Chapter 24: The Digestive System

Ascites

- Abnormal accumulation of fluid in the abdomen. - In certain diseases, the peritoneal cavity may become distended by the accumulation of several liters of fluid, a condition called ascites.

Accessory digestive organs

- Accessory digestive organs include the teeth, tongue, salivary glands, liver, gallbladder, and pancreas. - Teeth aid in the physical breakdown of food, and the tongue assists in chewing and swallowing. - The other accessory digestive organs never come into direct contact with food. They produce or store secretions that flow into the GI tract through ducts and aid in the chemical breakdown of food.

Villi

- Also present in the small intestine are villi, fingerlike projections of the mucosa that are 0.5-1 mm long. - Large number of villi vastly increases the surface area of the epithelium available for absorption and digestion and gives the intestinal mucosa a velvety appearance. - Each villus (singular form) is covered by epithelium and has a core of lamina propria; embedded in the connective tissue of the lamina propria are an arteriole, a venule, a blood capillary network, and a lacteal, which is a lymphatic capillary

Tongue

- An accessory digestive organ composed of skeletal muscle covered with mucous membrane. Together with its associated muscles, it forms the floor of the oral cavity. - The tongue is divided into symmetrical lateral halves by a median septum that extends its entire length, and it is attached to the hyoid bone, styloid process of the temporal bone, and mandible.

Mesentery

- Another fold of the peritoneum, called the mesentery, is fan‐shaped and binds the jejunum and ileum of the small intestine to the posterior abdominal wall. - This is the most massive peritoneal fold and is typically laden with fat, which contributed extensively to a large abdomen in obese individuals.

Identify the sections of the colon that occupy the retroperitoneal space?

- Ascending colon and descending colon

Microvilli

- Besides circular folds and villi, the small intestine also has microvilli, which are projections of the apical (free) membrane of the absorptive cells. - Each microvillus is a 1‐μm‐long projection of the cell membrane that contains a bundle of 20-30 actin filaments. - When viewed through a light microscope, the microvilli are too small to be seen individually; instead they form a fuzzy line, called the brush border, extending into the lumen of the small intestine

Liver and gallbladder (functions)

- Bile salts, which are sodium salts and potassium salts of bile acids (mostly cholic acid and chenodeoxycholic acid), play roles in (1) emulsification, the breakdown of large lipid globules into a suspension of droplets about 1 μm in diameter, and (2) the absorption of digested lipids. - Between meals, bile flows into the gallbladder for storage because the sphincter of the hepatopancreatic ampulla or sphincter of Oddi.

Feces

- By the time chyme has remained in the large intestine 3-10 hours, it has become solid or semisolid as a result of water absorption and is now called feces. - Chemically, feces consist of water, inorganic salts, sloughed‐off epithelial cells from the mucosa of the gastrointestinal tract, bacteria, products of bacterial decomposition, unabsorbed digested materials, and indigestible parts of food.

Which of the following types of teeth are adapted for tearing and shredding?

- Canines

Other functions of the liver

- Carbohydrate metabolism. The liver is especially important in maintaining a normal blood glucose level. When blood glucose is low, the liver can break down glycogen to glucose and release glucose into the bloodstream. The liver can also convert certain amino acids and lactic acid to glucose, and it can convert other sugars, such as fructose and galactose, into glucose. When blood glucose is high, as occurs just after eating a meal, the liver converts glucose to glycogen and triglycerides for storage. - Lipid metabolism. Hepatocytes store some triglycerides; break down fatty acids to generate ATP; synthesize lipoproteins (HDLs, LDLs, VLDLs), which transport fatty acids, triglycerides, and cholesterol to and from body cells; synthesize cholesterol; and use cholesterol to make bile salts. - Protein metabolism. Hepatocytes deaminate [remove the amino group (2NH2) from] amino acids so that the amino acids can be used for ATP production or converted to carbohydrates or fats. The resulting toxic ammonia (NH3) is then converted into the much less toxic urea, which is excreted in urine. Hepatocytes also synthesize most plasma proteins, such as alpha and beta globulins, albumin, prothrombin, and fibrinogen. - Processing of drugs and hormones. The liver can detoxify substances such as alcohol or secrete drugs such as penicillin, erythromycin, and sulfonamides into bile. It can also inactivate hormones such as thyroid hormones, estrogens, and aldosterone. - Excretion of bilirubin. Bilirubin, derived from the heme of aged red blood cells, is absorbed by the liver from the blood and secreted into bile. Most of the bilirubin in bile is metabolized in the small intestine by bacteria and eliminated in feces. - Synthesis of bile salts. Bile salts are used in the small intestine for the emulsification and absorption of lipids, cholesterol, phospholipids, and lipoproteins. - Storage. In addition to glycogen, the liver is a prime storage site for certain vitamins (A, B12, D, E, and K) and minerals (iron and copper), which are released from the liver when needed elsewhere in the body. - Phagocytosis. The stellate reticuloendothelial (Kupffer) cells of the liver phagocytize aged red blood cells and white blood cells and some bacteria. - Activation of vitamin D. The skin, liver, and kidneys participate in synthesizing the active form of vitamin D

Which of the following is a component of the gastrointestinal (GI) tract?

- Cecum

Chief (zymogenic) cells

- Chief (zymogenic) cells secrete pepsinogen and gastric lipase. The secretions of the mucous, parietal, and chief cells form gastric juice, about 2000-3000 mL (roughly 2-3 qt) per day. In addition, gastric glands include a type of enteroendocrine cell, the G cell, which is located mainly in the pyloric antrum and secretes the hormone gastrin into the bloodstream.

In the figure shown, what is the function of the indicated modification of the muscularis layer of the stomach?

- Churning and mixing

Small intestine (function)

- Chyme entering the small intestine contains partially digested carbohydrates, proteins, and lipids (mostly triglycerides). - The completion of the digestion of carbohydrates, proteins, and lipids is the result of the collective action of pancreatic juice, bile, and intestinal juice in the small intestine.

As a result of the again process, a 73-year-old male may be more susceptible to miss the early warning signs of which of the following diseases that affects the large intestine?

