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Virtual EM Micrograph List
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Virtual Electron Micrograph Slide List for Histology Course
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282
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Zona Pellucida of a Secondary Follicle: Higher magnification view of another secondary follicle. Note the penetration of the zona pellucida by processes from the oocyte and from the granulosa cells of the corona radiata. | |
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283
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Theca Interna and Externa of a Secondary Follicle: The cells of the theca interna will eventually differentiate into endocrine cells and show characteristics of steroid-producing cells. The theca externa consists of a mixture of smooth muscle cells and connective tissue. | |
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285
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Corpus Luteum: You do not need to be able to identify theca and granulose lutein cells based on their EM appearances. However, note the difference in their cytoplasmic contents and know their secretory products. | |
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288
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Epithelium of the Oviduct: Cilia and their basal bodies are clearly visible in the apical cytoplasm of the ciliated cells. Note short microvilli on the non-ciliated secretory cells. | |
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279
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Primordial Follicle: Note an incomplete layer of flat granulose cells around the oocyte. | |
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280
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Primary Oocyte: Note the highly organized appearance of the primary follicle and the considerable size difference to a primordial follicle. | |
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281
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Secondary Follicle: In this low magnification view of a secondary follicle, examine the characteristics of the thecal layer, granulosa cells, corona radiata and the ooplasm. Note particularly the basal lamina which separates the thecal and granulosa cell layers and the acellular zona pellucida that surrounds the oocyte. |
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289
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Placental Villus (mid pregnancy): Examine the ultrastructure of the syncytiotrophoblast cells, particularly their external surface. Note the paucity of cytotrophoblast cells at this stage of development. Be certain that you know the components of the placental barrier, how they may change during pregnancy and why. | |
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290
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Mammary Gland: Observe the process of true apocrine secretion. Lipid granules are released covered with a small amount of mammary gland cell cytoplasm, as well as the cell membrane. On the other hand, the protein components are released by the usual mechanism of exocytosis. |
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294
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Lymph Node (Subcapsular Sinus and Cortex): Find the subcapsular sinus and the reticular cells of the node. | |
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296
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Medullary Cord (Lymph Node): Blood vessels are restricted to the medullary cords. Plasma cells occur abundantly in the cords. Review the function and origin of plasma cells. Note that the free, circulating lymphocytes are either small or medium size. | |
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297
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Postcapillary High Endothelial Venule (Lymph Node): Note the unusual height of the lining endothelial cells and the lymphocytes of different sizes in transit from the vessel into the lymph node. A small fraction of lymphocytes enter the node through afferent lymphatic vessels. | |
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298
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Medullary Sinus (Lymph Node): Observe the loose arrangement of lymphoid tissue in the medulla of lymph nodes. The sinuses interconnect and their lumen is traversed by reticular cells, some of which can trap antigens and some of which are true phagocytes. In addition, reticular cells wrap around the bundles of reticular fibrils and thereby isolate them from lymphocyte access. | |
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303
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White and Red Pulp (Spleen): Note the very dense arrangement of lymphoid cells in the white pulp and the loose arrangement of reticular cells, some lymphoid cells and extravasated erythrocytes in the pulp cords between the venous sinuses. Note also the marginal zone and recall that this is where most antigen presentation occurs in the spleen. | |
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306
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Marginal Zone (Spleen): The marginal zone is a cell rich region at the interphase between white and red pulp. As it is the region of antigen presentation, a large number of macrophages and different types of lymphocytes reside here. | |
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310
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Red Pulp with Venous Sinus (Spleen): Find the venous sinuses and observe the movement of erythrocytes across the wall. The presence of many macrophages in the interstitial space of the red pulp is obvious. | |
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318
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Thymus (Cortex and Medulla): Note that the thymus does not have lymph nodules. However, small lymphocytes (thymocytes) are aggregated in the cortex and larger, epithelial reticular cells can be identified in the center (medulla), giving the appearance of a “nodular” area. | |
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319
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Thymus (Medulla): Remember that Hassall’s corpuscles (or bodies) are found only in the thymus. | |
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321
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Blood-Thymus Barrier: Review the components of the blood-thymus barrier. |
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258
