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[ Ссылка ] Welcome to LY Med, where I go over everything you need to know for the USMLE STEP 1, with new videos every day.

Follow along with First Aid, or with my notes which can be found here: [ Ссылка ]

This video will wrap up renal physiology and transition us to pathology. Let's talk the stages of kidney activity that we talked about in our last video:
1) Blood supply to the kidney via the afferent arteriole via the glomerulus (prerenal)
2) Renal filtration and function - the nephron works it's magic (intrarenal or intrinsic renal)
3) Clearance (postrenal)
When any of these three steps are disrupted you can harm your kidneys and cause azotemia - or a buildup of nitrogenous waste. These cause acute renal failure.
Prerenal causes is anything that disrupts the blood supply. This can be ischemia, shock, HF, MI, etc. Postrenal is due to an obstruction of clearance like benign prostate hyperplasia (BPH), kidney stones, cancer, etc. Intrarenal is the most difficult. Any renal pathology can cause this but there are a few that I want to talk about today. These include:
Acute tubular necrosis: this can be from nephrotoxic drugs like acetaminophen, radiocontrast agents like those seen in CT, crush injuries and cancer/leukemias, ischemia (which affects your medulla, your proximal convoluted tubule and your loop of henle),. When your tubules die, they plug your kidneys and causes muddy brown casts and decreased GFR. Now there are three stages: inciting stage oliguria maintenance stage, and recovery stage.
Drug induced nephritis: from a bad drug reaction. A few days to weeks after taking a drug, you start to develop a fever and rash. You'll see eosinophils in your blood and urine. Stop the drug!
Renal papillary necrosis: your renal papilla, being furthest away from the blood supply can get damaged in ischemia, sickle cell, diabetes, and NSAID use. Causes gross hematuria.
Diffuse cortical necrosis: this is due to extreme hypoperfusion like in shock, DIC and obstetric emergencies. Now let's talk about some lab findings seen in azotemia. Just some background information: when your kidneys stop working you cause a buildup of creatinine and BUN, which is measured by BUN:Creatinine ratio. Also your kidneys can't reabsorb salt and concentrate urine (measurued by urine osmolarity, urine sodium and FENa). Now that you know the basics, we'll go over the lab findings seen in prerenal, intrarenal and postrenal azotemia!

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