Internal Organs
In biology, an organ is a collection of tissues joined in a structural unit to serve a common function. In anatomy, a viscus /ˈvɪskəs/ is an internal organ, and viscera is the plural form.
There is a main tissue, parenchyma, and "sporadic" tissues, stroma. The main tissue is the one that is unique for the specific organ. For example, the main tissue in the heart is the myocardium, while sporadic tissues include the nerves, blood and connective tissues. Functionally related organs often cooperate to form whole organ systems.
Organ systems
Two or more organs working together in the execution of a specific body function form an organ system, also called a biological system or body system. The functions of organ systems often share significant overlap. For instance, the nervous and endocrine system both operate via a shared organ, the hypothalamus. For this reason, the two systems are combined and studied as the neuroendocrine system. The same is true for the musculoskeletal system because of the relationship between the muscular and skeletal systems.
Mammals such as humans have a variety of organ systems. These specific systems are also widely studied in human anatomy.
* Cardiovascular system: pumping and channeling blood to and from the body and lungs with heart, blood and blood vessels.
* Digestive system: digestion and processing food with salivary glands, esophagus, stomach, liver, gallbladder, pancreas, intestines, colon, rectum and anus.
* Endocrine system: communication within the body using hormones made by endocrine glands such as the hypothalamus, pituitary gland, pineal body or pineal gland, thyroid, parathyroids and adrenals, i.e., adrenal glands.
* Excretory system: kidneys, ureters, bladder and urethra involved in fluid balance, electrolyte balance and excretion of urine.
* Immune System: structures involved in the transfer of lymph between tissues and the blood stream, the lymph and the nodes and vessels that transport it including the Immune system: defending against disease-causing agents with leukocytes, tonsils, adenoids, thymus and spleen.
* Integumentary system: skin, hair and nails.
* Muscular system: movement with muscles.
* Nervous system: collecting, transferring and processing information with brain, spinal cord and nerves.
* Reproductive system: the sex organs, such as ovaries, fallopian tubes, uterus, vagina, mammary glands, testes, vas deferens, seminal vesicles, prostate and penis.
* Respiratory system: the organs used for breathing, the pharynx, larynx, trachea, bronchi, lungs and diaphragm.
* Skeletal system: structural support and protection with bones, cartilage, ligaments and tendons.