Carnivore External Genitalia

Summarize the main components of the male reproductive tract

Paired testes

• Production of gametes & hormones

Paired gonadal tracts

• Epididymis (Divided into head, body and tail), ductus deferens - carry spermatozoa from testes into urethra (common channel draining repro tract & urinary bladder)

Accessory glands

• Ampulla, Prostate, Bulbourethral gland & Vesicular glands

Urethra

Penis

What are the main functions of the male reproductive tract?

Production of:

• Gametes/ spermatozoa

• Androgenic hormones (testosterone)

• Semen (Supportive fluid keeping sperm alive)

Introduction of sperm into female reproductive tract

What are the main external features of male genitalia?

• Penis

• Prepuce

• Scrotum

• Testes

What type of penis do canines have?

- Musculo-cavernous type

• Means it contains large amounts of cavernous sinus tissue which is extensive erectile tissue (erectile tissue distends with blood to create the erection)

What parts make up the canine penis?

Parts that make up penis:

- Root (located just behind pubic bone in perineal area)

- Body (narrower portion of penis)

- Glans (distal end which is subdivided into Bulbus Glandis & Pars Longa Glandis)

What is notable about the OS penis?

Another notable feature in the canine penis:

- Internal bone known as the os penis, seen in most carnivore species

- In dogs, easily visible on radiographs

Where is the canine penis located?

Penis has an intermediate location between thighs attached from ventral abdominal wall.

What erectile tissues does the root of the canine penis contain?

3 Erectile tissues

• Two cura and the bulb of the penis

What are the cura and how do they form the root?

• The crura of the penis are two elongated structures (left and right crus) that form part of the root of the penis. Each crus is attached to the ischial arches of the penis. They will then converge and join forming a single body.

What encloses the crura in the canine penis?

• Additionally what does each crura consist of

Each crura consists of a cavernous tissue core (corpus cavernosum) which is enclosed within a thick connective tissue casing called the tunica albuginea. - NB: the tunica albuginea (white tunic) is name given to capsule of testes too!

• There is a septum between the corpora cavernosa in the proximal region of the penile body, dividing left and right

• The structure is grooved ventrally to accommodate the urethra which is enclosed within a vascular sleeve known as the corpus spongiosum. 

The distal end of corpus cavernosum becomes the __ ____.

os penis

What is the corpus spongiosum?

• Where does it begin from?

• Vascular spongy erectile tissue

• Begins at the pelvic outlet, enlargement of this corpus spongiosum tissue which is covered by bulbospongiosus muscle, forming the bulb of the penis

• Continues as thin vascular sleeve surrounding urethra as it goes through pelvic canal and penile body

• Corpus spongiosum expands at distal end forming the glans

• Urethral orifice at the top of the penis

• Larger blood spaces than corpus cavernosum

Summarize the differences between the corpus cavernosum and corpus spongiosum.

Corpus cavernosum: forms core of the crura and forms bulk of spongy vascular tissue within body & root of penis

Corpus spongiosum: largely a thin sleeve around urethra, enlargement of this tissue forms the bulb and glans of penis.

• Spongier than corpus cavernosum as has larger potential blood spaces (allows it to expand to greater degree) also more delicate.

Describe where the os penis is and what it contains?

• Formed from distal end of corpus cavernosum

• Vertical groove contains and protects urethra

Where and why do bladder stones often get stuck in dogs?

Proximal end as it cannot pass through urethra due to restriction by os penis

• Limited ability for urethra to expand

Where is the glans located?

Location: Distal end of penis

• Corpus cavernosum ends and glans formed by corpus spongiosum

What parts compose the glans?

Bulbus glandis:

- Proximal part of glans that swells during erection & mating (responsible for the 'tie' during copulation in canine) and firmly attached to os penis as runs through glans.

Pars longa glandis:

- Distal part of glans which is more elongated responsible for initial penetration and helps maintains rigidity during erection.

• Slightly less firmly attached to underlying os penis & has urethra orifice at tip.

What is a prepuce?

• Where is it usually located?

Invagination of ventral abdominal skin which covers and protects the glans penis when not erect

• Caudal to the umbilicus

Describe the two layers of the prepuce.

Two layers:

- Outer layer: lamina externa (orange) = continuous with skin and is basically just skin

- Inner layer: lamina interna (dark pink) = lines preputial cavity and continues on to cover the free end of the penis

Describe the lining of the surface of the lamina interna.

Can see that the surface of lamina interna is hairless & lined with lymphoid tissue (not surprising as it is the opening to outside world - remember immune surveillance, barrier protection, etc functions of this type of tissue)

• Prepuce has smegma-secreting preputial glands.

