1,844views
00:00 / 00:00
The ureters are fibromuscular tubes that transport urine from the renal pelvis to the urinary bladder, where it’s stored until it’s emptied through the urethra during urination.
The ureters, bladder, and the initial portion of the urethra are all lined with transitional epithelium, which is also called urothelium.
This specialized epithelium is only found in the urinary system and it allows the conducting passageways and bladder to expand a lot while staying impermeable to water and ions.
Let’s first take a look at a cross-section of the ureter at low magnification, which shows the four main concentric layers of the ureter: the transitional epithelium that lines the mucosa, the lamina propria, the muscularis externa, and the adventitia.
The transitional epithelium is also further divided into 3 layers.
At high magnification, we can see that the most superficial layer consists of large ovoid cells that are called dome or umbrella cells because of their curved apical surface and because they often cover other epithelial cells beneath them.
When the ureter is distended, there are fewer folds in the epithelium, but the epithelium is also able to expand further by flattening and decreasing the amount of overlap of the umbrella cells.
The second layer that comprises the transitional epithelium is an intermediate layer of cuboidal and low columnar cells.
When umbrella cells are damaged, cells from the intermediate layer are able to quickly differentiate in order to replace the damaged umbrella cells.
The third layer of the transitional epithelium is the basal layer, which is a single layer of cuboidal basal cells that rest on the basement membrane.
Although the basement membrane is often hard to identify when using light microscopy.
In this cross-section of the ureter, the lumen is on the far left.
So the first layer starting from the left is the transitional epithelium, which is purple when stained with hematoxylin and eosin.
The next main layer beneath the transitional epithelium is a supporting layer called the lamina propria, which is a thick layer of dense collagenous and elastic connective tissue.
Surrounding the lamina propria, is the muscularis externa, which is made of 2-3 layers of smooth muscle.
The histology of the ureters, bladder, and urethra share some common features, such as the concentric layers of transitional epithelium, lamina propria, muscularis externa, and adventitia. The transitional epithelium of these organs is composed of three layers, including a superficial layer with umbrella cells, an intermediate layer of cuboidal and low columnar cells, and a single layer of basal cells.
The muscularis externa of the ureters has an inner longitudinal layer and a circular outer layer of smooth muscle, while the distal ureters, bladder, and proximal urethra have an additional outer layer of longitudinal smooth muscle. Both males and females have a distal urethra lined with stratified squamous epithelium, but only males have pseudostratified and stratified columnar epithelium, which is found in the membranous and spongy portions of the urethra.
Copyright © 2024 Elsevier, its licensors, and contributors. All rights are reserved, including those for text and data mining, AI training, and similar technologies.
Cookies are used by this site.
USMLE® is a joint program of the Federation of State Medical Boards (FSMB) and the National Board of Medical Examiners (NBME). COMLEX-USA® is a registered trademark of The National Board of Osteopathic Medical Examiners, Inc. NCLEX-RN® is a registered trademark of the National Council of State Boards of Nursing, Inc. Test names and other trademarks are the property of the respective trademark holders. None of the trademark holders are endorsed by nor affiliated with Osmosis or this website.