Chapter 17 questions

1. List and describe the locations of the major parts of the alimentary canal.

a. Mouth—the oral cavity.

b. Pharynx—extends from the back of the nasal cavity to the top of the esophagus.

c. Esophagus—extends from the pharynx to the stomach.

d. Stomach—just below the diaphragm on the left side of the body.

e. Small intestine—extends from the stomach to the large intestine.

f. Large intestine—extends from the small intestine to the anus.

2. List and describe the location of the accessory organs of the digestive system.

a. Salivary glands—located in the oral cavity.

b. Liver—lies just below the diaphragm on the right side of the body.

c. Gallbladder—lies on posterior side of the liver.

d. Pancreas—located behind the stomach, attached to the duodenum.

3. Name the four layers of the wall of the alimentary canal.

a. Mucosa or mucous membrane

b. Submucosa

c. Muscular layer

d. Serosa or serous layer

4. Distinguish between mixing movements and propelling movements.

A mixing movement is a wavelike motion back and forth. A propelling movement is one where the muscle contraction occurs in the wall of the tube but the muscles just ahead in the tube relax.

5. Define peristalsis.

Peristalsis is defined as the rhythmic propelling movements that occur in the alimentary canal.

6. Explain the relationship between peristalsis and receptive relaxation.

Receptive relaxation is where the muscular wall ahead of peristaltic contraction relaxes. This allows the tubular contents to be pushed along the canal.

7. Describe the general effects of parasympathetic and sympathetic impulses on the alimentary canal.

Parasympathetic impulses generally increase the activity of the digestive system. Sympathetic impulses

generally are opposite of the parasympathetic impulses, thereby decreasing the activity of the digestive system.

This would then mean that peristalsis increases when innervated by the parasympathetic nervous system and would decrease when innervated by the sympathetic nervous system.

8. Discuss the functions of the mouth and its parts.

The mouth receives food and prepares it for digestion by mechanically breaking up the size of solid particles and mixing them with saliva. The cheeks are the outer layers of skin, pads of subcutaneous fat, and the muscles associated with expression and chewing. The lips are highly mobile structures that contain skeletal muscles and the sensory receptors that surround the mouth. They are used in distinguishing the temperature and texture of foods. The tongue is a body of skeletal muscle and taste receptors. The function of the tongue is to mix food particles with saliva during chewing and move food toward the pharynx during swallowing.

9. Distinguish among the lingual, palatine, and pharyngeal tonsils.

The lingual tonsils are found on the root of the tongue and are rounded masses of lymphatic tissues. The

palatine tonsils are masses of lymphatic tissues found in the back of the mouth, on either side of the tongue, and closely associated with the palate. The pharyngeal tonsils, also known as the adenoids, are masses of lymphatic tissue that occur on the posterior wall of the pharynx, above the border of the soft palate.

10. Compare the primary and secondary teeth.

Primary teeth are the first set of teeth that erupt through the gums at regular intervals between the ages of six months and two and one-half years. There are twenty primary teeth - ten in each jaw. The secondary teeth begin to appear about age six but may not be completed until somewhere between ages seventeen and twenty-five.

There are thirty-two secondary teeth—sixteen in each jaw.

11. Explain how the various types of teeth are adapted to perform specialized functions.

The incisors are chisel-shaped, and their sharp edges bite off relatively large pieces of food. The cuspids are cone-shaped, and they grasp and tear food. The bicuspids and molars have somewhat flattened surfaces and are specialized for grinding food particles.

12. Describe the structure of a tooth.

Each tooth consists of two main portions called the crown and the root. The crown is the portion above the

gum and is covered by glossy white enamel. Beneath the enamel is the bulk of the tooth, which is made up of dentin. Dentin surrounds the central cavity, which houses the blood vessels, nerves and connective tissue. The root is enclosed by cementum, which is surrounded by the periodontal ligament. The region where the crown and root meet is called the neck.

13. Explain how a tooth is anchored in its socket.

Cementum and the periodontal ligament anchor the tooth.

14. List and describe the locations of the major salivary glands.

The parotid glands are the largest salivary glands and are located in front of, and somewhat below, each ear between the skin of the cheek and the masseter muscle. The submandibular glands are located in the floor of the mouth on the inside surface of the lower jaw. The sublingual glands are the smallest of the salivary glands and are on the floor of the mouth under the tongue.

15. Explain how the secretions of the salivary glands differ.

The parotid glands secrete a clear, watery fluid that is rich in amylase. The submandibular glands secrete a

serous fluid with some mucous, making it more viscous than the parotid gland secretion. The sublingual glands secrete a thick and stringy mucous fluid.

16. Discuss the digestive functions of saliva.

The serous cells found in the salivary glands produce a watery fluid that contains amylase. Amylase is a digestive enzyme that splits starch and glycogen molecules into disaccharides. This is the first step of carbohydrate digestion.

17. Name and locate the three major regions of the pharynx.

a. Nasopharynx—located above the soft palate.

b. Oropharynx—located behind the soft palate and projects downward to the upper border of the epiglottis.

c. Laryngopharynx—located from the upper border of the epiglottis downward to the lower border of the cricoid cartilage of the larynx.

18. Describe the mechanism of swallowing.

The steps in the mechanism of swallowing are:

a. The soft palate raises, preventing food from entering the nasal cavity.

b. The hyoid bone and the larynx are elevated; the epiglottis closes off the top of the trachea so that food is less likely to enter.

c. The tongue is pressed against the soft palate, sealing off the oral cavity from the pharynx.

d. The longitudinal muscles in the pharyngeal wall contract, pulling the pharynx upward toward the food.

e. The lower portion of the inferior constrictor muscles relaxes, opening the esophagus.

f. The superior constrictor muscles contract, stimulating a peristaltic wave to begin in the pharyngeal muscles. This wave forces the food into the esophagus.

19. Explain the functions of the esophagus.

The esophagus functions as a tube that transports substances from the pharynx to the stomach.

20. Describe the structure of the stomach.

The stomach is a J-shaped, pouch-like organ. Thick folds called rugae mark its inner lining. Its mucous

membrane lining contains the gastric pits that are the openings for the gastric glands that secrete digestive enzymes.

21. List the enzymes in gastric juice, and explain the function of each enzyme.

a. Pepsin—is a protein-splitting enzyme, which is the beginning of nearly all types of dietary protein. The

chief cells secrete pepsinogen (the precursor of pepsin) that then combines with hydrochloric acid to

form pepsin.

b. Intrinsic factor—aids in the absorption of vitamin B12.

