Bio 233 @ Oit - Unit 1

Front 1

Name the parts of alimentary canal.

Back 1

The alimentary canal or gastrointestinal (GI) tract digests and absorbs food. It canal includes mouth, pharynx, esophagus, stomach, small intestine, and large intestine. Accessory digestive organs include teeth, tongue, gallbladder, salivary glands, liver, and pancreas
GI tract performs six essential activities:
o Ingestion – taking food into the digestive tract
o Propulsion – swallowing and peristalsis
o Mechanical digestion – chewing, mixing, and churning food
o Chemical digestion – catabolic breakdown of food
o Absorption – movement of nutrients from the GI tract to the blood or lymph
o Defecation – elimination of indigestible solid wastes

Front 2

Name accessory digestive organs.

Back 2

Accessory digestive organs include teeth, tongue, gallbladder, salivary glands, liver, and pancreas

Front 3

Describe 6 essential digestive processes. Where does each of them take place?

Back 3

GI tract performs six essential activities:
o Ingestion – taking food into the digestive tract
o Propulsion – swallowing and peristalsis
o Mechanical digestion – chewing, mixing, and churning food
o Chemical digestion – catabolic breakdown of food
o Absorption – movement of nutrients from the GI tract to the blood or lymph
o Defecation – elimination of indigestible solid wastes

Front 4

Compare the difference between peristalsis and segmentation.

Back 4

Peristalsis (peri=around, stalsis=constriction) is the major means of propulsion and involves alternate waves of contraction and relaxation of muscles in the argan walls. Its main effect is to squeeze food along the tract, but some mixing occurs as well.
Segmentation mixes food with digestive juices and increases the efficiency of absorbtion by repeatedly moving different parts of the food mass over the intestinal wall.
(p884)

Front 5

Describe the intrinsic and extrinsic control involved in regulation of digestion?
Explain the short reflexes and long reflexes.

Back 5

Many of the controlling systems of the digestive tract are intrinsic - a product of "in-house" nerve plexuses or hormone-producing cells. The wall of the alimentary canal contains nerve plexuses which spread like chicken wire along the entire length of the GI tract and influence each other both in the same and in different digestive organs. As a result, two kindso f reflex activity occur, short and long. Short reflexes are mediated entirely by the local (enteric) plexuses (the so-called gut brain) in response to GI tract stimuli. Long reflexes are intiated by stimuli arising inside or outside the GI tract and involve CNS centers and extrinsic autonomic nerves.
(p885-886)

Front 6

Define mesentery and describe the processes of its formation. Give examples of
peritoneal (intraperitoneal) organs and retroperitoneal organs.

Back 6

With respect to peritoneum, abdominal organs can be classified as:
o Retroperitoneal organs – organs outside the peritoneum
o Peritoneal organs (intraperitoneal) – organs surrounded by peritoneum
o Mesoperitoneal organs partially surrounded by peritoneum

Front 7

Describe hepatic portal circulation.

Back 7

The veins of the hepatic portal circulation drain the digestive organs, spleen, and pancreas and deliver the blood to the liver via hepatic portal vein. As blood percolates through the liver, some of the nutrients are stored or processed in various ways for release to the general circulation. The liver in turn is drained by the hepatic veins that enter the inferior vena cava.
The inferior mesenteric vein, draining the distal part of the large intestine, joins the splenic vein, which drains the spleen, pancreas and stomach. The splenic vein and the superior meseteric vein, which drains the small intestine and the proximal colon, unite to form the hepatic portal vein. The left gastric vein, which drains the lesser curvature of the stomach, drains directly into the hepatic portal vein.
(WikiAnswers - no specific definition found in book, referenced p887, p764-765)

Front 8

Describe the 4 tunics which form the wall of the GI tract.