Describe the muscles associated with the prepuce.

Muscles associated with prepuce: derived from thin skin muscles (cutaneous trunci) which twitch the abdominal skin.

Describe the prepuce and penis in neonates.

Neonates:

Prepuce and penis fused so not generally possible to extrude penis from prepuce. Separation breaks down before puberty.

If this breakdown fails can potentially cause infertility.

What does congenital narrowing of the preputial orifice cause?

preventing extrusion of penis (called phimosis): potential fertility issues

What does paraphimosis in the canine cause?

Why does it occur?

• Essentially inability to retract penis

• Causes:

  - Preputial orifice being slightly too narrow (penis goes out but gets swollen and can't retract)

  - Fur wrapping around penis when extruded creating a stricture

  Must be dealt with quickly as can impair circulation to penis if vascular constriction.

Describe the…

• Origin

• Insertion

• Function

• Muscle Type

Of the bulbospongiosus muscle.

Single

• Origin: continuation of urethralis muscle

• Insertion: encloses and inserts on corpus spongiosum

• Function: pumps blood into cavernous spaces

• Muscle Type: skeletal

Describe the…

• Origin

• Insertion

• Function

• Muscle Type

Of the Ischiocavernosi muscle.

Paired and Powerful

• Origin: ischium

• Insertion: encloses crura and inserts on corpus cavernosum

• Function: pumps blood into cavernous spaces

• Muscle Type: skeletal

• Describe the…

  • Origin

  • Insertion

  • Function

  • Muscle Type

  Of the Ischiourethralis muscle.

Single

• Origin: Ischium

• Insertion: Fibrous ring around penile veins

• Function: Occludes dorsal vein during erection

• Muscle Type: Skeletal

• Describe the…

  • Origin

  • Insertion

  • Function

  • Muscle Type

  Of the Retractor Penis muscle.

Paired, unlike other muscles, retain the non erect penis within prepuce: drawing penis caudally, mostly holds penis within pepuce which is why it is smooth muscle

• Origin: Caudal vertebrae

• Insertion: prepuce

• Function: draws penis caudally

• Muscle Type: smooth

What nerves innervate muscle associated with the penis?

Nerves accompany vessels

• Motor fibers to muscle predominantly parasympathetic - arising from pelvic nerves

Describe the penile arterial supply.

Two major supplies to penis & prepuce are the internal and external pudendal arteries.

Describe the branching occurring from the internal pudendal artery as it leads into the artery of the penis.

Perineal arteries come out from the internal pudendal artery as it connects with artery of the penis

- First branch: dorsal artery of penis: supplies the glans (bulbus glandis & pars longa) and some blood supply to prepuce.

- Second branch: deep artery of penis supplies corpus cavernosum within the crura in body of penis.

- Third branch: artery of bulb/ bulbourethral artery which supplies the corpus spongiosum in proximal part of penis.

Describe what arteries the external pudendal artery feeds into.

Preputial arteries

Describe the penile venous drainage.

- Pars Longa & prepuce

• Can either drain into bulbus glandis into the dorsal vein

• Or drain to external pudental vein

- Bulbus Glandis

• Drains via dorsal vein into internal pudendal vein

• Dorsal vein travels over dorsal surface of penis

- Corpus cavernosum & bulb of penis

• Drain into dorsal vein into internal pudendal vein

Dorsal vein is predominant drainage route for bulk of the penis

• Fibrous ring - associates with ischiourethralis muscle surrounding the vein

Vessels have marked valves in veins to prevent reflux.

Describe the first stage of the canine penile erection.

First stage:

- Increase blood flow via arteries into penis

- Occlusion of venous outflow via combo of ischiourethralis ring & valves

Results in blood building up within cavernous spaces within penis until arterial blood pressure is reached.

Stage 1: more blood in, less blood out, reach arterial pressure within cavernous spaces (so think lots of blood and expansion of spaces)

Describe the second stage of canine penile erection.

Second stage:

- Involves contraction of ischiocavernosus & bulbospongiosus muscles

- Muscles undergo rhythmic contractions to squeeze more blood into cavernous spaces to above arterial pressure

Stage 2: Rhythmic contraction of muscles forces blood into cavernous spaces above arterial pressure. (muscle contractions)

In dogs the ______ _______ expands more than the ____ _______.

corpus spongiosum, corpus canvernosum

Describe the tie occuring during canine copulation.

Idea of 'tie' in dogs:

- Male dismounts & faces away from bitch

- Further constricts venous drainage so bulbus glandis remains swollen & ties penis within vulva

- Eventually bulbospongiosus relaxes allowing blood to drain from bulbus glandis & erection will disappear & dogs to uncouple.

