My Digestive System 26

Name the 4 regions of the stomach

-Cardia -Fundus -Body -Pylorus

Describe the functions of each segment of the small intestine

-Duodenum: receives accessory organ secretions from the liver, gallbladder, and pancreas, as well as chyme from the stomach. -Jejunum: the primary region within the small intestine for chemical digestion and nutrient absorption. -Ileum: absorption of digested materials

Name the two serous membranes are associated with the abdominal cavity

-Parietal peritoneum lines the inner surface of the abdominal wall -visceral peritoneum covers the surface of the internal organs -between these layers is the peritoneal cavity.

Name the three pairs of salivary glands located external to the oral cavity

-Parotid -Submandibular -Sublingual

List the accessory organs and structures involved in the digestive process.

Accessory digestive glands produce secretions that empty into the GI tract and include the salivary glands, liver, and pancreas. Other accessory digestive organs are not glands. They include the teeth and tongue, which participate in the chewing and swallowing of food, and the gallbladder, which concentrates and stores bile.

Gallbladder

Attached to the inferior surface of the liver, the gallbladder is a organ that stores, concentrates, and releases bile that the liver produces. The gallbladder has three tunics: an inner mucosa, a middle muscularis, and an external serosa. The mucosa is thrown into folds that permit distension of the wall as the gallbladder fills with bile. Earlier we learned that the cystic duct connects the gallbladder to the common bile duct. At the neck of the gallbladder, a sphincter valve controls the flow of bile into and out of the gallbladder. Bile enters the gallbladder when the hepatopancreatic sphincter associated with the hepatopancreatic ampulla is closed. Concentrated bile is transported from the gallbladder through the cystic duct and then the common bile duct through the hepatopancreatic ampulla into the duodenum.

what forms the primary mass of a tooth

Dentin

Parotid Salivary Glands

Each parotid gland is located anterior and inferior to the ear. The parotid salivary glands produce about 25-30% of the saliva, which is transported through the parotid duct to the oral cavity. Only serous secretion

The digestive system includes the organs that

ingest the food, mix and move the ingested materials, add secretions to facilitate digestion of these materials into smaller usable components, absorb the necessary nutrients into the blood or lymph, and expel the waste products from the body.

porta hepatis

is the site at which blood and lymph vessels, bile ducts, and nerves extend from the liver.

name the three classes of carbohydrates

monosaccharides disaccharides polysaccharides

The esophagus has what type of epithelium

nonkeratinized stratified squamous to protect its lining from abrasion

voluntary phase

occurs after ingestion. It is controlled by the cerebral cortex. Ingested materials and saliva mix in the oral cavity. Chewing forms a bolus

gastroileal reflex

the ileum contracts, ileocecal sphincter relaxes, and the cecum (the first part of the large intestine) relaxes. Thus, contents within the GI tract are moved from the ileum through the open ileocecal sphincter into the cecum. Then, the ileocecal sphincter contracts to prevent backflow from the cecum into the ileum.

smooth muscle activity in the small intestine wall has three primary functions:

(1) mixing chyme with accessory gland secretions, (2) moving the chyme continually against new areas of the brush border, and (3) propelling the contents through the small intestine toward the large intestine.

chemical digestion of carbohydrates consists of

(1) the breakdown of starch into individual glucose molecules, and (2) the breakdown of disaccharides into the individual monosaccharides that compose them.

Small intestine secretions

*Between the intestinal villi are invaginations of the mucosa called inestinal glands, these mucosal cells secrete intestiestinal juice -Goblet cells produce mucin that when hydrated form mucus -Unicellular gland cells synthesize enteropeptidase -enteroendocrine cells release hormones such as CCK and secretin. Another type of gland housed within the submucosal layer and found only in the proximal duodenum is called a submucosal or duodenal gland. This gland produces a viscous, alkaline mucus secretion that protects the duodenum from the acidic chyme.

Describe the small intestine

*divided into 3 regions: duodenum, jejunum, ileum *receives chyme from stomach that is then mixed with accessory organ secretions. *Most chemical digestion and absorption occurs within the small intestine.

