Organs and Organ Systems

<h1>Text Preview</h1> <p>Recall that an organ is a group of tissues in the body with a specific function. Organs often consist of two or more types of tissue. For example skin consists of epithelial tissue and an underlying region of connective tissue.</p> <p>Organs are grouped together into organ systems. Although we’ll use the human as our example here, most vertebrates share the same major organs systems</p> <p>Since organ systems fit into natural pairings, we’ll look at two related systems at the same time.</p> <p>We’ll consider the reproductive and excretory systems together because they are anatomically very close together. In males, they even share the same opening to the outside of the body.</p> <p>The reproductive system enables the species to reproduce by producing eggs in the female and sperm in the male. </p> <p>The excretory system handles the disposal of organic waste and excess fluids which are filtered through the kidneys.</p> <p>The nervous system is the body’s wiring system. Together with the endocrine system, it regulates the body’s internal processes and its reaction to the external environment.</p> <p>The nervous system also includes input from our sense organs – eyes, ears, nose, tongue, and skin.</p> <p>The endocrine system is the body’s internal system of chemical communication. It consists of glands that secrete chemical signals involved in regulating the body’s functions. These chemical signals, called hormones, travel around the body in the body's fluids.</p> <p>The muscular system provides movement and locomotion.</p> <p>The skeletal system supports and gives rigidity to the body. </p> <p>The skeleton also provides anchor points for the muscles, so we can move our limbs.</p> <p>The circulatory system carries nutrients and other materials around the body in the blood. The fluids absorbed from the blood by the organs is returned to the blood by way of the lymphatic system. </p> <p>The respiratory system exchanges oxygen and carbon dioxide through the lungs, or gills in aquatic animals. The respiratory system and circulatory system work closely together – blood is enriched with oxygen as it passes through the lungs.</p> <p>These next two groups of systems are the defense systems that protect the body against injury and infection.</p> <p>The integumentary system is made up of the skin, hair, nails, and any other external surfaces of the body. Besides protection against injury and infection, the integumentary system also prevents the body from drying out. </p> <p>The immune and lymphatic systems make up the internal defense system of the body. </p> <p>This pair of systems consists of lymphocytes in the blood and in the network of lymph vessels throughout the body. Lymphocytes are white blood cells that fight infection in the body.</p> <p>The immune and lymphatic systems also includes specialized organs that produce and store these components, including the thymus in which lymphocyte mature, and the spleen, which produces some lymphocytes and acts as a reservoir for blood cells.</p> <p>The last organ system we’ll look at is the digestive system. </p> <p>The digestive system starts with the mechanical breakdown of food in the mouth, continues with the chemical digestion of food and absorption of nutrients in the intestines, and ends with the elimination of waste from the anus.</p> <p>The simplest multicellular animals may lack some organ systems altogether – flatworms, for example, have no skeleton or respiratory system.</p> <p>As a general rule, organ systems become more complex and interact in more ways as we move up through the evolutionary tree. </p> <p>Animals need an excretory system to get rid of water and to balance salt concentrations in the body, but the nature of the excretory system differs in complexity in different animals. </p> <p>One of the simplest examples is the flatworm, which carries out excretion using a network of tubes that open through pores on the surface of the worm.</p> <p>Vertebrates have evolved a complex excretory system, which includes kidneys, a urinary bladder, and hormonal control mechanisms.</p> <p>We’ve now looked at the components of an animal body and how they're put together. </p> <p>Now let’s consider how the body's internal environment is regulated.</p> <p id="TextCopyright">Copyright 2006 The Regents of the University of California and Monterey Institute for Technology and Education</p>