mesenteric border, where the mesentery (a fold of peritoneum) is attached, is an uncovered interval for the entrance and exit of arteries, veins, nerves, and lymphatics which pass between the layers of mesentery. The Muscular Coat. — This consists of an outer longitudinal and an inner circular set of muscle fibers. These muscular layers propel the food along the intestines, as well as assist by their action in mixing it with the intestinal juices during active digestion. The Submucous Coat. — This is composed of areolar tissue and holds the mucous and muscular coats together. It contains the branches of the nutrient arteries to the bowel, previous to their distribution to the mucous coat, also the lymph channels and nerves. The lymph nodules are lodged in this layer; they are pear-shaped with their apex lying in the mucous membrane. These are called solitary follicles and Peyer's patches. The submucous coat in the small intestines extends up into the valvulse conniventes. In the duodenum the duodenal glands are lodged in the submucous coat. The Mucous Membrane. — This is lined with columnar epithelium. It is soft and velvety in appearance. The membrane is highly vascular near the beginning of the duodenum, and gradually becomes paler as the lower portion of the bowel is reached. The membrane is thrown into folds called valvulse comiiventes. Each fold is simply two layers of membrane folded upon itself and held together by fibrous tissue. They increase the absorbing surface of the intestinal canal and retard the progress of the food, according to some authors. They measure J to J an inch in width, and THE SMALL INTESTINE 267 extend to about one-half to two-thirds of the circum- ference of the bowel. The villi in the mucous mem- brane are described under absorption (see page 287). The Intestinal Glands or Glands of Lieberkiihn. — These are found in the mucous membrane throughout the small intestines. They are minute tubular depressions seen at the base of the villi and communicate with the surface of the mucous membrane, upon which they pour out a special secretion from the columnar cells which line them; the latter rest on a thin basement membrane, which is surrounded by capil- lary vessels. The Duodenal or Brunner's Glands. — They are found only in the duodenum. They are small, branched, tubular glands situated in the submucouscoat and open upon the mucous membrane of the duodenum by very small ducts. The Lymph Nodules. — ^They are divided into solitary fol- licles and Peyer's patches. Their bodies are in the sub- mucous coat and their apices in the mucous membrane. The solitary follicles are found throughout the mucous and submucous layers of the small and large intes- tines. They are small, round, whitish collections of areolar tissue rich in leukocytes or white corpuscles, and blood capillaries, and communicate through their base with the lacteals of the villi. Each consists of a lighter, central area, the germinal centre, where the leukocytes are reproducing, and an outer darker zone, Intestinal gland in longitudinal section. (Testut.) 268 THE ORGANS OF DIGESTION where the cells are more numerous and closely packed (Gray). Fig. 104 Duodenal gland. _ (Frey.) Fig. 105 Aggregated lymph nodule (Peyer's patch). (Testut.) Peyer's patches are regarded as collections of solitary follicles, seen as oval or rounded patches, placed THE LARGE INTESTINE 269 lengthwise with the bowel, measuring from i to 4 inches in length. Usually ten to sixty are present. They are found mostly in the ileum. Peyer's patches are highly inflamed in typhoid fever, and ulcerate, giving rise to hemorrhage and perforation of the bowel in severe attacks of the disease. (See Fig. 83, page 204, for blood-supply of the small intestines.) THE LARGE INTESTINE The large intestine is that part of the alimentary canal which extends from the end of the ileum to the anus; it is about 5^ feet long. It commences by a dilated part, the cecum, in the right iliac fossa, ascends to the under surface of the liver, then runs transversely across the abdomen to the vicinity of the spleen, descends to the left iliac fossa, and forms the sigmoid flexure, and finally passes along back of the pelvis to end at the anus. The Cecum. — ^The cecum is the large cul-de-sac which is the beginning of the large intestine, and is about 3 inches broad and 2 j inches long. It is variously situated, being found upon and external to the psoas; upon the iliacus muscle it lies internal, on the pelvic brim, or entirely within the pelvis. In any of these positions it is entirely surrounded by peritoneum. The vermiform appendix comes off from the inner and back part of the cecum, near its lower end, and extends upward and inward behind it. This is a piece of