Cells, Tissues, and Organs -
Animals are made up of five basic types of tissues, organizations of cells that have certain basic structures and/or abilities in common. Each tissue type includes several slightly-different subtypes. The body's organs and structures, each made up of at least two tissues, do specific jobs. In this lab, with organs and structures of known functions, we will determine what sorts of tissues are present and how each contributes to the job(s) done; eventually, it's hoped that you'll learn how to visually recognize some tissues and use that recognition to make guesses about what they are the organ around them are doing.
Distinct features: epithelium always has a surface facing some sort of space, either on the outside of the body or around some internal space; the other side of the tissue lies on a shared basement membrane. Epithelium also contains no blood vessels, although they usually run close by.
Functions: Epithelium forms many linings, giving protection and containment on both the inside and outside of structures, and are often found where materials must be moved into or out of the blood - either absorptive or secretory. Cell shapes (flat squamous, tall columnar, and cuboidal) and layering (simple, compound, and transitional) are used to tell different types of epithelium apart. One other important function is found in a particular special epithelium subtype called secretory epithelium - this produces secretions, so it is a major part of any kind of gland, but also mucus linings, etc.
Distinct features: the cells in connective tissue are always surrounded by some sort of noncellular material, usually produced by those cells. It's usually the nature of that material that determines how a connective tissue subtype looks under the microscope.
Functions: The nature of the material - hard, flexible, fatty, liquid - gives connective tissues their functions. Most skeletal structures, such as bones, cartilage, and ligaments, are types of connective tissue, and are used to provide body structure as well as connect parts together. Several types of fibrous connective tissue hold organs together or provide internal and external shapes. Blood and fat are also subtypes of connective tissue.
Distinct features and functions: the cells of muscle tissue are unique in that they are capable of contracting, or getting shorter. There are three muscle subtypes which have their own particular features: Skeletal muscles are made up long cells with multiple nuclei and striations, stripes across the cells that actually show how millions of protein molecules are organized in there - these are powerful, high-energy muscles that are usually under conscious control of the brain. Cardiac muscles, like skeletal, are striated and powerful, but the cells are short and branched, not fused together in multi-nuclei fibers but "zipped" together with special connections (intercalated discs) that may be visible under the microscope; unlike skeletal muscles, cardiac muscles can contract with a set rhythm, as would be useful in a blood-pumping organ, and are not generally under any kind of conscious control. Smooth muscle cells are not striated, often short, single cells with points at each end; compared to the other muscle types, they are weaker, use less energy, but are almost tireless, often forming sheets or tube linings in organs that need to move materials along. They are not usually under conscious control.
Distinct features and functions: only the cells in nervous tissues can carry electrochemical messages called impulses, which allow us to process reflex, memory, and understanding in our spinal cords and brain; some nervous tissue can convert environmental information into those messages - they function as receptors for our senses, in sense organs. Elsewhere, the "wiring" of the system is usually too fine to be visible under a microscope.
Reproductive / Germ / Stem Tissue:
Distinct features and functions: cells in this tissue, which is known by several names, have the ability to take normal body-type cells, each of which contain two sets of chromosomes (one from each parent), and through a special cell division process called meiosis produce gametes, either sperm or egg cells, which contain only single sets of chromosomes and can be used to produce offspring. Sperm and egg cells are considered types of reproductive tissue.
Original Version 1994; Web Version 2004. M. McDarby.
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