Tissues

=Tissues=

There are 4 types of tissues: 1) epithelium 2) connective 3) muscle and 4) nervous.

Epithelium
Epithelial cells serve to cover or line organs and additionally absorb and excrete material. They utilize three types of cells to accomplish these functions: 1) sqaumous, 2) cubiodal and 3) columnar.

Squamous Cells
Squamous cells are flat and have a protruding nucleus. They can exist of dead cells that protect a body such as the skin, or take the shape of a distendable organ as found in the gut. These cells can be modified by stratification of acellular layers atop cellular layers.

Cuboidal Cells
Cuboidal cell have fairly equal dimension. Their volume allows excretion and absorption of fluids and are essential in both exocrine (having ducts) and endocrine (ductless) glands. Modified cells have cilia that assist in the transport of particles.

Columnar Cells
Columnar cells are extended in one dimension. They are also beneficial in excretion and absorption of fluids. Modified forms also have cilia.

Transplants
Transplants are living or dead tissues from a healthy donor site to replace damaged or diseased tissue of the patient. There are three classifications.
 * Autograft: Tissue implanted from a donor site of the patient. This technique is most preferred due to low tissue rejection. However, probability of donor site morbidity is high.
 * Homograft: Tissues transferred between humans. These transplants are limited in quantity causing patients to be placed on waiting lists. The chance of donor rejection is possible.
 * Xenograft: Tissues transferred between a human and another species. This term is synonymous with heterograft or allograft. Some certain for inflammoratory response and transfer of prions exists. Although donor availability is highest, transplants from animals such as livers, heart valves and hearts is a source of controversy.