gut of the diameter of a goose-quill, varying from 3 to 6 inches in length, curved upon itself, and ending in a blind extremity. It tapers gradually to its end, which is blunt, is completely invested by the peritoneum, which forms for it a mesentery (meso- appendix), and at its connection with the cecum is guarded by an imperfect valve (valve of Gerlach) . This is not always constant. The ileocecal valve guards the opening of the small 270 THE ORGANS OF DIGESTION intestine into the large gut. This junction is oblique and situated about 2 J inches above the lower extremity of the cecum. It is a double fold lying transversely to the long axis of the colon. Each fold of the valve is made up of the mucous and submucous coats, reinforced by some circular fibers from the muscular coat, of each portion of the gut, and is covered on the side toward the ileum with villi. The Colon. — The ascending colon runs from the cecum, above the ileocecal valve, upward to the under surface of the liver on the right side of the gall-bladder, and then turns forward and to the left to form the hepatic flexure. The peritoneum rarely forms for it a mesocolon; generally it covers only the front part and the sides. It occupies the right lumbar and hypochondriac regions. The transverse colon arches across the abdomen, the convexity looking toward the belly wall, and makes a sudden turn backward and downward beneath the spleen, forming the splenic flexure, and is completely invested by the peritoneum, which holds it to the anterior aspect of the pancreas and second portion of the duodenum; by two layers of peritoneum called the transverse mesocolon, the upper surface of which fuses with the posterior layer of the great omentum. It occupies the right hypochondriac, upper part of umbilical, and left hypochondriac regions. At the splenic flexure is attached the phrenocolic ligament, a fold of peritoneum extending to the diaphragm opposite the tenth or eleventh rib. The descending colon descends from the splenic flexure, to end at the left iliac fossa in the sigmoid flexure. It is covered in front and laterally by the peritoneum. It occupies the left hypochondriac and lumbar regions. The sigmoid flexure ends in the rectum. From the end of the descending colon it forms an S-shaped curve, ending opposite the left sacro-iliac joint. In THE LARGE INTESTINE 271 Fig. 106 The stomach and intestines, front view, the great omentum having been removed, and the liver turned up and to the right. The dotted line shows the normal position of the anterior border of the liver. The dart points to the foramen of Winslow. (Testut.) 272 THE ORGANS OF DIGESTION front of it are the belly wall and some coilsof small intestine. The peritoneum forms a loose mesocolon for it. It is the narrowest part of the colon. The Rectum. — This is the lowest part of the large intestine, and extends from the sigmoid flexure to the anus. It has been divided into three parts: the first part extends from the left sacro-iliac joint to the centre of the third piece of the sacrum; the second part, to the tip of the coccyx; and the third part, to the anus. The rectum is about 8 inches long and somewhat cylindrical in form, narrower above than the sigmoid flexure, but it enlarges as it descends, and just above the anus is remarkably dilated, forming the ampulla. The first part has a mesorectum; the second part is covered by peritoneum in front and laterally; the third part has no peritoneal covering. The cul-de-sac of Douglas (rectovaginal pouch) is the space in front of the rectum and behind the cervix of the uterus and upper fourth of the vagina. It is formed by the peritoneum reflected over the rectum to the vagina and uterus. In the male it is the space formed between the rectum and bladder, and is called the rectovesical space or pouch. The Structure of the Large Intestine. — The large intestine has three coats comprising its wall: A serous, muscular, and mucous. Its mucous membrane does not possess the valvulse conniventes nor villi; it is lined by columnar epithelium, and contains a large number of tubules lined by columnar epithelium; they resemble the glands of Lieberkiihn, and secrete a viscid fluid, rich in mucin. (See Fig. 83, page 204, for blood- supply of the large intestines.) QUESTIONS 273 QUESTIONS 1. What is the length of the alimentary canal? 2. What organs constitute the alimentary canal? 3. How many temporary teeth are there in the child? Perma- nent teeth in the adult? 4. Name the parts which form a tooth. 5. How are the temporary teeth divided as to name and number? The permanent teeth? 6. Give the position in the alveolar processes of the incisor teeth. The canines. The bicuspids. The molars. 7. Give the period of eruption of the temporary teeth. The permanent teeth. 