Cell and Tissues
ID: ANM11024
MEDICAL ANIMATION TRANSCRIPT: The cell is the structural and functional unit of the body. Together, cells construct tissues, and tissues combine to form organs. A human cell contains a nucleus and specialized structures called organelles. Inside the nucleus, the cell's DNA orchestrates activities integral to the cell's survival and functions in the body. Organelles suspended in a gel-like solution known as cytosol perform specific functions to assist with the cell's tasks and maintenance. For example, ribosomes synthesize protein, and the endoplasmic reticulum assembles and transports proteins for use by the cell. Mitochondria produce energy for the cell in the form of ATP, powering activities such as movement. The plasma membrane encloses the cell and serves as a site of exchange for nutrients, a point of attachment for molecules and other cells, and a conduit for communication between cells and their surroundings. When multiple cells organize into a group, they form a tissue. There are four basic types of tissues in the body - epithelial, nervous, muscle, and connective. Epithelial tissues cover and line body structures and exhibit specialized shapes and functions. For example, in the small intestinal lining or mucosa, a single layer of cells called enterocytes absorbs nutrients through surface extensions called microvilli. Nervous tissue in the brain, spinal cord, and nerves consists of specialized cells called neurons and neuroglia, the neurons' supporting cells. Inside the brain, gray matter contains neuron cell bodies and their extensions known as dendrites, and various neuroglia, such as astrocytes and oligodendrocytes. White matter contains axons, which are long fibers extending away from neuron cell bodies. Axons carry chemical and electrical impulses to body tissues, such as muscle. Muscle tissue is classified as smooth, cardiac, or skeletal muscle. For example, skeletal muscle fibers form whole muscles that attach to bones and move the body. Cells called myocytes, containing contractile protein fibers, comprise muscle. Connective tissues include bone, cartilage, ligaments, tendons, and blood. For example, cartilage is comprised of proteoglycan molecules in a gelatinous matrix surrounding a meshwork of collagen fibrils that impart tensile strength and chondrocytes that help maintain the tissue's integrity and flexibility. Two or more tissues that work together for a common purpose form an organ. For example, in the heart, cardiac muscle tissue in the ventricles contracts and pushes blood through the connective tissue valves into vessels lined by vascular epithelial tissue called endothelium. Together, various organs make up organ systems, which work collectively to create an organism.
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