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CHAPTER 17: DIGESTIVE SYSTEM

OBJECTIVES

1. Define the term digestion and explain its significance.

2. Distinguish between mechanical digestion and chemical digestion.

3. Discuss the five digestive processes that overview the many functions of the digestive system.

4. Distinguish between the alimentary canal and digestive accessory organs.

5. Name two synonyms for the alimentary canal.

6. List the organs that compose the alimentary canal and identify each on a diagram.

7. List the digestive accessory organs and identify each on a diagram.

8. Name the four layers that compose the wall of the alimentary canal from innermost (lining lumen) to outermost.

9. Compare and contrast the four layers of the alimentary canal wall (named above) in terms of their structure, function, and any distinguishing features.

10. Name the layer of the alimentary canal that is synonymous with visceral peritoneum.

11. Explain the significance of mesenteries or peritoneal extensions.

12. Describe how food is moved through the length of the alimentary canal and name the layer responsible for these actions.

13. Define the term digestive sphincter muscle, describe the structure of these muscles, name the function of these muscles, and denote the major five locations of digestive sphincter muscles.

14. Name two synonyms for the mouth.

15. Describe the overall structure and function of the mouth.

16. Discuss the three portions of the palate, in terms of location and give an overall function for the palate.

17. Name the tissue that composes the tonsils and name the overall function of tonsils.

18. Name the two sets of teeth we possess as humans, discuss the general structure of a tooth, and describe the four types of teeth we possess according to their location and function.

19. Name and locate the three sets of salivary glands in humans, name and describe the secretions from these glands, and name the two types of cells that compose these glands.

20. Discuss the enzyme "salivary amylase", in terms of its digestive function, location, and secretory gland.

21. Explain the process of deglutition.

22. Name the function of the epiglottis.

23. Define the term peristalsis and explain its digestive function.

24. Define the term gastric.

25. Describe the macroscopic structure of the stomach and locate it on a diagram or torso model.

26. Name the term used to describe the mucosal folds of the stomach lining and explain their significance.

27. Discuss the histology of the stomach wall.

28. Name the four types of cells that compose gastric glands, name the secretion(s) that each cell produce(s) that together compose gastric juice, and give the function of each component of gastric juice.

29. Define the term chyme.

30. Name one substance that is absorbed through the gastric mucosa.

31. Name the hormone that regulates the release of gastric juice, explain when it is released, and the results of its action.

32. Using anatomical terminology, describe the location of the pancreas in the abdominal cavity.

33. Explain how the pancreas aids in digestion by listing the components in pancreatic juice, and naming the action of each of those components.

34. Name the site of pancreatic enzyme action.

35. Name the regulatory hormone responsible for the release of pancreatic juice into the duodenum, and explain when it is activated.

36. Using anatomical terminology, describe the location of the liver in the abdominal cavity.

37. Name the functional unit of the liver and describe its general structure.

38. Define the terms hepatocyte and liver sinusoids.

39. Describe the many functions of the liver.40. Name the two blood vessels that supply the liver lobules with blood and track the flow of

blood into and out of the liver lobule.

41. Name the components of a portal triad.

42. Explain the significance and location of Kupffer's cell.

43. Define the term emulsification and explain its role in digestion.

44. Using anatomical terminology, describe the location of the gallbladder in the abdominal cavity.

45. Name the function of the gallbladder.

46. Name the "common" route that bile travels from either the liver or gallbladder and name the site where bile is deposited.

47. Name the regulatory hormone that is responsible for the release of bile into the duodenum and explain when it is activated.

48. Name the three parts of the small intestine, and locate each on a diagram or torso model.

49. Discuss the histology of the small intestinal wall.

50. Name the digestive enzymes that are secreted by the mucosa of the small intestines and explain the action of each.

51. Identify the simplest forms of food that are absorbed through the mucosa of the small intestine, name the transport process by which each is absorbed, and describe the fate of each absorbed nutrient.

