Human Anatomy Health Article

Organization of the body

The complex structures of the human body are organized into numerous hierarchies. The chemical level is the most basic level and is the foundation on which life is based. Many different chemicals are essential to sustain life; these include carbon (C), oxygen (O), nitrogen(N), potassium (K), sodium (Na), and calcium (Ca). Atoms (single particles of an element) combine to form molecules that in turn combine to form various structures that are the building blocks of cells. The cell is the basic functional unit of life; on the cellular level, however, it is evident that it is an extremely complex structure. Different types of cells found in the human body include muscle cells, nerve cells, blood cells, and epithelial cells.

Similar cells may unite to perform a specific function; these groups of cells are called tissues. These are organized on the tissue level into four major groups: epithelial tissue that covers the internal and external surfaces of the body, nervous tissue that transmits electrical signals, muscle tissue that is specialized for contraction, and connective tissue that provides a structural matrix for other tissues. At the organ level, different tissues (at least two types) combine to form an organ, a structure that is capable of performing specialized tasks. Examples of organs are the stomach, lungs, kidneys, and liver.

A system consists of groups of organs that have a common function. This next level of organization includes systems such as the respiratory system, reproductive system, and endocrine system. The organs of the respiratory system, for example, work together to accomplish the intake of oxygen and the output of carbon dioxide. The organ systems together make up the organism, the individual human being. The organismic level is the highest level in the structural hierarchy; it represents the unification of all body structures and their complex interaction.

ORGAN SYSTEMS. Numerous organ systems are found in the human body. Each corresponds to a group of specialized organs that perform related activities. The following list represents the major organ systems of the human body and their key functions:

• Integumentary system: This includes the skin, nails, hair, and sweat and sebaceous glands. The integumentary system provides an external protective covering for the body; helps to regulate body temperature; protects internal organs from injury; excretes sebum, a oily substance with antimicrobial activity; synthesizes vitamin D; and has sensory receptors that are sensitive to pain, pressure, temperature, and touch.
• Skeletal system: Bones, cartilage, and ligaments make up the skeletal system. It provides a point of attachment for muscles and a framework that supports them. Blood cells are produced in bone marrow (the spongy material found in the center of most large bones); bones also store essential minerals such as calcium.
• Muscular system: Muscles are the organs of the muscular system. They provide the force necessary for body movement, support organs or body parts, help to maintain posture, provide the main source of body heat, and help in breathing.
• Nervous system: This includes the brain, spinal cord, nerves, and sense organs. Nervous impulses are the means by which organs and tissues communicate with the brain; nerve tissues carry impulses from various structures to the brain and vice versa. The nervous system can quickly respond to changes in the internal or external environment.
• Endocrine system: The hormone-secreting glands (pituitary gland, pineal gland, thyroid gland, thymus, adrenal gland, pancreas, testis, ovary, and parathyroid gland) make up the endocrine system. They are important in the regulation of different processes such as growth, metabolism, reproduction, and milk production in nursing women.
• Cardiovascular system: This is composed of the heart, blood vessels (arteries and veins), and the blood. The cardiovascular system is the means by which gases, nutrients, and wastes are transported throughout the body; it is also responsible for disseminating hormones, maintaining the acid-base balance in blood, and preventing extensive blood loss by the formation of clots.
• Lymphatic system: The lymphatic vessels, thymus, spleen, lymph nodes, and red bone marrow are all components of the lymphatic system. It is important in activating the immune response against foreign substances, returning tissue fluid to the blood, and supporting the maturation and proliferation of white blood cells.
• Digestive system: This includes the oral cavity (mouth, tongue, and teeth), salivary glands, pharynx, esophagus, stomach, liver, gallbladder, pancreas, small and large intestines, rectum, and anus. The purpose of the digestive system is to break down food and absorb necessary nutrients. It is also important in the process of detoxification.
• Respiratory system: The nasal cavity, pharynx, larynx, trachea, bronchi, and lungs together make up the respiratory system. It is responsible for the intake of oxygen and the output of carbon dioxide, the exchange of gases through the walls of alveoli (air sacs), and the vocalization of sounds.
• Urinary system: The kidneys, ureters, urinary bladder, and urethra are the major components of the urinary system. It is important for removing wastes from the body; maintaining a balance of water and electrolytes in the blood; and producing, storing, and transporting urine (a fluid made up of water, electrolytes, and nitrogenous wastes such as urea, uric acid, and creatinine).
• Reproductive system: In males, the reproductive system is made up of the testes, scrotum, penis, epididymes, vas deferens, seminal vesicles, prostate gland, and urethra. Its purpose is to produce the male sex cell (sperm) and transfer sperm to the female reproductive tract. The reproductive system in females is composed of the ovaries, uterus, fallopian tubes, vagina, vulva, and mammary glands. Its purpose is to produce the female sex cell (egg), provide an environment for sperm to fertilize an egg, support a developing fetus, and produce milk to nourish a newborn baby.