Back 8

The wall of GI tract consists of four tunics. Each tunic has a predominant tissue type and a specific digestive function. From the lumen outward they are:
o Mucosa is a moist epithelial layer that lines the lumen of the alimentary canal. Its major functions are secretion of mucus, absorption of the end products of digestion, and protection against infectious disease. Mucosa Consists of three layers:
 Lining epithelium is a simple columnar epithelium and mucus-secreting goblet cells
The mucus secretions protect digestive organs from digesting themselves and ease food along the tract
 Lamina propria is formed by loose areolar and reticular connective tissue. It nourishes the epithelium and absorbs nutrients. It also contains lymph nodes important in defense against bacteria
 Muscularis– smooth muscle cells that produce local movements of mucosa
o Submucosa – dense connective tissue containing elastic fibers, blood and lymphatic vessels, lymph nodes, and nerves
o Muscularis externa is responsible for segmentation and peristalsis. It consists of at least two muscular layers: circular inner layer and longitudinal outer layer
o Serosa is the protective visceral peritoneum

Front 9

What is the enteric nervous system? Describe its functions.

Back 9

The enteric nervous system (ENS), also referred to as the efferent nervous system, is a subdivision of the peripheral nervous system (PNS), that directly controls the gastrointestinal system.
It is derived from neural crest.
The ENS is capable of autonomous functions such as the coordination of reflexes, although it receives considerable innervation from the autonomic nervous system and thus is often considered a part of the ANS. Its study is the focus of neurogastroenterology. The ENS can be damaged by ischemia.
The enteric nervous system has been described as a "second brain".[9] There are several reasons for this. The enteric nervous system can operate autonomously. It normally communicates with the CNS through the parasympathetic (eg, via the vagus nerve) and sympathetic (eg, via the prevertebral ganglia) nervous systems. However, vertebrate studies show that when the vagus nerve is severed, the enteric nervous system continues to function.
In vertebrates the enteric nervous system includes efferent neurons, afferent neurons, and interneurons, all of which make the enteric nervous system capable of carrying reflexes and acting as an integrating center in the absence of CNS input. The sensory neurons report on mechanical and chemical conditions. Through intestinal muscles, the motor neurons control peristalsis and churning of intestinal contents. Other neurons control the secretion of enzymes. The enteric nervous system also makes use of more than 30 neurotransmitters, most of which are identical to the ones found in CNS, such as acetylcholine, dopamine, and serotonin. The enteric nervous system has the capacity to alter its response depending on such factors as bulk and nutrient composition. In addition, ENS contains support cells which are similar to astroglia of the brain and a diffusion barrier around the capillaries surrounding ganglia which is similar to the blood-brain barrier of cerebral blood vessels
(Wikipedia)

Front 10

Describe the anatomy of mouth, lips, and palate.

Back 10

Oral or buccal cavity is bounded by lips, cheeks, palate, and tongue. It has the oral orifice as its anterior opening and continues with the oropharynx posteriorly. The two parts of oral cavity are:
o Vestibule – bounded by the lips and cheeks externally, and teeth and gums internally
o Oral cavity proper – area that lies within the teeth and gums
The mouth is lined with stratified squamous epithelium. The gums, hard palate, and dorsum of the tongue are slightly keratinized
Lips and Cheeks have a core of skeletal muscles. Labial frenulum – median fold that joins the internal aspect of each lip to the gum
Palate. Hard palate – formed by palatine bones and palatine processes of the maxillae. Soft palate – mobile fold formed mostly of skeletal muscle. It closes off the nasopharynx during swallowing. Uvula projects downward from its free edge

Front 11

Describe the functions of intrinsic and extrinsic muscles of the tongue

Back 11

Intrinsic muscles of the toungue change its shape, whereas extrinsic muscles alter the tongue’s position.

Front 12

Name three types of papillae on the surface of the tongue

Back 12

Tongue mucosa contains papillae of four types:
 Filiform
 Foliate
 Fungiform
 Circumvallate

Front 13

Name three pairs of extrinsic salivary glands.

