== Tongue ==
[[File:HistologicChapter11Tongue-anatomy.jpg|thumb|200px|Tongue Anatomy]]
The tongue is divided anatomically into an anterior 2/3 or body, and a posterior 1/3 or root by a posteriorly oriented V-shaped groove, the sulcus terminalis. A pit, the foramen caecum, is located at the apex of the sulcus terminalis. It represents the embryonic point of origin of the thyroid gland.
== Salivary Glands ==
[[File:HistologicChapter11SalivaryGlands.jpg|thumb|200px|Salivary Glands]]
The salivary glands are divided into two main divisions. The intramural or minor salivary glands (labial, buccal, and palatine) lie within the submucosal connective tissue of the oral cavity. These intrinsic glands secrete continuously to moisten the oral cavity. Three pairs of extrinsic or major salivary glands, the parotid, the submandibular, and the sublingual, lie outside the walls of the oral cavity and must convey their secretions to the mouth by means of excretory ducts which pass through the mucosa. The major glands secrete intermittently in response to specific stimuli. The major salivary glands are classified as compound tubuloalveolar, exocrine glands. The secretory alveoli of the parotid glands are wholly serous, producing a watery secretion; those of the submandibular glands are mixed, although preponderantly serous, and those of the sublingual glands are mixed but preponderantly mucous.
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== Pancreas ==
[[File:HistologicChapter11Pancreas.jpg|thumb|200px|Pancreas]]
The pancreas is both an exocrine and an endocrine gland. The exocrine pancreas is a compound tubuloacinar gland consisting of serous secretory cells arranged in acini. As a gland of external secretion, the serozymogenic products of the acini are conveyed to the lumen of the duodenum by means of a main excretory duct, the main pancreatic duct, and by an accessory pancreatic duct which in some individuals opens into the main duct before reaching the duodenum. The main duct extends the entire length of the gland receiving branches, interlobular ducts, from the individual lobules. Striated ducts are lacking in the pancreas. The only intralobular ducts are long narrow intercalated ducts with a low simple cuboidal epithelium, which open directly into interlobular ducts .
The endocrine pancreas secretes insulin and glucagon directly into the blood stream (capillaries) from irregularly dispersed aggregates of cells forming the pancreatic islets (of Langerhans). The islets are composed of anastomosing cords of cells, numerous capillaries and a fine framework of reticular fibers. They are usually directly surrounded by pancreatic acini, but islets can occur in the interlobular connective tissue. The islets range in size from only a few cells to islets containing thousands of cells. In the latter instance they are large enough to see with the unaided eye. The islets are more numerous in the tail than in any other portion of the pancreas.
== Esophagus ==
[[File:HistologicChapter11DigestiveSystemDiagram.png|thumb|200px|Digestive System Diagram]]
=== Slide 131, Middle Esophagus (H&E) ===
== Stomach ==
[[File:HistologicChapter11Stomach.jpg|thumb|200px|Stomach]]
The gross subdivisions of the stomach are the cardia, the fundus, the corpus (main body) and the pyloric region consisting of a pyloric antrum, a pyloric canal and the pylorus. Only three distinct histological regions are present since the microanatomy of the fundus and corpus is similar. In all regions of the stomach, the surface epithelium consists of tall, columnar mucus-secreting cells. The muscular coat consists of three layers of irregularly arranged smooth muscle.
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== Small Imtestine Intestine ==[[File:HistologicChapter11Intestine.jpg|thumb|200px|Small and Large Intestines]]
The three subdivisions of the small intestine are the duodenum, the jejunum and the ileum. The general microscopic structure is similar in all three parts. In the 21 to 23 feet of small intestine, digestion of food materials continues after leaving the stomach, and its selective absorption occurs.
A. === Mucosa===
1. Epithelium. The absorptive process is a function of columnar epithelial cells that possess on their surface numerous microvilli forming a striated border. The microvilli increase the surface area of the lining cells at least twenty fold. Irregularly scattered among the absorptive cells are goblet cells that provide a protective secretion of mucus. The absorptive intestinal cells and goblet cells are distinctive for the small intestine, and they serve to distinguish the small intestine from the stomach that has only mucous columnar cells lining it.
2. Plicae circulares (= valves of Kerckring). Within the small intestine are circular folds of mucosa and submucosa that can be seen grossly. These visible folds, called plicae circulares or valves of Kerckring, are most prominent in the distal duodenum and proximal portion of the jejunum. They extend to the mid-ileum.
