Chp 13 Digestive

Oral cavity disorders

Dental caries (cavities)

Dental caries

commonly called a cavity, is an erosion through the enamel into the dentin. If the erosion continues to the pulp cavity, bacteria may gain access and travel beyond the tooth's root. This infection is called an abscess.

gingiv/o

gums

Chemical digestion

the breakdown of complex molecules to their building blocks so that they can be absorbed. As a result proteins are broken down to their amino acids, carbohydrates to their monosaccharides, and lipids to their fatty acids and glycerol.

Mechanical digestion

the breakdown of large pieces of complex molecules to smaller pieces of complex molecules. Mechanical digestion must happen first before chemical digestion to take place.

Swallowing:

the four steps of deglutition.

hepatitis E

which causes an acute liver infection, is also uncommon in the United States but is common in other countries around the world. It is transmitted by ingestion of fecal matter. Outbreaks of hepatitis E are usually associated with contaminated water supplies.

Food Poisoning

various types of bacteria and/or their toxins, can cause food poisoning

emet/o

vomit

Col/o

colon

Chol/e

gall, bile

a reflex arc contains five parts: a receptor, an afferent neuron, an integration center, an efferent neuron, and an effector. In the defecation reflex,

(1) stretch receptors in the rectal wall (2) send messages via afferent sensory neurons (3) to the spinal cord (integration center). The spinal cord (4) sends motor messages via efferent motor neurons (5) to the rectal wall, causing it to contract (effector), and to the internal anal sphincter, causing it to relax (effector). The cerebrum determines whether the external sphincter will relax so that defecation can occur (this step is not part of the reflex).

Anatomy of the stomach

(a) gross anatomy, (b) internal surface of a cadaver's stomach, (c) radiograph of a stomach.

Gross anatomy of the liver:

(a) location, (b) anterior view, (c) inferior view.

Intestinal villi:

(a) micrograph—each villus in the image is about 1 mm high; (b) structure of a villus, showing simple columnar epithelial cells with a brush border of microvilli, goblet cells, capillaries, and a lacteal.

Segmentation and peristalsis of the small intestine:

(a) segmentation, (b) peristalsis.

Hepatic screening

A collection of several tests used to determine whether the liver is functioning properly. The test measures several different enzymes produced by the liver.

Irritable Bowel Syndrome

A condition characterized by abdominal pain and discomfort, a change in the frequency of bowel movements, and a change in the consistency of stool. Patients may experience cramping, diarrhea, and constipation. The cause of IBS is unknown. IBS is diagnosed by physical exam, stool cultures, sigmoidoscopy, colonoscopy, and blood tests. Treatment depends on the symptoms experienced by the patient.

Gallstones

A condition in which cholesterol in bile precipitates the forming of gallstones in the gallbladder.

Fecal occult blood test

A noninvasive procedure that detects the presence of blood in stool.

Colonoscopy

A procedure in which a lighted colonoscope is used to visualize the colon.

Proctoscopy

A procedure in which a lighted endoscope is used to visualize the rectum.

Laparoscopy

A procedure in which a lighted laparoscope is used to visualize, collect biopsies from, or perform surgical procedures in the abdomen or pelvic region.

Sigmoidoscopy

A procedure in which a lighted sigmoidoscope is used to visualize the lower colon and rectum.

Stool culture

A procedure that involves collecting a stool sample and performing various tests to detect the presence of disease-causing pathogens.

Circulation of Absorbed Nutrients

All blood from the capillaries in the stomach and intestines is circulated directly to the hepatic portal system so that it can be processed in the liver. The hepatic portal vein drains the nutrient-rich blood from the capillaries in the villi and carries it to the capillary beds in the liver. There, the liver removes excess glucose, amino acids, iron, vitamins, and other nutrients for storage. It also recycles the 80% of bile acids reabsorbed from the ileum to form bile for lipid digestion in the future. The fatty acids and glycerol absorbed into lacteals in the villi will join the bloodstream at the subclavian veins and eventually reach the liver through the hepatic artery.

Barium swallow/upper GI series

An X-ray test used to examine the upper digestive tract, which includes the esophagus, stomach, and small intestine.

Ultrasound

An imaging technique in which sound waves are used to visualize internal structures. In the digestive system, ultrasound may be used to visualize digestive organs for any abnormalities.

Computed tomography (CT)

An imaging technique used to visualize internal structures. The scan produces images in "slices" of areas throughout the body. In regard to digestive system disorders, CT can be used to determine changes in digestive organs that might indicate disease.

Magnetic resonance imaging (MRI)

An imaging technique used to visualize internal structures. This test provides great contrast between various soft tissues in the body. In regard to digestive system disorders, MRI can be used to detect changes in digestive organs that might indicate disease.

Regenerative cells

Are stem cells that divide and differentiate to replace any of the other cells of the gastric pits and gastric glands. Regenerative cells are very necessary because the cells lining the stomach are short-lived, lasting only 3 to 6 days due to the stomach's harsh, acidic environment. The gastric pits' cells must be continually replaced.

Pancreas

Chemical secreted, Route Taken to the Duodenum, Function: Bicarbonate Ions, Pancreatic duct to the duodenum, neutralizes the acids of chyme Enzymes for carbohydrates, Pancreatic duct to the duodenum, Chemically digest carbohydrates Enzymes for proteins, Pancreatic duct to the duodenum, chemically digests proteins Enzymes for lipids, Pancreatic duct to the duodenum, Chemically digests lipids

Gallbladder

Chemical secreted: Bile Route Taken to the Duodenum: Cystic duct to the common bile duct Function: Emulsifies lipids

Liver

Chemical secreted: Bile Route Taken to the Duodenum: Hepatic ductules to the hepatic ducts and then to the common bile duct; possibly overflows through the cystic duct into the gallbladder between meals Function: Emulsifies lipids

