Anatomy & Physiology

Anatomy & Physiology Study Guide

©2018 Achieve Page 21 is the term for maintaining the stability of an internal environment. The survival of an organism is dependent on homeostasis. Lack of it can lead to illness or death. Physiological systems have evolved to maintain homeostasis in an environment that is often inconsistent, unpredictable, and potentially dangerous. Essentially, homeostasis is the body’s way of preserving its internal state in an ever-changing external environment. Autoregulation and extrinsic regulation are two mechanisms involved in homeostasis. For example, when blood pressure drops, the kidneys release a chemical signal to vasoconstrict certain blood vessels. This constriction decreases blood flow to some areas and increases it in others to maintain body function and provide oxygen and nourishment to vital organs. Extrinsic regulation occurs through the activity of the nervous system or endocrine system. These systems control or adjust the activities of many other systems simultaneously. An example of this interaction is seen with exercise; the nervous system issues commands that increase the heart rate such that blood will circulate faster. The nervous system also reduces blood flow to less active organs, such as the digestive tract. The oxygen in circulating blood is thus available to the active muscles, where it is needed most. Regardless of the system involved, the function of homeostatic regulation is to keep the characteristics of the internal environment within certain limits. A homeostatic regulatory mechanism consists of three parts: (1) a receptor , a sensor that is sensitive to environmental change, or stimulus; (2) a control center, or integration center , which receives and processes the information supplied by the receptor, and which sends out commands; and (3) an effector , a cell or organ that of 368 The Digestive System • Major organs: Teeth, tongue, pharynx, esophagus, stomach, small and large intestine, liver, gallbladder, and pancreas • Functions: Processes and digests food; absorbs and conserves water and nutrients; stores energy The Urinary System • Major organs: Kidneys, ureters, bladder, and urethra • Functions: Excrete waste products; controls water balance; stores urine prior to voluntary elimination; regulates blood concentration and pH The Male Reproductive System • Major organs: Testes, epididymis, ductus deferens, seminal vesicles, prostate gland, penis, and scrotum • Functions: Produces male sex cells, suspending fluid and hormones The Female Reproductive System • Major organs: Ovaries, uterine tubes, uterus, vagina, labia, clitoris, and mammary glands • Functions: Produces female sex cells and hormones; supports developing embryo; provides milk 2.3 Maintenance of the Internal Environment Homeostasis