52. Define the term lacteal and explain its significance.

53. Distinguish between the duodenum and the distal small intestine (i.e. jejunum and ileum) in terms of function.

54. Name the four parts of the large intestine and locate each on a diagram or torso model.

55. Name the four parts of the colon and locate each on a diagram or torso model.

56. Identify the major digestive function of the large intestine.

57. Explain how the movements in the large intestine differ from those throughout the rest of the alimentary canal.

58. Define the terms feces and defecation.

59. Name the sphincter muscles that open to the outside and explain how their action is controlled.

60. List the four major organic macromolecules that we ingest, and explain how each is broken down by various enzymes within the alimentary canal. Be sure to include enzyme names, the location of enzyme action, and the breakdown products that result from the

enzymatic action, and explain any hormonal control of the breakdown. Finally, explain how and where these simplest food forms are absorbed into the bloodstream or lymphatic system.

I. INTRODUCTION

A. Definition: Digestion

The process by which food substances are changed into forms that can be absorbed through cell membranes.

B. Digestive Processes:

1. Ingestion = taking food into the mouth.2. Movement of Food = the passage of food along the gastrointestinal (GI)

tract.3. Digestion = the breakdown of food by chemical and mechanical means.4. Absorption = the passage of digested food from GI tract into bloodstream

(and lymph) for distribution to cells.5. Defecation = the elimination of undigested material from GI tract.

C. Digestive Organs

See Fig 17.1, page 645.

1. Two categories:

a. Alimentary canal (GI Tract), which extends from mouth to anus.

o Organs include: See Fig 17.2, page 646.

1. mouth2. pharynx3. esophagus4. stomach5. small intestine6. large intestine

b. Accessory organs release secretions into the alimentary canal that help digest food:

o Organs include:1. salivary glands2. liver3. gallbladder4. pancreas

II. GENERAL CHARACTERISTICS OF THE ALIMENTARY CANAL

A. Structure of the Wall = Four Distinct Layers

See Fig 17.3, page 647 and Table 17.1, page 646.

1. mucosa = innermost (surrounds lumen);

a. composed of epithelium + CT (areolar); and small amounts of smooth muscle

b. epithelium extends into lumen = villi (increases surface area);c. contains many glands that secrete mucus (lubrication & protection

from harmful action of digestive enzymes);d. functions:

o protectiono secretiono absorption (of nutrients).

2. submucosa = beneath mucosa;

a. composed of areolar CT, blood vessels, lymph vessels, and nerves;b. functions:

o nourishment of mucosa;o carrying absorbed nutrients away.

3. muscularis =2 layers of muscle

a. circular muscle layer around submucosa;b. longitudinal layer around circular layer;c. function: movements of food through canal (mixing & peristalsis).

4. serosa =outermost layer; a. visceral peritoneum;b. functions:

o lubricationo free movement of canal in abdominal cavity

c. Intestinal peritoneal extensions = mesenteries.o suspend the length of the intestine within abdominal cavity.

II. GENERAL CHARACTERISTICS OF THE ALIMENTARY CANAL

B. Movements of the tubeSee Figure 17.4, page 647.

1. Mixing: (mechanical digestion)

a. food + digestive juices + mucusb. circular muscle layer

2. Peristalsis:

a. accomplished by movements of longitudinal muscle layer;b. propelling action; c. As food passes, one section of tube relaxes (receptive relaxation),

opening next section & food moves on.

C. Sphincter Muscles play an important role in movements throughout the GI tract also.

1. Definition: Sphincter = a strong circular muscle which prevents regurgitation of food.

2. Locations: between (regions) organs of digestive tract.

a. esophagus and stomach o gastroesophageal sphincter;

b. stomach and small intestine o pyloric sphincter;

c. small and large intestine o ileocecal valve;

d. large intestine to outsideo internal anal sphincter and o external anal sphincter.

D. Innervation of the Tube

1. Autonomic Nervous Systema. Parasympathetic – activates digestionb. Sympathetic – slows digestion

2. Post-ganglionic networksa. Submucosal plexus = controls secretionsb. Myenteric plexus = controls peristalsis

III. ORGANS OF THE DIGESTIVE SYSTEM

A. The Mouth (oral/buccal cavity):

See Fig 17.5, page 649 and Fig 17.7, page 650.

