Male Carnivore External Genitalia (Mod. 5)

What are the 3 main products of the male reproductive tract?

1) Gametes / sperm

2) Androgenic hormones (testosterone)

3) Semen

The canine penis is termed as a “musculo-cavernous” type penis. What the fuck does this mean?

This means that the penis contains large amounts of cavernous sinus tissue

• Erectile tissue

  • Distends with blood to form an erection

What are the 4 main parts of the canine penis?

1) OS penis - internal bone in the penis

2) Root

3) Body

4) Glans

• Bulbus Glandis

• Pars Longa Glandis

Describe the root and body structure of the penis… What are the three major components? What are these made up of, and how are they arranged?

The three major components are the bulb of the penis, and the two crura on either side.

• The crura arise from the ischial arches of the pubic bone. As they get closer to the body of the penis, they converge and join to form a single body (see image)

Each crura consists of:

• Corpus cavernosum (cavernous tissue core)

• Encased in tunica albuginea (thick connective tissue)

*** Note: there is a ventral groove between the two crura to accommodate the urethra, which is encased in a vascular sleeve known as the corpus spongiosum

Since the previous card went more into the crura, describe the bulb of the penis… what is it made up of? How does this tissue change as it runs down the body of the penis?

Bulb is made up of an enlargement of corpus spongiosum tissue, which is covered by bulbospongiosus muscle

• Originates at the pelvic outlet (see image)

Corpus spongiosum tissue carries on as thin, vascular sleeve surrounding the urethra as it moves down the body of the penis

At the distal end of the penis, corpus spongiosum expands AGAIN to form the glans

If you were to take a cross section of the penis, describe how it looks and what tissues you would see.

On the top of the cross section, you would see the two crura with their cavernous tissue core

• These two will remain separated by a septum that runs between them

• Encased in tunica albuginea

Beneath the two crura is the corpus spongiosum casing that surrounds the urethra

Quick recap… describe the purpose and function of the corpus cavernosum and corpus spongiosum of the penis.

Corpus cavernosum - Forms the core of the crura, and forms the bulk of spongy vascular tissue within the body and root of the penis

Corpus spongiosum - Mostly a thin, vascular sleeve around the urethra… the two enlargements of this tissue form the bulb and glans of the penis

• Is MUCH spongier than the corpus cavernosum (hence the name), allowing for higher vascularity and higher potential for expansion

  • Is also more delicate

The distal end of the corpus cavernosum becomes what?

The OS penis

• Initially starts out as a fibrous outgrowth of the corpus cavernosum

Describe the structure of the OS penis…. what is its most notable feature, and why is this important?

The most notable feature is its ventral groove

• OS penis looks like a “U” shape in a cross section

• This is where the urethra passes through the area of the glans

IMPORTANT TO REMEMBER, because this gives the urethra limited capacity to expand

• Dogs passing bladder stones; stones often get stuck at the proximal end of the urethra due to restriction by the OS penis

Describe the structure of the glans… what tissue is it made up of, and what are its 2 main components?

Found on the distal end of the penis; corpus cavernosum ends and glans formed completely by corpus spongiosum

Made up of 2 different glands…

1) Bulbus glandis -

• Proximal portion of the glans that swells during erection and mating

  • Quite literally the “bulbous” looking portion of the tip of the penis

• Responsible for the “tie” during mating in canines

• Firmly attached to the OS penis

2) Pars longa glandis -

• The distal portion of the glans; more elongated

  • Responsible for initial penetration and helps penis maintain rigidity during erection

• Less attached to the OS penis

• Has urethral orifice at tip

What is the “prepuce” of the penis? What are its 2 main layers?

The prepuce is the invagination of the abdominal skin, which covers and protects the glans penis when not erect

Has 2 layers of tissue:

1) Lamina externa -

• Outer layer; continuous with the outer skin, and is basically just skin

2) Lamina interna -

• Inner layer; lines the preputial cavity and covers the free end of the penis

• Lined with lymphoid tissue; not very surprising, structure = function

*** NOTE: PREPUCE ALSO HAS SMEGMA GLANDS

What are two clinical problems that the prepuce can cause?

1) Congenital narrowing of preputial orifice -

• Prevents extrusion (exiting) of the penis from the prepuce… called “phimosis”

2) Paraphimosis -

• The inability to retract the penis into the prepuce

• Causes:

  • Orifice too narrow; penis goes out and swells, then can’t retract

  • OR fur wrapped around penis when extruded… causes stricture

What are the 4 main muscles associated with the penis?

1) Bulbospongiosus (sinlge muscle)

2) Ischiocavernosi (paired and powerful; look at the name and think about what it could be associated with)

3) Ischiourethralis (single muscle; again, look at the name, gives away association)

4) Retractor penis (paired)

Is the bulbospongiosus smooth or skeletal muscle? Where is its origin, insertion, and what is its function?

SKELETAL muscle

Origin: Continuation of the urethralis muscle

Insertion: On corpus spongiosum

Function: Pumps blood into cavernous spaces

Is the ischiocavernosi smooth or skeletal muscle? Where is its origin, insertion, and what is its function?

SKELETAL muscle

Origin: Ischium (in the name)

Insertion: Encloses crura and inserts on corpus cavernosum (again, the name)

Function: Pumps blood into the cavernous space

***** So basically, the bulbospongiosum and ischiocavernosi are both associated with their specific erectile tissue, AND have the same function of pumping blood into cavernous spaces to allow for erection. Basically, think of these as the erectile MUSCLES, which function to ERECT the penis by pumping in more blood upon contraction

Is the ischiourethralis smooth or skeletal muscle? Where is its origin, insertion, and what is its function?

