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Nurussama Patel In this assignment I am going to describe the main tissue types of the body which are epithelial, connective, muscle and nervous tissues. Each of these four tissues has an individual structural features and particular functions which are joined together to produce functioning organs. Also I am going to describe the roles they play in any two organs of our body. Epithelial tissue Firstly I am going to talk about epithelial tissue. Epithelial covers the lining of the body surfaces both internal and external. The outer layer of the skin is formed from the epithelial tissue and also the inner lining of digestive area and blood vessels. The cells of the epithelial tissue are tightly packed and rest on a thin basement membrane as the below picture shows. The free surface of the epithelium is exposed to air or fluid. There are no blood vessels present. Epithelial tissues are classified according to the shape of the component cells and the cells are arranged into one or more layers. Epithelial tissue can be divided into two groups; simple and compound. Simple epithelial is where there is an epithelial tissue of one cell thick whereas if the epithelial tissues are two or more cells thick then it’s known as compound epithelial. The types of simple epithelial are squamous, cuboidal and columnar. Squamous is thin, flat and square shaped and they form the lining cavities such as the mouth blood vessels. Cuboidal are square or cuboidal shaped and they are found in glands and in the lining of kidneys. Lastly the columnar is column shaped and the cells appear rectangular in side view with the nucleus displaced toward the base of the cell. All of these three are shown in the picture below. The compound epithelial tissue is where the linings have to continue wear and tear, the epithelia are composed of many layers of cells and they are called compound epithelium. The top cells are flat and scaly and it may or may not be keratinised which contains a tough, resistant protein called keratin. The mammalian skin is an example of dry, keratinised, stratified epithelium. Nurussama Patel Compound epithelium Connective tissue Secondly I am going to talk about the connective tissue. Connective tissues are fibrous tissues. They are made up of cells separated by non-living material, which is called extracellular matrix. Connective tissue gives shape to organs and holds them in place. Both blood and bone are examples of connective tissue. Connective tissue is a "connecting" function. It supports and binds other tissues. Connective tissue has cells scattered throughout an extracellular matrix. Regular connective tissue Dense connective tissue is characterized by an abundance of fibres with fewer cells, as compared to the loose connective tissue. It is also called fibrous or collagenous connective tissue because of the abundance of collagen (collagenous) fibres. Little intercellular substance is present. Nurussama Patel Cartilage Cartilage is a somewhat elastic, pliable, compact type of connective tissue. It is characterized by three traits: lacunae, chondrocytes, and a rigid matrix. The matrix is a firm gel material that contains fibres and other substances. There are three basic types of cartilage in the human body: hyaline cartilage, elastic cartilage and fibrocartilage. In this laboratory, you will examine the most common type of cartilage, the hyaline cartilage. Most of the skeleton of the mammalian fetus is composed of hyaline cartilage. As the fetus ages, the cartilage is gradually replaced by more supportive bone. In the mammalian adult, hyaline cartilage is mainly restricted to the nose, trachea, bronchi, ends of the ribs, and the articulating surfaces of most joints. The function of the hyaline cartilage is to provide slightly flexible support and reduce friction within joints. It also provides structural reinforcement. Areolar connective tissue Microscopic view of Areolar connective tissue Areolar connective tissue is the most widespread connective tissue of the body. It is used to attach the skin to the underlying tissue. It also fills the spaces between various organs and thus holds them in place as well as cushions and protects them. It also surrounds and supports the blood vessels. The fibres of areolar connective tissue are arranged in no particular pattern but run in all directions and form a loose network in the intercellular material. Collagen (collagenous) fibres are predominant. They usually appear as broad pink bands. Some elastic fibres, which appear as thin, dark fibres are also present. The cellular elements, such as fibroblasts, are difficult to distinguish in the areolar connective tissue. But, one type of cells - the mast cells are usually visible. They have course, dark-staining granules in their cytoplasm. Since the cell membrane is very delicate it frequently ruptures in slide preparation, resulting in a number of granules free in the tissue surrounding the mast cells. The nucleus in these cells is small, oval and light-staining, and may be obscured by the dark granules. Nurussama Patel Adipose connective tissue Microscopic view of adipose connective tissue The cells of adipose (fat) tissue are characterized by a large internal fat droplet, which distends the cell so that the cytoplasm is reduced to a thin layer and the nucleus is displaced to the edge of the cell. These cells may appear singly but are more often present in groups (Figure 11). When they accumulate in large numbers, they become the predominant cell type and form adipose (fat) tissue. Adipose tissue, in addition to serving as a storage site for fats (lipids), also pads and protects certain organs