Med-Surg - Renal System, part 2: RAAS, ADH, ANP/BNP, Labs
by Cathy Parkes December 03, 2021 Updated: August 09, 2023 4 min read
Hi. I'm Cathy with Level Up RN. In this video, I am going to talk about key regulatory systems that impact the kidneys as well as renal system LATs. If you have our Level Up RN Medical-Surgical Nursing Flashcards, definitely pull those out so you can follow along with me. At the end of the video, I'm going to give you guys a little quiz to test your understanding of some of the key points I will be making in this video. So definitely stay tuned for that. We're going to start things off by talking about RAAS, which stands for renin-angiotensin-aldosterone system, and the steps I'm going to talk through here can be found in our flashcard deck. So when there is low blood pressure in the body, that will cause decreased blood flow to the kidney, so decreased renal blood flow. And this will cause the kidneys to release renin. Renin, in turn, will convert angiotensinogen into angiotensin I, and then angiotensin I is converted into angiotensin II by ACE, which is angiotensin-converting enzyme, which is produced by the lungs. Then angiotensin II will cause three things to happen in order to bring up the blood pressure. The first thing it causes to happen is vasoconstriction of the afferent arterioles in the nephrons, which causes increased sodium and water reabsorption. The second thing it allows for is the release of aldosterone from the adrenal cortex, which in turn causes reabsorption of water and sodium at the kidneys. And then the third thing it does is it causes vasoconstriction of the peripheral blood vessels, which also helps to bring up blood pressure. So all three things, more water and sodium, and constriction of those blood vessels will bring up blood pressure in the body.
Let's now talk about other hormones that impact the kidneys. So antidiuretic hormone, or ADH, is secreted by the posterior pituitary gland in response to an increase in the blood osmolarity, meaning the blood is concentrated. ADH will cause the kidneys to reabsorb water, so not water and sodium but just water, and that will help to dilute the blood. It also brings up blood volume as well as blood pressure. Then we have natriuretic hormones, which include ANP and BNP, which are released by the cardiac muscle cells in response to stretch. So if the heart is being stretched due to excess volume, that will cause the release of BNP and ANP. In turn, ANP and BNP will stimulate diuresis, so it will cause the kidneys to excrete more water and more sodium, and this will bring down the body's blood volume as well as the blood pressure. So our little cool chicken hint here on the card is ANP and BNP will make you pee.
Let's now talk about renal system LATs. So when we run a urinalysis, the patient's urine specific gravity should be between one point zero one and one point zero two five. If the urine specific gravity is elevated, then that means we have concentrated urine. If the urine specific gravity is decreased, then that means we have dilute urine. So when we do the urinalysis, we should not have any of the following substances: glucose, ketones, blood, protein, bilirubin, nitrates, or leukocyte esterase. We do not want to have those things in the urine because that means there is something wrong. In terms of blood test, the two key blood tests you need to know for the renal system include creatinine and the BUN, blood urea nitrogen. Creatinine is more specific in the diagnosis of kidney dysfunction. So normal levels of creatinine are somewhere between zero point six and one point two. If we have elevated levels, that is indicative of kidney dysfunction. With BUN, blood urea nitrogen, we should have a level between 10 and 20. If we have an elevated BUN, that can also mean we have kidney dysfunction, but it could also mean the patient is dehydrated, so it's not as specific. So we do have a little cool chicken hint here on our card, which says 10 to 20 BUNs, like hamburger buns, are fine for our picnic.
All right, it's time for a quiz. I have three questions for you. First question is a fill in the blank question. Blank is released from the adrenal cortex, which causes the kidneys to increase reabsorption of sodium and water. The answer is aldosterone. Question number two is also a fill in the blank question. Blank is released from the posterior pituitary gland, which causes the kidneys to increase reabsorption of water. The answer is ADH or antidiuretic hormone. Question number three, if your patient has a urine specific gravity of one point zero zero two, does that mean your patient's urine is concentrated or dilute? The answer is dilute.
All right. That's it for this video. I hope you found that helpful. If so, be sure to like the video. And if you have a minute, leave me a comment. In my next video, we will start getting into disorders, starting with incontinence, as well as UTIs. So stay tuned. Natriuretic hormones such as ANP and BNP are released by the cardiac muscle cells, not the [inaudible].
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