Male Reproductive Anatomy

Anatomy of Male Reproduction

• Primary sex organs consist of the testes.
• The testes produce male gametes (sperm) and testosterone (male sex hormone).
• Secondary sex organs are present.
• The duct system transports sperm, exemplified by the ductus deferens.
• Accessory organs are present to provide fluids.
• Examples of accessory organs include the prostate gland, seminal vesicles, and bulbourethral glands.

Learning Objectives

• Ability to discuss and compare the reproductive anatomy of male domestic species.
• This includes the scrotum, testes, ducts, accessory sex glands, penis, and prepuce.
• Describe erection and ejaculation briefly.

The Main Anatomic Components

• Spermatic cord
• Scrotum
• Testis
• Excurrent duct system
• Accessory sex glands
• Penis
• Muscles for protrusion, erection, and ejaculation

Sperm Production & Semen Composition

• Spermatozoa are male gametes capable of fertilization.
• Semen is composed of spermatozoa and seminal plasma.

Spermatic Cord

• Extends from the inguinal ring to the dorsal pole of the testis.
• It provides a pathway to and from the abdomen, housing nerves, lymphatics, and the cremaster muscle.
• It contains extensive testicular vasculature and the ductus deferens for sperm transport.

Spermatic Cord Details

• It suspends the testis through the inguinal canal.
• Pathways for vasculature, lymph, and nerves exist from the body to the testis.
• Houses the ductus deferens for sperm transport.
• The cremaster muscle supports the testis and aids temperature control through the pampiniform plexus' pumping action.
• The pampiniform plexus provides a heat exchanger.

Testis Temperature Regulation

• Testes must be kept 4-6°C below body temperature for normal function.
• High temperatures can cause reduced sperm motility.
• They can also result in reduced embryo survival in normal ewes mated to heat-treated rams through DNA damage.
• Temperature is controlled by the pampiniform plexus and tunica dartos.

The Pampiniform Plexus

• It is an extensive venous network that facilitates keeping the testis at 4-6°C lower than body temperature.
• This acts as a counter-current heat exchanger.
• Venous blood from the testis cools arterial blood to the testis.
• Venous blood requires cooling by direct heat loss through the skin of the testis.
• It helps with pulse pressure elimination.
• Testicular artery pressure is 40mmHg, reduces to 10mmHg after the Panpiniform Plexus.

Cremaster Muscle

• The primary striated muscle supports the testis.
• It aids in temperature control
• The contraction of this muscle results in a "pumping" action of the PP (Pampiniform Plexus?).
• It increases blood flow and counter-current exchange.
• Leads to testis elevation short-term during sexual excitation and fear.

The Scrotum

• A 2-lobed sac consists of skin, tunica dartos, scrotal fascia, and parietal vaginal tunic
• The skin has lots of sweat glands to control testicular temperature
• Thermal-sensitive nerves govern the degree of sweating and respiration rate.
• It is a thermo sensor, a cooler, and a protective sac.

Tunica Dartos

• Mesh-like smooth muscle sustains contractions.
• It allows testes to be held against the body (wrinkles).
• It allows relaxation for increased surface area for active cooling (no wrinkles).
• It is under androgen control.
• Short scrotumed bulls and artificial cryptorchids exemplify androgen control.

Scrotal Temperature Control

• Sensory neurons in the scrotal skin and thermosenitive neurons in the hypothalamus are present.
• Muscles like the tunica dartos and cremaster muscle contribute.
• Blood flow occurs via the pampiniform plexus.
• Other reflexes include reflex sweating and reflex polypnea.

Testes Functions

• Paired organs.
• They produce spermatozoa, testosterone, and other hormones.
• The testes produce fluids to transport sperm.

Details of the Testes

• Testicular capsule: Has a visceral vaginal tunic and the tunica albuginea which helps to pump sperm around.
• Parenchyma: Contains the tubular compartment (seminiferous tubules) and interstitial compartment (interstitial cells of Leydig, capillaries, lymph vessels, and connective tissue).
• Mediastinum: Central connective tissue core which is continuous with the tunica albuginea
• Rete tubules: These are tiny tubes which transport sperm out of the testes toward the epididymides.

