Where is epithelial tissue found in animals

These fibres are composed of numerous fine fibrils, called myofibrils. Muscle fibres contract shorten in response to stimulation, then relax lengthen and return to their uncontracted state in a coordinated fashion.

Muscles contain special proteins called contractile proteins , which contract and relax to cause movement. Muscles are of three types, skeletal, smooth, and cardiac. Such muscles are called voluntary muscles. These muscles are also called skeletal muscles as they are mostly attached to bones and help in body movement.

Under the microscope, these muscles show alternate light and dark bands or striations. As a result, they are also called striated muscles. The cells of this tissue are long, cylindrical, unbranched and multinucleate having many nuclei. Skeletal muscle tissue is closely attached to skeletal bones.

In a typical muscle such as the biceps, striated striped skeletal muscle fibres are bundled together in a parallel fashion. A sheath of tough connective tissue encloses several bundles of such muscle fibres. Smooth Muscle Tissue — Involuntary Muscles The movement of food in the alimentary canal or the contraction and relaxation of blood vessels are involuntary movements.

We cannot really start them or stop them simply by wanting to do so! Smooth muscles or involuntary muscles control such movements. They are also found in the iris of the eye, in ureters and in the bronchi of the lungs. The cells are long with pointed ends spindle-shaped and uninucleate having a single nucleus. They are also called unstriated muscles. The smooth muscle fibres taper at both ends fusiform, spindle-shaped and do not show striations.

Cell junctions hold them together and they are bundled together in a connective tissue sheath. The wall of internal organs such as the blood vessels, stomach and intestine contains this type of muscle tissue. Cardiac Muscle Tissue — Involuntary Muscles The muscles of the heart show rhythmic contraction and relaxation throughout life. These involuntary muscles are called cardiac muscles. Heart muscle cells are cylindrical, branched and uninucleate.

Cardiac muscle tissue is a contractile tissue present only in the heart. Cell junctions fuse the plasma membranes of cardiac muscle cells and make them stick together. Communication junctions intercalated discs at some fusion points allow the cells to contract as a unit, i. Neurons, the unit of neural system are excitable cells.

The neuroglial cell which constitute the rest of the neural system protect and support neurons. Neuroglia make up more than one-half the volume of neural tissue in our body.

When a neuron is suitably stimulated, an electrical disturbance is generated which swiftly travels along its plasma membrane. All cells possess the ability to respond to stimuli. However, cells of the nervous tissue are highly specialized for being stimulated and then transmitting the stimulus very rapidly from one place to another within the body. The brain, spinal cord and nerves are all composed of the nervous tissue.

The cells of this tissue are called nerve cells or neurons. A neuron consists of a cell body with a nucleus and cytoplasm, from which long thin hair-like parts arise. Usually each neuron has a single long part, called the axon , and many short, branched parts called dendrites.

An individual nerve cell may be up to a metre long. Many nerve fibres bound together by connective tissue make up a nerve. Nerve impulses allow us to move our muscles when we want to. The functional Combination of nerve and muscle tissue is fundamental to most animals.

This combination enables animals to move rapidly in response to stimuli. Sharing is Caring!! Newsletter Updates Subscribe to our newsletter and never miss an important update!! Compounds April 29, Trending now. Shopping Cart. No products in the cart. Log in. M any functions are accomplished by epithelium: protection against mechanical assaults, prevention of water loss, filtering, selective absorption, secretion, exchange of gas and other molecules, substance transport over their surfaces, and may contain cells that work as sensory cells Figure 1.

S ome of the aforementioned functions are carry out with the help of the specializations of apical domain of the cell: microvilli, stereocilia and cilia Figure 2. E pithelial tissues are made up of tightly joined cells and show large cell-cell contact surfaces that leave very little extracellular matrix.

Several molecular complexes form these cell-cell junctions , such as tight junctions zonula occludens , desmosomes zonula adherens , and adherent junctions zonula adherens. Tight junctions establish strong cell-cell adhesion and get plasma membranes of neighboring cells so close between each other that the extracellular space is very narrow or nearly occluded. Desmosomes and adherent junctions are more abundant.

Cadherins mediate these two last cell junctions, connecting the cytoskeleton of adjoining cells and providing cohesion and strength to the whole epithelium. Cell adhesion may be modulated, either reinforced or weakened, depending on the physiological needs. Cytokeratins are the typical intermediate filaments of epithelial cells. E pithelial cells are organized in one or several strata that rest on a specialized sheet of extracellular matrix called basal lamina.

The basal lamina is a highly organized layer of extracellular matrix that completely covers the epithelial basal surface. It is produced by both epithelial cells and the underlying connective cells. Polarization is another feature of epithelial tissues. It means that they perform different functions in the apical domain facing the lumen of the organ or the exterior of the body compared with the basal domain in contact with the basal lamina Figure 3. Polarity is reflected in the epithelial the cell morphology, particularly when the epithelium is a single cell layer.

In this case, it is said that cells have an apical and a basal domain. E pithelial tissues do not have a blood capillary net except the stria vascularis of the inner ear. So, they get food by diffusion from the underlying connective tissue.

Nutrients need to cross the basal lamina. This cellular covering has cilia at the apical, or free, surface of the cells. The cilia enhance the movement of mucous and trapped particles out of the respiratory tract, helping to protect the system from invasive microorganisms and harmful material that has been breathed into the body.

Goblet cells are interspersed in some tissues such as the lining of the trachea. The goblet cells contain mucous that traps irritants, which, in the case of the trachea, keep these irritants from getting into the lungs. Pseudostratified columnar epithelia : Pseudostratified columnar epithelia line the respiratory tract. They exist in one layer, but the arrangement of nuclei at different levels makes it appear that there is more than one layer.

