Chapter 24 The Digestive System

What is the main function of the digestive system?

to break down food, absorb the nutrients that can be used by body cells, and eliminate the remaining waste.

List and define the six primary processes of the digestive system.

1) ingestion = entry of food; 2) mechanical digestion and propulsion = crushing and shearing of food to make it more susceptible to enzymes and the propelling of food along the digestive tract; 3) chemical digestion = the chemical breakdown of food into smaller products for absorption; 4) secretion = the release of water, acids, and other substances by the epithelium of the digestive tract and by glandular organs; 5) absorption = movement of digested particles across the digestive epithelium and into the interstitial fluid of the digestive tract; 6) defecation = the elimination of wastes as feces from the body.

What effect would a drug that blocks parasympathetic stimulation of the digestive tract have on peristalsis.

A drug that blocks parasympathetic stimulation, which increases muscle tone and activity in the digestive tract, would slow peristalsis.

does a high-fat meal raise or lower the level of cholecystokinin in the blood?

A high-fat meal would raise the cholecystokinin level in the blood.

What component of food would increase the number of chylomicrons in the lacteals?

Because chylomicrons are formed from the fats digested in a meal, fats increase the number of chylomicrons in the lacteals.

The digestion of which nutrient would be most impaired by damage to the exocrine pancreas?

Damage to the exocrine pancreas would most impair the digestion of fats, because it is the primary source of lipases. Even though such damage would also reduce carbohydrate and protein digestion, enzymes for digesting these nutrients are produced by other digestive system structures, including the salivary glands, the small intestine, and the stomach.

The digestion of which nutrient would be affected by damage to the parotid salivary glands?

Damage to the parotid glands, which secrete the carbohydrate-digesting enzyme salivary amylase would interfere with the digestion of complex carbohydrates.

Identify general digestive system changes that occur with aging.

General age-related digestive system changes include decreased mitotic activity of epithelial cells, decreased secretory mechanisms, decreased gastric and intestinal motility, and loss of muscle tome associated with tract sphincters: cumulative damage becomes more apparent, cancer rates increase, and dehydration occurs as a result of decreased osmoreceptor sensitivity.

Differentiate between haustral churning and mass movements.

In haustral churning, segmentation movements mix the contents of nearby haustra. In mass movements, which occur a few times per day, strong peristaltic contractions move material from the transverse colon through the rest of the large intestine.

How does a large meal affect the pH of blood leaving the stomach?

Large meals, especially meals with a high protein content, stimulate increased stomach acid secretion. When gastric glands are secreting, bicarbonate ions enter the bloodstream and increase the blood pH. This phenomenon is referred to as the alkaline tide.

Describe the portal triad.

Made up of hepatic artery, hepatic portal vein and bile duct

Identify the muscles associated with the pharynx and deglutition.

Muscles associated with the pharynx and deglutition are the palatal muscles, the palatopharyngeal, stylopharyngeus, and pharyngeal constrictors.

The absorption of which vitamin would be impaired by the removal of the stomach?

Removal of the stomach would interfere with the absorption of vitamin B12. Parietal cells of the stomach are the source of intrinsic factor, which is required for the vitamin's absorption.

Identify the functional relationships between the digestive system and other body systems.

The digestive system absorbs the organic substrates, vitamins, ions, and water required by cells of all other body systems.

Which type of epithelium lines the oral cavity?

Stratified squamous epithelium lines the oral cavity. It protects against friction or abrasion by food.

Name the structures associated with the oral cavity.

Structures associated with the oral cavity include the tongue, teeth, and salivary glands.

Where are the fauces located?

The fauces are the dividing line between the oral cavity and the pharynx.

Identify the four regions of the colon. Name some major histological differences between the large intestine and the small intestine.

The four regions of the colon are the ascending colon, transverse colon, descending colon, and sigmoid colon.

How would the pH of the intestinal contents be affected if the small intestine did not produce secretin?

The hormone secretin, among other things, stimulates the pancreas to release fluid high in buffers to neutralize the chyme that enters the duodenum from the stomach. If the small intestine did not produce secretin, the pH of the intestinal contents would be lower than normal.

