There are several main types of animal tissue including : epithelial, muscle, nervous tissue and connective tissues such as bone, cartilage, blood and loose connective tissue (sometimes called areolar tissue).
Video - Animal tissues introduction: http://www.youtube.com/watch?v=I2bSWCyKOz0&feature=related
Tissues of human body: http://www.mhhe.com/biosci/ap/histology_mh/tismodov.html
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Epithelial tissue
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Epithelial tissues are formed by cells that cover surfaces such as the surface of the skin, and line tubes and cavities, such as the digestive organs, blood vessels, kidney tubules and airways. The cells comprising an epithelial layer are linked via semi-permeable junctions; hence, this tissue provides a barrier between the external environment and the organ it covers. In addition to this protective function, epithelial tissue may also be specialized to function in secretion and absorption . Epithelial tissue helps to protect organisms from microorganisms, injury, and fluid loss. All epithelial tissues are free surfaces attached to the underlying layers by a basement membrane.
Muscle tissue
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Muscle cells form the active contracting tissue of the body known as muscle tissue. Muscle tissue functions to produce force and cause motion within internal organs. Muscle tissue is separated into three distinct categories: smooth muscle , which is found in the inner linings of organs; skeletal muscle , which is found attached to bone providing movement; and cardiac muscle which is found in the heart , allowing it to contract and pump blood throughout an organism.
Smooth muscle
Smooth muscle is unstriated (not striped) in appearance. The contraction of smooth muscle can be relatively slow and often happens automatically without our conscious control. Some call it involuntary muscle. It rarely becomes fatigued. Smooth muscle is found in the gut where it squeezes food along the intestines by peristalsis. It is found in the walls of our blood vessels where it can make the vessel wider or narrower allowing more or less blood to flow.
Skeletal muscle
Skeletal muscle or voluntary muscle appears striped or striated when seen through a microscope. This is due to banding from the pattern of actin and myosin protein filaments in the muscle. Skeletal muscle is attached to the bones of the skeleton. Skeletal muscle fatigues or tires quickly. It also contracts quickly and is controlled by the conscious part of our brain. The biceps is made of skeletal muscle and when the muscle contracts it shortens bringing the lower arm upwards. Skeletal muscles are often arranged in antagonistic pairs where if one muscle moves a limb one way the other muscle will move it back.
Cardiac Muscle
Cardiac muscle appears striated like skeletal muscle except in cardiac muscle there are cross bridges or cross connections linking muscle fibres together. Cardiac muscle is myogenic, in other words it generates its own impulse to contract from within itself. It is found only in the heart and it contracts rhythmically at a speed dictated by the brain without ever suffering fatigue.
Nerve tissue
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Cells making up the central nervous system and peripheral nervous system are classified as neural tissue. In the central nervous system , neural tissue forms the brain and spinal cord and, in the peripheral nervous system forms the cranial nerves and spinal nerves , including the sensory and motor neurons . The function of nerve tissue is to transmit electrical messages around the body.
Three Types of Nerve Cells
Sensory neurones
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Sensory nerve cells (or sensory neurones) carry impulses (electrical signals) from a receptor to the CNS (central nervous system). The cell body is located off to one side of the axon as it enters a vertebra (one of the boney discs of the spine).
Motor neurones
Motor neurones carry impulses out from the CNS to effectors, instructing them to do something. In most cases the effector is a muscle being told to contract but other effectors could be glands or colour cells (chromatophores). The cell body is at the head of a motor neurone in the vertebra and its tail or dendrites are attached to the muscle or other effector.
Relay or connector neurones
Relay neurones are very short especially compared to the other two types. They connect a sensory neurone with a motor neurone across the grey matter region in the CNS inside the spine. The impulse travels from the cell body at the head end along the short axon to the dendrites.
Connective tissue
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Connective tissues are made up of separate cells which are floating in a matrix. Connective tissues are fibrous tissues. They are made up of cells separated by non-living material, which is called matrix . Connective tissues give shape to organs and holds them in place. Both bone and blood are examples of connective tissue. As the name implies, connective tissue serves a "connecting" function. It supports and binds other tissues.
Cartilage
Cartilage is a flexible connective tissue found in many areas of the bodies of humans and other animals, including the joints between bones , the rib cage , the ear , the nose , the elbow, the knee, the ankle, the bronchial tubes and the intervertebral discs . It is not as hard and rigid as bone but is stiffer and less flexible than muscle .
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Cartilage is composed of specialized cells called chondroblasts that produce a large amount of extracellular matrix composed of collagen fibres, abundant ground substance and elastin fibers. Chondroblasts that get caught in the matrix are called chondrocytes . They lie in spaces, called lacunae, with up to eight chondrocytes per lacuna. Cartilage is classified in three types, elastic cartilage , hyaline cartilage and fibrocartilage , which differ in the relative amounts of these three main components.
Blood
Blood is a tissue because it is made up of several types of cell functioning together. In fact blood is composed of red blood cells, white blood cells and platelets floating in a yellow liquid called plasma.
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Red blood cells
Red blood cells are shaped like biconcave discs (round discs with a dimple in the top and another in the bottom). Their job is to carry oxygen round the body form the lungs to the tissues. They contain a red pigment (coloured chemical) called haemoglobin which is brilliant at carrying oxgen.
White blood cells
White blood cells are slightly larger than red ones. They are more irregular in shape and their job is to fight pathogens (disease-causing organisms like some bacteria and viruses). Some engulf 9swallow up pathogens), some produce chemicals called antibodies to kill the pathogens while a third type release antitoxins, chemicals which neutralize the poisons made by the pathogens. When looked at under a microscope white blood cells may appear purple because a dye is used to stain them.
Platelets
Platelets are fragments of cells floating in the plasma. They are important in clotting and stick together where a blood vessel is damaged to close the wound.
Plasma
Plasma is a yellow liquid in which the solid cells are suspended or floating. It carries many important chemicals around the body including the waste carbon dioxide from respiration, hormones, urea, and glucose and also transports heat.
