Male Repro Anatomy

Big Picture

Male reproductive system consists of:

• Spermatic Cord

• Testis

  • Produce spermatozoa and testosterone

  • Also produce inhibin, estrogen, proteins

• Epididymis

  • Provides environment for final maturation of spermatozoa

  • Serves as a storage organ for sperm

• Accessory sex glands

  • Produce seminal plasma

• Penis

  • Copulatory organ

Two Basic Compartments

Internal (gonads and tubular aspect)

• Gonads: the testicles/testes (what makes the sperm)

• Tubular component: excurrent ducts (epididymis and ductus deferens)

• Accessory components: glands and spermatic cord

External

• Penis and scrotum

Spermatic Cord

• Extends from inguinal ring to attachment on dorsal pole of testis

• Suspends testis in the scrotum

• Provides pathway to/from the body for testicular vasculature, lymphatics, and nerves

• Houses ductus deferens, cremaster muscle, and pampiniform plexus (vascular network)

Functions of the Spermatic Cord

• Provide vascular, lymphatic, and neural connection to the body

• Provide a heat exchanger

  • Decreases temp so that spermatogenesis can occur

  • Extra-abdominal location and concurrent heat exchange

• House the cremaster muscle

Testicular Artery and Veins

Highly specialized structures that are important for proper temperature control of the testis

• Artery: branches from the abdominal aorta that starts straight then becomes highly convoluted after passing through the inguinal canal

• Veins: branch into an elaborate network that forms finger-like wrappings surrounding the artery

  • Venous network = pampiniform plexus

Testis Temperature: Vascular Heat Exchange

Complex network of spermatic artery and veins forms a countercurrent heat exchanger

• Heat from the warm arterial blood from the body is transferred to the cooler venous blood leaving the testes surface

  • The blood going to the testes is cooled by direct heat loss from skin of scrotum

  • Exchange primarily occurs via diffusion

• Maintenance of lower testicular temp is obligatory for spermatogenesis

Blood Flow/Pressure

• Blood pressure determines blood flow

• To move fluid from point a to b, you need a pressure gradient that needs to be high: blood pressure difference is key

• Production of pressure gradient by the heart is high as blood leaves

• In the testicle it drops/slows which is good because we’re trying to exchange heat

  • To exchange optimally, it’s best to do it slower/over long periods of time

Testosterone Transfer

The close relationship b/w the venous and arterial blood supply in the spermatic cord results in some opportunity for exchange of testosterone

• Moves from vein to artery (at high [ ]s in the vein)

Cremaster Muscle

Primary muscle supporting the testis and coursing the length of the spermatic cord

• Also helps control temperature via a pumping action on the pampiniform plexus that facilitates blood flow/enhances cooling efficiency

  • Contracts/relaxes

• Damping pulse pressure

Scrotum

A two-lobed sac that protects and supports the testes

• Is required for proper temperature regulation (testes skin conveys sensory information on heat)

• Consists of four major layers: the skin, tunica dartos, scrotal fascia, and parietal vaginal tunic

• Sweat glands in the scrotal skin are vital to temp regulation (sweating cools by evaporative heat transfer)

Tunica Dartos

Mesh-like smooth muscle layer that lies just beneath the scrotal skin

• Can maintain sustained contractions

• Allows the testes to be held close to the body for longer periods during cold temperatures and vice versa in the heat (relaxes, pushes testes farther away from the body)

Testes: Big Picture

Primary reproductive organ whose primary function is to produce:

• Spermatozoa

• Hormones and proteins

• Fluids

Testes: What It Produces

Paired organs, vary in size/shape among species

• Produce spermatozoa, testosterone, inhibin, estrogens, proteins, and fluid that originates from seminiferous tubules

  • Fluid = a vehicle in which spermatozoa are suspended/facilitates their removal from testes

Testes: Structure

Consist of the:

• Testicular capsule

• Parenchyma

• Mediastinum

• Rete tubules

Testicular Capsule

• Covering of the testis; composed of two layers:

  • Visceral vaginal tunic

  • Tunica albuginea (connective tissue)

    • Seeds finger-like projections into the parenchyma which join with the mediastinum

Testicular Parenchyma

Consists of:

• Seminiferous tubules

  • Contain Sertoli cells

  • Eventually all lobules dump into mediastinum

  • Mediastinum has tubules that are continuous w/ epididymis

• Interstitial cells of Leydig

  • Produce testosterone

• Capillaries

• Lymphatic vessels

• Connective tissue

Testicular Lobule

The functional unit of the testicle, contains the seminiferous tubule

• Connective tissue separates lobules an individual tunica vasculosa surrounds each lobule/separates then