3. Villi. The mucosa also exhibits other projections or evaginations called intestinal villi that are covered mainly by columnar intestinal cells with striated borders and goblet cells. These finger-like processes, about 0.5 to 1.5 mm in height, increase the absorptive area of the small intestine in man at least five-fold. The center of each villus contains loose connective tissue of the lamina propria, a central lacteal (a lymphatic capillary), an arteriole and two venules, capillaries and slips of smooth muscle. In general the length and surface of the villi are maximal in the proximal duodenum, and they decrease gradually towards the terminal ileum.
4. Intestinal glands (crypts of Lieberkuhn). These simple tubular glands occupy the lamina propria proper. They open between the bases of the villi and extend for 0.1 to 0.7 mm through the lamina propria to the muscularis mucosae. The epithelium of the villi is continuous with the epithelium of the intestinal glands, but the striated border is progressively reduced towards the blind ends of the glands. In addition to absorptive cells and goblet cells within the crypts, cells of Paneth at the bases of the glands and scattered enteroendocrine cells (argentaffin cells) are also found.
5. Lamina propria. The intestinal glands are not as closely packed as are the gastric glands. A highly cellular lamina propria fills in the spaces between the glands or crypts and as previously mentioned, it also extends as a core of connective tissue into each villus. The main connective tissue fibers are argyrophilic reticular fibers. Elastic and delicate collagenous fibers are also present. Located within the lamina propria are large numbers of lymphocytes and plasma cells, other white cells, mast cells and scattered smooth muscle fibers. The lymphocytes may be organized into solitary nodules scattered all along the intestine. In particular, aggregates of nodules known as aggregated nodules or Peyer’s patches are found in the mucosa and submucosa of the ileum.
6. Muscularis mucosae. This thin region of smooth muscle is organized into an inner circular layer and an outer longitudinal layer, and sends strands of fibers into the lamina propria.
B. === Submucosa.===
1. The submucosa is a layer of loose connective tissue between the muscularis mucosae and the muscularis externa.
2. It contains the large blood vessels, lymphatics, nerve plexus and small parasympathetic ganglia (submucosal or Meissner’s plexuses).
3. Only in the duodenum are large duodenal glands (submucosal glands; Brunner’s glands) located in the submucosa.
C. === Muscularis externa.===
The muscularis externa of the small intestine has smooth muscle arranged into an inner circular layer and an outer longitudinal layer. In connective tissue between the two layers can be found the myenteric plexus containing parasympathetic ganglion cells and nerve fibers.
D. === Serosa.===
The serosa is typical, being a layer of mesothelial cells covering a thin loose connective tissue layer.
PYLORUS-DUODENAL JUNCTION
== Pylorus-Duodenal Junction == === Slide 150 Pylorus-duodenum, (H&E). ===
1. Find under low power the typical appearance of the pyloric stomach. Identify the simple columnar mucus-secreting epithelial cells covering the surface and the coiled pyloric glands towards the muscularis mucosae.
2. Scan the slide to identify the junction of the pyloric stomach with the duodenum. This is indicated by the appearance of mucous glands in the submucosa of the duodenum.
a. Note the somewhat abrupt change where typical stomach mucosa ends and small intestinal mucosa begins. Identify:
(1) *villi and the covering epithelium of absorptive cells and goblet cells.
Note that the absorptive cells of the duodenum are much taller than the mucus-secreting cells of the stomach lining. (Goblet cells are not easily identified here.)
(2) *the striated border of the absorptive cells.
(3) *the lamina propria forming the core of the villi and supporting the short
intestinal glands (crypts of Lieberkuhn) below the villi.
(4) *the muscularis mucosae of the duodenum, continuous with that of the stomach.
(5) *the duodenal glands (of Brunner) lying beneath the muscularis mucosae.
These highly branched tubular mucus-secreting glands reside in the submucosa, and their ducts penetrate the muscularis mucosae to empty into the bases of intestinal glands. The glands may extend for a short distance into the submucosa of the pyloric stomach.
(6) *the pyloric sphincter, formed by a great thickening of the circular muscle layer and inclusion of the inner oblique muscle layer of the stomach. The outer longitudinal layer does not take part in the sphincter.
(7) *the muscularis externa of the duodenum, an inner circular and an outer longitudinal layer, continuous with those of the stomach.
