How Bodies Work

Learning Outcomes

  • Discuss how different body systems interact with one another

The organ level of organization in the body may be the most familiar to us from our everyday experiences. Many of the common ailments we hear about—an upset stomach, a broken bone, lung disease, skin cancer—are named for the organs they affect.

An organ is made up of tissues that work together to perform a specific function for the body as a whole. Groups of organs that perform related functions are organized into organ systems, which perform more general functions. Table 1 describes the structures and functions of some common organs.

Table 1. Structure and Function of Organs
Organ Primary function(s) Tissues it contains Organ system(s) it is a part of
brain control of body systems and behavior; cognition nervous, connective, epithelial nervous system; endocrine system
skin protection; support and containment; temperature and fluid regulation epithelial, nervous, connective, muscular integumentary system
stomach chemical and mechanical digestion of food epithelial, connective, muscular, nervous digestive system
sternum (breastbone) support; protection; blood cell production epithelial, connective, nervous skeletal system; immune system; cardiovascular system
kidney waste removal; fluid regulation epithelial, connective, nervous urinary system

Organ Systems, The Whole Body, and Populations

Organ systems are made up of organs that work together to perform a specific function for the body as a whole. Table 2 describes the organ systems and their primary organs and physiological functions that we will cover in subsequent pages.

Note that we have opted to organize the rest of this module into three basic groups: systems involved in “control,” systems of “cell maintenance,” and systems of “support.” It is important to remember just as organs and systems work together that these categories are not mutually exclusive. For example, we have placed the reproductive system in the control category since it is involved in controlling the process and events of reproduction. However, the reproductive system is also a cell maintenance system, as it produces and maintains the actual cells used in reproduction. Just keep in mind these are groupings to help you mentally organize your learning more than they hard rules of anatomy and physiology.

Table 2. Organ Systems
Organ system Key Organ(s) Primary function(s)
nervous brain, spinal cord control of behavior and body systems; cognition
endocrine glands control of the body systems and development
reproductive penis, testes, prostate (male); uterus, ovaries, vagina (female) reproduction
cardiovascular or circulatory heart, blood vessels transport of materials through the body; regulation of temperature
respiratory trachea, lungs gas exchange; regulation of temperature
immune and lymphatic thymus, tonsils, spleen defense agains infection
digestive and excretory tongue, esophagus, stomach, small intestine, large intestine, gallbladder, rectum digestion of food; waste removal
urinary or renal kidneys, bladder removes excess water, salts, and waste products; controls pH
muscular muscles, tendons support; movement
skeletal bones, cartilage support; protection; movement; blood cell production
integumentary skin support; protection; regulation of fluid levels

The Whole Body

The organ systems of the body all work together to maintain proper physiological functions. Many times in the arena of anatomy and physiology, including in this course, we closely examine the molecules, cells, tissues and organs of the body to learn their forms and functions. However, it is important to consider that every molecule works as part of the entire system. Endocrine disorders such as diabetes affect glucose levels in the body. Altered blood glucose levels can affect many organ systems. For example, the immune system may not heal as well, the urinary system may experience kidney damage, and the cardiovascular system can experience vascular damage, even to the point of causing blindness. In the body, everything is interconnected.

Assigning organs to organ systems can be imprecise since organs that “belong” to one system can also have functions integral to another system. In fact, most organs contribute to more than one system.

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