The vessels and nerves of the kidney

The renal bloodstream is represented by arterial and venous vessels and capillaries, through which 1,500 to 1,800 liters of blood flow daily. Blood enters the kidney through the renal artery (a branch of the abdominal aorta), which divides into anterior and posterior branches at the renal hilum. There are additional renal arteries that enter the renal hilum or penetrate the kidney through its surface. In the renal sinus, the anterior and posterior branches of the renal artery pass in front of and behind the renal pelvis and divide into segmental arteries. The anterior branch gives off four segmental arteries: to the superior, superior anterior, inferior anterior, and inferior segments. The posterior branch of the renal artery continues into the posterior segment of the organ under the name of the posterior segmental artery. The segmental arteries of the kidney branch into interlobar arteries, which run between adjacent renal pyramids in the renal columns. At the border of the medulla and cortex, the interlobar arteries branch out and form the arcuate arteries, which are located above the bases of the renal pyramids, between the cortex and medulla of the kidney. From the arcuate arteries, numerous interlobular arteries branch off into the cortex, giving rise to the afferent glomerular arterioles. Each afferent glomerular arteriole (afferent vessel); (arteriola glomerularis afferens, s.vas afferens) breaks up into capillaries, the loops of which form the glomerular capillary network (rete capillare glomerulare), or glomerulus (glomerulus). The efferent glomerular arteriole, or efferent vessel (arteriola glomerularis efferens, s.vas efferens), emerges from the glomerulus; its diameter is smaller than the diameter of the afferent glomerular arteriole. After leaving the glomerulus, the efferent glomerular arteriole breaks up into capillaries that encircle the renal tubules (nephrons), forming a capillary network of the cortex and medulla of the kidney. This branching of the afferent arterial vessel into the capillaries of the glomerulus and the formation of the efferent arterial vessel from the capillaries is called the wonderful network (rete mirabili). Direct arterioles branch off from the arcuate and interlobar arteries and from some efferent glomerular arterioles into the renal medulla, which break up into capillaries that supply the renal pyramids with blood.

The efferent arterioles subsequently form the peritubular juxtamedullary capillary network.

Peritubular capillary network. In the middle and superficial zone of the cortex, the efferent glomerular arterioles form peritubular capillaries, which envelop the proximal and distal renal tubules, supplying them with blood. The capillaries of the cortex open into radially located interlobular veins, which sequentially flow into the arcuate veins (vv. arcuatae), and they in turn flow into the renal and inferior vena cava.

Juxtamedullary capillary network. In the juxtamedullary zone, each efferent glomerular arteriole runs toward the renal medulla, where it divides into bundles of straight arterioles (arteriolae rectae). Each bundle consists of approximately 30 descending vessels, with those on the periphery of the bundle branching into a capillary network in the outer zone of the medulla. The central part of the bundle of straight arterioles, consisting of descending and ascending vessels, penetrates deep into the medulla zone. These vessels follow the course of the limbs of the loop of Henle. Closer to the renal papilla, the vessels change their direction to the opposite. They divide into several branches and penetrate the renal medulla in the form of straight venules (venulae rectae). The venules flow into the arcuate veins (vv. arcuatae), which then pass into the interlobar veins (vv. interlobares) and, flowing into the renal vein, leave the kidneys through the renal hilum.

The blood supply to the kidney is significant (the renal blood flow is 1000-1200 ml/min - 20-25% of the cardiac output) and exceeds the blood supply to all other organs. The blood supply to the kidneys is uneven: the cortex accounts for 80-85% of the total renal blood flow, and the medulla accounts for less than 10%, however, it is believed that in quantitative terms, the medullary blood flow is approximately 15 times higher than the blood flow of a resting muscle and is equal to the blood flow through the brain.

Venules are formed from the capillary network of the renal cortex; merging, they form interlobular veins that flow into the arcuate veins located on the border of the cortex and medulla. The venous vessels of the renal medulla also flow here. In the most superficial layers of the renal cortex and in the fibrous capsule, so-called stellate venules are formed, which flow into the arcuate veins. They, in turn, pass into interlobar veins, which enter the renal sinus, merge with each other into larger veins, forming the renal vein. The renal vein exits the renal hilum and flows into the inferior vena cava.

The lymphatic vessels of the kidney accompany the blood vessels, together with them exit the kidney through its gates and flow into the lumbar lymph nodes.

The renal nerves originate from the celiac plexus, the sympathetic trunk nodes (sympathetic fibers), and the vagus nerves (parasympathetic fibers). The renal plexus is formed around the renal arteries, giving fibers to the substance of the kidney. Afferent innervation is carried out from the lower thoracic and upper lumbar spinal nodes.