8. What are the functions of the tongue? 9. What do you understand by the hard palate? The soft jpalate? 10. What is the isthmus of the fauces? 11. Give the location of the tonsils. 12. Name the salivary glands. 13. Which salivary gland is the largest? Give the weight of each. 14. When do the salivary glands pour out their secretions? And through what structure? 15. What structures does the pharynx communicate with? 16. How long is the pharynx, and what three parts is it subdivided into? 17. Which variety of epithelium lines the three portions of the pharynx? 18. What organ connects the pharynx with the stomach? 19. What is the distance from the incisor teeth to the cardiac opening in the stomach? 20. Name the portions of the stomach. 21 What orifices are found in the stomach and with what organs do they communicate? 22. How many borders and surfaces has the stomach? 23. Give its dimensions, weight, and average capacity. 24. Name the coats of the stomach wall. 25. How are the fibres in the muscular coat arranged? 26. Name the glands found in the membrane of the stomach. 27. What structures secrete the gastric juice? 28. Where are the pyloric glands in the stomach located? The cardiac glands? 29. Do the cardiac and pyloric glands communicate with the internal surface of the stomach? Through what structure is their secretion poured out? 30. Name the cells formed in a cardiac gland. 31. How long is the duodenum? 32. What portions of the alimentary canal does the duodenum connect and communicate with? 33. What are the divisions of the small intestine called? 34. Name the coats forming the structure of the small intestine. 35. Which variety of the epithelium lines the small intestine? 18 274 THE ORGANS OF DIGESTION 36. What arc the valvulsB conniventes? What is their function? 37. Where are the glands of Lieberkiihn found? Glands of Brunner? 38. Do the above glands communicate with the surface of the mucous membrane of the intestines? 39. Where are solitary lymph follicles found? Peyer's patches? 40. Describe a Peyer's patch. 41. How long is the large intestine? 42. What is the length of the appendix? 43. Name the portions of the colon. 44. How long is the rectum? 45. What is its lower opening called? 46. Name the coats of the large intestine. 47. What type of epithelium is present in the large intestine? 48. Are valvulae connivents found in the large intestine? 49. Does the mucous membrane of the colon contain glands? 50. What variety of secretion do the glands of the colon secrete?
Key Takeaways
- The small intestine contains villi and intestinal glands that aid in digestion.
- Peyer's patches are lymph nodules found in the ileum, which can be inflamed during typhoid fever.
- The large intestine has three coats: serous, muscular, and mucous.
Practical Tips
- Understand the structure of the intestines to better manage digestive issues or perform triage on injured individuals.
- Recognize the importance of maintaining a clean environment to prevent infections in the intestinal tract.
- Be aware of the presence of Peyer's patches and their potential for inflammation, which can lead to serious complications.
Warnings & Risks
- Inflammation of Peyer's patches can cause severe gastrointestinal issues, including hemorrhage and perforation.
- The large intestine is prone to blockages due to its narrowest part being the sigmoid flexure.
- Understanding the structure of the intestines is crucial for proper triage in survival situations.
Modern Application
While much of the anatomical information remains relevant, modern medical practices have improved diagnostic and treatment methods. Understanding the basic structure can still be vital for recognizing symptoms or performing initial assessments in a survival scenario.
Frequently Asked Questions
Q: What are Peyer's patches and why are they important?
Peyer's patches are lymph nodules found in the ileum of the small intestine. They play a crucial role in immune response, particularly against intestinal pathogens. In typhoid fever, these patches can become highly inflamed, leading to potential complications such as hemorrhage and perforation.
Q: How do the valvulae conniventes in the small intestine function?
The valvulae conniventes are folds in the mucous membrane of the small intestine that increase its surface area. They help to slow down the passage of food and enhance absorption by creating more contact between the intestinal walls and the contents.
Q: What is the main function of the large intestine?
The primary function of the large intestine is to absorb water, electrolytes, and some nutrients from the remaining indigestible food matter. It also forms and stores feces until they can be eliminated through defecation.