Back 13

Extrinsic salivary glands secrete serous, enzyme-rich saliva. They include:
o Parotid salivary glands lie anterior to the ear between the masseter muscle and skin.
Parotid (Stensen’s) duct opens into the vestibule next to the second upper molar
o Submandibular salivary glands lie along the medial aspect of the mandibular body.
Wharton’s ducts open at the base of the lingual frenulum
o Sublingual salivary glands lie anterior to the submandibular gland under the tongue. They open via 10-12 ducts into the floor of the mouth.

Front 14

Describe the functions and makeups of saliva.

Back 14

Saliva lubricates the bolus making its passage down the esophagus easier. It washes away bacteria from teeth, reducing incidence of cavities Saliva contain enzyme amylase which breaks down carbohydrate amylose (component of starch) to smaller sugars. Its pH is slightly alkaline.

Front 15

Describe the control of salivation.

Back 15

The intrinsic salivary glands secrete saliva continuously in amounts just sufficient to keep the mouth moist. But when food enters the mouth, the extrinsic glands are activated and copious amounts of saliva pour out. The average output of saliva is 1000-1500 ml per day.
Salivation is controlled primarily by the parasympatheitic division of the autonomic nervous system.

Front 16

Describe the classification of teeth. Recall and explain dental formula for deciduous and permanent teeth.

Back 16

Primary teeth include 20 deciduous (baby) teeth that erupt at intervals between 6 and 24 months. Between the ages of 6 and 12 years, permanent teeth enlarge and develop causing the root of deciduous teeth to be resorbed and fall out. There are usually 32 permanent teeth
o Incisors (8) – chisel-shaped teeth adapted for cutting or nipping
o Canines (4)– conical or fanglike teeth that tear or pierce
o Premolars= bicuspids (8) and molars (12) – have broad crowns with rounded tips and are best suited for grinding or crushing
Dental Formula is a shorthand way of indicating the number and relative position of teeth. It is written as ratio of upper to lower teeth for the mouth:
Primary: [2I (incisors), 1C (canine), 2M (molars)] x 2 (left and right) x 2 (upper and lower) = 20
Permanent: [2I, 1C, 2PM (premolars), 3M(molars)] x 2 (left and right) x 2 (upper and lower) = 32

Front 17

Describe the structure of crown and root of the tooth. Revisit the gomphosis joint.

Back 17

Tooth has two main regions – the crown (exposed part of the tooth above the gingiva (gum) and the root) and the root (portion of the tooth embedded in the jawbone).

Front 18

Describe the structure and functions of the pharynx.

Back 18

From the mouth, the oro- and laryngopharynx allow passage of food and fluids to the esophagus and air to the trachea. Pharynx is lined with stratified squamous epithelium and mucus glands. It contains skeletal muscle
Deglutition (Swallowing) involves the coordinated activity of the tongue, soft palate, pharynx, esophagus and 22 separate muscle groups. During the buccal phase, bolus is forced into the oropharynx. Bolus is passed into esophagus during the pharyngeal-esophageal phase; during this phase entrance into the nasopharynx is sealed by soft palate and entrance into the larynx and trachea is sealed by epiglottis. This process is coordinated by the medulla and lower pons. Peristalsis moves food through the pharynx to the esophagus.

Front 19

Describe the change of position of the soft palate during swallowing.

Back 19

It closes off the nasopharynx during swallowing.

Front 20

Compare the muscle types in different part of the esophagus (from superior to inferior).

Back 20

Esophageal mucosa is formed by nonkeratinized stratified squamous epithelium. Muscularis externa changes from skeletal (superiorly) to smooth muscle (inferiorly)

Front 21

Explain the digestive process in the mouth.

Back 21

Food is ingested and the mechanical digestion (chewing) begins: food breaks into small pieces, blends them with saliva produced by the salivary glands. Salivary amylase begins chemical breakdown of starch. Swallowing initiates the propulsion of the bolus. The pharynx and esophagus serve as conduits to pass food from the mouth to the stomach

Front 22

Identify different parts of stomach-cardiac region, fundus, body, pyloric region,
lesser curvature, and greater curvature.

