Blood pressure and irreducible complexity (Introduction)

by David Turell , Thursday, September 24, 2015, 00:41 (3348 days ago)

This article tries to do away with evolution. Forget that and look at the complexity of blood pressure control. Irreducibly complex? Obviously. This is why I believe in God-guided evolution:-http://www.evolutionnews.org/2015/09/controlling_blo099611.html-"Three of the most important chemicals involved in blood pressure control have already been mentioned within another context in previous articles. Norepinephrine and epinephrine, the neurohormones of the sympathetic nervous system, act quickly, within a split second. Angiotensin II, a hormone that comes about from the action of renin, secreted by the kidneys, and Anti-Diuretic Hormone, sent out by the posterior pituitary gland, are slower and usually act within a few minutes. It is important to realize that the effects of these chemicals is limited to only several minutes which allows the body to maintain moment to moment control of its blood pressure. The sensors, integrators and effectors that make up each of the systems for these chemicals to affect blood pressure will be looked at one at a time below. -"There are sensors located in the main arteries directly supplying blood to the brain, which can detect wall distension. These are the baroreceptors, which by sensing the stretching within the arterial walls are able to detect the arterial blood pressure. They are a type of mechanoreceptor that senses movement, in contrast to the chemoreceptors which detect chemicals like oxygen, carbon dioxide and hydrogen ion. The baroreceptors send their data on the blood pressure by way of nerves to the brain. The brain integrates this information, and if the blood pressure is too low, it causes the release of more norepinephrine and epinephrine from the sympathetic nerves. By attaching to specific receptors, increased sympathetic stimulation affects all three of the factors mentioned above, which makes the blood pressure rise. -"As noted previously, it makes the heart pump harder and faster, which increases the cardiac output. In addition, it causes the kidneys to absorb more Na+ ions and more water by the release of more ADH, which increases the blood volume. It also stimulates the systemic veins to send more blood back into the systemic arteries. Finally, it tells the muscles surrounding the arterioles to contract more which increases the peripheral vascular resistance. All of these actions combine to increase the blood pressure. However, if the blood pressure is where it should be or higher than normal, the sympathetic system releases less of these neurohormones, usually at only a basal rate. -"As we've already seen, there are wall motion sensors located within specialized cells within the kidneys where the blood enters to be filtered. These sensory cells release a hormone, called renin, in an amount that is inversely related to how much wall motion they detect. The more the walls stretch, the less renin is sent out, and the less the walls stretch, the more renin is sent out. Renin is an enzyme that starts a chemical reaction which results in the formation of a hormone called angiotensin II. By attaching to specific receptors, angiotensin II affects two of the three factors that make blood pressure rise. -"First, it causes the body to take in more salt and water and the kidneys to hold onto more as well. All of these actions increase the blood volume. And second, as its name denotes, angiotensin II makes the muscles surrounding the arterioles constrict, causing a rise in the peripheral vascular resistance. In fact, it is the most powerful vasconstrictor in the body, even more than norepinephine. Both of these actions make the blood pressure rise. -"The osmoreceptors in the hypothalamus, which detect the water content of the body, are shrink sensitive and affect the release of ADH. The less water in the body, the more they shrink, and the more ADH they cause to be sent out by the posterior pituitary gland. And the more water in the body, the less they shrink and the less ADH is sent out. By attaching to specific receptors ADH affects two of the three factors that impact the blood pressure. More ADH causes the body to take in more water and the kidneys to bring back more from the urine in production, all of which increases blood volume. Another name for ADH is, vasopressin, which like norepinephrine and angiotensin II increases the peripheral vascular resistance by making the muscles surrounding the arterioles contract more as well. Both of these actions increase the blood pressure. -"Each of the three systems mentioned above have their own sensors, integrators, and specific receptors, while using the same effectors to affect blood pressure."-Comment: Need more proof?