Human Anatomy - M.M. Kurepina, A.P. Ozhigova, A.A. Nikitina 2010

Internal Organs
General Overview of Internal Organs
Classification of Viscera into Organ Systems

Internal Organs include those that form the digestive, respiratory, and urogenital systems. Most of these organs are located within the internal cavities of the body—the thoracic and abdominal cavities—although some lie outside of them, such as the upper tracts of the digestive and respiratory systems. In anatomy, The Heart and Spleen are traditionally studied within The Vascular System, even though they are internal organs.

The Digestive System consists of the Oral Cavity, into which three pairs of Salivary Glands open, the Pharynx, Esophagus, Stomach, and small and large intestines. The Small Intestine is divided into the duodenum, where the ducts of The Liver and Pancreas open, the jejunum, and the ileum. The Large Intestine is also divided into several sections: the cecum, colon, and rectum.

The Respiratory system is formed by the Nasal cavity, pharynx (where the respiratory and digestive tracts cross), Larynx, Trachea, Bronchi, and Lungs. Gas exchange between the ambient air and the Blood takes place in the lungs; the organs through which air reaches them are referred to as the airways. Associated with the latter are:

the Olfactory Organ in the nasal cavity, and part of the motor apparatus for articulate speech in the larynx.

The Urogenital System comprises two groups of organs. The Urinary Organs include the Kidneys, Ureters, Urinary Bladder, and Urethra.

The reproductive organs perform a very specific function—reproduction and the continuation of the species. This group of organs is structured according to a common plan in both sexes and consists of organs that produce Germ Cells (spermatozoa and ova), store them, and transport them out of the body; in females, they also serve as the site for embryo development. The Male reproductive organs include the Testes and their epididymides, the vas deferens and ejaculatory ducts, accessory glands, and external genitalia; the female organs include the Ovaries, fallopian tubes, Uterus, Vagina, and external genitalia.

The reproductive organs develop partly from the same embryonic sources as the urinary organs, with which they remain anatomically connected; therefore, both can be grouped together as the Urogenital apparatus.

Except for the reproductive organs, the internal organs support the body's METABOLISM. In the digestive organs, ingested food undergoes Digestion—that is, changes that convert its nutrients into soluble compounds capable of being absorbed and assimilated. Through the respiratory organs, oxygen enters the body and Carbon dioxide is expelled. Nutrients and oxygen are delivered by the blood to the site of direct metabolism, namely, the body Tissues. During oxidative processes in the tissues, oxygen is consumed, producing carbon dioxide and other metabolic end products. These waste products can no longer be used by the body, becoming unnecessary or even harmful, and are excreted by various organs: carbon dioxide and Water through the lungs with exhaled air, and other substances by the kidneys, which produce urine containing water-soluble Protein metabolism products and salts. Excretion is also a function of the Skin and intestines.

The section on internal organs traditionally also covers the Organs of the Endocrine System, which regulates the Functions of all organs and systems in the body.