Back 22

Stomach can be subdivided into the following areas:
o Cardiac region
o Fundus
o Body
o Greater curvature
o Lesser curvature
o Antrum
o Pylorus
The stomach is continuous with the duodenum through the pyloric sphincter.
Lesser omentum runs from the liver to the lesser curvature. Greater omentum drapes inferiorly from the greater curvature to the small intestine.
Nerve supply of the stomach: parasympathetic (vagus n.) and sympathetic fibers of the autonomic nervous system
Blood supply of the stomach: Celiac trunk and corresponding veins (part of the hepatic portal
system)

Front 23

Describe the locations of greater omentum and lesser omentum.

Back 23

Lesser omentum runs from the liver to the lesser curvature. Greater omentum drapes inferiorly from the greater curvature to the small intestine

Front 24

Describe the blood supply of the stomach.

Back 24

Blood supply of the stomach: Celiac trunk and corresponding veins (part of the hepatic portal system)

Front 25

Describe the muscular arrangements of stomach wall.

Back 25

Muscularis externa has an additional oblique layer that allows the stomach to churn, mix, and pummel food physically and breaks down food into smaller fragments.
Epithelial lining is composed of simple columnar epithelium (mostly Goblet cells that produce a coat of alkaline mucus). The mucous surface layer traps a bicarbonate-rich fluid beneath it.
Gastric pits are the depressions in the epithelial lining. Gastric glands secrete gastric juice, mucus and gastrin, and open into the gastric pits

Front 26

What is the major functions of goblet cells?

Back 26

Goblet cells produce a coat of alkaline mucus

Front 27

Name 4 different secretory cells and describe their functions.

Back 27

Goblet cells produce a coat of alkaline mucus
o Parietal cells secrete hydrochloric acid (HCl) that serves to activate pepsin and kill bacteria; and Intrinsic factor that facilitates the absorption of vitamin B12
o Chief cells produce pepsinogen. Pepsinogen is converted into pepsin by HCl in the stomach or pepsin itself via a positive feedback mechanism. Pepsin converts proteins
into polypeptides
o Enteroendocrine cells produce gastrin that acts to increase HCl production in the stomach and increase motility of small intestines. They also produce other local hormones (serotonin and histamine) that increases motility of the stomach and increases HCl production.

Front 28

List four factors create mucosal barrier of stomach, and describe its importance.

Back 28

The stomach is exposed to the harshest conditions in the digestive tract. To keep from digesting itself, the stomach has a mucosal barrier with a thick coat of bicarbonate-rich mucus on the stomach wall. Epithelial cells of stomach mucosa are joined by tight junctions; they are capable of rapid regeneration. Gastric glands have cells impermeable to HCl.

Front 29

Describe excitatory and inhibitory events in cephalic, gastric, and intestinal phases of gastric secretion.

Back 29

Neural and hormonal mechanisms regulate the release of gastric juice. Stimulatory and inhibitory events occur in three phases
o Cephalic phase occurs before food enters the stomach. Stimulation of osmo- and taste receptors or sight and thought of food generates the signals relayed to hypothalamus, which leads to stimulation of vagal nucleus in the medulla oblongata (parasympathetic center).
Vagus nerve stimulation causes activation of gastric glands.
o Gastric Phase occurs when food enters stomach. Distention of stomach walls causes stimulation of stretch receptors. Vagus nerve activation results in increase production of gastric juice. Also protein-rich food and decreased acidity (high pH) stimulates G-
enteroendocrine cells to produce gastrin. Gastrin increases HCl production and has a negative feedback on gastrin production
o Intestinal phase. A short excitatory phase begins when acidic chyme enters duodenal bulb.
Duodenal wall produces enteric gastrin that increases gastric gland activity. When distal
duodenum is stretched, an inhibitory phase begins activating enterogastric reflex:
 Inhibition of vagal nucleus in medulla,
 Inhibition of enteric gastrin production,
 Pyloric constriction
Releases enterogastrones (CCK, secterin, etc.) inhibit gastric secretion

Front 30

Describe the regulation of gastric emptying.

