Study Guide to the Systems of the Body

Have you ever wondered how your food is digested, or how you can breathe, or even move your arms? If you think about it, it's pretty amazing that the human body can do all of these things and more. These actions are made possible by what are called organ systems which are collections of organs, body parts and tissues that work together for a common goal. For example, each one of your bones are part of the skeletal system; they work collectively to provide support and movement so that you can walk and run. Your bones also work together to protect your important internal organs, such as the heart, lungs and brain. Other organ systems present in your body are the circulatory, respiratory, muscular, digestive, integumentary, endocrine, reproductive, and nervous systems. All of these systems have specific functions but they cannot function independently, meaning that they rely on all the other systems in order to work properly. Each system is very important and every person has them. Below you will find a brief overview of each body system along with helpful educational links for adults and instructional links for teachers.

Circulatory System

The circulatory system consists of the heart and blood vessels which emcompasses all of the arteries, veins, and capillaries. The arteries carry oxygenated blood away from the heart, and veins return deoxygenated blood back to the heart. The main purpose of the circulatory system is to transport blood, oxygen, nutrients and hormones to and from different cells and tissues throughout the body. This system works hand-in-hand with the respiratory system to facilitate the exchange of oxygen and carbon dioxide within the blood per the alveoli in the lungs. It is also very important for the the removal of wastes and poisons within the body via the digestive and urinary systems.

Respiratory System

The respiratory system primarily consists of the trachea, bronchi, bronchioles, alveoli, lungs and diaphragm. It's primary functions are to absorb oxygen through the inhalation (inspiration) of air and to expel carbon dioxide back out into the atmosphere through exhalation (expiration). This process is commonly called ventilation, otherwise known as breathing, which facilitates the exchange of oxygen and carbon dioxide between the lungs and atmosphere. Within the lungs, oxygen and carbon dioxide are exchanged via the alveoli, which are tiny air sacs where this action takes place. During this process the newly oxygenated blood is pumped through the circulatory system by way of the heart to all of the cells, tissues, and organs throughout the body.

Skeletal System

The skeletal system is comprised of 206 bones in total and consists of several different types of bones such as long, short, flat, irregular and sesamoid. It also consists of all the joints, cartilage, tendons and ligaments within the body. The primary functions of the skeletal system are locomotion, support of the body, and the protection of internal organs such as the brain, heart, and lungs. Bones are also responsible for the production of red blood cells, platelets and most white blood cells. Minerals such as calcium, iron, magnesium and phosphorous are also stored within the bones, with 99% of the body’s calcium being stored here.

Muscular System

The muscular system consists of 650 skeletal, smooth (visceral), and cardiac (myocardium) muscles. The primary functions of this system are movement, joint stabilization, heat generation, maintenance of posture, and the facilitation of blood circulation. Skeletal muscles connect to bone and work hand-in-hand with the skeletal system to control voluntary movement such as walking and running. Smooth muscles are involuntary muscles that are responsible for the contraction of hollow muscles which include the stomach, intestines, bladder and uterus. Cardiac muscle is involuntary muscle found only in the heart and facilitates the circulation of blood by pumping it to the major arteries and out into the body via the circulatory system.

The Digestive System

The digestive system is mainly comprised of the gastrointestinal (digestive) tract which includes the mouth, esophagus, stomach, small intestine, and large intestine (colon). The liver, gallbladder, and pancreas are also a part of this system and are responsible for contributing to the chemical breakdown of ingested food. The main functions of the digestive system are digestion, absorption and the elimination of waste. Digestion is the breakdown of foods by mechanical and enzymatic processes into substances that can be utilized by the body. Absorption occurs primarily in the small intestine and is the process by which vitamins, minerals, carbohydrates, fats, and proteins are passed on to the blood for energy. Undigested and non-useful nutrients from food pass through to the large intestine and are eliminated as waste. The large intestine is also where the majority of water and sodium are absorbed into the body for use.

