Development of the intrarenal vascular system of the puppy kidney.

This study investigates the development of the vascular system of the puppy kidney (1-21 days after birth) after preparing casts of the renal vessels. At two days, the intrarenal vascular system distal to the afferent arteriole is strikingly different than that of the adult. The glomeruli of the outer cortex consist of a single dilated vessel while those of the mid and inner cortex posses an increasingly larger number of capillary loops. The efferent arterioles vary greatly in appearance from outer to inner cortex. Those in the nephrogenic zone are characteristically short and narrow and join a larger venous vessel termined a sinusoidal capillary. An efferent system somewhat similar to that of the adult is seen in the mid and inner cortex. One of the most obvious differences noted between the puppy and adult kidney is the relative lack of peritubular capillary networks throughout the cortex of the puppy kidney. The puppy possesses large, irregular vessels termed sinusoidal capillaries. The most rudimentary sinusoids are found in the outer cortex with more mature vessels in the inner cortex. The vascular arrangement of the efferent arteriole and sinusoidal capillary appears as a post-glomerular shunt. Functionally, the shunt would direct blood flow away from the proximal tubule and thus could result in a low extraction ratio and Tm for secreted solutes.