Transitional or uroepithelial cells appear only in the urinary system, primarily in the bladder and ureter. These cells are arranged in a stratified layer, but they have the capability of appearing to pile up on top of each other in a relaxed, empty bladder. As the urinary bladder fills, the epithelial layer unfolds and expands to hold the volume of urine introduced into it; the lining becomes thinner. In other words, the tissue transitions from thick to thin. Connective tissue is found throughout the body, providing support and shock absorption for tissues and bones.

Connective tissues are composed of a matrix consisting of living cells and a non-living substance, called the ground substance. The ground substance is composed of an organic substance usually a protein and an inorganic substance usually a mineral or water.

The principal cell of connective tissues is the fibroblast, an immature connective tissue cell that has not yet differentiated. This cell makes the fibers found in nearly all of the connective tissues.

Fibroblasts are motile, able to carry out mitosis, and can synthesize whichever connective tissue is needed. Macrophages, lymphocytes, and, occasionally, leukocytes can be found in some of the tissues, while others may have specialized cells.

The matrix in connective tissues gives the tissue its density. When a connective tissue has a high concentration of cells or fibers, it has a proportionally-less-dense matrix. The organic portion, or protein fibers, found in connective tissues are either collagen, elastic, or reticular fibers. Collagen fibers provide strength to the tissue, preventing it from being torn or separated from the surrounding tissues.

Elastic fibers are made of the protein elastin; this fiber can stretch to one and one half of its length, returning to its original size and shape. Elastic fibers provide flexibility to the tissues. Reticular fibers, the third type of protein fiber found in connective tissues, consist of thin strands of collagen that form a network of fibers to support the tissue and other organs to which it is connected. Loose connective tissue, also called areolar connective tissue, has a sampling of all of the components of a connective tissue.

Loose connective tissue has some fibroblasts, although macrophages are present as well. Collagen fibers are relatively wide and stain a light pink, while elastic fibers are thin and stain dark blue to black.

The space between the formed elements of the tissue is filled with the matrix. The material in the connective tissue gives it a loose consistency similar to a cotton ball that has been pulled apart. Loose connective tissue is found around every blood vessel, helping to keep the vessel in place. The tissue is also found around and between most body organs. In summary, areolar tissue is tough, yet flexible, and comprises membranes. Loose connective tissue : Loose connective tissue is composed of loosely-woven collagen and elastic fibers.

The fibers and other components of the connective tissue matrix are secreted by fibroblasts. Fibrous connective tissues contain large amounts of collagen fibers and few cells or matrix material. The fibers can be arranged irregularly or regularly with the strands lined up in parallel. Irregularly-arranged fibrous connective tissues are found in areas of the body where stress occurs from all directions, such as the dermis of the skin.

Regular fibrous connective tissue is found in tendons which connect muscles to bones and ligaments which connect bones to bones. Fibrous connective tissue : Fibrous connective tissue from the tendon has strands of collagen fibers lined up in parallel.

This arrangement helps the tissue resist tension that occurs from all directions. Cartilage is a connective tissue. The cells, called chondrocytes mature cartilage cells , make the matrix and fibers of the tissue. A cartilage with few collagen and elastic fibers is hyaline cartilage. The lacunae are randomly scattered throughout the tissue and the matrix takes on a milky or scrubbed appearance with routine stains.

Sharks have cartilaginous skeletons, as does nearly the entire human skeleton during some pre-birth developmental stages. A remnant of this cartilage persists in the outer portion of the human nose. Hyaline cartilage is also found at the ends of long bones, reducing friction and cushioning the articulations of these bones.

Hyaline cartilage : Hyaline cartilage consists of a matrix with cells called chondrocytes shown here embedded in it. The chondrocytes exist in cavities in the matrix called lacunae. Elastic cartilage has a large amount of elastic fibers, giving it tremendous flexibility. The ears of most vertebrate animals contain this cartilage, as do portions of the larynx, or voice box.

In contrast, fibrocartilage contains a large amount of collagen fibers, giving the tissue tremendous strength. Fibrocartilage comprises the intervertebral discs in vertebrate animals, which must withstand a tremendous amount of stress. Cartilage can also transform from one type to another.

For example, hyaline cartilage found in movable joints, such as the knee and shoulder, often becomes damaged as a result of age or trauma. Bone, adipose fat tissue, and blood are different types of connective tissue that are composed of cells surrounded by a matrix. Bone, or osseous tissue, is a connective tissue that has a large amount of two different types of matrix material.

The organic matrix is materially similar to other connective tissues, including some amount of collagen and elastic fibers. This gives strength and flexibility to the tissue.

The inorganic matrix consists of mineral salts, mostly calcium, that give the tissue hardness. Without adequate organic material in the matrix, the tissue breaks; without adequate inorganic material in the matrix, the tissue bends. There are three types of cells in bone: osteoblasts, osteocytes, and osteoclasts. Osteoblasts are active in making bone for growth and remodeling.

They deposit bone material into the matrix and, after the matrix surrounds them, they continue to live, but in a reduced metabolic state as osteocytes. Osteocytes are found in lacunae of the bone and assist in maintenance of the bone. Osteoclasts are active in breaking down bone for bone remodeling, providing access to calcium stored in tissues in order to release it into the blood.

Osteoclasts are usually found on the surface of the tissue. Bone can be divided into two types: compact and spongy. Compact bone is found in the shaft or diaphysis of a long bone and the surface of the flat bones, while spongy bone is found in the end or epiphysis of a long bone.