  • So an injury to one lobule won’t affect its neighbor

• Two distinct regions: seminiferous tubule (cytogenic function: where spermatogenesis occurs) and interstitial compartment (hormonal function/testosterone)

Tubular Compartment of the Parenchyma

AKA the seminiferous tubules consists of:

• Seminiferous epithelium

  • Contains the basal compartment and the adluminal compartment

• Sertoli cells

  • Somatic cells that hosts a max number of developing germ cells

  • Contain receptors for both FSH and testosterone

• Developing germ cells

• Peritubular cells

Blood Testis Barrier

Prevents immunologic destruction of developing germ cells

• The haploid gamete that’s formed in the seminiferous tubule needs to be separated from the rest of the body

• These molecules would recognize developing germinal elements as foreign bodies bc they divide by mitosis (normal cells are diploids), so the immune system would destory it

Sertoli Cells: Junctional Complexes

Form the blood-testis barrier

• Seminiferous tubule is striated longitudinally

• The sperm are at different stages of development along the length of the tubule

• Looking at a cross section: the tubule is also striated from basal aspect to luminal aspect

  • Progressively more differentiated going from basal compartment to lumen

Excurrent Duct System

Consists of:

• Efferent ducts

  • Convey newly formed spermatozoa and tubular fluid into the epididymal duct

• Epididymal duct

• Ductus deferens

Epididymis

Provides the environment for final maturation of spermatozoa (sperm is made in the testicle and stored in the epididymis)

• Also serves as a storage reservoir for spermatozoa

• Organized into the head (caput), body (corpus), and tail (cauda)

• Also controls the sperm exit from the repro system (ejaculation)

Epididymis Head

Spermatozoal characteristics:

• Not motile

• Not fertile

• Proximal cytoplasmic droplet

Epididymis Body

Lies parallel to the ductus deferens; spermatozoal characteristics:

• Some expression of motility

• Some expression of fertility

• Translocating cytoplasmic droplet

• Can bind to oocytes

Epididymis Tail

Contains the proximal and distal tail

• Continuous w/ ductus deferens: sperm here move through the ductus deferens and into the pelvic urethra during ejaculation

• Normal motility

• Fertile potential

• Distal droplet

• Can bind to oocytes

Extragonadal Reserve (ECR)

Total spermatozoal content of the epididymal duct, the ductus deferens, and the ampulla

• Number of sperm remains constant (rate that sperm leaves testicles → epididymis = rate that sperm leaves epididymis)

• Depletion of the reserves in the tail can occur rapidly w/ repeated ejaculations (if you’re continually forcing the animal to ejaculate)

  • If the sperm count decreases/reserve depletes, then the animal ejaculates sperm cells that aren’t mature

  • Distal droplets in ejaculated sperm confirm that the sperm is not mature/not capable of fertilization

• When the animal doesn’t ejaculate: the sperm cells die (vast majority of what happens)

Seminal Plasma

Non-cellular fluid vehicle for spermatozoal delivery to the female

• Not required for fertility

• Is produced by the: epididymis, ampulla, and vesicular glands (seminal vesicles), prostate gland, bulbourethral glands (Cowper’s glands)

• Contains balanced ions, plasma proteins, etc. that are all important in protecting the sperm cells from site of ejaculation to site of deposition

Penis

Copulatory organ composed of the base (root), the shaft (main portion) and the glans penis (specialized distal end)

• Means by which urine is removed and by which semen is removed and transported to the female

Glans Penis

Tip of penis, lots of species variation

• Represents outflow for urine or semen

• Urethral process = where sperm or urine exits

• Urethra itself = surrounded by tissues that are important for mating

• Urethra needs to move thru pelvic canal and exit the body/is continuous w/ the penis itself

Corpus Spongiosum and Corpus Cavernosum

Erectile tissues of the animals penis

• Fill with blood during mating

• Allows penis to enlarge

• Blood drains and pens returns to un-stimulated state when mating is done

Sigmoid Flexure

• Present in species with a fibroelastic penis

• Allows the penis to be retracted inside the body (within the sheath) until simulation/erection occurs)

• Maintained by the retractor penis muscles (smooth muscle)

Muscles Associated w/ Pelvic Urethra and Penis

All responsible for contracting and conveying material

• Urethralis

• Bulbospongiosus

• Ischiocavernosus

  • Makes up part of ability to suspend penis w/in the body

  • Outside the pelvic canal

• Retractor penis