Homeostasis: the ability of an organism to maintain its internal environment. Ectotherms: derive their heat from external environment. Endotherms: produce heat on the inside (through metabolic reactions) ex)iguana. Negative feedback: a change causes a responses to counteract the change. Positive feedback: a change produces a response that amplifies a change. Epithelial tissue: consists of sheets of cells firmly attached to one another. Simple epithelium: one cell thick -stratified; multiple cells thick hormones or digestive enzymes outside the cell. Glands: cells/ group of cells specialized to secrete substances such as. Exocrine: secrete substances in a body cavity or on the body"s surface. Dense connective tissue; tissue packed with collagen fibers, tightly packed. Specialized connective tissue: cartilage, bone, adipose (fat tissue), blood and lymph. Cardiac muscle: located only in the heart, spontaneously active and involuntary. Smooth muscle: makes up the walls of most organs. Nerve tissue: makes up the brain and nervous system.