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A tissue is a group of cells, such as epithelium, that performs functions that are different and more complex than each cell could perform by itself; bone tissue could do more than single bone cells.
The four types of tissues are nervous, epithelial, connective and muscle; bone is a type of connective tissue.
Epithelial cells usually line an external or internal body surface.
Squamous cells are named because they are flattened and simple refers to having one layer; they are thin enough to allow for diffusion through them.
Simple squamous epithelial cells are delicate and allow gases to be exchanged across the air sacs or lung alveoli.
Cuboidal cells perform secretion as well as protective functions and are found in several glands and organs.
The lining of the digestive tube is mainly simple columnar cells that are specialized for secretion and absorption.
Microvilli are microscopic cell projections that serve to increase the surface area and effectiveness of the cells, usually on simple columnar epithelium.
Pseudostratified columnar cells line the trachea and bronchi and have specialized cell processes called cilia.
Cilia are extensions found on the surface of pseudostratified columnar epithelial cells, found lining the respiratory tract.
The upper layer of the skin is comprised of dry stratified squamous epithelial cells; the presence of layers provides a measure of protection against friction injury.
Transitional epithelial cells have the ability to remain attached even when the bladder is full and stretched; it is named because of its changing appearance.
Glands lined with merocrine cells can produce secretions such as sweat without dying or becoming damaged.
Mucin is the protein in mucus which is found in the goblet cells of the gastro-intestinal columnar lining, as well as other areas.
In holocrine secretion, the entire cell often dies and is discarded with its secretion, which explains the texture of the sebum around areas such as hair follicles.
Connective tissue is complex because it has so many different cells and a diverse matrix.
The matrix includes fibers and a complex chemical ground substance.
The fibers such as collagen are produced by a single cell type the fibroblast; the term histiocyte refers to the phagocytic macrophages.
Macrophages belong to the system of phagocytic tissue cells called the reticulo-endothelial system; macrophages are usually the first cells to engulf particles such as viruses.
Mast (basophil) cells secrete heparin which controls clotting in tissues; they also produce the inflammatory substance histamine
Elastic fibers cause the area such as the skin to return to its shape after being stretched.
Loose or areolar connective tissue forms thin, delicate layers of lower skin areas; the main cell type is the fibroblast.
Adipocytes are cells that are specialized to store lipids or fats that make them physical cushions; lipids can be chemically broken down to produce energy.
Tendons and ligaments are among the strongest structures in the body because they contain dense, compacted fibrous tissue.
Cartilage repairs very slowly because of the lack of blood vessels and the consequent slow rate of cell division.
The chondrocyte is the main cell that deposits the cartilage tissue; words with 'chondro' refer to cartilage.
The osteoblast or chondrocyte lie in a fluid-filled space called a lacuna; this arrangement does not allow the cells to migrate to other areas.
Hyaline, or clear cartilage, is clear in appearance because it lacks fibers and is mainly comprised of the chondromucoprotein matrix.
The appendages are comprised mainly of hyaline cartilage which will be gradually replaced by bone tissue.
Fibrocartilage contains strong fibers that provides a matrix that makes this tissue the strongest type of cartilage, able to withstand the pressure between certain bones, such as the bodies of vertebrae.
Elastic cartilage has fibers that allow the ear to return to a semi-rigid position and shape after being moved.
As bone tissue develops, the osteoblasts become arranged in circular patterns that deposit the calcium matrix in concentric rings (lamellae) around a central blood vessel.
The osteoblasts are arranged around a blood vessel situated in the osteonic canal in the center of the lamellae or concentric rings.
A young bone cell originally has several processes that eventually become surrounded by solid bone matrix; in older osteons, these processes leave impressions or cracks in the osteons called canaliculi or little canals, through which nutrients can flow.
Although the term connective may be somewhat misleading, blood belongs to this group because it contains blood elements surrounded by a liquid plasma (matrix).
Bone marrow is the source of most of the blood cells; hematopoietic means blood-producing.
Macrophages are phagocytic cells that are found in body tissues but not in the blood; when in the blood they assume designations such as monocyte.
The reticuloendothelial system derives its name for the fact that it represents a network of cells in several tissues that have the function of phagocytosis in common.
Muscle cells are the only ones that have the ability to shorten in length and therefore cause movement of a structure.
Skeletal muscle is the only tissue that be contracted by way of voluntary impulses or the desires of the organism.
Smooth muscle is found in the organs and blood vessels and provides a means of movement.
The intercalated disks of cardiac muscle cells allow the cells to contract as a group and give heart muscle much of its unique properties.
The inability to divide is related to the ability to repair damage to a tissue; heart cells cannot repair damages, and this is the central reason that a heart attack is the most common cause of human death.
Neurons are cells specialized to conduct the impulses that communicate one part of the body with others and the brain through nerves.
Neurons are never phagocytic but are primarily involved with synthesizing fibers; the nervous tissue cells called the neuroglia do contain phagocytic cells.
There are many cell types that lose their ability to reproduce once they are mature; fibroblast cells retain the ability to divide.
The basement membrane is the lower surface that epithelial cells rest on.
Epithelial tissue usually does not have blood vessels within it; nutrients reach the cells by way of diffusion from surrounding tissues.
This is not necessarily always true since skin cells have a rapid rate of cell division and repair easily, and upper skin cells are epithelial cells with no direct blood supply.
Epithelial cells are named by their shape but connective tissues are more complex and named by several factors including cell type.
Microvilli are processes that increase surface area while the cells that are specialized to secrete mucus are called goblet cells.
Keratin is a protein found in dry cells and produces a waterproofing effect; hair and fingernails are largely keratin.
Sarcomas arise from connective tissue (mesenchyme) and carcinomas stem from epithelium.
Endocrine glands are ductless and secrete their hormones into the blood vessels; the exocrine glands have ducts that open to external surfaces such as the salivary glands
Serous fluid is watery and very slippery while mucous secretions are thick and tenacious.
The thickest fibers in the skin are the reticular type.
Tendons, ligaments, and bone tissue are comprised largely of collagen type fibers.
As one ages, the resiliency of the skin decreases due to a degeneration of elastic fibers; the proportion of heavy collagen fibers increases.
Bone tissue has a calcium matrix and blood supply that gives it a rigid structure in comparisonwith the more pliable cartilage; cartilage and bone are both derived from the same embryonic stem cells.
The intervertebral disks are the portions of the spinal column that employ fibro-cartilage which gives the backbone strength and some degree of pliability.
The solid nature of bone tissue is due to the presence of calcium salts that have been deposited by the bone cells.
The appearance of a group of bone cells within bone tissue forms an osteon, which is the same term as Haversian system; there is a tendency in newer usage's to change the name of a structure from the person credited with the discovery to general scientific names.
Red blood cells cannot normally leave the blood vessels because they are non-motile and cannot change their shapes; white cells can move and alter their shapes and subsequently can be found anywhere required for defense.
The first cells that phagocytize foreign bacteria or particles belong to cells in the reticuloendothelial system; many drugs are even recognized first by these tissue cells.
Smooth muscle is named by its lack of a striated appearance, and is found in organs and therefore is also referred to as visceral.
Although neurons cannot divide, nervous tissue also includes neuroglia cells which can reproduce.
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Esta actividad trata de completar un texto sencillo en inglés. Esta actividad esta dirigida para alumnos de 3º de la ESO