state. For example, during an emergency the body'sheart and respiration rate increases. After theemergency, the parasympathetic system will decreaseheart and respiration rate to normal. The sympatheticand parasympathetic systems counterbalance eachother to preserve a harmonious balance of bodyfunctions and activities.THE ENDOCRINE SYSTEMLEARNING OBJECTIVE:I d e n t i f yendocrine glands and the hormone(s) theyproduce, and determine the effect eachhormone has on the body.Homeostasis, the self-balancing of the body’sinternal environment, is achieved and maintained bythe endocrine system and the nervous systems. Thesesystems work alone and together to perform similarfunctions in the body: communication, integration,and control. Their communication capabilities providethe means for controlling and integrating the manydifferent functions performed by organs, tissues, andcells. The endocrine system, however, performs thesefunctions by different mechanisms than the nervoussystem.The endocrine system sends messages by way ofchemical messengers called hormones. Minuteamounts of these hormones are secreted fromendocrine gland cells into the blood and distributed bythe circulatory system. Endocrine glands secretehormones directly into the blood, because they have noduct system. The glands of this system are often calledductless glands. Cells that are affected by the hormoneare referred to as target organ cells.Today, many hormones can be extracted from theglands of animals or produced synthetically. Medicalofficers may prescribe these naturally derived orsynthetic hormones for patients who are deficient inthem or who might otherwise benefit from their use.For example, oxytocin (the hormone which stimulatesuterine contractions during pregnancy) has beensynthesized and is used during the delivery process forwomen who are deficient in this hormone.The hormone-producing glands include thehypothalamus, pituitary, thyroid, parathyroids,adrenals, pancreas, and gonads (the testes and ovaries)(fig. 1-47).HYPOTHALAMUSThe hypothalamus, a structure in the brain,synthesizes chemicals that are secreted to the pituitary1-41CRANIAL 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.AcousticSense of hearing and balance or equilibrium sense.GlossopharyngealTaste and other sensations of the tongue, swallowing movements, secretion ofsaliva.VagusSensations of movement (e.g., decrease in heart rate, increase in peristalsis, andcontracting of muscles for voice production).Accessory Shoulder movements, turning movements of the head, and voice production.Hypoglossal Tongue movements.Table 1-3.—Cranial Nerves
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