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Chapter 40 BASIC PRINCIPLES OF ANIMAL FORM AND FUNCTION Animals face common problems in their struggle to survive, e.g. need of oxygen and nourishment, excretion of wastes, and motility. Body structures are correlated to their function. Anatomy is the study of the structure of an organism. Physiology is the study of the functions an organism performs and of the chemical and physical processes involved. Physiology is explainable only in terms of the underlying anatomy. PHYSICAL LAWS AND ENVIRONMENT Physical laws and the environment constrain animal size and shape. Body plans and designs are fundamental aspects of form and function that significantly affect the way an animal interacts with its environment. The body plan of animal results from a pattern of development programmed by the genome. Evolutionary convergence reflects different species adaptations to similar environments. Physical requirements constraints what natural selection can invent. Each cell of a multicellular animal must have access to an aqueous environment. ANIMAL FORM AND FUNCTION ARE CORRELATED AT ALL LEVELS OF ORGANIZATION . The large size of animals is due to the greater number cells they have. Multicellularity allows the organisms to be more diverse and the cells to become specialized A tissue is made of a group of closely associated, similar cells adapted to carry out specific functions. TISSUES Animal tissues are classified as epithelial, connective, muscle and nervous tissue. 1. Epithelial tissue (epithelium) consists of fitted tightly together to form a continuous layer or sheet. Very often the cells are riveted together by tight junctions. It covers body surfaces and lines cavities. It functions as barrier for protection against mechanical injury, loss of fluid and infection by microorganisms.
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Epithelial tissues are also involved in absorption, secretion and sensation. The outer surface of this tissue is typically exposed because it lines cavities. The cell layer is attached to the underlying tissue by a noncellular membrane, the basement membrane , made of polysaccharides and fibers Epithelial cells may be organized or differentiated into epidermis (skin), membranes, glands and sensory receptors. Epithelial tissue may be simple, stratified or pseudostratified . Epithelial cells are cuboidal, columnar or squamous . Glands are made of epithelial cells specialized to secrete a substance, e.g. sweat, hormones, saliva, milk, enzymes. Epithelial membranes consist of a layer of epithelial cells and a layer of underlying connective tissue. Mucosas or mucous membranes line body cavities that open to the outside, e. g. digestive and respiratory track. The epithelial layer secretes mucus. Serous membranes
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