The kidneys and ureters
The upper urinary tract consists of the two kidneys and the two ureters — the tubes that carry urine from the kidneys down to the bladder. The upper tract's job is to filter the blood, make urine, and deliver it reliably to the bladder for storage. Problems in the upper tract often cause back or flank pain, decreased kidney function, or recurrent infections.
The kidneys filter about 200 liters of blood every day, removing waste products and excess fluid to produce urine. They also regulate blood pressure, electrolytes, and red blood cell production. Each kidney is roughly the size of a fist, located in the back of the abdomen behind the abdominal organs.
When something goes wrong: Kidney stones can block drainage and cause severe pain. Obstruction from a stricture or tumor causes hydronephrosis (swelling of the kidney), which can silently damage kidney function over time if not relieved.
Each ureter is a thin muscular tube that carries urine from the kidney down to the bladder through rhythmic contractions (peristalsis). The ureter enters the back of the bladder at a valve-like junction that prevents urine from flowing back toward the kidney.
When something goes wrong: Ureteral strictures (narrowing) block urine flow and can cause kidney damage. They most commonly result from prior surgery, radiation, or kidney stones. Treatment typically involves surgery or robotic ureteral reconstruction.
How urine flows — upper tract
Filtration
Blood enters the kidney through the renal artery. Tiny filtering units (nephrons) remove waste and excess fluid to create urine.
Collection
Urine collects in the renal pelvis — the funnel-shaped center of the kidney — then funnels into the ureter.
Transport
The ureter carries urine down to the bladder through rhythmic squeezing contractions. This happens continuously, even while lying down.
Entry
Urine enters the bladder through the ureterovesical junction — a one-way valve that keeps urine from refluxing back toward the kidney.
The bladder, prostate, and urethra
The lower urinary tract stores urine and controls when and how it is released. In men, this involves the bladder, the prostate gland (which surrounds the urethra at the bladder outlet), and the urethra — the tube through which urine exits the body. Problems in the lower tract cause symptoms like difficulty urinating, leakage, frequency, or urgency.
The bladder is a hollow muscular organ that stores urine until it is convenient to void. A healthy bladder comfortably holds 300–500 mL (about 10–17 oz) and signals the brain when it's time to empty. The bladder wall is lined with specialized cells (urothelium) and surrounded by muscle (the detrusor) that contracts during urination.
When something goes wrong: Overactive bladder causes urgency and frequency. Neurogenic bladder from nerve injury causes poor storage or emptying. Radiation can damage the bladder lining, leading to hemorrhagic cystitis or contracture.
The prostate is a walnut-sized gland that sits just below the bladder and surrounds the first section of the urethra (the prostatic urethra). Its primary function is producing seminal fluid, but its location makes it central to male urinary health. The prostate grows with age (benign prostatic hyperplasia, BPH) and is the site of prostate cancer.
When something goes wrong: Prostate enlargement causes urinary obstruction. Prostate cancer surgery (radical prostatectomy) can affect the sphincter, causing incontinence, and may cause stricture at the urethral anastomosis.
Men have two sphincter mechanisms that keep urine in. The internal sphincter is at the bladder neck and is under involuntary control. The external sphincter (the rhabdosphincter) surrounds the urethra just below the prostate and is under voluntary control — the muscle you squeeze when you hold urine. Together these provide continence.
When something goes wrong: Prostatectomy can damage the external sphincter, causing stress urinary incontinence. This is treated with a male sling or the AMS 800 artificial urinary sphincter.
The male urethra is divided into several segments: the prostatic urethra (through the prostate), the membranous urethra (at the sphincter), the bulbar urethra (the longest segment, in the perineum), and the penile urethra (through the penis). Each segment has a different character and requires different surgical approaches when diseased.
When something goes wrong: Urethral strictures (scar tissue) can form at any segment — most commonly in the bulbar urethra from prior instrumentation or trauma, or at the bladder neck / anastomosis after prostatectomy. Treatment is urethroplasty or, for selected cases, Optilume balloon dilation.
How urination works — male
Filling
As the bladder fills, its walls relax (compliance). Stretch receptors send signals to the brain. At around 200–300 mL, you become aware of the need to urinate. The sphincter stays closed.
Coordination
When you decide to void, the brain sends signals down the spinal cord to the bladder. The sphincter relaxes first, then the bladder muscle (detrusor) contracts.
Voiding
Urine flows from the bladder through the prostatic urethra, past the sphincter, through the bulbar and penile urethra, and exits at the tip of the penis (the meatus).
Completion
The bladder empties fully, the detrusor relaxes, and the sphincter closes again. A small amount of urine remaining after voiding (post-void residual) is normal, but large residuals suggest obstruction or a weak bladder.
