Artlabeling Activity the Stomach Structure of the Stomach Wall 2 of 2
23.vi The Small and Large Intestines
Learning Objectives
By the end of this section, you will exist able to:
- Describe the functional beefcake of the small and large intestines
- Identify iii main adaptations of the small intestine wall that increment its absorptive capacity
- Depict the mechanical and chemic digestion of chyme upon its release into the minor intestine
- Draw any absorption that happens in the small and big intestines
- List three features unique to the wall of the large intestine and place their contributions to its office
- Identify the benign roles of the bacterial flora in digestive arrangement functioning
- Trace the pathway of nutrient waste from its signal of entry into the large intestine through its go out from the body equally carrion
The word intestine is derived from a Latin root significant "internal," and indeed, the two organs together nigh fill up the interior of the intestinal cavity. In add-on, called the small and large bowel, or colloquially the "guts," they plant the greatest mass and length of the alimentary culvert and, with the exception of ingestion, perform all digestive system functions.
The Small Intestine
Chyme released from the tummy enters the modest intestine, which is the principal digestive organ in the trunk. Non only is this where most digestion occurs, it is likewise where practically all assimilation occurs. The longest part of the alimentary canal, the small intestine is about 3.05 meters (10 feet) long in a living person (simply about twice as long in a cadaver due to the loss of muscle tone). Since this makes information technology about v times longer than the large intestine, you might wonder why it is called "small." In fact, its proper noun derives from its relatively smaller bore of simply near 2.54 cm (1 in), compared with seven.62 cm (three in) for the large intestine. Equally we'll run across shortly, in addition to its length, the folds and projections of the lining of the small intestine work to give it an enormous surface area, which is approximately 200 m2, more than 100 times the expanse of your pare. This large surface area is necessary for complex processes of digestion and assimilation that occur within it.
Structure
The coiled tube of the small-scale intestine is subdivided into iii regions. From proximal (at the breadbasket) to distal, these are the duodenum, jejunum, and ileum (Figure 23.6.1).
The shortest region is the 25.4-cm (ten-in) duodenum, which begins at the pyloric sphincter. Only by the pyloric sphincter, it bends posteriorly backside the peritoneum, becoming retroperitoneal, and and then makes a C-shaped curve around the head of the pancreas before ascending anteriorly again to return to the peritoneal cavity and join the jejunum. The duodenum tin therefore be subdivided into four segments: the superior, descending, horizontal, and ascending duodenum.
Of particular interest is the hepatopancreatic ampulla (ampulla of Vater). Located in the duodenal wall, the ampulla marks the transition from the anterior portion of the gastrointestinal tract to the mid-region, and is where the bile duct (through which bile passes from the liver) and the main pancreatic duct (through which pancreatic juice passes from the pancreas) join. This ampulla opens into the duodenum at a tiny volcano-shaped structure called the major duodenal papilla. The hepatopancreatic sphincter (sphincter of Oddi) regulates the flow of both bile and pancreatic juice from the ampulla into the duodenum.
The jejunum is about 0.9 meters (3 feet) long (in life) and runs from the duodenum to the ileum. Jejunum means "empty" in Latin and supposedly was so named by the ancient Greeks who noticed information technology was always empty at death. No clear demarcation exists between the jejunum and the final segment of the pocket-size intestine, the ileum.
The ileum is the longest part of the small intestine, measuring about 1.8 meters (six feet) in length. It is thicker, more vascular, and has more developed mucosal folds than the jejunum. The ileum joins the cecum, the first portion of the large intestine, at the ileocecal sphincter (or valve). The jejunum and ileum are tethered to the posterior abdominal wall past the mesentery. The large intestine frames these three parts of the small intestine.
Parasympathetic nervus fibers from the vagus nerve and sympathetic nerve fibers from the thoracic splanchnic nerve provide extrinsic innervation to the small intestine. The superior mesenteric avenue is its main arterial supply. Veins run parallel to the arteries and bleed into the superior mesenteric vein. Nutrient-rich claret from the pocket-sized intestine is then carried to the liver via the hepatic portal vein.
Histology
The wall of the small intestine is composed of the aforementioned four layers typically present in the alimentary system. Yet, 3 features of the mucosa and submucosa are unique. These features, which increase the absorptive surface expanse of the small intestine more than 600-fold, include round folds, villi, and microvilli (Figure 23.six.2). These adaptations are most abundant in the proximal two-thirds of the small intestine, where the bulk of absorption occurs.