and regions of the body. As well, it forms an insulating layer under the skin which helps regulate body temperature. Blood Blood is considered a connective tissue for two basic reasons: (1) embryologically, it has the same origin (mesodermal) as do the other connective tissue types and (2) blood connects the body systems together bringing the needed oxygen, nutrients, hormones and other signaling molecules, and removing the wastes. In circulating blood two different cell types are found: enucleated erythrocytes or red blood cells and nucleated leukocytes or white blood cells. Nurussama Patel Bone Bone tissue is a specialized form of connective tissue and is the main element of the skeletal tissues. It is composed of cells and an extracellular matrix in which fibers are embedded. Bone tissue is unlike other connective tissues in that the extracellular matrix becomes calcified. FUNCTIONS OF BONE TISSUE The skeleton is built of bone tissue. Bone provides the internal support of the body and provides sites of attachment of tendons and muscles, essential for locomotion. Bone provides protection for the vital organs of the body: the skull protects the brain; the ribs protect the heart and lungs. The hematopoietic bone marrow is protected by the surrounding bony tissue. The main store of calcium and phosphate is in bone. Bone has several metabolic functions especially in calcium homeostasis. Nervous tissue Nervous tissue is the main component of nervous system including the brain, spinal cord, nerves. The nervous tissue regulates and controls the body function. Nervous tissue has two types, one is neurones and the second is neuroglia. Nervous tissues that stem throughout the body are all made up of specialised of nerve cells called neurones. Neurones are stimulated and passed on impulses very quickly. Neurons are classified as either motor, sensory, or interneurons. Motor neurons carry information from the central nervous system to organs, glands, and muscles. Sensory neurons send information to the central nervous system from internal organs or from external stimuli. Interneurons send signals between motor and sensory neurons. Nurussama Patel Neurones Cell Body Neurons contain the same cellular components as other body cells. The central cell body is the largest part of a neuron and contains the neuron's nucleus, associated cytoplasm, and other cell structures. The cell body produces proteins needed for the construction of other parts of the neuron. Axons - typically carry signals away from the cell body. They are long nerve processes that may branch out to show the signals to different areas. Some axons are wrapped in an insulating coat of glial cells called oligodendrocytes and Schwann cells. These cells form the myelin covering which indirectly support in the transfer of impulses as myelinated nerves can carry out impulses quicker than unmyelinated nerves Axons end at the joint known as synapses. Dendrites - carry signals toward the cell body. Dendrites are usually more numerous, shorter and more split than axons. They have many synapses to receive signal messages from nearby neurons. Neuroglia: Collectively, cells that structurally and metabolically support neurons. They make up about half the volume of nervous tissue in vertebrates. Nurussama Patel The neuroglial cells are found in the parenchyma which is a functional part of brain and spinal cord and these are classified as: Macroglia, of neural origin, including astrocytes, oligodendrocytes, and glioblasts. Microglia, of mesodermal origin. Muscle tissue Muscle tissue has an ability to relax and contrast and so bring about movement and work in many parts of the body. There are other movements in the body too which are especially for the survival of the organism such as the heart beat. Muscles can be divided into three main groups according to their structure, e.g.: Smooth muscle tissue. Skeletal muscle tissue. Cardiac (heart) muscle tissue. Nurussama Patel Smooth muscle tissue is made up of thin muscle cells and fibres. These fibres are pointed at their ends and each has a single, large, oval nucleus. Each cell is filled with a specialised cytoplasm, the sarcoplasm and is surrounded by a thin cell membrane, which is the sarcolemma. They are not arranged in a definite striped pattern, as in skeletal muscles. Smooth muscle fibres connect to form layers of muscle tissue rather than bundles. Smooth muscle is involuntary tissue; it is not controlled by the brain. Smooth muscle forms the muscle layers in the walls of organs such as the digestive tract (intestines). Smooth muscle tissue Skeletal muscle is a form of striated muscle tissue and it is voluntarily controlled. Most skeletal muscles are attached to bones by bundles of collagen fibers which are known as tendons. Skeletal muscle is made up of each component known as muscle fibers. These fibers are formed from the fusion of developmental myoblasts (a type of cell that gives rise to a muscle cell). The muscle fibers are long and cylindrical. This is a single tissue only found in the walls of the heart. Cardiac (Heart) Muscle Tissue shows some of the characteristics of smooth muscle and some of skeletal muscle tissue. Its fibres like those of skeletal muscle have cross-striations and contain a lot of nuclei. However like smooth muscle tissue, it is involuntary. Cardiac muscle differs from striated muscle in terms of length because they are shorter and the sarcolemma is thinner and not clearly visible. There is only one nucleus present in the centre of each cardiac fibre. The spaces between different fibres are filled with areolar connective tissue which contains blood capillaries to supply the tissue with the oxygen and nutrients.