state.  For  example,  during  an  emergency  the  body's heart   and   respiration   rate   increases.   After   the emergency, the parasympathetic system will decrease heart and respiration rate to normal. The sympathetic and   parasympathetic   systems   counterbalance   each other   to   preserve   a   harmonious   balance   of   body functions and activities. THE ENDOCRINE SYSTEM LEARNING    OBJECTIVE: I d e n t i f y endocrine   glands   and   the   hormone(s)   they produce,    and    determine    the    effect    each hormone has on the body. Homeostasis,   the   self-balancing   of   the   body’s internal environment, is achieved and maintained by the endocrine system and the nervous systems. These systems  work  alone  and  together  to  perform  similar functions   in   the   body:   communication,   integration, and control. Their communication capabilities provide the  means  for  controlling  and  integrating  the  many different functions performed by organs, tissues, and cells. The endocrine system, however, performs these functions  by  different  mechanisms  than  the  nervous system. The endocrine system sends messages by way of chemical   messengers   called    hormones.   Minute amounts   of   these   hormones   are   secreted   from endocrine gland cells into the blood and distributed by the   circulatory   system.   Endocrine   glands   secrete hormones directly into the blood, because they have no duct system. The glands of this system are often called ductless glands. Cells that are affected by the hormone are referred to as  target organ cells. Today, many hormones can be extracted from the glands of animals or produced synthetically. Medical officers   may   prescribe   these   naturally   derived   or synthetic hormones for patients who are deficient in them or who might otherwise benefit from their use. For example, oxytocin (the hormone which stimulates uterine   contractions   during   pregnancy)   has   been synthesized and is used during the delivery process for women who are deficient in this hormone. The   hormone-producing   glands   include   the hypothalamus,   pituitary,   thyroid,   parathyroids, adrenals, pancreas, and gonads (the testes and ovaries) (fig. 1-47). HYPOTHALAMUS The   hypothalamus,   a   structure   in   the   brain, synthesizes chemicals that are secreted to the pituitary 1-41 CRANIAL NERVE FUNCTION(S) Olfactory Sense of smell. Optic Vision. Oculomotor Eye movement, size of pupil, and eye focus. Trochlear Eye movements. Trigeminal Sensations of head and face and chewing movements. Abducens Abduction of eye (muscles that turn eye outward). Facial Facial expressions, secretion of saliva, and sense of taste. Acoustic Sense of hearing and balance or equilibrium sense. Glossopharyngeal Taste and other sensations of the tongue, swallowing movements, secretion of saliva. Vagus Sensations of movement (e.g., decrease in heart rate, increase in peristalsis, and contracting of muscles for voice production). Accessory Shoulder movements, turning movements of the head, and voice production. Hypoglossal Tongue movements. Table 1-3.—Cranial Nerves