Urothelium

What is urothelium?

Urothelium is a protective barrier of tissue (epithelium) that lines the inside of your urinary tract. It’s made up of several layers of cells that keep pee (urine) and germs from getting into your blood and other tissues in your body.

Your urothelium is a unique type of epithelium. Unlike the lining of other parts of your body (like your lungs or your gut), it doesn’t need to let nutrients or oxygen pass through it. But it does have special cells that allow it to stretch and contract frequently — while maintaining its barrier of protection — to allow your bladder to fill and empty.

What does your urothelium do?

Your urothelium has many jobs, including:

• Protecting the rest of your body — like your blood vessels and muscles — from pee (which is acidic and could cause damage).
• Preventing infections from pathogens (germs), like bacteria that cause urinary tract infections (UTIs).
• Helping transmit messages about what’s happening in your bladder to your nervous system — for instance, letting you know your bladder’s full and you need to pee.
• Regulating the levels of water, salts and other substances in your pee.
• Expanding and contracting to enable your bladder to hold varying amounts of pee.

Where in your body is your urothelium?

Your urothelium lines your lower urinary tract, including your:

• Renal pelvis (part of your kidneys where pee collects).
• Ureters (tubes that connect your kidneys to your bladder).
• Bladder (pouch that holds pee).
• Urethra (tube that drains pee from your bladder out of your body).

What are the layers of urothelium?

Your urothelium has three main layers: the superficial layer of umbrella cells, the intermediate layer and the basal layer.

Superficial (apical) layer/umbrella cells

The superficial (top) layer of your urothelium is made up of umbrella cells. Umbrella cells get their name from their dome-like shape and their size — one umbrella cell covers multiple cells in the intermediate layer below. These cells can change shape, flattening when your bladder is full and returning to their original shape when your bladder empties.

Umbrella cells are packed tightly together. This prevents pee and germs from getting into the rest of your body. If a germ infects the superficial layer, umbrella cells die and shed into your urinary tract. There, the cells (and the germs) wash out of your body with your pee.

The superficial layer also contains receptors (proteins that act like antennae and can receive signals) that can alert immune cells to invading germs.

Intermediate layer

The middle part of your urothelium, made up of intermediate cells, can be several layers thick. The thickness of this layer varies, with fewer layers when your bladder is full. Intermediate cells are larger than the basal cells below but smaller than the umbrella cells above. They play a key role in repairing damage to the urothelium and can also replace umbrella cells when needed.

Basal layer

The lowest layer of your urothelium — the one closest to your connective tissues, muscles and blood vessels — is made up of basal cells. These are the smallest cells in your urothelium. They help repair and regenerate more epithelial cells.

What are some conditions and disorders that affect your urothelium?

Diseases and conditions that affect your urothelium include:

• Cancer. Urothelial carcinoma is the most common type of bladder cancer. It can also start in the lining of your kidney, urethra or ureter.
• Interstitial cystitis. Healthcare providers believe that damage to your urothelium may lead to interstitial cystitis, a condition that causes chronic pain, pressure, or discomfort in your bladder.
• Overactive bladder or urinary incontinence. Issues in your urinary tract, like kidney stones, can potentially cause changes to your urothelium that may cause it to send your body the wrong signals about emptying your bladder. This can lead to overactive bladder or leaking pee.

What are some common symptoms of urothelial conditions?

Common symptoms of issues that affect your urothelium include:

• Blood in your pee (hematuria).
• Cloudy pee.
• Abdominal pain.
• Painful or frequent urination.

What are some tests my provider might perform?

A healthcare provider might perform one of these tests if you have symptoms of a condition that affects your urothelium or urinary tract:

• Urinalysis. Healthcare providers can test your pee to look for blood cells and other substances that indicate issues in your urinary tract.
• Kidney functioning test. Blood or urine tests can give your provider an idea of how well your kidneys are working.
• Blood tests. Blood tests can give healthcare providers clues as to what’s going on inside your body.
• Urethral swab. Your provider will collect a sample of discharge from your urethra for testing.
• Imaging tests. Your provider may order imaging tests to diagnose certain conditions. These include ultrasound, MRI (magnetic resonance imaging) and CT (computed tomography) scan.

Your provider may also take a sample of tissue to diagnose cancer or infections.

Is it normal to have benign urothelial cells in your urine?

It can be normal to have urothelial cells in your pee, but ask your provider if you have concerns about test results or a pathology report. Urothelial cells can shed into your pee due to trauma (like if you’ve recently had a procedure or passed a kidney stone), infection, cancer or noncancerous (benign) growths. Benign (or benign-appearing) urothelial cells rarely indicate cancer.

What is dysplasia of the bladder urothelium?

Dysplasia of the urothelium can be a condition that happens when cells start to look abnormal under the microscope. It doesn’t necessarily mean the cells will become cancerous, but it may put you at higher risk for developing cancer.