Organs : An organ is a part of animal body formed by the combination of oneor more than one type of tissues performing a particular function is called an organ. That is to say, in any organ there may be one or more than one type of tissues and the organ can perform a particular work. The branch of biology where organs are discussed is called anatomy.
Necessary Organs of Human Body : According to location there are twotypes of organs in human body. The branch of Biology, where the morphology of external organs like eye, ear, nose, hand, foot, head etc. are discussed, is called
Morphology. Again, the branch of Biology where the internal organs of theorganism are discussed in detail is called Internal Anatomy. Eye, ear, nose, hand, foot, head etc. are external organs and stomach, duodenum, ileum, rectum, heart, liver, pancreas, spleen, lung, kidney, testis, ovary etc. are internal organs of human body.
Systems: For performing various physiological f~nctions, such. as digestion,respiration, excretion, reproduction etc. several organs together form the organ systems in animal body. These are:
1. Digestive System: This system ,is associated with ingestion, digestion,absorption of food and removal of undigested residues. Digestive system has two main parts as:
Digestive Canal: This canal consists of mouth opening, mouth cavity, pharynx,oesophagus, stomach, duodenum, ileum, rectum and anus.
Digestive Glands: In man salivary glands, liver and Panereas work. as digestiveglands.
2. Respiratory System: This system with the help of oxygen taken from theenvironment produces energy by the oxidation of food present in the body cells to help the body to do every days work. In man the respiratory system .consists of nasal aperture, pharynx, larynx, trachea, bronchus, bronchiole and a pair of lungs made of alveoli.
3. Nervous System: The function of this system is to receive external and internalstimuli of the body and to create appropriate sensation. Nerve system is formed of brain spinal cord and cranial nerves and spinal nerves. Besides, the nerve system has also a part named Autonomous Nervous system. This part of the nerve system controls the involuntary works of the body.
4. Excretory System: Due to various physiological metabolic activities some wastematerials are produced within the body as by products. These materials are generally toxic to the body, so they need to be removed. The process of removing unnecessary waste materials from the body is called excretion. The system by which the excretion is performed is called excretory system. The excretory system of human beings consists of a pair of kidney, a pair of ureter, one urinary bladder and one urethra.
5. Reproductive System: Through this system an animal produces one or moreoffsprings of its type to maintain the contiriuation of the species. On the maturity, the child becomes capable to reproduce. Man is unisexual. Both males and females have individual reproductive system of their own. Besides, males have a few more important systems, such as: .
a. Integumentary System: The membrane covering the body from outside iscalled integument or skin. This system covers the body, protects from external injury and control the movement of various material from outside and inside the body.
b. Endocrine System: There are few endocrine glands within the body of thehuman beings. Secretions of these glands are known as hormone. There are no ducts for transportation of hormone. Blood carries the hormone from one place to another. The endocrine system is formed with the endocrine glands like Pituitary, Thyroid, Parathyroid, Islets of Langerhans of Panqreas, and Suprarenal etc.