Centralized control removes contradictions and ensures harmony. The centralised master control of physiological functions is mediated by the nervous system, the endocrine system, and the
immune system. Underlying all these systems is the DNA molecule.
has 6x10E9 bits of information called codons that represent 10E7 genes. Each gene codes for one protein molecule and it is
these molecules that catalyze or mediate the biochemical functions of the body. The functions of DNA are control of all aspects
of cell functioning primarily through protein synthesis and transfer hereditary information to the next generation. DNA within
one organism is quite stable. The processes of mitosis and meiosis occur in millions of cells daily with few variations in
DNA structure. To ensure stability DNA replication is semi-conservative. Mutations are rare if we consider the billions of
DNA-related processes that occur
3.0 THE NERVOUS SYSTEM
The nervous system sends sensory impulses from the periphery to the brain and the spinal cord. It sends
motor impulses from the brain and spinal cord to the periphery. It controls, co-ordinates, and integrates body activity in
response to internal and external environmental stimuli. It correlates sensory information, motor co-ordination, memory, and
intellectual function. Most human activities are not under conscious control. The existence of the autonomic nervous system
enables many background life-sustaining activities to continue without sensory input into the cerebrum.
THE ENDOCRINE SYSTEM
secreted in minute amounts and transported by the blood profoundly influence target organs and tissues. Target tissues have
specific receptors for hormones. The hypothalamus-pituitary-target organ axis is one of the miracles of human biology. It
enables the endocrine system to respond to environmental signals, emotions, and thoughts mediated through the cerebral cortex.
The hypothalamus, the pituitary and individual endocrine gland secretions are controlled by negative feedback. As the product
mediated by the hormone accumulates and reaches a certain level, further hormone production is blocked. Hormones from the
hypothalamus and the pituitary affect secretions by other glands. The endocrine system has several functions: maintaining
homeostasis (fluid and end electrolytes), growth and development (tissue growth and sex differentiation), and adaptation to
physiological stresses (fight or flight reaction), reproduction (menstruation and other reproductive processes). The specific
functions of hormones are morphogenesis, metabolic regulation, and functional integration.
4.0 THE IMMUNE DEFENCE SYSTEMImmune defense is recognition and elimination of
non-self (foreign) material. Non-specific immunity
is innate while specific immunity is acquired. Non-specific immunity may be mechanical barriers like skin or mucous membranes,
chemical barriers such as transferrin or interferon, cells such as natural killer cells, granulocytes, and leukocytes. Specific
acquired immunity is based on lymphocytes. B lymphocytes produce antibodies (humoral immunity) whereas T lymphocytes attack
the bacteria directly (cell-mediated immunity). Cellular immunity is more important than humoral immunity.