22. Explain how gastric secretions are regulated.

Parasympathetic impulses and the hormone gastrin enhance the gastric secretions. The presence of the food in the small intestine reflexly inhibits the gastric secretions.

23. Describe the mechanism that controls the emptying of the stomach.

The chyme accumulates near the pyloric sphincter. This muscle begins to relax. The pyloric region of the

stomach then pumps the chyme a little at a time into the small intestine. The rate at which the stomach empties is dependent upon the fluidity of the chyme and the type of food present.

24. Describe the enterogastric reflex.

The enterogastric reflex inhibits the gastric peristalsis and the secretion when the food enters the small intestine.

25. Explain the mechanism of vomiting.

Sensory impulses travel from the site of stimulation to the vomiting center in the medulla oblongata, and a number of motor responses follow. These include taking a deep breath, raising the soft palate and thus closing the nasal cavity, closing the opening to the trachea (glottis), relaxing the circular muscle fibers at the base of the esophagus, contracting the diaphragm so that it moves downward over the stomach, and contracting the abdominal wall muscles so that pressure inside the abdominal cavity increases. As a result, the stomach is squeezed from all sides, forcing its contents upward and out through the esophagus, pharynx, and mouth.

26. Describe the location of the pancreas and the pancreatic duct.

The pancreas is an elongated, somewhat flattened organ that is posterior to the stomach and behind the parietal peritoneum. It is attached to the duodenum by the pancreatic duct, which runs the length of the pancreas.

27. List the enzymes in pancreatic juice, and explain the function of each enzyme.

a. Pancreatic amylase—functions to digest carbohydrates.

b. Pancreatic lipase—functions to digest triglycerides.

c. Trypsin—functions to digest protein.

d. Chymotrypsin—functions to digest protein.

e. Carboxypeptidase—functions to digest protein.

f. Nucleases—functions to break nucleic acids into nucleotides.

28. Explain how pancreatic secretions are regulated.

Secretin stimulates the release of pancreatic juice that has a high bicarbonate ion concentration.

Cholecystokinin stimulates the release of pancreatic juice that has a high concentration of digestive enzymes.

Acidic chyme in the duodenum triggers the release of pancreatic juice. As the chyme moves through the

intestine the pancreatic juice is inhibited.

29. Describe the structure of the liver.

The liver is enclosed in a fibrous capsule and divided into lobes by connective tissue. Each lobe is further subdivided into hepatic lobules. These are the functional units of the liver. Each lobule consists of hepatic cells that radiate outward from a central vein.

30. List the major functions of the liver.

a. Carbohydrate metabolism

b. Lipid metabolism

c. Protein metabolism

d. Glycogen and vitamin storage

e. Blood filtering

f. Detoxification

g. Secretion of bile

31. Describe the composition of bile.

Bile is composed of bile salts, bile pigments (bilirubin and biliverdin), cholesterol, and electrolytes.

32. Trace the path of bile from a bile canaliculus to the small intestine.

The bile flows from the bile canal into hepatic ducts. The ducts then merge to form the common hepatic duct. It then can flow into the gallbladder for storage. The common hepatic and cystic duct form the common bile duct. This then empties into the duodenum.

33. Explain how gallstones form.

Gallstones form as a result of cholesterol precipitating out of solution and crystallizing. This can result if the bile becomes too concentrated, the hepatic cells secrete too much cholesterol, or the gallbladder is inflamed.

34. Define cholecystokinin.

Cholecystokinin is a hormone that is released in response to chyme in the duodenum. It then triggers the release of pancreatic juice from the pancreas, and bile from storage in the gallbladder.

35. Explain the functions of bile salts.

Bile salts emulsify fats and aid in the absorption of fatty acids, cholesterol, and certain vitamins.

36. List and describe the locations of the parts of the small intestine.

a. Duodenum—the first twenty-five centimeters of the small intestine, it lies behind the parietal peritoneum.

It is the most fixed portion of the small intestine.

b. Jejunum—the proximal two-fifths of the remainder of the small intestine.

c. Ileum—the remainder of the small intestine.

37. Name the enzymes of the intestinal mucosa, and explain the function of each enzyme.

a. Peptidases—splits peptides into amino acids.

b. Sucrase—splits sucrose into glucose.

c. Maltase—splits maltose into fructose.

d. Lactase—splits lactose into galactose.

e. Intestinal lipase—splits fats into fatty acids and glycerol.

38. Explain regulation of the secretions of the small intestine.

These secretions are stimulated by the direct contact with chyme, which provides both chemical and mechanical stimuli, and by reflexes triggered by distention of the intestinal wall. It is inhibited by the lack of chyme in the small intestine.

39. Describe the functions of the intestinal villi.

a. The villi serve to increase the surface area of the intestinal wall.

b. Monosaccharides, amino acids, fatty acids, and glycerol are absorbed by the villi.

c. Fat molecules with longer chains of carbon atoms enter the lacteals of the villi.

d. Other digestive products enter the villi and are carried away by the blood.

40. Summarize how each major type of digestive product is absorbed.

a. Monosaccharides are absorbed by the villi by diffusion, facilitated diffusion, or active transport. The

blood then carries them away.

b. Amino acids are absorbed by the villi by means of active transport. The blood then carries them away.

c. Fatty acids and glycerol are absorbed by diffusion into the lacteals of the villi. They are then carried away by lymph.

d. Diffusion and active transport into the villi absorb electrolytes.

e. Water is absorbed by osmosis into the villi.

41. Explain control the movement of the intestinal contents.

The major mixing movement is segmentation, in which small, ring-like, contractions occur periodically, cutting the chyme into segments moving it back and forth. Peristaltic waves propel the chyme through the small intestine. These are weak waves so that the chyme moves slowly through the small intestine.

42. List and describe the locations of the parts of the large intestine.

The cecum is a dilated, pouchlike structure that hangs slightly below the ileocecal opening. This represents the beginning of the large intestine. The colon is divided into four parts. The ascending colon begins at the cecum and travels upward against the posterior abdominal wall to a point just below the liver. It turns sharply to the left and becomes the transverse colon. This is the longest and most movable part of the large intestine. As the transverse colon approaches the spleen, it turns abruptly downward and becomes the descending colon. At the brim of the pelvis, the descending colon makes an S-shaped curve, called the sigmoid colon, and then becomes the rectum. The rectum is firmly attached to the sacrum and it ends about five centimeters below the tip of the coccyx. It now is known as the anal canal. The anal canal is the last two and one-half to four centimeters of the large intestine. It ends at the anus, which opens to the outside of the body.

