INTRODUCTION
The brain is a delicate and very complex organ located in the head of vertebrate and invertebrate animals. The brain can be said to be the controller of the actions and coordination of an animal. Therefore, the brain should remain unchanged no matter what we take into the body. Nowhere in the body is there more need for homeostasis than in the brain.
The blood is a body fluid that circulates constantly. It transports oxygen to the cells by the work of the red blood cells which contain haemoglobin. White blood cells attack, destroy and remove abnormal and old cells and also fight infectious agents and foreign substances. Platelets take part in blood clotting. Plasma which constitutes about 55% of the blood circulates dissolved nutrients
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It is there to provide protection for the brain. The blood brain barrier is like a percolation scheme that enables materials such as water and glucose into the brain but denies the entrance of possibly harmful ones. It serves to restrict and control the movement of substances between the general circulation and brain extracellular fluid. The blood-brain barrier is a diffusion barrier, which impedes influx of most compounds from blood to brain (Ballabh et al., 2004). It partakes in directing the volume and organization of liquid encompassing the cerebrum through particular transport procedures, and hence adds to homoeostasis of the focal sensory system (Peterson, 2012).
The blood-brain barrier is a mechanism that controls the passage of substances from the blood into the brain. It lets essential metabolites, such as oxygen and glucose, pass from the blood to the brain and central nervous system. It is a cellular and metabolic barrier located at the capillaries in the brain that alters permeability, restricting the passage of some chemical substances from the bloodstream into the neural tissue, while allowing other substances to pass into the