Back 30

Neural and hormonal mechanisms regulate the release of gastric juice. Stimulatory and inhibitory events occur in three phases
o Cephalic phase occurs before food enters the stomach. Stimulation of osmo- and taste receptors or sight and thought of food generates the signals relayed to hypothalamus, which leads to stimulation of vagal nucleus in the medulla oblongata (parasympathetic center).
Vagus nerve stimulation causes activation of gastric glands.
o Gastric Phase occurs when food enters stomach. Distention of stomach walls causes stimulation of stretch receptors. Vagus nerve activation results in increase production of gastric juice. Also protein-rich food and decreased acidity (high pH) stimulates G-enteroendocrine cells to produce gastrin. Gastrin increases HCl production and has a negative feedback on gastrin production
o Intestinal phase. A short excitatory phase begins when acidic chyme enters duodenal bulb.
Duodenal wall produces enteric gastrin that increases gastric gland activity. When distal duodenum is stretched, an inhibitory phase begins activating enterogastric reflex:
 Inhibition of vagal nucleus in medulla,
 Inhibition of enteric gastrin production,
 Pyloric constriction
Releases enterogastrones (CCK, secterin, etc.) inhibit gastric secretion

Front 31

Describe the lobes and ligament of the liver.

Back 31

Liver is the largest gland in the body. It has four lobes: right, left, caudate and quadrate.
Ligaments of liver include:
o The falciform ligament separates the right and left lobes anteriorly and suspends it from the diaphragm and anterior abdominal wall
o Right and Left triangular ligaments attach liver to the diaphragm superiorly and
posteriorly
o The ligamentum teres is a remnant of the fetal umbilical vein. It runs along the free edge of the falciform ligament on the inferior surface of the liver
o The lesser omentum anchors the liver to the stomach

Front 32

Explain the structure anatomically anchors the liver to the stomach.

Back 32

The lesser omentum anchors the liver to the stomach

Front 33

Describe the anatomical relationship between the liver and the gallbladder.

Back 33

The gallbladder is a thin-walled, green muscular sac that rests in a recess on the inferior surface of the right lobe.

Front 34

Describe the microscopic structure of the liver? Name the components of portal triads.

Back 34

Hexagonal-shaped liver lobules are the structural and functional units of the liver. They are composed of hepatocyte (liver cell) plates radiating outward from a central vein. Central vein drains the blood into hepatic veins. Portal triads are found at each of the six corners of each liver lobule. Portal triads consist of a bile duct, a branch of hepatic artery proper and a branch of hepatic portal vein. From the vessels of portal triad blood is delivered into the liver sinusoids – enlarged, leaky capillaries located between hepatic plates. Therefore, blood in the sinusoids is a mixture of arterial and portal venous blood.

Front 35

Describe the functions of hepatocytes.

Back 35

Hepatocytes’ functions include:
o Production of bile
o Processing of blood-borne nutrients
o Production of plasma proteins
o Storage of fat-soluble vitamins
o Detoxification
o In the fetus, the liver is a major site of hematopoiesis.

Front 36

Describe the duct system transporting bile.

Back 36

Bile leaves the liver via bile ducts, which fuse into the common hepatic duct. The common hepatic duct fuses with the cystic duct, forming the common bile duct (Choledoch). Choledoch joins with main pancreatic duct forming a wide ampulla of Vater. It opens on the surface of major duodenal papilla into the duodenum

Front 37

Describe the compositions and functions of bile.

Back 37

Bile is a yellow-green, alkaline solution containing bile salts, bile pigments, cholesterol, neutral fats, phospholipid lecithin and electrolytes. Its color is due to a bile pigment bilirubin, a waste product of heme. Bile salts are derived from cholesterol serve to emulsify fat. This process facilitates fat and cholesterol absorption. After it emulsified fat in the small intestine, bile can be reabsorbed and recycled or it can be excreted with feces. Abundance of fiber in chime traps bile, increasing its excretion. This is an effective way to lower cholesterol. The Gallbladder stores and concentrates bile by absorbing its water and ions and releases bile via the cystic duct, which flows into the common bile duct.