43. Explain the general functions of the large intestine.

a. It has little or no digestive function.

b. It secretes mucous.

c. Absorption is generally limited to water and electrolytes.

d. Formation and storage of feces.

44. Describe the defecation reflex.

A person holds a deep breath and contracts the abdominal wall muscles. This increases the internal abdominal pressure and forces the feces into the rectum. As the rectal wall distends, this triggers the defecation reflex.

Peristaltic waves in the descending colon are stimulated, and the internal anal sphincter relaxes. The external sphincter relaxes and the feces are forced to the outside.

45. What are the effects of altered rates of absorption, due to aging, in the small intestine?

Because the small intestine is the site of absorption of nutrients, it is here that noticeable signs of aging on digestion arise. Subtle shifts in the microbial species that inhabit the small intestine alter the rates of absorption of particular nutrients. With age, the small intestine becomes less efficient at absorbing vitamins A, D, and K and the mineral zinc. This raises the risk of deficiency symptoms—effects on skin and vision due to a lack of vitamin A; weakened bones from inadequate vitamin D; impaired blood clotting seen in vitamin K deficiency;

and slowed healing, decreased immunity, and altered taste evidenced in zinc deficiency.

46. How does digestive function change with age?

Older people sometimes do not chew food thoroughly because thinning enamel makes teeth more sensitive to hot and cold foods, gums recede, and teeth may loosen.

Slowing peristalsis in the digestive tract may cause heartburn and constipation.

Aging affects nutrient absorption in the small intestine.

Accessory organs to digestion also age, but not necessarily in ways that affect health.

Chapter 17 out line

I. Introduction

A. Digestion is the breakdown of foods into forms that cell membranes can absorb.

B. Mechanical digestion breaks large pieces of food into smaller ones without altering their chemical composition.

C. Chemical digestion breaks down food into simpler chemicals.

D. The organs of the digestive system carry out the processes of ingestion, propulsion, absorptions, defecation, and digestion.

E. The alimentary canal is composed of the mouth, pharynx, esophagus, stomach, small intestine, large intestine, and anal canal.

F. The accessory organs of the digestive system are salivary glands, liver, gallbladder, and pancreas.

II. General Characteristics of the Alimentary Canal

A. Introduction

1. The alimentary canal is a muscular tube that passes through the body’s ventral cavity.

2. The structure of its wall, how it moves food, and its innervation are similar throughout its length.

B. Structure of the Wall

1. The four layers of the alimentary wall are the mucosa, submucosa, muscular layer, and serosa.

2. The mucosa is located as the inner lining and is composed of epithelial tissue, a small amount of connective tissue, and some smooth muscle.

3. The functions of the mucosa are to protect the tissues beneath it, secrete mucus and enzymes, and to absorb nutrients.

4. The submucosa is located deep to the mucosa and is composed of loose connective tissue, glands, blood vessels, lymphatic vessels, and nerves.

5. The functions of the submucosa are to nourish surrounding tissues and to carry away absorbed substances.

6. The muscular layer is located between the submucosa and serosa and is composed of two coats of smooth muscle tissue.

7. When the circular fibers contract, the diameter of the tube decreases.

8. When the longitudinal fibers contract, the tube shortens.

9. The serosa layer is located superficial to the muscular layer and is composed of the visceral peritoneum.

10. The functions of the serosa are to moisten and lubricate the outside of the organ.

C. Movements of the Tube

1. The two types of motor functions of the alimentary canal are mixing and propelling.

2. Mixing occurs when smooth muscles in small segments of the tube contract rhythmically.

3. Peristalsis is a wavelike motion.

4. Peristalsis occurs when a ring of contraction moves down the wall of the tube.

D. Innervation of the Tube

1. Branches of the sympathetic and parasympathetic nervous system innervate the alimentary canal.

2. The innervation of the alimentary canal maintains muscular tone

and regulates strength, rate, and velocity of muscular contractions.

3. The submucosal plexus is important for controlling secretions by the gastrointestinal tract.

4. The myenteric plexus is important for gastrointestinal motility.

5. The functions of parasympathetic impulses are to increase the activities of the digestive system.

6. The functions of sympathetic impulses are to decrease the activities of the digestive system.

III. Mouth

A. Introduction

1. The functions of the mouth are to receive food and to begin digestion.

2. Mastication is chewing.

3. The mouth is surrounded by lips, cheek, tongue, and palate.

4. The oral cavity is the space between the tongue and palate.

5. The vestibule of the mouth is the space between the teeth, cheeks, and lips.

B. Cheeks and Lips

1. The cheeks form the lateral walls of the mouth and consist of skin, fat, muscles, and an inner moist lining.

2. The lips surround the mouth opening and consist of skeletal muscles, sensory receptors, and skin.

3. The reddish color of lips is due to the many blood vessels near their surfaces.

C. Tongue

1. The tongue is located in the floor of the oral cavity.

2. Mucous membranes cover the tongue.

3. The frenulum of the tongue is a membranous fold that anchors the tongue to the floor of the mouth.

4. The body of the tongue is composed of skeletal muscles.

5. Muscles of the tongue function to mix food particles and push food to the back of the throat during swallowing.

6. Papillae of the tongue are rough projections on the surface of the tongue.

7. Functions of papillae are to provide friction and to house taste buds.

8. The root of the tongue is anchored to the hyoid bone.

9. Lingual tonsils are located on the root of the tongue.

D. Palate

1. The palate forms the roof of the oral cavity and consists of a hard part and a soft part.

2. The hard palate is formed by the palatine processes of the maxillary bones and palatine bones.

3. The soft palate is formed by a mucous membrane and muscles.

4. The uvula is a downward extension of the soft palate.

5. The function of the uvula is to prevent food or liquids from entering the nasal cavity.

6. Palatine tonsils are located in the back of the mouth on either side of the palate.

7. Pharyngeal tonsils are located on the posterior wall of the pharynx, above the border of the soft palate.

E. Teeth

1. The primary teeth are the first set of teeth to develop.

2. The secondary teeth are the permanent teeth.

3. The secondary teeth consist of 32 teeth.

4. The arrangement of secondary teeth are two incisors, cuspid, two bicuspids, and three molars (from midline to back).

5. Wisdom teeth are the third set of molars.

6. Chewing increases the surface area of food particles.

7. Incisors are specialized to bite off large pieces of food.

8. Cuspids are specialized to grasp and tear food.

9. Bicuspids and molars are specialized to grind food.

10. The crown of a tooth is the portion of the tooth above the gum line.

11. The root of a tooth is the portion of the tooth below the gum line.

12. The neck of a tooth is the area where the crown and root meet.

13. Enamel consists of calcium salts.

14. Dentin is living cellular tissue beneath enamel.

15. The root canal is located in the root of a tooth and contains blood vessels and nerves.

16. The pulp cavity is located in the crown of the tooth and contains blood vessels, nerves and connective tissue called pulp.

