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Red Blood Cells
The main function of human red blood cells or erythrocytes is to carry oxygen to different parts of the body. Their natural red color comes from a biomolecule called hemoglobin which binds oxygen and occupies the cytoplasm of the cell. Unlike most human cells, red blood cells do not have nuclei or other organelles (the components or subunits of most cells). Their biconcave appearance can clearly be seen in this image that was captured using a scanning electron microscope (SEM). Looking like doughnuts without holes, they are flat and depressed in the center and have a dumbbell-shaped cross-section. This unusual form is important for their function since it aids in their smooth passage through small and large blood vessels.
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Cytoskeleton of a Skin Cell
Would you believe that even the smallest unit of the body has a “skeleton"? The framework of a cell or its cytoskeleton is made out of proteins and is involved in many functions such as intracellular transport of substances and cellular division. Although miniscule, cells are always busy synthesizing, transporting, metabolizing and reproducing. During these processes the proteins making up the cell’s supporting structure play a vital role. Through fluorescence microscopy this image of a skin cell (keratinocyte) was taken and shows the actin fiber organization which makes up its cytoskeleton.
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Pigment cells contain melanin and are called melanocytes. Melanin-producing cells in mammals are found in the deepest layer of the skin's epidermis, the middle layer of the eye, the inner ear, the bones, and the heart. There are about 1000 to 2000 melanocytes per square millimeter of skin.
By using transmission electron microscopy, the development of this melanosome (an immature melanocyte) from a human fetus is revealed.
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Retinal Pigmented Epithelial Cells
These pigmented cells protect the retina from exposure to too much light and act as a self-contained ocular immune system. By supplying omega-3 fatty acids, glucose and other substances to the eye, these cells help to nourish its cells. Diseases related to this layer of cells include age-related macular degeneration and retinitis pigmentosa. People who genetically lack skin pigmentation (albinos) also lack retinal pigmented cells.
In order to appreciate the pigmented cells overlying the inner lining of the eye (retinal layer), special staining and fixation techniques were employed to this specimen, which is seen through fluorescence microscopy. The blue oval shapes represent the nuclei of the retinal pigmented cells which are hexagonal in shape when viewed from the outer surface.
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Cilia and Microvilli
Certain cells of the body which are involved in moving or transporting substances like mucus have hair-like projections called cilia and microvilli that sway in a propelling manner. These structures that look like hairy sea creatures are actually parts of a female oviduct or fallopian tube where eggs cells pass through. Mature egg cells rupture from the ovary and travel through these ducts towards the uterus where they may be fertilized by sperm cells. Cilia and microvilli help propel the egg forward to achieve this function of the egg. In this image the long tufts of cilia project from individual cells while non-ciliated cells are covered by shorter microvili. They have been magnified by a scanning electron microscope.
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The pancreas is an excretory organ with cells that release hormones such as insulin and glucagon. With the aid of transmission electron microscopy, secretory granules in an alpha cell from the islet of Langerhans are seen in this image. Islets of Langerhans are regions of the pancreas where alpha, beta, delta and other types of cells produce regulatory hormones. Alpha cells produce glucagon while beta cells release insulin. These hormones are primarily involved in maintaining blood sugar levels, and an imbalance may lead to chronic disease such as diabetes mellitus.
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To capture the movement of live human sperm cells within a couple of hours following ejaculation, the sample was diluted with a buffer, plated and examined through phase contrast microscopy. A sperm cell looks like a tadpole and consists of a head, a midpiece and a tail. The genetic material in the nucleus is contained in the head part of the sperm, while the midpiece contains a central filamentous core with many mitochondria, the energy powerhouses of cells. The tail or flagellum has a vital role in fertilization.
Sperm motility, or the ability of a sperm cell to move towards an egg cell and penetrate its layers, is necessary for fertilization to take place. Movement is accomplished by lashing movements that enable a sperm cell to swim through a woman’s cervix towards the egg.
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This scanning electron micrograph image shows the microvilli found in HeLa cells. These are dispersed cells grown in vitro, referring to cells that have been isolated from a biological organism and maintained in a laboratory environment for experimentation or observation.
