<P> The study of human and animal tissues is known as histology or, in connection with disease, histopathology . For plants, the discipline is called plant anatomy . The classical tools for studying tissues are the paraffin block in which tissue is embedded and then sectioned, the histological stain, and the optical microscope . In the last couple of decades, developments in electron microscopy, immunofluorescence, and the use of frozen tissue sections have enhanced the detail that can be observed in tissues . With these tools, the classical appearances of tissues can be examined in health and disease, enabling considerable refinement of medical diagnosis and prognosis . </P> <P> 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 . </P> <P> Animals such as humans have a variety of organ systems . These specific systems are also widely studied in human anatomy . </P> <Ul> <Li> Cardiovascular system: pumping and channeling blood to and from the body and lungs with heart, blood and blood vessels . </Li> <Li> Digestive system: digestion and processing food with salivary glands, esophagus, stomach, liver, gallbladder, pancreas, intestines, colon, rectum and anus . </Li> <Li> 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 . </Li> <Li> Excretory system: kidneys, ureters, bladder and urethra involved in fluid balance, electrolyte balance and excretion of urine . </Li> <Li> Lymphatic 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 . </Li> <Li> Integumentary system: skin, hair and nails of mammals . Also scales of fish, reptiles, and birds, and feathers of birds . </Li> <Li> Muscular system: movement with muscles . </Li> <Li> Nervous system: collecting, transferring and processing information with brain, spinal cord and nerves . </Li> <Li> Reproductive system: the sex organs, such as ovaries, fallopian tubes, uterus, vulva, vagina, testes, vas deferens, seminal vesicles, prostate and penis . </Li> <Li> Respiratory system: the organs used for breathing, the pharynx, larynx, trachea, bronchi, lungs and diaphragm . </Li> <Li> Skeletal system: structural support and protection with bones, cartilage, ligaments and tendons . </Li> </Ul>

Organ which have same origin and same structure is known as