URINARY SYSTEM

URINARY BLADDER

The urinary bladder is a hollow muscular organ, which acts as a temporary reservoir of urine brought to it by the ureters.

The stored urine is passed out through the urethra, when the bladder is distended enough to feel the desire to micturate.

Diagram of the urinary system showing the positions of the urinary bladder. 

 

LOCATION 

The urinary bladder is situated in the anterior part of the lesser pelvis immediately behind the pubic symphysis and in front of rectum in male, and uterus in the female.

 The location of the urinary bladder varies with the amount of urine it contains and with age.

 (i). When the bladder is empty it lies entirely within the lesser pelvis but when it becomes distended with urine, it expands upward and forward into the abdominal cavity.

 (ii). In children, the bladder is an abdominopelvic organ even when it is empty because the pelvic cavity is small and the neck of bladder lies at the level of the upper border of pubic symphysis.

 It begins to enter the enlarging pelvis at the age of six years but does not become a pelvic organ entirely until after puberty.

SIZE AND SHAPE 

 The size and shape of the urinary bladder vary according to the amount of urine that it contains.

 It is tetrahedral in shape when empty and ovoid in shape when distended. 

CAPACITY 

Normally in adult male the capacity varies from 120 to 320 ml. The mean capacity is about 220 ml.

1. An amount of urine beyond 220 ml causes a desire to micturate but the bladder is usually emptied at about 250– 300 ml.

2. The filling of urine up to 500 ml may be tolerated but beyond this, it causes pain due to tension of its wall. On collection of urine about 800 ml, the micturition is beyond one’s voluntary control.

EXTERNAL FEATURES AND RELATIONS 

An empty and contracted bladder as seen in a cadaver is tetrahedral in shape and presents the following external features:

 1. Apex.

 2. Base.

 3. Neck.

 4. Three surfaces (superior and two inferolateral surfaces).

 5. Four borders (anterior, posterior and two lateral).

EXTERNAL FEATURES OF THE BLADDER  

APEX

It provides attachment to the median umbilical ligament and lies posterior to the upper margin of the pubic symphysis.

BASE (POSTERIOR SURFACE/FUNDUS)

The urinary bladder is triangular in shape and directed posteroinferiorly toward the rectum.

 Its superolateral angles are joined by the ureters while its inferior angle gives rise to the urethra.

 In the male, its relations are

1. Upper part is separated from rectum by the rectovesical pouch containing coils of the small intestine.

2. Lower part is separated from rectum by the terminal parts of vasa deferentia and seminal vesicles. The vasa deferentia lie medial to the seminal vesicles.

3. The triangular area between the vasa deferentia is separated from the rectum by rectovesical fascia (of Denonvilliers).

 In the female, it is separated from the cervix of uterus by the vesicouterine pouch.

NECK

 It is the lowest and most fixed part of the bladder. It is situated where the inferolateral and the posterior surfaces of the bladder meet. It is pierced by the urethra. It lies about 3– 4 cm behind the lower part of pubic symphysis.

 Its relations are:

 In the male, it rests on the upper surface of the prostate.

In the female, it is related to the urogenital diaphragm.

 SUPERIORSURFACE

It is triangular in shape and bounded on each side by the lateral borders which extend from ureteric orifices posterolaterally to the apex anteriorly and posteriorly by the posterior border which joins the ureteric orifices.

 In the male, it is completely covered by the peritoneum which separates it from: coils of the ileum and sigmoid colon.

In the female, it is covered by the peritoneum except for a small area near the posterior border, which is related to the supravaginal part of the uterine cervix.

INFEROLATERAL SURFACES

Each inferolateral surface slopes downward, forward, and medially to meet its fellow of the opposite anteriorly in the midline.

These surfaces are separated from each other, anteriorly by the anterior border, and from the superior surface by the lateral borders.

The inferolateral surfaces are devoid of peritoneum and in both male and female are related:

In front to:

– retropubic space,

– pubic symphysis, and 

– puboprostatic ligaments.

 Behind to:

– obturator internus muscle above, and 

– levator ani muscle below.

SUPPORTS OF THE URINARY BLADDER

 The fixation of the bladder is helped by the different ligaments of the urinary bladder.

LIGAMENTS: The ligaments of the bladder are of two types—true and false.

A. True Ligaments: These are formed by the condensation of pelvic fascia around the neck and the base of the bladder and have a supportive function for the bladder.

 1. Lateral ligaments (two in number, right and left): They extend from the side (inferolateral surface) of the bladder to the tendinous arch of pelvic fascia.

 2. Puboprostatic ligaments (four in number, two on each side—lateral and medial): They fix the neck of bladder.

 3. Median umbilical ligament is the fibrous remnant of the urachus. It extends from the apex of the bladder to the umbilicus. It maintains the bladder in position anteriorly and superiorly.

 4. Posterior ligament (two in number, right and left): They extend as a sheet of loose areolar tissue from the side of the base of the bladder to the lateral pelvic wall. They enclose the vesical venous plexus.

FALSE LIGAMENTS 

 These are peritoneal folds and do not have supportive function as performed by true ligaments. They are seven in number Anteriorly there are three folds:

Median umbilical fold,

Two medial umbilical folds

Laterally a pair of false lateral ligaments is formed by the reflection of the peritoneum from the bladder to the side wall of the pelvis and forms the floor of paravesical fossae.

