Cell - The Basic Structural and Functional Unit of Human Body

Questions: Analyse the human body in terms of organ systems, organs, tissues and cells?. Discuss the morphology and microanatomy of cells in connective and muscle tissues?. Analyse the functions of the skeletal system including the main type of joints and the role of connective tissues?. Analyse development of the skeleton?. Discuss relationships between structures of bones and their functions?. Analyse structure and function in a range of joints?. Discuss how muscular forces are transmitted by the skeletal system?. Explain the types of muscle cells, the contractile response, innervation of muscle and their component muscle cells?. Analyse the structure of typical muscles?. Answer: The organ Systems, Organs, Tissues, and Cells: The human body is made up of cells. Cells are the structural unit of life. Cells with specific structure and function make tissues. Each kind of cells helps in making a particular tissue. Epithelial tissue helps in protection of the body by skin. It is present in inner surfaces of the body example stomach, lungs and protects it from injury and infection. Connective tissue supports the body. Constituents of connective tissue are bones, cartilages, and fatty tissues. Characteristic stretchability is an important feature of this tissue. Nerve tissueforms the information network of the body. They are called ganglia. Nerve cells have long branching dendrites which enable to pass impulses with one another. Muscle tissues they help form the structural unit of the body. Three types of muscle are present in the body. Voluntary muscle which can be moved by will, Involuntary or smooth muscles which cannot be moved by will of human and cardiac muscles helps the pumping action of the heart muscle (Carson et al 2015). Organs are composed of a group of tissues functioning in a similar way. Tissues are present in everywhere, hair, nerve, blood, skin. An organ system comprises of functioning organs in a regular rhythm. Morphology and Microanatomy of Cells in Connective and Muscle Tissues Morphology Cells of connective tissue are arranged in a row, and they are embedded in the matrix of fibers. Collagen and elastin are present in the outer periphery of the cells. The fibers are usually present in parallel arrangement. Microanatomy Cells found in connective tissues include Fibroblasts- these make collagenous tissue fibers which have great flexibility and tensile strength. Macrophages monocytes are also present that helps to get rid of debris of dead cells. Constituents include collagen fibers and reticular fibers. Microfibril and elastic fibers. Ground substances are made up of proteoglycans (Carson et al 2015). Morphology Skeletal Muscles- these are elongated or tubular with multiple nuclei present on the periphery. They are striated that is they have alternating light and dark band pattern. Cardiac Muscle- they are comparatively short in length. They are often branched and striated. These muscles can either be mononucleated or binucleated. The position of the nuclei is central most of the time. They contain intercalated disc. Smooth muscles- these are spindle-shaped wide in the middle and tapered to narrow at both ends. They contain a centrally located nucleus. No visible striation are present. Proteins present are same as that of skeletal and cardiac muscles. Microanatomy- Epimysium is a connective tissue which forms a protective layer around skeletal muscles. They anchor the muscles tissues to the tendons. It also protects muscles from friction. Myocytes are cells encased within the endomysium. The cells of muscle contain myofibrils, which are complex strands of protein filaments bound together to form Sarcomeres. Regular patterns of sarcomeres form the striated appearance. Sarcomere is composed of actin and myosin protein (Ofli et al 2014). Functions of Joints and Role of Connective Tissue: The skeletal system is made of 206 bones providing four basic functions Support, Protection, Movement, storage of minerals and blood cells production by bone marrow. The skeletal system is made of bones, cartilages, joints and ligaments, muscles. There are two types of bones Compact bones and Spongy bones. Bones can be of different sizes long, short, flat, irregular. Bone cells include Osteocytes, Osteoblasts, and Osteoclasts. (Kemp et al 2013). Joints are the place where two bones come together. Joints can be Fibrous immovable but do not help in any kinds of movement. For example skull and pelvis. Cartilaginous- this joint is slightly movable and cartilages join the bones. Present in spine and ribs. Synovial- they are freely movable joint that facilitates more movement than the cartilaginous joints. Synovial fluid lubricates and protects the bones. Synovial joints can be of types- Plane joint Pivot joint, Condyloid joint. They help in the movement of the body; they act as lever and provide structural support along with the muscles. Gliding joints are ones present in carpals or on surfaces where