Front 38

Explain the chemical and neural regulations of bile release, and list the functions of cholecystokinin.

Back 38

Acidic, fatty chyme causes the duodenum to release of cholecystokinin (CCK) and secretin into the bloodstream. Cholecystokinin causes the gallbladder to contract and sphincter Oddi to relax. As a result, bile enters the duodenum. Vagal stimulation also causes weak contractions of the gallbladder. Bile salts and secretin transported in blood stimulate the liver to produce bile.

Front 39

List the exocrine functions of pancreas.

Back 39

The bulk of the pancreas is composed of pancreatic exocrine cells and their associated ducts. Embedded in the exocrine tissue are the endocrine cells of the pancreas, the Islets of Langerhans. They secrete insulin, glucagon and several other hormones.
The structural unit of exocrine pancreas is acinus; Acinar cells are packed with membrane-bounded zymogene granules containing digestive enzymes.
Each acinus drains into intercalated ducts. They have flattened cuboidal epithelium that extends up into the lumen of the acinus to form what are called centroacinar cells duct. Small ducts fuse to form larger ones.
Main pancreatic duct fuses with choledoch at ampulla of Vater and empties into duodenum on the surface of major duodenal papilla. Accessory pancreatic duct opens into duodenum on the surface of minor duodenal papilla

Front 40

Describe the composition of pancreatic juice. Explain the functions of trypsinogen
and procarboxypeptidase in digestion.

Back 40

Pancreatic juice is a clear alkaline fluid that neutralizes acid chyme (primarily HCO3 – ) and provides optimal environment for pancreatic enzymes. Fluid and bicarbonate ions of the pancreatic juice are secreted by the cells which form the intercalated ducts of the pancreas.
Bicarbonate ions in the pancreatic juice neutralize the acidic contents which the stomach empties into the duodenum.
Enzymes are secreted by the secretory cells of the pancreatic acini.

Front 41

Describe the chemical and neural regulation of pancreatic secretion.

Back 41

Secretin and Cholecystocytokinin (CCK) are released when fatty or acidic chyme enters the duodenum. These hormones enter the bloodstream and travel to pancreas, where CCK induces the secretion of enzyme-rich pancreatic juice and secretin causes secretion of bicarbonate-rich pancreatic juice
Vagal stimulation also causes release of pancreatic juice

Front 42

Name different divisions of small intestine.

Back 42

Small Intestines consist of three segments:
o Duodenum a short retroperitoneal segment, starts at the pyloric sphincter
o Jejunum,
o Ileum,
Ileum continues is separated from the large intestines by ileocecal valve. Both ileum and jejunum are intraperitoneal organs
A bulk of the small intestine is suspended from the body wall by an extension of the peritoneum called the mesentery

Front 43

Define plicae, villi and microvilli.

Back 43

Mucosa and submucosa form permanent cirular folds, = plicae. On each plica mucosa forms small projections, =Villi. Each villus contains a capillary bed and a blunt-ended lymphatic vessel referred to as the "central lacteal". Simple columnar epithelium of each villus has additional projections, =microvilli on the apical surface

Front 44

List the cells found in the epithelium of the mucosa in small intestine. Describe
the stimuli which trigger and release of intestinal juice from intestinal glands.

Back 44

The epithelium of the mucosa is made up of three types of cells:
o Absorptive cells and goblet cells
o Enteroendocrine cells
o Interspersed T cells called intraepithelial lymphocytes (IELs). IELs immediately release cytokines upon encountering Ag
Intestinal Juice is secreted by intestinal glands in response to distension or irritation of the mucosa. It is slightly alkaline and isotonic with blood plasma. It mostly consists of water and some mucus; it is relatively poor in enzymes.

