VAN 221: Veterinary Splanchnology and Applied Anatomy (1+1)

URINARY BLADDER (OX)

• The urinary bladder is a musculo-membranous sac, differs in form, size and position according to the amount of its contents
• When contracted, it is a dense pyriform mass about the size of a fist and lies on the ventral wall of the pelvic cavity at a variable distance behind the pelvic inlet
• When moderately full, it is oval in shape and extends into the abdominal floor. Its capacity is about 3 to 4 litres.
• The bladder has 3 parts-a vertex, a body and neck
• The cranial part or the vertex is a blind end and presents in its middle a rounded cul-de-sac called as cicatrix - the vestige of the urachus, which forms a connection between the bladder and the allantois in the fetus
• The middle part or body is rounded and somewhat flattened from above downwards
• It presents two surfaces- superior and inferior which are convex when full
• The caudal narrow extremity is the neck and it joins the urethra

Relations

• They vary according to the amount of the contents and sex
• The ventral surface is related to the floor of the pelvis and extends into the abdomen as it distends
• The dorsal surface in the male is related to the rectum, the genital fold, and the terminal parts of the vas deferens, the seminal vesicle and the prostate
• In the female, it is related to the body of uterus and vagina. When the bladder is full, the vertex reaches the rumen and small intestine

Ligaments

• The bladder is fixed in position by three peritoneal folds -the ligaments of the bladder
• The ventral or middle ligament is a median triangular fold extends from the ventral face of the bladder to the floor of the pelvis and abdomen
• In the newborn animal, it is extensive and reaches to the umbilicus
• The lateral ligaments are two and extend on either side of the lateral aspects of the bladder to the lateral wall of the pelvis. Each contains in its free edge a round cord the round ligament, which is the remnant of the fetal umbilical artery
• The caudal part of the bladder has no peritoneal covering and is attached to the surrounding parts by fat and connective tissue.
• The mucous membrane is pale, thin and is loosely attached to the submucous tissue
• It forms numerous folds when bladder is empty and contracted
• It is modified over a triangular area on its dorsal wall close to neck called the trigonum vesicae where the mucous membrane is firmly attached without any folds
• The two cranial angles of the trigonum vesicae present the openings of the two ureters and the caudal angle shows the opening of the bladder into the urethra -internal urethral orifice
• The two urethral orifices are placed near each other on either side of the median line. From each urethral orifice, a fold of mucous membrane passes backward and inward, uniting with its fellow to form a median urethral crest in the first part of urethra.
• The terminal part of ureter after piercing the muscular coat of the bladder and passes for a distance of about 2.5 cm between the muscular and mucous coats before piercing the latter
• This arrangement constitutes a valve, which prevents the return of urine from the bladder into ureter
• The internal urethral orifice lies at the apex of the trigonum