Round folds
Also chosen plica circulares, or circular folds, are deep ridges in the mucosa and submucosa. Commencement virtually the proximal part of the duodenum and ending near the middle of the ileum, these folds facilitate absorption. Their shape causes the chyme to spiral, rather than movement in a straight line, through the small intestine. Spiraling slows the movement of chyme and provides the time needed for nutrients to be fully absorbed.
Villi
Inside the circular folds are pocket-size (0.5–1 mm long) hairlike vascularized projections called villi (singular = villus) that give the mucosa a furry texture. There are about 20 to 40 villi per square millimeter, increasing the surface area of the epithelium tremendously. The mucosal epithelium, primarily composed of absorptive cells, covers the villi. In addition to muscle and connective tissue to support its structure, each villus contains a capillary bed equanimous of one arteriole and one venule, as well as a lymphatic capillary called a lacteal. The breakdown products of carbohydrates and proteins (sugars and amino acids) can enter the bloodstream direct, but lipid breakdown products are absorbed by the lacteals and transported to the bloodstream via the lymphatic system.
Microvilli
As their name suggests, microvilli (singular = microvillus) are much smaller (ane µone thousand) than villi. They are cylindrical apical surface extensions of the plasma membrane of the mucosa's epithelial cells, and are supported by microfilaments inside those cells. Although their small size makes it difficult to run into each microvillus, their combined microscopic appearance suggests a mass of bristles, which is termed the castor border. Stock-still to the surface of the microvilli membranes are enzymes that terminate digesting carbohydrates and proteins. At that place are an estimated 200 million microvilli per square millimeter of pocket-sized intestine, greatly expanding the surface surface area of the plasma membrane and thus greatly enhancing absorption.
Intestinal Glands
In addition to the 3 specialized absorbent features simply discussed, the mucosa between the villi is dotted with deep crevices that each lead into a tubular intestinal gland (crypt of Lieberkühn), which is formed by cells that line the crevices (see Figure 23.vi.2). These produce intestinal juice, a slightly alkaline (pH seven.4 to 7.eight) mixture of water and mucus. Each day, near 0.95 to ane.9 liters (1 to 2 quarts) are secreted in response to the distention of the small intestine or the irritating furnishings of chyme on the intestinal mucosa.
The submucosa of the duodenum is the but site of the complex mucus-secreting duodenal glands (Brunner's glands), which produce a bicarbonate-rich alkali metal mucus that buffers the acidic chyme equally it enters from the stomach.
The roles of the cells in the small intestinal mucosa are detailed in Table 23.7.
| Cells of the Pocket-sized Intestinal Mucosa (Table 23.7) | ||
|---|---|---|
| Cell type | Location in the mucosa | Function |
| Absorptive | Epithelium/abdominal glands | Digestion and absorption of nutrients in chyme |
| Goblet | Epithelium/intestinal glands | Secretion of mucus |
| Paneth | Abdominal glands | Secretion of the bactericidal enzyme lysozyme; phagocytosis |
| G cells | Intestinal glands of duodenum | Secretion of the hormone intestinal gastrin |
| I cells | Abdominal glands of duodenum | Secretion of the hormone cholecystokinin (CCK), which stimulates release of pancreatic juices and bile |
| K cells | Intestinal glands | Secretion of the hormone glucose-dependent insulinotropic peptide, which stimulates the release of insulin |
| One thousand cells | Intestinal glands of duodenum and jejunum | Secretion of the hormone motilin, which accelerates gastric emptying, stimulates intestinal peristalsis, and stimulates the production of pepsin |
| S cells | Intestinal glands | Secretion of the hormone secretin |
Abdominal MALT
The lamina propria of the pocket-sized intestine mucosa is studded with quite a bit of MALT. In addition to solitary lymphatic nodules, aggregations of intestinal MALT, which are typically referred to as Peyer'south patches, are concentrated in the distal ileum, and serve to keep bacteria from entering the bloodstream. Peyer'south patches are most prominent in young people and go less distinct as y'all age, which coincides with the general action of our immune system.
