Central nervous system blood supply

Carbohydrates are more plentiful and constant in food supplies throughout the world when compared to other nutrients, such as proteins, vitamin A, folic acid, and iodine. A naturally occurring deficiency specifically in carbohydrates is im-known. However, deliberate omission of carbohydrates from the diet with continued consumption of fat as an energy source can lead to specific problems. Glucose is required as an energy source by the central nervous system. When there is a deficiency of glucose, the body adjusts its metabolism to provide ketone bodies, nutrients derived from fat, which can be utilized by the brain and other parts of the central nervous system. However, excessive production of the ketone bodies can result in acidosis, a lowering of the pH of the blood, which is potentially toxic. 

The acetylcholine is accumulated in the parasympathetic nerve endin that supply the smooth muscle action to the iris, ciliary body of the eye, tl bronchial tree, blood vessels, gastrointestinal tract, and urinary bladder. Tl secretory glands of the respiratory tract are similarly inhibited, as are the sympathetic nerve endings to the sweat glands. Voluntary muscles are paralyzed through accumulations of acetylcholine in the motor nerve endings. The central nervous system is likewise affected. 

Although the physiological events occurring subsequent to a- or P-recep-tor stimulation are beyond the scope of this article, a brief outline of the major events following pharmacological stimulation or blockade of these receptors may be of some use to the reader. Activation of a receptors is associated with a peripheral excitatory action on certain types of smooth muscle, such as in blood vessels supplying skin and mucous membranes a peripheral inhibitory action on other types of smooth muscle, such as in the gut and excitatory actions generalized in the central nervous system, such as... 

Because of the restrictions imposed by the blood-brain barrier, the brain also must synthesize its own lipids. An adequate supply of lipids is vital to the central nervous system because they are constituents of the myelin sheath that surrounds the neurons and allows them to conduct impulses normally. The neurodegenerative disorders, such as multiple sclerosis, are a consequence of varying degrees of demyelination of the neurons. 

Fig. 1.6 Cross-section illustrating the distribution of blood to the walls of the midbrain. The tectum is supplied by branches of the superior cerebellar artery. The medial aspects of the peduncular and tegmental regions are vascularized by branches of the basUar artery. The lateral peduncular and tegmental regions are supplied by branches of the posterior communicating artery. Note that these small arteries, which enter the walls of the central nervous system from the periphery, are functional end arteries and do not anastomose with adjacent arteries (See also Color Insert)...

Shlmamoto and Honjo concluded from animal studies that bromhexlne affects tracheobronchial secretions by an action on central nervous system structures, probably In the areas of the emetic center In the medulla oblongata occurring both as a direct effect and Indirectly via stimulation of the gastric mucous membrane. Other animal tests Indicated bronchial secretions were Increased by bromhexlne as a result of an Improved permeability ratio between the bronchial mucous membrane and Its blood supply. The lytic effect of bromhexlne on human bronchial mucosa, observed vitro by electron microscopy, appears due to Increased secretion... 

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