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Seminiferous Tubule: In this electron micrograph, showing a seminiferous tubule and adjacent interstitial tissue, you can see in more detail the same structures you have been viewing with the light microscope. In the seminiferous tubule, the large, round nuclei belong to more mature primary spermatocytes. Toward the lumen from these are the nuclei of spermatids. Note the occasional Sertoli cell nuclei and try to follow the extensive Sertoli cell cytoplasm as it passes up to enfold the spermatocytes and spermatids. In the interstitial tissue, observe the Leydig cells and capillaries (the latter are somewhat swollen because the testis was fixed for electron microscopy by perfusion of the fixative through the blood vessels). | |
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259
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Seminiferous Epithelium: This electron micrograph shows the seminiferous epithelium at a higher power than the previous electron micrograph (EM #258). Note the different appearances of the cell nuclei in spermatogonia, primary spermatocytes, Sertoli cells and spermatids. | |
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262
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Testis (Interstitial tissue): Clearly visible are a number of Leydig cells in the interstitial tissue of the testis: Also note a postcapillary venule, a capillary and lymphatic spaces. | |
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264
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Epididymis (Pseudostratified Epithelium): Tall cells of uniform height extend to the lumen, while short basal cells are limited to the base of the tubule. Note most of the stereocilia are transversely sectioned. |
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032
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Skeletal Muscle (longitudinal section): Identify a sarcomere. Relate the sarcomeric structure seen in the LM to the structure seen here. Note that there is also lots of glycogen in the region between the two myofibrils in this picture, a storage form for glucose (which is metabolized to provide energy for muscle contraction). At the border of the I and A-bands, note triads consisting of a central T (transverse) tubule and flanking cisternae of the sarcoplasmic reticulum. | |
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034
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Skeletal Muscle (cross section, low magnification): Note location of muscle fiber nuclei. You can see cross sections of A bands (darker) and I bands (lighter) side by side in the same cell because of the fact that the myofibrils don't line up perfectly. Identify the approximate outline of a single myofibril. | |
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037
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Skeletal Muscle (longitudinal section, low magnification): Find the skeletal muscle nuclei and note their peripheral location. Note the intimate contact between capillaries and muscle cells and be sure you can tell where one muscle cell or fiber stops and another begins (you can see parts of four fibers in this picture). Make sure you know which is the longitudinal axis of the cell. Identify sarcomeres, A bands, I bands, Z lines and H zones. Note that, as you saw at the LM level, the individual myofibrils do not line up perfectly across the fiber. | |
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041
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Cardiac Muscle (Intercalated Disc, longitudinal section): Note the somewhat irregular course of the intercalated disc. In this preparation, the I bands are very short, indicating that the sarcomere is in a contracted state. Review the types of junctions present in an intercalated disc and their functions. | |
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043
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Cardiac Muscle (longitudinal section): Note central location of muscle nuclei. Note the "stacks" of mitochondria between myofibrils. Cardiac muscle is even richer than skeletal muscle in mitochondria (again, important for energy production). An intercalated disc is present in the upper left region of the picture. | |
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044
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Smooth Muscle (cross section): Here you can see the filaments in cross-section, appearing as dots. Also, the dark areas, which are membrane-associated, are called dense plaques and are sites of filament attachment. | |
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207
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Smooth Muscle (longitudinal and cross section): Study the orientation of the smooth muscle layers in the intestine and their appearance. The micrograph will help you understand the patterns, which arise from longitudinal and cross-sections of smooth muscle. |
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057
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Multipolar Neurons (Celiac Ganglion): The celiac ganglia are autonomic ganglia. Note the large ganglion cells with somewhat eccentrically placed nuclei in several cells, a characteristic feature of autonomic ganglion cells. | |
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059
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Myelinated Nerve with Endoneurium and Perineurium (cross section): Between the axons you will see delicate connective tissue and an occasional fibroblast, which constitute the endoneurium. At the periphery of the fascicle, observe the perineurium, made up of several layers of flattened cells; it is a highly specialized layer that acts as a barrier and protects the nerve from the environment. | |
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060
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Neuromuscular Junction: This is a motor end plate. Note that the nerve axon loses its myelin sheath as it approaches the motor end plate and it terminates as a bulbous expansion in a trough of the muscle cell surface. The bulbous knob reveals numerous mitochondria and small synaptic vesicles, which contain cholinergic neurotransmitter substances. When these vesicles fuse the cell membrane of the axon bulb (the presynaptic membrane) and the content is released into the synaptic clefts to be taken up by the postsynaptic membrane (muscle cell membrane). | |
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061
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Neuromuscular Spindle: Note the two types of intrafusal muscle fibers, the nuclear bag fibers and nuclear chain fibers are enclosed by a delicate internal capsule. This arrangement serves as a muscle stretch receptor. The sensory nerve endings are activated by the stretching of the intrafusal fibers and the nerve impulse generated excites the somatic motor neurons in the spinal cord to evoke a reflex contraction of extrafusal fibers. | |
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049