Front 45

Describe how chyme is digested in the small intestine.

Back 45

As chyme enters the duodenum carbohydrates and proteins are only partially digested, and no fat digestion has taken place at all. When chyme is slowly released into the duodenum, it is hypertonic and has low pH. Therefore mixing and neutralization is required for proper digestion.
Digestive juices are mostly delivered from pancreas. Virtually all nutrient absorption takes place in the small intestine

Front 46

Describe the neural control of mobility of the small intestine. Explain the roles of gastroileal reflex and gastrin.

Back 46

The most common motion of the small intestine is segmentation. It separates contents into smaller portions and moves them steadily toward the ileocecal valve. After nutrients have been absorbed, peristalsis begins: meal remnants, bacteria, mucosal cells, and debris are moved into the large intestine
Local enteric neurons of the GI tract coordinate intestinal motility. Cholinergic neurons cause contraction and shortening of the circular muscle layer and shortening of longitudinal muscle. Other impulses relax the circular muscle.
The gastroileal reflex and gastrin relax the ileocecal sphincter allowing chyme to pass into the large intestine

Front 47

Briefly describe the processes of fatty acid, nucleic acids, electrolyte, and water
absorption.

Back 47

Water: Absorption of water occurs due to osmosis. Water simply follows sodium that is co-transported into the enterocytes with glucose and amino acids.
Lipids
Most oils and fats are composed of glycerol and fatty acids. Lipids (triglycerides) are emulsified by bile and digested by pancreatic lipase to monoglycerides and glycerol and fatty acids. Smaller fatty acids are absorbed directly through intestinal cells into blood.
Longer chain fatty acids and monoglycerides form micelles and these micelles diffuse through the microvilli into the intestinal cells. In intestinal cells fatty acids and triglycerides reassemble into triglycerides. Than they are packaged in special transport units, chylomicrons, that act as micelles to carry fat-soluble substances in the blood. Chylomicrons are lipoproteins. Chylomicrons enter lymphatic system and joint bloodstream near the heart. Therefore, large molecules of fat bypass detoxification in liver.

Front 48

Name different divisions of large intestine.

Back 48

Large Intestine is subdivided into the cecum, colon and rectum.
o Cecum is the saclike projection that lies below the ileocecal valve in the right iliac fossa. It contains a wormlike vermiform appendix.
o Colon has distinct regions:
ascending colon, hepatic flexure, transverse colon, splenic flexure, descending colon, and sigmoid colon. The transverse and sigmoid portions are anchored via mesenteries called mesocolons. The sigmoid colon joins the rectum.
o Rectum has three valves that stop feces from being passed with gas. The anal canal, the last segment of the large intestine, opens to the exterior at the anus. The anus has two sphincters: internal anal sphincter composed of smooth muscle; external anal sphincter composed of skeletal muscle. These sphincters are closed except during defecation

Front 49

Describe the bacterial flora found in the large intestine and their functions.

Back 49

The bacterial flora of the large intestine consists of dead bacteria, bacteria that survived the small intestine and entered the cecum and bacteria that entered via the anus. Microorganisms colonize the colon, ferment indigestible carbohydrates, releasing irritating acids and gases (flatus) and synthesize vitamins of B complex and vitamin K

Front 50

List the functions of the large intestine.

Back 50

Other than digestion of enteric bacteria, no further digestion takes place. Vitamins, water, and electrolytes are absorbed here. The major function of large intestine is propulsion of fecal material toward the anus.

Front 51

Describe haustral contraction.

Back 51

Local enteric neurons of the GI tract coordinate intestinal motility. Cholinergic neurons cause contraction and shortening of the circular muscle layer and shortening of longitudinal muscle. Other impulses relax the circular muscle.

Front 52

Describe the neural control of defecation.

Back 52

Defecation: distension of rectal walls caused by feces stimulates contraction of the rectal walls and relaxes the internal anal sphincter. Voluntary signals from primary motor cortex stimulate relaxation of the external anal sphincter and defecation occurs