Which type of tooth is most useful for chopping off bits of rigid food?

The incisors are the teeth most useful for chopping pieces of relatively rigid food, such as raw vegetables.

Name some major histological differences between the large intestine and the small intestine.

The large intestine is larger in luminal diameter than the small intestine. The thin walls of the large intestine lack villi and have an abundance of mucous cells and intestinal glands.

Name the layers of the gastrointestinal tract beginning at the surface of the lumen.

The layers of the gastrointestinal tract, beginning at the surface of the lumen, are serosa.

Discuss the significance of the low pH in the stomach.

The low pH of thee stomach creates an acidic environment that kills most microorganisms ingested with food, denatures proteins and inactivates most enzymes in food, helps break down plant cell walls and meat connective tissue, and activates pepsin.

What is the importance of the mesenteries?

The mesenteries—sheets consisting of two layers of serous membrane connected by their loose connective tissue—support and stabilize the organs in the abdominopelvic cavity and provide a route for the associated blood vessels, nerves, and lymphatic vessels.

Compared to other segments of the digestive tract, what is unusual about the muscular layer of the esophagus?

The muscular layer of the esophagus is an unusual segment of the digestive tract because it contains skeletal muscle ells along most of the length of the esophagus and is surrounded by an adventitia.

Name the nutrients the body requires.

The nutrients the body requires are carbohydrates, lipids, proteins, vitamins, electrolytes, minerals, and water.

Describe the structure and function of the pharynx.

The pharynx is an anatomical space that receives a food bolus or liquid and passes it to the pharynx.

What body systems may be affected by inadequate calcium ion absorption?

The skeletal, muscular, nervous, endocrine, and cardiovascular systems may all be affected by inadequate absorption of calcium ions.

How is the small intestine adapted for nutrient absorption?

The small intestine has several adaptations that increase its surface area and thus its absorptive capacity for nutrients. The walls of the small intestine have folds called circular folds. The mucosa that covers the circular folds has fingerlike projections, the villi. The epithelial cells that cover the villi have an exposed surface covered by small fingerlike projections, the microvilli. In addition the small intestine has a very rich supply of blood vessels and lymphatic vessels, which transport the nutrients that are absorbed.

Name the structure connecting the pharynx to the stomach.

The structure connecting the pharynx to the stomach is the esophagus.

Name the three regions of the small intestine from proximal to distal.

The three regions of the small intestine from proximal to distal are the duodenum, jejunum, and ileum.

When a person suffers from chronic gastric ulcers, the branches of the vagus nerves that supply the stomach re sometimes cut in an attempt to provide relief. Why might this be an effective treatment?

The vagus nerves contain parasympathetic motor fibers that can stimulate gastric secretions, even if food is not present in the stomach. Cutting the branches of the vagus nerves that supply the stomach would prevent this type of secretion from occurring and thereby reduce the likelihood of ulcer formation.

Which is more efficient in propelling intestinal contents from one place to another: peristalsis or segmentation?

The waves of contractions responsible for peristalsis are more efficient in propelling intestinal contents than segmentation, which is basically a churning action that mixes intestinal contents with digestive fluids.

Why is diarrhea potentially life threatening, but constipation is not?

When someone with diarrhea loses fluid and electrolytes faster than they can be replaced, the resulting dehydration can be fatal. Although constipation can be quite uncomfortable, it does not interfere with any life-supporting processes; the few toxic wastes normally eliminated by the digestive system can move into the blood and be eliminated by the kidneys.

What is occurring when the soft palate and larynx elevate and the glottis closes?

When the soft palate and larynx elevate and the glottis closes, swallowing is occurring.

Name the four major regions of the stomach.

cardia, fundus, body, pyloric part

Identify the organs of the digestive system

oral cavity, pharynx, esophagus, stomach, small intestine, large intestine, and accessory organs (teeth, tongue, gallbladder, salivary glands, liver, and pancreas)

What is the main function of the gallbladder?

stores and concentrates bile