(8) *serosa.
DUODENUM<peir-vm>UAB-Histology-00150</peir-vm>
On slide 140, == Duodenum (PASH):==
1. Observe the plicae circulares at lowest power.=== Slide 140, Duodenum (PASH) ===
2. Examine Observe the slide to note the numerous villi and occasional solitary lymphatic nodulesplicae circulares at lowest power.
3. With high power, study Examine the epithelium of slide to note the numerous villi. Observe the PAS-positive goblet cells and the columnar intestinal absorptive cells with their striated border. The glycoproteins and mucopolysaccharides of the glycocalyx (surface coat) associated with the microvilli (striated border) accounts for the PAS-positive nature of the striated border. The villi contain a connective tissue core, the lamina propria, as described previouslyoccasional solitary lymphatic nodules.
4. The intestinal glands (= crypts of Lieberkuhn) open between With high power, study the bases epithelium of the villi. The glands extend to Observe the muscularis mucosae. Only a few PAS-positive goblet cells are present in and the lower region columnar intestinal absorptive cells with their striated border. The glycoproteins and mucopolysaccharides of the glands. Cells glycocalyx (surface coat) associated with the microvilli (striated border) accounts for the PAS-positive nature of Paneth are not easily identified; their secretion has been liberated and few or no granules remainthe striated border. (See slide 139 belowThe villi contain a connective tissue core, the lamina propria, as described previously.)
5. Beneath the muscularis mucosae the submucosa contains the mucus-secreting, highly branched tubular duodenal The intestinal glands (= Brunner’s glands, = submucosal glands crypts of Lieberkuhn) open between the bases of the duodenum)villi. The glands extend to the muscularis mucosae. Only a few goblet cells of these glands are PAS-positive but the mucin stains less intensely than does present in the mucin lower region of the goblet cellsglands. The ducts Cells of these glands empty into crypts of Lieberkuhn after they penetrate the muscularis mucosaePaneth are not easily identified; their secretion has been liberated and few or no granules remain. (See slide 139 below.)
Study slide 139Beneath the muscularis mucosae the submucosa contains the mucus-secreting, Duodenum highly branched tubular duodenal glands (H&E= Brunner’s glands, = submucosal glands of the duodenum). (The mucosa is disrupted from postcells of these glands are PAS-mortem changes, villi may not be presentpositive but the mucin stains less intensely than does the mucin of the goblet cells. The ducts of these glands empty into crypts of Lieberkuhn after they penetrate the muscularis mucosae.)
1<peir-vm>UAB-Histology-00140</peir-vm> === Slide 139, Duodenum (H&E) === (The mucosa is disrupted from post-mortem changes, villi may not be present. ) Observe in favorable areas the straight tubular crypts with the large pyramidal or columnar cells of Paneth at their blind ends. Paneth cells are easily identified by the large acidophilic granules in the apical regions of the cells. The round or oval nucleus is located at the base of the cell.
2. By diligent searching, find an enteroendocrine cell (argentaffin cell) with the orange-staining granules located in an infra-nuclear position, i.e., between the nucleus and the base of the cell. These cells are smaller than Paneth cells and their granules are less coarse. A variety of enzymes are secreted into capillaries by such cells. This slide is excellent for studying duodenal (Brunner’s) glands. Note especially how the ducts open into the crypts. In the connective tissue between the two muscle layers of the muscularis externa find ganglion cells which belong to the myenteric plexus.
3. This slide is excellent for studying duodenal (Brunner’s) glands. Note especially how the ducts open into the crypts.<peir-vm>UAB-Histology-00139</peir-vm>
4. In the connective tissue between the two muscle layers of the muscularis externa find ganglion cells which belong to the myenteric plexus.== Jejunum ==
JEJUNUMThe jejunum lacks the submucosal glands of Brunner.
1. The jejunum lacks the submucosal glands of Brunner.=== Slide 142, Jejunum (PASH) ===
2. On slide 142, Jejunum (PASH) identify Identify with medium power the villi on the plicae circulares, the villi located in between the plicae circulares, the lamina propria, the intestinal glands (crypts of Lieberkuhn), the submucosa and the muscularis externa.
3. The villi of the human jejunum are said to have rounded ends, but they appear somewhat variable according to the plane of sectioning.
4. Observe the goblet cells with high power. The nuclei of these cells often stain more darkly than the nuclei of adjacent absorptive cells. They are also usually narrower or more triangular in shape than in the absorptive cells.
