Once formed in the nephrons, urine passes from the collecting ducts to enter the calyces of the kidney, and then through the renal pelvis and one of the ureters into the bladder.
Ureters
Once formed in the nephrons, urine passes from the
collecting ducts to enter the calyces of the kidney, and then through the renal
pelvis and one of the ureters into the bladder. The urethra passes urine to
outside the body via the ureteral
openings, which are slit-like in appearance. Each thin ureter is about 30 cm long, descending behind the parietal
peritoneum to run parallel to the vertebral column. The ureters begin at the
spinal L2 level, continuing from the renal pelvis. They descend behind the
peritoneum and join the uri-nary bladder by running obliquely through its
poste-rior wall from underneath.
The wall of each ureter has three layers: the mucous coat
(transitional epithelium), muscular coat, and fibrous coat. Urine is propelled
by the muscular walls of the ureters. A flap-like fold of mucous mem-brane
covers the opening through which urine flows from each ureter into the bladder.
These folds keep urine from backing up and flowing back into ureters from the
bladder. Backflow of urine is also stopped by any increase in bladder pressure,
which compresses and closes the distal ureter ends.
The ureters are distended by incoming urine, which
stimulates their musculari to contract. This propels the urine into the
bladder, assisted by grav-ity. Peristaltic waves vary in strength and frequency
according to the urine formation rate. Neural control of the peristaltic waves
is believed to be insignificant in comparison with how the smooth muscles of
the ureters stretch. Each ureter is innervated by both sym-pathetic and
parasympathetic fibers.
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