QuestionSBA
QuestionChoice
The body is the large area situated between the apex and the fundus.
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d
The body
QuestionChoice
The fundus or base is the posteroinferior part of the bladder. It is usually triangular in shape and is directed downward and backwards towards the rectum.
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b
The fundus
QuestionChoice
This is the external opening of the urethra where urine exits in both females and males and semen in males.
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e
The external urethral meatus
QuestionChoice
The internal urethral meatus or opening is found surrounded by the internal urethral sphincter found in the neck of the bladder leading into the urethra. It is usually crescent-shaped. The neck of the bladder is the constricted part of the bladder that leads to the urethra.
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a
The internal urethral meatus
QuestionChoice
The apex is the anterosuperior part of the bladder that points towards the abdominal wall.
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c
The apex
Concept
Chapter
## Summary

The urinary bladder is the most anterior element of the pelvic viscera and a part of the urinary system. It occupies the pelvic cavity when empty but expands into the abdominal cavity as it fills. It is an extraperitoneal organ.

## Anatomy

The bladder resembles the shape of a 3D pyramid when empty. It consists of a base, apex, a superior surface and 2 inferolateral surfaces.

* **Base (or fundus)** - shaped like an inverted triangle and faces posterolaterally. At the upper corners of the base, the 2 ureters enter the bladder and at the lower corner of the base the urethra exits the bladder.
* **Apex** - located superiorly and directed towards the pubic symphysis. The median umbilical ligament (an embryological remnant of the urachus) continues from the apex up the anterior abdominal wall to the umbilicus.
* **Superior surface** - domed when the bladder is empty and balloons upwards as it fills
* **Inferolateral surfaces** - located between the levator ani muscles and the adjacent obturator internus muscles

In the inside of the bladder, the smooth triangular area between the openings of the ureter and the urethra is known as the trigone. The smooth walls of the trigone are distinct from the rest of the bladder which is explained by its embryological origin from the mesonephric ducts.

The ureters course down the posterior abdominal wall and the posterolateral aspect of the pelvis. They run _inferior to the vas deferens_ in males and _inferior to the broad ligament_ in females to reach the base of the bladder. 

This relation can be remembered as *"water (ureters) under the bridge"*. The ureters enter the bladder at an angle through the mucosa and the muscle. A flap valve is created to prevent the backflow of urine (vesicoureteric reflux).

The neck of the bladder is anchored by ligaments to the pelvis floor and the body of the pubis:

* In females this is the pubovesical ligament
* In males this is the puboprostatic ligament as it blends with the fibrous capsule of the prostate

The walls of the bladder are made of smooth muscle and detrusor muscle. The mucosa of the bladder is lined by transitional epithelium which is able to withstand the toxic urine that the bladder holds and the stretching of the bladder as it fills.

**Urethral sphiincters:**
- Internal urethral sphincter: Located at the base of the bladder and blends with the detrusor muscle. It is under involuntary autonomic control. It is the dominant sphincter for maintaining continence.
- External urethral sphincter: Located in the perineal pouch. In women this is just inferior to the bladder, in male this is just inferior to the prostate (in the membranous urethra).

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## Blood Supply

**Arterial:**
* Superior, middle and inferior vesical arteries - derived from the anterior trunk of the hypogastric
* Obturator artery
* Inferior gluteal artery
* In females additional branches are derived from the uterine and vaginal arteries.

**Venous**
Venous drainage occurs via a vesical venous plexus that drains into the internal iliac veins.

## Innervation
The detrusor muscle has both parasympathetic and sympathetic innervation for micturition and closure of the bladder neck (during ejaculation) respectively. The parasympathetic supply is via the pelvic splanchnic nerves, S2-S4. The preganglionic sympathetic fibres arise from the L1-L2 spinal cord and the postganglionic fibres are from the ganglia within the hypogastric plexus.

Somatic innervation is via the pudenal nerve which innervates the external urethral sphincter. This enables the voluntary control of micturition.

## Function
* Storage of urine
* Expulsion of urine through the contraction of the muscles of the bladder


## Clinical points
- Prostate surgery can injury the internal urethral sphincter causing incontinence.
- The bladder is an extraperitoneal organ but there is peritoneal reflection of it's dome. If there is a rupture of the bladder at the dome, the fluid is leak into the peritoneum. However, if any other part ruptures then the leak will be exxtraperitoneal.

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Urinary bladder
Topic
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Pelvic Anatomy
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Pelvic Anatomy
Which specific structure of the bladder is annotated here?

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a