the bones meet flat surfaces; they allow bones to glide past each other in any direction. Hinge joints are present in knees, elbows. They limit the movements in one direction. They gain strength from surrounding connective tissues ligaments and muscles. Saddle joints found in the metacarpal, trapezium bone. The bones can move along two axes. Ball and Socket joints are located in shoulders and hips. They provide full circle movement. They are very prone to dislocation (Kemp et al 2013). The connective tissues primarily function to connect the muscles to bones and to connect joints together. Tendons connect muscle to bone. They are an extension of muscle fibers. They are more elastic than ligaments. Ligaments- connect bones to bones. They contain collagen and elastin which provides them flexibility. They allow some limited joint movement. Cartilages- are firm, elastic and flexible. They are white in colour. They are found in nose, ears, ribs. They act as shock absorber. Its function also includes acting as a lubricant in some joint. It has no blood supply, unlike tendons and ligaments. Diffusion method helps to obtain nutrients and oxygen (Nishida et al 2016). Development of the Skeleton: The skeletal system begins to develop from the third week of conception. It forms notochord-which differentiate into the brain, spinal cord, and spine. By the end of the fifth week, a tail-like structure called coccyx is seen, the lowermost point of the spinal cord. The newborn baby has about 300 bones during birth, which reduces to 206 when some of the bones fuse. Bone formation is called Ossification. Ossification begins in the third month of fetal life. It completes in late adolescence. Two separate processes are required for Compact bones- which is 80% of the skeleton. The Cancellous bones- that includes skull parts, shoulder parts, and ends of long bones. Compact bones start as cartilages, then forms bones. This process is called endochondral ossification. Skull bones begin as fibrous membranes made up of collagen and blood vessels. Osteoid secreted by osteoblasts and forms networks of sponge-like bony elements called trabeculae. This process is inter-membranous ossification (Sc hilder 2013). Relationships between Structures of Bones and their Functions: Two bone structures seen in the human body are the Axial skeleton- that forms the skull, vertebral column, ribs and rib cage. These features as a support system or protects organs. The appendicular skeleton is of various sizes present in the upper and lower limbs. They form the girdles of shoulder and hip. One of its functions is to attach girdles to axial bones. This type of bones facilitates locomotion. From the pisiform bone of the wrist to the femur in the leg. Each bone have a different shape to fulfill a particular need of the body. Long bones- hollow elongated present in the fingers, limbs, ankles, and wrist. They function as support providing structure. Short bones- cube-shaped present in wrist and ankle. Flat bones- thin flattened and sometimes curved, present in the sternum, shoulder blades, ribs and skull. Irregular bones do not have a fixed shape, forms complicated structure like vertebrae and hipbones. Helps to protect and facilitates movement (Schilder 2013). Structure and Function in a Range of Joints: Joints are made when two ones meet. The joints make the skeleton flexible and allow movement. Joints are classified according to their structure, Hinge joint- one direction movement, Pivot joint-rotating and twisting and Ball and socket joints- allows greatest freedom of movement are present in the body and allows movement (Xia et al 2012). Mechanism of muscles as aLever: Skeletal muscles and bones act together to form a system that represents a lever that enables the movement. The muscle contracts which provides the effort. This effort then applied to the muscle attached to the bone. The bone and the overlying tissues represent the load which is then moved with the help of the lever. The skeleton overall has a series of muscle which contracts during movement. This movement provides the energy or the pull push effect which acts on the bones and move them. Just like a lever, the muscle allows effort given to take up load, if this load is situated close to the fulcrum and effort given away from the fulcrum, then the load can be moved with less effort. Such a lever is called Mechancal Advantage. The muscle acts on this theory. They are also called power lever. There are three classes of levers based on this position of effort with respect to the fulcrum. They are First-class lever- where the effort is applied to one end of the lever and the load is at t he other end. The muscles working as first-clas lever are present when the head is lifted off the chest. Some of these muscle are working at a Mechanical Advantage but some like the triceps of arms extending outwards against a resistance works at a Mechanical disadvantage. The Second-class lever- where the effort is applied at one end of the lever and the