Name and describe the 5 mesenteries of the abdominopelvic cavity

-Greater omentum extends inferiorly from the stomach and covers most of the abdominal organs. It often accumulates large amounts of adipose connective tissue, and serves to both insulate the abdominal organs and as a storage for excess fat. -Lesser omentum connects the superomedial surface of the stomach (lesser curvature) and the proximal end of the duodenum to the liver. -Falciform ligament is a flat, thin, crescent-shaped peritoneal fold that attaches the liver to the internal surface of the anterior abdominal wall. -Mesentery proper is a fan-shaped fold of peritoneum that suspends most of the small intestine (the jejunum and the ileum) from the internal surface of the posterior abdominal wall. -Mesocolon is a fold of the peritoneum that attaches parts of the large intestine to the posterior abdominal wall. The mesocolon has several distinct sections, each named for the portion of the colon it suspends.

Other components are added by cells of the salivary glands, including salivary amylase, mucin, and lysozyme. These components permit saliva to participate in various functions:

-Moistens ingested food as it is formed into a bolus -Initiates the chemical breakdown -Acts as a watery medium into which food molecules are dissolved so taste receptors may be stimulated -Cleanses the oral cavity structures -Helps inhibit bacterial growth in the oral cavity

List the 4 tunics that compose the GI Tract from the esophagus through the large intestine

-Mucosa -Submucosa -Muscularis -Adventitia

name and describe the types of movement in the large intestine

-Peristalsis: rhythmic contractions that propel material through tubes in the GI - Haustral churning: occurs after a relaxed haustrum fills with digested or fecal material until its distension stimulates reflex contractions in the muscularis. These contractions increase churning and move the material to more distal haustra. -Mass movements: are powerful, peristaltic-like contractions involving the teniae coli, which propel fecal material toward the rectum. -Gastrocolic reflex: is initiated by stomach distension to cause a mass movement -The defecation reflex: the elimination of feces from the GI tract by the process of defecation

Five types of secretory cells of the gastric epithelium are integral contributors to the process of digestion. Four of these cell types produce the gastric juice associated with the stomach. The fifth type of cell secretes a hormone into the blood. Name these cells

-Surface mucous cells: -Mucous neck cells: -Parietal Cells: are responsible for the additional 2 substances into the lumen of the stomach *Intrinsic factor: absorption of vitamin B12 in ileum for normal erythrocyte production *Hydrochloric acid: responsible for the low pH in the stomach. -Chief cells: -G-Cells: secrete gastrin hormone into the blood to stimulate stomach motility and secretions.

Explain the processing in the oral cavity that initiates carbohydrate digestion

1. Digestion of starch begins in the oral cavity. It is catalyzed by salivary amylase, pancreatic amylase. 2. The completion of starch breakdown is accomplished by brush border enzymes embedded within the epithelial lining of the small intestine. These enzymes include dextrinase and glucoamylase, which break the bonds between glucose subunits of oligosaccharides, and maltase that breaks the bond between the two glucose molecules that compose maltose.

describe the accessory organs of the

Accessory organ secretions include bile and pancreatic juice. Bile is produced by the liver and then stored, concentrated, and released by the gallbladder. Pancreatic juice contains numerous digestive enzymes and is produced and released by the pancreas.

The digestive system has two separate categories of organs: those composing the __________________ and ________________

Gastrointestinal (GI) Tract Accessory Digestive Organs

histology of the stomach

It is lined by a simple columnar epithelium supported by lamina propria. The lining is indented by numerous depressions called gastric pits. Several gastric glands extend deep into the mucosa from the base of each gastric pit.

