What is Urinary Incontinence?

Urinary incontinence (UI) in canines refers to the involuntary leakage or loss of urine from a dog’s bladder, leading to unwanted urine leakage.  It is a common problem in dogs and can manifest in various ways, including dribbling, puddles of urine left behind, or wetting their bedding or surroundings.

Dogs suffering from UI are typically unaware of or unable to control the passage of urine, leading to involuntary urination. This condition can vary in severity, from occasional small leaks to more significant and frequent episodes of urinary leakage.

The Structure and Anatomy of the Urinary Bladder

The structure and anatomy of the urinary bladder in humans and pets, such as dogs and cats, are quite similar in terms of function and basic structure, as both serve the same basic function of storing urine before it is expelled from the body. However, it’s important to note that there can be variations in the size, shape, anatomy and function of the urinary bladder among different species of pets. For example, the shape and size of the bladder may vary in dogs, cats, and other animals with male dogs having a longer and more complex urethra than female dogs, making them more prone to urinary obstructions. Cats have a unique urinary system with their own set of characteristics and potential health issues.

The location of the urinary bladder in the dog

The location of the urinary bladder in the dog

Additionally, the mechanisms and reflexes controlling urination may differ among species. Understanding the specific anatomy and physiology of the urinary system in a particular pet species and breed is important for veterinary care and management of urinary issues as variations in anatomy and function impacts the susceptibility to certain urinary tract issues, such as urinary stones, infections, or bladder tumors, which may vary between species.

1. General Structure and Location:

The urinary bladder is a hollow, muscular organ located in the pelvic cavity. In humans, the urinary bladder is located in the pelvic cavity, just behind the pubic bone. In pets, the location of the bladder varies depending on the species. In dogs and cats, it is also situated in the pelvic cavity, similar to humans.

2. Shape and Size:

The shape of the urinary bladder can vary among individuals, but it typically has a rounded, sac-like shape. The size of the bladder can vary significantly between species and even among individuals within a species. For example, a human bladder can typically hold around 400-600 milliliters of urine, while the bladder in pets like dogs and cats may be smaller and hold less urine in proportion to their body size. In dogs and cats, the size and shape can vary based on the breed and size of the animal.

3. Muscular Wall and Internal Structures:

The urinary badder is made up of several layers of tissue, including mucosa, submucosa, muscularis, and serosa. The outer most layer surrounding the bladder, also called the outer connective tissue layer or adventitia or serosa, anchors the bladder to surrounding structures providing structural support. The muscularis layer , also called the detrusor muscle, of the urinary bladder contains smooth muscle fibers that contract to expel urine from the bladder.

The contraction of the muscular wall is under voluntary control in humans, allowing us to control when we empty our bladders. In most pets, it is under involuntary control. The submucosa, a layer of connective tissue that supports the mucosal layer, contains blood vessels and nerves that regulate bladder function. The innermost layer, called the mucosa, is lined with specialized cells known as transitional epithelium, which can stretch to accommodate urine without leaking.

4. Nerves and Blood Supply:

Nerve control of the urinary bladder and urination (micturition)

Nerve control of the urinary bladder and urination (micturition)

Both humans and pets have a complex network of nerves and blood vessels that supply the urinary bladder. These nerves are responsible for signaling when it’s time to empty the bladder.

Illustration adapted from www.veteriankey.com

Illustration adapted from www.veteriankey.com

The urinary bladder receives its blood supply from various arteries, including the superior and inferior vesical arteries plus branches of the internal iliac artery in both humans and animals. Nerves, including the autonomic nervous system, play a crucial role in controlling bladder function. The bladder receives nerve signals from the autonomic nervous system, controlling involuntary contractions for urination. These nerves regulate the contraction of the detrusor muscle and the relaxation of the internal and external sphincters to control urination.

5. Urethra Connection:

Adapted from https://veteriankey.com/reproductive-system-2/

Adapted from https://veteriankey.com/reproductive-system-2/

The bladder is connected to the external environment through the urethra, which is a tube that carries urine from the bladder to the external urinary meatus (opening). The length and structure of the urethra can vary among species, with males typically having longer urethras than females.

6. Sphincters:

Both humans and pets have sphincters, which are muscles that control the flow of urine in and out of the bladder. There are two main types:

   i) Internal Sphincter: Involuntary smooth muscle located at the bladder neck, which relaxes during urination.

   ii) External Sphincter: Voluntary skeletal muscle that surrounds the urethra and allows for conscious control over urination.

7. Supportive Structures:

In humans, the bladder is supported by ligaments and the pelvic floor muscles.

In pets, the bladder is also supported by surrounding various structures and connective tissues that help maintain its position and functionality. These supportive structures are crucial for the proper functioning of the bladder. The supportive structures of the urinary bladder in both pets (such as dogs and cats) and humans include:

i). Pelvic Floor Muscles: The pelvic floor muscles play a significant role in supporting the urinary bladder in both humans and pets. These muscles form a supportive hammock-like structure that helps maintain the position of the bladder within the pelvic cavity.

ii). Ligaments: Ligaments provide additional support to the bladder by attaching it to surrounding structures. In humans, the pubovesical ligament and the puboprostatic ligament (in males) or the pubourethral ligament (in females) help anchor the bladder in place. In pets, similar ligaments may exist, depending on the species.

iii). Connective Tissues: The bladder is surrounded by connective tissues, including fascia and other supporting structures, which help maintain its structural integrity and position within the pelvic cavity.