Physiology of Digestion in the Large Intestine

Chyme (minus the absorbed nutrients) enters the large intestine in a very liquid state. The large intestine functions to absorb water, and this compacts its contents into feces. This process can take 12 to 24 hours. During that time, the large intestine also absorbs some electrolytes (especially sodium and chloride ions) and vitamin K produced by bacteria living in the large intestine. The large intestine then stores fecal matter until it is removed (defecation). The absorption of water in the large intestine is important to maintain homeostasis. Even after the water is absorbed and the feces have been compacted, feces are still typically composed of 75% water and 25% solid matter. The solid matter consists of bacteria that normally live in the colon, indigestible carbohydrates (dietary fiber), lipids, and a mixture of sloughed-off epithelial cells, digestive juices, mucus, and a small amount of protein. The lipids and proteins are not from the cheeseburger. They are from broken-down epithelial cells and bacteria, which normally live in the colon and have died. Indigestible carbohydrates from the cheeseburger feed the bacteria that reside in the large intestine. In return, the bacteria produce some B vitamins and vitamin K, a necessary vitamin for the production of clotting factors. Although these bacteria provide a very beneficial service, they also produce a gas called flatus, which is not so desirable, as it can cause a bloated feeling and an unpleasant odor. The amount of flatus produced depends on the amount of bacteria present in the colon and the type of food ingested. The large intestine normally contains 7 to 10 L of gas. A typical human expels approximately 500 mL of flatus per day. How do materials move through the large intestine? Upon entering the large intestine, materials pass up the ascending colon by peristalsis to the transverse colon, where the materials stop. Distension (expansion) of the stomach and duodenum causes a mass movement, which moves the feces from the transverse colon to the descending colon, to the sigmoid colon, and on to the rectum. Distension of the walls of the rectum triggers the defecation reflex. This reflex drives the feces downward and relaxes the internal anal sphincter. Even though this is an involuntary reflex, defecation occurs only if the external anal sphincter is voluntarily relaxed.

Control of Digestion

Control of digestion is through the autonomic nervous system. Parasympathetic fibers of the vagus nerve stimulate digestion, while sympathetic neurons from the celiac ganglion suppress digestion in part by diverting blood to skeletal muscles and the heart.

Physiology of Digestion in the Stomach

During swallowing, the medulla oblongata sends signals to the stomach telling it to relax. As the bolus is moved down the esophagus by peristalsis to the stomach, the stomach's cardiac sphincter opens to allow the bolus to enter. This relaxation of the stomach and the opening of the cardiac sphincter allow the stomach to fill. As the stomach fills, the three layers of smooth muscle in the stomach's walls stretch, causing the muscular walls to contract. These contractions result in peristaltic waves in the direction of the pyloric canal. The pyloric sphincter remains closed, making sure the contents stay in the stomach. As the bolus enters the stomach, the endocrine cells of the gastric pits produce the hormone gastrin. Gastrin targets chief cells and parietal cells, telling the chief cells to produce pepsinogen and gastric lipase and telling the parietal cells to produce hydrochloric acid and intrinsic factor. The hydrochloric acid (HCl) produced by the parietal cells has a pH of 0.8. It converts pepsinogen (produced by the chief cells) to pepsin, which partially breaks down proteins (the burger) in the bolus. This is the start of the chemical digestion of proteins in the bolus. The hydrochloric acid also activates lingual lipase from the saliva that mixed with the bolus in the mouth. The activated lingual lipase works together with the gastric lipase produced by the chief cells to partially break down the lipids in the bolus (the cheese). This is the start of chemical digestion of the lipids in the bolus. The intrinsic factor produced by parietal cells allows vitamin B12 to be absorbed later in the small intestine. Spot Check 5 Consider the composition of muscle tissue. What would happen to the walls of the stomach if the stomach did not have the protective mechanisms mentioned earlier? The churning of the stomach continues mechanical digestion by mixing all the gastric juices with the bolus. This liquefies the contents of the stomach, now called chyme. At this point, the carbohydrates have been partially digested in the mouth by amylase, the lipids have been partially digested in the stomach by lingual lipase and gastric lipase, and the proteins have been partially digested in the stomach by pepsin. As the mixing continues, the pH of the chyme falls due to hydrochloric acid's low pH. As the pH of the stomach's contents approaches 2, the endocrine cells of the gastric pits are prevented from producing any more gastrin. With less and less gastrin, the chief and parietal cells are also prevented from producing their products. This is a good example of maintaining homeostasis using a negative feedback mechanism. This low pH also causes the pyloric sphincter to begin to open, allowing approximately 3 milliliters (mL) of chyme to leave the stomach at a time. Digestion in the stomach is complete when the chyme exits the pyloric sphincter. Chyme travels within the first part of the small intestine—the duodenum. However, accessory structures play a large role in the digestion occurring in the duodenum. Therefore, we focus next on the anatomy of these accessory structures—the liver, the gallbladder, the pancreas, and the relevant ducts connecting these structures to the duodenum.

True or false bile contains digestive enzymes.

False

Anatomy of a tooth

Figure 13.7 shows that a tooth is held in its bony socket (alveolus) in the jaw by periodontal ligaments. The tissue surrounding a tooth is the gingiva commonly called the gum. The portion of the tooth emerging from the gingiva is called the crown. The crown is covered by a very hard, smooth, white layer called enamel. The enamel's function is to protect the underlying layer, the dentin. The root of the tooth, below the gum line, is not covered by enamel. Deep to the dentin is a pulp cavity that contains the blood vessels and nerve for the tooth.

Gastric pits and gastric glands. Regenerative cells are not shown

Gastric pits and gastric glands. Regenerative cells are not shown

Cholelithiasis

If the gallbladder concentrates the bile too much, the cholesterol in bile may precipitate (settle out as a solid), forming gallstones (cholelithiasis).

Constipation

If the large intestine absorbs too much water, the feces will become harder to move, leading to constipation. Increased fluid intake, increased dietary fiber, and exercise can help move feces along. The increased pressure to push with constipation can cause hemorrhoids, which are bulging anal veins. They may be internal to the rectum or external to the anus. On the other hand, if the large intestine absorbs too little water, diarrhea may occur. A runny stool can result from irritation of the intestine caused by bacteria. In the case of diarrhea, the ileum's contents pass through the colon too quickly for adequate water absorption and compaction of feces to take place.

Hepatitis

Inflammation of the liver, usually caused by a viral infection. It is a serious condition that can lead to cirrhosis, liver cancer, and liver failure. Other medical conditions such as excessive alcohol and drug use, and certain medications, can also cause hepatitis. The symptoms of hepatitis include an enlarged liver, fluid in the abdomen, and jaundice. Hepatitis can be diagnosed by ultrasound, liver function tests, liver biopsy, and blood tests for the presence of the virus.

