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 bodys
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