5. In favorable regions one can locate the PAS-stained basement membrane on which the epithelial cells rest.
6. Identify the striated border and note its reduction or absence on cells at the bases of the crypts of Lieberkuhn. Small apical granules in the gland cells may form a somewhat uniform PAS stained border, but do not confuse this with a striated border. The gland cells are shorter or less columnar than the cells lining the villi.
ILEUM<peir-vm>UAB-Histology-00142</peir-vm> == Ileum ==
This is the longest part of the small intestine. As in the jejunum, submucosal glands of Brunner are lacking.
Aggregated nodules (Peyer’s patches) form a characteristic feature of the ileum.
1. === Slide 168, Ileum (H&E). This is probably from a rhesus monkey; its structure is generally similar to human, but it is small enough in diameter so that a complete cross section can be obtained for study.===
This is probably from a. Observe most of the features described rhesus monkey; its structure is generally similar to human, but it is small enough in diameter so that a complete cross section can be obtained for duodenum and jejunum. Note especially the several plicae circulares with the core of submucosa extending into them and the muscularis mucosae forming the boundary between mucosa and submucosa as usualstudy.
b*Observe most of the features described for duodenum and jejunum. Paneth cells are not conspicuous (will be seen better in slide 172 below)Note especially the several plicae circulares with the core of submucosa extending into them and the muscularis mucosae forming the boundary between mucosa and submucosa as usual.
c. Aggregated nodules *Paneth cells are not conspicuous (Peyer’s patches) form a prominent feature of the ileum. These are aggregates of lymphatic nodules, present will be seen better in the anti- mesenteric wall of the ileum. They originate in the lamina propria, may extend through the muscularis mucosae into the submucosa. If they reach the lumen of the ileum, they are covered by a layer of cells (called M-cellsslide 172 below), not villi.
2*Aggregated nodules (Peyer’s patches) form a prominent feature of the ileum. Slide 172 These are aggregates of lymphatic nodules, Ileumpresent in the anti- mesenteric wall of the ileum. They originate in the lamina propria, human may extend through the muscularis mucosae into the submucosa. If they reach the lumen of the ileum, they are covered by a layer of cells (H&Ecalled M-cells). This was removed during surgery and is therefore free of postmortem changes, not villi.
a. Identify all features of the ileum. Note, only a small part of a Peyer’s patch is present.b. Study the villi that show typical normal structure. The striated border is prominent.<peir-vm>UAB-Histology-00168</peir-vm>
c. Note especially the Paneth cells=== Slide 172, whose granules stain a brilliant pink. AlsoIleum, in the lamina propria, observe eosinophils containing reddish granules.human (H&E) ===
d. Look for submucosal plexuses (Meissner’s) as well as for myenteric plexusesThis was removed during surgery and is therefore free of postmortem changes.
APPENDIX*Identify all features of the ileum. Note, only a small part of a Peyer’s patch is present.
1. As a blind diverticulum of *Study the cecum, the appendix has a small and generally irregular lumenvilli that show typical normal structure. The appendix often exhibits inflammation accompanied by infiltration of large numbers of neutrophils. A constant feature of the appendix striated border is the vast amount of lymphatic tissue presentprominent.
2*Note especially the Paneth cells, whose granules stain a brilliant pink. Scan slide 145Also, Appendix (H&E) to find in the 4 layers: mucosalamina propria, submucosa, muscularis externa, and serosa. The tissue may show postmortem changes and artifacts of preparationobserve eosinophils containing reddish granules.
3. Note that the appendix lacks villi and plica circulares. The crypts of Lieberkuhn appear similar to the glands of the large intestine, although they may be more variable in length and less numerous per given area. The crypts contain absorptive columnar cells, goblet cells, and occasional cells of Paneth and enteroendocrine cells. Find a favorable crypt *Look for study to identify these cell types. The striated border of the simple columnar surface cell is thin. The enteroendocrine cells are difficult to identify on our preparations but they are perhaps more numerous in the appendix submucosal plexuses (5 to 10 per glandMeissner’s) than in the small intestine. Mitotic figures are easily found in the lower ends of the glandsas well as for myenteric plexuses.