- Colon cancer

Digestive System

- Consists of a group of organs that break down the food we eat into smaller molecules that can be used by body cells. - Composed of two groups of organs: the gastrointestinal (GI) tract and the accessory digestive organs. - Gastrointestinal (GI) tract, or alimentary canal (alimentary=nourishment), is a continuous tube that extends from the mouth to the anus through the thoracic and abdominopelvic cavities. --> Organs of the gastrointestinal tract include the mouth, pharynx, esophagus, stomach, small intestine, and large intestine.

Which of the following ligaments suspends the liver from the diaphragm?

- Coronary ligament

Which is NOT a lobe of the liver?

- Coronary lobe

Bile enters the duodenum from the gall bladder through the

- Cystic duct, common bile duct, hepatopancreatic ampulla

What is another name for swallowing?

- Deglutition

Dentin

- Dense tissue forming the bulk of a tooth. - Consists of a calcified connective tissue that gives the tooth its basic shape and rigidity. It is harder than bone because of its higher content of hydroxyapatite (70 percent of dry weight). - It also differs from bone in that it lacks blood vessels, gets deposited incrementally (in successive waves a little at a time), and does not remodel. - Dentin contains dentinal tubules, parallel microscopic tubules radiating through the dentin from the pulp cavity.

Enamel

- Dentin of the crown is covered by enamel, which consists primarily of calcium phosphate and calcium carbonate. - Enamel is also harder than bone because of its even higher content of calcium salts (about 95 percent of dry weight). - Enamel is the hardest substance in the body. It is thickest over the cusps and tapers to a thin edge at the neck of the tooth, where it terminates. - Enamel arises as a cellular secretion during development. - The dentin of the root is covered by cementum, another bonelike substance, which attaches the root to the periodontal ligament.

Small intestine

- Digestive organ where most chemical digestion and absorption of food takes place - Most digestion and absorption of nutrients occur in a long tube called the small intestine. - Length alone provides a large surface area for digestion and absorption, and that area is further increased by circular folds, villi, and microvilli. - The small intestine begins at the pyloric sphincter of the stomach, coils through the central and inferior part of the abdominal cavity, and eventually opens into the large intestine.

What is the name of the structure labeled with the arrow? (intestines)

- Duodenum

Identify the correct order through which chyme moves as it passes through the small intestine.

- Duodenum, jejunum, ileum

Development of the digestive system

- During the fourth week of development, the cells of the endoderm form a cavity called the primitive gut, the forerunner of the gastrointestinal tract. Soon afterward the mesoderm forms and splits into two layers (somatic and splanchnic). The splanchnic mesoderm associates with the endoderm of the primitive gut; as a result, the primitive gut has a double‐layered wall. The endodermal layer gives rise to the epithelial lining and glands of most of the gastrointestinal tract; the mesodermal layer produces the smooth muscle, blood vessels, and connective tissue of the tract. - Primitive gut elongates and differentiates into an anterior foregut, an intermediate midgut, and a posterior hindgut. - Until the fifth week of development, the midgut opens into the yolk sac; after that time, the yolk sac constricts and detaches from the midgut, and the midgut seals. - In the region of the foregut, a depression consisting of ectoderm, the stomodeum. This develops into the oral cavity. The oropharyngeal membrane is a depression of fused ectoderm and endoderm on the surface of the embryo that separates the foregut from the stomodeum. - Another depression consisting of ectoderm, the proctodeum, forms in the hindgut and goes on to develop into the anus. The cloacal membrane is a fused membrane of ectoderm and endoderm that separates the hindgut from the proctodeum.

Pancreas (functions)

- Each day the pancreas produces 1200-1500 mL of pancreatic juice, a clear, colorless liquid consisting mostly of water, some salts, sodium bicarbonate, and several enzymes. - The sodium bicarbonate gives pancreatic juice a slightly alkaline pH (7.1-8.2) that buffers acidic gastric juice in chyme, stops the action of pepsin from the stomach, and creates the proper pH for the action of digestive enzymes in the small intestine. - The enzymes in pancreatic juice include a starch‐digesting enzyme called pancreatic amylase; several enzymes that digest proteins into peptides called trypsin, chymotrypsin, carboxypeptidase, and elastase; the principal triglyceride (fat and oil)‐digesting enzyme in adults, called pancreatic lipase; and enzymes called ribonuclease and deoxyribonuclease that digest ribonucleic acid (RNA) and deoxyribonucleic acid (DNA) into nucleotides.

Stomach (functions)

- Each peristaltic wave moves gastric contents from the body of the stomach down into the antrum, a process known as propulsion. - The pyloric sphincter normally remains almost, but not completely, closed. - Because most food particles in the stomach initially are too large to fit through the narrow pyloric sphincter, they are forced back into the body of the stomach, a process referred to as retropulsion. - The net result of these movements is that gastric contents are mixed with gastric juice, eventually becoming reduced to a soupy liquid called chyme. Once the food particles in chyme are small enough, they can pass through the pyloric sphincter, a phenomenon known as gastric emptying. Gastric empyting is a slow process: only about 3 mL of chyme move through the pyloric sphincter at this time. - Enzymatic digestion of proteins begins in the stomach. In the adult, this is achieved mainly through the enzyme pepsin, secreted by chief cells in an inactive form called pepsinogen. Pepsin breaks certain peptide bonds between the amino acids making up proteins. Thus, a protein chain of many amino acids is broken down into smaller fragments called peptides. Pepsin also brings about the clumping and digestion of milk proteins. Another enzyme of the stomach is gastric lipase. Gastric lipase splits triglycerides (fats and oils) in fat molecules (such as those found in milk) into fatty acids and monoglycerides (a glyceride molecule attached to one fatty acid molecule). - Enzyme has a limited role in the adult stomach. To digest fats and oils, adults rely almost exclusively on the lingual lipase secreted by lingual glands in the tongue, in the acid environment of the stomach, and pancreatic lipase, an enzyme secreted by the pancreas into the small intestine.

The primitive gut forms from this embryonic germ layer.

- Endoderm

What is the name of the structure labeled with the arrow? (throat)

- Esophagus

The adventitia layer of the GI tract is associated with the

- Esophagus and rectum

Which of the following attaches the liver to the anterior abdominal wall and diaphragm?

- Falciform ligament

Falciform ligament

- Falciform ligament attaches the liver to the anterior abdominal wall and diaphragm. - This remnant of the ventral mesentery of the embryo was the path of the umbilical vein from the umbilical cord to the inferior vena cava in the fetus.

