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The key objects to concentrate on during this lab are listed below. You need to learn 1) how to recognize each object, 2) understand it's primary functions, and 3) understand how structure is related to function.
Cells in Connective Tissue:
These additional structures are helpful to know for this lab. They are not required to know (yet), but may be helpful if you are asked to find the types of epithelia or connective tissue listed above. Other terms are cells that you have seen previously in Lab 1 but now have exited the blood stream and maybe changed a little—things like plasma cells (formerly lymphocytes), macrophages (formerly monocytes) and neutrophils (still neutrophils).
Connective Tissue & Epithelium
In this second lab the main emphasis is on connective tissue and epithelium. These tissues are two of the four basic tissue types (can you remember the other two?).
The connective tissues are characterized by cells that produce and maintain a wide variety of extracellular material around themselves. Extracellular material can be fluid, fibers, ground substance molecules, and minerals. It is the extracellular matrix that determines the physiological and physicochemical properties of the connective tissue, e.g., the difference between bone, cornea, and blood.
Connective tissue classification includes connective tissue proper: loose connective tissue (fasciae, framework of organs, sheaths of blood vessels and nerves, etc.), dense connective tissue (tendons, ligaments, cornea, dermis, periosteum, organ capsules), reticular connective tissue (lymphoid tissues and bone marrow), adipose tissue, and the specialized connective tissues of cartilage, bone and blood. The connective tissue literally holds our bodies together.
The main cell types in connective tissue proper include fibroblasts, macrophages, mast cells, plasma cells, fat cells and blood leukocytes.
Epithelia line all of the cavities and free surfaces of the body. The cells are tightly bound together to form barriers to water, solutes and cells, thus separating one body compartment from another. Epithelia are avascular. They depend on the underlying connective tissue (lamina propria) for nutrition. Please notice the relationship of the connective tissue to the epithelia in the slides for this lab.
After viewing these slides you should be able to recognize the following structures in addition to the connective tissue cell types mentioned above:
In the ovary you will find three different types of epithelium. The surface of the ovary is covered with simple cuboidal epithelium. Follow [1,1,1].
There are many developing follicles in this ovary. The cells surrounding the oocyte are stratified cuboidal in nature. Zoom out twice and then click link 2. This is an oocyte in a developing follicle. The follicular cells form a stratified cuboidal epithelium called the granulosa layer.
Zoom out twice. Try to recognize the veins in the ovary. They have an irregularly-shaped lumen and appear near the center of the tissue section. Follow [3,1]. Find the labeled veins. Then continue by following  and notice the red blood cells in the vein lumen. The walls of the veins are simple squamous epithelium (called endothelium). Follow  and look at the endothelial cells more closely.
Practice finding the simple cuboidal epithelium on the surface of the ovary, the Stratified cuboidal epithelium surronding an oocyte, and the endeothelium of a vein on this comparable virtual slide: W63 ovary,monkey.
W41bpl and W41b are two nearly identical tissue sections that will be used for multiple labs. Do not get lost trying to understand all of the labeled structures.
We will start at the lumen side of the jejunum. Briefly, going from lumen outward (right to left in this specimen), there are three layers in the wall of the GI tract. (1) The mucosa consists of epithelium, the lamina propria (loose connective tissue) and the muscularis mucosa. (2) The submucosa consists of dense connective tissue with collagen and elastic fibers. (3) The muscularis externa consists of two substantial layers of smooth muscle, an inner circular and an outer longitudinal layer.
Now switch to W41b, jejunum dog, and for the moment turn off the links (drop down menu, choose "- --").
You should be able to recognize the villi in the 12x magnification (far right edge of the section). The villi greatly increase the surface area for absorption of food.
The villus is covered with simple columnar epithelium with a brush border. Follow [1,1] to see a high magnification view of the epithelium that lines the villus. Click the thumbnail and follow [3,1,2,2] to find a higher magnification view of the epithelium. One of the absorptive epithelial cells is labeled. The brush border, which increases the surface area, is also labeled. The individual microvilli that compose the brush border can almost be resolved in some regions of this photograph. Enzymes that reside in the glycocalyx of the brush border accomplish the final digestion of oligosaccharides and oligopeptides to monosaccharides and amino acids, respectively. A TEM view of the intestinal brush border reveals bundled actin filaments within the microvilli. Click here to return to where you were in slide W41b.
Interspersed between the epithelial cells are goblet cells that secrete mucus, whose function is to protect and lubricate the lining of the intestine. One of several goblet cells visible in this picture is labeled. Goblet cells look like a drinking goblet, with the pedestal or base toward the basal side. They contain large pale granules that may be more or less confluent.
Notice that the nuclei of the absorptive cells are all in the basal half of the cell. You'll learn next year that a characteristic of cancer or neoplastic epithelial cells is that the nucleus is much larger and not confined to the basal surface.