17. Cementum is bonelike material that surrounds the root.

18. A periodontal ligament is a fibrous structure that surrounds cementum and anchors the tooth to the jaw.

IV. Salivary Glands

A. Introduction

1. Salivary glands secrete saliva.

2. The functions of saliva are to moisten food, bind food together, and begin the chemical digestion of carbohydrates.

3. The three pairs of major salivary glands are parotid glands, submandibular glands, and sublingual glands.

B. Salivary Secretions

1. Two cell types of salivary glands are serous and mucous.

2. Serous cells produce watery fluid that contains amylase.

3. Mucous cells produce mucus.

4. Amylase digests carbohydrates.

5. Salivary glands are innervated by both sympathetic and parasympathetic nerves.

6. Sympathetic fibers stimulate the glands to secrete a small volume of viscous saliva.

7. Parasympathetic fibers stimulate the glands to secrete a large volume of watery saliva.

C. Major Salivary Glands

1. The largest of the major salivary glands is the parotid.

2. The parotid glands are located anterior and inferior to each ear.

3. A parotid duct is located within the buccinator muscle and opens into the mouth just opposite the upper second molar on either side of the jaw.

4. The parotid glands secrete a water fluid rich in amylase.

5. The submandibular glands are in the floor of the mouth on the inside surfaces of the lower jaws.

6. The submandibular glands secrete primarily serous fluid.

7. Ducts of submandibular glands open inferior to the tongue.

8. The sublingual glands are located on the floor of the mouth inferior to the tongue.

9. The sublingual glands secrete primarily mucus.

10. The ducts of sublingual glands open beneath the tongue.

V. Pharynx and Esophagus

A. Introduction

1. The pharynx is a cavity posterior to the nasal and oral cavities.

2. The pharynx and esophagus function in swallowing.

B. Structure of the Pharynx

1. The pharynx connects the nasal and oral cavities with the larynx and esophagus.

2. The three divisions of the pharynx are the nasopharynx, oropharynx, and laryngopharynx.

3. The nasopharynx is located behind the nasal cavity.

4. The nasopharynx provides a passageway for air.

5. The oropharynx is located behind the oral cavity.

6. The oropharynx is a passageway for food and air.

7. The laryngopharynx is located just inferior to the oropharynx.

8. The laryngopharynx is a passageway to the esophagus.

9. Constrictor muscles function to pull the pharyngeal walls inward during swallowing.

C. Swallowing Mechanism

1. The events of the first stage of swallowing are chewing of food and the mixing of food with saliva.

2. The events of the second stage of swallowing are pushing of food toward the pharynx and the triggering of the swallowing reflex.

3. The events of the third stage of swallowing are movements of food through the esophagus and to the stomach.

4. The actions of the swallowing reflex are raising of soft palate, elevation of larynx and hyoid bone, pressing of tongue against soft palate, contraction of pharyngeal muscles, opening of the esophagus, and movement of food into the esophagus.

D. Esophagus

1. The esophagus is a passageway for food.

2. The esophagus propels food from the pharynx to the stomach.

3. The esophagus descends through the thoracic cavity.

4. The esophageal hiatus is an opening in the diaphragm.

5. Mucous glands are scattered throughout the submucosa of the esophagus.

6. The lower esophageal sphincter is located where the esophagus and stomach join and functions to prevent regurgitation of food.

VII. Stomach

A. Introduction

1. The shape of the stomach is J-shaped.

2. The location of the stomach is just inferior to the diaphragm in the upper left portion of the abdominal cavity.

3. Rugae are thick folds in the lining of the stomach.

4. The functions of the stomach are to mix food with gastric juice, begin protein digestion, to begin a small amount of absorption, and movement of food into the small intestine.

B. Parts of the Stomach

1. The four parts of the stomach are cardiac, fundic, body, and plyloric.

2. The cardiac region is the region near the esophageal opening.

3. The fundic region is a pouch that extends superior to the cardiac portion.

4. The body of the stomach is the main part of the stomach.

5. The pyloric region is the narrow region that is continuous with the small intestine.

6. The pyloric sphincter is located between the pylorus and the duodenum and functions to control the movement of food into the small intestine.

C. Gastric Secretions

1. Gastric pits are openings of gastric glands.

2. The three cell types of gastric glands are parietal, chief, and mucous.

3. Mucous cells secrete mucus.

4. Chief cells secrete digestive enzymes.

5. Parietal cells secrete hydrochloric acid and intrinsic factor.

6. Gastric juice is a mixture of the secretions of mucous, parietal, and chief cells.

7. Pepsin is an enzyme that digests proteins.

8. The function of pepsinogen is to be converted to pepsin when needed.

9. The function of hydrochloric acid in the stomach is to convert pepsinogen into pepsin and to destroy pathogens.

10. The coating of the stomach is important for protecting the stomach wall from digestive enzymes and acids.

11. The function of intrinsic factor is to aid in the absorption of vitamin B₁₂.

D. Regulation of Gastric Secretions

1. Somatostatin is produced in the stomach and functions to inhibit acid secretion.

2. Parasympathetic innervation stimulates the release of gastric juice.

3. Gastrin is produced the stomach and functions to increase the secretory activity of gastric glands.

4. The three stages of gastric secretion are cephalic, gastric, and intestinal.

5. The events of the cephalic phase are secretion of gastric juice before food enters the stomach.

6. The events of the gastric phase are distension of the stomach and the release of more gastric juice.

7. The events of the intestinal phase are the movement of food into the small intestine.

8. Cholecystokinin is produced by the small intestine and functions to inhibit gastric secretions and decreases gastric motility.

E. Gastric Absorption

1. The stomach absorbs alcohol, some drugs, salts, and a small amount of water.

2. Most nutrients are absorbed in the small intestine.

F. Mixing and Emptying Actions

1. A stomachache results from the rise of internal pressure in the stomach.

2. Chyme is food substances that have been mixed with gastric juice.

3. Peristaltic waves push chyme toward the pylorus of the stomach.

4. Stomach contractions push chyme a little at a time into the duodenum

and backwards into the stomach, mixing it further.

