Organ systems are groups of organs that work together for a purpose, with interdependence fundamental to normal life functions. Mammals have ten organ systems: digestive, respiratory, circulatory, urinary, nervous, muscular, skeletal, reproductive, endocrine, and integumentary. Other animal life forms have multiple systems, with the most primitive animals having only a few organs that function differently from mammals.
In biology, an organ system is a group of organs that work together for a purpose. Their interdependence on each other is fundamental to normal life functions, and if one were to fail, it would place stress on the others, causing the entire group to shut down, with fatal results. Some organs may be part of more than one system: for example, the pancreas is part of the digestive and endocrine systems of mammals. Groups of related organs exist in most members of the animal kingdom. While the details may vary, all mammals, including humans, have the same ten organ systems in terms of function: digestive, respiratory, circulatory, urinary, nervous, muscular, skeletal, reproductive, endocrine, and integumentary.
Digestive
The purpose of this organ system is to convert the essential nutrients in food into a form that can be absorbed by the body. It consists of the mouth, esophagus, stomach, pancreas, liver and intestines. After the food is chewed, it passes into the stomach, where enzymes that digest proteins are released, and then into the intestines, where nutrients are absorbed. Absorption is aided by fluids released by the pancreas and liver, which aid in the breakdown of carbohydrates and fats.
Respiratory
This system allows the body to absorb oxygen, which is needed to extract energy from food, and to expel carbon dioxide, which is a byproduct of this process that would otherwise reach toxic levels. It consists of the lungs and airways. The air passages divide many times within each lung, ending in alveoli – tiny cavities from which oxygen is absorbed by red blood cells and where carbon dioxide flows, to be expelled when an animal exhales.
circulatory
The circulatory system is responsible for carrying nutrients and oxygen around the body to where they are needed and for protecting the body from disease-causing organisms. These two functions are sometimes classified separately as the cardiovascular and lymphatic systems, respectively. The cardiovascular organs are the heart, blood and blood vessels. The lymphatic system involves glands such as the spleen and thymus, which produce or modify cells called lymphocytes that are released into the bloodstream and destroy harmful organisms.
Urinary
Digestive and other processes within the body produce a variety of waste materials which are released into the bloodstream and would build up in toxic amounts if not removed. The urinary system, made up of the kidneys, bladder, and connecting tubes, provides the means to remove these substances. The kidneys filter the blood to remove waste products to form urine, which is then stored in the bladder, to be passed out at intervals.
Nervous
The nervous system consists of the brain, spinal cord, nerves, and sense organs. Its function is twofold. Firstly, it allows external stimuli, such as images, sounds, smells and sensations, to be conveyed from the sense organs to the brain, where they are interpreted. Second, it allows signals from the brain to be sent, via the spinal cord and nerves, to the muscles, causing them to move as instructed.
Muscular
Muscles are made up of long, thin cells that can contract to cause movement. The muscular system involves three types of muscles: skeletal, cardiac, and smooth. Skeletal muscles are under conscious control and move when the brain tells them to. The heart muscles keep the heart beating and work automatically. This also applies to smooth muscles, which control various other internal processes, such as digestion.
Skeletal
As the name suggests, this system is essentially the skeleton, although it also includes ligaments and cartilage. The most obvious purpose of the bones that make up the skeleton is to provide support for the body, but they also help protect vulnerable organs and function as levers that skeletal muscles pull. Other, less obvious functions are the production of blood cells in the marrow and the storage of essential minerals, such as calcium and phosphorus, which can be released when required.
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The reproductive system is responsible for producing the cells that unite to form a new organism, making fertilization of the egg cells possible, and ensuring the safe early development of offspring. The organs differ between males and females. In males the main organs are the testicles, prostate and penis, while in females the main organs are the ovaries, uterus and vagina. The ovaries produce eggs which are fertilized by male sperm, produced in the testicles. The embryo then develops in the uterus or uterus.
Endocrine
This system deals with the production of various hormones which maintain body chemistry and influence many functions of the body. It is controlled by the hypothalamus gland in the brain, but involves many other organs, including the thyroid, pituitary, kidneys and pancreas. Hormones produced by the endocrine system influence, among other things, growth, sexual development, water absorption and energy consumption.
outgrowths
The integumentary system is better known as skin, hair and nails. Its functions are to protect the body from injury, water loss and infection; prevent overheating by producing sweat; and to create vitamin D, which is produced in response to sunlight. Hair keeps the body warm even in cold weather.
Organ systems in non-mammals
Most animal life forms have multiple systems. In general, those in birds and reptiles are not dissimilar to those in mammals in terms of function. The most primitive animals may have only a few organs, and these may function differently from their more familiar mammalian counterparts. For example, insects breathe through openings on the sides of their bodies, and earthworms do this by absorbing oxygen directly through their skin. Jellyfish have little in the way of an organ system, but they do have a network of nerves and a basic digestive mechanism.
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