1. adapted to receive food and start digestion by chewing & mixing with saliva;

2. surrounded by cheeks, lips, tongue and palate:

a. Cheeks and Lipso cheeks – lateral walls of moutho lips = surround opening of mouth, important in monitoring

food temperature

b. Tongue See Figure 17.6 page 649o muscular (skeletal) organ on floor of moutho important in mixing food (mechanical digestion) and

swallowingo contains many bumps called papillae, which house taste

budso posterior root contains lymphatic tissue called the lingual

tonsil

c. palate = roof of moutho anterior portion = hard palate;o posterior portion = soft palate;o median extension of soft palate = uvula.o tonsils:

1. Palatine tonsils = masses of lymphatic tissue lateral to palate;

2. Pharyngeal tonsils = adenoids; lymphatic tissue on posterior pharynx

3. Tonsillitis = inflammation of palatine tonsils

3. composed of 2 chambers:a. oral cavity proper = chamber that extends from teeth/gums to

pharynx;b. vestibule = narrow space between teeth, cheeks and lips.



4. filled with teeth:

a. two sets of dentitions: See Fig 17.8, page 651 and Table 17.2, page 651. o deciduous teeth

1. number 20,2. erupt from 6 - 32 months,3. lost between 6 - 12 years.

o permanent (secondary) teeth1. number 32,2. erupt from 6 yrs - adulthood.3. See Fig 17.9, page 651.

b. function: to break food into smaller pieces. (mechanical digestion)o increasing surface area of food;o increasing effectiveness of digestive enzymes.

c. 4 types with different functions:


o incisors = front teeth;

1. break food into bite-size pieces;

o cuspids = canine (eye) teeth;

1. grasps and tears food;

o bicuspids = grinding food particles;

o molars = grinding food particles.

d. Tooth Structure: located in alveolar fossa of maxilla and mandibleSee Fig 17.10, page 652.

o crown = exposed area of tooth;

o root = area below gum (gingiva);

o enamel =covering on crown; Ca+ salts; hardest substance in body;

o dentin = bulk of tooth.



5. Salivary Glands secrete saliva.


a. digestive functions:

o lubrication,

o bind food together,

o begin chemical digestion of carbohydrates.

1. Enzyme = salivary amylase;

2. break polysaccharides into disaccharides;

a. starch disaccharides.b. glycogen disaccharides.

b. three types of salivary glands: See Figure 17.11 page 654.

o parotid = largest; lies over masseter, mostly serous cells

o submandibular = floor of mouth; lateral, mix of serous and mucous cells

o sublingual = floor of mouth, medial. Mostly mucous cells

c. Each salivary gland is composed of 2 types of cells:


o mucous cells secretes mucus;

o serous cells secrete watery substance containing the enzyme salivary amylase.


B. Pharynx: See Fig 17.14, page 657.

1. throat;

2. 3 partsa. nasopharynx – superior to soft palate, posterior to nasal cavityb. oropharynx – posterior to mouth down to epiglottisc. laryngopharynx – inferior to oropharynx from epiglottis to cricoid

cartilage

3. passageway of food into esophagus (and air into larynx/trachea);

4. Swallowing mechanism (deglutition): 3 stages

a. Stage 1 (voluntary); Chew food & mix with saliva into bolus at back of pharynx;

b. Stage 2 (involuntary): Swallowing reflex triggered

o epiglottis closes over larynx (no breathing),

o muscles in lower pharynx relax,

o esophagus opens & food moves in.

c. Stage 3 (involuntary); Esophagus brings bolus to stomach by peristalsis

C. Esophagus: See Fig 17.15, and Fig 17.16, page 657.

1. passageway for food from pharynx to stomach;

2. location: mediastinum; behind trachea; goes through diaphragm at esophageal hiatus

3. many mucous glands;

4. movement of food:

a. gravity;b. peristaltic waves from esophagus meet gastroesophageal

sphincter muscle (cardiac sphincter)c. sphincter muscle relaxes,d. food moves into stomach all at once.