External Website
Watch this animation that depicts the structure of the small intestine, and, in particular, the villi. Epithelial cells go on the digestion and absorption of nutrients and ship these nutrients to the lymphatic and circulatory systems. In the small intestine, the products of food digestion are absorbed by different structures in the villi. Which structure absorbs and transports fats?
Mechanical Digestion in the Small Intestine
The movement of intestinal polish muscles includes both sectionalisation and a course of peristalsis called migrating motility complexes. The kind of peristaltic mixing waves seen in the stomach are not observed here.
If you could meet into the small intestine when it was going through division, it would look as if the contents were being shoved incrementally back and forth, equally the rings of smooth muscle repeatedly contract and then relax. Segmentation in the small intestine does not force chyme through the tract. Instead, information technology combines the chyme with digestive juices and pushes food particles confronting the mucosa to be absorbed. The duodenum is where the about rapid segmentation occurs, at a rate of about 12 times per minute. In the ileum, segmentations are only about eight times per infinitesimal (Figure 23.half-dozen.3).
When most of the chyme has been absorbed, the pocket-sized intestinal wall becomes less distended. At this indicate, the localized segmentation procedure is replaced past transport movements. The duodenal mucosa secretes the hormone motilin, which initiates peristalsis in the form of a migrating motility circuitous. These complexes, which brainstorm in the duodenum, force chyme through a curt section of the modest intestine then stop. The next wrinkle begins a little bit farther down than the first, forces chyme a fleck farther through the small intestine, so stops. These complexes move slowly down the small intestine, forcing chyme on the way, taking around ninety to 120 minutes to finally reach the end of the ileum. At this point, the process is repeated, starting in the duodenum.
The ileocecal valve, a sphincter, is usually in a constricted state, just when motility in the ileum increases, this sphincter relaxes, assuasive food residue to enter the beginning portion of the large intestine, the cecum. Relaxation of the ileocecal sphincter is controlled by both nerves and hormones. First, digestive action in the stomach provokes the gastroileal reflex, which increases the forcefulness of ileal segmentation. 2d, the tummy releases the hormone gastrin, which enhances ileal motion, thus relaxing the ileocecal sphincter. After chyme passes through, astern pressure level helps close the sphincter, preventing backflow into the ileum. Because of this reflex, your lunch is completely emptied from your tummy and small intestine past the time yous eat your dinner. It takes near three to 5 hours for all chyme to leave the small intestine.
Chemic Digestion in the Minor Intestine
The digestion of proteins and carbohydrates, which partially occurs in the stomach, is completed in the small intestine with the assist of intestinal and pancreatic juices. Lipids get in in the intestine largely undigested, so much of the focus here is on lipid digestion, which is facilitated by bile and the enzyme pancreatic lipase.
Moreover, abdominal juice combines with pancreatic juice to provide a liquid medium that facilitates absorption. The intestine is likewise where most water is captivated, via osmosis. The small intestine's absorptive cells also synthesize digestive enzymes and and so place them in the plasma membranes of the microvilli. This distinguishes the small intestine from the stomach; that is, enzymatic digestion occurs non just in the lumen, just besides on the luminal surfaces of the mucosal cells.
For optimal chemical digestion, chyme must be delivered from the tum slowly and in pocket-sized amounts. This is considering chyme from the stomach is typically hypertonic, and if large quantities were forced all at in one case into the small intestine, the resulting osmotic water loss from the blood into the intestinal lumen would event in potentially life-threatening low blood volume. In addition, continued digestion requires an upward adjustment of the low pH of stomach chyme, along with rigorous mixing of the chyme with bile and pancreatic juices. Both processes take time, so the pumping activity of the pylorus must exist carefully controlled to prevent the duodenum from beingness overwhelmed with chyme.
Disorders of the…Small Intestine: Lactose Intolerance
Lactose intolerance is a condition characterized by indigestion caused past dairy products. It occurs when the absorptive cells of the minor intestine do not produce enough lactase, the enzyme that digests the milk sugar lactose. In most mammals, lactose intolerance increases with age. In contrast, some human being populations, most notably Caucasians, are able to maintain the power to produce lactase as adults.
In people with lactose intolerance, the lactose in chyme is not digested. Leaner in the large intestine ferment the undigested lactose, a process that produces gas. In addition to gas, symptoms include abdominal cramps, bloating, and diarrhea. Symptom severity ranges from mild discomfort to severe hurting; yet, symptoms resolve once the lactose is eliminated in feces.