Submucosa

Many large blood vessels, lymph vessels, nerves, and glands are within the submucosa. Fine branches of the nerves extend into the mucosa and along with their associated autonomic ganglia are collectively referred to as the submucosal nerve plexus. The areolar connective tissue of the lamina propria and the submucosa house (MALT). In the small intestine larger aggregates of lymphatic nodules in the submucosa are called Peyer patches. The presence of MALT helps prevent ingested microbes from crossing the GI tract wall and entering the body

function of oral cavity and salivary glands

Mechanical digestion (mastication) begins in the oral cavity. Saliva is secreted from the salivary glands in response to food being present within the oral cavity. It is mixed with the ingested materials to form a wet mass called a bolus.q

bacterial flora

Numerous normal bacterial flora inhabit the large intestine. These bacteria are responsible for the chemical breakdown of complex carbohydrates, proteins, and lipids that remain in the chyme after it has passed through the small intestine.

functions of the stomach

One significant function of the stomach is to serve as a "holding bag" for controlled release of partially digested materials into the small intestine, where most chemical digestion and absorption occurs. However, the only essential function performed by the stomach is the release of intrinsic factor (a substance required for the absorption of vitamin B12, which occurs within the small intestine).

Intraperitoneal organs

Organs within the abdomen that are completely surrounded by visceral peritoneum are called intraperitoneal organs. They include the stomach, most of the small intestine, and parts of the large intestine.

protein breakdown in the stomach

Protein digestion begins within the stomach lumen with the enzyme pepsin. Pepsin is formed from pepsinogen, an inactive precursor released by chief cells. Hydrochloric acid that is released from parietal cells causes a low pH within the stomach that both activates pepsinogen to pepsin and denatures proteins to facilitate their chemical breakdown

Identify the enzyme that initiates protein digestion in the stomach, and explain its activation and action.

Proteins are broken down into amino acids by enzymes that target peptide bonds either between specific adjacent amino acids within the protein or nonspecifically release amino acids from either end of a protein. All enzymes that digest protein are released from both the stomach and pancreas as inactive enzymes. These enzymes must be activated (e.g., pepsinogen is activated to pepsin within the low pH of the stomach). This is because the proteolytic enzymes would destroy the proteins within the cells that produce them or in the case of protein-digesting enzymes produced in the pancreas would destroy the cells lining the main and accessory pancreatic ducts as they pass through those ducts.

Protein breakdown in the small intestine

Protein—trypsin→ polypeptide and peptide fragments Protein—chymotrypsin→ polypeptide and peptide fragments Protein—carboxypeptidase→ amino acids from carboxy-end of peptides

Salivary Glands

Salivary glands, which produce saliva (sa-li′va), are located both within the oral cavity (intrinsic salivary glands) and outside the oral cavity (extrinsic salivary glands). Intrinsic salivary glands are unicellular glands that continuously release relatively small amounts of secretions independent of the presence of food. Only the secretions from the intrinsic salivary glands contain lingual lipase, an enzyme that begins the digestion of triglycerides. Most saliva, however, is produced from multicellular exocrine glands outside the oral cavity called extrinsic salivary glands.

bile canaliculus

Sandwiched between each cord of hepatocytes is a bile canaliculus. This is a small channel that transports bile produced by hepatocytes to the bile ductule in the portal triad.

Secretin

Secretin is released from the small intestine primarily in response to an increase in chyme acidity. Secretin primarily causes the release of an alkaline solution that contains HCO3− from both the liver and ducts of the pancreas. Upon entering the small intestine, this alkaline fluid helps neutralize the acidic chyme. Secretin also inhibits gastric motility and secretions.

histology of the oral cavity

The epithelial lining of the oral cavity is a stratified squamous epithelium that protects against the abrasive activities associated with mechanical digestion. The nonkeratinized type of epithelium lines most of the oral cavity; the keratinized type lines the lips, portions of the tongue, and a small region of the hard palate.

Mesentery refers to

The general term mesentery refers to the double layer of peritoneum that supports, suspends, and stabilizes the intraperitoneal GI tract organs. Blood vessels, lymph vessels, and nerves that supply the GI tract are sandwiched between the two folds.

describe the anal canal

The internal lining of the anal canal contains relatively thin longitudinal ridges, called anal columns, between which are small depressions termed anal sinuses. As fecal material passes through the anal canal during defecation, pressure exerted on the anal sinuses causes their cells to release mucin to form mucus. The extra mucus lubricates the anal canal during defecation. At the base of the anal canal are the involuntary smooth muscle internal anal sphincter and voluntary skeletal muscle external anal sphincter, which generally close off the opening to the anal canal. The muscles composing these sphincters relax and allow the sphincter to open during defecation.

describe the large intestine

The large intestine continues absorption, primarily of water, electrolytes, and vitamins. The digestive process is completed as feces is produced and then eliminated through the anus.