D. Stomach (Gastric) See Fig 17.17, page 658.

1. description = J-shaped, pouch-like organ; 2. contains extra oblique layer in muscularis3. location = under diaphragm; left side;4. capacity = 1 liter;5. Parts of Stomach:

a. cardiac region - around esophagusb. fundic region - large ballooned areac. body – main portion d. pyloric region - near duodenum

o The pyloric region narrows into pyloric canal.

o The pyloric sphincter muscle lies between pylorus & duodenum.

d. greater curvaturee. lesser curvaturef. body

6. Functionsa. mechanical digestion – churningb. chemical digestion of proteins – gastric juice

7. Mucosal Structure

a. Note the macroscopic rugae (mucosal folds) in Fig 17.17b, page 658.

b. Microscopically, these rugae are formed by: See Fig 17.19, page 660

o gastric villi that project into the lumen which result in the formation of;

o gastric pits that are located between the gastric villi.

1. gastric glands are located along these gastric pits ;

a. gastric juice is secreted by these gastric glands.


D. Stomach (Gastric) See Fig 17.17, page 658.

8. Gastric Juice: See Table 17.5, page 661.

a. composed of:o mucus,

Function: lubrication, protection of mucosa from digestion;

o digestive enzyme pepsin, Function: protein digestion (into peptides);

o hydrochloric acid (HCl), Functions:

1. denatures proteins,2. kills microbes in food,

o intrinsic factor, Function: aids absorption of Vitamin B12. needed

for erythropoiesiso gastrin,

Function: regulatory hormone.

9. Four types of gastric cells in Gastric Glands:See Fig 17.19, page 660

a. Mucous cells secrete mucus;b. Chief cells secrete pepsin;c. Parietal cells secrete HCl & intrinsic factor;d. G-cells secrete gastrin.

10. Regulation of Gastric Secretions: See Fig 17.20, page 661, and Table 17.6 page 662.

a. Neuralo parasympathetic – increases gastric secretiono sympathetic – decreases gastric secretion

b. Hormonalo Gastrin – increases gastric secretiono Somatostatin – decrease acid secretion from parietal cellso Cholecystokinin – decreases gastric motility


D. Stomach (Gastric)

10. Regulation of Gastric Secretions:

c. 3 phases of Gastric Secretiono Cephalic Phase (30-50% of control)

Increased parasympathetic due to sight, taste, smell, thought of food

o Gastric Phase (40-50% of control) Stretch of stomach wall increases gastrin, which

increases gastric secretions pH changes alter Gastrin release

food enters increasing pH the reflexive increase in gastrin lowers pH when pH lowers to 1.5 gastrin release stops

HCl released from parietal cells comes from blood Blood pH needs to maintain 7.4 So parietal cells release bicarbonate to blood Called the alkaline tide

o Intestinal Phase (5% of control) Initially releases intestinal gastrin which increases

gastric secretions As duodenum fill a sympathetic reflex inhibits

gastrin release Proteins and fats in duodenum stimulate

cholecystokinin release which decreases gastric motility

11. Gastric Absorption = Minimal (5%) some salts, water, lipid-soluble drugs, alcohol

12. Gastric Movements See Fig 17.21, page 662 & Fig 17.22, page 663.a. mixing of bolus of food + gastric juice = chyme;b. Peristaltic waves of stomach push chyme toward pyloric sphincter;

it relaxes; food moves into duodenum a little at a time!!! c. Enterogastric reflex – ensures stomach

slows down as duodenum fillsd. Vomiting may occur to quickly remove

toxins


E. Pancreas See Fig 17.23, page 664.

1. Inferior to stomach – retroperitoneal

2. Structure of the Pancreasa. Shrimp–like with head in concave curve of duodenum, tail extend to the left to the spleenb. Few cells produce hormones (insulin and glucagon)c. Most cells make up pancreatic acini, which produce pancreatic juice

3. Secretes pancreatic juice into a pancreatic duct; pancreatic duct leads to duodenum (small intestine);

4. Pancreatic duct joins bile duct at the Hepatopancreatic ampulla (ampulla of Vater) before passing through the Hepatopancreatic sphincter (sphincter of Oddi) to enter duodenum

5. Function of pancreatic juice:

Contains four classes of enzymes that break down:

a. Carbohydrates (Starch and Glycogen)

o pancreatic amylase disaccharides;

b. Fats/Triglycerides

o pancreatic lipase 2 fatty acids + monoglyceride;

c. Proteins

o trypsin, chymotrypsin, and carboxypeptidase proteins peptides;

o stored and released as inactive form in zymogen granuleso trypsinogen is activated to trypsin by enterokinaseo trypsin then activates chymotrypsin and carboxypeptidase

d. Nucleic Acids

o nucleases nucleotides.

