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Animal Systems Organization and Homeostasis Organization in Living Things • Cells are organized into tissues • Tissues are organized into organs • Organs are organized into systems • Systems form an organism Four tissue types • Epithelial • Connective • Nervous • Muscular Epithelial tissue • Epithelial cells form the outer covering, line the internal cavities, and make up the glands. • Examples: Skin, mucous membranes. Connective tissue • Consists of living cells in a secreted matrix. • Examples: bone, cartilage, blood. Muscular tissue • Specialized protein fibers allow these cells to contract. • Examples: skeletal muscle, smooth muscle, cardiac muscle. Nervous tissue • Neurons have the ability to pass an “electrical” signal from one cell to another, or to target cells (muscles, glands, organs). Tissues form organs • The skin is an example of an organ made up of multiple tissues: epithelial, muscular, nervous, and connective tissues. Homeostasis • Homeostasis is the act of keeping the internal environment of a living organism within an acceptable range of conditions. • Homeostasis controls temperature, pH, blood volume, oxygen levels, blood sugar levels, and other conditions. • Negative feedback maintains homeostasis. Negative Feedback • Negative feedback keeps conditions within an ideal range. • As conditions exceed the limits of the ideal range, chemical signals (hormones) regulate conditions. Most often this is controlled by the hypothalamus in the brain. Positive Feedback • Positive feedback takes a condition out of the normal range, often to some end point. • During labor, oxytocin increases contractions, which stimulate more oxytocin production, until birth occurs. Maintaining Temperature • Ectotherms are animals that derive body heat from the environment. Their body temperature may vary widely. • Endotherms rely on metabolic reactions and physiological systems to maintain a steady body temperature. Maintaining Temperature Blood Glucose Regulation