In 1951 cervical cancer cells taken from a patient named Henrietta Lacks were propagated and used for research. Being remarkably durable and prolific, the HeLa cells as they were later called have since then been used in numerous research studies. They are considered “immortal“ as they continue to divide when maintained in a suitable environment. This makes them ideal for studies on cancer, AIDS, and many other diseases.
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Human Embryonic Stem Cells
This image of a live cell preparation taken by using phase contrast microscopy shows two colonies of human cells taken from an early stage embryo. These cells are growing on a feeder layer of mouse embryonic fibroblasts (the elongated cells) which provide nutrition and keeps them from differentiating into different cell types. Stem cells have the potential to replicate indefinitely and develop into different types of cells. Because of these properties their uses are being investigated, especially for regenerative medicine and tissue replacement as a cure for some diseases.
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Mitosis in an Epithelial Cell
Many cellular functions may be observed in the laboratory through the use of special visualization and imaging techniques.
Epithelial cells are types of cells that usually line cavities and surfaces of the different body structures. They are highly proliferative and undergo constant regeneration.
Cells that have a nucleus such as epithelial cells undergo a process called mitosis, where the chromosomes in the nucleus are divided and separated into two identical sets, followed by the division of the cell into two identical daughter cells.
This epithelial HeLa cell is shown in the process of mitosis. The bright green flourescent structure represents the mitotic membranes of the nucleus and the blue labeled structures are the dividing chromosomes.
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Apoptotic Mitochondrial Changes
Apoptosis is a type of cell death that occurs naturally in a regulated process in living cells. It is also referred to as programmed cell death or cell suicide. It occurs as a series of changes in the different parts of the cell, including the mitochondria. The mitochondria are specialized subunits within the cell that are often described as "cellular power plants" since they produce energy.
Using special methods of culturing, fixing and labeling HeLa cells, fluorescent microscopy demonstrates the rod-like mitochondria in red, undergoing apoptotic changes. These changes result from the swelling of the mitochondrial membranes and the release of enzymes which lead to cell degradation. Apoptosis usually occurs as a response to stress that triggers a cascade of cellular changes leading to cell death.
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Synaptic Transmission in Nerve Endings
Ever wondered how sensory and motor functions are accomplished by the nerves? These are carried out by a process called neurotransmission or synaptic transmission between nerve endings. Nerve endings possess vesicles containing neurotransmitters which are signalling molecules released during transmission of signals between nerve endings. To propagate signals for motor or sensory functions the released neurotransmitters bind to the adjoining nerve ending and cause a series of cell changes that result in nerve impulses. These ultimately lead to muscle action, release of bodily secretions and other organ functions.
The orange and blue vesicles in this image captured by scanning electron microscopy contain neurotransmitters that are released from nerve endings (green) during synaptic transmission.
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Inflammatory Cellular Response
Body cells react to offending stimuli like infection or other irritants by producing inflammatory responses. These changes are part of the body’s protective mechanisms to control damage and start the healing process. In this image the lining of the duct of the gallbladder of a patient is seen as having highly polarized cells with dark nuclei. The reason for the patient’s disease may have been related to the excess cholesterol found in the foamy macrophages (the white blood cells on top) that have migrated through blood vessels into the site of inflammation in a process called chemotaxis. This initial response later leads to pain, swelling and other signs of inflammation. This patient later underwent removal of his gallbladder which had been filled with gallstones.
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Breast Cancer Cells
Fluorescence in situ hybridization (FISH) has become one of the most widely used tools in microbiology and the study of cancer. Using this technique and fluorescence microscopy, mutations in genes (marked here by the green and red spots representing the ERBB2 and MYC genes respectively) can be found which helps with the detection of breast cancer. The blue oval shapes are the nuclei of breast cells.
Mutations of the ERBB2 genes are also found in several other types of cancer, such as ovarian, brain, stomach, and lung cancers, while MYC gene changes have been discovered in patients with Burkitt’s lymphoma.
National Institutes of Health, The Cell, an Image Library