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Polycystic Kidney Disease: Affected Locations, Signs & Treatments

Polycystic Kidney Disease:  Affected Locations, Signs & Treatments
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  • 0:01 Bubble Wrap Kidneys
  • 0:30 Polycystic Kidney Disease
  • 1:10 Pathophysiology of PKD
  • 4:29 Signs, Diagnosis, & Treatments
  • 5:36 Lesson Summary
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Lesson Transcript
Instructor: Artem Cheprasov
This lesson will discuss an inherited disorder known as polycystic kidney disease as well as the latest understanding of why it occurs in people with this condition and how it can be diagnosed and treated.

Bubble Wrap Kidneys

The kidneys in your body serve to filter your blood. They remove waste products, form urine, and therefore keep you healthy and happy. But the most common inherited disorder of the kidneys, one we'll cover in this lesson, disfigures the kidneys over time, resulting in their failure and a person's death. The kidneys end up looking like bubble-wrap kidneys in this disease, and you'll find out how and why in just a second.

Polycystic Kidney Disease

Polycystic kidney disease is an inherited disorder characterized by the formation of cysts within the kidneys. A cyst is a fluid, semi-solid, or air-filled membranous sac. Don't get a cyst confused with an abscess, though, as this refers to a collection of pus. Polycystic kidney disease (PKD) is actually inherited in an autosomal dominant fashion (although autosomal recessive inheritance is possible). What this means is that during dominant inheritance, only one copy of the defective gene is necessary to cause the disorder.

The Pathophysiology of PKD

When a person inherits this genetic defect, their kidneys' function and structure becomes compromised. Normally, the kidneys filter the blood using the glomerulus. The glomerular filtrate flows into the renal tubule, from there into the collecting duct, and thereafter out of the kidneys.

The renal tubule that is involved in this process has little hair-like projections, called cilia, that sense the flow rate of the glomerular filtrate. They look and function like those windsocks you see at regional airports that sense direction and speed of the wind - except the cilia sense the flow of urine instead of air. It is suspected that the mutations in PKD lead to the dysfunction of these cilia. As a result of this dysfunction, the cells of the renal tubule begin to divide in a haphazard fashion.

This improper hyperplasia (which refers to proliferation) of renal tubular cells results in an out-pouching of the renal tubule that is still connected to the tubule itself. You can imagine taking a balloon filled with water and using your fingers to gently pinch off a bit of the main balloon out to the side. The balloon is like the renal tubule and the part you have separated out just a little bit is the out-pouching. The out-pouching initially fills with glomerular filtrate passing by, which causes the out-pouching to dilate more and more with time.

This, and further hyperplasia, causes the out-pouching to eventually separate from the tubule it originated from completely, resulting in a separated cyst. The cyst continues to fill with fluid by way of transepithelial secretion, which is the secretion of fluid through the membrane of the cyst itself. All of this, combined with further cell proliferation, dilates the cyst even more with time. Unfortunately, the dilating cyst is not only dysfunctional itself, but its size, location, and growth compresses and interferes with the normal structure and function of the kidney, leading to eventual kidney failure.

The other problem with PKD is that it is 'poly'cystic, where 'poly' is a term that refers to 'many' or 'more than one.' Therefore, the kidneys develop many cysts all over the place, which only further exacerbates kidney dysfunction and damage. Some of these cysts are small and others are really big. It's like bubble wrap. It comes in all sorts of sizes, small and large.

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