What is the function of the digestive system?

Ingestion

Functions of the Digestive System

Ingestion. This function involves the intake of food into the mouth. By her smile, you can see that Lisa has seen an orthodontist to straighten her teeth. Healthy teeth and a properly aligned bite will help Lisa begin the next function of this system. Digestion. Lisa begins mechanical digestion of her cheeseburger as soon as she starts to chew. Mechanical digestion breaks down large pieces of complex molecules to smaller pieces of complex molecules. This type of digestion continues in the stomach. Chemical digestion breaks complex molecules into their building blocks. It, too, begins in the mouth, where carbohydrates are partially broken down, and it continues in the stomach, where proteins and lipids are partially broken down. Chemical digestion is completed in the small intestine, where the carbohydrates are completely broken down to monosaccharides, the lipids are completely broken down to fatty acids and glycerol, and the proteins are completely broken down to amino acids. Absorption. The products of digestion are absorbed through the villi in the small intestine. Monosaccharides and amino acids are absorbed through facilitated diffusion into the villi's epithelial cells and then into capillaries to travel to the liver through the hepatic portal vein. Using simple diffusion, the epithelial cells of the villi absorb fatty acids and glycerol. They are then coated with protein and endocytosed to lacteals in the villi to travel with lymph to subclavian veins. Defecation. The stretching of Lisa's stomach and duodenum during the consumption of this meal will initiate a mass movement in her colon. When the previously undigested materials and bacteria stretch the walls of Lisa's rectum, a defecation reflex will result, but it will be Lisa's decision as to when to defecate. It is important to understand that most of the feces removed from the body are not metabolic wastes, produced by chemical processes in cells. They are simply what was inserted in the mouth and never absorbed by the body's cells.

Heart burn/Gastroesophageal reflux disease

It is crucial that the cardiac sphincter closes tightly after the bolus has entered the stomach, as the mucosa lining the esophagus provides insufficient protection from the gastric juices produced in the stomach. Irritation, creating a burning sensation, results if gastric juices leak back to the esophagus. This is commonly called heartburn because of the close proximity of the end of the esophagus to the heart. Chronic leakage of gastric juices back to the esophagus is called gastroesophageal reflux disease (GERD).

What components of the digestive system are specific to the alimentary canal?

It passes through the thoracic and abdominopelvic cavities, It includes the mouth, esophagus, stomach, intestines and anus.

The two enxymes contained in saliva are: _______, which is antibacterial, and ______, which begins carbohydrate digestion

Lysozyme, amylase

Absorption of Nutrients in the Small Intestine

Monosaccharides and amino acids are absorbed into capillaries through the epithelium of the villi by facilitated diffusion. Fatty acids and glycerol are absorbed across the epithelial membranes of the villi by diffusion. They are then coated with proteins and exocytosed to the lacteals, the small lymph vessels located in the villi. They will continue to travel through lymph vessels to the thoracic duct to the left subclavian vein, where they will enter the bloodstream. The ileum reabsorbs 80% of the bile acids in the chyme, while the other 20% will leave the body during defecation. This is the body's way of removing cholesterol. The liver will make new bile acids from cholesterol to replace the lost 20% of bile acids. What was not absorbed moves through the ileocecal sphincter into the large intestine.

Physiology of Digestion from the Mouth to the Stomach

Once the bolus has been sufficiently masticated in the mouth, it is time to swallow. Swallowing, called deglutition, is a very complex process controlled by the medulla oblongata. It requires four cranial nerves (V, VII, IX, and XII) to stimulate the muscle contractions necessary to move the bolus from the pharynx to the esophagus. Swallowing begins with the tongue pushing the bolus back to the pharynx (1). The larynx pushes up, causing the epiglottis to close over the glottis (2). This ensures that the bolus moves into the esophagus and not into the larynx as the pharyngeal muscles push the bolus down (3). Once in the esophagus, the muscular walls move the bolus along its length in wavelike contractions called peristalsis (4). Gravity aids in the movement toward the stomach if the individual is in an upright position, but being upright is not necessary. The bolus can still move to the stomach even if the individual is upside down.

The anatomy of the digestive system is like a complicated tube

One end of the tube is the mouth and the other end is the anus.

Salivary Glands

Produce about 1.0 to 1.5 liters of saliva a day, consist of the parotid glands (anterior to the ears), the submandibular glands (inferior to the angle of the mandible on each side), and the sublingual glands (below the tongue). Each gland produces saliva that travels to the oral cavity through ducts. The saliva, which is mostly water also contains enxymes amylase and lingual lipase, along with mucus, lysozymes and antibodies. Saliva secretion is initiated by taste receptors that send signals by way of the facial and glossopharyngeal nerves to centers in the medulla oblongata and pons. These control centers also receive other stimuli so that odors, sight, or even the thought of food may stimulate saliva secretion.

Gastric lipase

Produced by Chief cells, Function: Partially breaks down lipids

Mucus

Produced by Mucous cells Function: Protects the stomach walls

Pepsinogen

Produced by chief cells Function: Changes to pepsin to partially break down proteins

Gastrin

Produced by endocrine cells, funtion: tells chief and parietal cells to produce their products

Hydrochloric acid

Produced by parietal cells Function:Converts pepsinogen to pepsin, which partially breaks down proteins through chemical digestion Activates lingual lipase, which, along with gastric lipase, partially breaks down lipids through chemical digestion Converts iron in the diet to a usable form that can be absorbed Destroys some bacteria

The small intestine is a tubular organ that extends from the ______ sphicter to the beginning of the large intestine

Pyloric

Saliva

Saliva from the salivary glands mixes with the bite of cheeseburger in the mouth. The saliva's pH is 6.8 to 7.0. At this pH, amylase partially breaks down the carbohydrates from the bun. This is the beginning of chemical digestion. Lingual lipase does nothing at this pH, but it is activated later by the lower pH of the stomach. Amylase, however, will no longer function at the lower pH in the stomach. Thus, it is important to masticate the bite of cheeseburger thoroughly because doing so allows for mechanical digestion and also gives amylase sufficient time to partially break down the carbohydrates in chemical digestion before the food is swallowed. The mucus in the saliva moistens the bite of food (now called a bolus), making it easier to swallow. The lysozymes and antibodies in the saliva are not used for digestion. They destroy and inhibit the growth of bacteria that may have entered with the bite. Digestion is finished in the mouth when the tongue pushes the bolus to the pharynx.

