Vestibule

The vestibule is a part of the female external genitalia, located within the vulva. It is the area between the labia minora and houses the openings of both the urethra and the vagina. The vestibule extends from the clitoris down to the posterior end of the vaginal opening, bordered laterally by the labia minora. This space also contains the openings of the Bartholin’s glands and Skene’s glands, which help lubricate the vaginal and urethral areas. The vestibule is lined with mucous membrane, making it a sensitive region that plays a role in both urination and sexual function.

Structure and Anatomy

The vestibule of the vulva is a significant part of the external female genitalia, anatomically structured to support various openings and glandular secretions. Below is a detailed breakdown of its anatomy.

Location and Boundaries

The vestibule is a small, triangular-shaped area located within the vulva. It is situated between the labia minora and extends from the clitoral hood (anteriorly) to the posterior edge of the vaginal orifice. Its boundaries are:

• Anterior Boundary: The clitoris and the clitoral hood form the front of the vestibule.
• Posterior Boundary: The posterior commissure, a thin band of tissue, marks the posterior limit of the vestibule, near the perineum.
• Lateral Boundaries: The labia minora border the vestibule on either side, creating a protective enclosure for the structures within.

Urethral Opening (External Urethral Orifice)

Located in the upper part of the vestibule, just below the clitoris, is the external urethral orifice. This is the opening through which urine exits the body. The urethral meatus is usually a small, slit-like or round structure and is surrounded by sensitive mucosal tissue. It is positioned anteriorly within the vestibule, directly above the vaginal opening.

Vaginal Opening (Introitus)

The vaginal opening, or introitus, is situated just below the urethral orifice and occupies the central part of the vestibule. The size and shape of the vaginal opening can vary, and in individuals who have not given birth, the vaginal opening may be partially covered by the hymen, a thin membrane. After childbirth or sexual activity, the hymen may be torn or absent. The introitus serves as the entry point to the vagina and is one of the most prominent structures within the vestibule.

Openings of the Bartholin’s Glands

On either side of the vaginal opening, at approximately the 5 and 7 o’clock positions, are the Bartholin’s gland ducts. These glands are small and normally not visible, but their duct openings are located within the vestibule. The Bartholin’s glands produce mucus to lubricate the vaginal opening, especially during sexual arousal. The glandular openings in the vestibule ensure that secretions are appropriately delivered to the vaginal entrance.

Openings of the Skene’s Glands

The Skene’s glands, also known as the paraurethral glands, are located on either side of the urethral opening, within the vestibule. These small glands open near the urethral meatus and are responsible for secreting fluids that help lubricate the urethral opening. Although these glands are small and their openings are microscopic, they are integral to the vestibule’s anatomical structure.

Mucosal Lining

The vestibule is lined with a delicate mucous membrane. This mucosa is continuous with the inner surfaces of the labia minora and extends into the vaginal and urethral openings. Unlike the keratinized skin of the outer vulva, the mucosa of the vestibule is softer and more prone to irritation, given its exposure to bodily fluids and external stimuli. The mucosal surface provides protection to the sensitive tissues underneath, while also allowing for some flexibility and movement.

Hymenal Remnants

In individuals who have passed puberty or experienced sexual activity, the remnants of the hymen may still be visible along the edges of the vaginal opening within the vestibule. These fragments are known as carunculae myrtiformes, small, fleshy nodules that may persist after the hymen has been ruptured or stretched.

Vascular Supply

The vestibule has a rich blood supply, which comes from branches of the internal pudendal artery, a key artery supplying the external genitalia. This blood flow is crucial for maintaining the health of the mucous membranes and tissues in the vestibule, especially during periods of sexual arousal when increased blood flow leads to engorgement of the tissues.

Nerve Supply

The vestibule is innervated by branches of the pudendal nerve, which provides sensory input to the area. The numerous nerve endings in the vestibule contribute to its sensitivity, making this region responsive to touch and pressure. The nerves play a role in the sensations felt during sexual activity and urination.

Vestibular Bulbs

Although not part of the visible vestibular structure, the vestibular bulbs are paired erectile tissues located just beneath the skin of the vestibule, running along the sides of the vaginal opening. These bulbs are part of the clitoral complex and engorge with blood during sexual arousal. They surround the vaginal opening and are involved in enhancing sexual sensation by swelling and increasing pressure on the surrounding structures.

Histology

The mucosal surface of the vestibule is composed of stratified squamous epithelium, similar to that found in other parts of the vulva. This epithelium is non-keratinized, making it softer and more vulnerable to irritation compared to the external skin of the vulva. Underneath the epithelium is a layer of connective tissue rich in blood vessels, which provides structural support and nourishment to the area.

Glandular Openings and Secretions

The vestibule’s anatomical structure is designed to facilitate the secretion of fluids from the Bartholin’s and Skene’s glands, which help lubricate the area and protect the mucosal surfaces from friction and irritation. These glands’ ducts open directly into the vestibule, ensuring that their secretions are delivered effectively.

Function

The vestibule plays a central role in various functions related to urination, sexual activity, and maintaining the overall health of the vulva. Below is a detailed explanation of its functions.

Urinary Function

One of the key functions of the vestibule is related to the passage of urine.

• Housing the Urethral Opening: The vestibule contains the external urethral orifice, which is responsible for the discharge of urine from the body. Positioned just below the clitoris, this opening allows for the flow of urine from the bladder through the urethra. The vestibular space ensures that the urethral opening is protected but accessible for the process of urination.
• Directing Urine Flow: The location of the urethral opening within the vestibule helps in guiding the flow of urine away from the body, ensuring that the urine is expelled in a controlled manner. This reduces the chances of urine backflow, which could otherwise increase the risk of irritation or infections in the genital region.

