Male Carnivore Internal Genitalia

What main functions and location are the carnivore testis found?

Functions

• Endocrine & exocrine functions

• Production of gametes (optimal below body temperature)

Found

• Contained within vaginal tunic

• Relatively small compared to farm animals

What surrounds the testis?

• Outer capsule - Tunica albuginea (Also covers crura)

  • Composed of connective tissue and smooth muscle

• Large vessels

What is the parenchyma of the testis?

• Contained in a capsule under pressure

  • Invaginations of capsule forms lobules

• Usually soft, yellow-brown color, tissue made up of:

  • Interstitium: leydig cells and connective/vascular frame

  • Also supports seminiferous tubules

What is the mediastinum of the testes?

• Contains the rete testis (Where seminiferous tubules drain into)

Describe the pathway of sperm flow through the testis.

Sperm drains from seminiferous tubules, to mediastinum to rete testis, to efferent ductules, to head of epididymus (Sperm travel through the epididymis from the head (where they enter) to the tail, where they mature and are stored, eventually being propelled into the vas deferens during ejaculation), then urehtra.

Describe the relative location of the epididymus and it’s function.

Location

• Lies along dorsal margin of testis (Carnivores

Function

• Allows sperm storage and maturation

• Sperm travels from head to body to tail to ductus deferens

• Efferent ductules combine to form convoluted epididymal duct

  - Exits tail of epididymis to form deferent duct / vas deferens

What three components can the epididymus be divided into and what features does each component have?

Head:

- Attached to testicular capsule

- Receives efferent ductules

Body:

- Loosely attached to surface of testis

- Creates space called testicular bursa

Tail:

- Attached to testis by proper ligament of testis

- Also attached to parietal layer by ligament of the tail of epididymis

Describe the three ligamentous structures which support the testicles.

Ligamentous structures:

Proper ligament of testis

• Attaches tail of epididymis to testis

Ligament of tail of epididymis

• Attaches tail of epididymus to parietal tunic

Scrotal ligament

• Attaches parietal tunic to scrotum

Where is the spermatic cord found?

• Running to and from the testis, contained within the vaginal tunic

What are the main structures contained within the vaginal tunic?

- Deferent Duct

- Deferent Artery & Vein

• Arise from Prostatic Vessels

- Testicular Artery & Vein

- Lymphatics

• Lymphatic drainage to sublumbar nodes

- Testicular Nerves

• Sympathetic

- Cremaster Muscle

• Technically sits on outside of vaginal tunic but is associated with the spermatic cord

What is the main function of the deferent duct?

• Function: Carries sperm to prostatic urethra

Describe the location of the deferent duct.

• Describe the key feature about this anatomical structure varying between dogs and cats.

• Undulates initially then straightens

• Runs with testicular vessels in spermatic cord through inguinal ring

• Crosses dorsal bladder neck

• Enters prostate & joins urethra

Dogs

• Slight dilation or ampulla at entry to prostrate

Cats

• Not present

What forms the bulk of the spermatic cord?

What are the functions of these structures?

• Vessels - Testicular Arteries

• Testicular artery:

  - Direct branch from abdominal aorta

  - Runs down to vaginal ring

  - Extremely convoluted distally

  - Cranial & caudal epididymal branches

Function: Supplies oxygenated blood to the testes & involved in counter current heat exchange system with pampiniform plexus of veins.

Testicular veins drains blood into the pampiniform plexus, what is the structure and function of this?

Elaborate pampiniform plexus

- Wrapped around distal convoluted testicular artery

- Function: Heat exchange/ vascular drainage

• Arterial blood is cooled by veinous blood, helping to reduce temp of blood entering the testis, helps maintain lower body temperature

• Pampiniform plexus combines to form single vein running to caudal vena cava

• Anastomoses between arteries & veins.

Describe the origin, insertion and function of the cremaster muscle.

• Origin:

- Internal Abdominal Oblique

- Caudal to Deep Inguinal Ring

Runs along parietal vaginal tunic

- Supported by spermatic fascia

• Insertion: Parietal tunic of testis

• Function: Allows retraction of testis to increase testicular heat

What regulates the descent of the testis and how is this done?

Gubernaculum testis

• Mesenchymal structure

• Expanding from abdominal testis to inguinal canal to scrotum

• Incorporates peritoneum, partially forming vaginal tunic

• Descent mediated by swelling of gubernaculum which opens inguinal canal & draws testis into scrotum

What are the three layers of the gubernaculum testis?

Three layers

- Pars propria: within visceral layer of vaginal process

- Pars vaginalis: around parietal layer of vaginal process

- Pars infravaginalis: distal to invagination

What is cryptorchidism?

Failure of testes to descend from abdomen/inguinal canal - retained testicle.

• Testes should be in scrotal sac by 2 months of age

• Undescended testes commonly located in region of inguinal canal

• May also be found in abdominal cavity

• May be unilateral or bilateral

• Undescended testes: more likely to develop neoplasia

• May recommend castration

Dogs and cats do not have _____ glands or _______ glands.

Bulbourethral glands are found in ____ but not ____.

ampulla, vesicular

cats, dogs

What is the most significant pelvic gland in carnivores and what is it’s function?

• Prostate

- Most significant gland in carnivores

- Function: Produce bulk of semen volume

Describe the location and structure of the urethra.

• Runs from internal orifice to external orifice

• Mucosal tube with vascular submucosa & muscular tunic

What are the two regions of the urethra?

- Pelvic or Internal Urethra

• Running through pelvic canal

- Penile or External Urethra

• Through penis itself

Where is the pelvic urethra contained?

• Initially contained within prostate

• Dorsal ridge in lumen:

• Seminal Colliculus

• Openings of deferent ducts

• Openings of prostatic ducts

• Caudally lies on pelvic floor

• Muscular sleeve: urethralis muscle (striated)

• Contains thin layer of cavernous tissue

• Widens caudal to prostate

• Narrows over pelvic outlet

Describe the location of the penile urethra.

• Runs through penis between cavernous tissues

• Runs through groove of os penis

• Potential obstruction by bladder stones

Describe the location and function of the ampullary glands.

• Dilation of terminal vas deferens before entering prostrate

• Lies dorsal to bladder

• Not present in cat or dog

• Lined with glandular tissue

• Function: Produce a small proportion of ejaculate

• Capsule & septa with smooth muscle

• Assist in expulsion of fluid

Describe the function of the prostate.

• Produces bulk of seminal fluid (exocrine gland)

What two parts can the prostate be divided into?

Two parts:

- Large compact part around proximal urethra (bilobed)

- Vestigial disseminated part within urethral mucosa

Describe where the prostate is located when the animal is small, mature, and in cats.

• Within pelvic cavity when small

• May be intra-abdominal if enlarged or in entire mature dogs

• Smaller in cats

Describe how the prostate is divided.

• Divided into left & right lobes by dorsal groove & internal septum

• Smooth capsule with smooth muscle

• Prostate completely encloses urethra (dogs)

• Ventral urethra free (cats)

• Drains via multiple small ducts into urethra

• Vascular supply via prostatic artery

What may cause prostatic enlargement?

• Most commonly due to hormonal influence

• Benign Prostatic Hyperplasia

• Seen with inflammation, neoplasia & cystic disease too

• May compress rectum (or urethra)

• Leading to constipation

How can the testis, urethra and prostate be best imaged?

• Testis: Easily imaged using ultrasound to detect testicular masses

• Urethra: Contrast radiography (pelvic urethra difficult to see via ultrasound)

• Prostate: Ultrasound (best), can see on radiographs if enlarged