HTN, Vasoconstriction,hypotension, vasodilation

[AngelofSeduction]

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

[hodgieRN]

"at first you said c02 is a potent vasodilator but in that same sentence you said it causes vasodilation."

Sorry if that was confusing. I said CO2 is a potent vasodilator, meaning higher CO2 causes more vasodilation and then I said "as we blow it off, vasoconstriction ensues (meaning CO2 drops as we blow it off, causing vasoconstriction.

[hodgieRN]

Now when it comes to electrolytes, it can be a little tricky. First, you have to think of ions in terms of where there are and how they interact. Ions can be inside the cell and outside the cell. For example, there's more sodium outside the cell than in...there is more potassium inside the cell than out. When you draw blood work, you are measuring serum, which means you are measuring ions outside the cell. That's why sodium is 145 and potassium is only 4, b/c you are only reading the serum. But the ions need a certain balance. They constantly move inside and outside the cell based on the cell wall's permeability. Calcium also works in this fashion. But don't think about hypocalcemia vs hypercalcemia in terms of just serum levels, but how abnormal levels affect it's ability to move across the membrane...it's chemistry. To help remember, think that calcium works better when there is normal level of it. Low calcium levels change it's ability to move in and out. When it is too low, it tends to stay in one spot. The in-and-out movement of calcium is what helps make a muscle relax and contract.

Now, the physiology of it is were it might get confusing but would love to explain it as additional info. When the brain wants to make a muscle contract, an action potential travels down nerves to neuron end plate. Calcium alone doesn't cause the contraction. The action potential causes a change in permeability. This change causes neurotransmitters to communicate. (Now, there is a structure called the sarcoplasmic reticulum [sR}...it houses it's own dose of Calcium and this doesn't include serum for arguments sake). The neurotransmitter causes the SR to release calcium. The calcium causes the muscle molecules to move... causing contraction (which is in simple terms. There are other things going on as well). For the muscle to relax, the SR must REABSORB the calcium, making the muscle molecules go back to original position. So, the SR needs to move calcium in and out of itself...it has to have nice permeability. When serum calcium levels are low, there is a dysfunction in the permeability. Instead of calicum being reabsorbed into the SR, it stays in one space and causes constant contraction. But as said before, it's not really about how higher calcium levels cause more calcium to stay in the space. It about how hypocalcemia changes the characteristics of permeability.

Now for an example, lets talk about rigor mortis. When death occurs, there is a period when the body becomes very stiff. The SR doesn't have the ability to reabsorb the calcium from the sarcoplasm space. Being more specific, the permeability is very poor. The calcium simply stay in the sarcoplasm space. This causes a constant contraction. So, hopefully this example shows that we are talking about calcium's permeability, not just serum levels.

Other things like neural excitability or decreased threshold also play a factor, but that in itself is vast subject b/c it includes the neurological system. To just help you remember the concept, think that calcium works better when there is an abundance it (not hypercalcemia, but a nice, good level)... it doesn't simply cause a contraction b/c it reflects the level. It works best when levels are normal. Low calcium levels = poor SR permeability = twitching (fast contraction, relaxation, contraction, relaxation). I know that twitching would make sense if you thinking there was an overreaction of permeability, but remember, if the calcium doesn't fully re-absorb into the SR, more stays in the space and that over abundance causes a twitch, twitch, twitch. There isn't good reabsorption, so there is a rapid fire. If the calcium could readily reabsorb (nice permeability), there would be a nice relaxation If calcium levels are low enough, it can even cause convulsions b/c the dysfunction is even greater. It's all about how it affects permeability, not simply what is floating around in the serum.

[AngelofSeduction]

makes a little more sense thx