HTN, Vasoconstriction,hypotension, vasodilation

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    ok when it comes to blood pressure i get myself confused. i know the important thing the body needs is oxygen and the RBC carries oxygen and the nutrients the body need to survive. so when it comes to high blood pressure there is vasoconstriction right so the heart has to work harder to pump blood throughout the rest of the body but it can only do it for so long. so does that mean that some parts of the body will not get blood.and with vasodilation why would there be hypotension? and some of the manifestations of too much oxygen and too little.how come when there is not enough you feel tired, fatigue and so on but when there is too much you are restless? i don't know if i got them right but i am confused when it comes to those terms so can someone give some insight on the heart and the mechanisms related to the kidneys and decreased cardiac output and so on.by the way i had a horrible teacher for A&P 2 so i basically learned what i had to to pass the class.i'm just now getting a better understanding of A&P but sometimes it's confusing with all the intricacy of how things work and so on
  2. 14 Comments so far...

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    Think of when the body has blood loss, say to trauma or something...
    less blood = less O2 = less blood pressure through the body = higher heart rate ( compensatory mechanism) so you have hypotension and tachycardia.

    Also, with the above s/s you would get Shortness of breath or dyspnea r/t:

    Low O2 = weakness, yes? no energy to cells or brain, = no O2 = death
    high O2 = excess energy to all cells and brain = confusion, delerium, restlessness
    Does that make any sense to you? Hope so. good luck
    PhoenixTech likes this.
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    yes it does .but why would there be confusion with too much oxygen. i know blood pressure is defined as the pressure exerted through the walls of the arteries but in simple term does it mean how much blood and the force of it.so if there is not enough blood then there will be hypotension right? and also im reading for my class in hypoxemia why would hypertension be a symptom,i'm confused sometimes the signs and symptoms don't make sense.like for example with hypercalcemia you would think there would be muscle twitching but it's the opposite. that's so weird it just dont make sense sometimes but i guess sometimes you just have to go with what it is and not question
  5. 0
    When you put your thumb on the end of a water hose and constrict the opening, does the water come out under less pressure or more pressure? That's the way I have to think of the vessels and BP.
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    I suggest the book, A & P Made Incredibly Easy I would not suggest you just go with it & not question it. It's very vital to understand the processes when it's time to apply the nursing process in practice. The fact that you are inquiring here on AN shows that you want to understand so take the extra step & acquire the above mentioned book.
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    I'd love to help. Loved A and P.

    You are right with vasoconstriction and the heart needing to work harder. As said before, vasoconstriction is a compensatory mechanism. This is a process to raise pressure but also shunt blood to vital organs. You're right saying that some parts of the body get less blood flow than others. The biggest organ in the body is the skin. It is less vital than the brain or kidneys, so when you loss a lot of blood, blood is shunted away from the skin to vital organs...which is why people become pale during blood loss. With vasodilation, BP goes down b/c there is either more space or less volume. BP is a measurement of pressure in the vessel when the heart contracts and relaxes. If you have decreased cardiac output (blood loss or heart failure), then the pressure exerted on the vessels wall is less. With acute heart failure, you can expect low BP. With chronic heart failure, you can find low, normal, or high BP's b/c of compensatory mechanisms or other issues ....and that is where the kidneys come in.

    The kidneys not only produce urine and act as a filter, they also release hormones and balance electrolyte levels. Water follows sodium. The more sodium you have in your body, the more water you will retain. Thats why heart pts are put on low-sodium diets. High sodium levels cause HTN. The kidneys can absorb sodium or excrete sodium based on your BP ( and also absorb/excrete water and other electrolytes). Don't forget Aldosterone, which is hormone secreted by the kidneys that regulates salt and water. It happens when sodium levels are low. Aldosterone release causes the body to retain sodium, which means retaining water = higher BP levels. If blood levels are low, the kidney releases Renin. Renin actively converts angiotension to angiotension I. The lungs then release angiotension converting enzyme (ACE) which converts angiotension I to angiotension II. Angiotension II causes: secretion of aldosterone, sensation of thirst ( so you intake more water), and triggers anti-diuretic hormone ( a hormone that causes the kidneys to hold onto water instead excreting it). Angiotension II also cause vasoconstriction. So this feedback system helps regulate blood pressure. If a patient is given Lisinopril or Altace, the BP will down. Why? Because they are ACE-inhibitors. If you take an ACE inhibitor, angiotension does not get converted, so the BP will be blocked from going up. Also, the kidneys can release a hormone called erythropoietin (Epo) if blood levels are low. Epo causes the body to produce more red blood cells. It is also made as a medication for anemia. This is the same drug that long distance runners or cyclists use for "blood doping." Epo causes more RBC to be produced, which causes better oxygen levels, which = more blood volume. Dialysis pts are usually anemic, because the kidneys don't produce Epo. When the heart needs to work harder, has less oxygen supply, and has less nutrients... fatigue ensues.