Cholecystectomy

Surgery—a cholecystectomy—may be necessary to remove the gallbladder and the gallstones within.

What is try regarding the secretion of pancreatic juice?

The Pancreatic duct that extends along the pancreas collects the pancreatic juice. The hepatopancreatic sphincter controls the movement of pancreatic juices into the duodenum

Ascending Colon

The ascending colon begins at the ileocecal valve and passes up the right side of the abdominal cavity toward the right lobe of the liver. As it approaches the liver, it forms a right-angle bend called the right colic (hepatic) flexure.

Cecum

The cecum is a blind pouch (does not lead anywhere) inferior to the juncture of the ileocecal valve in the lower right quadrant of the abdomen. The appendix is a dead-end tube extending approximately 7 cm from the inferior portion of the cecum. It contains many lymphocytes.

Common Bile Duct

The common bile duct is a tube running from the common hepatic duct to the duodenum. The cystic duct also feeds into the common bile duct. The hepatopancreatic sphincter at the opening to the duodenum regulates the passage of materials from the common bile duct and pancreatic duct into the duodenum.

Tapeworms

The larvae of these worms—from undercooked beef, pork, or fish—infect the digestive tract. They attach to the intestinal wall by suckers and feed off the partially digested materials passing by. Tapeworms are segmented worms, and their segments may break off and appear in the feces. Tapeworms may live in the digestive tract for years, and can grow up to 6 meters in length.

Plaque

The daily bacteria buildup that forms on the tooth is plaque. Plaque can be flossed and brushed away, but if it is allowed to remain, it hardens to form tartar, which must be removed by a dental professional.

Descending Colon

The descending colon is a continuation of the large intestine that extends from the left colic flexure down the left side of the abdominal cavity.

The digestive system, including accessory structures.

The digestive system, including accessory structures.

Duodenum

The duodenum is the first 25 cm (10 inches) of the small intestine; it is located immediately after the stomach's pyloric sphincter. As with the entire small intestinal tract, there is smooth muscle in the duodenal walls, and the duodenal lining has circular folds with many tiny projections called villi. The villi are covered with simple columnar epithelial cells and mucus-producing goblet cells. The simple columnar epithelial cells have a brush border of microvilli to give these cells extra surface area for absorbing nutrients. Inside the villi are capillaries and small lymphatic vessels called lacteals. Absorption of nutrients takes place through the villi, either into the capillaries or into the lacteals. The lining of the duodenum also contains endocrine cells. These cells make two hormones—secretin and cholecystokinin that target the gallbladder and pancreas, telling them to release bicarbonate ions, digestive enzymes, and bile to be delivered to the duodenum. The duodenum, like the jejunum and ileum, has tight junctions between cells of the epithelial lining to protect itself from the acidic chyme. Only small amounts of chyme should enter the duodenum at any one time. This helps keep the mucous lining from becoming overwhelmed, and it gives the duodenum time to neutralize the chyme.

Effects of Aging on the Digestive System

The effects of aging on the digestive system can be seen in many of the structures along the alimentary canal, starting with the mouth. The effects of aging can be seen in the mouth. The enamel on the teeth thins and the gingiva recedes, allowing for increased tooth decay and loosening of the teeth. This interferes with proper mastication. Proper dental hygiene can minimize these effects. The receptors in the taste buds and nose become less sensitive, leading to a decreased appetite. This may compromise the nutritional status. Although the person may be eating less because of a diminished appetite, there may be weight gain due to a slower metabolism. The lining of the stomach begins to atrophy with age. This can result in less intrinsic factor produced. With less intrinsic factor, less vitamin B12 is absorbed from the diet, possibly leading to pernicious anemia. The liver may metabolize drugs differently as it ages. Geriatric patients may need to have dosages adjusted for drugs they had been taking long-term. Movement through the large intestine slows with age. The longer materials stay in the large intestine, the more water is absorbed. This can lead to constipation.

Epiglottis

The epiglottis is made of elastic cartilage connective tissue. It is one of the cartilages of the larynx. It stands guard over the glottis, which is the opening of the larynx.

Esophagus

The esophagus is a straight, muscular tube that extends from the laryngopharynx, travels through the mediastinum, penetrates the diaphragm, and connects to the stomach. It is lined by stratified squamous epithelial tissue. Deep to the epithelial lining is a submucosa of connective tissue containing esophageal glands that secrete protective mucus for the esophagus. The upper one-third of the esophagus has skeletal muscle in its walls, while the middle one-third has a mixture of skeletal and smooth muscle and the lower one-third has just smooth muscle in the walls of the esophagus. Unlike the trachea that is held open by C-shaped cartilages, the esophagus is normally collapsed.

Ileum

The ileum is the last part of the small intestine, measuring 3.3 to 3.6 m in length. Its walls are less muscular and thinner than the jejunum's. The ileum's lining is characterized by nodules of lymphocytes called Peyer's patches. These nodules increase in size as they approach the large intestine, and they function to destroy any bacteria or other pathogens entering the small intestine from the large intestine. The ileocecal valve is a sphincter muscle at the juncture of the ileum and the large intestine; it regulates the passage of materials from the ileum to the large intestine.

Roundworms.

The ingested eggs of this parasite hatch into larvae in the upper intestine, enter the bloodstream, and travel to the lungs. Here, they cause respiratory symptoms. When coughed to the pharynx, the larvae are then swallowed, returning the worms to the intestine. The adult worms may stay in the intestine, or they may migrate, cutting through intestinal walls.

Jejunum

The jejunum—the second part of the small intestine has a very rich blood supply that gives it a pink appearance. The jejunum measures approximately 2.2 to 2.4 m in length and its villi are slightly smaller than those in the duodenum. Circular folds in the lining allow extra surface area for absorption. Most of the absorption of nutrients takes place in the jejunum.

Anatomy of the Large Intestine

The large intestine (colon) is made up of six regions: the cecum, the ascending colon, the transverse colon, the descending colon, the sigmoid colon, and the rectum. Altogether, these regions measure about 1.5 m in length and 6.5 cm in diameter. Although the large intestine is shorter than the small intestine, it is termed large because its diameter is greater.

