Epithelial Tissue and Connective Tissue - Essay Example

Epithelial cells are closely packed together, with almost no intercellular space and a small amount of intercellular substance. The epithelium has a high regenerative capacity and is supported by an underlying layer of connective tissue, called the basement membrane, which provides structural support and binds it to the neighboring structures. Epithelial tissue can be classified based on the number of layers present, or the basis of the shape of the cells. Epithelial tissue, which is only one layer thick, is called simple epithelium while stratified epithelium is two or more cells thick.

Based on shape, simple epithelial cells can be classified as (1) Simple squamous: the cells are flat, thin, fish-scale shaped, and have elliptical nuclei. They form the outer layers of the skin and the lining of cavities, such as the mouth, blood vessels, heart, and lungs. (2) Simple cuboidal: the cells are square or cuboidal, with spherical nuclei. They are found in the ducts of glands, and lining of the kidney tubules and also form the germinal epithelium, which produces eggs and sperms. (3) Simple columnar: the cells are columnar, with elongated nuclei, and form the lining of the digestive tract. The simple columnar ciliated epithelium has fine, hair-like outgrowths on its’ free surface. Cilia are capable of rapid, rhythmic movement of mucous in the nose and the movement of the ovum towards the uterus. (4) Simple pseudo-stratified columnar: the columns are all of varying heights, giving a false impression of multiple layers. They are found in the nasal cavity, larynx, and trachea.

Stratified, or compound, the epithelium consists of external layers which are flat and scaly and may contain a tough, resistant protein called keratin, as in the skin. Unkeratinized stratified epithelium is found in the oral cavity and the vagina.

Epithelial cell functions include (1) Protection of underlying tissues from mechanical injury, toxic chemicals, invading bacteria, and excessive loss of water (2) Sensation through the penetration of sensory stimuli in the taste buds and olfactory membrane. (3) Secretion of hormones, enzymes, and fluids (4) Absorption of nutrients (5) Excretion of waste products (6) Diffusion of gases, liquids, and nutrients (7) Cleaning of dust particles and foreign bodies (8) Reduction of friction between the blood and the walls of the blood vessels.

Connective Tissue.
Connective tissue is composed of relatively few living cells, which are widely separated by a non-living extracellular matrix, or amorphous ground substance, which contains protein fibers and tissue fluids. Connective tissue can be classified into (1) Connective tissue proper, which is further subdivided. (a) Loose connective tissue, which can be areolar (elastic for easy movement and found in blood vessels, nerves, and subcutaneous tissue); adipose (fatty tissue which insulates and stores nutrients); reticular (forms internal framework of lymph nodes, spleen, and bone marrow (b) Dense connective tissue, which can be regular, with bundles of collagen fiber running in the same direction (tendons, ligaments); or irregular, with collagen fibers arranged in an irregular fashion (dermis). (2) Cartilage is tough, semi-transparent, elastic, and flexible, is covered by the dense membrane called the perichondrium, and has no nerves or blood vessels. It is differentiated into (a) Hyaline cartilage which is very strong and flexible. It is found in the trachea, larynx, joints, and tip of the nose.

It reduces friction at the joints, facilitates movement between bones, and provides support in keeping the windpipe open (b) Fibrocartilage which is extremely tough and withstands heavy pressure, as in the intervertebral discs and the pelvic bones. It acts as a shock absorber, deepens sockets, and provides sturdiness. (c) Elastic cartilage has extreme stretchability. It is found in the ear lobe, epiglottis, and larynx and maintains the shape and flexibility of the organs, and provides strength and support. (3) Bone (osseous tissue) is hard because of the additional collagen fibers and calcium salts found in the extracellular matrix.

The bone cells (osteocytes) are surrounded by fluid-filled cavities, called the lacuna. Bone tissue can be compact or spongy. Bone tissue provides a supportive framework, giving shape and rigidity to the body, forms a system to which muscles are attached for locomotion, protects the organs, manufactures red blood cells in the marrow, and helps maintain calcium homeostasis. (4)
Blood is liquid tissue that consists of blood cells and blood plasma.  Read More