Phlebotomy Handbook 8th Edition
Anatomy and Physiology Overview
The design of the human body is elaborate and sophisticated. Anatomy is the study of its physical structure and physiology is the study of its functional processes. A human body can be divided into eight structural levels: atoms (carbon, hydrogen, oxygen, nitrogen, iron, etc.), molecules (chemical constituents), organelles or small structures within cells, cells (the basic living units of all plants and animals), tissues (groups of similar cells), organs (two or more tissues), organ systems (groups of organs), and the organism (the human body) itself. Trillions of cells make up each individual. Similar groups of cells are combined into tissues, such as muscles or nerves, and tissues are combined into systems, such as the circulatory or reproductive system. These organ systems work simultaneously to serve the needs of the body. No one system works independently of the others (Figures 6-2 and 6-3).
The size and shape of a cell depend on its function. Some cells fight disease causing viruses and bacteria; some transport gases, such as oxygen (O2) and carbon dioxide (CO2); some produce movement, store nutrients, or manufacture proteins, chemicals, or liquids; and others, such as the egg and the sperm, can create a new life. Despite such diverse functions, most cells have basic structural elements in common.
Survival is the primary function of the human body, and many complex processes work independently and together to achieve this function. In human physiology, the body strives for a steady state, or homeostasis. Literally, homeostasis means “remaining the same.” It is a condition in which a healthy body, although constantly changing and functioning, remains in a normal, healthy state of equilibrium. Homeostasis, or a steady state condition, allows the normal body to stay in balance by compensating for changes. For example, if the body is taking in too much water, it responds to this imbalance by excreting water from the kidneys (urine), skin (perspiration), intestines (feces), and lungs (water in expiration). Another important concept of homeostasis is metabolism, which includes both the process of making necessary substances (anabolism—cells use energy to make complex compounds from simpler ones) or breaking down chemical substances in order to use energy (catabolism—chemical reactions to change complex substances into simpler ones while simultaneously releasing energy for the body to use). Both phases are required to maintain metabolic functions in a healthy individual. Body energy is always needed, whether for moving a chair, for allowing the heart to beat, for making tears, or for producing perspiration. A healthy body maintains constancy of its chemical components and processes in order to survive when environmental conditions are changing. Each organ system and body structure plays a part in maintaining homeostasis.
Health care workers can help assess homeostasis, or normal functioning, by taking “vital signs,” for example, temperature, pulse rate, and respiration rate (together known as TPR), and blood pressure. [...] In addition, clinical laboratory testing can provide a wealth of information about the individual organ systems and the integrated processes. Specimens, such as blood, bone marrow, urine, cerebrospinal fluid (CSF), synovial (joint), fluid, pleural fluid (from around the lungs), ascites or peritoneal fluid (from the abdominal cavity), pericardial fluid (from around the heart), biopsy tissue, semen, and others, can be microscopically analyzed, assayed, and cultured to determine pathogenesis (the origin of the disease). Health care workers may have a part in the collection, processing, or testing of these specimens.