Sexual Function

The vestibule plays a significant role in sexual arousal and activity due to its proximity to important sexual structures and its involvement in lubrication and sensation.

• Clitoral and Vestibular Sensitivity: The vestibule is rich in nerve endings, which contribute to the sensitivity of the vulva during sexual stimulation. Although the vestibule itself is not the primary erogenous zone, its proximity to the clitoris and clitoral bulbs, along with the surrounding erectile tissues, makes it an essential part of the sexual response system.
• Vestibular Bulbs and Sexual Arousal: The vestibule contains the vestibular bulbs, paired erectile tissues that engorge with blood during sexual arousal. As these bulbs swell, they exert pressure on the surrounding structures, increasing sensitivity and contributing to the pleasurable sensations experienced during sexual activity.
• Facilitating Vaginal Penetration: The vestibule surrounds the vaginal opening, helping to facilitate comfortable penetration during sexual intercourse. Its mucosal surface allows for flexibility and stretch, accommodating the insertion of the penis or other objects while maintaining the structural integrity of the vaginal orifice.

Lubrication and Moisture Control

The vestibule plays a crucial role in maintaining lubrication and moisture levels in the vulvar area.

• Bartholin’s Glands Secretion: The vestibule contains the duct openings of the Bartholin’s glands, which secrete mucus into the vestibule, particularly during sexual arousal. This lubrication is essential for reducing friction during sexual intercourse and preventing irritation to the mucosal lining of the vestibule and vaginal opening.
• Skene’s Glands Secretion: The Skene’s glands, located near the urethral opening, also contribute to lubrication by secreting fluid into the vestibule. This fluid helps to maintain a moist environment around the urethral opening, reducing the risk of irritation or infection, especially during urination or sexual activity.
• Moisture Distribution: The mucosal lining of the vestibule plays a role in distributing the glandular secretions, ensuring that the area remains moist and lubricated. This moisture helps protect the tissues of the vulva from dryness, cracking, or irritation, which can occur due to friction or exposure to external factors.

Protection of Vaginal and Urethral Openings

The vestibule serves as a protective space for the sensitive vaginal and urethral openings.

• Shielding the Urethral and Vaginal Openings: The vestibule provides a protective environment for the vaginal and urethral openings, ensuring they are not directly exposed to external factors that could cause injury, irritation, or infection. The labia minora, which surround the vestibule, further enhance this protective function by creating a physical barrier.
• Hygiene Maintenance: By housing the urethral and vaginal openings, the vestibule helps maintain hygiene. It provides a controlled space where secretions and bodily fluids can be expelled without direct exposure to the surrounding skin. This reduces the risk of bacterial or fungal infections that could occur if fluids were allowed to accumulate around the more external parts of the vulva.

Assisting in the Reproductive Process

The vestibule plays an important role in reproduction, particularly in facilitating intercourse and the potential for conception.

• Facilitating Sperm Entry: During sexual intercourse, the vestibule provides the passage through which sperm enters the vaginal canal. The vestibular space surrounding the vaginal opening ensures that sperm can be easily deposited near the vaginal introitus, increasing the likelihood of successful sperm entry into the vagina and, ultimately, the uterus for fertilization.
• Stretch and Flexibility: The mucosal lining of the vestibule, along with the tissues surrounding the vaginal opening, is highly flexible and capable of stretching to accommodate the size of the penis during intercourse. This flexibility also plays a critical role during childbirth, allowing for the passage of the baby through the vaginal canal.

Sensory Function

The vestibule is innervated by branches of the pudendal nerve, which gives it a rich supply of sensory nerve endings. These nerve endings make the vestibule a sensitive region, contributing to tactile sensations and sexual pleasure.

• Nerve Endings: The vestibule’s rich nerve supply enhances sensitivity in the area, allowing it to respond to tactile stimuli such as touch, pressure, and changes in temperature. This sensitivity contributes to the overall sexual response, enhancing pleasure during sexual activity.
• Coordination with Surrounding Structures: The vestibule works in tandem with other sensitive structures in the vulva, such as the clitoris and labia minora, to provide sensory feedback. During sexual arousal, the heightened sensitivity in the vestibule helps increase overall sexual enjoyment and pleasure.

Role in Defense Mechanism

The vestibule’s mucosal surface and glandular secretions play a defensive role in preventing infections and maintaining the health of the vulvar region.

• Barrier to Pathogens: The vestibular area serves as an initial barrier to pathogens, with its mucous membrane offering some protection against external contaminants. The secretions from the Bartholin’s and Skene’s glands have antimicrobial properties that can help defend against bacterial and fungal infections.
• Acidic Environment: The fluids produced in the vestibule, especially those from the Skene’s glands, help maintain the acidic pH of the vulvar area. This acidic environment is important for keeping harmful microorganisms at bay, particularly around the urethral and vaginal openings.

Clinical Significance

The vestibule is clinically significant as it plays a key role in various conditions affecting the vulva. Infections, such as vulvovaginitis, can occur in the vestibule due to bacterial, fungal, or viral pathogens, causing inflammation, itching, and discomfort. Vestibulitis, a condition characterized by chronic inflammation of the vestibular area, can result in pain during intercourse (dyspareunia) and other activities.

Bartholin’s gland cysts, which develop in the vestibule when the duct becomes blocked, can lead to swelling, pain, and even abscess formation if infected. Additionally, trauma or irritation to the vestibule, whether from sexual activity, improper hygiene, or allergic reactions, can cause discomfort or injury.