Final answer:
The blood supply to the glomerulus is unusual due to its two capillary beds connected by an arteriole—a feature not seen in typical vascular arrangements. High pressure in the glomerulus, necessary for kidney filtration, is maintained by the size difference between afferent and efferent arterioles, while the peritubular capillaries and vasa recta reabsorb filtered substances.
Step-by-step explanation:
The blood supply to and from the glomerulus is unusual because it involves two capillary beds connected in series by an arteriole. The afferent arteriole delivers blood to the glomerular capillary bed, which is under high pressure due to the larger diameter of the afferent arteriole compared to the efferent arteriole. This high pressure is essential for the filtration process in the kidneys. After filtration, the blood leaves the glomerulus through the efferent arteriole and enters the second capillary network, which consists of the peritubular capillaries and vasa recta. This network is involved in the reabsorption of water and solutes back into the circulation.
Most capillary beds in the body are served by arterioles and drained by venules, with no second capillary bed or arteriole in between. However, in the kidney, the connection of the glomerulus, via the efferent arteriole, to the peritubular capillaries and vasa recta, all within the same nephron, is unique. This arrangement qualifies as a portal system, which is typically found only in certain parts of the body, such as between the intestines and the liver (hepatic portal system) or between the hypothalamus and the anterior pituitary (hypothalamic-pituitary portal system).