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Horse · Splanchnology (organs)

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Model: "Heart (horse) Plastinated" by the Veterinary Faculty, University of Sarajevo (UNSA-VF on Sketchfab), CC BY 4.0

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Urinary bladder

Vesica urinaria

Hollow organ that stores urine. Empty, it lies on the pelvic floor; when full, it advances into the abdomen. In the mare the urethra is short and wide and opens on the floor of the vagina without a suburethral diverticulum.

Laterality:: Unpaired

Draft, not yet reviewed by a veterinarian. Content may contain errors. It is published so the community can review it.

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Overview

The equine urinary bladder (vesica urinaria) is pear-shaped and large. Empty, it retracts into the pelvic cavity, on the pelvic floor; as it fills it advances cranially along the abdominal floor. It has an apex, a body and a neck, which continues as the urethra. The ureters open in the dorsal wall, near the neck, at the trigone of the bladder.

Relations and ligaments

Lateral ligaments: carry in their free border the round ligament of the bladder, the remnant of the umbilical artery.
Median ligament: joins the ventral surface to the floor of the pelvis and abdomen; in the fetus it contains the urachus, which connects the bladder to the allantois through the umbilicus.
In the mare: the uterus and vagina lie dorsally. The urethra is short and wide and opens on the floor of the vagina, at the junction with the vestibule; there is no suburethral diverticulum, so catheterisation is easy.
In the male: the deferent ducts, vesicular glands and prostate lie dorsally. The urethra is long and ends at the urethral process, which projects into the fossa of the glans.

Clinical relevance

Urolithiasis: equine bladder stones are calcium carbonate, often spiculated; they are more common in males and cause haematuria at the end of urination or after exercise, stranguria and incontinence. They are felt per rectum and seen by cystoscopy.
Bladder rupture in the foal: usually occurs at foaling, mainly in colts; urine in the abdomen (uroperitoneum) causes abdominal distension, hyponatraemia, hypochloraemia and hyperkalaemia. The peritoneal fluid to plasma creatinine ratio confirms the diagnosis.
Patent urachus: urine drips from the navel of the foal; it may be complicated by umbilical infection.
Paralytic bladder and sabulous cystitis: with lesions of the sacral spinal cord or cauda equina (for example in equine herpesvirus 1 myeloencephalopathy), the bladder distends and accumulates sediment.
Eversion and prolapse: in the mare, during foaling, the bladder can evert through the urethra or protrude through a vaginal tear.