Describe the liver

The liver is an accessory digestive organ. It is located in the right upper quadrant of the abdomen, immediately inferior to the diaphragm. It has numerous functions, but its main function in digestion is the production of bile.

Muscularis

The muscularis contains two layers of smooth muscle. The smooth muscle cells of the inner layer are oriented circumferentially within the GI tract wall and are called the inner circular layer. The cells of the outer layer are oriented lengthwise and are called the outer longitudinal layer. Fine branches of nerves are located between these two layers of smooth muscle; these nerve branches control muscle contractions and are collectively referred to as the myenteric nerve plexus. Both the submucosal nerve plexus and the myenteric nerve plexus together compose the enteric nervous system. The function of the muscularis is to mix and propel the contents within the GI tract. Contractions of these smooth muscle layers are associated with two primary types of motility: peristalsis and mixing. Peristalsis is the alternating contraction of both the inner circular and outer longitudinal muscle layers for the purpose of propelling ingested materials through the GI tract. Mixing is the "backward-and-forward," or kneading, motion that occurs at any point within different regions but lacks directional movement. Mixing is for the purpose of blending ingested materials with the secretions within the GI tract.

Adventitia

The outermost tunic may be either an adventitia or a serosa. An adventitia is composed of areolar connective tissue with dispersed collagen and elastic fibers and is associated with portions of the GI tract that are located outside the peritoneal cavity A serosa has the same composition as the adventitia, but it is completely covered by a serous membrane called the visceral peritoneum and is associated within portions of the GI tract within the peritoneal cavity.

Describe the functions of the pancreas cells

The pancreas has both endocrine and exocrine functions. Endocrine cells produce and secrete hormones such as insulin and glucagon. Exocrine cells produce pancreatic juice to assist with digestive activities.

Describe the regulation of salivary secretions

The salivary nuclei within the brainstem regulate salivation. A basal level of salivation in response to parasympathetic stimulation ensures that the oral cavity remains moist. Input to the salivary nuclei is received from chemoreceptors or mechanoreceptors in the upper GI tract. These receptors detect various types of stimuli, including the introduction of substances into the oral cavity

define essential nutrients and list the 6

The term essential nutrients indicates substances that must constitute part of the diet for survival. The six essential nutrients are carbohydrates, proteins, lipids, minerals, vitamins, and water.

what is the purpose of gastric folds

They're the internal stomach lining that allow the stomach to expand greatly when it fills then return to its normal j shape when it empties.

what is gastric mixing

mechanical digestion that changes bolus into chyme

The lower GI consists of

small intestine accessory organs large intestine

Pancreas histology

the pancreas contains modified simple cuboidal epithelial cells called acinar cells that are arranged in saclike acini. These cells are organized into large clusters termed lobules. Acinar cells produce and release digestive enzymes. Small ducts lead from each acinus into larger ducts that empty into larger pancreatic ducts that lead to the duodenum (as described earlier). The simple cuboidal epithelial cells lining the pancreatic ducts have the important function of secreting alkaline HCO3- fluid.

