Renal Corpuscle Anatomy

The Renal Corpuscle

The cortex of the kidney contains the first capillary bed where filtrationThe process by which fluid moves out of capillaries into surrounding tissues due to hydrostatic pre takes place.  The capillary bed is called the glomerulusA network of capillaries in the nephron where blood filtration occurs..  The glomerulus is wrapped in a double-layer serous membrane. This membrane is similar to the pleuraThe double-layered membrane surrounding the lungs and lining the thoracic cavity. of the lungs. It is also like the pericardiumThe membrane surrounding the heart. of the heart. 

There is a visceral layer that hugs the capillary and has specialized cellsThe basic structural and functional units of life. called podocytesSpecialized cells in the glomerulus that form filtration slits, preventing large molecules from ente.  The outer parietal layer consists of simple squamous cells. There is a distinct capsular spaceThe space between the glomerular capsule and the glomerulus where filtrate collects. between it and the visceral-wrapped glomerulus.  All of these structures include the glomerulus, the visceral podocytes, the capsular space, and the parietal layer. Together, these are collectively called the renal corpuscleThe structure in the nephron that consists of the glomerulus and Bowman’s capsule, where filtratio. 

Histologically, renal corpuscles look like little bull’s eye scattered in the cortex of the kidney.  Only in the cortex.  The capsular space is always easy to identify.  The glomerulus is contained within and the thin layer of simple squamous cells separates the renal corpuscle from surrounding tissues.

The Glomerulus

Glomerulus is the specific name we give the first capillary bed blood experiences in the filtration.  The glomerulus is fed by an afferent arterioleThe small artery that carries blood into the glomerulus of the nephron. that comes off the cortical radiate artery.  What makes the glomerulus special is that it is drained by an arteriole instead of a venule.  This drainage vessel is called the efferent arterioleThe small artery that carries blood away from the glomerulus after filtration. and it leads to the second capillary bed that blood experiences. 

Recall from the section A cut or slice of the body or an organ for study. of blood vessels that there were three types of capillariesThe smallest blood vessels where gas, nutrient, and waste exchange occurs between blood and tissues.: continuous, fenestrated, and sinusoidal.  Fenestrated capillaries has relatively large intercellular clefts compared to the more common continuous capillaries.  However, they were not as large as intercellular clefts of the sinusoidal capillaries that allow red blood cells to escape.  The glomerulus contains a fenestrated capillaryCapillaries with pores (fenestrations) that allow rapid exchange of fluids and small solutes (found, specifically sized to allow anything smaller than albuminA plasma protein that helps maintain osmotic pressure and transport substances. to escape. 

The glomerulus is wrapped in that visceral layer made of specialized cells called podocytes.  The root word podo- mean foot.  These cells wrap around the fenestrated capillary forming a second layer of filtration.  Podocytes have these feet that come together kind of like intertwined fingers.  They form these filtration slits through which anything trying to escape from the capillary bed would have to fit.  Again, anything smaller than the protein albumin would fit. 

Blood enters this capillary bed via the afferent arteriole.  As the blood circulates, things smaller than albumin escape the fenestrated capillary AND the filtration slits of the podocytes.  The substance would end up in the capsular space. This area is drained by this thingy right here. It eventually leads to the renal basin. 

Anatomy of the Filtration Membrane

We will work with this diagram on the bottom left again. We will identify more structures present in the renal corpuscle.  The afferent arteriole brings blood into the glomerulus and the efferent arteriole carries it away.  The glomerulus in these two, more enhanced pictures, has red blood cells in it. Simple squamous endothelial cells surround the capillary. The podocytes in these cross-section diagrams are the blue cells wrapping around the capillary. 

These podocytes and the fenestrated capillaries are crucial structures. Something must move through them to be filtered out of blood. Only then can it enter into the urineThe liquid waste excreted by the kidneys..  These two layers of cells are the boundary between what’s in the blood and what is in the renal capsuleThe fibrous covering that surrounds and protects the kidney.. This is the filtration membrane. Remember that fluid-fille space bounded by the simple squamous epithelial cells of the parietal layer of the capsule?  Well, remember them now.  This capsule is filled with all kinds of small stuff that escaped from the glomerulus.  This is not urine, it is filtrateThe fluid that is filtered from the blood into the nephron and will eventually become urine..  It still has to go through the second capillary bed of the kidney.