Testicular Parenchyma Compartments

• Peripheral adluminal compartment
• Deep adluminal compartment
• Basal compartment
• Interstitial compartment

Excurrent Duct System

• Efferent ducts convey sperm and fluids.
• The epididymal duct assists with final maturation and storage and is composed of the head (caput), body (corpus), and tail (cauda).
• It is highly convoluted and 30-60m long.
• The ductus deferens delivers sperm to the pelvic urethra.

Epididymis

• The head absorbs fluids (PH) and secretes fluids (DH).
• The body is parallel to the DD, and is involved in translocation of proximal droplets.
• The tail functions in ejaculation storage and transports them to the ductus deferens.

Seminal Plasma

• It is a non-cellular fluid vehicle for spermatic delivery to the female.
• Produced by: -Epididymis -Ampulla (enlargement of ductus deferens) -Vesicular glands (seminal vesicles) -Prostate gland -Bulbourethral glands (Cowpers glands) – small in bull stallion and ram
• Contains a large variety of components and ions.

Comparative Anatomy: Accessory Sex Glands

• Bull: Ampulla, vesicular glands, prostate gland, and bulbourethral glands are present.
• Stallion: Ampulla, vesicular glands, prostate gland, and bulbourethral glands are present.
• Ram: Ampulla, vesicular glands, prostate gland, and bulbourethral glands are present.
• Boar: Vesicular glands, prostate gland, and bulbourethral glands are present.
• Dog: Prostate gland is present.

The Penis

• Copulatory organ
• It consists of the base, shaft, and glans penis featuring lots of nerves to initiate ejaculation.
• Boars, bulls, and rams have a fibroelastic penis
• With limited erectile tissue and the sigmoid flexure (allowing penis to be retracted within the sheath – controlled by retractor penis muscles), and no increase in diameter
• Shaft is spongy erectile tissue (corpus cavernosum, corpus spongiosum surrounds penile urethra).

Penis (Cross Section)

• Multi-cavernous body capable of becoming erect.
• Surrounds the urethra.
• Retractor penis muscles serves in support and affects penis length (flexure).
• Bulbospongiosus muscle contracts for semen transport.

Musculo-cavernosum vs Fibroelastic Penises

• Contrasting tissue types of penises.

Erection Physiology

• Blood is pumped by the ischiocavernosus muscle into the corpus cavernosum and corpus spongiosum.
• Elongation and straightening of the penis results (sigmoid flexure).
• Relaxation of the retractor penis muscle.
• Ultimately culminates in the penis protruding from the prepuce.

Sheath and Prepuce

• The sheath is the hair-covered skin running from cranial to the scrotum to the umbilicus.
• The prepuce is the pink skin contained within the sheath.

Stallion Prepuce

• Consists of several folds of skin.

Comparative Sperm

• Considerable morphological variation is present between species.
• The basic structure and function remains the same.

Neuroendocrine Reflex: Emission

• Sensory stimulation leads to stimulation of nerves in the supraoptic and PVN.
• Oxytocin is released from the PP
• Contractions of the smooth muscle occur in the distal tail of the epididymis and DD.
• It involves the transport of sperm into an ejaculatory position.

Male Erection: Step-by-Step

• Step 1: Erotogenic stimuli cause sensory nerves to fire.
• Step 2: Sensory nerves activate the "Reproductive Behavior Center" in the hypothalamus.
• Step 3: Stimulation of parasympathetic nerves innervate penile arterioles.
• Step 4: Parasympathetic nerve terminals release nitric oxide (NO).
• Step 5: Nitric oxide initiates a biochemical cascade that causes erection.

Intromission

• Successful entry of penis into vagina.
• Time varies depending on ejaculate volume: -Ram: 2 seconds -Stallion: <1 minute -Boar: 7 minutes
• After ejaculation, the pressure is removed, and the sigmoid flexure withdraws the penis into the prepuce.

Ejaculation Dynamics

• Ejection of semen from the penis with smooth muscle contractions, especially the urethra and bulbospongiosus muscles.
• The free end of some species' penis spirals.