* Note bicarbonate ions are also released to neutralize acidic chyme entering from the stomach


E. Pancreas See Fig 17.23, page 664.

4. Regulation of pancreatic secretions: See Fig 17.24, page 666.

a. Hormones = Secretin; cholecystokinin

b. Secretin Activation:

o When duodenum fills with acidic chyme, o secretin is released from the intestinal wallo which stimulates the release of bicarbonate rich pancreatic

juice into duodenum.

c. Cholecystokinin Activation:o Once acid is neutralizedo Proteins and fats signal cholecystokinin release from the

intestinal wallo Which stimulates the release of enzyme rich pancreatic

juice into the duodenum

F. Liver (Hepatic) See Fig 17.25-17.26, pages 667

1. Location: below diaphragm / right side; largest internal organ

2. Structure: 4 lobes: Fig 17.26, page 667.

a. large right & small left;b. quadrate and caudate lobe in posteriorc. each lobe is made up of:

o Hepatic lobules = functional unit of the liverSee Fig 17.27, page 668.1. hexagon shaped around a central vein;2. contains hepatocytes which provide most functions3. also contains Kupffer’s cells (macrophages)

See Fig 17.28, page 668.a. remove and destroy:

microbes; foreign matter. worn platelets and erythrocytes.


F. Liver (Hepatic)

3. Liver Functions:

a. metabolism of monosaccharides, lipoproteins, amino acids.b. storage (glycogen, Vitamin A, B12, D, iron),c. filtering of blood (worn blood cells and debris),d. destruction of toxic chemicals (alcohol and drugs),e. production/secretion of bile.

See Table 17.7, page 670 for more specifics on liver functions.

4. Blood Supply: See Figure 17.28, page 668.

a. from 2 sources:o hepatic artery supplies oxygenated blood;o hepatic portal vein supplies deoxygenated blood filled

with: 1. newly absorbed nutrients from small intestine, 2. toxins from stomach, and 3. worn blood cells from spleen.

b. blood enters the liver sinusoids where hepatocytes remove the following:o oxygen,o nutrients (stored or used to make new materials),o poisons (detoxified),o worn cells and debris (phagocytosis).

c. Blood leaving the liver cells (deoxygenated plus liver secretions) drains into central veins, which come together and leave the liver as the hepatic vein.


F. Liver (Hepatic)

4. Blood Supply: d. Overall scheme of Liver Blood Flow:

Hepatic Artery Hepatic Portal Vein(Oxygenated Blood) (Deoxygenated Blood with from aorta) newly

absorbed nutrients from Small intestine, etc.)

Liver Sinusoids(Exchange)

Central Vein of Hepatic Lobule

Hepatic Vein

Inferior Vena Cava

5. Composition of Bile

a. composition:o bile salts (digestive function)o bile pigments (biliverdin and bilirubin)

breakdown products of hemoglobino cholesterolo electrolytes


G. Gall Bladder See Fig 17.26, page 667 and Fig 17.29, page 671.

1. Stores bile between meals;2. Location: underside of liver, connected via cystic duct;3. Bile can flow to small intestine by either of 2 routes:

the liver or gall bladder (see below);4. Bile secretion, storage, flow:

From liver: From Gall Bladder:

Common Hepatic duct Cystic Duct

COMMON *BILE DUCT

Duodenum

*Hepatopancreatic Sphincter muscle usually keeps common bile duct closed.

5. Regulation of bile release See Fig 17.30, page 673.

a. Hormone = CHOLECYSTOKININ (CCK);

b. When small intestine fills with fatty chyme, o cholecystokinin is released into blood;o CCK stimulates walls of gallbladder to contract;o Bile passes down into cystic duct and common bile

duct; o Hepatopancreatic sphincter in common bile duct

opens;

c. Functions of Bile Salts: Emulsification of fat molecules!

o Emulsification = breaking up of fat globules into small droplets (increases SA and increases effectiveness of lipases).

o bile is released into duodenum to emulsify fat.o Also aids in absorption of fats and fat-soluble vitamins


G. Small Intestine See Fig 17.31, page 673.

1. Parts of Small Intestine:

a. duodenum - nearest stomach,b. jejunum - mid-region,c. ileum - near large intestine.

o The distal end of the ileum narrows to form the ileocecal valve (sphincter muscle between small & large intestine).

o Jejunum and ilium are attached to the posterior abdominal wall by fold in peritoneum called mesentery

o See Figure 17.33 page 674.