The hydrogen breath examination is used to aid diagnose lactose intolerance. Lactose-tolerant people have very little hydrogen in their breath. Those with lactose intolerance breathe hydrogen, which is ane of the gases produced by the bacterial fermentation of lactose in the colon. Later the hydrogen is captivated from the intestine, it is transported through blood vessels into the lungs. In that location are a number of lactose-free dairy products available in grocery stores. In addition, dietary supplements are available. Taken with nutrient, they provide lactase to help assimilate lactose.
The Big Intestine
The large intestine is the terminal part of the comestible canal. The primary office of this organ is to cease absorption of nutrients and water, synthesize certain vitamins, as well every bit to grade, shop, and eliminate feces from the torso.
Structure
The large intestine runs from the appendix to the anus. It frames the small intestine on iii sides. Despite its beingness about half as long as the small intestine, it is chosen large because information technology is more than twice the diameter of the pocket-sized intestine, about 3 inches.
Subdivisions
The big intestine is subdivided into iv chief regions: the cecum, the colon, the rectum, and the anus. The ileocecal valve, located at the opening between the ileum and the large intestine, controls the menses of chyme from the small intestine to the large intestine.
Cecum
The first office of the large intestine is the cecum, a sac-like construction that is suspended junior to the ileocecal valve. Information technology is about vi cm (2.four in) long, receives the contents of the ileum, and continues the absorption of h2o and salts. The appendix (or vermiform appendix) is a winding tube that attaches to the cecum. Although the 7.vi-cm (3-in) long appendix contains lymphoid tissue, suggesting an immunologic function, this organ is generally considered vestigial. However, at least ane recent report postulates a survival reward conferred past the appendix: In diarrheal illness, the appendix may serve equally a bacterial reservoir to repopulate the enteric leaner for those surviving the initial phases of the disease. Moreover, its twisted anatomy provides a haven for the aggregating and multiplication of enteric bacteria. The mesoappendix, the mesentery of the appendix, tethers information technology to the mesentery of the ileum.
Colon
The cecum blends seamlessly with the colon. Upon entering the colon, the food residue first travels up the ascending colon on the right side of the abdomen. At the inferior surface of the liver, the colon bends to form the right colic flexure (hepatic flexure) and becomes the transverse colon. The region defined as hindgut begins with the last 3rd of the transverse colon and continues on. Nutrient residue passing through the transverse colon travels across to the left side of the abdomen, where the colon angles sharply immediately inferior to the spleen, at the left colic flexure (splenic flexure). From there, food residuum passes through the descending colon, which runs down the left side of the posterior abdominal wall. Afterwards inbound the pelvis inferiorly, it becomes the s-shaped sigmoid colon, which extends medially to the midline (Figure 23.6.4). The ascending and descending colon, and the rectum (discussed next) are located in the retroperitoneum. The transverse and sigmoid colon are tethered to the posterior intestinal wall by the mesocolon.
Homeostatic Imbalances – Colorectal Cancer
Each year, approximately 140,000 Americans are diagnosed with colorectal cancer, and another 49,000 die from information technology, making information technology 1 of the near mortiferous malignancies. People with a family history of colorectal cancer are at increased risk. Smoking, excessive alcohol consumption, and a diet loftier in animal fat and protein as well increase the take chances. Despite popular opinion to the contrary, studies back up the determination that dietary fiber and calcium practice not reduce the risk of colorectal cancer.
Colorectal cancer may exist signaled by constipation or diarrhea, cramping, abdominal pain, and rectal bleeding. Bleeding from the rectum may exist either obvious or occult (subconscious in feces). Since most colon cancers arise from benign mucosal growths called polyps, cancer prevention is focused on identifying these polyps. The colonoscopy is both diagnostic and therapeutic. Colonoscopy not simply allows identification of precancerous polyps, the procedure besides enables them to be removed before they become cancerous. Screening for fecal occult blood tests and colonoscopy is recommended for those over 50 years of historic period.
Rectum
Food residue leaving the sigmoid colon enters the rectum in the pelvis, well-nigh the third sacral vertebra. The final xx.3 cm (8 in) of the gastrointestinal tract, the rectum extends anterior to the sacrum and coccyx. Even though rectum is Latin for "straight," this structure follows the curved profile of the sacrum and has three lateral bends that create a trio of internal transverse folds called the rectal valves. These valves assistance divide the feces from gas to prevent the simultaneous passage of feces and gas.
