In order to understand chronic kidney disease (CKD), it is important to understand the internal working of a kidney. Each person has two kidneys, each one being approximately the size of your clenched fists. They are located on either side of the spine on the lower ribs. The kidneys as an organ clean your blood of waste and water produced by the breakdown of food, medication and other bodily processes.
The renal arteries receive about 20-25% of the cardiac output - amount of blood pumped by the heart per minute. This translates to approx. 40z or 5 cups of blood per minute (20-25% of 5000 mL ).
Inside kidney, the actual removal of waste is done by millions of tiny structures called nephrons. This process is called filtration. There are approximately 1 million nephrons in one kidney. While the nephrons reabsorb most of the water and other important elements from the blood, the waste and remaining water are removed as urine.
PCT : Proximal Convoluted Tubule (Reabsorption of water, electrolytes, glucose, and amino acids. )
DCT : Distal Convoluted Tubule (Fine-tuning of electrolyte and water balance)
CD: Collecting Duct (Final adjustment of urine concentration and composition)
Renal Corpuscle: Consists of Bowman capsule and encloses Glomerulus.
Classification of Nephrons in the Kidney: Nephrons are distinguished by the location of their renal corpuscle and the length of their loop of Henle. Cortical nephrons have short loops of Henle that barely enter the medulla. Juxtamedullary nephrons have long loops of Henle that extend deep into the medulla and are crucial for concentrating urine.
Nephron framework inside Kidney: 85% nephrons are cortical nephrons and rest 15% are juxtamedullary nephrons. Renal cortex receives 95% of the blood that kidney receives and rest with renal medulla. 8-12 renal pyramids (triangular or cone-shaped masses located within the renal medulla) in each kidney having Henle’s loop of Juxtamedullary nephron and collecting ducts of all nephrons.
The heart continuously pumps blood into the kidneys for proper filtration. Blood travels from the aorta in the heart to the renal arteries in each of the kidneys. The renal artery branches into smaller arteries called the afferent arterioles (14 to 28 micrometers (𝜇m)). The blood travels from the afferent arterioles to the glomerulus, located in the nephron. The glomerulus is a cluster of small blood vessels where filtration of water and removal of waste occurs. The Bowman’s capsule is a round casing that contains the tiny blood vessels of the glomerulus. The water and waste separate from the blood like sifting through a sieve and collect into the capsule. Small sized particles (electrolytes, glucose, and small acids) can be filtered easily from the blood supply while larger particles (blood cells and proteins) are not filtered. The clean blood leaves the nephron through the efferent arterioles and joins larger vessels to return to the body. The waste and water travel through the hollow tubules of the nephron to form urine. A distinct feature of the renal circulation is the double capillary bed in the glomerulus (where large amounts of fluid and solutes except the plasma proteins are filtered) and around the tubules. The peritubular capillaries are followed by the venous system that runs in parallel to the arteriolar vessels and progressively form the interlobular, arcuate, interlobar, and renal vein, which leaves the kidney beside the renal artery and ureter.
