Extracellular Components of the Metazoan Body
Extracellular
Components of the
Metazoan Body
In addition to hierarchically arranged cellular structures discussed in the preceding text, metazoan animals contain two important noncellular components: body fluids and extracellular structural elements. In all eumetazoans, the body fluids are subdivided into two fluid “compartments”: those that occupy intracellular space, within the body’s cells, and those that occupy extracellular space, outside the cells. In animals with closed vascular systems (such as segmented worms and vertebrates), the extracellular fluids are subdivided further into blood plasma (the fluid portion of the blood outside the cells; blood cells are really part of the intracellular compartment) and interstitial fluid. Interstitial fluid, also called tissue fluid, occupies the space surrounding cells. Many invertebrates have open blood systems, however, with no true separation of blood plasma from interstitial fluid. We will explore these relationships further in Internal Fluids and Respiration.
If we were to remove all specialized cells and body fluids from the interior of the body, we would be left with the third element of the animal body: extracellular structural elements. This is the supportive material of the organism, including loose connective tissue (especially well developed in vertebrates but present in all metazoa), cartilage (molluscs and chordates), bone (vertebrates), and cuticle (arthropods, nematodes, annelids, and others). These elements provide mechanical stability and protection (Support, Protection and Movement). In some instances, they act also as a depot of materials for exchange, and serve as a medium for extracellular reactions. We describe diversity of extracellular skeletal elements characteristic of different groups of animals in Pseudocoelomate Animals , Molluscs , Segmented Worms, Arthropods , Aquatic Mandibulates, Terrestrial Mandibulates, Lesser Protostomes , Lophophorate Animals , Echinoderms , Chaetognaths and Hemichordates, Chordates , Fishes, Early Tetrapods and Modern Amphibians, Reptilian Groups, Birds and Mammals.
In addition to hierarchically arranged cellular structures discussed in the preceding text, metazoan animals contain two important noncellular components: body fluids and extracellular structural elements. In all eumetazoans, the body fluids are subdivided into two fluid “compartments”: those that occupy intracellular space, within the body’s cells, and those that occupy extracellular space, outside the cells. In animals with closed vascular systems (such as segmented worms and vertebrates), the extracellular fluids are subdivided further into blood plasma (the fluid portion of the blood outside the cells; blood cells are really part of the intracellular compartment) and interstitial fluid. Interstitial fluid, also called tissue fluid, occupies the space surrounding cells. Many invertebrates have open blood systems, however, with no true separation of blood plasma from interstitial fluid. We will explore these relationships further in Internal Fluids and Respiration.
If we were to remove all specialized cells and body fluids from the interior of the body, we would be left with the third element of the animal body: extracellular structural elements. This is the supportive material of the organism, including loose connective tissue (especially well developed in vertebrates but present in all metazoa), cartilage (molluscs and chordates), bone (vertebrates), and cuticle (arthropods, nematodes, annelids, and others). These elements provide mechanical stability and protection (Support, Protection and Movement). In some instances, they act also as a depot of materials for exchange, and serve as a medium for extracellular reactions. We describe diversity of extracellular skeletal elements characteristic of different groups of animals in Pseudocoelomate Animals , Molluscs , Segmented Worms, Arthropods , Aquatic Mandibulates, Terrestrial Mandibulates, Lesser Protostomes , Lophophorate Animals , Echinoderms , Chaetognaths and Hemichordates, Chordates , Fishes, Early Tetrapods and Modern Amphibians, Reptilian Groups, Birds and Mammals.
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