A tissue is an assemblage of similar cells and cell products performing a specific activity and are located in different organs of the body. Tissues form the building blocks of an organism. They are composed of individual cells which consequently are composed of several organelles. There are four types of tissues in animals and they include the epithelial, muscular, nervous and connective tissue. The images of the various tissue types as viewed under a light microscope have been attached below. The Epithelial tissue covers the body surface and is also the lining for most internal cavities. The skin is an example of an organ made up of this tissue. They are either columnar, squamous or cuboidal in shape. The major functions of epithelial tissue are protection, absorption, filtration and secretion. This tissue is found in the kidney.
The connective tissue is responsible for connecting various organs in our body. It is the most widely spread in the body. Examples include fat tissue, blood tissue, and dense fibrous tissue amongst others.
The muscle tissue is responsible for muscular movement and coordination. There are three types and they include smooth, skeletal and cardiac muscle tissue. Smooth and cardiac muscle are involuntary meaning they do not require direct commands from the brain. Skeletal muscle on the other hand is under voluntary control and this means that it needs to be commanded on what to do.
The nerve tissue is composed of cells that receive and conduct impulses to and from all parts of the body. It’s composed of organelles whose major task is to allow passage and receiving of information.
There are two classification of cells; prokaryotes and eukaryotes. By classifying under kingdoms, the prokaryote kingdom refers to bacteria while eukaryotes include animals, plants, fungi and protoctista. Eukaryotes are organisms whose cells are in-bound by membranes and a cytoskeleton. They have a ‘true’ nucleus that contains their DNA. The organelles in prokaryotes are not membrane bound. Most happen to be unicellular though some are multicellular. Prokaryotic cells are much older and diverse than eukaryotic cells as they’re believed to have been there for millions of years. The organelles found in both cells perform specific functions and influence the overall task of the tissue. The table below mentions certain organelles, their function and whether they are found in prokaryotes or eukaryotes.
Organelle Function Cell Found
Golgi Body Transports proteins from the Rough Endoplasmic Reticulum to the cell membrane for export. Eukaryotes.
Lysosome Contain digestive enzymes that break down unwanted chemicals toxins or even the entire cell. Eukaryotes.
Cell Wall Separates the content of the cell from the outside environment and thus controlling the exit and entry of materials. Offers rigidity to the cell. Mostly found in Prokaryotes.
Nucleus Contains DNA that carries the genes of the cell. It’s not membrane bound in prokaryotes or a nucleoid. Both prokaryotes and eukaryotes.
Ribosomes Responsible for protein synthesis. In Eukaryotes, they’re larger (80S) while in Prokaryotes, they are smaller (70S) type. Both prokaryotes and eukaryotes.
Endoplasmic Reticulum Form a transport highway within the cell allowing movement of molecules. Plays an important role in protein synthesis. Composed of RER and (Smooth endoplasmic reticulum) SER. Eukaryotes.
Cytoskeleton Protein fibers extending through cells to offer support, transport and motility. Allows for cytoplasmic streaming. Eukaryotes.
Mitochondria Allows for aerobic respiration. Provision of energy through the breakdown of glucose. Eukaryotes.
Flagella Responsible for propelling and movement activities. It’s complex in eukaryotes and consists of two protein building blocks. Both prokaryotes and Eukaryotes.
Task 4.Different cell components in a tissue influences the function of that tissue. As each has a specific role which it undertakes, the synchrony of these activities enable a tissue to perform the overall specialized task that it is supposed to handle. The number of various cell components will depend on the general function of the tissue. Cell differentiation is the process whereby a less specialized cell becomes more specialized. Differentiation occurs continually in a multicellular organism. It is important as it enables adult cells to give rise to daughter cells which in turn become specialized to perform a certain function. Each type of cell that develops creates tissue-specific proteins only available in that cell type. Cells need to have different structures as they perform different functions. During differentiation, the shape and structure of the cell changes. As stated earlier, the number of certain cell components/organelles in a tissue influences the overall role of the tissue. Take for example mitochondrion; structures that convert food energy into a form that can easily be used by cells. Through respiration, energy is released from glucose and is used for various body processes. Tissues that require large amounts of energy will always have a high number of mitochondrion. An example is the muscle tissue. The energy requirements of voluntary and involuntary muscles is high. This thus creates an energy deficit that is compensated by an increase in the number of mitochondrion in these tissues.
Task 5.The muscle tissue is comprised of cells whose purpose is contraction. They contract upon receiving a stimulus by a chemical released at a nerve end known as a neuromuscular junction. All cells contain actin or myosin proteins in their filaments. There are three types of muscle tissue; cardiac, smooth and skeletal and each have their distinct characteristics. In skeletal and cardiac muscles, these filaments contain desmin resulting into refractile bands called cross-striations. Smooth muscle cells however are not highly ordered and thus are not striated. The different types of cells can be distinguished by their appearance as viewed under a microscope. This task will aim at differentiating between smooth muscles and cardiac muscle. The major difference is in the structure, function and location.
Skeletal muscle tissue are attached to bones and is responsible for general body movements. They are cylindrical in shape and have voluntary control of activities. They have regularly spaced traverse bands and thus striated. The cells are syncytial; they are multinucleated since myoblasts fuse to make the adult muscle cell. The muscle cell is long and threadlike. The nuclei is rectangular in shape and is located in the periphery of the cell beneath the cell membrane. All muscle tissue is organized into bundles due to wrappings of individual muscle fibers, group muscle fibers and multiple muscle fibers to form a large muscle mass.
On the other hand, the cardiac muscle tissue is found in the heart and is under involuntary control; contraction is not consciously controlled. Cardiac fibers form long chain of cells which branch and intertwine resulting into ‘wringing.’ Cells are cylindrical in shape with a central oval nucleus. The nuclei is rectangular in shape. Though cross striations are visible, they are not as prominent as those of skeletal muscle. The cardiac muscles are branched and are joined together by intercalated disks. Striations run across the cells at right angles.
Gerard, J. T. & Sandra, R., G. 2000. Principles of Anatomy and Physiology. New York: John Wiley & Sons, Inc.
Alberts B, Johnson A, Lewis J. et al. 2002. Molecular Biology of the Cell. (4th Ed.). Garland.
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