An important function of the esophagus is to secrete digestive enzymes that are carried with the food to the stomach for digestion.

- False

Pancreatic acini are clusters of exocrine cells that produce the hormones glucagon, insulin, and somatostatin.

- False

Saliva

- Fluids secreted by the buccal glands, minor salivary glands, and the three pairs of major salivary glands constitute saliva. - Saliva is 99.5 percent water and 0.5 percent solutes and has a slightly acidic pH. - The solute portion includes mucus, an enzyme that destroys bacteria (lysozyme), the digestive enzymes salivary amylase and lingual lipase, and traces of salts, proteins, and other organic compounds. --> Salivary amylase plays a minor role in the breakdown of starch in the mouth into maltose, maltotriose, and α1‐dextrins.

Bile is stored in the ______________.

- Gallbladder

Gallbladder

- Gallbladder is a pear‐shaped sac that is located on the inferior surface of the liver. It is 7-10 cm (3-4 in.) long and part of it typically hangs below the anterior inferior margin of the liver. - Stores bile. - Parts of the gallbladder are the broad fundus, which projects downward beyond the inferior border of the liver; the central portion, called the body; and a tapered portion called the neck. The body and neck project superiorly.

Gastric glands

- Gastric glands contain three types of exocrine gland cells that secrete their products into the stomach lumen: mucous neck cells, chief cells, and parietal cells. Both mucous surface cells and mucous neck cells secrete mucus. Parietal cells produce intrinsic factor and hydrochloric acid.

The medical specialty that deals with the structure, function and diseases of the stomach and intestines is called _______________.

- Gastroenterology

Greater omentum

- Greater omentum, the longest peritoneal fold, drapes over the transverse colon and coils of the small intestine like a "fatty apron". - The greater omentum is a double sheet that folds back upon itself, giving it a total of four layers. - Normally contains a considerable amount of adipose tissue. Its adipose tissue content can greatly expand with weight gain, contributing to the characteristic "beer belly" seen in some overweight individuals.

Uvula

- Hanging from the free border of the soft palate is a finger‐like muscular structure called the uvula. - During swallowing, the soft palate and uvula are drawn superiorly, closing off the nasopharynx and preventing swallowed foods and liquids from entering the nasal cavity. - Lateral to the base of the uvula are two muscular folds that run down the lateral sides of the soft palate: (1) anteriorly, the palatoglossal arch extends to the side of the base of the tongue; (2) posteriorly, the palatopharyngeal arch extends to the side of the pharynx.

In the figure shown, what structures are indicated?

- Haustra

A hallmark feature of mechanical digestion in the large intestine is_____.

- Haustral churning

Dentitions

- Humans have two sets of teeth, or dentitions: deciduous and permanent. - The first set is the deciduous teeth (decidu‐=falling out), also called primary teeth, milk teeth, or baby teeth. - They begin to erupt (emerge) at about 6 months of age, and one pair of teeth appears at about each month thereafter, until all 20 are present. - The incisors, which are closest to the midline, are chisel‐shaped and adapted for cutting into food. They are referred to as either central incisors or lateral incisors on the basis of their position. - Next to the incisors, moving posteriorly, are the canines, which have a pointed surface called a cusp. Canines are used to tear and shred food. - Incisors and canines have only one root. Posterior to them are the first and second deciduous molars, which have four cusps.

Mucosa

- Inner lining of the GI tract, is a mucous membrane. It is composed of: (1) A layer of epithelium in direct contact with the contents of the GI tract. (2) Areolar connective tissue. (3) A thin layer of smooth muscle (muscularis mucosae).

Insoluble/ soluble fiber

- Insoluble fiber, which does not dissolve in water, includes the woody or structural parts of plants such as the skins of fruits and vegetables and the bran coating around wheat and corn kernels. Insoluble fiber passes through the GI tract largely unchanged and speeds up the passage of material through the tract. - Soluble fiber dissolves in water and forms a gel, which slows the passage of material through the tract; it is found in abundance in beans, oats, barley, broccoli, prunes, apples, and citrus fruits.

Salivary glands

- Is a gland that releases a secretion called saliva into the oral cavity. - When food enters the mouth, however, secretion of saliva increases to lubricate, dissolve, and begin the chemical breakdown of the food.

Palate

- Is a wall or septum that separates the oral cavity from the nasal cavity, and forms the roof of the mouth. This important structure makes it possible to chew and breathe at the same time. - The hard palate—the anterior two‐thirds of the palate—is formed by the maxillae and palatine bones and is covered by a mucous membrane. - The soft palate, which forms the posterior portion of the roof of the mouth, is an arch‐shaped muscular partition between the oropharynx and nasopharynx that is lined with mucous membrane.

Lamina propria

- Is an areolar connective tissue layer containing many blood and lymphatic vessels that carry the nutrients absorbed by the GI tract back to the heart. - The lamina propria also contains most of the cells of the mucosa‐associated lymphatic tissue (MALT). These prominent lymphatic nodules contain immune system cells that protect against disease. - MALT is present all along the GI tract, especially in the tonsils, small intestine, appendix, and large intestine, and it contains about as many immune cells as are present in all the rest of the body.

Salivation

- Is controlled by the nervous system. Normally, parasympathetic stimulation promotes continuous secretion of a moderate amount of saliva, which keeps the mucous membranes moist and lubricates the movements of the tongue and lips during speech. - The saliva is then swallowed and helps moisten the esophagus.

Mouth (oral or buccal cavity)

- Is formed by the cheeks, hard and soft palates, and tongue. The cheeks form the lateral walls of the oral cavity. - They are covered externally by skin and internally by a mucous membrane, which consists of nonkeratinized stratified squamous epithelium. - Buccinator muscles and connective tissue lie between the skin and mucous membranes of the cheeks. - The anterior portions of the cheeks end at the lips.

Epithelium in the mouth, pharynx, esophagus, and anal canal

- Is mainly nonkeratinized stratified squamous epithelium that serves a protective function. - Simple columnar epithelium, which functions in secretion and absorption, lines the stomach and intestines.

lLower esophageal sphincter

- Just superior to the level of the diaphragm, the esophagus narrows slightly. - This narrowing is a physiological sphincter in the inferior part of the esophagus composed of smooth muscle, known as the lower esophageal sphincter (LES) or gastroesophageal sphincter. - It is also called the cardiac sphincter because of its proximity to the heart.

