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What Are the Medullary Pyramids?

Bowman's capsule is part of the filtration system in the nephrons of the kidneys.
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  • Written By: Franklin Jeffrey
  • Edited By: Rachel Catherine Allen
  • Last Modified Date: 01 July 2014
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Medulla means middle, so in anatomy, medullary pyramids are areas in the middle of an organ that are shaped like a pyramid. The medulla oblongata pyramid of the brain is one such area. Most often, however, when medical professionals discuss the medullary pyramids, they are referring to the renal pyramids of the kidneys. The renal medullary pyramids are an important element in the production of urine, which is how the body rids itself of toxins and wastes that have been filtered from the blood by the kidneys.

Each human kidney has between seven and 15 medullary pyramids. They consist primarily of tubes through which the urine produced in the outer portion of the kidney travels. The end of the pyramid extends into a cup-shaped calyx where the urine collects, then is passed to bladder. Interlobar arteries, located in the space between the pyramids, carry blood to the inner and outer layers of the kidneys through a network of capillaries and arteries.

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Nephrons are miniature structures within the medullary pyramids and the cortex, or outer layer, of the kidneys. Each kidney contains a million or more nephrons, which use a system of small tubes to filter the blood received. Nephrons receive liquids through a wide opening called the renal corpuscle, which consists of an area named the Bowman's capsule and the glomerulus, a ball-shaped construction. Elements of the renal tubule include the distal and proximal tubules; these carry urine to collecting tubules, which in turn pass the urine to the bladder through the ureter.

Not all liquids that the body takes in are expelled. Large quantities are reabsorbed passively when the pressure within the proximal tubules forces the fluids to return to capillaries, where the liquids are then carried throughout the body in the blood. These fluids also return sugar, salt and other nutrients that the body needs.

One abnormality that can occur in the medullary pyramids is a condition known as Medullary Sponge Kidney (MSK). The condition is defined as congenital, meaning that patients are born with the condition. Patients with MSK cysts that form in the collecting tubules; the condition may affect as few as one pyramid in one kidney, or it may affect all pyramids in both. Most cases of MSK are discovered during an examination for kidney stones or infection, as the condition itself seldom produces symptoms. Researchers have found only a few rare cases where the condition is present in both a parent and child, and MSK is not considered to be an inherited abnormality.

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Kidney stones are formed from by minerals in the urine. About eighty percent of those with kidney stones are men.

Kidney stones generally leave the body through the urine stream and are usually not a problem. If a stone manages to grow to a certain size, usually 3 millimeters, they can cause great pain.

This pain is often felt in the abdomen or flank (lower back area).

Pain in the groin also called renal colic is another symptom. This can be paired with nausea, fever, vomiting, blood or pus in the urine and painful urination. These waves of renal colic come in 20 to 60 minute periods.

Diagnosis is generally by blood tests, urinalysis, examination and maybe ultrasounds.

Once diagnosed pain management is the first step, using an anti-inflammatory drug. If the stone is too big or there is no progress, a surgical option may be explored. Surgery can sometimes involve using extracorporeal shock wave lithotripsy where a stone is shattered and allowed to pass as a type of smaller gravel. In some cases a tube is inserted to bypass the obstruction and alleviate the issue.

To lower the risk, drinking lots of water and eliminating dehydration goes a long way. A high intake of sugars, sodium and animal protein increase your risk factor. There are other metabolic issues involved that can be diagnosed by your doctor if you have persistence with these stones.

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