What Are Renal Pyramids? Anatomy, Function & Relevance for Students
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.
Interstitium
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.
Pyramids
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.
Papilla
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.
Clinical Significance
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.
FAQs on Renal Pyramids: Key to Kidney Function and Health
1. What are renal pyramids and where are they located in the kidney?
Renal pyramids, also known as Malpighian pyramids, are cone-shaped tissues found within the human kidney. They are located in the innermost part of the kidney, an area called the renal medulla. The base of each pyramid faces the outer renal cortex, while its tip, called the renal papilla, points inward towards the centre of the kidney.
2. What is the main function of the renal pyramids?
The primary function of the renal pyramids is to act as a channel for urine to be transported from the outer part of the kidney, where it's filtered, to the cup-like structures called calyces. They house the collecting ducts and the loops of Henle, which are critical for the final stages of urine concentration and modification before it is excreted from the body.
3. What gives the renal pyramids their characteristic striped or striated appearance?
The striped appearance of the renal pyramids is due to the parallel arrangement of thousands of microscopic tubules within them. These structures are primarily the loops of Henle and collecting ducts, which run in a straight, parallel fashion from the base of the pyramid to its apex (papilla), giving it a distinctly striated look.
4. What specific parts of the nephron are found within the renal pyramids?
While the main filtering unit of the nephron (glomerulus and convoluted tubules) is in the cortex, the renal pyramids contain the following crucial parts:
- The Loop of Henle, which descends from the cortex into the medulla.
- The collecting ducts, which receive filtrate from several nephrons and transport it through the pyramid.
- The vasa recta, which are capillaries that surround the Loop of Henle and are vital for maintaining the concentration gradient.
5. How do the renal pyramids, renal cortex, and renal medulla work together in kidney function?
These three regions work in a sequential process. The renal cortex is the site of initial blood filtration by the glomeruli. The filtrate then moves into the tubules, which dip into the renal medulla (composed of the renal pyramids). Within the pyramids, the crucial process of water and salt reabsorption occurs via the counter-current mechanism. Finally, the concentrated urine exits the pyramids into the renal pelvis for excretion.
6. How do the renal pyramids play a critical role in concentrating urine?
The renal pyramids are essential for concentrating urine because they provide the physiological environment for the counter-current mechanism to operate. The long loops of Henle within the pyramids create a high salt concentration (hypertonicity) in the medullary tissue. As the filtrate passes through the collecting ducts surrounded by this salty environment, water is drawn out via osmosis, resulting in highly concentrated urine.
7. What are the Columns of Bertin and how do they differ from renal pyramids?
The Columns of Bertin are extensions of the renal cortex that project downwards between the renal pyramids. Unlike the pyramids, which are part of the medulla and contain loops of Henle and collecting ducts, the Columns of Bertin are made of cortical tissue. Their primary role is to provide a supportive framework and house blood vessels that travel to the cortex.
8. What would happen if the renal pyramids were damaged or unable to function properly?
Damage to the renal pyramids would severely disrupt the kidney's ability to concentrate urine. Since the structures responsible for the counter-current mechanism are located here, their dysfunction would prevent water reabsorption. This would lead to the production of large volumes of very dilute urine, causing conditions such as severe dehydration and dangerous electrolyte imbalances in the body.