Now, click on the thumbnail to go directly back to 12x magnification. Between the villi are small openings to tubular glands called intestinal crypts of Lieberkuhn. You can see these by following link 6 and checking the labels. The stem cells for the epithelium are located in the crypts. These cells divide and differentiate into new epithelial cells, replacing the old ones that die and are sloughed away from the the villus tip. The epithelium of the villi turn over approximately every two to three days. Follow link 4 to see the crypts at high magnification. There are dividing cells in crypt epithelium, as indicated by the labeled mitotic figures in this picture. Go to link 3 to see mitotic figures at high magnification.
Zoom out once. In between the glands is the lamina propria. In this slide, there are many plasma cells. Follow link 2 for labeled plasma cells. Plasma cells are activated, terminally differentiated B-cells that produce antibodies. Plasma cells often show a large, light pink (acidophilic) area next to the nucleus, which is the Golgi apparatus (you can see this very clearly in the left-most labeled plasma cell). The cytoplasm is otherwise lightly basophilic (due to abundant RER).
Also find a mast cell in the lamina propria. Its cytoplasm is filled with small, dark purple, evenly sized, regularly shaped granules.
Click the thumbnail and then follow [1,1] to see a better example lamina propria. This is an example of loose connective tissue, defined by moderately abundant, loosely interwoven fibers, and a large proportion of cells.
In contrast, the submucosa is a good example of dense connective tissue. Dense connective tissue is defined by abundant and densely packed fibers, and a much smaller proportion of cells. Click the thumbnail and then follow [4,2]. The dense connective tissue of the submucosa contains a large amount of densely packed collagen fibers (pink) with interspersed fibroblasts (very basophilic nuclei). Fibroblasts are the main producers of collagen and ground substance in connective tissues. A network of nerve cells and fibers called Meissner's plexus is located in the submucosa. Mouse-over to find the neurons (or ganglion cells), which are large (huge) with pale, euchromatic (light staining) nuclei and very prominent nucleoli.Now do a quick review on this comparable virtual slide: w41bjejunum, dog. Can you identify the mucosa, submucosa, and muscularis externa? How about the villi and crypts of Lieberkuhn? Practice identifying absorbive cells covering the villi, and goblet cells. Can you identify the lamina propria, including examples of plasma cells and mast cells? Practice finding the submucosa and then zoom in to see individual fibroblasts. There is a very nice example of a Meissner's plexus in the submucosa. Can you find it?
Go to link 2 and click the Mouse-over button. Move the cursor around to find the capsule, subcapsular sinus, cortex and medulla. You don't need to memorize (yet) these parts of the lymph node, but it helps to know where you are finding the macrophages.
The two major cell types within the cortex and medulla of the lymph node in this slide are lymphocytes and macrophages. The macrophages have ingested carbon particles that appear as black granules in the cytoplasm. Continue with [4,1,1,1]. Macrophages have an irregular shape, with many pseudopods and filopodia. Note the vacuoles in the otherwise basophilic, abundant cytoplasm. Zoom out once. Also labeled are the smaller, rounded, rather undistinguished-looking lymphocytes.
The middle circular structure is the bronchus. The bronchus is surrounded by a discontinuous layer of hyaline cartilage. Cartilage is a type of connective tissue. Follow [3,1] and find the cartilage. Notice that the cartilage matrix is extremely basophilic; it's quite distinctive and you should be able to recognize it easily in other tissue sections. Surrounding the cartilage is a layer of dense connective tissue, the perichondrium.
Click the thumbnail and follow [3,3,1,1]. Find the labeled epithelial lining. This lining is pseudostratified columnar, ciliated epithelium with goblet cells. The cilia move mucus up the airway passage (rather than down). Why?
A goblet cell and a ciliated epithelial cell are also labeled. This is an excellent view and it also contains mast cells and neutrophils within the lamina propria. Note the well preserved mucus-containing secretory vesicles in the goblet cell. This is also a beautiful view of cilia. You can almost imagine the metachronal waves of cilliary beating as they move the mucus over the epithelial surface. The lamina propria here serves the same connective tissue function as in the gut.
Click the thumbnail. This bronchus is lined with a layer of mucus that contains many PMNs (polymorphonuclear leukocytes), and mononuclear leukocytes. Follow [3,2,3,1] to find neutrophils (the most prevalent PMN) in the mucus.Use this virtual slide W51a bronchus, dog to practice finding the pseudostratified columnar, ciliated epithelium with goblet cells lining the bronchus. Can you also find the hyaline cartilage and its associated perichonrium?