MALT

- Lamina propria of the small intestinal mucosa contains areolar connective tissue and has an abundance of mucosa‐associated lymphoid tissue (MALT). - Solitary lymphatic nodules are most numerous in the distal part of the ileum. Groups of lymphatic nodules referred to as aggregated lymphatic follicles or - Peyer's patches are also present in the ileum. As it does throughout the digestive tract, the muscularis mucosae consists of smooth muscle. - The submucosa of the duodenum contains duodenal glands or Brunner's glands, which secrete an alkaline mucus that helps neutralize gastric acid in the chyme. - The muscularis of the small intestine consists of two layers of smooth muscle. - The outer, thinner layer contains longitudinal fibers; the inner, thicker layer contains circular fibers. Except for a major portion of the duodenum, which is retroperitoneal, the serosa completely surrounds the small intestine.

When an individual swallows a bolus of food, through which two regions of the pharynx will the bolus travel?

- Laryngopharynx and oropharynx

Lesser omentum

- Lesser omentum arises as an anterior fold of the serosa of the stomach and duodenum. - It connects the stomach and duodenum to the liver. - It is the pathway of blood vessels entering the liver and contains the hepatic portal vein, the common hepatic artery, and the common bile duct, along with some lymph nodes.

Ankyloglossia

- Lingual frenulum is abnormally short or rigid—a condition called ankyloglossia, the person is said to be "tongue‐tied" because of the resulting speech impairment. It can be corrected surgically.

Lingual lipase

- Lingual lipase and mucus are secreted by lingual glands on the dorsum (upper surface) of the tongue. - This enzyme, which is active in the stomach, can digest as much as 30 percent of dietary triglycerides (fats and oils) into simpler fatty acids and diglycerides.

Lips

- Lips or labia are fleshy folds surrounding the opening of the mouth. They contain the orbicularis oris muscle and are covered externally by skin and internally by a mucous membrane. - The inner surface of each lip is attached to its corresponding gum by a midline fold of mucous membrane called the labial frenulum

Which of the following organs deaminates amino acids for ATP production?

- Liver

Liver

- Liver is the largest internal organ and heaviest gland of the body, weighing about 1.4 kg (about 3 lb) in an average adult. - Of the organs of the body, it is second in size only to the skin. - The liver is inferior to the diaphragm and occupies most of the right hypochondriac and part of the epigastric regions of the abdominopelvic cavity - The liver is divided into two principal lobes—a large right lobe and a smaller left lobe—by the falciform ligament, a mesenteric fold from the parietal peritoneum of the diaphragm and anterior abdominal wall to the visceral peritoneum of the liver. -The right lobe is considered by many anatomists to include an inferior quadrate lobe and a posterior caudate lobe. - The free border of the falciform ligament is the ligamentum teres, a fibrous cord that is a remnant of the umbilical vein of the fetus; it extends from the liver to the umbilicus. - The right and left coronary ligaments are narrow extensions of the parietal peritoneum that suspend the liver from the diaphragm.

Enteroendocrine cells

- Located among the absorptive epithelial cells are exocrine cells that secrete mucus and fluid into the lumen of the tract, and several types of endocrine cells, collectively called enteroendocrine cells, which secrete hormones.

Esophagus

- Long collapsible muscular tube that lies posterior to the trachea. - It begins at the inferior end of the laryngopharynx, passes through the inferior aspect of the neck, enters the mediastinum and descends anterior to the vertebral column, pierces the diaphragm through an opening called the esophageal hiatus, and ends in the superior portion of the stomach.

Which is NOT a layer of the GI tract?

- Lumen

During which large intestine mechanical movement is the colonic contents driven into the rectum?

- Mass peristalsis

Defecation (reflex)

- Mass peristaltic movements push fecal material from the sigmoid colon into the rectum. - The resulting distension of the rectal wall stimulates stretch receptors, which initiates defecation, the elimination of feces from the rectum through the anus. - The defecation reflex occurs as follows: In response to distension of the rectal wall, the receptors send sensory nerve impulses to the sacral spinal cord.

What is the name of the structure labeled with the arrow? (woman torso)

- Mesentery

Major salivary glands

- Most saliva is secreted by the major salivary glands, which lie beyond the oral mucosa. Their secretions empty into ducts that lead to the oral cavity. - The parotid glands are located inferior and anterior to the ears, between the skin and the masseter muscle. - Each secretes saliva into the oral cavity via a parotid duct or Stensen's duct that pierces the buccinator muscle to open into the vestibule opposite the second maxillary (upper) molar tooth. - The submandibular glands, found in the floor of the oral cavity beneath the base of the tongue, are medial and partly inferior to the mandible. - Their ducts, the submandibular ducts (Wharton's ducts), run under the mucosa on either side of the midline of the floor of the mouth and enter the oral cavity proper lateral to the lingual frenulum. - The sublingual glands are superior to the submandibular glands. Their ducts, the lesser sublingual ducts (Rivinus' ducts), open into the floor of the mouth in the oral cavity proper.

The chemical digestion of starch begins in which region of the gastrointestinal (GI) tract?

- Mouth

Reflux of hydrochloric acid from the stomach may irritate which of the following layers of the esophagus?

- Mucosa

Muscularis

- Muscularis of the mouth, pharynx, and superior and middle parts of the esophagus contains skeletal muscle that produces voluntary swallowing. Skeletal muscle also forms the external anal sphincter, which permits voluntary control of defecation. - The muscularis also contains the second major plexus of the enteric nervous system—the myenteric plexus, or plexus of Auerbach, which contains enteric neurons, parasympathetic ganglia and postganglionic fibers, and sympathetic postganglionic fibers that are vasomotor to the blood vessels of this layer. This plexus mostly controls GI tract motility, in particular the frequency and strength of the contractions of the muscularis.

Muscularis cont.

- Of the superior third of the esophagus is skeletal muscle, the intermediate third is skeletal and smooth muscle, and the inferior third is smooth muscle.

Circular folds

- Or plicae circulares are folds of the mucosa and submucosa. - These permanent ridges, which are about 10 mm (0.4 in.) long, begin near the proximal portion of the duodenum and end at about the midportion of the ileum. - Some extend all the way around the circumference of the intestine; others extend only part of the way around. - Circular folds enhance absorption by increasing surface area and causing the chyme to spiral, rather than move in a straight line, as it passes through the small intestine.

