Published: 2021-06-23 13:15:04
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1 discuss how the brain blood flow is controlled under normal circumstances
The brain is an organ
The brain blood flow must be maintained constant. For blood flow to be maintained constant there is need for mechanisms which prevents the blood supply from either rising too high or from falling too low. The blood flow to the brain is autoregulated.Metabolic factors are involved in metabolic auto regulation of the brain blood flow. The factors include adenosine, hydrogen ion concentration of brain tissue, potassium ions, low oxygen content and excess carbon dioxide. When there is reduced perfusion to the brain, the metabolic factors will cause dilatation of the brain blood vessels. This will cause blood supply to the brain to be improved. When the blood supply to the brain is increased the metabolic factors are carried away from the brain causing constriction of blood vessels. When there is hypoxia the carbon dioxide and hydrogen ion content of the brain tissue increases. This causes vasodilatation which increases blood supply to the brain. When there is increased oxygen supply to the brain the carbon dioxide and hydrogen ion content decreases causing vasoconstriction of blood vessels will cause dizziness. There is hyperventilation which causes carbon dioxide to be washed out of the body. Then the carbon dioxide levels fall leading to reduced hydrogen ion concentration of the body fluid.Hyperventilion supplies more oxygen to the lungs hence all body tissues including the brain.
Reflex regulation of the brain blood flow with intracranial pressure
Intracranial pressure is the pressure inside the bony skull. The skull encloses the brain blood vessels of the brain and cerebral spinal fluid.Cerbral spinal fluid has to maintain pressure as well as the blood in the brain.
How intracranial pressure may increase
Main causes of increased intracranial pressure increase are blockages of cerebral spinal fluid drainages. This causes the cisterns to expand leading to increased intracranial pressure. Brain tumours will cause the brain to expand encroaching on the intracranial space .Because of the increased brain volume there is increased intracranial pressure on the brain blood vessels and the cerebral spinal fluid. The blood vessels are then compressed leading to brain ischaemia.The central nervous system ischemia response will then come in.
Central Nervous system Ischemic Response
This is a reflux stimulated by brain ischaemia.Brain ischemia leads to hypoxia which stimulates the cardiovascular regulating centre in the medulla oblongata. Sympathetic to the heart and blood vessels is stimulated leading to increased cardiac output and peripheral resistance .This cause the mean systemic arterial blood pressure to increase. Blood flow in the brain vessels will increase. This restores brain blood flow to normal. When the mean arterial blood pressure increases the baroreceptor reflex will slow the heart mediated.
2 Describe the relationship between the ECG and the cardiac cycle
ECG is a machine which measures the electrical activity of the heart. It records electrical changes in the myocardium during a cardiac cycle. It uses six limb leads and six chest leads. It measures using the P, QRS and T waves. Cardiac cycle is defined as events that occur in the period between one heart beat and the next. This is the periods of rest followed by contraction. At rest there is filling of the heart chambers with blood and contraction also known as systole where there is blood ejection of blood known as systole.
The relationship between these two is that the waves will represent electrical activity of the heart. The Pwave represent arterial depolarization that is upward deflection showing beginning of arterial contraction .The QRS complex represents ventricular depolarization meaning ventricular contraction. The T wave represents ventricular repolarisation that is upward deflection showing beginning of ventricular relaxation .R shows activation of most of the ventricle by large upward deflection. Shows depolarization of the ventricle septum by small downward deflection. Shows last stage of ventricular depolarization by downward deflection. There is the P-R interval which indicates the time for the cardiac impulse to travel from Sino-arterial node through the arterial ventricular node. There is the QT interval which slows the duration of ventricular depolarisation and repolarisation. The ventricular action potential takes place during this interval. The heart rate can be calculated from the electrocardiogram by measuring the interval between the peaks of two successive QRS complexes.
Reference:physiology for health sciences module BSHN111/NSD105 S.K.Arthur,C,T.Musabayana Rosner MJ.DaughtonS.Cerbral perfusion pressure managementin head injury.J Trauma

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