5. The lower esophageal sphincter prevents regurgitation of food.

6. The rate at which the stomach empties depends on the fluidity of the chyme and its contents.

7. Liquids usually pass first through the stomach.

8. The enterogastric reflex is a reflex involving the small intestine and the stomach. It is triggered by distension of the small intestine wall and inhibits peristalsis in the stomach to slow down movement of food into the duodenum.

9. Vomiting results from a complex reflex that empties the stomach in the reverse of the normal direction.

VIII. Pancreas

A. Structure of the Pancreas

1. The pancreas is located close to the duodenum posterior to the parietal peritoneum.

2. Pancreatic acinar cells produce digestive enzymes and make up the bulk of the pancreas.

3. Acini are clusters of acinar cells.

4. The pancreatic ducts extend the hepatopancreatic ampulla and empties into the duodenum.

5. Hepatopancreatic ampulla is a dilated tube that receives the pancreatic duct and hepatic duct.

6. The hepatopancreatic sphincter is the sphincter that surrounds the hepatopancreatic ampulla.

B. Pancreatic Juice

1. Pancreatic juice contains many enzymes and bicarbonate ions.

2. The function of pancreatic amylase is to digest carbohydrates.

3. The function of pancreatic lipase is digest lipids.

4. The functions of trypsin, chymotrypsin, and carboxypeptidase are to digest proteins.

5. Zymogen granules are granules that store pancreatic enzymes.

6. The function of trypsinogen is to be converted to trypsin.

7. The functions of nucleases are to digest nucleic acids.

C. Regulation of Pancreatic Secretion

1. Parasympathetic fibers cause the pancreas to release pancreatic juice.

2. The function of secretin is to stimulate the pancreas to release pancreatic juice with a high concentration of bicarbonate ions.

3. The release of cholecystokinin is triggered by the presence of chyme in the small intestine.

4. The action of cholecystokinin on the pancreas is to release pancreatic juice that has a high concentration of digestive enzymes.

IX. Liver

A. Introduction

1. The largest internal organ is the liver.

2. The liver is located in the upper right abdominal quadrant.

B. Liver Structure

1. The two large lobes of the liver are the right and left.

2. The falciform ligament is a fold that separates the lobes of the liver and anchors the liver to the posterior abdominal wall.

3. The two small lobes of the liver are caudate and quadrate.

4. The porta hepatis is where blood vessels and ducts enter or exit the liver.

5. The coronary ligament is a ligament that attaches the liver to the diaphragm.

6. Hepatic lobules are divisions of a liver lobe.

7. A hepatic lobule consists of many hepatic cells radiating outward from a central vein.

8. Hepatic sinusoids are vascular channels in hepatic lobules.

9. Kupffer cells are macrophages of the liver.

10. Bile canaliculi are canals within hepatic lobules that receive secretions from hepatic cells.

11. Hepatic ducts are formed from bile ductules of neighboring hepatic lobules.

C. Liver Functions

1. The liver carries on many important metabolic activities.

2. The liver plays a key role in carbohydrate metabolism by helping maintain the normal blood glucose concentrations.

3. The liver plays a key role in lipid metabolism by oxidizing fatty acids, synthesizing lipoproteins, phospholipids, and cholesterol.

4. The liver plays a key role in protein metabolism by deaminating amino acids, forming urea, synthesizing plasma proteins, and converting amino acids to other forms of amino acids.

5. The liver stores glycogen, iron, and vitamins A,D, and B₁₂.

6. Liver cells help destroy worn out red blood cells.

7. The liver removes toxic substances from the blood.

8. The liver’s role in digestion is to secrete bile.

D. Composition of Bile

1. Bile is secreted by hepatic cells.

2. Bile contains water, bile salts, bile pigments, cholesterol, and electrolytes.

3. Hepatic cells use cholesterol to make bile salts.

4. Bile pigments are products of the breakdown of hemoglobin.

5. Jaundice results from an accumulation of bile pigments in the blood stream.

E. Gallbladder

1. The gallbladder is located inferior to the liver.

2. The cystic duct is the duct of the gallbladder and opens into the common bile duct.

3. The common bile duct is formed from the cystic duct and common hepatic duct and opens into duodenum.

4. Gallstones form when bile is too concentrated, hepatic cells secrete to much cholesterol, or if the gallbladder is inflamed.

F. Regulation of Bile Release

1. Cholecystokinin triggers the gallbladder to release bile.

2. Cholecystokinin is released in response to presence of lipids and proteins in the small intestine.

G. Functions of Bile Salts

1. Functions of bile salts are to aid digestive enzymes by emulsifying fats, and facilitate the absorption of fat soluble vitamins.

2. Emulsification is the breaking of fat globules into smaller droplets.

3. Lack of bile salts results in poor lipid absorption and vitamin deficiencies.

X. Small Intestine

A. Introduction

1. The small intestine extends from the pyloric sphincter to the large intestine.

2. The small intestine receives secretions from the pancreas, gallbladder, and liver.

3. The functions of the small intestine are to complete digestion, absorption of nutrients, and movement of solid wastes to the large intestine.

B. Parts of the Small Intestine

1. The three parts of the small intestine are duodenum, jejunum, and ileum.

2. The duodenum is located posterior to the parietal peritoneum just beneath the stomach.

3. The jejunum is located in the abdominal cavity between the duodenum and ileum.

4. The ileum is located in the abdominal cavity between the jejunum and large intestine.

5. Mesentery is double-layered fold of peritoneum and supports the blood vessels, nerves, and lymphatic vessels that supply the intestinal wall.

6. The greater omentum is a double fold of peritoneal membrane that drapes like an apron from the stomach, over the transverses colon, and the small intestine.

7. The functions of the omentum are to prevent the spread of infections in the peritoneal cavity.

C. Structure of the Small Intestinal Wall

1. The velvety appearance of the inner wall of the small intestine is due to intestinal villi.

2. Intestinal villi are tiny projections of the mucosa of the small intestine.

3. The functions of villi are to increase the surface area of the lining of the small intestine.

4. Each villus consists of a layer of simple columnar epithelium and a core of connective tissue containing blood capillaries, a lacteal, and nerves.

5. A lacteal is a lymphatic capillary.

6. Microvilli increase the surface area intestinal cells.

7. Intestinal glands are between the bases of adjacent villi.

8. Plicae circulares are circular folds in the mucosa of the small intestine.

D. Secretions of the Small Intestine

1. Brunner’s glands are mucous-secreting glands and are located in the submucosa of the proximal portion of the duodenum.