Adapted from https://vetcheck.it/dog_anatomy/

Adapted from https://vetcheck.it/dog_anatomy/

iv). Peritoneum: The urinary bladder is partially covered by a serous membrane called the peritoneum. The peritoneum helps to support and stabilize the bladder within the abdominal cavity.

v). Adventitia or Serosa: The outermost layer of the bladder wall is composed of connective tissue known as adventitia or serosa. This layer provides additional support and helps anchor the bladder to surrounding structures.

vi). Pelvic Bones: The bony pelvis provides a stable foundation for the urinary bladder. The bladder is situated within the pelvic cavity and is supported by the pelvic bones, contributing to its overall stability.

vii). Urogenital Diaphragm: In both humans and some animals, including dogs, the urogenital diaphragm is a muscular structure that provides support to the bladder and other urogenital organs. This diaphragm is formed by the external urethral sphincter muscle and associated connective tissues.

These supportive structures work together to maintain the position and function of the urinary bladder. The pelvic floor muscles, ligaments, connective tissues, and bony structures collaborate to ensure that the bladder can adequately store urine and release it when necessary. Dysfunction or weakness in these supportive structures can contribute to conditions such as urinary incontinence or pelvic organ prolapse. Understanding the anatomy and function of these supportive structures is essential for the diagnosis and treatment of bladder-related issues in both humans and pets.

What is the basic Function of the urinary bladder?

The primary function of the urinary bladder in both humans and pets is to store urine produced by the kidneys until it is ready to be eliminated from the body. When the bladder fills with urine, stretch receptors signal the nervous system, and when it’s appropriate, the bladder contracts to expel urine through the urethra.

Urination mechanism illustration

Urination mechanism illustration

While the basic structure and function of the urinary bladder are similar in both humans and pets, there can be variations in size, shape, and specific anatomical features depending on the species. Additionally, the control of bladder function may differ, with humans having more voluntary control over urination compared to most pets.

What causes Urinary Incontinence (UI) in Pets?

Urinary incontinence, often referred to as UI, is a medical condition characterized by  the involuntary leakage or loss of urine from a dog’s bladder in dogs of any age, breed, or gender, but it is more commonly observed in certain groups or conditions, such as:

1. Spayed Female Dogs: Female dogs that have been spayed (neutered) are more prone to develop urinary incontinence, especially as they age. This condition is often associated with a weakening of the urethral sphincter muscle. Urethral Sphincter Mechanism Incompetence (USMI) is more frequently seen in spayed female dogs but can also affect males and intact females. It often develops several years after spaying and can result from changes in hormonal levels, leading to a weakening of the muscles that control the closure of the urethra.

A female undergoing spaying (Ovariohysterectomy)

A female undergoing spaying (Ovariohysterectomy)

2. Larger Breeds: Some large dog breeds, such as Doberman Pinschers, Boxers, and Old English Sheepdogs, are more susceptible to urinary incontinence.

3. Aging Dogs: As dogs get older, their muscles and tissues can weaken, including those responsible for maintaining bladder control. This can lead to an increased risk of incontinence.

An old dog

An old dog

4. Medical Conditions: Certain medical conditions, such as urinary tract infections (UTIs), bladder stones, and neurological disorders, can also contribute to urinary incontinence in dogs.

5. Congenital (anatomical) Abnormalities: In some cases, urinary incontinence may be due to congenital abnormalities, such as ectopic ureters, which can lead to improper urine flow.

6. Other potential causes of UI in dogs include behavioural problems. Behavioral issues leading to incontinence are less common than medical causes, but they can still contribute to urinary problems. Some of the behavioral problems that may lead to incontinence in dogs include:

i) Excitement Urination: Some dogs may urinate involuntarily when they are excited or anxious. This is more common in puppies and young dogs and often occurs in response to new people, visitors, or during play. It is generally not a medical issue but a behavioral one.

ii) Submission or Submissive Urination: Dogs may urinate as a submissive gesture, especially when they feel intimidated or in the presence of dominant individuals. This is more common in shy or anxious dogs and can be triggered by specific situations or interactions.

iii) Marking Behaviour: Marking is a normal behaviour in which dogs deposit small amounts of urine to establish territory or communicate with other dogs. However, inappropriate marking indoors can lead to accidents and incontinence issues.

iv) Separation Anxiety: Dogs with separation anxiety may exhibit various behaviours, including inappropriate urination. When left alone, anxious dogs may urinate as a response to stress or fear. This is different from true incontinence, as it is related to emotional distress.

v) Territorial Issues: Some dogs may urinate indoors as a way of marking their territory. This behavior is more common in unneutered males, but spayed females and neutered males may also exhibit territorial marking.

Accurate diagnosis and identification of the underlying cause are essential to determine the most appropriate treatment for the affected dog.

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