The order in which organisms are composed from simple to complex is cells, tissues, organs, and systems.
Cells are the basic structural and functional units of organisms and the most basic life system. It is composed of organic matter and inorganic matter, has an independent metabolic system, and can carry out life activities.
Tissues are composed of a group of cells and intercellular matrix that are similar in shape, structure and function. Common tissues include epithelial tissue, connective tissue, muscle tissue and nervous tissue.
Organs are composed of different tissues joined together in a certain order. Each organ has its specific function, such as sensory organs such as eyes, ears, nose, and tongue, and internal organs such as heart, liver, lungs, stomach, kidneys, etc.
A system refers to a whole formed by the regular combination of components that interact with each other and depend on each other. The human body has eight major systems, including the motor system, nervous system, endocrine system, circulatory system, respiratory system, digestive system, urinary system and reproductive system. These systems work together to make the human body a complete organism.
The eight major systems of the human body
The eight major systems of the human body refer to the motor system, nervous system, endocrine system, circulatory system, respiratory system, digestive system, urinary system and reproductive system. These systems coordinate and cooperate to enable various complex life activities in the human body to proceed normally.
Movement system: has the functions of movement, support and protection. It mainly includes bones, joints and skeletal muscles, accounting for 60% of human body weight. Bones and joints are connected together to form bones, which play a role in shaping the human body, supporting body weight, and protecting internal organs.
Nervous system: It is an important regulatory system. The nervous system is divided into central and peripheral parts. The central nervous system includes the brain and spinal cord, and the peripheral nervous system includes cranial nerves and spinal nerves. The nervous system controls and regulates the activities of other systems to maintain the balance of the body's internal environment and the adaptation to the external environment.
Endocrine system: It belongs to the regulatory system of the body. It works together with the nervous system to maintain a stable environment inside the human body and regulate the growth and development, reproduction and various metabolic activities of the human body.
Circulatory system: a closed duct system distributed in various parts of the human body, including the cardiovascular system and lymphatic system. Responsible for transporting oxygen and nutrients to all parts of the body, while transporting waste and carbon dioxide out.
Respiratory system: It consists of the lungs and respiratory tract. The respiratory tract is divided into upper respiratory tract and lower respiratory tract. Usually the upper respiratory tract is divided into nose, pharynx and larynx, and the lower respiratory tract is trachea and bronchi. The main function of the respiratory system is to take in oxygen and get rid of carbon dioxide.
Digestive system: It is mainly composed of the digestive tube and digestive glands. The digestive tube usually refers to the tube from the mouth to the anus, including the mouth, pharynx, esophagus, stomach, small intestine and large intestine. The shape and function of each part There will be some differences. The main function of the digestive system is to digest and absorb food.
The urinary system: including the kidneys, ureters, bladder and urethra, is responsible for expelling excess water and metabolic waste during the body's metabolism, and maintaining a certain stability of the body's internal environment. Reproductive system: has the function of reproducing offspring and forming and maintaining secondary sexual characteristics.