4. The lamina propria is completely infiltrated by lymphocytes. Note how lymphatic nodules may interrupt the somewhat poorly developed muscularis mucosae.<peir-vm>UAB-Histology-00172</peir-vm>
5. Other prominent cells present here are active macrophages. The “foamy” granulated or vacuolated cytoplasm of these cells stains a darker red than that in other cells of the lamina propria. The smaller cells with bilobed nuclei and reddish cytoplasm are eosinophils.== Appendix ==
6. Examine slide 146, Appendix (Masson’s stain). No special features are present, but note As a blind diverticulum of the blue-stained connective tissuececum, the myenteric plexus with ganglion cells, appendix has a small and the lymphatic nodulesgenerally irregular lumen. The granules in the cells appendix often exhibits inflammation accompanied by infiltration of large numbers of Paneth are darkly stainedneutrophils. Observe that A constant feature of the circular layer of smooth muscle appendix is thicker and better developed than the longitudinal layervast amount of lymphatic tissue present.COLON
1. In the colon=== Slide 145, the 4 layers of the alimentary tract are present, but the longitudinal layer of the muscularis externa is modified to form 3 separate thick longitudinal bands of muscle called the taeniae coli, between which is a thin layer of muscle.Appendix (H&E) ===
2. The straight tubular intestinal glands Scan slide 145, Appendix (crypts of LieberkuhnH&E) are longer and more numerous than in to find the small intestine4 layers: mucosa, submucosa, and they contain more numerous mucous goblet cells. Some glands almost appear to consist of goblet cells only. Plicae circularesmuscularis externa, villi and Paneth cells are lackingserosa. The mucosa tissue may show postmortem changes and artifacts of the human colon therefore has a rather smooth surface. The simple columnar epithelial cells still exhibit a thin absorptive striated borderpreparation.
3Note that the appendix lacks villi and plica circulares. The lamina propria crypts of the colon is Lieberkuhn appear similar to the lamina propria glands of the small large intestine, although they may be more variable in length and less numerous per given area. The crypts contain absorptive columnar cells, goblet cells, and occasional cells of Paneth and enteroendocrine cells. Find a favorable crypt for study to identify these cell types. Lymphocytes The striated border of the simple columnar surface cell is thin. The enteroendocrine cells are abundant with scattered lymphatic nodules either limited difficult to identify on our preparations but they are perhaps more numerous in the lamina propria or extending through appendix (5 to 10 per gland) than in the muscularis mucosae into the submucosasmall intestine. Peyer’s patches Mitotic figures are absent. The muscularis mucosae presents two layers easily found in the lower ends of smooth muscle, an inner circular layer, and an outer longitudinal layerthe glands.
4. Slide 144 Colon, (PASH, rhesus monkey, complete cross-section, shows three taeniae coli). Scan the slide to see these three taeniae. Mucigen of the goblet cells The lamina propria is very well demonstratedcompletely infiltrated by lymphocytes. Study this slide for the features noted above. Find an area where the glands are cut longitudinally to see that they are straight and extend almost to Note how lymphatic nodules may interrupt the somewhat poorly developed muscularis mucosae. Study the surface epithelium to see that in some areas more goblet cells appear in the glands than on the luminal surface between glands. Large blood vessels occur in the submucosa. Temporary folds are present. Note that the surface of the mucosa is smooth; the colon lacks villi.