2. Functions of Small Intestine

a. Major site of chemical digestion (duodenum);o bile depositiono pancreatic juice depositiono small intestinal digestive enzymes

b. Secretionso mucuso digestive enzymes

c. Major site of ABSORPTION of Nutrients o about 90% of all;o through the proximal mucosa.

3. Mucosal Structure See Fig 17.35 & 17.36, page 675.

a. intestinal villi project into lumen (increasing surface area);

b. each villus is composed of simple columnar epithelium (with microvilli See Figure 17.37 page 676) and connective tissue with many blood & lymph vessels (lacteals);

c. absorbed nutrients are carried away by blood & lacteals;

d. intestinal glands are located between villi. (increase SA more)

e. submucosal folds called plicae circulares further increase SASee Figure 17.38 page 676.

f. muscularis and serosa are typical


G. Small Intestine

4. Secretions of Small Intestine

a. mucus, from Brunner’s glands in submucosa and goblet cellsb. digestive enzymes:

o peptidases

* peptides amino acids;

o sucrase, maltase, lactase

* disaccharides monosaccharides;

o intestinal lipases

* TG 3 fatty acids + glycerol.

*See Table 17.9 page 677 for Summary of Major Digestive Organs

5. Regulation of Small Intestinal Secretionsa. Mechanical and chemical stimulation of

duodenal wall by entering chyme regulates intestinal secretions.

6. Absorption in Small Intestine (90% of total) Fig 17.42, pg 679.

a. Intestinal villi (and microvilli, See Fig 17.37, page 676) increase absorptive surface area;

b. Simplest forms of ingested food molecules are absorbed into the intestinal mucosa:o monosaccharides

1. by facilitated diffusion;2. carried away by submucosal blood capillary.

o amino acids 1. active transport;2. carried away by blood capillary.

o fatty acids and monoglyceride 1. by simple diffusion into intestinal mucosa;2. Once is mucosal cells, the fats are reformed into

chylomicrons (lipoproteins) by the endoplasmic reticulum

3. , which are absorbed by lacteals (lymphatic capillary) and into the lymphatic system.

o Ions and water are also absorbed


G. Small Intestine

7. Movements through Small Intestinea. Mixing of chyme + intestinal juices by segmentation (mechanical

digestion)b. Peristaltic waves push residual chyme toward ileocecal

sphincter; it relaxes, moving food into large intestine.

c. Irritation or overdistension may cause peristaltic rush which is rapid emptying of small intestine resulting in diarrhea.

H. Large Intestine

1. Parts of Large Intestine: See Fig 17.43, page 681.

a. cecum - nearest ileum of small intestine; (appendix is a blind pouch in this region);

b. colon - majority of length;c. rectum - distal region of colon;d. anal canal - narrowing of rectum & opening to outside;

2. Colon is divided into four (4) portions:

a. ascending colon - from cecum to liver (right);b. transverse colon - runs across top of abdomen;c. descending colon - from spleen downward (left);d. sigmoid colon - S-shaped portion, which becomes rectum.

3. Structure of the Large Intestinal Wall

a. mainly same a typical See pages 645-646.b. lacks villic. longitudinal muscularis layer forms 3 bands called teniae colid. pouches or haustra develop due to the tension of the teniae colie. serosa may have fatty extensions called epiploic appendages

4. Functions of Large Intestine:

a. secretion = only mucus,b. absorption = water & electrolytes,c. storage = feces.d. intestinal flora = bacteria = digestion of substances humans can

not digest


H. Large Intestine

5. Movements in Large Intestine:a. mass movements only 2-3 times a day;b. Peristaltic waves of large intestine move residual chyme toward

anal sphincter muscles.