Anal Culvert
Finally, nutrient residue reaches the last role of the big intestine, the anal canal, which is located in the perineum, completely exterior of the abdominopelvic cavity. This 3.8–v cm (1.5–2 in) long structure opens to the outside of the body at the anus. The anal culvert includes ii sphincters. The internal anal sphincter is made of smooth muscle, and its contractions are involuntary. The external anal sphincter is fabricated of skeletal muscle, which is under voluntary control. Except when defecating, both usually remain closed.
Histology
At that place are several notable differences betwixt the walls of the large and pocket-sized intestines (Effigy 23.6.5). For instance, few enzyme-secreting cells are found in the wall of the large intestine, and there are no circular folds or villi. Other than in the anal canal, the mucosa of the colon is simple columnar epithelium fabricated mostly of enterocytes (absorptive cells) and goblet cells. In addition, the wall of the large intestine has far more intestinal glands, which contain a vast population of enterocytes and goblet cells. These goblet cells secrete mucus that eases the movement of feces and protects the intestine from the effects of the acids and gases produced by enteric bacteria. The enterocytes blot water and salts too every bit vitamins produced by your intestinal leaner.
Anatomy
3 features are unique to the big intestine: teniae coli, haustra, and epiploic appendages (Effigy 23.6.six). The teniae coli are three bands of smooth musculus that make up the longitudinal muscle layer of the muscularis of the big intestine, except at its terminal finish. Tonic contractions of the teniae coli bunch upwards the colon into a succession of pouches called haustra (singular = hostrum), which are responsible for the wrinkled appearance of the colon. Attached to the teniae coli are small-scale, fatty-filled sacs of visceral peritoneum called epiploic appendages. The purpose of these is unknown. Although the rectum and anal canal accept neither teniae coli nor haustra, they practice take well-developed layers of muscularis that create the strong contractions needed for defecation.
The stratified squamous epithelial mucosa of the anal canal connects to the pare on the outside of the anus. This mucosa varies considerably from that of the rest of the colon to accommodate the high level of abrasion every bit carrion pass through. The anal canal'southward mucous membrane is organized into longitudinal folds, each called an anal column, which house a grid of arteries and veins. Two superficial venous plexuses are institute in the anal canal: one within the anal columns and ane at the anus.
Depressions between the anal columns, each called an anal sinus, secrete fungus that facilitates defecation. The pectinate line (or dentate line) is a horizontal, jagged ring that runs circumferentially simply beneath the level of the anal sinuses, and represents the junction between the hindgut and external peel. The mucosa to a higher place this line is fairly insensitive, whereas the surface area beneath is very sensitive. The resulting difference in hurting threshold is due to the fact that the upper region is innervated by visceral sensory fibers, and the lower region is innervated by somatic sensory fibers.
Bacterial Flora
Most bacteria that enter the alimentary canal are killed by lysozyme, defensins, HCl, or protein-digesting enzymes. However, trillions of bacteria live within the large intestine and are referred to as the bacterial flora. Virtually of the more than 700 species of these bacteria are nonpathogenic commensal organisms that cause no harm as long every bit they stay in the gut lumen. In fact, many facilitate chemical digestion and assimilation, and some synthesize certain vitamins, mainly biotin, pantothenic acid, and vitamin K. Some are linked to increased immune response. A refined system prevents these bacteria from crossing the mucosal barrier. Commencement, peptidoglycan, a component of bacterial cell walls, activates the release of chemicals by the mucosa's epithelial cells, which draft allowed cells, peculiarly dendritic cells, into the mucosa. Dendritic cells open the tight junctions between epithelial cells and extend probes into the lumen to evaluate the microbial antigens. The dendritic cells with antigens then travel to neighboring lymphoid follicles in the mucosa where T cells inspect for antigens. This process triggers an IgA-mediated response, if warranted, in the lumen that blocks the commensal organisms from infiltrating the mucosa and setting off a far greater, widespread systematic reaction.