Bulbus glandis in dogs penis particularly important in concept of tie.

Never try to force two dogs apart as can do a lot of damage to both.

Describe the…

• Type:

• Features:

• General anatomy:

Of the feline penis.

• Musculocavernous

• Features: shorter than canine penis and has os penis present too

  • Two crura coming back from ischial arch fusing together to form body.

  • Glans forming corpus spongiosum at distal end.

• In cats, penis remains in embryonic position with apex directed caudoventrally.

  • Opening of cat’s prepuce faces caudoventrally

  • Urethral groove therefore dorsal on penis (Ventral in dogs as it curves around)

  • Prepuce thick and quite short, preputial orifice also faces caudally

Describe the structure of the feline penis.

• Penis shorter in cats than dogs. Os penis present in cats but not commonly seen during diagnostic imaging.

• Glans is small with less division but covered in small keratinised spines (seen in these diagrams). Spines develop as secondary sexual characteristic at sexual maturity.

• The bulbourethral glands are located near bulb of penis in cats.

• Erection occurs: Curvature to penis, so apex of glans directed cranioventral direction.

• Spines covering glans, these are responsible for triggering induced ovulation in female cat (or queen).

Describe general features of the scotum in cats and dogs.

Scrotum location varies depending on species.

Dog: intermediate location between hindlimbs.

Cat: perineal location, underneath the anus.

Describe the external anatomical features of the scrotum.

Scrotum:

- Thin skin

- Copious sweat & sebaceous glands

- Hair covering variable

Most notable external feature:

- Groove dividing scrotum into left & right halves

- Correlates to an internal septum dividing scrotum internally

Why is the scrotal skin important as a thermoregulatory mechanism?

• Furthermore what anatomical structures allow it to function in this way?

Scrotal skin important in as a thermoregulatory mechanism as it allows the maintenance of testicular temperature

• Optimal testicular production occurs when the testes are slightly below body temp.

• Contraction of the dartos causes the scrotum to also contract & results in the testicles being drawn closer to body to increase testicular temperature 

  • Dartos = another thermoregulatory mechanism

Describe the internal anatomical features of the scrotum.

• Skin lined internally by fibromuscular layer

- Called Dartos: smooth muscle and fibrous tissue

• Internal septum formed from dartos

- Divides scrotum into right & left compartments

• Inside the dartos & supporting testes are layers of fascia (Usually fatty) which support the vaginal tunic (Outer layer of testes) called the:

• External spermatic fascia

• Innermost layer: tunica albuginea

What is the vaginal tunic?

- Outpouching of parietal peritoneum through inguinal canal

• The vaginal tunic encloses spermatic cord and the structures that supply testes (vas deferens & testicular vessels, etc). It also encloses testes & epididymis

  • Parietal Layer (Outer)

  • Visceral Layer (Inner) - closely adhered to testes

**Testes technically peritoneal organs

What is the space between the layers of the vaginal tunic and why is it important?

There is a space between the two layers which can contain a small amount of fluid, this communicates directly with peritoneal cavity.

• Why is this important? Well if not scrupulous with surgical prep & surgical asepsis during castration = open route to peritoneal cavity and risk developing full blown peritonitis.

What is the main function of the inguinal canal?

Potential space between body wall: allows passage of testes & testicular vessels & vas deferens.

Slit between caudal abdominal wall muscles, two rings: superficial & deep inguinal rings.

In males, what is the function of the inguinal canal?

Function (male):

- Allows transmission of testes to scrotum as animal develops.

- Testes develop inside abdominal cavity & will descend to scrotum either during gestation or just after.

• Failure of normal descent: retained testes or cryptorchidism

In males, what does the inguinal canal contain?

• In male, the inguinal canal contains the spermatic cord structure (ductus deferens & testicular vessels), outpouching of peritoneum (vaginal tunic) and external pudendal vessels (supply prepuce & some of body wall).

What is the superficial inguinal ring?

• Contained in division of aponeurosis of External Abdominal Oblique

• Found with close attachment to linea alba to pubic bone, so it sits in front of pelvis

• Caudal edge of ring palpable as sharp edge in aponeurosis

What is the deep inguinal ring and what are the cranial, medial and caudolateral borders?

• What muscle arises caudal to the deep inguinal ring?

- Cranial: free edge of Internal Abdominal Oblique

- Medial: Rectus Abdominis

- Caudolateral: aponeurosis of external abdominal oblique

Males: cremaster muscle arises from internal abdominal oblique caudal to deep inguinal ring, accompanies spermatic cord structures down to the testes