Oral cavity (vestibule)

- Oral vestibule of the oral cavity is the space bounded externally by the cheeks and lips and internally by the gums and teeth. - The oral cavity proper is the space that extends from the gums and teeth to the fauces, the opening between the oral cavity and the oropharynx.

Intrinsic muscles of the tongue

- Originate in and insert into connective tissue within the tongue and alter the shape and size of the tongue for speech and swallowing. - The intrinsic muscles include the longitudinalis superior, longitudinalis inferior, transversus linguae, and verticalis linguae muscles.

This structure produces digestive juices, insulin, and glucagon, and empties them into the duodenum and blood stream.

- Pancreas

Which of the following organs does NOT belong to the alimentary canal?

- Pancreas

Pancreas (histology)

- Pancreas is made up of small clusters of glandular epithelial cells, about 99 percent of which are arranged in clusters called acini and constitute the exocrine portion of the organ. - The cells within acini secrete a mixture of fluid and digestive enzymes called pancreatic juice. The remaining 1 percent of the cells are organized into clusters called pancreatic islets, the endocrine portion of the pancreas. - These cells secrete the hormones glucagon, insulin, somatostatin, and pancreatic polypeptide.

Identify the salivary gland that lies inferior and anterior to the ears.

- Parotid

The structure indicated in the figure is which of the following salivary glands?

- Parotid

An infection in a tooth that has become so decayed that it is loose has likely effected the

- Periodontal ligament

Peristalsis

- Peristalsis occurs in other tubular structures, including other portions of the GI tract, the ureters, bile ducts, and uterine tubes; in the esophagus it is controlled by the medulla oblongata. The steps of peristalsis are as follows: 1.The circular muscle fibers in the section of the esophagus above the bolus contract, constricting the wall of the esophagus and squeezing the bolus downward. 2.Longitudinal muscle fibers around the bottom of the bolus contract, shortening the section below the bolus and pushing its walls outward. 3.After the bolus moves into the new section of the esophagus, the circular muscles above it contract, and the cycle repeats. The contractions move the bolus down the esophagus toward the stomach. As the bolus approaches the end of the esophagus, the lower esophageal sphincter relaxes and the bolus moves into the stomach.

Peritoneum

- Peritoneum is the largest serous membrane of the body; it consists of a layer of simple squamous epithelium (mesothelium) with an underlying supporting layer of connective tissue. - The peritoneum is divided into the parietal peritoneum, which lines the wall of the abdominal cavity, and the visceral peritoneum or serosa, which as you just learned covers some of the organs in the cavity.

Which of the following is FALSE regarding the pancreas?

- Produces pancreatic lipase which breaks down triglycerides (fats)

What is the name of the region of the stomach labeled with the arrow? (stomach)

- Pyloric canal

Which of the following is a function of the upper esophageal sphincter?

- Regulates movement of food from the pharynx into the esophagus

The salivary glands, liver, and pancreas facilitate which of the following digestive processes?

- Secretion

From superficial to deep, what is the correct order of layers of the gastrointestinal (GI) tract?

- Serosa, muscularis, submucosa, mucosa

Which region of the gastrointestinal (GI) tract is responsible for most digestion and absorption of nutrients?

- Small intestines

Retroperitoneal organs

- Some organs lie against the posterior abdominal wall and do not project into the peritoneum. These organs are called retroperitoneal organs. - Ascending and descending colon, duodenum, and pancreas, are covered by peritoneum only on their anterior surfaces. - Other retroperitoneal organs are separated from the peritoneum by fat and have no peritoneum on them at all, including the kidneys and adrenal glands.

Infants can sometimes have a condition called pyloric stenosis (narrowing). This condition makes it difficult for chyme to pass out of the _____ into the _____.

- Stomach, duodenum

The lesser omentum arises as an anterior fold in the serosa between which of the following two organs?

- Stomach, duodenum

The pancreas is located behind the_____ in the _____ space.

- Stomach, retroperitoneal

Which enteric system plexus innervates the mucosa and submucosa of the gastrointestinal tract?

- Submucosal

Adventitia

- Superficial layer of the esophagus is known as the adventitia. - Unlike the serosa of the stomach and intestines, the areolar connective tissue of this layer is not covered by mesothelium

Teeth

- Teeth, or dentes, are accessory digestive organs located in sockets of the alveolar processes of the mandible and maxillae. - The alveolar processes are covered by the gingivae., or gums, which extend slightly into each socket to form the gingival sulcus. - The sockets are lined by the periodontal ligament or membrane, which consists of dense fibrous connective tissue and is attached to the socket walls and outer covering (cementum) of the roots of the teeth. - Typical tooth consists of three principal regions: --> The crown is the visible portion above the level of the gums. --> One to three roots are embedded in each socket. --> The neck is the constricted junction of the crown and root near the gum line.

Which of the following sentences correctly describes the process of peristalsis in the esophagus?

- The circular muscle fibers above the bolus contract, thereby pushing the bolus downward.

Papillae

- The dorsum and lateral surfaces of the tongue are covered with papillae, projections of the lamina propria covered with stratified squamous epithelium. - Many papillae contain taste buds, the receptors for gustation. As their name implies, fungiform papillae are mushroomlike elevations distributed among the more numerous filiform papillae. - They are scattered over the dorsum of the tongue, but are concentrated mainly around the margins of the tongue. - Vallate papillae or circumvallate papillae are arranged in an inverted V‐shape on the posterior surface of the tongue; all of them contain taste buds. - Foliate papillae are located in small trenches on the lateral margins of the tongue, but most of their taste buds degenerate in early childhood. - Filiform papillae are pointed, threadlike projections distributed in parallel rows over the anterior two‐thirds of the tongue. Although filiform papillae lack taste buds, they contain receptors for touch and increase friction between the tongue and food, making it easier for the tongue to move food in the oral cavity.