2. Brunner’s glands secrete alkaline mucus.

3. The enzymes embedded in the membranes of epithelial cells of the small intestine are peptidase, sucrase, maltase, lactase, lipase, and enterokinase.

4. The functions of peptidases are to digest proteins.

5. The functions of sucrase, maltase, and lactase are to digest sucrose, maltose, and lactose.

6. The functions of intestinal lipase are to digest lipids.

E. Regulation of the Small Intestinal Secretions

1. Stomach contents entering the small intestine stimulate the duodenal mucous glands to release mucus.

2. Direct contact with chyme chemically and mechanically stimulates the goblet cells and intestinal glands to secrete their products.

3. Distension of the intestinal wall stimulates the parasympathetic reflexes that cause intestinal secretions.

F. Absorption in the Small Intestine

1. The most important absorbing organ is the small intestine.

2. Carbohydrate digestion begins in the mouth and is completed in the small intestine.

3. Monosaccharides are absorbed by facilitated diffusion and active transport.

4. Protein digestion begins in the stomach and is completed in the small intestine.

5. Amino acids are absorbed by active transport.

6. Fat molecules are digested almost entirely by the small intestine.

7. Chylomicrons are lipoproteins that contain lipids and proteins.

8. Chylomicrons are carried to the blood by lymph.

9. Chylomicrons in the blood transport dietary fats to muscles and adipose cells.

10. VLDL molecules, produced in the liver, transport triglycerides synthesized from excess dietary carbohydrates.

11. LDL delivers cholesterol to tissues, HDL remove cholesterol from tissues and deliver it to the liver.

12. The ions absorbed by the intestinal villi are sodium, potassium, chloride, nitrate, and bicarbonate.

13. Water is absorbed by osmosis.

G. Movements of the Small Intestine

1. Segmentation is the major mixing movement of the small intestine.

2. Chyme moves slowly through the small intestine.

3. Parasympathetics enhance mixing and peristaltic movements and sympathetics inhibits mixing and peristaltic movements.

4. A peristaltic rush is the rapid sweeping the contents into the large intestine.

5. Diarrhea results from a peristaltic rush.

6. The ileocecal sphincter joins the small intestine’s ileum and large intestine’s cecum.

XI. Large Intestine

A. Introduction

1. The large intestine is located primarily in the abdominal cavity and part of the pelvic cavity.

2. The functions of the large intestine are to form feces, eliminate solid wastes, and to absorb remaining water and electrolytes from chyme.

B. Parts of the Large Intestine

1. The parts of the large intestine are cecum, colon, rectum, and anal canal.

2. The cecum is the initial portion of the large intestine.

3. The vermiform appendix is located off the cecum and consists of lymphatic tissue.

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

5. The ascending colon is located on the right side of the abdominal cavity.

6. The transverse colon is located between the ascending and descending colon.

7. The descending colon is located on the left side of the abdominal cavity.

8. The sigmoid colon is an s-shaped portion of the colon off the descending colon.

9. The rectum is the continuation of the sigmoid colon.

10. The anal canal is the continuation of the rectum.

11. Anal columns are folds of mucous membranes in the anal canal.

12. The anus is the opening of the anal canal.

13. Two sphincters of the anus are the internal and external.

14. The internal anal sphincter is composed of smooth muscle.

15. The external anal sphincter is composed of skeletal muscle.

C. Structure of the Large Intestinal Wall

1. Teniae coli are bands of smooth muscle that extend the length of the large intestine.

2. Haustra are pouches of the large intestinal wall created by teniae coli.

3. Epiploic appendages are collections of fat in the serosa on the outer surface of the large intestine.

D. Functions of the Large Intestine

1. Mucus secretion into the large intestine is controlled by mechanical stimulation and parasympathetic impulses.

2. The functions of mucus in the large intestine are to form and store feces, eliminate feces, and absorb remaining water and electrolytes from chyme.

3. Chyme entering the large intestine contains few nutrients, nondigestible materials, water, electrolytes, mucus, and bacteria.

4. The large intestine can absorb water and electrolytes.

5. Intestinal flora is a bacterial population that exists in the large intestine.

6. The functions of intestinal flora are to synthesize some vitamins and to produce gas.

E. Movements of the Large Intestine

1. The movements of the large intestine are similar although less frequent than those of the small intestine.

2. Mass movements are produced when a large section of the intestinal wall constricts vigorously.

3. The defecation reflex is triggered by holding a deep breath and contracting the abdominal wall muscles.

4. The actions of the defecation reflex are to increase internal abdominal pressure and the forcing go feces into the rectum. Peristaltic waves are triggered and anal sphincters relax.

5. A person can inhibit defecation by contracting the external anal sphincter.

F. Feces

1. Feces are composed of materials that were not digested or absorbed, some water, electrolytes, mucus, and bacteria.
2. The pungent odor or feces results from a variety of compounds that bacteria produce.

XII. Life-Span Changes

A. Maintaining healthy teeth requires frequent dental checks, cleaning and plaque removal, plus care of the gums.

B. The effects of aging on teeth include thinning of enamel, thickening of cementum, receding of gums, and loosening of teeth.

C. Dry mouths in elderly people are usually a result of side effects of drugs.

D. Frequent heartburn may be the result of the slowing of peristalsis in the stomach.

E. Effects of aging on the small intestine include decreased efficiency in absorbing nutrients and vitamins.

F. The effects of aging on the large intestine include thinning of the lining and decreased mucus production that leads to constipation.

G. The effects of aging on the pancreas, liver, and gallbladder include a decline in their secretions.

Chapter 16 questions

1. Explain how the lymphatic system is related to the cardiovascular system.

The lymphatic and cardiovascular systems include a network of capillaries and vessels that assist in circulating the body fluids. The lymphatic vessels transport excess fluid away from the interstitial spaces of tissues and return it to the bloodstream. The walls of both vessels are alike. For instance, they both contain a single layer of epithelial cells that allows fluids and substances to cross into them.

2. Trace the general pathway of lymph from the interstitial spaces to the bloodstream.

The lymphatic capillary system is found next to the systemic and pulmonary capillary networks. It then travels through lymph vessels into lymph nodes. It returns to lymph vessels and then is returned into the bloodstream at various points.

3. Identify and describe the locations of the major lymphatic trunks and collecting ducts.

The lymphatic trunks are named for the regions they serve. The locations can be found in fig. 16.4, on page 623.

The collecting ducts are:

Thoracic duct—It begins in the abdomen. It passes upward medially through the diaphragm to the left subclavian, where it empties.