Digestive Functions of the Big Intestine
The rest of chyme that enters the large intestine contains few nutrients except water, which is reabsorbed as the remainder lingers in the large intestine, typically for 12 to 24 hours. Thus, it may not surprise you lot that the large intestine can be completely removed without significantly affecting digestive functioning. For case, in astringent cases of inflammatory bowel disease, the large intestine tin exist removed by a procedure known as a colectomy. Often, a new fecal pouch can be crafted from the small intestine and sutured to the anus, but if non, an ileostomy can be created by bringing the distal ileum through the intestinal wall, allowing the watery chyme to exist nerveless in a bag-like adhesive apparatus.
Mechanical Digestion
In the large intestine, mechanical digestion begins when chyme moves from the ileum into the cecum, an action regulated by the ileocecal sphincter. Right later on you eat, peristalsis in the ileum forces chyme into the cecum. When the cecum is distended with chyme, contractions of the ileocecal sphincter strengthen. Once chyme enters the cecum, colon movements begin.
Mechanical digestion in the large intestine includes a combination of 3 types of movements. The presence of food residues in the colon stimulates a slow-moving haustral wrinkle. This blazon of movement involves sluggish segmentation, primarily in the transverse and descending colons. When a haustrum is distended with chyme, its muscle contracts, pushing the residue into the next haustrum. These contractions occur about every xxx minutes, and each terminal about 1 minute. These movements likewise mix the food residue, which helps the large intestine absorb h2o. The second type of move is peristalsis, which, in the large intestine, is slower than in the more proximal portions of the alimentary canal. The third type is a mass motion. These potent waves get-go midway through the transverse colon and quickly force the contents toward the rectum. Mass movements usually occur iii or four times per day, either while you eat or immediately afterward. Distension in the stomach and the breakdown products of digestion in the small-scale intestine provoke the gastrocolic reflex, which increases motility, including mass movements, in the colon. Cobweb in the diet both softens the stool and increases the power of colonic contractions, optimizing the activities of the colon.
Chemical Digestion
Although the glands of the large intestine secrete mucus, they do not secrete digestive enzymes. Therefore, chemical digestion in the large intestine occurs exclusively because of leaner in the lumen of the colon. Through the process of saccharolytic fermentation, leaner break down some of the remaining carbohydrates. This results in the discharge of hydrogen, carbon dioxide, and methyl hydride gases that create flatus (gas) in the colon; flatulence is excessive flatus. Each mean solar day, up to 1500 mL of flatus is produced in the colon. More is produced when you swallow foods such as beans, which are rich in otherwise indigestible sugars and complex carbohydrates like soluble dietary fiber.
Assimilation, Feces Formation, and Defecation
The small intestine absorbs nigh 90 percent of the water you ingest (either equally liquid or within solid food). The large intestine absorbs most of the remaining water, a process that converts the liquid chyme residuum into semisolid feces ("stool"). The large intestine also absorbs B vitamins, vitamin K, and sodium under the influence of the hormone aldosterone. Feces is composed of undigested food residues, unabsorbed digested substances, millions of bacteria, one-time epithelial cells from the GI mucosa, inorganic salts, and enough water to permit it pass smoothly out of the body. Of every 500 mL (17 ounces) of food residuum that enters the cecum each 24-hour interval, virtually 150 mL (5 ounces) become feces.
Feces are eliminated through contractions of the rectal muscles. You assistance this process by a voluntary procedure chosen Valsalva's maneuver, in which yous increase intra-intestinal pressure by contracting your diaphragm and abdominal wall muscles, and closing your glottis.
The process of defecation begins when mass movements force carrion from the colon into the rectum, stretching the rectal wall and provoking the defecation reflex, which eliminates feces from the rectum. This parasympathetic reflex is mediated by the spinal string. It contracts the sigmoid colon and rectum, relaxes the internal anal sphincter, and initially contracts the external anal sphincter. The presence of feces in the anal canal sends a signal to the encephalon, which gives you the pick of voluntarily opening the external anal sphincter (defecating) or keeping information technology temporarily closed. If you decide to delay defecation, information technology takes a few seconds for the reflex contractions to stop and the rectal walls to relax. The next mass motility volition trigger additional defecation reflexes until you defecate.
If defecation is delayed for an extended time, boosted h2o is absorbed, making the feces firmer and potentially leading to constipation. On the other hand, if the waste product matter moves too quickly through the intestines, non enough water is captivated, and diarrhea tin can result. This can be caused past the ingestion of foodborne pathogens. In general, nutrition, wellness, and stress decide the frequency of bowel movements. The number of bowel movements varies profoundly betwixt individuals, ranging from two or iii per twenty-four hour period to three or 4 per calendar week.
