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Body Architecture
symmetry, body plans, development
| Term | Definition |
|---|---|
| asymmetry | lacking symmetry; lack of proportion between parts |
| radial symmetry | the body is arranged around a central axis such that splitting it lengthwise through the center at any angle always results in two equal halves. |
| bilateral symmetry | a single lengthwise cut through the central axis will yield two symmetrical halves |
| aboral | an opening opposite the mouth |
| oral | the mouth area |
| sessile | an organism that lives attached to a surface. |
| anterior | toward the head |
| posterior | toward the tail end |
| dorsal | back surface |
| ventral | belly surface |
| cephalization | the development of a head region usually with sensory organs |
| Primary Germ layers | ectoderm, endoderm and mesoderm |
| Ectoderm | develops into the outermost covering of the body, the epidermis, and nervous tissues |
| Endoderm | develops into the innermost lining of the gut tube |
| mesoderm | most tissues in between the ecto and endoderm. In humans makes up the muscles and bones. |
| morula | During early development, a solid ball of cells that forms after cleavage |
| blastula | During development when the embryo is a hollow ball with a single layer of cells and a fluid center |
| gastrula | During development when part of the ectoderm invaginates and forms the endoderm (germ layers form) |
| gastrulation | The process of reorganizing the blastula into germ layers |
| cleavage | rapid cell division during development with little cell growth. |
| fertilization | The union of gametes to form a zygote. It can be internal or external. |
| zygote | a fertilized egg. |
| gamete | a sex cell that is haploid (has half the number of chromosomes) |
| Body cavity types | acoelomate, pseudocoelomate, coelomate |
| acoelomate | an animal without a body cavity between the body wall and the gut. |
| pseudocoelomate | an animal with a body cavity formed between the mesoderm and endoderm but not completely surrounded by mesoderm. |
| coelomate | an animal with a true body cavity formed completely within the mesoderm |
| diploblast | an animal that developed from two primary germ layers, an ecto and endoderm. |
| triploblast | an animal that has three primary tissue layers: endo, ecto and mesoderm |
| blind sac gut | an organism with a simple gut that has only one opening, the mouth. |
| complete gut | an organism with a gut tube through the entire body that has both a mouth at the anterior end and an anus toward the posterior. |
| exoskeleton | organisms that secrete a skeleton from the ectodermal tissues. |
| endoskeleton | organisms that secrete substances from the mesodermal tissues forming internal skeletons |
| hydrostatic skeleton | Internal fluids in a confined space acting as a skeleton |
| jointed appendages | anatomical structures that extend from the main trunk of the body that act as levers or joints to move the body. |
| Four tissue types | epithelial, connective, muscle and neural |
| Epithelial tissue | Lines cavities and the outside. Acts as a barrier and controls what enters and exits the body. |
| Muscle tissue | Contracts (shortens). Creates leverage from movement and moves substances through tubes. Three types (cardiac, smooth and skeletal) |
| Neural tissue | Conducts electrical impulses. Basic cell type is a neuron. Dendrites receive impulse and axon transmits it. |
| Connective tissue | Consists of cells and a matrix (ground substance and fibers). Supports, connects and protects the body. Examples include bone, blood, and dense regular (tendons). |
| deuterostome | an animal whose mouth develops second. The first opening in gastrulation develops into the anus |
| protostome | an animal in which the first opening that forms in the gastrula forms the mouth. |
| cortical reaction | A slow block process after fertilization that prevents other sperm from entering the egg. It involves the release of granules into the space between the membrane and the egg causing an influx of water that separates the membrane from the egg. |
| polarity | Some eggs have a vegetal and animal pole. The end of the egg with the most yolk is the vegetal pole. |
| direct development | when lots of yolk is present and the embryo develops into an miniature adult |
| indirect development | when little or no yolk is present and the embryo enters a larval stage that can feed before developing into an adult. |
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