List and describe the six general functions of the digestive system

-Ingestion: intro of solid and liquid nutrients into the oral cavity. -Motility: voluntary and involuntary muscular contractions for mixing and moving materials through the gastrointestinal tract. -Secretion: the process of producing and releasing substances such as digestive enzymes, acid, and bile into the gastrointestinal tract. These secretions facilitate digestion -Digestion: the breakdown of ingested food into smaller structures that may be absorbed from the gastrointestinal tract. Mechanical digestion occurs when ingested material is physically broken down into smaller units by chewing and mixing without changing their chemical structure. Chemical digestion involves the activity of specific enzymes to break chemical bonds to change larger complex molecules into smaller molecules that can then be absorbed. -Absorption: involves membrane transport of digested molecules, electrolytes, vitamins, and water from the gastrointestinal tract into the blood or lymph. -Elimination: the expulsion of indigestible components that are not absorbed.

function of pharynx

The bolus is moved into the pharynx, where swallowing occurs. Mucus secreted in saliva and in the superior part of the esophagus provides lubrication to facilitate swallowing.

reticuloendothelial cells

These cells are macrophages that are responsible for engulfing potentially harmful substances as the blood is transported through the liver sinusoids.

lipid breakdown in the stomach

Triglyceride—lingual lipase→ monoglyceride and fatty acids (limited amounts) Triglyceride—gastric lipase→ monoglyceride and fatty acids (limited amounts)

lipid breakdown in the small intestine

Triglyceride—pancreatic lipase→ monoglyceride and fatty acids (within micelles)

The biliary apparatus is

a network of thin ducts that include the left and right hepatic ducts, which drain the left and right lobes of the liver

a tooth has

an crown, neck, and roots.

esophageal phase

bolus passes through the esophagus and into the stomach. The superior and inferior esophagueal sphincters relax to allow the bolus to pass through the esophagus. the inferior esophagual sphincter contracts after passage of the bolus to prevent reflux.

Cholecystokinin (CCK)

causes stimulation of the smooth muscle in the gallbladder wall to strongly contract, causing the release of concentrated bile.

Muscosa

consists of an epithelium, an underlying lamina propria, and a thin layer of muscularis mucosae. The epithelium allows for secretion and absorption. The lamina propia consists of blood vessels and nerves and absorption occurs when substances are moved through the epithelial cells that line the GI tract wall, and are absorbed into blood or lymphatic capillaries located within the lamina propria. The muscularis mucosae contracts and causes movement in the mucosa that facilitates secretion and absorption.

Two sets of teeth develop and erupt during a normal lifetime . In an infant, 20 ____________ _________,, erupt between 6 months and 30 months after birth. These teeth are eventually lost and replaced by 32 _________________ _________

deciduous teeth permanent teeth.

the teeth are collectively known as the

dentition

Circular folds

folds of the small intestines mucosal and submucosal layers that increase surface area and slow down the movement of of chyme and ensures that it remains in the small intestine for maximum nutrient absorption

Retroperitoneal organs

lie outside the parietal peritoneum directly against the posterior abdominal wall, so only their anterolateral portions are covered with the parietal peritoneum. Retroperitoneal digestive organs include most of the duodenum (the first part of the small intestine), the pancreas, ascending and descending colon (parts of the large intestine), and the rectum

lipid reabsorption

lipids are contained within micelles. Micelles transport lipids to the simple columnar epithelial lining of the small intestine. Here, the lipids enter the epithelial cells, whereas the bile salts remain in the small intestine lumen to be recycled and reused.

Mechanical digestion in the oral cavity is called mastication or chewing. It requires the coordinated activities of teeth, skeletal muscles in lips, tongue, cheeks, and jaws that are controlled by nuclei within the medulla oblongata and pons, collectively called the

mastication center

Together, secretions of acinar cells and cells that line the pancreatic ducts form

pancreatic juice. Pancreatic juice is an alkaline fluid containing mostly water, HCO3-, and a versatile mixture of digestive enzymes

the teeth are bound to the alveolar processes to form a gomphosis joint by the _________________, ___________________, and _____________________

roots dental alveoli periodontal ligaments

describe the anatomy of the pharynx

serves as the passageway for both air and food. Three skeletal muscle pairs called the superior, middle, and inferior pharyngeal constrictors form the wall of the pharynx

Some digestive reflexes do not involve the CNS. Instead, they are local and occur only within the neurons of the enteric nervous system that are housed within the GI tract wall. These are called

short reflexes

Sublingual Salivary Glands

sublingual salivary glands are inferior to the tongue. Each sublingual salivary gland extends multiple tiny sublingual ducts that open onto the inferior surface of the oral cavity, posterior to the submandibular duct papilla. These tiny glands contribute only about 3-5% of the total saliva. both serous and mucus secretions

function of the stomach

the bolus is mixed with gastric secretions as smooth muscle in the stomach wall contracts. These secretions are produced by epithelial cells of the stomach mucosa and include acid (hydrochloric acid [HCl]), digestive enzymes, and mucin. The mixing continues as an acidic "purée" called chyme is formed.

