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Revision:Anatomy and physiology chapter 4In the very early stages, the ball of cells is divided into the ectoderm, mesoderm, and endoderm. From the ectoderm develops the skin, enamal, and other epithelial tissues. From the mesoderm develops muscle, bone, fat, and some of the internal organs. From the endoderm develops the lining of the alimentary and respiratory tracts. A tissue is a group of cells and their products developed to carry out a special function. The tissue diagram: The purpose of epitlelial tissue(as in diagram) is to provide covering and lining and form the glands. Epithelia do not contain blood vessels. Simple epithelium consists of a single layer of cells attatched to a basement membrane. It is found where there is little wear and tear. The cells of simple pavement epithelium are flat and found lining the blood vessels and forming the peritoneum. The cells of simple cuboidal epithelium are cube-shaped and found covering the ovaries. The cells of simple columnar epithelium are taller and are found lining the stomach and small intestines. Ciliated columnar epithelium are found in the respiratory tract. Brush borders are found in the small intestine. Stratified epithelium is made up of many layers of cells, the deepest of which lie on the basement membrane. These cells are columnar and found in the germinal layer. When they divide, the parent cells are pushed nearer the surface and become flattened. If the surface of the epithelium is dry, keratin forms. If it is moist, the cells survive and keratin does not form. Transitional epithelium cells are rounded - summary - simple - single layer, - stratified - many layers, - transitional - rounded cells. Transitional epithelium is found lining organs which must expand and be waterproof, such as the bladder. Exocrine glands pour their secretions out through a duct. Simple glands have one duct leading from a single secretory unit. Simple tubular glands are found in the walls of the small intestine and stomach. Simple coiled glands pour sweat onto the surface af the skin. Simple saccular glands secrete sebum which lubricates hair and skin. Compond glands have many ducts leading from one or more secretory units. Compound tubular glands are found in the duodenum. Compound saccular glands are also known as racemose glands. An example of one is the salivary glands. Endocrine glands pour their secretions directly into the blood stream. These secretions are called hormones. Connective tissue supports and binds together all other tissues. It originates from mesenchyme cells, which originate in the mesoderm. Connective tissue consists of cells, matrix, and fibres. The matrix and fibres, or the non-living parts form the supportimg material. There are teo types of fibres: collagenous and elastic. Collagenous fibres originate from fibroblasts, which also secretes a substance that becomes collagen. Collagen occurs in wavy bundles and will stretch only a little without tearing. Loose connective tissue is found between and around organs of the body. fatty tissue protects delicate organs such as the eye and kidney. Hyaline cartilage is found in the trachea and covering the ends of bones. Fibrocartilage is found between bones forming slightly movable joints. Elastic cartilage is found in the epiglottis and auricle of the ear. Bone is also a connective tissue. It consists of collagen impregnated with calcium salts, osteocytes, and has a rich blood supply. Muscular tissue is specialised for contraction and is therefore able to produce movement. Muscle cells are long and thin so that the shortening that occurs during contraction may be as effective as possible. Skeletal muscle is found in the flesh of the limbs and trunk. Each long cell can be described as a fibre. Each cell contains myofibrils. Each fibril is enveloped in sarcolemma. fibrils are bound together by connective tissue and enclosed in the endomysium, then the perimysium, then the epimysium. It is striped. Skelatal or voluntary muscle contracts strongly but tires quickly. Smooth or involuntary muscle is found in the walls of the internal organs. It is not under the control of the will and acts without any conscious effort. It is supplied by autonomic nerves which regulate contractions. It is designed for slow contraction and does not tire easily. Cardiac muscle is irregularly striped. It consists of short cylindrical fibres with centrally placed nuclei. It is found in the heart. Nervous tissue is specially designed to receive stimuli and carry impulses to other tissues. It consists of neurones and a connective tissue called neuroglia. A nerve cell consists of the cell body, an axon/s and a dendrite/s. Membranes consist of epithelium. They secrete lubricating fluids. Synovila membranes secrete a very thick fluid. They are found lining joint cavities, over bony prominences, between ligaments/tendons and bones. |
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