The main system of human body consists of skull, facial muscle, trunk bone, trunk muscle, limb bone, digestive system of limb muscle, oral cavity, esophagus, liver, stomach, intestine, anal respiratory system, nasal cavity, trachea, pulmonary circulatory system, heart, artery, vein, capillary urinary system, kidney, ureter, bladder, urethral nervous system, brain, spinal cord, neuroendocrine system, pituitary gland, thyroid gland, thymus gland and so on. Cell is the basic unit that constitutes the morphological structure and function of human body. Cells with similar mentality and functions form structures and tissues through the combination of intercellular substances. Several tissues combine to perform a specific function and have certain morphological characteristics, which constitutes an organ. Several functionally related organs are combined to complete a specific continuous physiological function and form a system. The human body is composed of nine systems, including exercise system, digestive system, respiratory system, urinary system, reproductive system, endocrine system, blood circulation system and nervous system. 1. The exercise system consists of bones, joints and skeletal muscles, accounting for about 60% of the adult's weight. The bones of the whole body are connected by joints to form bones, which play a role in supporting weight, protecting internal organs and maintaining the basic shape of the human body. Skeletal muscles are attached to bones and contract and relax under the control of the nervous system. When contracting, the joint is used as the fulcrum to pull the bone to change its position and produce movement. Bones and joints are passive parts of the exercise system, while skeletal muscle is the active part of the exercise system. The common diseases of sports system include: scapulohumeral periarthritis, growth pain, hyperosteogeny, (cervical hyperosteogeny, lumbar hyperosteogeny), fluorosis, rickets, (congenital rickets, infantile rickets, childhood rickets, adolescent rickets), osteoporosis, fracture, femoral head necrosis, etc. Second, the digestive system The digestive system consists of two parts: the digestive tube and the digestive gland. Digestive tract refers to the pipeline from oral cavity to anus, which can be divided into mouth, pharynx, esophagus, stomach, small intestine, large intestine and anus. This part of the pipeline from the mouth to the duodenum is usually called the upper digestive tract. Digestive glands can be divided into large digestive glands and small digestive glands according to their size and location. Large digestive glands are located outside the digestive tract, such as the liver and pancreas. Small digestive glands are located in the mucosa and submucosa of digestive tract, such as gastric glands and intestinal glands. Common diseases of digestive system include: hepatobiliary diseases (gallstones, fatty liver, cirrhosis, hepatitis), hemorrhoids, diarrhea, gastrointestinal spasmodic diarrhea, digestive tract ulcer, chronic gastroenteritis, hyperacidity and so on. Third, the respiratory system The respiratory system consists of respiratory tract, pulmonary blood vessels, lungs and respiratory muscles. The nose, pharynx and larynx are usually called upper respiratory tract. Organs and bronchi at all levels are lower respiratory tract. The lung consists of parenchyma and stroma. The former includes the number of bronchi and alveoli, while the latter includes connective tissue, blood vessels, lymphatic vessels and nerves. The main function of the respiratory system is gas exchange. Common respiratory diseases include: lung diseases (infant pneumonia, cor pulmonale, tuberculosis), bronchospasm, respiratory failure (respiratory alkalosis, respiratory acidosis, cold) and so on. 4. Urinary system The urinary system consists of kidney, ureter, bladder and urethra. Its main function is to discharge the waste and excess liquid produced by metabolism in the body and maintain the balance and stability of the internal environment of the body. The kidney produces urine, and the ureter transports urine to the bladder, which is an organ for storing urine, and urine is excreted through the urethra. Common diseases of urinary system include: nephropathy (acute nephritis, acute renal failure, chronic renal failure), urinary calculi (ureteral calculi, kidney calculi's disease, bladder calculi) and so on. V. Reproductive system The function of the reproductive system is to breed offspring, form and maintain secondary sexual characteristics. Male reproductive system and female reproductive system include internal genitalia and external genitalia. The internal genitalia is composed of gonads, reproductive ducts and accessory glands, and the external genitalia is mainly an organ with sexual intercourse function. Common diseases of reproductive system include perimenopausal syndrome, infertility and dysmenorrhea. 6. Endocrine system The endocrine system is an important regulatory system other than the nervous system, including diffuse endocrine system and endogenous endocrine system. Its function is to transmit information, participate in regulating the metabolism, growth and reproductive activities of the body, and maintain the stability of the internal environment. Common endocrine system diseases include obesity, diabetes, parathyroid diseases, thyroid diseases (hypothyroidism, thyroid dysfunction), Cushing's syndrome and so on. Seven, the blood circulation system including cardiovascular system and lymphatic system, distributed in all parts of the human body, is a closed pipeline system. The cardiovascular system includes the heart, arteries, capillaries and veins. The lymphatic system consists of lymphatic vessels, lymphoid tissues and lymphoid organs. The vascular system has the functions of substance transport and endocrine. Common diseases of blood circulation system include arteriosclerosis, heart disease, (angina pectoris, myocardial infarction, arrhythmia, myocarditis, pericarditis, sudden death) and pregnancy-induced hypertension. Eight, the nervous system The nervous system consists of the brain, spinal cord and peripheral nerve tissue attached to the spinal cord. The nervous system is the most complex system in human structure and function, which is composed of nerve cells and plays a leading role in the body. The nervous system is divided into central nervous system and peripheral nervous system. The central nervous system includes brain and spinal cord, and the peripheral nervous system includes cranial nerve, spinal nerve and visceral nerve. The nervous system controls and regulates the activities of other systems and maintains the unity of the external environment. Common nervous system diseases are: low IQ, nervous decline, epilepsy, ADHD, Alzheimer's disease and so on.