Name the three regions that comprise the large intestine

the cecum, colon, and rectum

describe the anatomy of the esophagus

the inferior region of the esophagus connects to the stomach, where it passes through an opening in the diaphragm called the esophageal hiatus The superior esophageal sphincter is closed during inhalation of air so air does not enter the esophagus and instead enters the larynx and trachea The inferior esophageal sphincter isn't strong enough alone to prevent materials from refluxing back into the esophagus; instead, the muscles of the diaphragm at the esophageal opening contract to help prevent materials from regurgitating from the stomach into the esophagus.

The upper gastrointestinal tract is where initial processing by both mechanical and chemical means takes place. It consists of

the oral cavity and salivary glands, pharynx, esophagus, stomach, and duodenum.

common bile duct

the union of the cystic duct from the gallbladder and the common hepatic duct forms the common bile duct that opens into the duodenum.

Both muscular contractions of the stomach wall and secretions released by the stomach are regulated by nervous reflexes and hormones. These processes are organized into three phases:

-Cephalic Phase: initiated by the thought, smell, sight, or taste of food. The medulla oblongata increases parasympathetic stimulation of the stomach via the vagus nerve which causes both an increase in contractile force in the gastric wall (increases motility) and secretory activity of the gastric glands. -Gastric Phase: The gastric reflex is initiated as food enters the stomach. Baroreceptors in the wall of the stomach detect increased distension in the stomach wall, and chemoreceptors detect both protein and an increase in pH of gastric contents. Nerve signals are relayed along sensory neurons to the medulla oblongata, resulting in the same effects as described in the cephalic reflex—an increase in both stomach motility and secretory activity of gastric cells. Presence of food also causes release of gastrin causing contactions of pyloric sphincter to slow stomach emptying. -Intestinal Phase: The intestinal reflex opposes the other two reflexes (cephalic reflex and gastric reflex). It protects the small intestine from being overloaded with chyme. The intestinal reflex is initiated with entry of acidic chyme into the duodenum, which causes a decrease in nerve signals relayed to the medulla oblongata. Consequently, vagal stimulation to the stomach is decreased with a concomitant decrease in both motility and secretory activity of the stomach.

Identify the six organs that make up the GI Tract

The GI tract organs essentially form a continuous tube that includes the oral cavity (mouth), pharynx (throat), esophagus, stomach, small intestine, and large intestine, and ends at the anus.

pharyngeal phase

The arrival of the bolus at the entryway to the oropharynx initiates the swallowing reflex of the pharyngeal phase. The pharyngeal phase is involuntary. Tactile sensory receptors around the fauces are stimulated by the bolus and initiate nerve signals along sensory neurons to the swallowing center in the medulla oblongata. Nerve signals are then relayed along motor neurons to effectors to cause the following response: 1.Entry of the bolus into the oropharynx 2.Elevation of the soft palate and uvula to block the passageway between the oropharynx and nasopharynx 3.Elevation of the larynx by the extrinsic muscles move the larynx anteriorly and superiorly, resulting in the epiglottis covering the laryngeal opening; this prevents ingested material from entering the trachea overall bolus passes through the pharynx to the esophagus

function of esophagus

The bolus is transported from the pharynx through the esophagus into the stomach. Mucus secretion by the esophagus lubricates the passage of the bolus.

nucleic acid breakdown in the small intestine

The breakdown of the nucleotides is further accomplished by brush border enzymes embedded in the epithelial lining of the small intestine. These enzymes include (1) phosphatase, which breaks the bond holding the phosphate to the rest of the nucleotide (without the phosphate, this molecule is called a nucleoside); and (2) nucleosidase, which breaks the bond between the sugar and the nitrogenous base of the nucleoside, releasing the sugar and nitrogenous base.

