Introduction to the Human Body Help (page 2)
Introduction to the Human Body
Anatomy and Physiology are subdivisions of the science of biology, the study of living organisms. Human anatomy is the study of body structure and the relationships between body structures. Human physiology is concerned with the functions of the body parts. In general, function is determined by structure.
Humans as Biological Organisms
Human beings (Homo sapiens) are biological organisms. The basic physical requirements of humans, as with all organisms, are: water, for a variety of metabolic processes; food, to supply energy, raw materials for building new living matter, and chemicals necessary for vital reactions; oxygen, to release energy from food materials; heat, to promote chemical reactions; and pressure, to allow breathing.
Levels of Organization of the Human Body
The levels of organization of the human body are, from the simplest to the most complex: chemical, cellular, tissue, organ, system, and organism. Each level of body organization represents an association of units from the preceding level.
Chemical and cellular levels are the basic structural and functional levels.
A tissue is an aggregation of similar cells that performs a specific function. There are four types of tissues found in humans.
An organ is composed of several tissue types that are integrated to perform a particular function.
A system is an organization of two or more organs and associated tissues working as a unit to perform a common function or set of functions. The body systems are:
- The muscular and skeletal systems function in body support and locomotion.
- The endocrine and nervous systems function in integration and coordination by maintaining consistency of body functioning.
- The digestive, respiratory, circulatory, lymphatic, and urinary systems are involved with processing and transporting body substances. The digestive system mechanically and chemically breaks down foods for cellular use and eliminates undigested wastes. The respiratory system supplies oxygen to the blood, eliminates carbon dioxide, and helps regulate acid-base balance. The circulatory system transports respiratory gases, nutrients, wastes, and hormones; helps regulate body temperature and acid-base balance; and protects against disease and fluid loss. The lymphatic system transports lymph from tissues to the blood stream, defends the body against infections, and aids in the absorption of fats. The urinary system functions to remove wastes from the blood; regulate the chemical composition, volume, and electrolyte balance of the blood; and helps to maintain the acid-base balance of the body.
- The integumentary system functions to protect the body, regulate body temperature, eliminate wastes, and receive sensory stimuli.
- The reproductive system functions to produce gametes for sexual reproduction and to produce sex hormones.
Homeostasis is the process by which a nearly stable internal environment is maintained in the body so that cellular metabolic functions can proceed at maximum efficiency. Homeostasis is maintained by muscles or glands that are regulated by sensory information from the internal environment.
Anatomical Position and Terminology
All terms of direction that describe the relationship of one body part to another are made in reference to a standard anatomical position. In anatomical position, the body is erect, feet are parallel and flat on the floor, eyes are directed forward, and arms are at the sides of the body with the palms of the hands turned forward and the fingers pointing downward.
Descriptive and directional terms are used to communicate the position of structures, surfaces, and regions of the body with respect to anatomical position. Commonly used terms are listed and defined in Table 1.2.
In addition to the terms listed in Table 1.2, three planes of reference are used to locate and describe structures within the body. The midsagittal plane is the plane of symmetry, dividing the body into right and left halves. A coronal plane divides the body into front and back portions, and a transverse (horizontal or cross-sectional) plane divides the body into superior and inferior portions.
Body Regions and Body Cavities
The principal body regions are the head, neck, trunk (divided into the thorax and the abdomen), upper extremity (two), and lower extremity (two).
The body cavities are confined spaces in which organs are protected, separated, and supported by associated membranes. The posterior (dorsal) cavity includes the cranial and vertebral cavities and contains the brain and spinal cord.
The anterior (ventral) cavity includes the thoracic, abdominal, and pelvic cavities and contains the visceral organs. The abdominal cavity and the pelvic cavity are frequently referred to collectively as the abdominopelvic cavity because there is no physical division between these two regions. The visceral organs located in the thoracic cavity are the heart and lungs. The thoracic cavity is partitioned into two pleural cavities, one surrounding each lung and the pericardial cavity surrounding the heart. The area between the two lungs is known as the mediastinum. The viscera of the abdominal cavity include the stomach, small intestine, large intestine, spleen, liver, and gallbladder.
The body cavities serve to segregate organs and systems by function: the major portion of the nervous system occupies the posterior cavity; the principal organs of the respiratory and circulatory systems are in the thoracic cavity; the primary organs of digestion are in the abdominal cavity; and the reproductive organs are in the pelvic cavity.
Body membranes, composed of thin layers of connective and epithelial tissue, serve to cover, protect, lubricate, separate, or support visceral organs or to line body cavities. The two principal types are mucous membranes and serous membranes.
Mucous membranes secrete a thick, viscous substance called mucous that lubricates and protects the body organs where it is secreted. Examples of mucous membranes are the epithelial membranes lining the nasal cavity, the trachea, and the oral cavity. Mucous membranes are found lining the inside walls of many other body organs.
Serous membranes line the thoracic and abdominopelvic cavities and cover the visceral organs (described above). They are composed of thin sheets of epithelial tissue that lubricate, support, and compartmentalize visceral organs. Serous fluid is the watery lubricant they secrete. The serous membranes of the thoracic cavity are the parietal and visceral pleura, lining the thoracic walls and diaphragm and the outer surface of the lungs respectively, and the parietal and visceral pericardium surrounding the heart. The serous membranes of the abdominopelvic cavity are the parietal and visceral peritoneum, lining the abdominal wall and covering the abdominal viscera respectively; and the mesentery, a double fold of which supports the viscera and loosely anchors it to the abdominal body wall.
Practice problems for these concepts can be found at: