# Glomerulus --- The **glomerulus** (sometimes called the **glomerular capillary** or referred to as **Bowman's capsule**) is a specialized [[capillaries|fenestrated capillary]] located in the [[kidneys]]. This is where the process of [[glomerular filtration]] occurs, and all the blood that passes through it is filtered of most solutes. ![[glomerulus.png]] ## Anatomy The glomerulus itself is a small knot of capillary that exists inside the **glomerular capsule**. Blood enters the glomerulus via the **afferent arteriole** and, after passing through the capillary, it exits through the **efferent arteriole**. Generally speaking afferent arteriole is larger in diameter than the efferent arteriole in order to build up a sufficient localized blood [[hydrostatic pressure]], in order to perform [[glomerular filtration]]. It works in much the same way as putting your thumb partially over the end of a garden hose to spray water further. The contractile cells around the glomerulus are called **mesangial cells**, and they are very important in the regulation of the [[glomerular filtration|glomerular filtration rate]]. If they contract they reduce the overall blood flow through the glomerulus (and thus the GFR), and if they dilate they increase it (and the GFR). ### Filtration Membrane The **filtration membrane** acts as basically a strainer or sieve for the blood during [[glomerular filtration|filtration]] The glomerulus also makes up a portion of the filtration membrane, and are closely associated with the [[glomerular filtration|podocytes]] of the Bowman's capsule. The filtration membrane is made up of A) the endothelium of the glomerulus (which is an example of a [[capillaries|fenestrated capillary]]), B) the basement membrane of the glomerulus (which is porous, but still blocks large plasma proteins), and C) the visceral (inside) layer of the glomerular capsule, which is composed of specialized cells called **podocytes**. The podocytes have little footlike processes called **pedicles** that fit together like little zipper teeth, which leaves little gaps called **filtration slits** that are small enough to block the passage of most small proteins. ![[filtration membrane.png]] ## The Juxtaglomerular Apparatus The **juxtaglomerular apparatus**, or the **JG apparatus** is little bit of the [[nephron#Renal Tubule|DCT of the renal tubule]] bunches back around and meets up with glomerulus right where the arterioles enter into it. It functions as a sensor, monitoring the blood for salt levels and blood pressure. There are a bunch of special cells that make up these segments of the DCT and the afferent arteriole. The **macula densa cells** are in the DCT and are chemoreceptors that detect NaCl levels in the blood. The **granular cells** are in the afferent arteriole and the are mechanoreceptors monitor [[blood pressure]]. If the BP becomes too low they release [[renin-angiotensin-aldosterone system|renin]]. The extraglomerular mesangial cells exist around the rest of the JG apparatus are also there and they help control the [[glomerular filtration#Intrinsic Controls|glomerular filtration rate]] by releasing cell signals. ## Problems with the Glomerulus - [[glomerulonephritis]] ___