Summary — Animal Tissues and Frog Organ Systems

This chapter has worked through animal structural organisation at two levels: first the four basic tissue types that are the common building blocks of every animal organ, and then, using the frog as the WBCHSE-prescribed case-study organism, how those tissues are assembled into the organ systems of a real, functioning animal.

At the tissue level, epithelial tissue covers and lines surfaces using tightly packed cells on a basement membrane, appearing as simple squamous, cuboidal, columnar or ciliated epithelium (one cell layer) or as compound stratified epithelium (many layers, for protection against wear). Connective tissue, by contrast, is defined by relatively sparse cells embedded in an abundant matrix, and ranges from loose (areolar, adipose) through dense (regular and irregular, as in tendons/ligaments and the dermis) to skeletal (cartilage and bone) and fluid (blood) forms. Muscular tissue is built for contraction, and its three types — striated/skeletal (voluntary, multinucleate, clearly banded), unstriated/smooth (involuntary, uninucleate, unbanded, lining hollow organs) and cardiac (involuntary but rhythmic, uninucleate, joined by intercalated discs, found only in the heart) — are distinguished chiefly by fibre shape, nucleation and striation. Nervous tissue, finally, is built of neurons (cell body, dendrites and axon) communicating across synapses, supported by neuroglia. …