Right lymphatic duct—It begins as the union of the right jugular, right subclavian, and right bronchomediastinal trunks. It empties into the right subclavian vein.

4. Distinguish between tissue fluid and lymph.

Lymph is tissue fluid that has entered into a lymphatic capillary.

5. Describe the primary functions of lymph.

The primary functions of lymph are to return the proteins to the bloodstream that have leaked out of the blood capillaries and to transport bacteria and other foreign particles to the lymph nodes.

6. Explain why physical exercise promotes lymphatic circulation.

The contractions of the skeletal muscles, pressure changes due to the actions of breathing muscles, and smooth muscle contractions of the larger lymphatic trunks all aid in the movement of lymph through the body.

7. Explain how a lymphatic obstruction leads to edema.

Continuous movement of fluid from the interstitial spaces into the lymphatic system stabilizes the volume of fluids in these spaces. When an obstruction occurs, the tissue fluid builds up and causes edema.

8. Describe the structure and functions of a lymph node.

Each lymph node is enclosed in a capsule of fibrous connective tissue and subdivides into compartments. The compartments contain dense masses of lymphocytes and macrophages. These masses, called nodules, are the structural units of a lymph node. Lymph nodes function in lymphocyte production and phagocytosis of foreign substances, damaged cells, and cellular debris.

9. Locate the major body regions occupied by lymph nodes.

The major body regions include: cervical region, axillary region, inguinal region, pelvic cavity, abdominal cavity, thoracic cavity, and supratrochlear region.

10. Describe the structure and functions of the thymus.

The thymus is a soft, bilobed structure whose lobes are surrounded by a capsule of connective tissue. It is composed of lymphatic tissue, which is subdivided into lobules by connective tissues. The lobules contain many lymphocytes. It functions to produce T-lymphocytes that help in the immune response. It also secretes thymosin, which is thought to stimulate the maturation of T-lymphocytes after they leave the thymus.

11. Describe the structure and functions of the spleen.

The spleen is the largest lymphatic organ. It resembles a large lymph node and is subdivided into chambers or lobules. The spaces within the chambers are filled with blood instead of lymph. There are two types of tissues within the lobules of the spleen. They include:

White pulp - distributed throughout the spleen in tiny islands, composed of splenic nodules, and containing large numbers of lymphocytes.

Red pulp - surrounds the venous sinuses and contains many red blood cells along with numerous lymphocytes and macrophages.

The spleen functions to filter the blood.

12. Distinguish between innate (nonspecific) and adaptive (specific) body defenses against infection.

Nonspecific body defenses include species resistance, mechanical barriers such as the skin and mucous membranes, and chemical barriers such as enzymes, interferon, inflammation, and phagocytosis. Specific body defenses include immune mechanisms, where certain cells recognize the presence of particular foreign substances and act against them. Lymphocytes and macrophages achieve this.

13. Explain species resistance.

Species resistance is referring to the fact that a given kind of organism or species develops diseases that are unique to it. A species may be resistant to diseases that affect other species, because its tissues somehow fail to provide the temperature or chemical environment needed by a particular pathogen.

14. Name three mechanical barriers to infection.

The skin, hair, and the mucous membranes are three mechanical barriers to infection.

15. Describe how enzymatic actions function as defense mechanisms against pathogens.

Enzymes provide a chemical barrier to pathogens. By splitting components of the pathogen or decreasing the pH, the enzyme can have lethal effects on pathogens.

16. Distinguish among the chemical barriers (interferons, defensins, collectins, and complement proteins), and give examples of their different actions.

Interferons stimulate uninfected cells to synthesize antiviral proteins that block proliferation of viruses;

stimulate phagocytosis; and enhance activity of cells that help resist infections and stifle tumor growth.

Defensins make holes in bacterial cell walls and membranes.

Collectins provide broad protection against a wide variety of microbes by grabbing onto them.

Activation of complement proteins in plasma stimulates inflammation, attracts phagocytes, and enhances phagocytosis.

17. Describe Natural Killer (NK) Cells and their action.

NK cells are a small population of lymphocytes. NK cells defend the body against various viruses and cancer by secreting cytolytic substances called perforins.

18. List the major effects of inflammation, and explain why each occurs.

Localized redness—result of blood vessel dilation and the increase in blood volume of affected tissues.

Swelling—result of increased blood volume and increased permeability of nearby capillaries.

Heat—due to the presence of blood from deeper body parts, which is generally warmer than that near the surface.

Pain—results from the stimulation of nearby pain receptors.

19. Identify the major phagocytic cells in the blood and other tissues.

The most active phagocytic cells of the blood are neutrophils and monocytes. Macrophages are fixed phagocytic cells found in lymph nodes, spleen, liver, and lungs. This constitutes reticuloendothelial tissue.

20. List possible causes of fever, and explain the benefits of fever.

Viral or bacterial infection stimulates certain lymphocytes to secrete IL-1, which temporarily raises body temperature.

Physical factors, such as heat or ultraviolet light, or chemical factors, such as acids or bases, can cause fever.

Elevated body temperature and the resulting decrease in blood iron level and increased phagocytic activity hamper infection.

21. Distinguish between an antigen and a hapten.

An antigen is a foreign substance, such as a protein, polysaccharide or a glycolipid, to which lymphocytes

respond. A hapten is a molecule that by itself cannot stimulate the immune response. It must combine with a larger molecule.

22. Review the origin of T cells and B cells.

T cells originate in the thymus. B cells are those processed in another part of the body, probably the fetal liver.

23. Explain the immune response.

The lysosomal digestive process of phagocytosis of an invading bacterium releases antigens. They are moved to the macrophage’s surface membrane. They are then displayed on the membrane with major histocompatibility complex. If the antigen then fits the helper T cell, it becomes activated. At this point, the

helper T cell seeks out the appropriate T cell and by attaching to it, activates the T cell into a response. Cell-mediated

immunity (CMI) is when a T cell, for example, attaches itself to antigen-bearing cells and interacts with the foreign cells directly.

24. Define cytokine.

Cytokines (lymphokines) are a variety of polypeptides that are synthesized and secreted by T cells and macrophages. These enhance various cellular responses to antigens. They stimulate the synthesis of

lymphokines from other T cells, help activate resting T cells, cause T cells to proliferate, stimulate the

production of leukocytes in the red bone marrow, cause growth and maturation of B cells, and activate macrophages.