Pulp (cavity)

- The enlarged part of the space, the pulp cavity, lies within the crown and is filled with pulp, a connective tissue containing blood vessels, nerves, and lymphatic vessels. - Narrow extensions of the pulp cavity, called root canals, run through the root of the tooth. - Each root canal has an opening at its base, the apical foramen, through which blood vessels, lymphatic vessels, and nerves enter a tooth

Small intestine (anatomy)

- The first part of the small intestine, the duodenum, is the shortest region, and is retroperitoneal. - The jejunum, the next portion, is about 1 m (3 ft) long, and extends to the ileum. --> Jejunum means "empty," which is how it is found at death. The jejunum is mostly in the left upper quadrant (LUQ). - The final and longest region of the small intestine, the ileum, measures about 2 m (6 ft) and joins the large intestine at a smooth muscle sphincter called the ileocecal sphincter. --> The ileum is mostly in the right lower quadrant (RLQ).

Proctology

- The medical specialty that deals with the diagnosis and treatment of disorders of the rectum and anus is called proctology.

Gastroenterology

- The medical specialty that deals with the structure, function, diagnosis, and treatment of diseases of the stomach and intestines is called gastroenterology.

Upper esophageal sphincter

- The passage of food from the laryngopharynx into the esophagus is regulated at the entrance to the esophagus by a sphincter (a circular band or ring of muscle that is normally contracted) called the upper esophageal sphincter (UES). - AKA pharyngoesophageal sphincter. It consists of skeletal muscle (cricopharyngeus muscle) attached to the cricoid cartilage

Rectum

- The rectum lies anterior to the sacrum and coccyx. The terminal of the large intestine is called the anal canal. - The mucous membrane of the anal canal is arranged in longitudinal folds called anal columns that contain a network of arteries and veins. The opening of the anal canal to the exterior, called the anus, is guarded by an internal anal sphincter of smooth muscle (involuntary) and an external anal sphincter of skeletal muscle (voluntary).

Hepatic acinus

- The smallest structural and functional unit of the liver. Its popularity and appeal are based on the fact that it provides a logical description and interpretation of (1) patterns of glycogen storage and release and (2) toxic effects, degeneration, and regeneration relative to the proximity of the acinar zones to branches of the portal triad

Stomach (Histology)

- The surface of the mucosa is a layer of nonciliated simple columnar epithelial cells called surface mucous cells. - The mucosa contains a lamina propria (areolar connective tissue) and a muscularis mucosae (smooth muscle). - Inward folds of epithelial cells extend down into the lamina propria, where they form columns of secretory cells called gastric glands. - Several gastric glands open into the bottom of narrow channels called gastric pits.

Large intestine (function)

- There are three types of movement characteristic of the large intestine: 1. In haustral churning, the haustra remain relaxed and distended while they fill up. When the distension reaches a certain point, the wall contracts and squeezes the contents into the next haustrum. 2. Peristalsis also occurs, although at a slower rate (3 to 12 contractions per minute) than in other portions of the GI tract. 3. In mass peristalsis, a strong peristaltic wave begins at about the middle of the transverse colon and quickly drives the colonic contents into the rectum. Mass peristalsis usually takes place three or four times a day, during or immediately after a meal.

Serosa

- Those portions of the GI tract that are suspended in the abdominal cavity have a superficial layer called the serosa. - As its name implies, the serosa is a serous membrane composed of areolar connective tissue and simple squamous epithelium (mesothelium). - The epithelial portion of the serosa is also called the visceral peritoneum because it forms the portion of the peritoneum that surrounds the organs suspended in the peritoneal cavity. - The esophagus and lower aspect of the rectum are the only organs of the GI tract that completely lack a serosa; instead, only a single layer of areolar connective tissue called the adventitia surrounds them.

Portal triad

- Together, a bile duct, branch of the hepatic artery, and branch of the hepatic portal vein are referred to as a portal triad.

The lamina propria of the small intestine contains a lymphatic capillary called a lacteal. Identify the digestive nutrient that is absorbed by the lacteal.

- Triglycerides

The anus has two sphincters.

- True

Mesocolon

- Two separate folds of peritoneum called the mesocolon bind the transverse colon (transverse mesocolon) and sigmoid colon (sigmoid mesocolon) of the large intestine to the posterior abdominal wall. --> These folds carry blood vessels (superior and inferior mesenteric vessels) and lymphatic vessels to the intestines.

Small intestine movements

- Two types of movements of the small intestine—segmentations and a type of peristalsis called migrating motility complexes—are governed mainly by the myenteric plexus of the enteric nervous system. - Segmentations are localized, mixing contractions that occur in portions of the intestine distended by a large volume of chyme. Segmentations mix chyme with the digestive juices and bring the particles of food into contact with the mucosa for absorption; they do not push the intestinal contents along the tract. A segmentation starts with the contractions of circular muscle fibers in a portion of the small intestine, an action that constricts the intestine into segments. - The type of peristalsis that occurs in the small intestine, termed a migrating motility complex (MMC), begins in the lower portion of the stomach and pushes chyme forward along a short stretch of small intestine before dying out. --> These forms are monosaccharides from carbohydrates; single amino acids, dipeptides, and tripeptides from proteins; fatty acids, glycerol, and monoglycerides from lipids; and pentoses and nitrogenous bases from nucleic acids. Passage of these digested nutrients from the gastrointestinal tract into the blood or lymph is called absorption. - Absorption occurs by diffusion, facilitated diffusion, osmosis, and active transport.

Stomach (Anatomy)

- Typically a J‐shaped enlargement of the GI tract directly inferior to the diaphragm in the epigastric, umbilical, and left hypochondriac regions of the abdomen. - Connects the esophagus to the duodenum, the first part of the small intestine. - The rounded portion superior and to the left of the cardia is the fundus. - Inferior to the fundus is the large central portion of the stomach, called the body. The pyloric part is divisible into three regions. - First region, the pyloric antrum, connects to the body of the stomach. - The next region, the pyloric canal, leads to the third region, the pylorus, which in turn connects to the duodenum. - When the stomach is empty, the mucosa lies in large folds, called rugae, which can be seen with the unaided eye. - The pylorus communicates with the duodenum of the small intestine via a smooth muscle sphincter called the pyloric sphincter (valve). - The concave medial border of the stomach is called the lesser curvature, and the convex lateral border is called the greater curvature.

