Lecture 15: The Reproductive System III

what is the perineum?

The perineum is the area between your thighs, at the bottom of the pelvis. It's where your private parts (genitals and anus) are located.

what are the two parts of the perineum?

It has two parts:

1. Urogenital Triangle (front): where pee and (for people with a vagina) vaginal openings are.

2. Anal Triangle (back): where the anus is.

RECALL: what are the hiatuses in the perineum?

Hiatuses = Openings in the Pelvic Floor

• Urogenital Hiatus = Urethra and vagina

• Rectal Hiatus = Rectum/anus

Your pelvic stands upright.. true or false???

FALSE!

• Most people think the pelvis stands upright, but in real life, your pelvis tilts forward a bit naturally.

• Points your genitals downward

• Aims your anus backward

What is the perineal membrane?

The perineal membrane is ONE sheet of strong connective tissue (like a thick trampoline) that sits across the urogenital triangle. It creates two layers or "pouches":

what are the 2 pouches the membrane creates

1. Superficial pouch = closer to the skin

2. Deep pouch = deeper, closer to the inside of the body

think of like a big mac…

• Top Bun = skin/external genitals

• Top Filling = superficial perineal pouch

• Middle Bun = perineal membrane

• Another filling = deep perineal pouch

• Bottom Bun = pelvic floor muscles

what is the perineal body?

• The perineal body is a small but super important fibrous (strong connective tissue) structure that sits in the middle of the perineum—right between your genitals (front) and anus (back).

where is the perinial body in males? females?

• In males: between the bulb of the penis and the anus

• In females: between the vaginal opening and the anus

what are the contents of the superficial and deep perinal pouch in ASSIGNED MALE AT BIRTH

Superficial Perineal Pouch

• Contains: Muscles of external genitalia/muscles for genital movement (like muscles that help with erection or stabilize the base of the penis).

  • These structures are attached to the perineal membrane for support.
    

Deep Perineal Pouch

• Contains: External urethral sphincter, which is a circular muscle that wraps around the urethra.

  • This sphincter is under voluntary control (so you can “hold it in” when you need to pee).

what are the contents of the superficial and deep perinal pouch in ASSIGNED FEMALE AT BIRTH

Superficial Perineal Pouch

• Contains: External genitalia, like the clitoris and associated muscles (These muscles help with sexual function and stabilization of structures)

  • These structures are attached to the perineal membrane for support.

Deep Perineal Pouch

• Contains: 

  • External urethral sphincter – wraps around urethra to hold in pee (voluntary control!)

  • Compressor urethrae – squeezes the urethra from the front like a clamp

  • Urethrovaginal sphincter – wraps around both urethra and vagina

  • Deep transverse perineal muscle – supports the pelvic floor

PENIS; EXTERNAL GENITALIA - what is th penis made of? why is this beneficial?

• The penis is made of special spongy tissue (erectile tissue) that can fill with blood during arousal → helps with erection.

• Think of it like a sponge that soaks up blood!

PENIS; EXTERNAL GENITALIA - what are the 3 colums of erectile tissue in the penis?

1. Corpus Cavernosa

2. Corpus Cavernosa

3. Corpus Spongiosum

• 2 eyes = Corpus Cavernosa (dorsal = top side when erect)

• 1 mouth = Corpus Spongiosum (ventral = bottom side, holds the urethra)

PENIS; EXTERNAL GENITALIA - what sits in the root of the penis?

• Bulb of the Penis

• Crura (plural of Crus)

  • Made of Corpus Cavernosa - one for each

PENIS; EXTERNAL GENITALIA - what muscle are associated with each of the 3 colums of erectile tissue in the penis?

1. Corpus Cavernosa ~ Ischiocavernosus

2. Corpus Cavernosa ~ Ischiocavernosus

3. Corpus Spongiosum ~ Bulbospongious

VULVA; EXTERNAL GENITALIA - similar to the penis, what is the many tissue in the vulva?

• The vulva is made of special spongy tissue (erectile tissue) that can fill with blood during arousal → helps with erection.

• Think of it like a sponge that soaks up blood!

  • corpus caveronosum

  • corpus spongiosum

VULVA; EXTERNAL GENITALIA - where is corpus cavernosum found in the vulva

Crua and body of the clitoris

• Crura of the clitoris = attaches clitoris to bones (like penis root)

• Body of the clitoris = middle part

• Like the penis, the clitoris can become erect when blood fills the erectile tissue.

