Small Intestines
Brunner's (submucosal) gland
brush border
cells: enteroendocrine (APUD), dividing enterocyte, enterocyte, Paneth
duodenum, jejunum, and ileum
intestinal gland (crypt of Lieberkuhn)
Peyer's patch
plicae circulares

Appendix-- be able to identify

Colon-- be able to identify this organ and the following components:
taeniae coli

Pancreas-- be able to identify this organ and the following components:
exocrine pancreas
endocrine pancreas (islets of Langerhans)

Liver-- be able to identify this organ and the following components:
anatomical lobule
bile canaliculus
bile ductule
central v.
hepatic a.
hepatic sinusoid
macrophage (Kupffer cell)
portal lobule
portal triad
portal v.


I. Small Intestine

The small intestine is divided into three segments: duodenum, jejunum, and ileum. It is structured to provide a large surface area for absorption. Histological differences occur gradually in the transition from one division to the other. Before discerning the major differences, you should be aware of the many similarities shared by the different segments.

Plica Circularis -
Folds in mucosa and submucosa
Villi - mucosal projections
Columnar epithelium - with increasing numbers of Goblet cells as it approaches the large intestine
Crypts of Lieberkuhn (intestinal glands)-
Paneth cells - eosinophilic, granular cells at base of intestinal glands of Lieberkuhn
Enteroendocrine cells (APUD cells)








Villus in the duodenum showing the simple columnar epithelium on the surface and the lacteal running down the center of the villus surrounded by lamina propria.




















Submucosal (Meissner's) plexus
(found scattered in the submucosa)

Muscularis Externa
inner circular smooth muscle layer
outer longitudinal smooth muscle layer
Myenteric (Auerbach's) plexus (found beween the two layers of the muscularis externa)

Connective tissue of mesentery or peritoneum is found on the outermost surface of the digestive tube within the peritoneal cavity. Mesothelium lines the outer surface of the parts that are not retroperitoneal.

As you look through the slides, be thinking of the four basic layers and how their components may differ from one part of the small intestine to the other.

Remember? - Text to Lab?









Slides #34 & #181
Using scanning power, identify the four layers of the intestinal wall. In many sections on slide #34, the epithelial lining has been detached so all you see on each villus is the lamina propria bounded by a naked basement membrane. Crypts of Lieberkuhn are intestinal glands, which contain Paneth cells, which in turn, contain eosinophilic granules. The submucosa is marked by pockets of Brunner's glands (mucous-producing glands). Slide #181 is best.







Slides #37 & #179
In contrast to the duodenum, villi are more abundant and the epithelium has a prominent brush border (abundant microvilli) with more Goblet cells. Also, there are no glands in the submucosa.











Slides #38, #180, & 184
Goblet cells continue to increase in number and villi are shorter than in the jejunum. An important aid in identification of the ileum is the frequent presence of Peyer's patches, (numerous lymphatic nodules). These extend in places into the mucosa, may have germinal centers or not, and are found mainly within the submucosa.

Helpful Hint
There are specific features to look for when attempting to identify a particular portion of the small intestine:
Duodenum - Brunner's glands in submucosa, some Goblet Cells
Jejunum - large plicae with many villi, more Goblet Cells
Ileum - aggregates of Peyer's patches, even more Goblet Cells

II. Large Intestine

The large intestine is about one-fifth the length and double the width of the small intestine. It includes cecum, appendix, colon and rectum. The dominant histological features are: a tremendous number of Goblet cells, lack of plicae and villi. Crypts of Lieberkuhn are still present but Paneth cells are sparse.

Slide #39
The most conspicuous trait of this structure is the infiltration of lymphocytes into the lamina propria and the nearly complete ring of lymphatic nodules that invade the submucosa The muscularis externa and serosa are typical.

Slide #40 There are no plicae or villi in the colon so the mucosal surface is relatively smooth. This surface is pitted with Crypts of Lieberkuhn, which contain a tremendous number of Goblet cells. The outer longitudinal layer of the muscularis externa varies in thickness. Its thickest region is seen grossly as three bands of muscle on the outside surface called taenia coli.

Anal Canal
Slide #83
Identify the junction of upper rectum (structure similar to colon, i.e. many goblets and columnar epithelium) and anal canal (stratified squamous epithelium). The epithelium becomes keratinized as the anal orifice is approached (not visible on all slides). Concurrent with keratinization, is the presence of hair follicles, sebaceous and sweat glands in the submucosa. Anal sphincters are represented by bundles of skeletal muscle in and below the submucosa.

III. Pancreas

Slides #42 & #128 This digestive gland is both exocrine and endocrine in function. The exocrine portion is represented by abundant, tubulo-alveolar serous acini. Observe the various sizes of ducts that accompany these glands. The endocrine pancreas is represented by islets of Langerhans. Often, islets are difficult to identify, but characteristically are seen by lower power as lightly stained, rounded masses of anastomosing cords of specialized epithelial cells, separated by capillaries. Individual islet cells (i.e. Alpha, Beta, Delta, etc.) are not distinguishable in these slides. The Beta cells of the islets produce insulin and will be discussed with the endocrine glands.