Large intestine (histology)

- Wall of the large intestine contains the typical four layers found in the rest of the GI tract: mucosa, submucosa, muscularis, and serosa. - The mucosa consists of simple columnar epithelium, lamina propria, and muscularis mucosae (smooth muscle). The epithelium contains mostly absorptive and goblet cells. - The absorptive cells function primarily in water absorption; the goblet cells secrete mucus that lubricates the passage of the colonic contents. - Both absorptive and goblet cells are located in long, straight, tubular intestinal glands or crypts of Lieberkühn that extend the full thickness of the mucosa. - The submucosa of the large intestine consists of areolar connective tissue. - The muscularis consists of an external layer of longitudinal smooth muscle and an internal layer of circular smooth muscle. - Unlike other parts of the GI tract, portions of the longitudinal muscles are condensed and thickened, forming three conspicuous bands called the teniae coli that run most of the length of the large intestine. - Tonic contractions of the bands gather the colon into a series of pouches called haustra, which give the colon a puckered appearance. - A single layer of circular smooth muscle lies deep to the teniae coli. - The serosa of the large intestine is part of the visceral peritoneum. Small pouches of visceral peritoneum filled with fat are attached to teniae coli and are called omental (fatty) appendices or epiploic appendices

Small intestine (histology)

- Wall of the small intestine is composed of the same four layers that make up most of the GI tract: mucosa, submucosa, muscularis, and serosa - Absorptive cells of the epithelium release enzymes that digest food and contain microvilli that absorb nutrients in the small intestine. - Goblet cells secrete mucus. The small intestinal mucosa contains many deep crevices lined with glandular epithelium. - Cells lining the crevices form the intestinal glands or crypts of Lieberkühn and secrete intestinal juice. - Three types of enteroendocrine cells (cells that secrete hormones) are found in the intestinal glands of the small intestine: - S cells, CCK cells, and K cells, which secrete the hormones secretin, cholecystokinin, and glucose‐dependent insulinotropic peptide, respectively. - Paneth cells secrete lysozyme, a bactericidal enzyme, and are capable of phagocytosis. Paneth cells may have a role in regulating the microbial population in the small intestine.

Large intestine (anatomy)

- Which is about 1.5 m long and 6.5 cm in diameter in living humans and cadavers, extends from the ileum to the anus. - The ascending colon and descending colon are retroperitoneal, while the remaining parts of the colon and cecum are attached to the posterior abdominal wall by their mesocolon, a double layer of peritoneum connecting the parietal peritoneum to the visceral peritoneum that contains the vascular and nervous supply to the organs. - Structurally, the four principal regions of the large intestine are the cecum, colon, rectum, and anal canal. - Opening from the ileum into the large intestine is guarded by a fold of mucous membrane called the ileocecal sphincter or valve, which allows materials from the small intestine to pass into the large intestine. - Hanging inferior to the ileocecal valve is the cecum, a small pouch about 6 cm (2.4 in.) long. - Attached to the cecum is a twisted, coiled tube, measuring about 8 cm (3 in.) in length, called the appendix or vermiform appendix. - The mesentery of the appendix, called the mesoappendix, attaches the appendix to the inferior part of the mesentery of the ileum. - Open end of the cecum merges with a long tube called the colon, which is divided into ascending, transverse, descending, and sigmoid portions. - Both the ascending and descending colon are retroperitoneal; the transverse and sigmoid colon are not. - The ascending colon ascends on the right side of the abdomen, reaches the inferior surface of the liver, and turns abruptly to the left to form the right colic flexure. - The colon continues across the abdomen to the left side as the transverse colon. It curves beneath the inferior end of the spleen on the left side as the left colic (splenic) flexure and passes inferiorly to the level of the left iliac crest as the descending colon. - The sigmoid colon begins near the left iliac crest, projects medially to the midline, and terminates as the rectum at about the level of the third sacral vertebra.

Extrinsic muscles of the tongue

- Which originate outside the tongue and insert into connective tissues in the tongue, include the hyoglossus, genioglossus, and styloglossus muscles. - Move the tongue from side to side and in and out to maneuver food for chewing, shape the food into a rounded mass, and force the food to the back of the mouth for swallowing.

The effects of aging on the digestive system include all BUT the following:

- increased peristalsis

What overall changes in the digestive system appear with age?

-Decreased secretory mechanisms -Decreased motility of the digestive organs -Diminished response to pain and internal sensations

An exocrine secretion of the organ at B: _______________

-Is stored and concentrated in the gall bladder -Is enters the lumen of the duodenum at the -Duodenal papillae -Acts to emulsify fatty substances

Which part(s) of the pharynx does food normally pass through? Select all that apply.

-Laryngopharynx -Oropharynx

Which of the following structural features of the small intestine are specially adapted for the functions of digestion and absorption?

-long length -circular folds -villi -microvilli

Hepatocytes, bile duct system, and hepatic sinusoids can be organized into anatomical and functional units in three different ways:

1. Hepatic lobule. For years, anatomists described the hepatic lobule as the functional unit of the liver. According to this model, each hepatic lobule is shaped like a hexagon. At its center is the central vein and radiating out from it are rows of hepatocytes and hepatic sinusoids. Located at three corners of the hexagon is a portal triad. This model is based on a description of the liver of adult pigs. In the human liver it is difficult to find such well‐defined hepatic lobules surrounded by thick layers of connective tissue. 2. Portal lobule. This model emphasizes the exocrine function of the liver, that is, bile secretion. Accordingly, the bile duct of a portal triad is taken as the center of the portal lobule. The triangular shape of the portal lobule is defined by three imaginary straight lines that connect three central veins closest to the portal triad. This model has not gained widespread acceptance. 3. Hepatic acinus. In recent years, the preferred structural and functional unit of the liver has become the hepatic acinus. Each hepatic acinus is an approximately oval mass that includes portions of two neighboring hepatic lobules.