The stomach has several mechanisms it uses to protect itself from the harsh environment created by the cells of the gastric pits and gastric glands. These mechanisms include the following:

The lining has the highly alkaline mucous coat that resists the hydrochloric acid and digestive enzymes. There is epithelial cell replacement of the lining by the regenerative cells. There are tight junctions between epithelial cells, so acid and enzymes cannot get to the submucosa and smooth muscle walls made of mostly protein.

Liver

The liver is a large, reddish-brown organ immediately inferior to the diaphragm on the right side of the abdominal cavity. It has four lobes: the right and left lobes, separated by the falciform ligament; the quadrate lobe, next to the gallbladder; and the caudate lobe, which is the most posterior lobe. The falciform ligament is a sheet of mesentery that suspends the liver from the diaphragm and anterior abdominal wall. The round ligament is a remnant, or leftover piece, of the umbilical vein, which had delivered blood from the mother's placenta to the liver in the fetus. The liver is a highly vascular organ that is arranged in hepatic lobules. Each hepatic lobule has a central vein as a hub and sheets of liver cells (hepatocytes) radiating out like spokes on a wheel. The liver receives oxygenated blood from the hepatic artery and nutrient-rich blood from the hepatic portal vein. The hepatic vein drains blood from the liver. The digestive function of the hepatocytes is to produce bile. Bile is a yellow-green fluid containing bile acids, synthesized from cholesterol (a steroid), and lecithin (a phospholipid). Both of these components function to aid in the digestion of lipids by emulsifying lipid droplets. Emulsification involves breaking the lipids into smaller droplets, a process much like the way detergents emulsify grease when you wash your dishes. Enzymes can then complete chemical digestion of lipids more efficiently. The other contents of bile are waste products that include bilirubin (from the breakdown of hemoglobin), cholesterol, neutral fats, bile pigments, and minerals. Bile travels within the liver from the hepatocytes, to hepatic ductules, to the right and left hepatic ducts, and to the common hepatic duct, which exits the liver and leads to the common bile duct. The liver produces approximately 500 to 1,000 mL of bile per day, which is equivalent to one-quarter to one-half of a large 2 L bottle of soda.

Gingivitis

The mouth is full of bacteria. Every time you eat, bits of food are wedged between the teeth and between each tooth and the gingiva. Bacteria feed on this buffet left out for them, digest the food, and then excrete their acidic waste in the same location. This waste erodes the enamel to form a caries and irritates the gingiva, causing it to become inflamed and infected (gingivitis). As gingivitis progresses, the gingiva pulls away from the tooth and recedes. This allows more food to become wedged between the tooth and the gingiva and more unprotected dentin to be exposed. If gingivitis goes untreated, the inflammation and infection can spread to the ligaments and bone that hold the teeth in place (periodontitis). This causes the teeth to become loose and eventually fall out. Periodontitis is the most common cause of tooth loss in adults.

Oral cavity

The mouth, the roof consists of the hard palate, formed by the maxilla and palatine bones, and the soft palate is composed of soft tissue. The soft palate ends with the uvula, a posterior projection that directs materials downward to the pharynx so that they do not travel to the nose. The sidewalls of the oral cavity are the cheeks, and the floor of the cavity is where the tongue is attached. The oral cavity is lined by stratified squamous epithelial tissue, which is a very durable epithelial tissue that can withstand the abrasions of manipulating solid food in the mouth.

Pharynx

The nasopharynx leads from the nasal cavity to the oropharynx. The oropharynx is a funnel leading from the oral cavity to the laryngopharynx. This funnel is lined by stratified squamous epithelial tissue and has smooth muscle in its walls. The laryngopharynx leads to the trachea and the esophagus. The respiratory and digestive pathways intersect in the pharynx.

Mastication is

The process of chewing

To maintain homeostasis, the digestive system must absorb these nutrients from the diet.

The proteins in the burger were chemically digested to amino acids and were absorbed into the blood of capillaries in the small intestine. The carbohydrates in the bun were chemically digested to monosaccharides and were also absorbed into the blood of capillaries in the small intestine. The lipids of the cheese were chemically digested to fatty acids and glycerol and were absorbed into the lacteals in the small intestinal villi. Other nutrients, like vitamins and minerals, are also absorbed by the digestive system. Vitamins can be categorized as fat soluble or water soluble. Fat-soluble vitamins (A, D, E, and K) are absorbed along with the products of lipid digestion, so they must be ingested with fats to be absorbed. On the other hand, water-soluble vitamins (the B complex and C) are absorbed by simple diffusion. Vitamin B12 is an exception. It must first bind to intrinsic factor in the stomach and then be endocytosed by cells of the ileum for absorption. A list of vitamins and their RDAs can be found in Appendix B. Minerals are electrolytes that are absorbed along the length of the small intestine, and some, like sodium and chloride, can also be absorbed in the large intestine. Sodium is absorbed with sugars and amino acids. Chloride ions are mostly absorbed by active transport in the ileum. Potassium is absorbed by simple diffusion once water has been absorbed. Most minerals are absorbed at a constant rate. The kidneys excrete whatever excess may have been absorbed. Calcium and iron are an exception, as the body absorbs them to meet its level of need. You may recall from the skeletal system chapter that the hormone PTH regulates the absorption of calcium in the small intestine.

Rectum

The rectum is approximately 15 cm long, and it ends with the anal canal. The anus contains two sphincter muscles: the smooth muscle internal anal sphincter, controlled by the autonomic nervous system, and the skeletal muscle external anal sphincter, controlled by the somatic nervous system. All of the large intestine's regions contain smooth muscle in the walls, but the ascending, transverse, descending, and sigmoid colons also contain longitudinal bands of smooth muscle called taenia coli. The taenia coli cause the large intestine's walls to bulge, forming pouches called haustra. Unlike the small intestine, the large intestine does not contain villi. Instead, it is lined by simple columnar epithelial tissue, except for the lower part of the anal canal, which is stratified squamous epithelial tissue. This tissue needs to be stratified to withstand the abrasion of materials leaving the body.

The alimentary canal starting at the oral cavity and ending at the anus

The relative length of each section is shown.