25. List three types of T cells and describe the function of each in the immune response.

a. Helper T cells—mobilize the immune system to stop a bacterial infection through a series of complex steps.

b. Memory T cells—provide for no delay in the response to future exposures to an antigen.

c. Cytoxic T cells—recognize non-self antigens that cancerous or virally infected cells display on their surfaces.

26. Define clone of lymphocytes.

Clone of lymphocytes refers to cells that are derived from one early cell that are capable of responding to a certain antigen. As there are many differing antigens, there are also many differing varieties of clones.

27. Explain humoral immunity.

A B cell is activated when it binds to an activated T cell.

An activated B cell proliferates, enlarging its clone.

Some activated B cells specialize into antibody-producing plasma cells.

Antibodies react against the antigen-bearing agent that stimulated their production.

An individual’s diverse B cells defend against a very large number of pathogens.

28. Explain how a B cell is activated.

B cells become activated when they encounter an antigen whose molecular shape fits the shape of the B cell’s antigen receptors. As a result of this combination, the B-cells proliferate by mitosis and its clone is enlarged.

This mechanism for activation is similar to the lock and key model used by enzymes and substrates.

29. Explain the function of plasma cells.

Plasma cells are some of the newly formed members of the activated B cell’s clone. They make use of their DNA information and protein-synthesizing mechanism to produce antibody molecules.

30. Describe an immunoglobulin molecule.

An immunoglobulin molecule consists of two identical light changes of amino acids and two identical heavy chains of amino acids. See figure 16.20, page 637.

31. Distinguish between the variable region and the constant region of an immunoglobulin molecule.

Variable regions are the portion of one end of each of the heavy and light chains consists of variable sequences of amino acids making them specific for specific antigen molecules. Constant regions are the remaining portions of the chains whose amino acid sequences are very similar from molecule to molecule.

32. List the major types of immunoglobulins, and describe their main functions.

Immunoglobulin G (IgG)—occurs in plasma and tissue fluids.

Immunoglobulin A (IgA)—occurs in milk, tears, nasal fluid, gastric juice, intestinal juice, bile, and urine.

Immunoglobulin M (IgM)—develops in blood plasma.

Immunoglobulin D (IgD)—is important in activating B cells.

Immunoglobulin E (IgE)—occurs in exocrine secretions and is associated with allergic reactions.

33. Describe three ways in which antibody attack on a direct antigen helps in the removal of antigen.

Agglutination—antibodies combine with antigens and clumping results.

Precipitation—antibodies combine with antigens and insoluble substance forms.

Neutralization—antibodies cover the toxic portions of antigen molecules and neutralize their effects.

Lysis—antibodies cause the cell membranes to rupture.

34. Explain the function of complement.

It is a group of inactive enzymes that become activated when certain IgG or IgM antibodies combine with

antigens and the reactive sites become exposed. The activated enzymes produce chemotaxis, agglutination, opsonization, and lysis. It can also promote the inflammation reaction.

35. Distinguish between a primary and a secondary immune response.

A primary immune response occurs when B cells or T cells become activated after first encountering the antigens to which they are specifically reactant. A secondary immune response happens when memory cells are activated and increased in size, so they can respond rapidly to the antigen to which they were previously sensitized.

36. Distinguish between active and passive immunity.

Active immunity can be either naturally acquired or artificially acquired. Naturally acquired active immunity is stimulated as a result of exposure to live pathogens. Artificially acquired active immunity is stimulated by exposure to a vaccine containing weakened or dead pathogens. Passive immunity can also be either naturally acquired or artificially acquired. Naturally the antibodies passed to a fetus from a mother with active immunity stimulate acquired passive immunity. Artificially acquired passive immunity is stimulated by an injection of gamma globulin that contains antibodies.

37. Define vaccine.

A vaccine is a substance that contains an antigen that can stimulate a primary immune response against a

particular disease-causing agent, but does not cause severe disease symptoms.

38. Explain how a vaccine produces its effect.

A vaccine contains bacteria or viruses that have been killed or weakened so they cannot cause a serious

infection; or it may contain a toxin of an infectious organism that has been chemically altered to destroy its toxic effects. The antigens present still retain the characteristics needed to simulate a primary immune response.

39. Describe how a fetus may obtain antibodies from the maternal blood.

Receptor-mediated endocytosis utilizing receptor sites on cells of the fetal yolk sac transfers IgG molecules to the fetus.

40. Explain the relationship between an allergic reaction and an immune response.

Allergic reactions are closely related to immune responses in that both may involve the sensitizing of lymphocytes or the combining of antigens with antibodies. Allergic reactions are likely to be excessive and to cause tissue damage.

41. Distinguish between an antigen and an allergen.

An antigen is a substance that stimulates cells to produce antibodies. An allergen is a foreign substance capable of stimulating an allergic reaction.

42. Describe how an immediate-reaction allergic response may occur.

In an immediate-reaction allergy, the individuals have an inherited ability to synthesize abnormally large quantities of antibodies in response to certain antigens. In this instance, the allergic reaction involves the activation of B-cells.

43. List the major events leading to a delayed-reaction allergic response.

It results from repeated exposure of the skin to certain chemical substances. As a consequence of these

repeated contacts, the foreign substance and a large number of T cells collect in the skin and eventually

activate the T cells. Their actions and the actions of macrophages they attract cause the release of various chemical factors. This causes eruptions and inflammation of the skin. It is called delayed since it takes about forty-eight hours to occur.

44. Explain the relationship between a tissue rejection and an immune response.

Tissue rejection is when the immune system sees transplanted tissue as foreign and starts the immune response to try to rid the body of it.

45. Describe two methods used to reduce the severity of a tissue rejection reaction.

Matching the donor and recipient tissues may reduce it. It can also involve giving drugs that suppress the immune system.

46. How do immunosuppressant drugs increase the likelihood of success of a transplant, yet place the patient at a higher rise of developing infections?

An immunosuppressive drug interferes with the recipient’s immune response by suppressing formation of antibodies or production of T cells. This will ultimately leave the recipient relatively unprotected against infection.

47. Explain the relationship between autoimmunity and an immune response.

Autoimmunity occurs when the immune system does not distinguish between self and nonself and manufactures autoantibodies that attack the body’s own cells. For whatever reason, the autoantibodies treat a certain cell type in the body as a foreign object and signal the immune system to defend against the perceived invader.

48. Describe the causes for a decline in the strength of the immune response in the elderly.

The immune system begins to decline early in life, in part due to the decreasing size of the thymus.

Numbers of T cells and B cells do not change significantly, but activity levels do.

Proportions of the different antibody classes shift.