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| Summary |
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 All higher multicellular animals, called eumetazoans, exhibit a tissue and higher levels of organization |
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 There are four primary tissues in animals epithelial, muscular, connective and nervous |
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 Epithelial tissue (epithelium) is the simplest. It is avascular and develops from all the three primary germ layers. |
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 Epithelial cells are almost always compactly arranged and have abundant cytoplasm with prominent nucleus. |
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 Epithelium can be distinguished into simple, stratified and pseudostratified |
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 Simple epithelium consists of a single layer of cells on a basement membrane. It is further distinguished into squamous, cuboidal, columnar, ciliated and glandular |
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 Stratified epithelium has more than one layer of cells on a basement membrane. It can be further differentiated into stratified squamous, stratified cuboidal, stratified columnar and transitional epithelium |
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 In the skin of vertebrates stratified squamous epithelium undergoes a process called keratinization. |
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 Pseudostratified epithelium has a single layer of cells on a basement membrane giving a false appearance of many layers |
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 Muscular tissue (muscle) is responsible for movements in the body |
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 Muscular tissue is formed by muscle fibres in which the cytoplasm is specialized (sarcoplasm) by enclosing contractile units called myofibrils |
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 Muscular tissue is distinguished into smooth muscle, striated muscle and cardiac muscle |
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 Smooth muscle has spindle shaped uninucleate muscle fibres without a sarcolemma |
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 Smooth muscle is involuntary in nature. It does not easily experience fatigue |
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 Smooth muscle occurs in almost all the hollow visceral organs of the body |
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 Striated muscle is characterised by elongated cylindrical, multinucleate muscle fibres with a distinct sarcolemma |
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 Striated muscle is voluntary in nature. It experiences fatigue very easily |
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 Striated muscle is usually formed attached to bores |
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 Cardiac muscle is characterised by long, cylindrical, branched multinucleate muscle fibres with an indistinct sarcolemma |
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 Cardiac muscle is involuntary in nature. It never experiences fatigue |
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 Cardiac muscle occurs exclusively in the heart |
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 Connective tissue is the most abundant tissue in the animals body. It is characterised by the presence of a large amount of matrix, few cells and supporting fibres |
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 Connective tissue can be distinguished into three types connective tissue proper, supporting tissue and fluid connective tissue |
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 Connective tissue proper is typical. It includes Areolar tissue, fibrous tissue, elastic tissue and adipose tissue |
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 Areolar tissue is most abundant. It has a matrix containing white fibres, yellow fibres and different types of cells |
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 Supporting tissue includes cartilage and bone |
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 Cartilage has a matrix (chondrin) rich in organic substances. It encloses chondriocytes inside spaces called lacunae |
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 Cartilage forms the embryonic endoskeleton in most vertebrates. In sharks and rays it forms the adult endoskeleton |
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 Bone has a matrix (ossein) rich in calcium phosphate. In mammals it is deposited in the form of concentric rings called lamellae, together forming a Haversian system |
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 Fluid connective tissue includes blood and lymph |
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 Blood is the chief circulating fluid in the body. It consists of a plasma enclosing three types of cells RBC (erythrocytes) WBC (leukocytes) and platelets (thrombocytes) |
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 Lymph differs from blood in the absence of RBC |
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 Nervous tissue is the most highly specialized animal tissue |
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 The functional units of nervous tissue are called neurons |
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 A typical neuron is multipolar. It has a cell body (cyton) and a long fibre (axon) |
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 The axon has a noncellular covering of myelin sheath and a cellular covering called neurilemma |
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 The axon ends in branched projections called telodendrons. |
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