This slide will be used for later labs also. For now we will focus on the connective tissue and the epithelium. Follow [1,3]. This view is part of the mucosa, which is closest to the lumen. Notice the basophilic epithelium, and the abrupt change to the lighter connective tissue to the left. Click the Mouse-over button to identify these different tissues.
Click link 1. The inner surface of the esophagus is lined with stratified squamous epithelium. Contrast this with what you saw in the bronchus. Why would there be such a difference in epithelial structure? What goes down (or back up) these tubes?
Click link 1. The cells in the stratum basale are stem cells that divide to provide cells for the layers above. As the cells are pushed to the surface they become squamous in shape, lose their nuclei and die, to be sloughed off.Now practice on this virtual slide: W34 esophagus,dog. Can you find the stratified squamous epithelium and the underlying connective tissue? Can you find the stratum basale, the stratum spinosum, and the statum corneum?
You will be seeing this slide frequently also. The covering of the tongue in a rat is keratinized, stratified squamous epithelium. Click link 1 to find skeletal muscle sectioned in many different planes. Continue with link 1. The keratinized, squamous epithelium is labeled.
Click the thumbnail. The tongue contains many nerve fibers and a few enteric neurons. Follow [4,1,1] to find neuron cell bodies that look very similar to the ones in the jejunum. Zoom out once to find the nerve fibers bundled together.
The tongue contains connective tissue that includes fat cells, called adpiocytes. Find the connective tissue labeled in the current view. Next, follow link 1 to return again to the view of the enteric neurons. Also labeled in this view are several adipocytes in the surrounding connective tissue. These are unilocular adipocytes that look white because the single, large fat droplet that these cells normally contain was extracted during tissue preparation.Practice finding the keratinized, stratified squamous epithelium, skeletal muscle, connective tissue, adipocytes, and enteric neurons on this virtual slide: W29 tongue, rat.
The urinary system, specifically the bladder and the ureter and the upper part of the urethra, are the only places that are covered in transitional epithelium. To view this transitional epithelium, follow [1,3,1,1]. The cells are stacked on top of each other, five or six cells thick, and the ureter surface is thrown into folds. The superficial cells are rounded and bulge into the lumen. This ureter was sectioned when empty. When the ureter fills, the folds expand. When the ureter is stretched, the epithelium is only three or four cells in thickness and the superficial cells become squamous. This allows the ureter, and especially the bladder, to change volume without rupturing the epithelium. Some researchers believe that each epithelial cell extends to the basal lamina.Can you find the transitional epithelium in this virtual slide: W58 ureter,monkey.
Do not try to memorize the structure of the liver. You are here to find macrophages. In the liver, macrophages are in the sinusoids, small irregularly shaped blood channels between the hepatocytes (liver cells).
Follow [1,1,3,1]. Before you click any menus or buttons try to find the macrophage. It has an irregular shape and several basophilic granules of various sizes. Macrophages have uneven borders and the abundant cytoplasm contains dark granules and light vacuoles of various sizes. Notice also a neutrophil and a lymphocyte in this view. Click the thumbnail, then follow [1,1,1,2] to see another good example of a macrophage. This one has phagocytosed two erythrocytes, which appear as large, darkly stained bodies. On your own explore other links to find additional examples of macrophages. Also practice using this virtual slide: w45a liver,dog.
The ganglion contains neuron cell bodies. Click on link 2 and mouse-over to find the ganglion and the nerve roots. Follow [1,1] to find the ganglion cell bodies. They are large cells (like in the jejunum) with large euchromatic nuclei and prominent nucleoli.
The smaller darker staining nuclei belong to glial cells. In the periphery the glial cells are called Schwann cells. The Schwann cells are developed from neural crest tissue and migrate during fetal development to the periphery. They support the neurons and wrap around the nerve axons to form the myelin sheath.Practice finding ganglion cell bodies and Schwann cells in this virtual slide: W84 spinal ganglion and nerve.
Bone is built by osteoblasts located at the outside and inside surfaces of the bone tissue. The osteoblasts are incorporated into the growing bone and are then called osteocytes, which maintain the bone. The osteocyte occupies a small lacuna (little lake) or hole within the bone matrix. Follow [1,2,3,1] to see an osteocyte. Typical for the osteocyte are the numerous cell extenstion (that make it look spider according Dr. Kokko-Cunningham). The periosteum, a layer of dense connective tissue, surrounds the bone. Zoom out twice. Mouse-over to find the periosteum, bone and bone marrow.
Bone marrow fills the cavity inside the bone. Several megakaryocytes are visible. Follow link [1,1] to see higher magnification view. Megakaryocytes produce platelets by pinching off small cell fragments.Practice finding osteocytes, periostium, and megakaryocytes in this virtual slide: W11 skull, rat.
If you wish to spend more time looking at other examples of the structures for this lab the following hyperlinks will take you directly to the object list.
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