A tissue is a large collection of cells that carry out a specific function together. Organisms are made up of groups of different tissues. There are four main types of tissues, these are: Epithelial tissue, Muscle tissue, Connective tissue and Nervous tissue. These four tissue types each have their own specific function vital the human body. Because of this, each type of tissue contain cells with specific organelles appropriate to the tissues function. The addition, removal, or adaption of cell features can impact greatly on a tissue, giving it the properties it needs in order to accomplish its role in the body.
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Epithelial tissue covers the whole of the body’s surface. Epithelial cells are packed closely together in one or more layers. Epithelial tissue specialises in covering the body’s external and internal surfaces. The epithelial tissue located in the body’s interior is known as endothelium. Epithelial tissue can be split into two groups depending on the number of layers it’s composed of. When the epithelial tissue is only one cell thick it’s known as simple epithelium. However if the epithelium tissues is two or more cells thick, such as the skin, it’s known as stratified epithelium.
The main purpose of the epithelial cell is to protect the surfaces it covers, in some cases however specialised epithelial tissues are able to take part in absorption, excretion, secretion, diffusion, and cleaning. Epithelial tissue has the ability to repair itself this is due to the basement membrane which is a selectively permeable membrane. The epithelial tissues ability to repair itself is very useful as it comes under constant wear and tear because of its protective function. The repair process requires a lot of protein to be produced, therefore a large rough endoplasmic reticulum is needed in order to synthesise large amounts of protein. The top layer of cells within the epithelial tissue is often keratinised, making it stronger and more resistant to damage.
The nucleus within the epithelial tissue cells are able to change shape depending on the overall shape the cell structure will take on. The nucleus does this in order for the epithelial cells to fit closely together. Epithelial cells can also contain appendages known as cilia, depending on the tissues function. Cilia are often found in epithelial tissue located in areas such as the throat. Cilia waft the mucus with in the throat, reducing restriction and build up.
Muscle tissue
There are three types of muscle tissue: Smooth muscle tissue, skeletal muscle tissue and cardiac (heart) muscle tissue. The main function of muscle tissue is to create movement of, and in the body.
A large of amount of energy is needed within the muscle tissue due to its function, movement. This energy comes from ATP which is made within the tissues cells. Because of this muscle cells contain a vast amount of mitochondria which is responsible for creating ATP. The large number of mitochondria means vast amounts of ATP can be produced and then converted into kinetic energy needed for the muscle movement. Muscle tissues need to be sturdy and resilient due to the amount and type of movement carried out by the cell. This is accomplished by the cell membranes of the muscle cells, known as the sarcolemma. Smooth muscle tissue controls slow, involuntary movements. Skeletal muscle tissue is responsible for the movement of the various bones of the skeleton. Cardiac muscle tissue is found only on the hearts walls, it shows characteristics of both smooth muscle tissue and skeletal muscle tissue. Cardiac muscle tissue is responsible for the contraction of the atria and vesicles of the heart.
Muscle tissue is strong due to its outer layer of collagen fibre, which covers the inner layer known as the plasma membrane. Muscle tissue needs to be able to contract to perform its function. To do this calcium is needed. The calcium needs to be stored within the cell and transferred when needed. The calcium needed is packaged and kept in the cells sarcoplasmic reticulum this is an organelle similar to the SER. The cytoplasm of muscle tissues, called sarcolemma, is unique because it contains large particles of glycogen (storage of energy) and has a high concentration of calcium. This enables the muscle to contract efficiently
Connective Tissue
Connective tissue can be found within and throughout the human body, taking on many forms varying on its function. Whether its tendons and bones, or blood and skin.
The main function of connective tissue is to support the human body and connect together different types of tissues. Connective tissue usually has scattered cells throughout an extracellular matrix. Connective tissues are composed of three main types of cells: Fibroblasts, Macrophages, and Mast cells.
Fibroblasts are responsible for creating an extracellular matrix within the tissue, this gives the connective tissue elasticity needed so the tissue can stretch and then return to its original shape when needed. Collagen and proteins mostly make up the matrix providing strength to the tissues as well as flexibility. Macrophages are cells that come from blood cells and clean any
Foreign particles present through the process of phagocytosis. The final primary cell type is the Mast cell. The mast cell communicates with the body’s blood chemically, instructing it when to clot its blood, or inflame particular tissues. Mast cells provide the connective tissues with vital reparative properties that are needs when damage takes place.
Nervous tissue
Nervous tissues are built of nerve cells. The main function of the nervous tissue is relaying electrical impulses from one are in the body to another, collecting, sending and managing information from area to area.
The nervous tissue is made up of special nerve cells called neurones. Neurones transmit impulses at a very fast rate and are easily stimulated. The three main neurone types are: Sensory neurone, Motor neurone and connector neurones. Nervous cells are built of a standard cell body, contain cell organelles such as; nucleus, nucleolus, mitochondria, ribosomes, cell membrane and cytoplasm. The Golgi apparatus however is slightly different, not only can it process and package proteins it can also process and package neurotransmitters.
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At either end of the cell body are protrusions. One of these protrusions is known as the axon, this is a nerve fibre that attaches to the soma, carrying impulses away from it. The axon has a specially adapted membrane that can connect with the membrane of a targeted cell, letting impulses be carried into it. These connections are known as synapses. The dendrite which stems from the other end of the soma, works differently to the axon, picking up impulses from surrounding neurones and transmitting it to its own soma.
A material made of protein and fat known as the myelin sheath, acts as a sheath around the axon of a nerve cell. Its primary functions are to protect and insulate the nerve fibre, stopping impulses leaving he cell from incorrect areas, and also increase the speed of the impulses. Ranvier are regular gaps that are located along the sheath, these let nutrients and waste enter and leave the neurone. They also let the impulses move along the neurone itself.
These features are what give the nervous tissue the ability to send information to different areas of the body and coordinate bodily functions allowing the body to carry out its intended purpose
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