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How does blood travel through the kidney? The renal arteries carry blood to the kidneys, where it is filtered and then returned to the body via the renal veins.
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The renal arteries and veins
The renal arteries and veins are the blood vessels that carry blood to and from the kidneys. The renal arteries branch off from the aorta and enter the kidneys at the hilum, where they divide into smaller arteries that lead to the cortex and medulla of the kidney. The renal veins leave the kidney at the hilum and join together to form the vena cava, which carries blood back to the heart.
The glomerulus and Bowman’s capsule
The glomerulus is a small cluster of blood vessels located in the nephron, the functional unit of the kidney. Blood flows into the glomerulus from the renal artery and is filtered by the capsule. The filtered blood then flows out of the glomerulus into the efferent arteriole. The efferent arteriole then carries blood away from the glomerulus and into the peritubular capillaries.
The proximal and distal convoluted tubules
The proximal and distal convoluted tubules are the two main types of renal tubules. Each has a different function in blood filtration.
The proximal tubule is the first section of the nephron, and its job is to reabsorb glucose, amino acids, and other small molecules from the glomerular filtrate. It also reabsorbs about two-thirds of the water and sodium that is filtered out by the glomerulus.
The distal tubule is the second section of the nephron. Its main function is to reabsorb potassium and magnesium ions and to secrete hydrogen ions into the urine. It also plays a role in controlling blood pressure by regulating the amount of water that is reabsorbed back into the bloodstream.
The loop of Henle
The loop of Henle is a U-shaped tube that is found in the medulla, or inner part, of each kidney. This loop is important in the function of the kidney because it helps to create a concentration gradient of salt and other minerals. This gradient is necessary for the reabsorption of water and other molecules by the kidneys.
The loop of Henle begins at the point where the descending limb enters the medulla. It then bends back on itself, forming a U-shape, before ascending out of the medulla and joining with the collecting duct. The descending limb is permeable to water but not to salt, while the ascending limb is permeable to both water and salt.
As water moves down the descending limb, it is reabsorbed by osmosis into the blood. This causes the concentration of salt in the tubule to increase. When this salty solution reaches the U-bend, it enters the ascending limb.
The cells in the wall of the ascending limb are impermeable to water but allow salt to pass through them by active transport. This means that as salt moves up the tubule, water is forced out by osmosis into the surrounding tissue fluid. This process concentrates salt in tubule fluid, making it more hypotonic than blood plasma.
When this hypotonic solution reaches the end of the ascending limb and enters The distal convoluted tubule (DCT), water will be reabsorbed back into circulation leaving a more concentrated solution of salts (such as sodium chloride) behind in The DCT which will eventually be eliminated in urine
The collecting ducts
The collecting ducts are the final step in the path of urine formation. Urine flows from the renal pelvis, through the calyces, and into the cup-like renal papillae. From there, it enters the minor calyx or medullary ray, and finally into the collecting duct system. The collecting ducts are a series of tubes that empty into the ureters.
The walls of the collecting ducts are lined with two types of cells: principal cells and intercalated cells. Principal cells make up about 95% of the cells in the collecting ducts. These cells are responsible for water reabsorption. Intercalated cells make up about 5% of the cells in the collecting ducts. These cells secrete acids and bicarbonate ions, which help to regulate pH levels in the body.
The ureters
The ureters are two thin tubes that drain urine from the kidneys to the bladder. Each kidney has a ureter that enters the bladder through a hole in the back called the urethra. The urethra is also the tube that drains urine from the bladder when you urinate.
The bladder
The bladder is a sac-like organ that stores urine. The urine is produced by the kidneys and travels down the ureters to the bladder. The walls of the bladder are made up of elastic tissue, which allows the organ to expand as it fills with urine. When the bladder is full, it signals the brain that it needs to be emptied. During urination, urine is excreted from the body through the urethra.
The urethra
Blood enters the kidney through the renal arteries. These arteries branch into smaller arteries and then arterioles. The arterioles branch into even smaller vessels called capillaries. The blood is finally collected in venules, which join to form veins. The veins leave the kidney and return the blood to the heart through the renal vein.
The urethra is a tube that carries urine from the bladder to the outside of the body.
