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Epithelial Tissues Neuron (Nerve Cell) - I The pictures to the left are light micrographs of neurons (nerve cells). The light micrographs show the typical appearance of neurons when stained with basic dyes. The nucleus is pale; often a heavily stained nucleolus is evident within it. Nissl bodies are prominent in the cytoplasm near the nucleus. These three are scanning electron micrographs. They show a three dimensional view of a neuron (nerve cell). The main part or body of the neuron is pear shaped. It contains the nucleus and most of the organelles and structures in the cell. The long thin “arms” or processes of the nerve cells connect to other nerve cells. Signals from one nerve cell to the other travel along these processes. Neuron (Nerve Cell) - II The electron micrograph shows part of the cell of a neuron. Part of the nucleus is at center-left. Stacks of rough endoplasmic reticulum are evident in the cytoplasm. They are what are called the Nissl bodies at the light microscopic level. This neuron was labeled with a marker. The location of that marker is represented by the black granules, many of which localize in the vicinity of the Golgi apparatus. The black marker is taken up at one end of the cell by one of the arms and transported by the cytoskeleton back towards the nucleus. Neurons “talk” to other neurons using chemical messages. The chemical messages are special molecules that the neuron makes and stores in very small vacuoles close to the cell membrane at the ends of its processes. When the neuron wants to talk to the next neuron, the tiny vesicles inside the cell move to and fuse with the neuron’s cell membrane, dumping the special chemicals outside of itself. The next neuron gets the chemical signal because special protein molecules in its cell membrane capture the special chemicals and move them inside. Bone Cell - I Scanning electron micrograph (colour enhanced) of a bonedegrading osteoclast Bone is a living tissue that is constantly being broken down and rebuilt. This image shows an osteoclast, a type of cell responsible for degrading bone. The space surrounding the cell is known as a resorption cavity. Young bone cells (osteoblasts produce the intercellular bone matrix, an organic material consisting of collagen fibers and ground substance. This matrix gradually calcifies and hardens Bone Cell - II This photograph of a normal bone was taken through the microscope. Bone is green. The white dots are fat cells in the bone marrow and the other bone marrow cells are dark red. Goblet Cells – Intestines I Goblet cells secrete mucus, a viscous fluid composed primarily of proteins called mucins. Mucus serves many functions, including protection against stress and chemical damage, and, especially in the respiratory tree, trapping and elimination of particulate matter and microorganisms. Goblet cells are found scattered among other cells in the epithelium of many organs, especially in the intestinal and respiratory tracts. In some areas, their numbers are rather small relative to other cell types, while in tissues such as the colon, they are much more abundant. Secretion of mucus occurs by exocytosis of secretory granules The mucus in goblet cell granules is condensed, but upon secretion, expands in volume tremendously and almost instantaneously (picture a pressurized can of shaving foam or whipped cream). In some systems studied, the mucin gel increases in volume 500-fold during a period of only 20 milliseconds! Increased numbers of goblet cells are observed in several disease states. Chronic brochitis and cystic fibrosis are examples of diseases in which goblet cell hyperplasia or metaplasia occurs. Goblet Cells – Intestines II Skin Cell pinosum is composed of several layers of polyhedral cells, which flatten as the stratum granulosum is approached. Se ch are specific for keratin pairs 1 and 10. Individual cells appear to be separated by spaces that are traversed by t be seen as fine lines between adjacent cells. They account for the prickly appearance of the cells and for their fre tifacts caused when water is removed during the dehydration step. Spinous cells are attached to their neighbors by main as the fragile Skeletal Muscle I Cardiac Muscle I A special type of muscle found only in the heart. It shares the characteristics of both other types of muscle found in the human body. Each cell has only one centrally located nucleus. Note the faintly stained transverse bands called intercalated disks (indicated by the blue arrows) that mark the boundaries between the ends of the cells. These specialized junctional zones are unique to cardiac muscle. Cardiac Muscle II In this electron micrograph, a part of the nucleus appears as an thin oval body in the lower right side of the picture. Around it is a small area of cytoplasm. The bulk of the cardiac muscle cytoplasm is occupied by the actin and myosin protein fibers that are responsible for muscle movement. Right next to each group of fibers is a mitochondron. Skeletal Muscle II Sperm Cell Mid-piece region of a mammal sperm showing the numerous mitochondria that provide the energy for motility. , Egg Cell I EM of an oocyte with its nucleus (5) at the bottom of the micrograph. The nuclear envelope is sectioned tangentially so that nuclear pores are clearly visible (arrows). 1 = Crystalline bodies or plaques (typical of oocyte cytoplasm); 2 = Mitochondria; 3 = Multi vesicular body; 4 = Cortical granules (typical of oocyte); 5 = Nucleus. Egg Cell II Pancreatic Cell Islets of Langerhans Cell Normal islet stained for insulin (right) and glucagon (left): Tissue sections from a 24-h duct-ligated rat pancreas. a: Semi-thin section illustrating an islet of Langerhans (IL) in which some cells located either at the periphery or in the core of the islet display some zymogen-like granules (arrows). Ac, Acinar cells. Magnification = ×2,800. b: Electron micrograph of an insulin-secreting cell (Ins) surrounded by 2 acinar cells. Islet cell displays some zymogen-like granules (arrows). Delineation of each cell is particularly conspicuous by differences in electron density of the cytoplasm. DL, duct lumen. Magnification = ×10,000. Tendon – Connective Tissue Tendon, which is a strap like body that connects bone to muscle, is made of dense, regular connective tissue. You can find an example in slide 9. The fibers are oriented in parallel arrays. Note the thin, dark staining nuclei of the fibroblasts. Their cytoplasm cannot be distinguished. How does the arrangement of the fibers help a runner sprint or a k ngaroo jump? Fat Cell Here you see ADIPOSE cells (adipocytes), exhibiting their characteristic "chicken-wire" look. The large empty spaces represent the cytoplasmic areas originally filled with lipid, extracted during slide preparation. Only a very attenuated rim of cytoplasm is present with the nuclei squeezed between the lipid and the internal face of the plasma membrane. The arrows indicate some of the adipocyte nuclei. Some capillaries are also visible; adipose tissue is wellvascularized. White Blood Cells - I White blood cells (colourenhanced scanning electron micrograph) The cells of the immune system (these white blood cells) play key roles in the inflammatory response. In this image we can see three white blood cells - a macrophage (brown) and two Tlymphocytes (blue). White Blood Cells PLASMA CELLS are seen here as the largest cells with a dark, "cart-wheel" heterochromatin pattern in the eccentric nucleus, with highly basophilic cytoplasm. (a) indicates a large lymphocyte, as defined by the lack of an extensive cytoplasmic skirt. The smaller cells are lymphocytes and some plasma cells. Lymphocytes will have a dark, "smudged" nucleus and very little cytoplasm in relation to nuclear volume. An EM of a plasma cell, indicating that the extreme basophilia seen in the preceding slide is caused by an abundance of rough endoplasmic reticulum producing antibody molecules for export. Liver Cell