In hot weather, we may not visit the restroom to pass out urine but when the weather is cold, you would understand why it is called convenience. Oh!! that was a joke if you get it. Anyways, today I will be taking a deep dive into how Urine is filtered from our blood and urine is formed before being passed out. There have been several myths about Urine and Urine formation, and I will try to share them before we continue with the post. One myth that some people might be familiar with is that water taken into the body is the only thing that becomes urine. It is believed that the more water you take, your body only absorbs a little, and the rest runs down the pipe hole of the urethra. Another myth says that you are likely to urinate more if you drink water while standing to when sitting because the water will quickly get to the bladder. Have you also heard of the myth that says drinking urine can cure disease? There is a myth that says urine is medicinal. The myth says that drinking urine can cure diseases such as cancer, and other severe diseases. People also believe that urine can serve as a sanitizer to sterilize wounds but that's not true, it's just another myth. Getting the myths out of the way, let's begin the business of the day. We will be looking at the nephron, how blood gets to the nephron, and how blood starts to get filtered.
The Nephron is the functional unit of the kidney. It is responsible for filtering waste from the blood supply to it, and it is responsible for regulating fluid balance. There are millions of Nephrons in each kidney, and remember that there are two kidneys (which are bean-shaped). Looking at one Nephron, I will quickly look at some functional anatomy of the Nephron. When blood is supplied to the nephron, it isn't going to the nephron to give it blood, rather it is going to the nephon for filtration. When the blood reaches the Glomerulus where the filtration happens. From the glomerulus, in the tubules where the filtrate from the blood moves in. The blood moves through the Afferent Arteriole into the glomerulus and goes downward in an arteriole known as the Efferent arteriole which continues as the peri tubular capillaries. 99% of the filtrate that goes into the nephron gets reabsorbed back into the blood, and this is done with the help of the peri tubular capillary.
The Nephron starts with the glomerular capsule, then to the proximal convulated tubule, which is followed by the loop of henles, which is also known as the nephron loop. The Henles loop is made up of the thin descending loop and the thick ascending loop, which is followed by the distal convulated tubule, then the collecting duct. Urine formation is a combination of Glomerular filtration (where there is a high pressure up to 50mmHg) which pushes substances within the blood plasma (except proteins and cells as a result of their size and as a result of their charges in protein) through. At the proximal convulated tubules, 65% of the filtrate is reabsobed into the peritubular capillary. At the loop of heles, about 15% of filtrate goes back into the blood vessel, at the distal convulated tubule, another 15% of filtrate is reabsorped back into the blood vessel, while at the collecting duct, 4% of filtrate is reabsorbed back into the blood vessel. This is not always constant but it revolves around this figures. Also, ther are secretions from the blood into the tubules.
At the proximal convulated tubule, certain basic nutrients are reabsorbed back into the bloodstream and these includes sodium ion, Calcium ion, Chloride Ion, Calcium ion, and magnesium ion. AlsoBicarbonate is being reabsorbed, water, amino acid, urea, and glucose are also reabsorbed back into the blood vessel. Glucose is only reabsorbed at the proximal convulated tubule, if it doesn't leave at the convulated tubule, then it would lead to something we know as diabetes. If glucose isn't reabsorbed back into the bloodstream, it would attract more water causing more water in urine. In the thin descending limb, water is only reabsorbed back into the blood. AT the thick ascending loop of henles ions, and bicarbonates are reabsorbed back to the bloodstream. At the distal convulated tubule, ions, bicarbonate and water are reabsorbed back into the bloodstream. At the collecting duct, sodium ion, cloride ion, bicarbonate, water, and urea are being reabsorbed back into the bloodstream.
The process of secretion is different as nutrients from the bloodstream goes into the tubule.At the proximal convulated tubule, Urea, uric acid, creatine, hydrogen ions, amonia and drugs are secreated into the nephron. In the descending loop of henles, Urea is secreted from the bloodstream into the nephron, and in the collecting tubule, and distal tubule, hydrogen ions, drugs, and amonia are secreted into the tubules.
The Urinary systems primary function is to make urine and get rid of it, but it isn't the only function. It helps to regulate blood volume and blood pressure, regulation of plasma concentrations of sodium, stabilize blood pH, and Converses valuable nutrients.
Reference
National Library of Medicine - The cell biology of renal filtration
Khan Academy - Renal physiology: Glomerular filtration
sciencedirect.com - Proximal Convoluted Tubule