Nervous System

The nervous system is made up of two major parts: the central nervous system (CNS) and the peripheral nervous system (PNS). The central nervous system is made up of the brain and spinal cord and acts as the main control system for the body. The peripheral nervous system is made up of all the nerves and ganglia (nerve cell clusters) found outside of the central nervous system; its role is receiving information from various stimuli and sending it to the brain. The main purpose of the nervous system is perceiving information from inside the body and/or from the external environment (PNS) and determining how the body responds to any changes (CNS). An example of this would be pricking your finger on a needle, your body will immediately pull your finger away in direct response to painful stimuli. This system also regulates basic bodily functions such as breathing, blood pressure, digestion, and the control of body temperature.

Endocrine System

The endocrine system is primarily made up of the hypothalamus, thyroid, parathyroid, pituitary, pineal body, adrenal glands, pancreas, and reproductive glands. The main function of this system is to help regulate and maintain assorted functions of the body by releasing hormones into the bloodstream to maintain homeostasis. Homeostasis is the condition of maintaining balance within the body in relation to its external environment and is vital for life. Hormones are chemical substances produced by a gland, or glands, to affect other parts of the body. Together these glands are responsible for growth and development, breathing and heart rate, reproduction, metabolism, mood, sleep, tissue function, digestion, the release of insulin, and much more.

Integumentary System

The integumentary system consists of the skin, sweat and oil glands, nails, and hair. Skin is the largest organ in the body and is made up of three layers: the epidermis, dermis, and subcutaneous tissue. This system performs several functions that are vital to maintaining homeostasis. These functions are: protecting the body’s internal organs and tissues; protection from dehydration by helping to retain body fluids; protection from infectious organisms; maintaining a body temperature that is consistent with life; receptor site for pressure, sensation, pain, and temperature; excretion of waste materials through sweating; storing fat, water, and glucose; production of vitamin D. Hair is responsible for helping to protect the skin from ultraviolet radiation, while nails help to protect from injury and provide support for the tips of the fingers and toes.

Urinary/Excretory System

The urinary system is made up of the kidneys, ureters, bladder and urethra. The kidneys filter and remove extra fluid, toxins and waste from the bloodstream in the form of urine. Every day this system produces at least 1 to 2 quarts of urine. Other primary functions of the urinary system are maintaining the body’s relative state of homeostasis by keeping the levels of electrolytes in balance, producing hormones that regulate blood pressure, producing red blood cells, and helping to keep bones healthy by maintaining the right amounts of phosphorous and calcium within the body.

Lymphatic System

The lymphatic system consists of the lymphatic vessels, tonsils, adenoids, spleen and thymus gland. Lymphatic vessels are similar to the circulatory system’s capillaries and veins and are connected to hundreds of lymph nodes within the body. Lymph nodes produce and store the cells that fight infection and disease. Tonsils take in bacteria and viruses that enter through the mouth and nose and are considered the first line of defense for the immune system. The spleen is the largest lymphatic organ and is responsible for producing both red and white blood cells and helps to detect dangerous microorganisms, viruses and bacteria within the blood. As part of the immune system, the primary function of the lymphatic system is to transport a clear and colorless infection-fighting fluid called lymph, which contains white blood cells, throughout the body via the lymphatic vessels. Other functions of this system are absorbing fats and fat-soluble vitamins from the digestive system and transporting them into the bloodstream, restoring excess proteins and interstitial fluids to the blood, and helping to rid the body of toxic byproducts.

Reproductive System

The reproductive system in men consists of the penis, scrotum and testicles and in women it consists of the ovaries, fallopian tubes, uterus, vagina, breasts and mammary glands. Together there are four main functions of the reproductive system: the production of hormones such as testosterone, progesterone and estrogen; the production of egg and sperm cells; the sustenance and transportation of these cells; and the development and nurturing of offspring. This system is vital to the survival of the human species through creating new life.

See also our heart anatomy chart for specific information on the heart.