Pancreas

The ribbonlike pancreas has a pebbly appearance, and it is retroperitoneal, meaning it is posterior to the parietal peritoneum. The pancreas functions as two glands: (1) as an endocrine gland, because it produces the hormones insulin and glucagon secreted into the blood, and (2) as an exocrine gland, because it produces the bicarbonate ions and enzymes for protein, lipid, and carbohydrate digestion that are secreted into the pancreatic duct. The bicarbonate ions work to neutralize the low pH of the chyme entering the duodenum from the stomach. The pancreatic duct runs the length of the pancreas and joins with the common bile duct as it opens to the duodenum. The liver, gallbladder, and pancreas—are not part of the cheeseburger's path. These organs secrete digestive chemicals that are delivered to the small intestine through ducts. Their digestive juices go to the duodenum; the cheeseburger does not go through these ducts to these accessory organs.

Sigmoid Colon

The sigmoid colon is a continuation of the large intestine that forms an S shape in the pelvic cavity. It connects to the last part of the large intestine, the rectum.

Anatomy of the Small Intestine

The small intestine is composed of the duodenum, the jejunum, and the ileum. Digestion is completed in the duodenum, and absorption takes place throughout the small intestine. Although it may look as though the small intestine is very unorganized, the mesentery membranes neatly arrange the blood vessels and nerves traveling to and from each section of the small intestine.

Anatomy of the Stomach

The stomach is a J-shaped organ found in the upper left quadrant of the abdomen, immediately inferior to the diaphragm. It is a muscular sac capable of holding 1.0 to 1.5 L after a meal, but it can stretch to hold up to 4 L when extremely full. The cardiac sphincter (lower esophageal sphincter) controls the opening to the stomach from the esophagus. This circular muscle's purpose is to allow food to enter the stomach and make sure it does not return to the esophagus. The stomach can be described in terms of the following areas: the lesser curvature on the inside of the J; the greater curvature on the outer side of the J; the fundus, superior to the cardiac sphincter; the body, making up the majority of the stomach; and the pyloric region leading to the smooth muscle pyloric sphincter, which regulates the passage of materials to the duodenum. There are three layers of smooth muscle in the walls of the stomach: outer longitudinal muscles, middle circular muscles, and inner oblique muscles. Having muscles oriented in different directions allows for maximum churning of the stomach's contents. Longitudinal wrinkles called gastric rugae can be seen inside the stomach when the stomach is empty. These wrinkles become less apparent as the stomach stretches. They also allow for more surface area to accommodate microscopic depressions in the lining, called gastric pits, that extend to form gastric glands. Five different types of cells line the gastric pits and gastric glands.

Transverse Colon

The transverse colon is a continuation of the large intestine that extends from the right colic flexure across the abdomen to the area of the spleen. There, the colon forms another right angle called the left colic (splenic) flexure.

Giardia

These protozoans are prevalent in streams, lakes, and rivers, especially where beavers are present. This infection results from ingesting untreated, contaminated water. The symptoms of nausea, abdominal cramps, and weight loss may last for weeks.

Pinworms

These small, white worms commonly live in the digestive tract of humans and feed on the partially digested food going by. They crawl out the anus to lay their eggs, which causes an itching sensation. Contaminated fingers then spread the eggs to surfaces on which they are able to survive.

Veins of the hepatic portal system

Veins drain nutrient-rich blood from capillary beds in the digestive organs and deliver it to capillary beds in the liver through the hepatic portal vein. Once processed, the blood leaves the liver through the hepatic vein on its way to the inferior vena cava and then the heart..

Physiology of Digestion in the Small Intestine

When the acidic chyme enters the duodenum, the endocrine cells of the duodenum begin to secrete their hormones—secretin and cholecystokinin. One minor role of these two hormones is to target the stomach's parietal and chief cells, telling them to stop producing hydrochloric acid and pepsinogen. If chyme is now entering the duodenum, there is no further need for digestion in the stomach. This is a second negative feedback mechanism to stop digestion in the stomach and maintain homeostasis. It complements the negative feedback mechanism of low pH in the stomach, mentioned earlier. Another role of these two hormones is to target the pancreas, telling it to release enzymes to complete carbohydrate, lipid, and protein digestion. These digestive enzymes travel through the pancreatic duct to the common bile duct and through the hepatopancreatic sphincter. Then they move into the duodenum to complete lipid, carbohydrate, and protein digestion. The low pH of the chyme entering the duodenum stimulates the duodenal endocrine cells to secrete secretin. This hormone mainly targets the pancreas, telling the pancreas to release bicarbonate ions to neutralize the acidic chyme. This bicarbonate solution from the pancreas carries pancreatic enzymes for lipid, protein, and carbohydrate digestion from the pancreas, through the pancreatic duct, to the common bile duct, and to the duodenum. The bicarbonate ions combine with the hydrogen ions of the hydrochloric acid to form carbon dioxide and water. The carbon dioxide is absorbed into the blood and carried to the lungs, where it is eventually expelled. All of these steps are necessary to help protect the duodenum from the low pH and maintain homeostasis. When partially digested lipids enter the duodenum, the duodenum's endocrine cells release cholecystokinin, which travels through the blood to its main target tissues—the gallbladder and the hepatopancreatic sphincter. Cholecystokinin tells the gallbladder to squeeze (contract) and release its bile through the cystic duct to the common bile duct. Cholecystokinin also tells the hepatopancreatic sphincter to relax so that the bile in the common bile duct can enter the duodenum. Bile helps complete lipid digestion by emulsifying (breaking up) the lipids to tiny droplets so that the lipases (enzymes) from the pancreas can break the lipids down to their building blocks—fatty acids and glycerol. Bile also helps activate some of the other digestive enzymes from the pancreas. The pancreatic enzymes complete protein digestion by breaking the protein molecules down to their building blocks, amino acids, while carbohydrate-digesting enzymes from the pancreas break down the chyme's carbohydrates to their building blocks, monosaccharides (simple sugars). In the small intestine, the mechanical and chemical digestion of the cheeseburger introduced in the beginning of the chapter is complete. The fats in the cheese are broken down to fatty acids and glycerol. The proteins of the burger are broken down to amino acids. And the carbohydrates of the bun are broken down to monosaccharides. The nutrients, waste products from the bile, and the indigestible materials continue on to the jejunum and ileum, where nutrient absorption occurs through the villi. The chyme moves through the sections of the small intestine via two types of contractions. Segmentation is a stationary constriction of the smooth muscle in ringlike patterns. This type of contraction further churns the chyme, mixing in the bile and digestive enzymes to finish chemical digestion. It also allows for maximum contact between chyme and the villi, facilitating maximum absorption of nutrients. Once the chyme has churned and mixed with the bile and digestive enzymes, it continues to move through the jejunum and ileum through peristalsis

Cholecystitis

When the gallbladder is directed to release its bile, the stones may block the cystic duct, causing pain and inflammation (cholecystitis).

polyps

With age, the cumulative effects of ingested carcinogens on the walls of the large intestine may lead to polyps, which are precancerous growths. A colonoscopy is recommended to check for polyps on a routine basis for individuals with a family history of colon cancer. The incidence of colon cancer increases with age.

