Role Cardiovascular System and Kidney in The Homeostatic Regulation of Blood Pressure
Introduction
The kidney and the cardiovascular system are vital in the control and maintenance of blood pressure. Starting with the Kidneys, they have the ability to effectively respond to changes in blood pressure. The Kidneys are instrumental to blood pressure regulation since blood pressure is essential to the functioning of the kidney. The function of the kidney nephron, which is reabsorption filtration and secretion are all dependent on blood pressure.
Figure 1The forces that drive glomerular filtration.
From the figure above, it can be deduced that the glomerular capillaries, blood pressure affects the glomerular filtration rate (GRF). The blood pressure in the capillaries is, in turn, affected by the systemic blood pressure (p.132).
If, for instance, the systemic blood pressure and by extension, glomerular blood pressure reduces, the GFR will dropsimilarly. If the blood pressure reduction is significant, the GFR will drop below 15 ml min−1, leading to acute renal failure. On the contrary, if blood pressure is high, the GFR will also increase, which will lead to the overload of the nephrons, and hence permanent renal damage may be induced. Therefore, the Kidneys must regulate blood pressure and maintain it within the normal rate. (p.134).
Blood pressure Regulation
Sodium is very instrumental in blood pressure since it is stored in blood plasma and responsible for osmolarity. If we ingest too much sodium, it will lead to an increase in the amount of sodium in the blood, which will increase plasma osmolality and, hence, increase water retention. The volume of blood will increase, which will lead to an increase in systemic blood pressure (p.136). It, therefore, means that the lower the sodium concertation, the lower the blood pressure and vice versa. The mechanism to control sodium ions is regulated by specialized cells found in the juxtaglomerular apparatus.
Figure 2Components of a Nephron.
Figure 3The juxtaglomerular apparatus
The Macula densacells’ surface receptors perceive the NaCl ions in the distal tube (Fig.3). If there is a dropin NaCl concentration, the Macula densa cellsproduceparacrine factorsthat diffuse to the juxtaglomerular cells leading to the release of enzyme renin. Renin triggers the reduction of blood vessels diameter, thus increasing pressure. This vasoconstrictive effect happens in the efferent arteriole. (p.140).
Figure 4. Functions of the juxtaglomerular apparatus.
If there is a reduction in systemic blood pressure, the GFR will drop. This will lead to a decrease of the amount of sodium chloride that is filtered into the blood, and therefore the level of sodium ions will reduce in the renal tube. The reduction in ion concentration will trigger the manufacture of prostaglandins by the macula densa cells. Renin production will be increased, which will lead to vasoconstriction, which will lead to an increase in GFR and blood pressure. It is important to note that renin doesn’t control blood pressure directly, but though known as the renin-angiotensin system (RAS).
Regulation of blood pressureHomeostatically
For the cardiovascular system to operate optimally, it has to be determined by blood pressure. If blood pressure is elevated, it will destroy blood vessels, and if it is reduced significantly, perfusion of tissues will occur, and organs won’t meet their needs, so they will fail. Therefore, blood pressure is homeostatically regulated so that it stays within the acceptable range.
Figure 5Part of the ventricle and aorta. (a) Discharge of blood when the ventricle contracts. (b) Closing of the semilunar valves when the aorta elastically recoils (c) Flow of blood along the aorta whenthe aortaelastically recoils.
The nerve endings called baroreceptors are very instrumental in blood pressure regulation. Their location is in the aortic arch, and the walls of carotid arteries. The Baroreceptors are triggered when the walls of the artery ‘stretch’ due to changes in blood pressure. When they perceive a variation in blood pressure, they communicate the information to centers of the brain called the cardioacceleratory and cardioinhibitory, which will influence the autonomic nervous system’s output.
Elevation of blood pressure will trigger the baroreceptors to relay impulses to the cardioacceleratory and cardioinhibitory centers. This will lead to a rise in the parasympathetic stimulation of the SAN, which will lead to a reduction in heart rate. The sympathetic stimulation of blood vessels will be inhibited, which will cause vasodilation that will reduce peripheral resistance. Reduction of heart rate reduces cardiac output and, together with the reduction of peripheral resistance, will lead to a reduction in blood pressure getting it back to its normal range.
When the baroreceptors realize a reduction in blood pressure, the information will be sent to the brain, which will elevate the sympathetic stimulation of the SAN. This will lead to an elevation of the heart rate, the cardiac output, and the contractibility of the heart muscles. At this time, blood pressure will be increased due to the sympathetic stimulation of the blood vessels that triggers vasoconstriction and increase of the peripheral resistance.
Chemoreceptors are also instrumental in blood pressure regulation. They diligently monitor CO2 and O2 levels in the blood. The chemoreceptors’ location is in the carotid and aortic bodies, which are found in carotid arteries and the aortic arch, respectively. The chemoreceptors greatly influence the output of cardiovascular centers when a severe disturbance occurs in the body. When a disturbance occurs, the Chemoreceptors detect it, which leads to sympathetic stimulation in the medulla’s cardiovascular center. This will cause the blood pressure to rise and therefore getting it back to its normal level.
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