🔥 URINARY BLADDER

1. SURFACES + POSITION (MOST TESTED)

Empty bladder = pelvic cavity.

Full bladder = rises into abdomen (suprapubic).

Surfaces (memorize this):

• Apex → urachus/median umbilical ligament
• Base (posterior surface)
• Male: related to seminal vesicles + vas deferens
• Female: fused to anterior vaginal wall + cervix (no peritoneum)
• Inferolateral surfaces → cradle on levator ani + obturator internus
• Neck → continuation to urethra
• Male: sits on prostate
• Female: in anterior vaginal wall
• Superior surface → covered by peritoneum, contacts small intestine/uterus

EXAM TRIGGER:

→ Full bladder allows suprapubic catheterization WITHOUT entering peritoneum

(because distension strips peritoneum upward).

2. TRIGONE (SUPER HIGH-YIELD)

The most important anatomical area of the bladder.

Boundaries:

• 2 ureteric orifices (upper corners)
• Internal urethral orifice (lower corner)

Key characteristics (memorize):

• Smooth mucosa (does NOT change with distension)
• Least mobile part
• Male → fixed by prostate
• Female → stabilized by tissues around upper urethra/anterior vagina
• Interureteric bar connects ureteric openings
• Formed by longitudinal smooth muscle continuity

Ureter entry mechanism:

• Pierce bladder wall obliquely → prevents reflux
• Intravesical pressure closes the slit-like orifices except during peristaltic “jets”

EXAM TRIGGER:

→ Oblique intramural ureter prevents vesicoureteral reflux.

3. BLOOD SUPPLY + LYMPH (SUPER COMMON MCQs)

Arteries:

• Superior vesical (branch of umbilical)
• Inferior vesical (male)
• Uterine + vaginal branches (female)

Small contributions: obturator, inferior gluteal.

Veins:

• Form vesical venous plexus
• Drains to vesicoprostatic plexus (male) → internal iliac veins
• Female plexus communicates with broad ligament veins

Lymph:

EXAM FAVOURITE — MOST drainage → external iliac nodes

Some → internal iliac + obturator nodes

4. NERVE SUPPLY (PASS/FAIL SECTION)

Parasympathetic (Pelvic splanchnic nerves S2–S4)

• Motor to detrusor → contraction (voiding)
• Carry normal distension sensation

Sympathetic (T11–L2 via hypogastric plexus)

• Inhibitory to detrusor
• Motor to internal sphincter (bladder neck in males)
• Carry pain signals (with parasympathetic)

Somatic (Pudendal nerve) indirectly controls external urethral sphincter.

EXAM TRIGGER:

→ Micturition reflex = parasympathetic (S2–S4).

5. RETROPUBIC SPACE (OF RETZIUS) — SURGICAL MUST-KNOW

A real favourite in clinical questions.

Located behind pubic symphysis, containing:

• Fat
• Pubovesical ligaments
• Surgical approach for prostate/bladder operations

Fill-in line for exams:

→ Accessed during Burch colposuspension, urethropexy, and suprapubic catheterization.

6.The pubocervical ligament

• A double band of connective tissue within the endopelvic fascia
• Extends from posterior surface of pubic bone → cervix + anterior vaginal wall
• Provides anterior support to the pelvic organs
• Helps maintain bladder position and prevent cystocele
• Part of the pelvic support system along with:
• uterosacral ligaments
• cardinal (transverse cervical) ligaments
• levator ani

Clinical relevance:

• Weakness/tear → anterior vaginal wall prolapse, bladder descent
• Seen after childbirth, menopause, chronic cough/raised abdominal pressure

7.Pubovesical Ligament — Key Points

• A fibrous band connecting bladder to pubic bones
• Runs from:
• Neck of bladder + proximal urethra
• → to inferior pubic rami / pubis
• Helps anchor and suspend the bladder anteriorly
• Important for continence by stabilizing the urethra–bladder junction
• Present in both sexes:
• In males sometimes called puboprostatic ligament (bladder anchored indirectly via prostate)
• Considered part of the visceral pelvic fascia / endopelvic fascia

🔥 CONTROL OF MICTURITION

1. THE BASIC MECHANISM (THE HEART OF EVERYTHING)

Micturition = Detrusor contracts + External sphincter + pelvic floor relax.

Storage Phase (Filling):

• Detrusor relaxed → sympathetic (T11–L2)
• Internal sphincter (male) tightens → sympathetic
• External sphincter actively contracted → pudendal nerve

Voiding Phase (Emptying):

• Detrusor contracts → parasympathetic (S2–S4)
• Internal sphincter relaxes
• External sphincter relaxes voluntarily

THE ONE-LINE SUMMARY:

👉 Sympathetic = Store; Parasympathetic = Pee; Pudendal = Permit (voluntary control).

2. THE REFLEX ARC (THE EXAM FAVOURITE)

Bladder fills → stretch receptors fire → impulses go via pelvic splanchnic nerves (S2–S4) → spinal cord → parasympathetic efferents return → detrusor contracts.

Infant bladder

This spinal reflex = normal in infants (no cortical inhibition yet).