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Motor Neuron Cell Body: In this electron micrograph, note some of the features you saw in ventral horn motor neurons with the light microscope, such as the large, pale nucleus, prominent nucleolus, Nissl bodies, dendrites and axon. Adjacent to the neuron, note myelinated axons of various sizes and also that there are no spaces between cell processes. All spaces are occupied either by the processes of neurons or glia or by capillaries (these capillaries are somewhat swollen here because the tissue was fixed by perfusion). | |
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052
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Node of Ranvier (longitudinal section): Remember that the node of Ranvier is actually a short segment of the axon that is bare at the junction between two Schwann cells, making "saltatory conduction" possible. Note the manner in which the myelin ends in each Schwann cell at the junction, by a "peeling off" of successive myelin layers, which come to lie against the axon as small cytoplasmic swellings. | |
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053
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Myelinated Nerve Fibers (longitudinal section): This image shows the typical appearance of a myelinated nerve, consisting of parallel bundles of axons (light areas) wrapped with sheaths of myelin (dark areas). As in the peripheral nervous system each Schwann cell myelinates only one axon, the discontinuous appearance of the axon labeled 5 in a Schwann cell is probably due to its curvature around the nucleus. | |
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054
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Schwann Cell with Myelinated Nerve Fiber (cross section): In this cross section of a myelinated nerve process, note the axon, containing microtubules and neurofilaments and bounded by a plasma membrane ("axolemma"). Outside the plasma membrane of the axon is the myelin sheath, which you will remember is composed of tightly wrapped plasma membranes of the Schwann cell. Also, note the nucleus and cytoplasmic organelles of the Schwann cell. Remember that the myelin is part of the Schwann cell, not of the axon. | |
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055
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Unmyelinated Nerve Fibers (cross section): The axons seen in this electron micrograph are all non-myelinated. They are embedded in grooves in the Schwann cell surface (in some cases there may be more than one axon per groove), with each Schwann cell thus supporting a considerable number of these small, unmyelinated axons. Although the axons are very close together, you will observe thin partitions of Schwann cell between them. |
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115
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Alveoli: Study the organization of the alveoli. Note that individual alveoli border on each other and therefore share the wall, which is referred to as alveolar septum. Within the septum are found capillaries. Be able to recognize type I cells, type II cells and macrophages. Type II cells secrete surfactant and can be identified on the basis of their lamellar or multilamellar bodies, which cannot be seen well at this magnification. The type I cell lining the alveolus is also better identified at higher magnification (see EM #161). | |
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148
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Olfactory Epithelium: Two types of cells are shown in this EM micrograph; olfactory bipolar neurons with vesicles and cilia and supportive cells with microvilli on their apical surface. Note the absence of goblet cells in this neurosensory epithelium. | |
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153
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Respiratory/Pseudostratified Epithelium in the Trachea: Compare the morphology of the goblet cells with that of the other cells of the epithelium. Note that most of them are filled with secretory product (mucus) and that they do not have cilia. The line indicates the plane of section on the next wall chart #154. | |
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154
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Respiratory Epithelium (tangential section): The yellow colored area indicates the outline of one cell (see previous wall chart #153 for plane of section). Note the tops of the goblet cells protruding between the cilia. | |
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156
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Cilia: Review the fine structure of the cilium. | |
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157
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Bronchus: Note that the epithelium, although still pseudostratified, is not as tall as in the trachea (EM #153). Smooth muscle separates the lamina propria from the submucosa. Note the presence of a pulmonary artery and vein and that of a much smaller bronchial artery. | |
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161
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Alveolus (Blood-Air Barrier): Study the cellular and acellular components of the blood air barrier. Also study the type II pneumocyte in the upper right corner of this micrograph. Unfortunately, the lamellar bodies are not well preserved in this preparation. |
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065
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Epidermis: Review the layering of the epidermis. Remember that there is a continuous process of cell migration and differentiation from the basal cell layer to the most superficial layer. Review the features of the epidermal-dermal junction. | |
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067
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Epidermis - Details of the Stratum Spinosum: Observe the abundance of tonofibrils (= keratin intermediate filaments) and ribosomes and the small number of mitochondria. Note the absence of Golgi apparatus and granular endoplasmic reticulum. Epidermal cells do contain these organelles but in reduced amount, as the bulk of synthesis is for structural proteins, not exportable ones. | |
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069
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Epidermis – Details of the Stratum Granulosum and Stratum Corneum: Note the keratohyaline granules in the cells of the stratum granulosum. The keratinization process is completed in the cell layers above the stratum granulosum, indicated by the disappearance of nuclei and cell organelles. Note that the cornified cells are of variable appearance (some "dark" and some "light") a reflection of the tissue processing rather than of a functional difference. | |
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290
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Mammary Gland: Observe the process of true apocrine secretion. Lipid granules are released covered with a small amount of mammary gland cell cytoplasm, as well as the cell membrane. On the other hand, the protein components are released by the usual mechanism of exocytosis. |