third is smooth muscle.

What is the upper esophageal sphincter's (UES) role?

It helps prevent air from entering the esophagus during respiration.

What permits belching, according to the chapter?

Relaxation of the upper esophageal sphincter allows trapped air to escape.

What is another name for the lower esophageal sphincter (LES)?

The cardiac sphincter.

What is a hiatal hernia?

A condition in which the esophageal hiatus enlarges enough for part of the stomach to push upward through the diaphragm into the chest.

What is an upper GI x-ray study used to detect?

It evaluates the lower esophagus, stomach, and duodenum for ulcerations, tumors, inflammation, obstruction, or anatomical malpositions such as hiatal hernia.

Where is the stomach located?

Just below the diaphragm.

What are the four named regions of the stomach?

Cardia, fundus, body, and pylorus.

What is the fundus of the stomach?

The enlarged portion to the left and above the opening of the esophagus into the stomach.

What is the body of the stomach?

The central part of the stomach.

What is the pylorus?

The lower portion of the stomach.

What is the cardia?

The small collar or margin of the stomach at its junction with the esophagus.

What do sphincter muscles do at the stomach openings?

They regulate passage of material into and out of the stomach.

What does the lower esophageal (cardiac) sphincter control?

The opening of the esophagus into the stomach.

What does the pyloric sphincter control?

The opening from the pyloric portion of the stomach into the duodenum.

What are rugae?

Folds in the epithelial lining of the stomach.

What are gastric pits?

Marked depressions within the stomach's rugae.

What are gastric glands?

Coiled tubular glands below the gastric pits that secrete most of the gastric juice.

What do chief cells secrete?

The enzymes of gastric juice, including pepsinogen.

What do parietal cells secrete?

Hydrochloric acid (HCl) and intrinsic factor.

What do gastric endocrine cells secrete?

Ghrelin and gastrin.

What is the role of ghrelin?

It stimulates the hypothalamus to increase appetite and is described as stimulating growth hormone secretion.

What is the role of gastrin?

It influences digestive functions and stimulates gastric secretion.

What are the three smooth-muscle sublayers of the stomach muscularis?

Longitudinal, circular, and oblique layers.

Why is the stomach's three-layer muscle arrangement useful?

It allows strong contractions at many angles and makes mixing efficient.

What are the major functions of the stomach?

Food reservoir; secretion of gastric juice and intrinsic factor; churning and mixing food with gastric juice; limited absorption; production of gastrin and ghrelin; and destruction of swallowed pathogenic bacteria.

How does the stomach help protect the body from pathogens?

Its acid helps destroy pathogenic bacteria swallowed with food or respiratory mucus.

What are the approximate dimensions of the small intestine in the chapter?

About 2.5 cm (1 inch) in diameter and 6 m (20 ft) long.

Name the three divisions of the small intestine in proximal-to-distal order.

Duodenum → jejunum → ileum.

What is the duodenum?

The uppermost division of the small intestine, attached to the pyloric end of the stomach; it is about 25 cm (10 inches) long.

What are the approximate length and position of the jejunum?

It follows the duodenum and extends about 2.5 m (8 ft).

What are the approximate length and position of the ileum?

It is the final division of the small intestine and is about 3.5 m (12 ft) long.

What are plicae?

Circular folds of the small-intestinal lining.

What are villi?

Tiny projections on the mucosa of the small intestine.

What structures are found inside each intestinal villus?

An arteriole, a venule, and a lymph vessel called a lacteal.

What other cell types are found on intestinal villi?

Mucus-secreting goblet cells and endocrine cells that produce intestinal hormones.

What are microvilli?

Tiny projections covering the surface of cells on the villi.

How do plicae, villi, and microvilli help the small intestine?

They greatly increase surface area, allowing efficient digestion and absorption of nutrients.

What are the approximate dimensions of the large intestine?

About 1.5 to 1.8 m (5 to 6 ft) long, with a larger diameter than the small intestine.

What are the three broad divisions of the large intestine?

Cecum, colon, and rectum.

What is the cecum?

The first 5 to 8 cm (2 to 3 inches) of the large intestine; a blind pouch in the lower right quadrant of the abdomen.