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Acid-base map and compensatory mechanisms
Buffering and Henderson-Hasselbalch equation
Physiologic pH and buffers
The role of the kidney in acid-base balance
Plasma anion gap
Renal system anatomy and physiology
Body fluid compartments
Movement of water between body compartments
Measuring renal plasma flow and renal blood flow
Regulation of renal blood flow
TF/Px ratio and TF/Pinulin
Phosphate, calcium and magnesium homeostasis
Free water clearance
Kidney countercurrent multiplication
Distal convoluted tubule
Loop of Henle
Proximal convoluted tubule
Tubular reabsorption and secretion
Tubular reabsorption and secretion of weak acids and bases
Tubular reabsorption of glucose
Tubular secretion of PAH
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Renal blood flow refers to the amount of blood that the kidneys receive over a period of time.
Blood gets to the kidneys through the renal artery.
Blood from the renal artery flows into smaller and smaller arteries, eventually forming the tiniest of arterioles called the afferent arterioles.
After the afferent arteriole, blood moves into a tiny capillary bed called the glomerulus. The glomerulus is part of the functional unit of the kidney, called the nephron.
There’s about 1 million nephrons in each kidney, and each of them consists of a renal corpuscle - made up of the glomerulus and the Bowman’s capsule surrounding it - and a renal tubule.
Interestingly, once the blood leaves the glomerulus, it does not enter into venules. Instead the glomerulus funnels blood into efferent arterioles which divide into capillaries a second time. These capillaries are called peritubular capillaries - because they are arranged around the renal tubule.
Now, blood filtration starts in the glomerulus, where an urine precursor called filtrate is formed.
The amount of blood filtered into the nephrons by all of the glomeruli each minute is called the glomerular filtration rate, and it’s actually just a small fraction of the blood that gets to the kidneys, because the glomerulus doesn’t allow red blood cells and proteins to pass through and be excreted into urine.
So right from the start, what passes through the glomerulus is mostly plasma - which normally makes up about 55% of blood. What is more, the glomerulus only filters about 20% of that plasma in one go. So when all is said and done, of those around 1.25 liters that the heart pumps out every minute, glomerular filtration rate is normally around 125 milliliters. That plasma-derived filtrate then enters the renal tubule.
The renal tubule is made up of a proximal convoluted tubule, the nephron loop - also known as the loop of Henle - which has an ascending and a descending limb - and finally the distal convoluted tubule.
As filtrate makes its way through the renal tubule, waste and molecules such as ions and water are secreted from the peritubular capillaries into the tubule, and they are also absorbed from the tubule back into the capillaries.
Renal plasma flow (RPF) is the volume of blood plasma passing through the kidneys per minute; whereas renal blood flow (RBF) is the volume of blood flowing through the renal arteries per minute. Both RPF and RBF are measured in milliliters per minute (ml/min), and both are important measures of kidney function. High values indicate good kidney function, while low values indicate poor kidney function.
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