腎小体

The renal corpuscle consists of two main parts: the glomerulus, a cluster of fenestrated capillaries with high permeability, and the Bowman's capsule, a cup-shaped structure that encloses it. The Bowman's capsule has two layers—an outer parietal layer of simple squamous epithelium providing structural support, and an inner visceral layer composed of specialized cells called podocytes that participate in filtration.

Podocytes are specialized visceral layer cells with foot-like extensions called pedicels that attach to the glomerular basement membrane. Filtration slits between adjacent pedicels allow solute-rich fluid to pass from the blood into the Bowman's capsule while preventing larger molecules like proteins and blood cells from entering the filtrate.

The glomerular capillaries feature a fenestrated endothelium with numerous pores that create high permeability. This structure allows rapid transfer of solute-rich fluid from the blood into the Bowman's capsule, forming the initial filtrate that becomes the basis for urine production and subsequent glomerular filtration rate and its regulation.

The parietal layer is composed of simple squamous epithelium that forms the outer wall and provides structural support but does not participate in filtration. The visceral layer contains podocytes with pedicels that directly contact the glomerular basement membrane and actively participate in creating the filtration barrier and producing filtrate.

After filtrate enters the capsular space through filtration slits between podocyte pedicels, it collects in Bowman's space. The filtrate then extends into the lumen of the renal tubule and collecting duct, where it undergoes further processing through reabsorption and secretion to form concentrated urine.

The basement membrane is a shared structure between the glomerular endothelial cells and the podocytes' pedicels. It forms a critical component of the filtration barrier, working with the fenestrated endothelium and filtration slits to selectively allow small solutes and water through while blocking passage of large proteins and blood cells into the filtrate.

The afferent arteriole delivers blood to the glomerulus while the efferent arteriole carries blood away, creating high pressure within the glomerular capillaries. This pressure gradient facilitates the transfer of solute-rich fluid across the fenestrated endothelium into the Bowman's capsule, enabling efficient blood filtration and initial urine formation.