Posteriorly a pair of false posterior ligaments is formed.

 These are the sacrogenital folds which are the folds of peritoneum extending from the side of the bladder, posteriorly, on either side of the rectum, to the anterior aspect of the third sacral vertebra.

LAYERS OF THE BLADDER 

 The bladder wall from within outward is composed of:

 _ A mucous membrane.

 _ A muscularcoat.

 _ Adventitia.

MUCOUS MEMBRANE : It is pale pink in colour and covered with a transitional epithelium. It is thrown into folds (rugae) when the bladder is empty. The mucosal area covering the internal surface of the base of the bladder is termed

“trigone.”

 MUSCULAR COAT : It constitutes the detrusor muscle which consists of three layers of smooth muscle fibres.

 INTERIOR OF THE BLADDER

1. In an empty bladder, the greater part of mucosa shows irregular folds (rugae).

2. At the posterior wall is a triangular-shaped structure called trigone of the bladder.

The limits of trigone are defined superiorly by the openings of the ureters and inferiorly by the Urethra . The trigone presents the following features:

1. Anteroinferior angle, formed by the internal orifice of the urethra.

 2. Two posterosuperior angles, formed by openings of the ureters.

3. Uvula vesicae, a slight elevation in the mucous membrane immediately above and behind the internal urethral orifice. It is produced by the median lobe of prostate.

4. Interureteric ridge/crest (bar of Mercier) forms the superior boundary of trigone and connects the two ureteric orifices.

 5. Two uretero-urethral ridges (Bell’s bars) extend from the ureteric orifice to the urethral orifice.

Relations of the urinary bladder Base is related to:

Rectovesical pouch in the male

• Vesico uterine pouch in the female

• Ductus deference and seminal vesicles

Superior surface

• Peritoneal cavity containing loops of ileum

• Coils of ileum

• Sigmoid colon

• Uterine cervix (in female)

 

RELATIONS OF THE FEMALE URINARY BLADDER 

Anterior surface is related to:

• inferolateral surfaces

• Retropubic space

• Puboprostatic ligaments

• Obturator internus and levator ani muscles 

Apex is related to: median umbilical Ligament. 

Neck is related to:

 • Prostate gland (in male)

 • Urogenital diaphragm (in female)

ARTERIAL SUPPLY

It is by the following arteries:

 1. The principal arteries supplying blood to the bladder are superior and inferior vesical arteries which are the branches of anterior division of internal iliac arteries.

 2. The other arteries which make small contribution in supplying the lower part of the bladder are:

(a) Obturatorand inferior gluteal arteries.

(b) Uterine and vaginal arteries in the female.

VENOUS DRAINAGE

The veins of the bladder do not follow the arteries. They form a complicated plexus on the inferolateral surfaces near the prostate called vesical venous plexus.

 1. This plexus passes backward in the posterior ligaments of the urinary bladder to drain into the internal iliac veins.

 2. It communicates:

(a) In the male with the prostatic venous plexus.

(b) In the female with the veins at the base of broad ligament.

NERVE SUPPLY

Motor Innervation

It is provided by the parasympathetic, sympathetic, and somatic fibres.

1. Parasympathetic fibres (nervi erigentes) are derived from S2, S3, S4 (spinal micturition centre) segments of the spinal cord. They are motor to the detrusor muscle and inhibitory to the sphincter vesicae (internal urethral sphincter).

2. Sympathetic fibres are derived from T11, T12 thoracic and L1, L2 lumbar segments of the spinal cord. They are inhibitory to the detrusor and motor to the sphincter vesicae.

3. Somatic fibres (pudendal nerve) are derived from S2, S3, S4 spinal segments. They are motor to the external urethral sphincter.

 SENSORY INNERVATION 

The majority of sensory fibres run along the parasympathetic fibres (pelvic splanchnic nerves/nervi erigentes; S2, S3, S4). Some fibres also run with the sympathetic fibres. 

APPLIED ANATOMY 

1• Trabeculated bladder: It results due to chronic obstruction to the outflow of the urine by enlarged prostate or stricture of the urethra. The bladder becomes distended and its musculature hypertrophies.

Its muscular fasciculi increase in size and interface in all the directions giving rise to an open weave appearance of the bladder wall, known as the “trabeculated bladder.”

2. Neurogenic bladder: any defect in the neural mechanism of micturition leads to neurogenic bladder.

The neurogenic bladder lacks the normal neural control of micturition.

The types of neurogenic bladder are:

(a) Automatic reflex bladder: It results from complete transection of the cord above the lower micturition centre (S2, S3, S4) involving pyramidal tracts (upper motor neurons) clinically it presents as:

 – The voluntary inhibition and initiation of micturition are lost.

 – The bladder empties reflexly every 1 to 4 hours. When the filling reaches a certain level, the detrusor muscle contracts reflexly as in early infancy. This is called automatic or reflex Bladder. 

 (b) Autonomous bladder: It Results from the destruction of S2, S3, S4 segments of the spinal cord (lower centre of micturition). Clinically it presents as:

– The reflex and nervous control of micturition is lost.

The bladder wall becomes flaccid and capacity of bladder is greatly increased. The result is continuous dribbling and this type of bladder is called an autonomous bladder.

– The bladder may be emptied by the manual compression or by the abdominal muscular contraction.

 3. Injury to the urinary bladder

 4. Cancer of the urinary bladder etc.