Urinary bladder - structure and position, fixation and syntopy in male and female (draw scheme)

Temporary Storage of Urine:
- The bladder is a hollow, distensible organ with an internal lining of folds (rugae) that allows it to hold 400-600 mL of urine in adults.
Urine Expulsion:
- During micturition, the bladder's detrusor muscle contracts while the internal and external sphincters relax.

Shape: The bladder’s appearance varies:
- Full bladder: Oval-shaped, extending superiorly into the abdominal cavity.
- Empty bladder: Flattened and situated entirely within the pelvis.
External Features:
- Apex: Directed anteriorly toward the pubic symphysis; connected to the umbilicus by the median umbilical ligament (remnant of the urachus).
- Body: The main central region between the apex and fundus.
- Fundus: Posterior, triangular region; in males, closely related to the rectum, and in females, to the uterus and vagina.
- Neck: Located at the inferior aspect where the fundus meets the inferolateral surfaces. It is continuous with the urethra.
Trigone: A smooth, triangular area on the internal surface of the fundus. The three angles are marked by:
- The right and left ureteral orifices (where urine enters).
- The internal urethral orifice (where urine exits).

Detrusor Muscle:
- Composed of smooth muscle fibers arranged in multiple directions, ensuring structural integrity during stretching and contraction.

Arterial Supply:
- Primarily from the superior vesical arteries (branches of the internal iliac artery).
- Supplementary supply:
  - Males: Inferior vesical artery.
  - Females: Vaginal arteries.
Venous Drainage:
- Via the vesical venous plexus, which drains into the internal iliac veins.

Autonomic Nervous System:
- Sympathetic: From the hypogastric nerve (T12-L2); relaxes the detrusor muscle to facilitate urine retention.
- Parasympathetic: From the pelvic nerve (S2-S4); contracts the detrusor muscle to promote micturition.
Somatic Nervous System:
- Pudendal nerve (S2-S4) innervates the external urethral sphincter, allowing voluntary control over urination.
Bladder Stretch Reflex:
- A primitive reflex where bladder distension triggers detrusor contraction. This reflex is modulated by higher brain centers for voluntary control.

Males:
- Anterior: Pubic symphysis.
- Posterior: Rectovesical pouch, rectum, and seminal vesicles.
- Inferior: Prostate gland.
Females:
- Anterior: Pubic symphysis.
- Posterior: Vesicouterine pouch, uterus, rectouterine pouch, and vagina.
- Superior: Uterus (when anteverted).