The ventricle of the brain and the central canal of the spinal cord
contain, a clear fluid similar to plasma called cerebrospinal fluid (CSF).
CSF is formed by a group of cells called the choroid plexus located inside
the four ventricles. In human the volume of CSF is 150 ml and the rate of its
secretion is 550 ml/day.
Functions:
1. CSF cushions the brain against mechanical shock when the head moves.
2. It acts as a protective covering for the CNS and confers buoyancy to
brain.
3. The CSF also provides a reservoir of hormones and nutrition for the brain
and spinal cord.
4. It acts as a mechanical buffer. Remaining inside and outside the CNS, it
equalizes the mechanical pressure. If the intracranial pressure tends to rise
the CSF is pressured out. If the pressure tends to fall, more CSF is retained.
Chemical co-ordination
The two major systems of the human body that coordinate, regulate
and integrate almost all physiological functions are the nervous system and
the endocrine system. The information transmitted by the nervous system in
the form of electric impulses is conducted rapidly in the neurons. The signals from the endocrine glands or ductless glands are communicated by means of chemical substances called hormones. The hormones are secreted into and carried by the blood stream from their point of origin to the target organs or tissues. In the target tissues, the hormone action is manifested.
A hormone may be defined as a chemical substance synthesized by
the cells of endocrine glands and carried by blood to the site of action where
it exerts its physiological effects. Hormones are considered as chemical
messengers.



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