M5(6) Ureters, Kidney Stones, Bladder, Urethra

Ureters

Slender tubes that convey urine from kidneys to the bladder

• Runs obliquely through posterior bladder wall

Ureters Running Obliquely

When the ureters enter the bladder at an angle, they act like a one-way valve:

• Bladder fills and pressure rises → distal (end) ureter gets compressed

Ureter Layers

3 layers of ureter wall (from inside out)

1. Mucosa

2. Muscularis

3. Adventitia

Ureter Mucosa

Innermost layer, lining the lumen (where urine flows); protects ureter wall from urine, allows stretching when urine passes

• Contains transitional epithelium that is continuous with the mucosae of the kidney pelvis superiorly and the bladder medially

Muscularis

Smooth muscle layer arranged in 3 layers; facilitates peristalsis

1. Internal longitudinal layer

2. External circular layer

3. additional external longitudinal layer appears in the lower third of the ureter

Ureter Adventitia

Outer fibrous connective tissue; anchors ureter to surrounding tissues

Muscularis and Urine

When the ureter distends, it stimulates its muscularis to contract thereby propelling urine into the bladder

• Urine does not reach the bladder through gravity alone

Kidney Stones (Renal Calculi)

Occurs when calcium, magnesium salts, or uric acid are concentrated in urine and crystallize

• Nephrolithiasis

• Ureterolithiasis

Nephrolithiasis

Calculi in the kidneys

Ureterolithiasis

Calculi in the ureters

Kidney Stone Removal

Most small calculi pass w/o intervention. Larger calculi or those that lodge in the ureter can be removed endoscopically or surgically

Lithotripsy

A noninvasive procedure that uses acoustic wave energy to break calculi into smaller pieces

• Many calculi (esp those in the kidney) can be treated this way

Kidney Stone Risk Factors

Obesity, elevated blood calcium

• Best way to prevent recurrence is to dilute urine via adequate hydration

Urinary Bladder

Stores urine

• When empty, it collapses into a pyramidal shape

• When it expands, it becomes pear-shaped

• Has openings for both ureters and the urethra

Trigone

A triangular region of the bladder base outlined by the three openings (two ureter openings, opening to urethra)

• It’s important clinically because infections tend to persist in this region

Urinary Bladder Layers

1. Mucosa

2. Detrusor (Muscular Layer)

3. Fibrous Adventitia

Urinary Bladder Mucosa

Innermost lining of the bladder; protects bladder from urine, allows stretching when urine passes

• Made of transitional epithelium (urothelium)

Bladder Rugae

Bladder has rugae (folds) that can expand and accommodate more urine as needed

Detrusor

Intermingled smooth muscle fibers arranged in; contracts to expel urine

• Inner longitudinal layer

• Middle circular layer

• Outer longitudinal layer

Urinary Bladder Fibrous Adventitia

Covers most of bladder, anchors to surrounding tissues

• On the superior surface of the bladder, it is covered by the peritoneum (not the adventitia)

Urinary Bladder Storage

1. When empty, the bladder collapses into its basic pyramidal shape (at this point the walls are thick and the mucosa forms folds known as ‘rugae’)

2. As urine accumulates, the bladder expands and becomes pear-shaped (transitional epithelium and muscular wall stretch and thin, rugae disappear). It rises superiorly into the abdominal cavity

These changes allow the bladder to store more urine w/o a significant rise in internal pressure

Urethra

Thin-walled muscular tube that drains urine from the bladder and coveys it out of the body

• Sphincters at the distal end

Urethra Epithelium

The mucosal epithelium is mostly pseudostratified columnar epithelium

• However, near the bladder, it becomes transitional epithelium and near the external opening it changes to a protective stratified squamous epithelium

Pseudostratified Columnar Epithelium

A type of epithelial tissue that looks like it has multiple layers, but actually only has one layer of cells

Sphincters

There are two sphincters of the urethra

1. Internal urethral sphincter

2. External urethral sphincter

Internal Urethral Sphincter

Involuntary sphincter controlled by the ANS

• Keeps urethra closed when urine is not being passed and during urination it relaxes automatically

• Formed by thickening of the detrusor muscle at the bladder-urethra junction

External Urethral Sphincter

Voluntary sphincter

• Surrounds the urethra as it passes through the urogenital diaphragm

• Formed of skeletal muscle

Female Urethra

Around 3-4 cm long

• The external opening (external urethral orifice) lies anterior to the vaginal opening and posterior to the clitoris

Male Urethra

Around 20 cm long

• Has 3 regions

  • Prostatic Urethra

  • Intermediate part of Urethra

  • Spongy Urethra

Prostatic Urethra

Runs within the prostate

• Around 2.5 cm long

Intermediate Part of the Urethra

Runs through urogenital diaphragm and extends about 2 cm from the prostate to the beginning of the penis

• AKA membranous urethra

Spongy Urethra

Passes through the penis and opens at its tip via the external urethral orifice

• About 15 cm long