Liver and gallbladder (histology)

1. Hepatocytes. Hepatocytes are the major functional cells of the liver and perform a wide array of metabolic, secretory, and endocrine functions. These are specialized epithelial cells with 5 to 12 sides that make up about 80 percent of the volume of the liver. Hepatocytes are arranged in rows called hepatic laminae. The hepatic laminae are plates of hepatocytes one cell thick bordered on either side by endothelial‐lined vascular spaces called hepatic sinusoids. The hepatic laminae are highly branched, irregular structures. Grooves in the cell membranes between neighboring hepatocytes provide spaces for canaliculi (described next), into which the hepatocytes secrete bile. Bile, a yellow, brownish, or olive‐green liquid secreted by hepatocytes, serves as both an excretory product and a digestive secretion. 2. Bile canaliculi. These are small ducts between hepatocytes that collect bile produced by the hepatocytes. From bile canaliculi, bile passes into bile ductules and then bile ducts. The bile ducts merge and eventually form the larger right and left hepatic ducts, which unite and exit the liver as the common hepatic duct. The common hepatic duct joins the cystic duct from the gallbladder to form the common bile duct. From here, bile enters the duodenum of the small intestine to participate in digestion. When the small intestine is empty, the sphincter around the common bile duct at the entrance to the duodenum closes, and bile backs up into the cystic duct to the gallbladder for storage. 3. Hepatic sinusoids. These highly permeable blood capillaries between hepatic laminae receive oxygenated blood from branches of the hepatic artery and nutrient‐rich deoxygenated blood from branches of the hepatic portal vein. Recall that the hepatic portal vein brings venous blood from the gastrointestinal organs and spleen into the liver. Hepatic sinusoids converge and deliver blood into a central vein. From central veins the blood flows into the hepatic veins, which drain into the inferior vena cava. Whereas blood flows toward a central vein, bile flows in the opposite direction. Also present in the hepatic sinusoids are a modified macrophage, fixed phagocytes called stellate reticuloendothelial cells, Kupffer cells, or hepatic macrophages, which destroy worn‐out white and red blood cells, bacteria, and other foreign matter in the venous blood draining from the gastrointestinal tract.

Digestive system performs six basic functions:

1.Ingestion. Ingestion involves taking foods and liquids into the mouth (eating). 2.Secretion. Each day, cells within the walls of the GI tract and accessory digestive organs secrete a total of about 7 liters of water, acid, buffers, and enzymes into the lumen (interior space) of the tract; this process is called secretion. 3.Mixing and propulsion. Alternating contraction and relaxation of smooth muscle in the walls of the GI tract mix food and secretions and move them toward the anus. This capability of the GI tract to mix and move material along its length is termed motility.. 4.Digestion. Digestion is the breakdown of ingested food into small molecules for use by body cells. In mechanical digestion the teeth cut and grind food before it is swallowed, and then smooth muscles of the stomach and small intestine churn the food to further assist the process. As a result, food molecules become dissolved and thoroughly mixed with digestive enzymes. Chemical digestion is the breakdown of the large carbohydrate, lipid, protein, and nucleic acid molecules present in food into smaller molecules that can be absorbed. Digestive enzymes produced by the salivary glands, tongue, stomach, pancreas, and small intestine speed up these breakdown reactions. A few substances in food can be absorbed without chemical digestion, including amino acids, cholesterol, glucose, vitamins, minerals, and water. 5.Absorption. The entrance of ingested and secreted fluids, ions, and the products of digestion into the epithelial cells lining the lumen of the GI tract is called absorption. The absorbed substances pass into the blood or lymph and circulate to cells throughout the body. 6.Defecation. Wastes, indigestible substances, bacteria, cells sloughed from the lining of the GI tract, and digested materials that were not absorbed leave the body through the anus in a process called defecation. The eliminated material is called feces or stool.

Which of the structures listed below develop(s) from the midgut? 1. ascending colon2 . cecum 3. appendix 4. ileum 5. jejunum 6. stomach

- 1,2,3,4,5 only

How many layers of smooth muscle does the stomach contain?

- 3

After which of the following weeks of embryonic development does the cloacal membrane rupture to form a continuous tube from mouth to anus?

- 7th week

Intestinal juice

- A clear yellow fluid secreted in amounts of 1 to 2 liters each day. - It has a pH of 7.6, which is slightly alkaline (due to its high concentration of bicarbonate ions), and contains water and mucus. - Together, pancreatic juice and intestinal juice provide a vehicle for the absorption of substances from chyme as they come in contact with the villi. - Absorptive epithelial cells synthesize several digestive enzymes, called brush‐border enzymes, and insert them in the plasma membrane of the microvilli. - Among the brush‐border enzymes are four carbohydrate‐digesting enzymes called α‐dextrinase, maltase, sucrase, and lactase; protein‐digesting enzymes called peptidases; and two types of nucleotide‐digesting enzymes, nucleosidases and phosphatases. - Also, as cells slough off into the lumen of the small intestine, they break apart and release enzymes that help digest nutrients in the chyme.

Lingual frenulum

- A fold of mucous membrane in the midline of the undersurface of the tongue, is attached to the floor of the mouth and aids in limiting the movement of the tongue posteriorly.

Submucosa

- A layer of the human digestive system that contains nerves, blood vessels, and lymph nodes. - Contains areolar connective tissue with blood vessels and mucous glands and numerous elastic fibers that assist in closing the distended tube.

Submucosa

- A layer of the human digestive system that contains nerves, blood vessels, and lymph nodes. - Thin meshwork that contains collagen fibers, nerves, and blood vessels. It consists of areolar connective tissue that binds the mucosa to the middle layer, the muscularis. - The submucosa is highly vascular and contains the submucosal plexus, or plexus of Meissner, a subdivision of the autonomic nervous system called the enteric nervous system

Pancreas (anatomy)

- A retroperitoneal gland that is about 12-15 cm (5-6 in.) long and 2.5 cm (1 in.) thick, lies posterior to the greater curvature of the stomach. - The head is the expanded portion of the organ near the curve of the duodenum. - Projecting from the lower portion of the head is the hooklike uncinate process that arches behind the superior mesenteric artery and vein, encircling them with pancreatic tissue. Superior to and to the left of the head are the central body and the tapering tail. - The larger of the two ducts is called the pancreatic duct. - In most people, the pancreatic duct joins the common bile duct from the liver and gallbladder and enters the duodenum as a dilated common duct called the hepatopancreatic ampulla. - The ampulla opens onto an elevation of the duodenal mucosa, the major duodenal papilla, that lies about 10 cm (4 in.) inferior to the pyloric sphincter of the stomach. - The smaller of the two ducts, the accessory duct (duct of Santorini), leads from the pancreas and empties into the duodenum about 2.5 cm (1 in.) superior to the hepatopancreatic ampulla.

Muscularis mucosae

- A thin layer of smooth muscle fibers called the muscularis mucosae (mū‐KŌ‐sē) causes the mucous membrane of the stomach and small intestine to form many small folds, increasing the surface area for digestion and absorption. - Movements of the muscularis mucosae ensure that all absorptive cells are fully exposed to the contents of the GI tract.