Level of Structural Organization of Body
Before you begin to study the different structures and functions of the human body, it is helpful to consider its basic architecture; that is, how its smallest parts are assembled into larger structures. It is convenient to consider the structures of the body in terms of fundamental levels of organization that increase in complexity: subatomic particles, atoms, molecules, organelles, cells, tissues, organs, organ systems, organisms, and biosphere.
The Levels of Organization
The human body has different structural levels of the organization, starting with atoms molecules and compounds and increasing in size and complexity to cells, tissues, organs, and the systems that make up the complete organism.
Atomic And Molecular Level: To study the chemical level of organization, scientists consider the simplest building blocks of matter: subatomic particles, atoms, and molecules. All matter in the universe is composed of one or more unique pure substances called elements, familiar examples of which are hydrogen, oxygen, carbon, nitrogen, calcium, and iron. The smallest unit of any of these pure substances (elements) is an atom. Atoms are made up of subatomic particles such as the proton, electron and neutron. Two or more atoms combine to form a molecule, such as the water molecules, proteins, and sugars found in living things. Molecules are the chemical building blocks of all body structures.
Cellular Level: A cell is the smallest independently functioning unit of a living organism. Even bacteria, which are extremely small, independently-living organisms, have a cellular structure. Each bacterium is a single cell. All living structures of human anatomy contain cells, and almost all functions of human physiology are performed in cells or are initiated by cells.
A human cell typically consists of flexible membranes that enclose cytoplasm, a water-based cellular fluid together with a variety of tiny functioning units called organelles. In humans, as in all organisms, cells perform all functions of life. A tissue is a group of many similar cells (though sometimes composed of a few related types) that work together to perform a specific function. An organ is an anatomically distinct structure of the body composed of two or more tissue types. Each organ performs one or more specific physiological functions. An organ system is a group of organs that work together to perform major functions or meet the physiological needs of the body.
Tissue Level: Tissue is made up of many similar cells that perform a specific function. The various tissues of the body are divided into four groups. These are epithelial, connective, nervous, and muscle tissue.
Epithelial tissue: – Found in the outer layer of skin, the lining of organs, blood and lymph vessels, and body cavities. Connective tissue: – Connects and supports most parts of the body. They constitute most parts of skin, bone, and tendons. Muscle tissue: – Produces movement through its ability to contract. This constitutes skeletal, smooth, and cardiac muscles. Nerve tissue: – Found in the brain, spinal cord, and nerves. It responds to various types of stimuli and transmits nerve impulses.
Organ Level: An organ is an integrated collection of two or more kinds of tissue that works together to perform a specific function. For example The stomach is made of different types of tissues, which perform a collective function.
System Level: When different organs work interdependently to perform a major function, it is called a system. Each organ has its own job, but their jobs are dependent on those of one another. For example, the Respiratory system contains several organs.
Organism level: The combination of systems run by different organs, forms an organism or in other words, the various organs of the body form the entire organism.
The organism level is the highest level of organization. An organism is a living being that has a cellular structure and that can independently perform all physiologic functions necessary for life. In multicellular organisms, including humans, all cells, tissues, organs, and organ systems of the body work together to maintain the life and health of the organism.
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