VULVA; EXTERNAL GENITALIA - where is corpus spongiosum found in the vulva

1. Bulbs of the Vestibule

• Two sponge-like structures on either side of the vaginal opening.

• Made of corpus spongiosum (same erectile tissue in penis).

• Engorge with blood during arousal → help vaginal opening stretch & lubricate.

VULVA; EXTERNAL GENITALIA - what isthe tip of the vulva called

• Glans of the clitoris = tip (very sensitive)

• Covered by a foreskin (prepuce), like a mini hoodie!

VULVA; EXTERNAL GENITALIA - what muscle are associated with each of the 2 sets of erectile tissue in the vulva?

1. Corpus Cavernosa ~ Ischiocavernosus

2. Corpus Spongiosum ~ Bulbospongious

VULVA; EXTERNAL GENITALIA - what are 2 other features of the vulva unique to females?

1. Labia Majora & Labia Minora

• Labia Majora = outer "lips" (skin + fat, like scrotum)

• Labia Minora = inner "lips" (thinner, moist skin)

• Surround and protect the vaginal and urethral openings

What are the bulbourethral glands/greater vestibular glands? what are the location differences in females + males?

• Both glands provide lubrication and are involved in sexual function

In Males:

• Secretes pre-ejaculate fluid

• Lubricates the urethra

• Neutralizes acidity in the urethra to protect sperm

• Bulbourethral glands are deep in males

In females:

• Secretes mucus for lubrication during sexual arousal

• Greater Vestibular Glands are superficial in females!

what are the three types of innervation in the pelvis

KEY IDEA: Three Types of Innervation in the Pelvis

1. Somatic: Feeling (touch, pain), movement 

• VOLUNTARY

2. Autonomic - Parasympathetic: “Rest & Digest” (relaxation)

• INVOLUNTARY

3. Autonomic - Sympathetic: “Fight or Flight” (tension)

• INVOLUNTARY

how does somatic innervation work? key nerve involved?

The Star Nerve: Pudendal Nerve (S2, S3, S4)

• A somatic nerve that gives you voluntary control over your pelvic muscles. Think peeing, pooping, and sexual function!

• "S2, S3, S4 keep the penis off the floor"

how does autonomic (parasympathetic) innervation work? key nerve involved?

Parasympathetic (Pelvic Splanchnic Nerves ~ S2-4)

Think "peaceful" → rest, digest, relax

• Relaxes sphincters - Helps you pee and poop

• Contracts detrusor (bladder) muscle - Helps you urinate

• Relaxes uterine muscle - During non-labor states

• Vasodilation of erectile tissues - Starts erection/clitoral engorgement!

how does autonomic (sympathetic) innervation work? key nerve involved?

Sympathetic (Lumbar & Sacral Splanchnic Nerves ~ T12 - L2)

Think "stressful" → fight, hold, push

• Contracts sphincters - Holds pee/poop in

• Relaxes bladder (detrusor) - Prevents urination

• Contracts uterus - Labor contractions or period cramps

• Constricts erectile tissue - Involved in ejaculation

Now moving onto the anal triangle,,, what is the The Ischiorectal (Ischioanal) Fossa

Think of this like a fatty triangle of space around the rectum that:

• Allows room for expansion when poop moves through

• Contains blood vessels and nerves

what are the three stages of poopong? what muscles and nerves are involved?

Innervation to the Rectum and Anal Canal

Let’s break it down step-by-step with the 3 stages of pooping:

1. The Reflex Begins

• When poop enters the rectum from the sigmoid colon → it stretches the wall

• This triggers the defecation reflex

2. Muscles Get Ready

• Parasympathetic nerves (pelvic splanchnic from S2–S4) tell:

• The sigmoid colon & rectum to contract

• The internal anal sphincter to relax

• This builds pressure = the urge to poop. But you don’t always go immediately! That’s because your pudendal nerve (somatic) tells:

• Puborectalis muscle and external anal sphincter to stay contracted

• So you can hold it until a bathroom is nearby

3. Go Time!

• When it’s safe to go, you relax:

• Puborectalis

• External anal sphincter

• 💩 = out