Term used in Anatomy

TERMS USED IN ANATOMY 

Organization: It refers to the kind of construction of the body

  • A cellular or protoplasmic level of organization: Body is not differentiated into cells. Example: Protozoa (Subkingdom: Protozoa); All other animals except protozoa come under the Subkingdom: Metazoa (Body is composed of numerous cells).
  • Cellular level of organization: The cells of the body are more or less loose and independent, Eg. Amoeba.
  • Tissue level of organization: In some animals, body cells form tissues, Eg. Coelenterata and Ctenophora
  • Organ system level of organization: In most of the animals, tissues combine into organs, which, in turn, combine to form organ systems, Eg. Human being, fish, reptiles, etc.,

Germ layers

  • The fundamental cell layers laid down in an early embryo of the Metazoa are called germ layers. The Coelenterata have only two layers: ectoderm and endoderm. They are termed the diploblastic animals. Most other Metazoa possess three germ layers: ectoderm, mesoderm and endoderm. They are known as the triploblastic animals, Eg. Animals except Coelenterata

Symmetry

  • It refers to the similarity in size, shape and number of parts on the opposite sides of a median line. Parts of an animal body are often so arranged that it is possible to cut it into two similar halves by one or more planes. Such animals are said to be symmetrical. Some animals, like amoeba and snail, cannot be divided into equal parts by any plane. They are said to be asymmetrical. The symmetrical animals show one of the three types of symmetry: spherical, radial and bilateral.

Spherical (universal) symmetry

  • Body is divisible into similar halves by any plane passing through the center, Eg. Sea urchin

Radial symmetry

  • Body is with a number of similar parts radiating out from a central axis. The body can be split up into equal halves by any plane passing through the middle from top to bottom. The animals with radial symmetry are called radiata, Eg. Sponge and most coelenterates.

Bilateral symmetry

  • Symmetrical arrangement, as of an organism or a body part, along a central axis, so that the body is divided into equivalent right and left halves by only one plane.
Last modified: Sunday, 18 September 2011, 4:37 AM