Interlobar arteries and veins in the kidney have a fundamental role in supporting its overall function. These blood vessels are part of the kidney's intricate vascular system, crucial for delivering blood to be filtered and for carrying away filtered blood. The interlobar arteries, which branch off from the renal artery, travel between the renal pyramids within the renal columns. They extend towards the cortex, providing blood to the arcuate arteries, which in turn supply blood to the smaller cortical radiate arteries and ultimately to the nephrons for filtration. This efficient supply of blood is essential for the kidney's primary function of filtering waste and regulating various substances in the body. After filtration, the blood, now cleared of excess waste and balanced in terms of electrolyte content, is collected by the interlobar veins. These veins also travel between the renal pyramids and drain into the renal vein, which then returns the purified blood to the general circulation. The effective functioning of these arteries and veins is vital for maintaining the kidney's filtration rate and ensuring the organ's overall health and efficiency.

The renal pelvis is an integral part of the kidney's excretory function. Located at the center of the kidney, the renal pelvis is a funnel-shaped space that collects urine produced in the nephrons. After filtration and reabsorption processes in the nephrons, the urine, which now contains waste products and excess water, flows into the collecting ducts. These ducts lead into the renal pelvis. The primary role of the renal pelvis is to act as a reservoir for the collected urine before it is transported to the bladder via the ureters. The pelvis's ability to gather and temporarily hold urine is vital for controlling the rate at which urine is passed to the bladder, ensuring a steady, manageable flow. This regulation is crucial to prevent overfilling or rapid emptying of the bladder, maintaining a balanced urinary system. The renal pelvis also plays a role in initiating the reflex that triggers the muscular contractions of the ureters, which propel urine towards the bladder. These contractions, known as peristaltic movements, are essential for the efficient and controlled transportation of urine.

Renal corpuscles in the cortex are the primary sites for the initiation of urine formation. Each renal corpuscle consists of two main components: the glomerulus and the Bowman's capsule. The glomerulus is a tiny ball of capillaries where blood is initially filtered. As blood flows through these capillaries, pressure forces water and small solutes, such as ions, glucose, amino acids, and urea, out of the blood and into the Bowman's capsule. This filtration process is selective, allowing only small molecules to pass through while retaining larger molecules like proteins and blood cells within the bloodstream. The filtrate collected in the Bowman's capsule then moves into the renal tubules, where further processing occurs. In the tubules, essential substances like glucose, certain ions, and water are reabsorbed back into the bloodstream, while waste products and excess substances are left in the filtrate to form urine. Thus, the renal corpuscles play a critical role in determining the composition of the initial filtrate, setting the stage for the selective reabsorption and secretion processes that follow in the nephron, leading to the formation of urine.

The renal capsule, a tough, fibrous layer that encases the kidney, plays several crucial roles in kidney function. Firstly, it provides a protective barrier, shielding the delicate tissue of the kidney from physical damage and infection. This protection is essential given the kidney's critical role in filtering blood and maintaining homeostasis. Secondly, the capsule maintains the shape of the kidney, ensuring its structure remains intact and functional. This is important as the shape and structure of the kidney are integral to its efficient operation, particularly in the processes of filtration and reabsorption. Thirdly, the renal capsule helps to anchor the kidney in place within the abdominal cavity. This stability prevents excessive movement or displacement of the kidneys, which could disrupt their connection to blood vessels and the urinary tract, thereby impairing their function. Additionally, the pressure exerted by the capsule on the kidney tissue aids in the filtration process. The capsule's firmness helps maintain a high pressure within the glomeruli, facilitating the efficient filtration of blood into the nephrons.

The arrangement of nephrons in the cortex and medulla is strategically designed to maximise efficiency in kidney function. In the cortex, the nephrons begin with the Bowman's capsule and the glomerulus, where the initial blood filtration occurs. This filtration removes waste and excess substances while retaining essential components like nutrients and electrolytes. The filtrate then travels through the proximal convoluted tubule, which is also in the cortex, where significant reabsorption of water, glucose, and ions takes place. This step is crucial for conserving vital substances. The nephron then extends into the medulla with the Loop of Henle, where further water reabsorption occurs, significantly concentrating the urine. This structure is particularly important in regulating the body's water balance. The distal convoluted tubule, back in the cortex, fine-tunes the reabsorption and secretion processes, ensuring precise control over ion balance and pH levels. Finally, the collecting duct, traversing through the medulla, allows for further water reabsorption, regulated by hormones like ADH, fine-tuning the urine concentration before it is excreted. This arrangement allows for a sequential and highly efficient process of filtration, reabsorption, and concentration.