The histology (from Greek: hydton = fabric + logos = studies) is the science that studies biological tissues, from their formation (origin), structure (differentiated cell types) and functioning.
But what is fabric?
The body of a multicellular organism is made up of different cell types that specialize in performing various functions. Cells with a certain type of specialization are organized into groups, constituting the tissues. Some tissues are formed by cells that have the same structure; others are formed by cells that have different shapes and functions, but together collaborate in the realization of a larger general function.
Tissue differentiation and the conquest of the terrestrial environment
Among the several adaptations that favored the conquest of the terrestrial environment by vertebrates, one stands out waterproofed body lining, an adequate skeletal support system of the organism and its organs and a skillful mechanism that allows the body to move through the environment. In man, these three tasks are performed, in order, by the skin, the connective bones of the skeletal system, and the numerous muscles component of the muscular system. Bones and muscles constitute the locomotor system.
How are tissues formed?
All tissues present in adult vertebrates are formed from three types of germ leaflets: endoderm, ectoderm and mesoderm. Each of these, during embryonic development, is responsible for a specialized cell genealogy of form and function.
The final destinations (organogenesis) of these germinal leaflets in the formation of human tissues and organs are as follows.
- Skin epidermis and appendages (hair and mucous glands);
- All structures of the nervous system (brain, nerves, nerve ganglia and spinal cord);
- Epithelium lining the nasal, oral and anal cavities.
- Forms the inner layer of the skin (dermis);
- Smooth and skeletal muscles;
- Circulatory system (heart, blood vessels, lymphatic tissue, connective tissue);
- Skeletal system (bones and cartilage);
- Excretory and reproductive system (genitals, kidneys, urethra, bladder and gonads).
- Lining epithelium and digestive tract glands, except oral and anal cavity;
- Respiratory system (lung);
- Liver and pancreas.