Anatomy of the female urogenital triangle

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Introduction0:00–0:30

Anatomy is so much easier when we compartmentalize things. For this reason, the perineum can be divided into two triangles, the anterior eurogenital triangle and the posterior anal triangle.
The urogenital triangle can be further divided into a superficial pouch and a deep pouch by a layer of deep fascia called the perineal membrane.
In females, the eurogenital triangle houses the female external genitalia and the perineal muscles. Let's start with talking about the female external genitalia, also called the vulva, which includes the Mons pubis, the paired labia majora, labia minora, and the clitoris.

External genitalia0:30–0:50

As well as deeper structures, the bulbs of the vestibule, the greater vestibular glands, and the lesser vestibular glands.
The Mons pubis is a rounded, fatty eminence that lies anterior to the pubic symphysis, pubic tubercles, and superior pubic rami.

Mons pubis0:50–1:03

This eminence has a coarse pubic hair that grows after puberty. Now, from the mons pubis, two folds of skin called the labia majora arise and extend posteriorly towards the anus.

Labia majora1:03–1:27

These labia meet anteriorly to form the anterior commissure and posteriorly to form the posterior commissure. Also, the labia majora is the termination point of the round ligament of the uterus, which is the embryonic remnant of the gubernaculum in females.
All right, now the labia majora lie on each side of a central depression called the pudendal cleft, which houses the labia minora and the vestibule of the vagina.

Labia minora1:27–2:16

The labia minora are paired hairless folds of skin that contain spongy connective tissue, erectile tissue, and many blood vessels.
These labia unite posteriorly to form a fold of skin called the frenulum of the labia minora, or the foresha. Anteriorly, each labium divides into medial and lateral folds.
The medial folds unite below the clitoris, forming a pointy extension called the frenulum of the clitoris. The lateral folds unite to form a fold of skin called the prepu or foreskin of the clitoris.
This fold covers the clitoris, which is the main female erectile organ and counterpart to the penis in males. The clitoris has 3 parts, called the root, the body, and the gland's clitoris.

Clitoris2:16–2:57

The root of the clitoris consists of two crura that attach to the inferior pubic rami and the perineal membrane deep to the labia.
These crurua consist of erectile tissue called the corpora cavernosa, which extends into the body at the angle of the clitoris.
Up to this point, the clitoris seems pretty similar to the penis, right? Well, the gland's clitoris, unlike the gland's penis, doesn't have an external urethral opening.
This means that the clitoris doesn't have a urinary function, and functions solely as an organ of sexual arousal. The gland's clitoris is the most highly innervated portion of the clitoris, and the only portion that can be seen externally.
Alright, now the labia minora surrounds an area called the vestibule of the vagina, where the orifices of the urethra and vagina and the ducts of the greater vestibular glands open.

Vestibule of the vagina2:57–3:51

The urethra opens through the external urethral orifice, which lies posterior to the clitoris and anterior to the vaginal orifice.
Lateral and deep to the vaginal orifice are the bulbs of the vestibule, which are paired elongated masses of erectile tissue.
A comparable structure in males is the bulb of the penis. These bulbs are covered inferiorly and laterally by the bulbospongiosis muscles, which we will discuss further in just a bit.
Next are the greater vestibular glands, which are paired round glands that lie posterolateral to the vaginal orifice. These glands are also partially covered by the bulbospongiosis muscles.
During sexual arousal, they secrete mucus into tiny ducts that open on each side of the vaginal orifice. OK, now let's look at the blood supply and innervation of the vulva.

Blood supply and innervation of the vulva3:51–5:09

Arterial blood supply of the vulva comes from the external and the internal pudendal arteries. These branches include the anterior labial arteries, which arise from the external pudendal artery to supply the anterior part of the labia majora.
Next are the posterior labial arteries, which arise from the perineal artery, which is a branch of the internal pudendal artery.
The posterior labial arteries supply the labia minora and the posterior part of the labia majora. Next are the labial veins, which drain the vulva.
These veins then drain into the internal pudendal veins, which drain into the internal iliac veins. Finally, let's talk about the sensory innervation of the vulva.
The mons pubis in the anterior part of the labia majora are innervated by the anterior labial nerves, which arise from the ilio inguinal nerve.
The anterior labia majora are also innervated by the genital branch of the genitofemoral nerve. The posterior part of the labia majora and the labia minora are innervated by the posterior labial nerves, which arise from the superficial perineal nerve, which, in turn, is a branch of the pudendal nerve.