IV. Liver

Slide #44 (Pig Liver) The anatomical liver lobules are very easy to see in the pig liver because it contains a lot of connective tissue between lobules, as well as on the surface. Use it to become familiar with the various histologic features of the liver such as the portal triad, consisting of small branches of the portal vein, hepatic artery, and bile ductule. There may also be a smaller lymphatic vessel or two in the triad area, which are smaller than the blood vessels and contain no RBCs. Locate the central vein, sinusoids, and hepatocytes. Using the 43X objective you should be able to see small dark spots or threads between the hepatocytes, which are bile canaliculi. See demonstration.











Slide #45 (Human Liver) & Slide #182 (Monkey Liver ­ thin section) The architecture of the liver can be described in 2 ways. Try to understand the relationship between the anatomical and functional lobules. The anatomical lobule with the central vein in the center is useful for the study of liver morphology, but doesn't give much information about the functional units of the liver. With the portal triad in the center of the functional lobule and blood flowing from this center in all directions toward various "central veins" some liver disease can be better explained. For example reduced arterial blood supply would manifest itself initially by affecting the cells nearest the central vein while toxic substances in the blood would show up first in cells near the portal triad. Liver macrophages, called Kupffer Cells, are present in sinusoids.












Kidney-- be able to identify this organ and the following components:
vascular pole (part of renal corpuscle)
renal glomerulus (part of renal corpuscle)
Bowman's capsule (part of renal corpuscle)
urinary pole (part of renal corpuscle and beginning of PCT)
proximal convoluted tubule
proximal straight (thick descending) tubule
thin part of loop of Henle
distal straight (thick ascending) tubule
macula densa (part of DCT)
distal convoluted tubule
collecting duct
papillary duct (of Bellini)
renal papilla
minor calyx
afferent and efferent arterioles
arcuate vessels aa. and vv.
brush border
renal cortex and medulla
interlobar vessels
medullary ray
peritubular capillary
renal pyramid
vasa recta

Miscellaneous-- be able to identify
transitional epithelium
urinary bladder



Again, although we try every year to get better slides, some of our kidney slides are still inferior. If what you see doesn't look like the images in your atlases, call a faculty member over and he'll tell you if you should borrow someone else's slide.

Slide #85 (Human kidney) & Slide #109 (Mammalian kidney) & Slide #126 (Mammalian kidney) The first slides (#85 and #109) show the boundary between the cortex and medulla quite clearly. Extensions of the tubules of the medulla out into the cortex are obvious on this slide and are called medullary rays. (What tubules do you find in medullary rays?) You may see some arteries and veins at the junction of the cortex and medulla. See if you can figure out which arteries these might be.

















The outer cortical region of the kidney is recognized by the presence of renal corpuscles, [small capillary tufts (glomeruli {Glom}), enclosed in a structure called Bowman's Capsule]. Many renal tubules are seen in the cortex. Most are either proximal or distal convoluted tubules (PCT&DCT) and are arranged in irregular configurations.














Slides #85 #109, & #160 In the cortex find: renal corpuscle, vascular pole (entrance of afferent and efferent arterioles into glomerulus) and urinary pole (opening of bowman's space into a Proximal Convoluted Tubule) of the renal corpuscle (not always visible on some slides), glomerulus, proximal (PCT) and distal convoluted tubules (DCT). What is the juxtaglomerular apparatus? Locate a macula densa. What is its functional significance of each of these structures?



















This is a cross section of the Renal Medulla.The Medulla has no renal corpuscles and its tubules are generally thinner walled and straighter (thick and thin loops of Henle and collecting ducts). Be sure you can identify descending and ascending thick limbs of Henle's loop, thin loops of Henle, and collecting ducts. In the medulla find: collecting ducts, thin and thick portions of Henle's Loop, and blood vessels.


You do not have a slide like this one in your slide boxes but a demonstration will be available in the laboratory.
















In this logitudinal section of the Renal Medulla be sure you can identify descending and ascending thick limbs of Henle's loop and collecting ducts.


You do have slides in your slide boxes that look like this example or at least look similar to this one.















Excretory Passages



Slide #109 (Mammalian renal pelvis). You have already used this slide to look at the medulla. Now look at a calyx of the renal pelvis that is shown on this slide. Identify the transitional epithelium lining the renal pelvis. You should have seen this epithelium before ­ yes? - where?

















Higher magnification of renal papilla. In this image you can see papillary ducts (of Bellini) which empty into the renal calyx at the tip of the papilla. Papillary ducts are the result of the joining together of collecting ducts from the outer layers of the renal medulla forming ducts that are much thicker than collecting ducts. These thicker walled papillary ducts have a much higher columnar epithelium forming their walls.




















Slide #116 & #155 (Human ureter). The layers from the inside outward are: transitional epithelium, then lamina propria, which gradually gives way to the muscular layer, leaving no room for a submucosal layer. The muscular layer consists of an inner longitudinal and outer circular layer, not clearly shown in most slides.


















Slide #111 (Human urinary bladder). Similar structurally to the ureter except the smooth muscle layer is much thicker. In addition, a third outer longitudinal muscle layer is added (this third part of the muscular layer actually begins at the distal end of the ureter). The layering within the muscularis is not nearly as regular as in the intestine. You might see nerve tissue here. If so, what types of nerves are they? The Lamina Propria of the bladder is two layered with the outer layer (part two) being denser than the inner layer (part one) which is loose irregular CT
















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