Brain Tour : Our Brain :

The brain is well supplied with oxygen and nutrients from a special circulatory route at the base of the brain called the cerebral arterial circle or the circle of Willis.

Although the brain comprises only about 2% of the total body’s weight, it requires 20% of the total oxygen supply. The brain is one of the most metabolically active organs of the body, and the amount of oxygen it uses varies with the degree of mental activity.

If blood flow into the brain is interrupted even briefly, unconsciousness may result. If the cells are totally deprived of oxygen for 4 or more minutes, many are permanently injured because lysosomes of brain cells are extremely sensitive to decreased oxygen. If the condition persists, they break apart and release enzymes that bring about the self-destruction of the brain cells.

Blood supplying the brain also contains glucose, the principal source of energy for the brain cells. Because carbohydrate storage in the brain is limited, the supply of glucose must be continuous. If blood entering the brain has a low glucose level, mental confusion, dizziness, convulsion and loss of consciousness occurs.

Glucose, oxygen and certain ions pass rapidly from the circulating blood into the brain cells. Other substances enter slowly or not at all. The different rates of passage of certain materials from the blood into most parts of the brain are due to the blood-brain barrier (BBB).

The blood-brain barrier protects the chemical environment of the neurons and neuroglia (supporting cells around the brain cell) in brain tissue, keeping it within precise limits. Blood vessels and capillaries in the brain are lined with a closeknit layer of cells that restrict the movement of substances between them. The cells also have limited permeability, so only few substances can pass through them, from blood into the brain. Brain cells are protected from harmful substance this way. Unfortunately, most antibiotics cannot enter either. Trauma, inflammation, and toxins can cause a breakdown of the blood-brain barrier.