fulcrum is at the other side of the lever. The load is situated in between the two. Muscles in body working according to this class of lever work at a mechanical advantage. Example is standing on tiptoes. The muscles of this kind is rare in the body but these muscle have greater strength but not speed. Third-class lever- the levers of this kind have the effort applied in between the fulcrum and load. Most skeletal muscles in the body acts according to this class of lever system. Example: the bicep muscles in the arm, when the hand carries a load (Toedebusch et al 2015). This lever system allows muscles to be inserted close to the joints. The movement occurs across this joints, rapid and extensive movements like throwing a ball is done by contraction of the muscles. Muscles working according to third class of lever are thicker and powerful (Toedebusch et al 2015). Muscle Cells, Responses, and Components: Skeletal muscle- One muscle to move the bone in one direction and vice versa. Muscles contraction is normally voluntary. They can perform short, single contraction celled twitch or long contractions, tetanus. Will of the person acts as impulses from the nerves that makes the muscles move. Smooth muscle- found in the digestive system, blood vessels, airways, gastrointestinal tract, and uterus. They have the ability to stretch and maintain tension. Its contraction is involuntary. The nervous system controls the muscles like swallowing, breathing. Cardiac muscle- found in heart, endurance and consistency are the characteristics of this muscle. Stretching is limited. The nerve impulses from the brain, lungs and heart together form the message that helps the heart pump. Contractions are involuntary (Toedebusch et al 2015). The structure of typical Muscles: A muscle fiber is made up of hundreds of filamentous structure called myofibrils. Each of these myofibrils has bundles of filamentous myofilaments. They can be either thick or thin. Thicker myofilaments are composed of myosin while thinner ones consist of actin protein. Many myofilaments forms sarcomeres, thick myofilaments are attached to the center while thin myofilaments are present in the ends of sarcomere to the center. This creates a crisscross structure and form muscle. Muscle fibers are soft and fragile, but they can endure tremendous pressure. Each myofibril has a connective tissue sheath for protection. A fascicle is a term given to a numerous myofibril sheathed with thick connective tissue. Many fascicles bundled together by an even tougher coat of connective tissue forms the muscle (Xia et al 2012). Reference: Carson, J.A., Hardee, J.P. and VanderVeen, B.N., 2015, December. The emerging role of skeletal muscle oxidative metabolism as a biological target and cellular regulator of cancer-induced muscle wasting. In Seminars in cell developmental biology. Academic Press. Cohen, B.J., 2015. Memmler's Structure and Function of the Human Body, SC. Cronin, N.J., Avela, J., Finni, T. and Peltonen, J., 2013. Differences in contractile behaviour between the soleus and medial gastrocnemius muscles during human walking. The Journal of experimental biology, 216(5), pp.909-914. Jalal, A., Sarif, N., Kim, J.T. and Kim, T.S., 2013. Human activity recognition via recognized body parts of human depth silhouettes for residents monitoring services at smart home. Indoor and Built Environment, 22(1), pp.271-279. Kemp, C.M., Oliver, W.T., Wheeler, T.L., Chishti, A.H. and Koohmaraie, M., 2013. The effects of gene inactivation on skeletal muscle growth, development, and atrophy, and the compensatory role of other proteolytic systems. Journal of animal science, 91(7), pp.3155-3167. Nishida, I., Maeda, M., Kawano, T. and Shirase, K., 2016. Method of Movement Simulation in Lifting Operation Considering the Role of Antagonistic Muscles and Biarticular Muscle. J Ergonomics, 6(158), p.2. Ofli, F., Chaudhry, R., Kurillo, G., Vidal, R. and Bajcsy, R., 2014. Sequence of the most informative joints (smij): A new representation for human skeletal action recognition. Journal of Visual Communication and Image Representation, 25(1), pp.24-38. Peake, J., Della Gatta, P., Suzuki, K. and Nieman, D., 2015. Cytokine expression and secretion by skeletal muscle cells: regulatory mechanisms and exercise effects. Exercise immunology review, 21, pp.8-25. Schilder, P., 2013. The image and appearance of the human body (Vol. 163). Routledge. Sciote, J.J. and Morris, T.J., 2015. Skeletal muscle function and fibre types: the relationship between occlusal function and the phenotype of jaw-closing muscles in human. Journal of orthodontics. Toedebusch, R., Ruegsegger, G. and Booth, F., 2015. The role of skeletal muscle characteristics in the decline of VO2peak in rats. The FASEB Journal, 29(1 Supplement), pp.1055-9. Xia, L., Chen, C.C. and Aggarwal, J.K., 2012, June. View invariant human action recognition using histograms of 3d joints. In Computer Vision and Pattern Recognition Workshops (CVPRW), 2012 IEEE Computer Society Conference on (pp. 20-27). IEEE.