SPLANCHNOLOGY (THE STUDY OF INTERNAL ORGANS)

GENERAL SPLANCHNOLOGY

The viscera are the organs located in the cavities of the head, neck, chest, abdomen and pelvis. The organs belonging to the viscera are also referred to as internal organs. However, in Anatomy the term "internal organs" has a broader interpretation. Internal organs include muscles, bones, blood vessels and nerves, sensory organs, endocrine glands. Depending on their functional properties and structure the viscera are classified into systems of organs (digestive, respiratory, urinary, genital system, etc.).

The alimentary system converts the eaten food to the substances, which can be absorbed by the tissues; it also eliminates the undigested residues. The respiratory system provides oxygen flow into the body and carbon dioxide removal. Urinary organs evacuate the metabolic waste products. Finally, organs of the genital system are needed for reproduction.

THE PRINCIPLES OF VISCERAL STRUCTURE

In terms of structure all internal organs are divided into tubular (hollow) and parenchymal organs (Fig. 1).

Fig. 1. Scheme of a tubular organ (small intestine) structure, transverse and longitudinal section: 1 - mucosa; 2 - fold of the mucosa; 3 - lamina muscularis of the mucosa; 4 - submucosa; 5 - circular layer of the muscular coat; 6 - longitudinal layer of the muscular coat; 7 - serosa (serous coat)

The general plan of the tubular (hollow) organ structure is similar. The wall of each organ (including the ducts of glands) usually consists of three layers: the inner mucosa with submucosa, the middle muscular layer, and the outer connective tissue layer (the serous coat or adventitia). Each internal organ contains blood and lymphatic vessels engaged in the transport of nutrients and metabolic products, and nervous apparatus that provides for nervous regulation of various functions. All the above mentioned formations are situated in different coats. Significant variations in the structure of these layers occur along the digestive tract. These variations are related to the specific functions of each organ and region.