External Website
Past watching this animation yous volition see that for the various food groups—proteins, fats, and carbohydrates—digestion begins in different parts of the digestion organization, though all end in the same identify. Of the three major food classes (carbohydrates, fats, and proteins), which is digested in the oral cavity, the tum, and the small intestine?
Chapter Review
The 3 main regions of the small intestine are the duodenum, the jejunum, and the ileum. The small intestine is where digestion is completed and well-nigh all assimilation occurs. These two activities are facilitated by structural adaptations that increase the mucosal surface area by 600-fold, including circular folds, villi, and microvilli. In that location are around 200 million microvilli per square millimeter of small-scale intestine, which comprise brush border enzymes that consummate the digestion of carbohydrates and proteins. Combined with pancreatic juice, intestinal juice provides the liquid medium needed to farther digest and absorb substances from chyme. The small intestine is also the site of unique mechanical digestive movements. Partition moves the chyme back and forth, increasing mixing and opportunities for absorption. Migrating motility complexes propel the residual chyme toward the large intestine.
The main regions of the large intestine are the cecum, the colon, and the rectum. The large intestine absorbs water and forms carrion, and is responsible for defecation. Bacterial flora break down additional carbohydrate residuum, and synthesize certain vitamins. The mucosa of the large abdominal wall is generously endowed with goblet cells, which secrete fungus that eases the passage of feces. The entry of carrion into the rectum activates the defecation reflex.
Interactive Link Questions
Watch this animation that depicts the structure of the small intestine, and, in particular, the villi. Epithelial cells continue the digestion and absorption of nutrients and send these nutrients to the lymphatic and circulatory systems. In the small intestine, the products of food digestion are absorbed by dissimilar structures in the villi. Which structure absorbs and transports fats?
Answers may vary.
By watching this animation, you will encounter that for the various nutrient groups—proteins, fats, and carbohydrates—digestion begins in different parts of the digestion organisation, though all end in the aforementioned place. Of the iii major food classes (carbohydrates, fats, and proteins), which is digested in the mouth, the stomach, and the small intestine?
Answers may vary.
Review Questions
Critical Thinking Questions
1. Explain how nutrients absorbed in the small intestine pass into the general circulation.
two. Why is information technology important that chyme from the breadbasket is delivered to the small-scale intestine slowly and in small amounts?
three. Describe iii of the differences betwixt the walls of the large and small intestines.
References
American Cancer Society (The states). Cancer facts and figures: colorectal cancer: 2011–2013 [Internet]. c2013 [cited 2013 Apr three]. Available from: http://www.cancer.org/Enquiry/CancerFactsFigures/ColorectalCancerFactsFigures/colorectal-cancer-facts-figures-2011-2013-folio.
The Nutrition Source. Cobweb and colon cancer: following the scientific trail [Internet]. Boston (MA): Harvard Schoolhouse of Public Health; c2012 [cited 2013 Apr 3]. Available from: http://www.hsph.harvard.edu/nutritionsource/diet-news/cobweb-and-colon-cancer/index.html.
Centers for Disease Control and Prevention (US). Morbidity and mortality weekly report: notifiable diseases and mortality tables [Cyberspace]. Atlanta (GA); [cited 2013 April iii]. Bachelor from: http://www.cdc.gov/mmwr/preview/mmwrhtml/mm6101md.htm?s_cid=mm6101md_w.
