Body Tissues and Membranes
A tissue is composed of specialized cells of one type perform a common function in the body. There are four major tissues: (1) Epithelial tissue, also called epithelium, covers body surfaces and organs and lines body cavities; (2) Connective tissue binds and supports body parts; (3) muscular tissue contracts; and (4) nervous tissue responds to stimuli and transmit impulses from one body part to another.
In epithelial tissue, the cells are tightly packed, with space between them. Externally, this tissue protects the body from drying out, injury, and bacterial invasion. On internal surfaces, epithelial tissue protects, but is also may have an additional function.
Epithelial cells readily divide to produce new cells that replace lost or damage ones. Skin cells as well as those that line the stomach and intestines are continually being replaced.
Epithelial tissues are classified according to the shape of cells and the number of cells layers. Simple epithelial tissue is composed of a single layer and stratified epithelial tissue composed of two or more layers.
Connective tissue binds structures together, provides support and protection, fills, spaces, produces blood cells, and stores fat. The body uses this stored fat for energy, insulation, and organ protection. As a rule, connective tissue cells are widely separated by an extracellular matrix composed of an organic ground substance that contains fibers and varies in consistency from solid to semifluid to fluid.
Fibrous Connective tissue includes loose connective tissue and dense connective tissue. The body’s membranes are composed of an epithelium and fibrous connective tissue.
Loose connective tissue commonly lies between other tissues or between organs, binding them together. The cells of this tissue are mainly fibroblasts—large, star-shaped cells that produce extacecellular fibers. The cells are located some distance from one another because they have a matrix with a jellylike ground substance that contains many white and yellow fibers. The white fibers occur in bundles and are strong and flexible. The yellow fibers form a highly elastic network that returns to its original length after stretching. Adipose tissue is a type of loose connective tissue in which the fibroblasts enlarge and store fat, and there is limited extracellular matrix.
Dense connective has a matrix produced by fibroblasts that contains bundles of white fibers regular connective tissue; the bundles are parallel as in tendons and ligaments.
Muscular tissue is composed of cells called muscular fibers. Muscular fibers contain actin and myosin, which are protein filaments whose interaction accounts for movement. The three types of vertebrate muscles are skeletal, smooth, and cardiac. Contractions of the skeletal muscles, which are attached to bones, cause the bones to move. Cardiac muscle contracts to force blood out of the heart and around the body. Smooth muscle can be found in several organs, including the digestive tract, reproductive organs, respiratory tract, and the lining of the bladder. Examples of smooth muscle activity are: contraction of the bladder to force urine out, peristaltic movement to move feces down the digestive system, and contraction of smooth muscle in the trachea and bronchi which decreases the size of the air passageway.
Nervous tissue, found in the brain and spinal cord, contains specialized cells called neurons that conduct nerve impulses. A neuron has three parts: (1) a dendrite collects signals that result in a nerve impulse; (2) the cell body contains the nucleus and most of the cytoplasm of the neuron; (3) the axon conducts nerve impulses.
Long axons are called fibers. Outside the brain and spinal cord, fibers are bounded together by connective tissue to form nerves. Nerves conduct impulses from sense organs to the spinal cord and the brain, where the phenomenon called sensation occurs. They also conduct nerve impulses away from the spinal cord and the brain to the muscles, causing the muscles to contract.
Thousands of patients who underwent tissue, bone and organ transplants are at risk of developing serious diseases due to the use of untested body parts. Recent criminal charges detailed the illegal sale of untested body parts and tissue to hospitals, distributors and medical device manufacturers. The FDA is concerned that the recipients of untested body parts and tissues are potentially at risk of developing HIV, Hepatitis B, Hepatitis C, Syphilis and other infectious diseases. An autoimmune disorder is a condition that occurs when the immune system mistakenly attacks and destroys healthy body tissue. There are more than 80 different types of autoimmune disorders. Normally the immune system's army of white blood cells helps protect the body from harmful substances, called antigens. Examples of antigens include bacteria, viruses, toxins, cancer cells, and blood or tissues from another person or species. The immune system produces antibodies that destroy these harmful substances.
Lead can our reach our body through mouth, skin or lung. Once arrived in the body in adults with a normal diet it is fixed at a rate of 30-40%. In children, the degree of absorption and storage of lead is higher; it keeps them even 40-50%. Either way its entry in the body, then get the lead in the blood, where it is directed either by tissue or the gut to be eliminated. Storage is done both in bone and in soft tissues - liver, kidney, pancreas, and lungs. The largest proportion of lead absorbed by the body but stays in the bones can remain for 25 years. In periods in which the body is weak or overbuys (illness, pregnancy, osteoporosis), stored in bone minerals, inclusive lead is put back in circulation by the blood. Lead accumulated can thus be released in the blood over the entire life of a person.
Joints of the body play very important role in keeping bones intact. The muscles, which surround the joints of the body, also need proper care. Bones work in coordination with the muscles to perform any movement. Muscles are joined to the bones with the help of the tendons. The tendons are connected in such a well manner that when one of the body muscles tightens itself, both the tendon and bone moves together with it.