Blood supply and innervation of the clitoris5:09–5:47

All right, now the blood supply and innervation of the clitoris is a bit special. The arterial blood supply comes mainly from branches of the internal pudendal arteries.
These branches include the deep artery of the clitoris, which supplies the corpora cavernosa of the clitoris, and the dorsal artery of the clitoris, which runs on the dorsum of the clitoris to supply the gland's clitoris.
This artery accompanies the dorsal nerve of the clitoris, which innervates the clitoris, and the deep dorsal vein of the clitoris, which drains into the vesicle plexus.
Finally, during the excitement stage of the sexual response, the clitoris enlarges as it fills with blood, very similarly to the penis during an erection.
OK, now let's take a deep breath and have a quick quiz. Can you name the different parts of the clitoris?

Quiz5:47–6:00

Alright, now the urogenital triangle also houses the perineal muscles, which are grouped into superficial and deep perineal muscles.

Superficial perineal muscles6:00–6:25

The superficial perineal muscles include the bulbospongiosis, the ischiocavernosis, and the superficial transverse perineal muscles.
These muscles lie in the superficial perineal pouch, which is superficial to the perineal membrane. Let's start with the superficial transverse perineal muscles, which originate from the internal surface of the ischiopubic rami and ischial tuberosities, and insert onto an irregular mass that lies in the middle of the perineum, called the perineal body.

Superficial transverse perineal muscle6:25–6:47

These muscles fix the perineal body, which helps support the abdominopelvic viscera. Next are the bulbospongiosis muscles, which originate from the perineal body and wrap around the bulbs of the vestibule to insert into the pubic arch.

Bulbospongiosus muscle6:47–7:12

These two muscles also anchor the perineal body, which supports the abdominopelvic viscera. They also constrict the vaginal orifice, compress the greater vestibular glands, which assists in releasing their secretions, and contributes to the erection of the clitoris.

Ischiocavernosus muscle7:12–7:39

Lastly are the ischiocavernosis muscles, which originate from the ischiopubic rami and the ischial tuberosities, and surround the crura of the clitoris to insert into the inferior and medial sides of the crura.
These muscles maintain the erection of the clitoris by compressing the veins that drain it. The superficial perineal muscles are innervated by the deep perineal nerve.
Next are the deep perineal muscles, which lie deep to the perineal membrane in the deep perineal pouch. First, we have the external urethral sphincter, which surrounds the urethra and compresses it to maintain urinary continence.

Deep perineal muscles7:39–8:25

In the female deep perineal pouch, there are two other muscles that are actually part of the external urethral sphincter complex, called the compressor urethra and the urethrovaginal sphincter.
Finally, contrary to traditional descriptions, the current understanding is that females do not have a sheet-like deep transverse perineal muscle.
In place of it, there is a massive smooth muscle at the posterior edge of the perineal membrane. The deep perineal muscles are innervated by the deep perineal nerve.
Alright, now let's wrap this up by discussing the lymphatic drainage of the vulva. First, lymph from the skin of the perineum, the inferior aspect of the vagina, the vaginal orifice, and the vestibule drain into the superficial inguinal lymph nodes.

Lymphatic drainage of the vulva8:25–8:59

Next, lymph from the clitoris in the anterior part of the labia minora drain into the deep inguinal lymph nodes or directly into the internal iliac lymph nodes.
Finally, lymph from the urethra drains into the internal iliac or sacral lymph nodes. Alright, as a quick recap, the Mons pubis is a rounded elevation that lies anterior to the pubic symphysis.

Review8:59–10:37

The labia majora surround the pedendal cleft, which houses the labia minora and the vestibule. The clitoris has 3 parts, called the root, the body, and the glands.
The vestibule of the vagina is the area between the labia minora where the urethral and vaginal orifices open. Deep and lateral to the vaginal opening, there are paired, elongated masses of erectile tissue called the bulbs of the vestibule.
The arterial blood supply of the vulva comes from the anterior labial arteries and the posterior labial arteries. Sensory innervation of the vulva is provided primarily by the anterior labial nerves and posterior labial nerves.
The arteries of the clitoris include the deep artery of the clitoris and the dorsal artery of the clitoris, while the main sensory nerve of the clitoris is the dorsal nerve of the clitoris, and the venous drainage is by the deep dorsal vein of the clitoris.
Finally, the superficial perineal muscles include the bulbospongiosis, ischiocavernosis, and superficial transverse perineal muscles.
Deep perineal muscles include the external urethral sphincter, the compressor urethra, the urethrovaginal sphincter, and smooth muscle in place of the deep transverse perineal