6. Control of Anal Sphincter Muscles:a. both voluntary & involuntary nervous control

7. Feces:a. undigested & unabsorbed material;b. color due to bile pigments;c. odor due to intestinal bacteria & bacterial products formed in

digestion;d. 75% water.

8. Defecation = emptying of rectum.

DIGESTIVE SYSTEM SUMMARY TABLE I (keyed at the end of this outline)

NAME OF DIGESTIVE ORGAN

ALIMENTARY CANAL OR ACCESSORY?

DESCRIPTION OF STRUCTURE

SECRETIONS

DIGESTIVEFUNCTION

HORMONAL CONTROL OF SECRETIONS?

DIGESTIVE SYSTEM SUMMARY TABLE I (CONTINUED)




SECRETIONS

DIGESTIVEFUNCTION


DIGESTIVE SYSTEM SUMMARY TABLE II (Keyed at the end of this outline)

MACRO-MOLECULEINGESTED

SITE OF DIGESTION

DIGESTIVEENZYME(S)

END-PRODUCT(S)

SITE AND MODE OF ABSORPTION

ABSORBED INTO BLOOD OR LYMPH

REGULA-TION

IV. LIFE SPAN CHANGES

A. Mouth changes that occur with age reduce chewing ability.1. Enamel thins increasing sensitivity to hot and cold.2. Gums recede.3. Teeth loosen.

B. Slowing peristalsis causes:1. Heartburn.2. Constipation.

C. Absorption of nutrients decreases with age.

V. Homeostatic Disorders/Diseases:

A. Tonsillitis. See blue box on page 649.B. Dental Caries. See Clinical Application 17.1, page 653.C. Hiatal hernia. See blue box on page 656.D. Hypertrophic pyloric stenosis. See blue box on page 659.E. Gastric Ulcers and Helicobacter pylori. See blue box on page 660.F. Stomach Aches. See Clinical Application 17.2, page 663.G. Acute pancreatitis. See blue box on page 665.H. Cystic Fibrosis. See blue box on page 665.I. Hepatitis. See Clinical Application 17.3, page 670.J. Gallbladder Disease. See Clinical Application 17.4, page 672.K. Lactose Intolerance. See blue box on page 677.L. Malabsorption. See blue box on page 679.M. Appendicitis. See blue box on page 681.N. Hemorrhoids. See blue box on page 682.O. Disorders of the Large Intestine. See Clinical Application 17.5, pages 684-685.

VI. Clinical Teems Related to the Digestive System See pages 686 and 688.

VII. Innerconnections of the Digestive System See Page 687.

DIGESTIVE SYSTEM SUMMARY TABLE I:


ORAL CAVITY SALIVARY GLANDS

PHARYNX


ALIMENTARYCANAL

ACCESSORY ALIMENTARY CANAL


SEE OUTLINE SEE OUTLINE SEE OUTLINE

SECRETIONS MUCUS SALIVA WITH AMYLASE

MUCUS

DIGESTIVEFUNCTION

MECHANICAL BREAKDOWN OF STARCH AND GLYCOGEN TO DISACCHARIDES

NONE


N/A N/A N/A



ESOPHAGUS STOMACH (GASTRIC)

LIVER


ALIMENTARY CANAL

ALIMENTARY CANAL

ACCESSORY



SECRETIONS MUCUS

MUCUS;

PEPSIN;

HYDROCHLORIC ACID;

INTRINSIC FACTOR;

GASTRIN

BILE

DIGESTIVEFUNCTION

NONE

PEPSIN BREAKS PROTEINS INTO PEPTIDES;

HCl DENATURES THE PROTEINS

EMULSIFICA-TION OF FATS


N/A

GASTRIN SECRETED BY G-CELLS PROMOTES RELEASE OF GASTRIC JUICE, ETC.