Teeth

You will develop two sets of teeth over life, a deciduous (primary) set and a permanent (secondary) set. The deciduous teeth begin to erupt or grow in at 6 months and will be complete by the age of 2 years. This primary set consists of 10 teeth in each jaw. The permanent teeth erupt, they push out the deciduous teeth. The secondary set begins to erupt at 6 years of age and will not fully complete, with 16 teeth in each jaw until 17-25 years of age.

Cirrhosis

a condition of the liver characterized by the formation of scar tissue. The scar tissue will eventually block blood flow to parts of the liver and interfere with the liver's ability to function properly. The two main causes of cirrhosis are excessive alcohol consumption and chronic hepatitis infection. Although symptoms in the early stages are uncommon, as the disease progresses, one might experience weakness, weight loss, fatigue, nausea, fluid accumulation in the abdomen, and itching. Physicians may use physical exams, blood tests for liver function, CT, MRI, and ultrasound to diagnose cirrhosis. Treatment for cirrhosis is geared toward treating the complications of impaired liver function and treating the causes of the disease. While the liver has the ability to regenerate new cells to replace damaged ones, a liver with advanced cirrhosis no longer has this capability. For this reason, a liver transplant may also be necessary.

Crohn's disease

a type of autoimmune inflammatory bowel disease that causes chronic inflammation along the gastrointestinal tract. While any part of the gastrointestinal tract may be affected, usually the inflammation associated with Crohn's affects the intestines. Symptoms of Crohn's disease include abdominal cramping, fever, fatigue, diarrhea, and weight loss. Physical exam, barium enema, colonoscopy, CT scan, endoscopy, MRI, sigmoidoscopy, upper GI series, blood tests, and stool culture can all be used when diagnosing this disorder. Treatment can involve dietary changes, medications, and surgery.

Teeth of the upper jaw

a) deciduous teeth, b) permanent teeth

The large intestine

a) gross anatomy b) the anal canal

Parasites

an organism that lives on or in another organism (the host) and obtains its nourishment there. Parasites may or may not be harmful to the host. With digestive parasites, it is important to understand what they eat.

Peptic Ulcers

are erosions of the digestive tract lining due to an imbalance of gastric juices (hydrochloric acid and pepsin) and the protection provided by the mucosa. Once through the mucosa, the gastric juices may continue to erode the protein-rich muscular walls. Peptic ulcers are named for where they occur, such as esophageal ulcers, gastric ulcers, or duodenal ulcers. (a) peptic ulcers, (b) stomach that has been opened and laid flat to show several ulcers. Contrary to popular belief, stress does not cause ulcers. Chronic stress may, however, increase the chances of an ulcer forming and can slow its healing. During chronic stress, the sympathetic nervous system reduces the production of mucus in the digestive tract, lowering the protection from the gastric juices.

Inguinal hernias

are protrusions into the groin. These hernias are more common in males due to weakness remaining in the abdominal wall following the descent of the testes through the inguinal canal into the scrotum

Abdominal Hernias

are protrusions of the contents in the abdomen through a weak portion in the abdominal wall. Although most hernias do not cause pain or discomfort, a bulge may be visible, resulting from the protrusion of the abdominal contents through the abdominal wall. Some hernias may resolve without treatment, and for those that do not resolve on their own, surgery is an option.

Incisional hernias

are protrusions through an incision from past abdominal surgery.

Umbilical hernias

are protrusions through the umbilicus. These hernias occur due to weakness in the abdominal wall where the umbilical cord was once attached.

cyst/o

bladder, sac

Inflammation of the appendix—appendicitis

can be extremely serious because the appendix can rupture and spill its contents into the abdominopelvic cavity. These contents are filled with bacteria, which may infect the entire abdominopelvic cavity if released.

hepatitis C

can lead to an acute condition but more likely causes a chronic infection that can eventually cause cirrhosis or liver cancer. Hepatitis C usually spreads through contact with infected blood by sharing contaminated needles during drug use.

Colon Cancer

cancer of the large intestine

Salmonellosis

caused by the bacteria in contaminated food (meat, poultry, milk). These bacteria are destroyed by heat. The symptoms of nausea, diarrhea, and vomiting can occur up to 36 hours after eating.

Botulism

caused by toxins made by a common bacterium found in the soil. This toxin is a powerful neurotoxin that prevents muscle contractions. You may eat a raw green bean directly from the garden and ingest the bacteria. This is not harmful. However, if the green beans are improperly canned and not all of the bacteria are destroyed in the process, the toxins they produce may be fatal

hepatitis D

causes a very serious liver disease, which is uncommon in the United States. The hepatitis D virus must have the hepatitis B virus present in order to spread throughout the body, causing damage to the liver. This virus spreads in the same way as hepatitis B.

Hepatitis A

causes acute liver disease that can last for a few months. It is transmitted by ingestion of fecal matter, direct contact with an infected person, or ingestion of contaminated food products.

Hepatitis B

causes liver disease that ranges in severity. Hepatitis B infections can be acute or chronic. This disease is transmitted by contact with infected blood or other body fluids, by sexual contact with an infected person, from mother to newborn, or by shared contaminated needles during drug use. Because health care providers are often exposed to blood and other body fluids from patients who may be infected with hepatitis, it is recommended that they receive the hepatitis B vaccination to reduce the risk of contracting the disease. The vaccine is also available and recommended for children and adults who may be at risk for contracting hepatitis B.

