Source: Video and Images Created by Amanda Soderlind
Welcome to this lesson on urine formation overview. Today, we will be discussing an overview on how urine is formed by the body. So urine is a substance formed by the kidneys in order to maintain homeostasis of extracellular fluids. So extracellular fluids are fluids found outside of the cells, such as blood, for example. So by forming urine, it helps to keep solute levels of those extracellular fluids from getting too high. And it also controls blood volume and pressure.
So nephrons are structures in the kidneys that filter water and solutes from the blood and then produce urine. So there are three steps to urine formation, filtration, reabsorption, and secretion. So as we talk about these three steps, we are going to refer to this diagram over here of a nephron.
So as I mentioned, filtration is the first step in urine formation, and it takes place in the Bowman's capsule, where water and solutes are filtered out of the blood in glomerular capillaries within the Bowman's capsule. This brown part of the nephron right here is the proximal tubule.
And reabsorption, which is our second step in urine formation, takes place mostly in the proximal tubule. So that's another structure of the nephron. This part that we have labeled here in orange is called the loop of Henle.
OK. So secretion, which is our third step in urine formation, starts at the proximal tubule, and it continues along the nephron tubule up through the distal tubule, which is in pink here. And then urine that has formed will move into the collecting duct. And then the collecting duct will deliver that urine into the renal pelvis of the kidney, and then filter it down into the ureters and then down into the urinary bladder where, it's stored until it's excreted.
So these nephrons, as I mentioned, which are structures in the kidney that are playing the role in urine formation through these three steps, they actually span the cortex and medulla of the kidney. So if you're familiar with the structure of a kidney, these nephrons span the cortex and medulla of a kidney. So this lesson has been an overview on urine formation and nephron structure.
The first step in urine formation in which urine is filtered from afferent arterioles in the bowman's capsule of a nephron.
The second step in urine formation in which valuable water and solutes are reabsorbed back into the blood.
The third step in urine formation in which filtrate moves toward collecting ducts; secretion helps maintain the body's acid-base balance.