Glossary
- anal canal
- last segment of the big intestine
- anal column
- long fold of mucosa in the anal canal
- anal sinus
- recess between anal columns
- appendix
- (vermiform appendix) coiled tube fastened to the cecum
- ascending colon
- offset region of the colon
- bacterial flora
- bacteria in the large intestine
- brush edge
- fuzzy advent of the pocket-sized intestinal mucosa created by microvilli
- cecum
- pouch forming the beginning of the big intestine
- circular fold
- (also, plica circulare) deep fold in the mucosa and submucosa of the small-scale intestine
- colon
- part of the large intestine between the cecum and the rectum
- descending colon
- part of the colon between the transverse colon and the sigmoid colon
- duodenal gland
- (too, Brunner's gland) mucous-secreting gland in the duodenal submucosa
- duodenum
- first part of the small intestine, which starts at the pyloric sphincter and ends at the jejunum
- epiploic appendage
- small sac of fat-filled visceral peritoneum attached to teniae coli
- external anal sphincter
- voluntary skeletal muscle sphincter in the anal canal
- feces
- semisolid waste material product of digestion
- flatus
- gas in the intestine
- gastrocolic reflex
- propulsive motion in the colon activated by the presence of nutrient in the stomach
- gastroileal reflex
- long reflex that increases the strength of division in the ileum
- haustrum
- minor pouch in the colon created by tonic contractions of teniae coli
- haustral contraction
- boring segmentation in the large intestine
- hepatopancreatic ampulla
- (besides, ampulla of Vater) seedling-similar signal in the wall of the duodenum where the bile duct and main pancreatic duct unite
- hepatopancreatic sphincter
- (also, sphincter of Oddi) sphincter regulating the flow of bile and pancreatic juice into the duodenum
- ileocecal sphincter
- sphincter located where the small intestine joins with the large intestine
- ileum
- cease of the small intestine between the jejunum and the large intestine
- internal anal sphincter
- involuntary smooth musculus sphincter in the anal canal
- intestinal gland
- (also, catacomb of Lieberkühn) gland in the small-scale intestinal mucosa that secretes intestinal juice
- intestinal juice
- mixture of water and mucus that helps absorb nutrients from chyme
- jejunum
- middle part of the small intestine between the duodenum and the ileum
- lacteal
- lymphatic capillary in the villi
- large intestine
- terminal portion of the gastrointestinal tract
- left colic flexure
- (besides, splenic flexure) signal where the transverse colon curves beneath the inferior finish of the spleen
- main pancreatic duct
- (also, duct of Wirsung) duct through which pancreatic juice drains from the pancreas
- major duodenal papilla
- point at which the hepatopancreatic ampulla opens into the duodenum
- mass movement
- long, slow, peristaltic wave in the large intestine
- mesoappendix
- mesentery of the appendix
- microvillus
- small projection of the plasma membrane of the absorptive cells of the small abdominal mucosa
- migrating motion circuitous
- form of peristalsis in the pocket-size intestine
- motilin
- hormone that initiates migrating motility complexes
- pectinate line
- horizontal line that runs like a ring, perpendicular to the inferior margins of the anal sinuses
- rectal valve
- one of three transverse folds in the rectum where feces is separated from flatus
- rectum
- part of the big intestine between the sigmoid colon and anal canal
- right colic flexure
- (too, hepatic flexure) point, at the inferior surface of the liver, where the ascending colon turns abruptly to the left
- saccharolytic fermentation
- anaerobic decomposition of carbohydrates
- sigmoid colon
- terminate portion of the colon, which terminates at the rectum
- small intestine
- section of the alimentary canal where most digestion and absorption occurs
- tenia coli
- ane of 3 smooth muscle bands that make upwards the longitudinal muscle layer of the muscularis in all of the large intestine except the final end
- transverse colon
- part of the colon between the ascending colon and the descending colon
- Valsalva'due south maneuver
- voluntary contraction of the diaphragm and abdominal wall muscles and closing of the glottis, which increases intra-abdominal pressure and facilitates defecation
- villus
- project of the mucosa of the small intestine
Solutions
Answers for Critical Thinking Questions
- Nutrients from the breakup of carbohydrates and proteins are absorbed through a capillary bed in the villi of the small-scale intestine. Lipid breakdown products are absorbed into a lacteal in the villi, and transported via the lymphatic system to the bloodstream.
- If big quantities of chyme were forced into the small intestine, it would effect in osmotic water loss from the blood into the abdominal lumen that could cause potentially life-threatening low claret volume and erosion of the duodenum.
- The mucosa of the small intestine includes circular folds, villi, and microvilli. The wall of the large intestine has a thick mucosal layer, and deeper and more abundant mucus-secreting glands that facilitate the shine passage of feces. There are three features that are unique to the big intestine: teniae coli, haustra, and epiploic appendages.
Source: https://open.oregonstate.education/aandp/chapter/23-6-the-small-and-large-intestines/
0 Response to "Artlabeling Activity the Stomach Structure of the Stomach Wall 2 of 2"
Post a Comment