Tongue

composed of skeletal muscle tissues anchored to the floor of the oral cavity by a medial fold called the lingual frenulum. On the tongues superior surface, stratified squamous epithelial tissue covers the lingual papillae, which house the taste buds. Taste buds contain nerve endings that sense sweet, sour, salt, bitter, and umami. The purpose of the tongue is to manipulate what is ingested and to provide the sense of taste.

peps/o

digestion

duoden/o

duodenum

esophagi/o

esophagus

Diverticulitis

inflammation of the diverticulum. Individuals suffering from diverticulitis have abdominal pain and tenderness. The pain can be mild to severe and can be accompanied by nausea, vomiting, fever, or diarrhea. In severe cases, diverticulitis can cause bleeding, infection, small tears (perforations), or blockages in the colon. Only some people with diverticulosis get diverticulitis, in which case a person is said to have diverticular disease.

Gastroenteritis

inflammation of the gastrointestinal tract caused by a bacterial, viral, or parasitic infection. Gastroenteritis can cause diarrhea, stomach cramping, vomiting, fever, weight loss, excessive sweating, and dehydration. A health care provider may perform an examination of the abdomen and rectum along with a stool culture to diagnose the cause of gastroenteritis. Although the body will usually fight off the infection, care must be taken to replace the fluids and electrolytes lost from the vomiting and diarrhea.

The different types of abdominal hernias

inguinal, umbilical, and incisional hernias

enter/o

intestine

hepat/o

liver

The process of chewing is called

mastication, uses the masseter and temporalis muscles to move the jaw in a crushing motion, while the tongue, orbicularis oris, and buccinator muscles work to keep the food between the teeth. This begins mechanical digestion—breaking the bite of cheeseburger into smaller pieces.

Esophageal ulcers

may happen in the lower esophagus if there is reflux of gastric juices through the cardiac sphincter.

two types of digestion

mechanical and chemical.

Intussusception

occurs when a portion of the intestines folds back into itself, similar to a telescope, resulting in obstruction of the intestines and possible ischemia. This condition usually occurs in children, in the area where the small and large intestines meet. Ultrasound is used to diagnose intussusception, and if confirmed, an air enema (introduction of air into the larger intestine) may be performed to reduce or "uncoil" the affected area. If the reduction using the air enema does not work, surgery is required. (a) normal small intestine compared to an intussuscepted section of the small intestine with constricted blood supply, (b) section of an intussuscepted section of the small intestine during surgical repair.

Gastric ulcers

of the stomach are often the result of a bacterium, Helicobacter pylori (H. pylori). Continued use of nonsteroidal anti-inflammatory drugs (NSAIDs), such as aspirin, may also cause these ulcers.

Parietal cells

produce and secrete hydrochloric acid and intrinsic factor.

Intrinsic factor

produced by parietal cells Function: Allows vitamin B12 to be absorbed

rect/o

rectum

Vomiting

result from irritation anywhere along the digestive tract. It is controlled by an emetic center in the medulla oblongata. It begins with a deep breath. The hyoid bone and larynx are elevated, closing off the glottis, while the soft palate is elevated, closing off the nasopharynx. The diaphragm and abdominal muscles forcefully contract, putting pressure on the stomach and its contents. The cardiac sphincter opens and the contents of the stomach are forcefully expelled.

Mucus cells

secrete a highly alkaline mucus to protect the stomach walls from the hostile environment caused by the acid and digestive enzymes produced in the stomach.

Endocrine cells

secrete many hormones, but we will focus on the hormone gastrin.

Chief cells

secrete pepsinogen and gastric lipase

sigmoid/o

sigmoid colon

Diverticular Disease

small pouches (diverticula) in the lining of the large intestine as they age. The diverticula tend to bulge outward through weak portions in the wall of the large intestine. A person with multiple diverticula has a condition known as diverticulosis. Diverticulosis is common in people over the age of 60. Although this condition usually does not cause symptoms of pain or discomfort, in some people it may cause bloating and constipation. Diverticular disease is diagnosed through colonoscopy to detect the presence of diverticula. Ultrasound and CT scans can reveal diverticulitis in specific locations within the colon. Diverticular disease is treated by maintaining the appropriate amount of fiber in the diet. Antibiotics and pain medications may also be used to help with any infection or discomfort associated with the condition.

gastr/o

stomach

Gallbladder

the gallbladder is a pear-shaped sac on the inferior side of the liver. It stores and concentrates the bile produced by the liver. As the liver continually produces bile, it fills the common bile duct. Between meals, any overflow of bile in the common bile duct accumulates in the gallbladder through the cystic duct because the hepatopancreatic sphincter remains closed. The gallbladder then concentrates the bile by absorbing some of the water and electrolytes. When needed for digestion, the smooth muscle in the walls of the gallbladder contracts, squeezing the bile through the cystic duct to the common bile duct through the relaxed hepatopancreatic sphincter to the duodenum.

alimentary canal or gastrointestinal (GI) tract

the gastrointestinal tract that begins at the mouth and ends at the anus. May be as long as 8 meters. It twists and turns, enlarges and narrows as it uses muscle contractions to push its contents toward its end.

Malabsorption

the inability to absorb the appropriate nutrients needed by the body. This inability results from problems with digestion of food, absorption of nutrients from food, or transport of nutrients from food to the bloodstream. Symptoms include diarrhea, weight loss (despite the amount of food consumed), and anemia. Malabsorption can be diagnosed on the basis of physical exams, blood tests, stool culture, endoscopy, and contrast imaging tests.

Duodenal ulcers

the most common—result when the acidic chyme entering the duodenum through the pyloric sphincter is not sufficiently neutralized.

The journey of food in the mouth

to the pharynx, esophagus, stomach, small intestine, large intestine, and anus, where the journey ends. All along the pathway, mucous membranes and mucosa-associated lymphatic tissue (MALT) line the alimentary canal to fight any foreign invaders—such as bacteria—that may enter with the food

gloss/o

tongue

Staphylococcal food poisoning

usually contracted from a food handler. Bacteria contaminating the food make toxins, which cause nausea, diarrhea, and vomiting. The symptoms occur 1 to 6 hours after eating the contaminated food.

Leukoplakia

white patches that occur on the surface of the tongue, inside the mouth, or on the inside surfaces of the cheek. The white patches are caused by constant irritation, usually from contact with rough surfaces like dentures, tobacco products, or teeth with rough surfaces. Hairy leukoplakia is a disorder commonly seen in people with HIV or with compromised immune systems. It is caused by the Epstein-Barr virus and is characterized by fuzzy, white patches on the tongue.