# Nephron --- A **nephron** is the functional unit of the [[kidneys]]. Each kidney about a million of these microscopic structures, all filtering the blood, reabsorbing the stuff we want to keep, and secreting the stuff we want to get rid of. ![[kidney.png]] There are two similar but distinct classes of nephron, the **cortical nephron** and the **juxtamedullary nephrons**. - The **cortical nephrons** (which is more numerous) can be identified by its relatively short **nephron loop** which just barely dips into the renal medulla and lacks a vasa recta. The juxtamedullary nephrons are "lower" than the cortical nephrons, very close to the medulla, and their nephron loops are longer with an associated **vasa recta**. The nephron loops of the juxtamedullary nephrons reach very far down into the medulla of the kidney and help maintain the steep osmolarity gradient necessary for concentrating urine. They do this with the help of the [[medullary osmolarity gradient]] - The **juxtamedullary nephrons** have a unique feature associated with them—the **vasa recta**. The vasa recta is a capillary formation associated with the nephron loop of juxtamedullary nephrons. They help concentrate urine by building up a steep osmolarity concentration gradient in the kidney medulla. ![[cortical vs juxtamedullar nephrons.png]] ## Anatomy A **nephron** is made up of two main parts, the **renal corpuscle** and the **renal tubule**. - The **renal corpuscle** is made up of a convoluted fenestrated capillary called the [[glomerulus]] surrounded by a membrane called the **glomerular capsule** (or **Bowman's capsule**). This is where the [[glomerular filtration]] happens. - The **renal tubule** is a long vessel that brings the filtrate from the glomerulus to the collecting duct, where it is eventually expelled as [[urine]]. Although often depicted in a relatively straightened out shape (as above), it actually is a scrunched up mess. This is by design, and also the the far end of the renal tubule (the distal convoluted tubule) actually bumps back up against the afferent arteriole of renal corpuscle to form the [[glomerulus#The Juxtaglomerular Apparatus|juxtaglomerular apparatus]] which is an important feature in [[glomerular filtration|GFR]] regulation. - The renal tubule can be divided up into three main parts, the **proximal convoluted tubule** (**PCT**), the **nephron loop** (or the **loop of Henle**) and the **distal convoluted tubule** (**DCT**). - The **proximal** and **distal convoluted tubules** are where the bulk of [[tubular reabsorption]] and [[tubular reabsorption]] take place. - The **nephron loop** is where the tubule dips down into the medulla of the renal pyramid. Their main purpose is to help build up a strong [[medullary osmolarity gradient]] which facilitates kidney function. There's a thick segment and a thin segment for very important reasons I'm sure. - The **collecting duct** is connected to the DCT by a short segment called the **collecting tubule**. This is where a lot of water levels are regulated. When filtrate leaves the collecting duct it is officially classified as [[urine]]. ![[nephron.png]] >[!health]- Detailed Nephron Anatomy >![[nephron detailed.png]] ## Physiology There are three main physiological process that happen in the nephron: **Filtration** of almost all the water and nearly every molecule from the blood, the **reabsorption** of a lot of that water and the molecules we want to keep, and the **secretion** of stuff back out of the blood that we know we don't want. Regulating - [[Glomerular filtration]] is the separation of **filtrate from the rest of the blood**. It happens in the [[glomerulus]] inside the corpuscle of the nephron. The filtrate is comprised of all the blood plasma and small enough solutes are physically separated from the rest of the blood, and this substance (now called *filtrate*) is sent through the renal tubule, where reabsorption and secretion take place. - [[Tubular reabsorption]] or the process where the useful and wanted things are taken out of the filtrate and **put back into the blood**. Often this is done through [[active transport]], so actually this is a part of the process that requires a lot of energy. - [[tubular reabsorption|Tubular secretion]], or when the body *definitely* doesn't want a thing, and puts it straight into the renal tubule to be **excreted**. **Collecting ducts** collect the filtrate and take it out of the kidney, where it is now classified as [[urine]]. ![[nephron functions.png]] ___