Any of the triangular tissue parts that make up the medulla, or inner material, of the kidney is referred to as a renal pyramid. Tubules convey urine from the cortical, or outer, portion of the kidney, where urine is produced, to the cup-shaped cavities or calyces, where urine collects before passing through ureter to the bladder. The point of each pyramid, known as papilla, projects into a calyx.
About Renal Pyramids
The papilla’s surface has a sieve-like appearance due to several small openings from which the urine droplets pass. Every opening represents a tubule known as the duct of Bellini, into which collecting tubules converge within the pyramid. Muscle fibres lead from the calyx to papilla. Urine flows through the calyx through the ducts of Bellini as the calyx's muscle fibres contract. Then, the urine flows to the bladder by the way of the renal pelvis and a duct called ureter, which is not a part of the renal pyramid.
Between the pyramids are primary arteries termed the interlobar arteries. Every interlobar artery branches over the pyramid’s base. The smaller capillaries and arteries divide off from the interlobar arteries to supply every pyramid and the cortex with a rich network of the blood vessels. The interlobar artery blockage may cause degeneration of a renal pyramid.
A few animals, such as rabbits and rats, have a kidney composed of one renal pyramid. In humans each of the kidneys contain either a dozen or more pyramids.
Renal Pyramid Function
Let us look at the renal pyramid function in detail.
The structures of the nephrons that keep the blood's water balance and salt balance are found in the renal medulla. These structures include the vasa recta (both vera and spuria), the medullary capillary plexus, the venulae rectae, the loop of Henle, and the collecting tubule. In the helps and nephron in water reabsorption, the renal medulla is hypertonic to the filtrate.
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Blood is filtered in the glomerulus by the size of solute. Ions such as chloride, sodium, calcium, and potassium are easily filtered, as is glucose. Proteins are not passed via glomerular filter due to their large size, and do not appear in the urine or filtrate unless the disease process has affected the glomerular capsule or the distal and proximal convoluted tubules of the nephron.
Though the renal medulla only receives a less percentage of the renal blood flow, the oxygen extraction is high by causing a low oxygen tension and more essentially, a critical sensitivity to the hypoxia, hypotension, and blood flow. By making it exquisitely responsive to subtle variations in renal blood flow, the renal medulla extracts oxygen at an 80 percent ratio. The mechanisms of several perioperative renal insults are based upon the disruption of adequate blood flow (and thus oxygen delivery) to the renal medulla.
The medullary interstitium is a tissue that surrounds the medulla's Henle loop. It aids renal water absorption by increasing hypertonicity, which pulls water out of the loop's thin descending limb of Henle and the collecting duct system. In turn, hypertonicity is created by an urea efflux from the inner medullary collecting duct.
Renal pyramids (also known as Malpighi's pyramids or Malpighian pyramids) are the kidney's cone-shaped tissues named after Marcello Malpighi, a 17th-century anatomist. In humans, the renal medulla is divided into 10 to 18 conical subdivisions. Every pyramid has a large base that faces the renal cortex and a papilla (or apex) that points internally towards the pelvis. Since the straight parallel segments of the Loops of nephrons of the Henle and collecting ducts form pyramids, they appear to be striped.
Every pyramid has a base at the corticomedullary boundary and an apex in the papilla, which is contained inside a minor calyx made up of parallel bundles of urine collecting tubules.
The renal papilla is the location where the medulla's renal pyramids empty urine into the kidney's minor calyx. The medullary collecting ducts converge to form a papillary duct to channel the fluid, and the transitional epithelium appears.
A few chemicals toxic to the kidney, known as nephrotoxins, damage the renal papillae. This damage may result in death to cells in this kidney’s region, known as renal papillary necrosis. The most common toxic causes of the renal papillary necrosis are the NSAIDs, such as acetylsalicylic acid, ibuprofen, and the phenylbutazone, in combination with the dehydration. Also, the perturbed renal papillary development has been represented to be associated with the onset of renal fibrosis and functional obstruction.
Also, the damage of renal papillary has been associated with the nephrolithiasis and may be quantified as per the papillary grading score that accounts for pitting, contour, Randall, and plugging plaque.