Submandibular Salivary Glands

The submandibular salivary glands are both inferior to the floor of the oral cavity and medial to the body of the mandible. The submandibular salivary glands produce most of the saliva (about 60-70%). A submandibular duct opens from each gland through a papilla in the floor of the oral cavity on either side of the lingual frenulum. both serous and mucus secretion

The muscularis of the stomach varies from the general GI tract pattern in that it is composed of three smooth muscle layers instead of two:

an inner oblique layer, a middle circular layer, and an outer longitudinal layer. The presence of a third layer of smooth muscle assists the continued churning and blending of the swallowed bolus to help mechanically digest the food. The muscularis becomes increasingly thicker as it progresses from the body to the pylorus.

name the 4 segments of the colon

ascending colon, transverse colon, descending colon, and sigmoid colon.

Accessory digestive organs do what?

assist in the breakdown of food.

Three primary hormones participate in the regulation of the processes of digestion:

gastrin that is released from the stomach; and secretin and cholecystokinin that are released from the small intestine.

the gingivae are the

gums. They are composed of dense irregular connective tissue, with an overlying nonkeratinized stratified squamous epithelium that covers the alveolar processes of the upper and lower jaws and surrounds the neck of the teeth.

Sensory input from both mechanoreceptors and chemoreceptors is relayed to the central nervous system (CNS) in response to stimulation. Autonomic motor output is then relayed through three cranial nerves

he facial, glossopharyngeal, and vagus nerves. to different digestive system effectors, such as salivary glands, the pancreas, and the muscularis layers in the GI tract wall. The result is coordinated secretory and smooth muscle contractions involved in digestive responses. These autonomic interactions of the CNS are described as long reflexes.

common bile duct becomes the

hepatopancreatic ampulla (or ampulla of vater), which is a swelling either adjacent to or within the posterior duodenal wall. The main pancreatic duct joins with the hepatopancreatic ampulla. Associated with the hepatopancreatic ampulla is the hepatopancreatic sphincter that regulates movement of bile (from the liver and gallbladder) and pancreatic juice (from the pancreas) into the duodenum. Within the duodenum, the major duodenal papilla is a projection where the hepatopancreatic ampulla penetrates the wall, and both bile and pancreatic juice enter the duodenum. An alternative way that a small amount of pancreatic juice may also enter the duodenum is through an accessory pancreatic duct. This duct penetrates the duodenal wall, forming the minor duodenal papilla.

what happens within the GI Tract

ingested food is broken down into smaller components that can be absorbed along its length

Pancreatic amylase

is synthesized and released by the pancreas as a component of pancreatic juice into the small intestine through the main or accessory pancreatic duct . This enzyme continues the digestion of starch into shorter strands of glucose

what is gastric emptying

movement of acidic chyme from the stomach into the duodenum.

Name the two types of secretory cells are housed within the large paired salivary glands and collectively produce the components of saliva

mucous cells and serous cells

histology of the liver

the liver's connective tissue capsule branches throughout the organ and forms septa that partition the liver into thousands of microscopic polyhedral hepatic lobules that are the structural and functional units of the liver (figure 26.20). Within hepatic lobules are liver cells called hepatocytes (hep′ă-tō-sīt). At the periphery of each lobule are several portal triads, composed of a bile ductule, and branches of both the hepatic portal vein and the hepatic artery. At the center of each lobule is a central vein that drains the blood flow from the lobule. Central veins collect the blood and merge throughout the liver to form numerous hepatic veins that eventually empty into the inferior vena cava.

Swallowing is called deglutition. It is the process of moving ingested materials from the oral cavity to the stomach. Swallowing has three phases:

the voluntary phase, the pharyngeal phase, and the esophageal phase

saliva is formed as

water and electrolytes are filtered from plasma within capillaries then through cells (acini) of a salivary gland.