Conditions affecting male urinary anatomy
The kidneys and ureters
The upper urinary tract is identical in function in women and men — two kidneys filter the blood and produce urine, and two ureters carry urine down to the bladder. The kidneys and ureters are positioned the same way in both sexes. Key differences begin in the lower tract.
The kidneys filter blood, produce urine, and regulate blood pressure and electrolytes. In women, the ureters course through the pelvis in close proximity to the uterus and ovaries — making them vulnerable to injury during gynecologic surgery.
When something goes wrong: The same conditions affect female kidneys — stones, obstruction, infection, and hydronephrosis from ureteral stricture. Ureteral injuries during hysterectomy or pelvic surgery are a common cause of ureteral stricture in women.
In women, each ureter passes very close to the uterine artery and the side wall of the uterus before entering the bladder. This anatomical proximity is why ureteral injuries are among the most common complications of hysterectomy — the ureter can be inadvertently ligated, kinked, or cut during the procedure.
When something goes wrong: Post-surgical ureteral strictures or ureterovaginal fistulae (a connection between the ureter and vagina) typically cause flank pain, leaking from the vagina, or loss of kidney function — sometimes weeks after the original surgery.
How urine flows — upper tract
Filtration
Blood enters the kidney and waste products are filtered out to form urine in the renal pelvis.
Ureteral transport
Urine travels down the ureter — coursing through the retroperitoneum and pelvis, passing near the uterus — to reach the bladder.
Bladder entry
Urine enters the bladder through the ureterovesical junction, a one-way valve that prevents reflux back to the kidney.
The bladder, sphincter, and urethra
The female lower urinary tract is significantly different from the male. The urethra is much shorter — about 3–4 cm compared to ~20 cm in men — and does not pass through a prostate. The bladder and urethra sit just in front of the vagina and uterus, which means gynecologic conditions, childbirth, and pelvic surgery all directly affect urinary function.
The female bladder stores urine and sits directly on top of the anterior vaginal wall. Pelvic floor support from the uterosacral and pubocervical ligaments helps keep the bladder in position. After hysterectomy, menopause, or vaginal delivery, these supports can weaken — contributing to bladder prolapse (cystocele) or incontinence.
When something goes wrong: Overactive bladder is very common in women — causing urgency, frequency, and urge incontinence. Bladder-vaginal fistulae (vesicovaginal fistulae) can occur after hysterectomy or pelvic radiation, causing continuous urine leakage from the vagina.
The female continence mechanism relies on both the intrinsic urethral sphincter (muscle within the urethral wall) and the pelvic floor muscles that support the urethra from below. The pubococcygeus and levator ani muscles form a muscular hammock that maintains urethral closure, particularly under pressure — like coughing or exercise. Childbirth and aging weaken these supports.
When something goes wrong: Stress urinary incontinence — leaking with cough, sneeze, or exercise — results from sphincter weakness or loss of urethral support. Treatment options include pelvic floor therapy, midurethral sling, and occasionally bulking agents or surgery for more complex cases.
The female urethra is very short — roughly the length of a fingertip — running from the bladder neck to the urethral meatus, which opens just above the vaginal opening. Its short length makes it easy to catheterize but also less resistant to ascending infection, which is why urinary tract infections are far more common in women than men.
When something goes wrong: Female urethral stricture is uncommon but can occur after trauma, instrumentation, or lichen sclerosus. Primary urethral carcinoma, though rare, is an important consideration in women with persistent urethral symptoms — Dr. Wiegand has published on this diagnosis.
The close anatomical relationship between the bladder, urethra, vagina, and uterus in the female pelvis means that problems in one structure often affect the others. Prolapse of the uterus or anterior vaginal wall can distort the bladder outlet. Endometriosis or pelvic inflammatory disease can involve the bladder or ureter. And gynecologic surgery remains the most common cause of iatrogenic urinary tract injury in women.
When something goes wrong: Vesicovaginal or ureterovaginal fistulae from gynecologic surgery or pelvic radiation are managed surgically, often requiring tissue interposition for successful repair in previously irradiated patients.
How urination works — female
Filling
Urine arrives from both ureters. The bladder expands as it fills. The sphincter and pelvic floor muscles stay contracted, keeping urine in.
Decision to void
When you relax the pelvic floor and external sphincter, the bladder muscle (detrusor) receives the signal to contract.
Voiding
Urine flows through the very short urethra and exits at the meatus, located just above the vaginal opening. Voiding is typically fast and efficient in women.
Closure
The detrusor relaxes and the sphincter and pelvic floor re-engage to maintain continence until the next void.