THE URINARY BLADDER ANATOMY AND

PHYSIOLOGY

Dr. Ali Kamal M. SamiM.B.Ch.B. M.A.U.A.F.I.B.M.S. M.I.U.A.

Gross Appearance

A hollow muscular organA reservoir for urineThe adult bladder normally has a capacity of 400–500 ml.

When empty, bladder lies behind the pubic symphysis &it is a pelvic organ.

In infants and children , it is situated higher.

When it is full, it rises above the symphysis and can readily be palpated or percussed.

When over distended, as in acute or chronic urinary retention, it may cause the lower abdomen to bulge visibly.

Extending from the dome of the bladder to the umbilicusis a fibrous cord, the median umbilical ligament, whichrepresents the obliterated

urachus .

Ureters enter the bladder posteroinferiorly are about 5 cm

apart .

The orifices,situated at interureteric ridge that forms the proximal border of the trigone, are about 2.5 cm apart .

The trigone occupies the area between the ridge and the bladder neck.

 

The internal sphincter, or bladder neck, is not a true

circular sphincter but a thickening formed by interlaced

and converging muscle fibers of the detrusor as they pass

distally to become the smooth musculature of the urethra.

RELATIONSIn males, the

bladder is related

posteriorly to the seminal

vesicles, vasa deferentia,

ureters, and rectum .

In females, the uterus and vagina are interposed

between the bladder and rectum .The dome

and posterior

surfaces are covered by peritoneum.

So in this area the

bladder is related to the small

intestine and sigmoid colon.

The bladder is related to

the posterior surface of

the pubic symphysis,

and, when distended, it is

in contact with the lower

abdominal wall.

Histology

The mucosa of the bladder is composed of transitional

epithelium.

Beneath

it ,is a submucosal layer formed of connective

and

elastic

tissues

External

to the submucosa is the

detrusor muscle

the detrusor muscle which is made up

of a mixture of

smooth muscle fibers

arranged at random

in a longitudin

al, circular,

and spiral manner without

any layer formation or specific orientatio

n

Except close to

the internal meatus, where

the detrusor muscle

assumes 3 definite

layers:Inner longitudinal,

middle circular,and outer

longitudinal.

Blood Supply

A. ARTERIAL

1-Superior Vesical, 2-Middle Vesical, 3-Inferior Vesical arteries, which arise fromthe anterior trunk of the internal iliac (hypogastric)artery, 4-The obturator artery.5-The inferior gluteal artery. In females, the 6-uterine and 7-vaginalarteries also send branches to the bladder.

B. VENOUS

Surrounding the bladder is a rich plexus of veins that ultimately empties into the internal iliac (hypogastric) veins.

Lymphatics

The lymphatics of the bladder drain into 1-the vesical,2-external iliac, 3-internal iliac (hypogastric), 4-common iliac lymph nodes.

Physiology

The nerves concerned in micturition are as follows.

1-The parasympathetic input; derived from the anterior primary divisions of the second, third and fourth sacral segments ( S2 ,S3,S4). These fibers pass through the pelvic splanchnic nerves inferior hypo gastric plexus, from which they are distributed to the bladder.

The pelvic plexus is easily damaged during excisions of the rectum, following which disturbances of micturition and sexual function may occur.

2-The sympathetic input;

These nerves arise in the 11th thoracic to the second lumbar segments (T11,T12,L1,L2). Pass via the presacral hypo gastric nerve and the sympathetic chains to the inferior hypo gastric plexus, which is situated lateral to the rectum, the bladder

3-Somatic innervations;

passes to the distal sphincter through the Pudendal nerves and through the inferior hypo gastric plexus .

The sympathetic nerves convey afferent painful stimuli following over distension of the fundus , from the mucosa where they respond to touch, temperature and pain, and also from the muscle of the detrusor and lamina propria where they convey stretch information. These afferents pass via the inferior hypo gastric plexus . Efferent fibers pass via the pelvic parasympathetics. Normal micturition is coordinated in the Pons in the midbrain where detrusor contraction is timed with inhibition of the distal sphincter mechanism.

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