5Other prominent cells present here are active macrophages. The “foamy” granulated or vacuolated cytoplasm of these cells stains a darker red than that in other cells of the lamina propria. The smaller cells with bilobed nuclei and reddish cytoplasm are eosinophils. <peir-vm>UAB-Histology-00145</peir-vm> === Slide 146, Appendix (Masson’s stain) === No special features are present, but note the blue-stained connective tissue, the myenteric plexus with ganglion cells, and the lymphatic nodules. The granules in the cells of Paneth are darkly stained. Observe that the circular layer of smooth muscle is thicker and better developed than the longitudinal layer. <peir-vm>UAB-Histology-00146</peir-vm> == Colon == In the colon, the 4 layers of the alimentary tract are present, but the longitudinal layer of the muscularis externa is modified to form 3 separate thick longitudinal bands of muscle called the taeniae coli, between which is a thin layer of muscle. The straight tubular intestinal glands (crypts of Lieberkuhn) are longer and more numerous than in the small intestine, and they contain more numerous mucous goblet cells. Some glands almost appear to consist of goblet cells only. Plicae circulares, villi and Paneth cells are lacking. The mucosa of the human colon therefore has a rather smooth surface. The simple columnar epithelial cells still exhibit a thin absorptive striated border. The lamina propria of the colon is similar to the lamina propria of the small intestine. Lymphocytes are abundant with scattered lymphatic nodules either limited to the lamina propria or extending through the muscularis mucosae into the submucosa. Peyer’s patches are absent. The muscularis mucosae presents two layers of smooth muscle, an inner circular layer, and an outer longitudinal layer. === Slide 144 Colon, (PASH, rhesus monkey, complete cross-section, shows three taeniae coli) === Scan the slide to see these three taeniae. Mucigen of the goblet cells is very well demonstrated. Study this slide for the features noted above. Find an area where the glands are cut longitudinally to see that they are straight and extend almost to the muscularis mucosae. Study the surface epithelium to see that in some areas more goblet cells appear in the glands than on the luminal surface between glands. Large blood vessels occur in the submucosa. Temporary folds are present. Note that the surface of the mucosa is smooth; the colon lacks villi. <peir-vm>UAB-Histology-00144</peir-vm> === Slide 180 Colon, (H&E, human, surgical specimen) === Slide 180 Colon, (H&E, human, surgical specimen) is part of a cross-section spread open. One taenia coli is present at one end of the section. No postmortem changes are present. Again study the glands; in longitudinal sections, note their openings into the lumen of the colon and the continuity of their epithelium with the intact surface epithelium. Study other features as above. Serosa (visceral peritoneum) covers the section. 6. <peir-vm>UAB-Histology-00180</peir-vm> === Slide 173 Colon, (H&E, human) === Slide 173 Colon, (H&E, human), is also a cross-section of the colon spread open. Much of the surface epithelium and outer parts of glands are missing, but aside from this, identify features that are listed above. Look for cell bodies of neurons in the submucosal plexuses (of Meissner). Determine if a band of the taenia coli has been sectioned and is present on your slide.RECTUM<peir-vm>UAB-Histology-00173</peir-vm> == Rectum == === Slide 170, Upper Rectum (H&E) === Scan the slide to observe that the longitudinal layer of the muscularis externa forms a continuous layer. Taenia coli are no longer present. Observe that the structure of the upper rectum is similar to that of the colon except for the taenia coli. Identify the layers of the wall and the structures within each layer as in the colon.
1. Slide 170, Upper Rectum (H&E).<peir-vm>UAB-Histology-00170</peir-vm>
a. Scan the slide to observe that the longitudinal layer of the muscularis externa forms a continuous layer. Taenia coli are no longer present.== Anal Canal ==
b. Observe that the structure of the upper rectum is similar to that of the colon except No slides are available for the taenia coli. Identify the layers study, but you should be aware of the wall and the structures within each layer as some modifications in structure which occur in the colon.lower rectum (upper anal canal)
ANAL CANAL*The outer layer of smooth muscle is replaced by skeletal muscle that serves as the external anal sphincter.
1. No slides are available for study, but you should be aware *The circular layer of some modifications in structure which occur in smooth muscle becomes thickened to form the lower rectum (upper anal canal)involuntary internal sphincter.
a*Longitudinal (vertical) ridges appear which form the rectal columns (columns of Morgagni or anal columns). They usually overlie small veins that contribute to the formation of internal hemorrhoids. The outer layer Anal valves are transverse folds of smooth muscle is replaced by skeletal muscle that serves as the external anal sphinctermucosa which connect the rectal columns at their bases.
b*The intestinal glands (crypts) become shorter and disappear at the level of the anal valves. Here an abrupt transition leads into the lower anal canal. The circular layer of smooth muscle epithelium becomes thickened to form noncornified, stratified squamous. Near the involuntary internal sphincteranal orifice, the epithelium becomes cornified, highly pigmented and it contains hairs, sebaceous glands and sweat glands.
c. Longitudinal (vertical) ridges appear which form the rectal columns (columns of Morgagni or anal columns). They usually overlie small veins that contribute to the formation of internal hemorrhoids. Anal valves are transverse folds of the mucosa which connect the rectal columns at their bases.{{Template:Histologic}}
d. The intestinal glands (crypts) become shorter and disappear at the level of the anal valves. Here an abrupt transition leads into the lower anal canal. The epithelium becomes noncornified, stratified squamous. Near the anal orifice, the epithelium becomes cornified, highly pigmented and it contains hairs, sebaceous glands and sweat glands.[[Category:Histologic]]