Adult bladder

Cortex adds inhibitory control → you don’t urinate automatically.

3. THE BRAIN CENTERS (VERY HIGH YIELD)

Two main centres in the pons:

(a) Pontine Micturition Center — PMC

• Located medial pontine reticular formation
• Coordinates voiding reflex
• Activates parasympathetic → detrusor contracts
• Inhibits pudendal → sphincter relaxes

(b) Pontine Storage Center

• Located lateral pontine reticular formation
• Excites pudendal → keeps external sphincter contracted
• Helps maintain continence during filling

Cortical Inhibition (Frontal Lobe)

• Centre in inferior frontal gyrus (medial surface)
• Sends fibers to PMC
• You consciously decide when to urinate

ONE-LINER TO REMEMBER:

👉 Frontal cortex controls Pons → Pons controls Sacral cord → Sacral cord controls bladder.

4. SPINAL INJURY PATTERNS (ALWAYS ASKED!)

Injury ABOVE S2 (Spinal cord transection):

• Cortex cannot inhibit reflex
• Sacral centre intact
• Bladder empties automatically when full
• Often called reflex bladder or automatic bladder
• Patient unaware of fullness

Injury AT S2–S4 (Sacral destruction):

• Reflex arc destroyed
• Detrusor paralysed
• Bladder fills massively → overflow incontinence
• Called atonic bladder

EXAM DIFFERENCE:

• Above S2 = Reflex bladder (spastic).
• At S2/S3/S4 = Atonic bladder (flaccid).

5. SPHINCTERS (SUPER HIGH YIELD)

External urethral sphincter

• Skeletal muscle
• Pudendal nerve (perineal branch)
• Controlled by Onuf’s nucleus (S2)
• Voluntary control

Internal sphincter (male)

• Circular smooth muscle
• Sympathetic (adrenergic)
• Function:
• NOT continence
• Prevents retrograde ejaculation into bladder

6. STRUCTURE OF THE BLADDER (ONLY THE MUST-KNOWS)

Detrusor muscle

• Smooth muscle arranged in interlacing bundles
• Parasympathetic contraction

Superficial Trigonal Muscle

• Different from detrusor
• Mainly sympathetic innervation
• Helps keep ureteric orifices closed during filling

Preprostatic sphincter (male)

• Smooth muscle collar
• Sympathetic
• Prevents semen reflux

Epithelium

• Transitional (urothelium)
• Thick and folded when empty; thin and smooth when full

7. DEVELOPMENT (ONLY 1% OF TEXT BUT 10% OF EXAM QUESTIONS)

Key lines to memorize:

• Bladder epithelium = endoderm (urogenital sinus)
• Trigone = mesonephric duct (mesoderm) incorporated into bladder
• Explains trigone’s different structure & innervation
• Allantois → urachus → median umbilical ligament

This developmental distinction is VERY exam-friendly.

🔥 URETERS IN THE PELVIS

1. ENTRY INTO THE PELVIS (SUPER HIGH YIELD)

• Pelvic ureter = ~12–13 cm (half the total length ~25 cm).
• Crosses pelvic brim at the bifurcation of the common iliac artery.
• Usually runs over the external iliac artery → then along lateral pelvic wall.

👉 Exam One-Liner:

Ureter crosses over external iliac artery at pelvic brim.

2. RELATIONSHIPS ON THE LATERAL PELVIC WALL (VERY IMPORTANT)

As ureter descends the lateral wall, in order from above → below, it crosses:

1. Obturator nerve
2. Obliterated umbilical artery (→ superior vesical artery)
3. Obturator artery
4. Obturator vein

👉 Mnemonic: N – A – A – V

(Nerve → Artery → Artery → Vein)

All crossed from pelvic brim downwards.

3. MALE RELATIONS (VERY EXAM-HEAVY)

Near the bladder:

• Vas deferens crosses ABOVE the ureter (“water under the bridge”)
• Then vas runs medial to it
• Upper part of seminal vesicle lies just below the ureter where it enters bladder

👉 Key Exam Phrase:

“In males, the vas deferens crosses superior to the ureter before entering the prostate.”

4. FEMALE RELATIONS (THE MOST CLINICAL LINE IN THE WHOLE CHAPTER)

The ureter is a MAJOR hazard in hysterectomy. Why?

Because of this relationship:

• On the pelvic floor, ureter runs in the base of the broad ligament
• Uterine artery crosses ABOVE the ureter
• At the lateral vaginal fornix, ureter lies 1–2 cm lateral to the cervix
• Then enters bladder anterior to the fornix

👉 THE GOLDEN LINE (Must-Know):

“Water under the bridge.”

• Ureter (water) lies under
• Uterine artery (bridge)

👉 Why surgeons injure it:

During uterine artery ligation → ureter is just BELOW it.

5. OBLIQUE ENTRY INTO BLADDER WALL (MEGAMARKS)

Before opening at the trigone, both ureters:

• Run obliquely through bladder wall for 1–2 cm
• This oblique tunnel acts as a valve during high bladder pressure → prevents reflux

👉 Exam One-Liner:

Ureters enter bladder obliquely → anti-reflux mechanism.