Our cells are organized into tissues and they are organized into 4 categories: Epithelial, Connective, Nervous and Muscular tissue. No one cell type carries out all of the body's vital functions — organs derive their function not from their cells alone, but from how the cells are organized, and cells specialize in certain tasks: defense, secretion, contraction, etc. An organ is a structure that is composed of two or more tissue types and frequently all four. Click on a button for a more detailed look at each tissue class:
Epithelial Tissue: Lines or Covers Surfaces and Body Cavities
Connective Tissue: Supports, Packages and Protects Body Organs
Nervous Tissue: Transmits Electrical Impulses, Body's Control System
Muscular Tissue: Allows Organ Movements
Mucous Membrane (mucosa) — mostly endodermal origin, covered in epithelium, which are involved in absorption and secretion. They line cavities that are exposed to the external environment and internal organs. They are at several places contiguous with skin: at the nostrils, the mouth, the lips, the eyelids, the ears, the genital area, and the anus. The sticky, thick fluid secreted by the mucous membranes and glands is termed mucus.
Serous Membrane (or serosa) — a smooth membrane consisting of a thin layer of cells, which secrete serous fluid, and a thin connective tissue layer. Serous membranes line and enclose several body cavities, known as serous cavities, where they secrete a lubricating fluid which reduces friction from muscle movement. Each serous membrane is composed of a secretory epithelial layer and a connective tissue layer underneath. All serous membranes found in the human body formed ultimately from the mesoderm.
Histology — the study of tissues and how they are arranged. Commonly performed by examining cells/tissues by sectioning and staining, and examination under a microscope.
Histopathology — the microscopic study of diseased tissue, requires histopathological examination of samples.