CHOLCYTO-KININ (CCK) OPENS COMMON BILE DUCT WHEN FATTY CHYME FILLS DUODENUM



GALL BLADDER PANCREAS SMALL INTESTINE


ACCESSORY ACCESSORY ALIMENTARYCANAL



SECRETIONS STORED BILE PRODUCED IN LIVER

AMYLASE;

PROTEASES (PROTEINASES);

LIPASES;

NUCLEASES

PEPTIDASES;

SUCRASE;

MALTASE;

LACTASE

DIGESTIVEFUNCTION

EMULSIFICA-TION OF FATS

AMYLASE: STARCH AND GLYCOGEN TO DISACCHS;PROTEASES: PROTEINS TO PEPTIDES;LIPASES: TRIGLYCERIDES TO FATTY ACIDS & MONOGLY-CERIDES;NUCLEASES: NUCLEIC ACIDS TO NUCLEOTIDES

PEPTIDASES: PEPTIDES TO AMINO ACIDS;SUCRASE, MALTASE, LACTASE: DISACCHARIDES TO MONO-SACCHARIDES


CCK CAUSES CONRTACTION OF GALLBALLDER AND OPENS COMMON BILE DUCT WHEN FATTY CHYME FILLS DUODENUM

SECRETIN CAUSES PANCREATIC JUICE TO BE DEPOSITED INTO DUODENUM

N/A

DIGESTIVE SYSTEM SUMMARY TABLE I


LARGE INTESTINE


ALIMENTARY CANAL


SEE OUTLINE

SECRETIONS MUCUS

DIGESTIVEFUNCTION

REABSORPTION OF WATER FROM CHYME


N/A

DIGESTIVE SYSTEM SUMMARY TABLE II

MACRO-MOLECULEINGESTED

CARBO-HYDRATES

PROTEINS FATS (TRI-GLYCERIDES OR TG)

NUCLEIC ACIDS

SITE OF DIGESTION

1.MOUTH;2.DUODENUM3.DUODENUM

1.STOMACH;2.DUODENUM3.DUODENUM

DUODENUM DUODENUM

DIGESTIVEENZYME(S)

1. SALIVARYAMYLASE2. PANC. AMYLASE,3. SUCRASE, LACTASE, MALTASE

1.PEPSIN;*HCl2.PANC. PROTEASES;3. PEPTIDASES;

LIPASES*BILE

PANCREATICNUCLEASES

END-PRODUCT(S)

1 & 2. STARCH AND GLYCOGEN TO DISACCS;

3. DISACCS TO MONO-SACCS

HCl DENATURES PROTEINS;1 & 2. PROTEINS TO PEPTIDES;3. PEPTIDES TO AMINO ACIDS

BILE EMULSIFIES TG’S;LIPASES BREAK TG’S INTO FATTY ACIDS & MONOGLY-CERIDES

NUCLEO-TIDES

SITE AND MODE OF ABSORPTION

DISTAL SM. INTESTINE; FACILI-TATED DIFFUSION

DISTAL SM.INTESTINE;ACTIVE TRANSPORT

DISTAL SM.INTESTINE;SIMPLE DIFFUSION

DISTAL SM. INTESTINE

ABSORBED INTO BLOOD OR LYMPH

BLOOD BLOOD LYMPH BY LACTEAL

BLOOD

REGULA-TION

SECRETIN FOR PANC. AMYLASE

GASTRIN FOR PEPSIN

CCK FOR BILE;SECRETIN FOR PANC. LIPASES

SECRETIN FOR PANC.NUCLEASES

Chapter 17: Digestive System

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 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 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 throat above 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 amount of viscous

saliva.

7. Parasympathetic fibers stimulate the glands to large amounts 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

inside of the cheek about the level of the second molar.

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

5. The submandibular glands are located 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 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.

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 portion, body, fundus, and plylorus.

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 enhance 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.

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 extends 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 canals are canals within liver lobules that receive secretions from hepatic

cells.

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

C. Liver Functions

1. The liver carries on many important metabolic functions.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.

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 in the absorption of fatty acids, and certain

vitamins, and to emulsify fats.

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 stomach 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 secreted by 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. Mechanical digestion and the presence of gastric juice in the small intestine stimulate the duodenal mucous glands to release large amounts of mucus.

2. Chyme stimulates the goblet cells and intestinal glands to secrete their

products.

3. Distension of the intestinal wall stimulates the parasympathetic reflex that

causes 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. The ions absorbed by the intestinal villi are sodium, potassium, chloride,

nitrate, and bicarbonate.

10. 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 of chyme into the large intestine.

5. Diarrhea results from a peristaltic rush.

6. The ileocecal sphincter joins the ileum and 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 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.

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