    Restlessness is a symptom of inadequate respiratory mechanisms. I make a new submission for that one
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    Obviously, the body needs oxygen, but carbon dioxide (CO2) levels are much more potent. In hypoxia, the body is not getting proper supply. The brain needs lots of O2. But if a pt is hypoxic, meaning they are not getting proper respiration, the CO2 levels will most likely rise. The body reacts a lot more to CO2 than O2. How fast we breath is dictated by our CO2 levels. We have specific receptors sensitive to CO2. If it's too high, we breath faster to blow it off. If it is too low, we breath slower to retain it. Running causes our body to use more O2 but it also produces more CO2 as a by-product, so breathing faster keeps homeostasis. But the body is amazing in how it compensates for different diseases. Some people can live with high CO2 levels, like COPD. CO2 is acidic. Acidosis will cause higher resp b/c we are trying to blow it off. In diabetic ketoacidosis (DKA), the body become so acidic that they have constant tachypnea and long sighs to blow off CO2, and they usually end up with very low CO2 levels. The kidneys try to help by secreting bicarbonate (a strong buffer). But when someone has chronic CO2 retaining, the body is able to compensate and they will have normal blood PH, even with high CO2 levels. If someone becomes hypoxic, less O2 goes to the brain. This causes delerium but high CO2 levels will also cause restlessness. Taking in O2 and blowing off CO2 fixes it.

    In everyday life, if you hyperventilate, you will become dizzy b/c Co2 levels will decrease. This is b/c CO2 is also a very potent vasodilator. Baroreceptors interpret CO2 and if you blow off CO2, vasoconstriction ensues. CO2 levels can affect BP related to certain disease processes. If a pt has an increased intracranial pressures ( elevated ICP), hyperventilating them will shortly lower the ICP (b/c of vasodilation).

    Usually, doctors don't really care about the O2 level as long as the saturation is fine. They are more concerned about CO2. As said before, the CO2 levels dictate how fast we breath. Any causes of the CO2 being too high or too low can be fatal. However, giving someone lots of O2 can be bad. This is called oxygen intoxication. It can cause seizures, retinal issues, and can develop free radicals. Scuba divers can suffer from oxygen toxicity. But if you give a COPD pt too much oxygen, it can actually stop the pt from breathing b/c it shut down the breathing drive. Any one of these factors can cause someone to become restless, confused, or comatose.
    Last edit by hodgieRN on Oct 15, '11
    Jay406, wink4clover, klag0915, and 1 other like this.
  9. 1
    Quote from AngelofSeduction
    yes it does .but why would there be confusion with too much oxygen. i know blood pressure is defined as the pressure exerted through the walls of the arteries but in simple term does it mean how much blood and the force of it.so if there is not enough blood then there will be hypotension right? and also im reading for my class in hypoxemia why would hypertension be a symptom,i'm confused sometimes the signs and symptoms don't make sense.like for example with hypercalcemia you would think there would be muscle twitching but it's the opposite. that's so weird it just dont make sense sometimes but i guess sometimes you just have to go with what it is and not question
    If you have less blood volume, then you will have hypotension. Giving blood or fluids will correct the problem. Hypertension could be an issue of low blood volume if the body is trying to compensate. If someone is in a car crash and lose lots of blood, you would have to break it down into stages. Initially, there would be hypertension. B/c of the "fight or flight" response, bp would go up. The adrenal glands would releases epinephrine, a very powerful vasoconstrictor. Epi also causes increased heart rate and increased cardiac output. There would be sympathetic nervous stimulation, causing a massive, systemic vasoconstriction action. As bleeding continues, there comes a point were no amount of reaction will do anything b/c of volume loss...then BP drops significantly.

    Calcium is an important ion that regulates different parts of the body. One part is muscle. Think in terms of action potential (basically, a nerve impulse). When calcium levels are low, there is more neural excitabililty and the action potential threshold lowers (less of an impulse is needed to cause a muscular reaction.) More excitability= muscle twitching and even tetany. With electrolytes (sodium, potassium, chloride, bicarbonate) you have to think in terms of chemistry. They are all ions but some hold a negative or positive charge. They work with or against of each other when crossing cell membranes. One will cause excitability or paralysis. The nervous system reacts based on what is high and what is low. Low calcium (excitability) causes the muscle to contract and stay contracted...it won't relax. With normal serum calcium, the threshold won't be low, so you have normal action potentials.
    PhoenixTech likes this.
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    Damn Hodgie! Do you tutor?!
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    lol yea hodgie is good but you lost me for a while.at first you said c02 is a potent vasodilator but in that same sentence you said it causes vasodilation.i'm still a lil confused about low calcium causes twitches.you would think that low calcium cause flaccid muscle since it's function is to contract muscle and since it's low there's no impulse to cause the muscles to contract


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