SKELETAL muscle

Origin: Ischium (name)

Insertion: Fibrous ring around penile veins

Function: SMALL BUT IMPORTANT; occludes dorsal VEIN during erection, preventing blood from draining from the penis

Is the retractor penis smooth or skeletal muscle? Where is its origin, insertion, and what is its function?

SMOOTH muscle

Origin: caudal VERTEBRAE

Insertion: PREPUCE

Function: DRAWS PENIS INTO PREPUCE… NOT INVOLVED IN ERECTION

Here’s a diagram to show where the muscles are in the penis…

What are the two major arterial supplies to the penis and prepuce? (think inside and outside)

Internal Pudendal Artery - Penis

External Pudendal Artery- Prepuce

Describe the blood supply to the penis, starting at the internal pudendal artery…

Goes from internal pudendal artery → Artery of Penis, which branches into three different arteries:

1) Dorsal Artery of Penis - Supplies the GLANS (both bulbus glandis and pars longa)

2) DEEP Artery of Penis - Supplies CORPUS CAVERNOSUM within the crura

3) Bulbourethral Artery - Supplies CORPUS SPONGIOSUM in proximal part of penis

** if you think about it, the names kinda relate to what they supply

Describe the penile venous drainage system… what roll does it have in erection? In what three areas of the penis is there venous drainage?

Veins in the penis have valves within them to PREVENT REFLUX during erection. The three main areas the penis is divided into are:

1) The pars longa and prepuce

2) Bulbus Glandis

3) Corpus cavernosum and bulb of penis

Describe the path of venous drainage from each of the 3 “areas” of the penis… what are the 3 main veins in the penis?

The 3 main veins are:

• External Pudendal Vein

• Dorsal Vein ***

• Internal Pudendal Vein

Pars Longa and Prepuce drainage -

• Can drain 2 different ways… either into the bulbus glandis, or into the external pudendal vein of the prepuce

Bulbus Glandis drainage -

• Drains into the Dorsal Vein → Internal Pudendal Vein

Corpus cavernosum and Bulb of Penis drainage -

• DORSAL vein runs along dorsal surface of penis… simply collects blood from corpus cavernosum and bulb of penis as it goes along

What is a notable feature of the Dorsal Vein?

The Dorsal Vein is the most important drainage route for the bulk of the penis.

• Runs the length of the dorsal surface of penis

• Has a FIBROUS RING ASSOCIATED WITH ISCHIOURETHRALIS MUSCLE (previously mentioned before)

  • Once this muscle contracts during erection, fibrous ring CONSTRICTS vein, preventing drainage

Describe the 2 stages of the canine erection and what happens during these stages…

1st Stage -

• INCREASED blood flow into penis via arteries

• OCCLUSION of VENOUS OUTFLOW via ischiourethralis ring and valves

• Results in blood building up within cavernous spaces in penis (swelling) until arterial blood pressure is reached

2nd Stage -

• Rhythmic CONTRACTION of ischiocanernosus and bulbospongiosus muscles

• Forces blood into cavernous spaces above arterial pressure

Describe why the “tie” happens in mating dogs…

Corpus spongiosum expands more than corpus cavernosum, so as the male dismounts and faces away from the bitch, this reduces venous drainage even more and bulbus glandis remains swollen

• “Ties” with vagina

• Once bulbospongiosus relaxes, blood drains from bulbus glandis and swelling goes down, allowing the dogs to uncouple

Describe the big differences in the FELINE penis compared to the canine penis…

CAUDOVENTRALLY DIRECTED (>) see image

• Therefore, opening of cat’s prepuce faces caudally as well

• Groove of OS Penis is DORSAL instead of ventral because of this reason as well

Penis is shorter

Glans is smaller, with keratinized spines (ouch)

• Responsible for triggering induced ovulation in female

As erection occurs:

• There is a curvature to this penis, so apex ends up directing CRANIOVENTRALLY for penetration

What is the overall importance of the scrotum? What is its most notable external feature?

Importance: thermoregulatory mechanism

• Allows maintenance of testicular temperature, which should be slightly below body temp

Notable feature:

• Median groove, dividing it into left and right halves

• Correlates to an internal septum

What is the important muscle layer within the scrotum? Describe it and what it does.

Dartos:

• Combination of smooth muscle and fibrous tissue

• Closely adhered to the skin, along with testes and fascia

• Is responsible for septum between the two testicles

In cold temperatures, the dartos actually contracts, drawing the testicles closer to the body to increase their temperature

• So another thermoregulatory mechanism

Also supports the vaginal tunic, which is the outermost layer of the testes

Describe the vaginal tunic and its two layers… why is it clinically important to know about this? (think of neutering…)

The vaginal tunic is an outpouching of the parietal peritoneum through the inguinal canal.

• Completely encloses testes, spermatic cord, and other structures that supply the testes

The two layers of the vaginal tunic:

1) Parietal outer layer - what we see

2) Visceral inner layer - CLOSELY ADHERED TO TESTES

******* There is a space between these two layers, filled with fluid… COMMUNICATES DIRECTLY WITH PERITONEAL CAVITY

• This is why it is clinically significant… if neuter not completely sterile, can result in full-blown peritonitis

Quick review of inguinal canal… What is its function, and what are its two different rings?

Function:

• Allows passage of testes to scrotum as animal develops

• Testes develop inside the abdominal cavity and will descend into scrotum (remember, covered by vaginal tunic)

Two rings:

1) Deep inguinal ring - essentially the canal’s “opening”

• Complex… associated with an additional muscle in males called the cremaster muscle

  • Detaches from internal abdominal oblique, and accompanies spermatic cord structures as testes drop

2) Superficial inguinal ring - the canal’s “exit”

• Close to the attachment of the linea alba to pubic bone…. sits just in front of pelvis

• Can be palpated in some patients