Animal Repro Practical Male

spermatogonia

diploid stem cells; self-renew and give rise to primary spermatocytes

primary spermatocytes

undergo meiosis I

secondary spermatocytes

undergo meiosis II (short-lived)

spermatids

haploid cells that differentiate into sperm (spermiogenesis)

spermatozoa

fully formed (but not yet functionally mature sperm cells)

Sertoli cells

nurse cells - don’t become sperm themselves but physically support and nourish developing germ cells at every stage, form the blood-testis barrier, phagocytose shed cytoplasm/droplets and defective cells, and secrete fluid that helps move sperm toward the rete testis. Also secrete Androgen Binding Protein (ABP) and, more broadly in reproductive physiology, inhibin (a hormone that feeds back on FSH)

Leydig Cells

located in the interstitial tissue outside the tubules; produce testosterone, which diffuses into the tubule to drive spermatogenesis locally

Myoid Cells

contract peristaltically to move newly formed sperm through the tubule toward the rete testis

spermatogensis is driven by

hypothalamic-pituitary-gonadal axis

GnRH

released from the hypothalamus, stimulates the anterior pituitary gland

LH (luteinizing hormone)

from the anterior pituitary gland, acts on leydig cells → stimulates testosterone production

FSH (follicle-stimulating hormone)

from the anterior pituitary gland, acts on Sertoli cells → supports spermatogenesis directly and stimulates ABP secretion

Testosterone

produced by Leydig cells; diffuses into the tubule and concentrated locally by ABP, drives spermatogenesis and maintains the germinal epithelium. This is also the hormone responsible for secondary sex characteristics, libido, and accessory gland function

Inhibin

secreted by Sertoli cells; provides negative feedback specifically on FSH release from the pituitary

LH Pathway

LH → Leydig Cells → Testosterone

FSH pathway

FSH + testosterone (via ABP) → Sertoli cells → spermatogenesis

Spermatogensis (testis, seminiferous tubules)

making the sperm cell

Epididymal Maturation (epididymis)

making sperm cell functional - motility, fertilizing ability

Seminiferous Tubules

site of spermatogenesis; germinal epithelium where sperm are produced. Sertoli cells here support developing sperm and form blood-testis barrier. no direct secretion, but sertoli cells secrete Androgen Binding Protein (ABP) which keeps local testosterone concentrated

Rete Testis

network of channels collecting sperm from all seminiferous tubules and funneling it toward the efferent ductules

Efferent Ductules

absorb the majority of testicular fluid, concentrating the sperm before it enters the epididymus

Caput Epididymis

sperm maturation begins here; stereocilia absorb fluid, further concentrating sperm. no hormones secreted but bathed in high local testosterone (via ABP carried from the testis)

Corpus Epididymis

continued maturation of spermatozoa (membrane changes, nuclear condensation, etc.)

Cauda Epididymis

final maturation and storage site - only sperm here are capable of fertilization. Maintains a low pH, low O2 environment that arrests sperm metabolism for long-term storage

Vas deferens

muscular tube that transports sperm during ejaculation via peristaltic contraction (low-level at rest, strong with arousal)

Ampulla

terminal, dilated portion of the vas deferens near the bladder; acts as a minor sperm reservoir, but sperm here age rapidly (no protective secretions)

Colliculus Seminalis

a small elevation in the pelvic urethra where the ejaculatory ducts (vas deferens + seminal vesicle duct). empty into the urethra - essentially a junction point

Urethra

shared passage for both urine and semen; conduct semen out of the body during ejaculation

Cowpers Gland/Bulbourethral

paired accessory gland located near the pelvic urethra. Produces a clear, pre-ejaculatory fluid that flushes and cleans the urethra of urine residue before sperm passes through - protecting sperm from the hostile, acidic urine environment. Major contributor to seminal plasma volume along with prostate and seminal vesicles. Boars produce gel fraction of the ejaculate to plug sow’s cervix after mating.

Tunica Alubinea

connective tissue that holds testis together, aids sperm movement

Pampiniform Plexus

dense network of veins surrounding the testicular artery in the spermatic cord; performs counter-current heat exchange, cooling arterial blood before it reaches the testis (~4 degree drop in ram)

Ischiocavernosus Muscle

skeletal muscle at the base of the penis; rhymically compresses the crura, boosting pressure inside the corpus cavernosum to help achieve and maintain erection

Crura

the proximal “roots” of the corpus cavernosum, anchored to the ischial/pubic bones; fill with blood during erection to anchor and rigidify the base of the penis

Prostate

accessory sex gland; secretes prostatic fluid that contributes to seminal plasma volume and buffering (major contributor along with seminal vesicles and cowper’s gland)

Urethralis Muscle

skeletal muscle surrounding the pelvic urethra; contracts rhythmically during ejaculation to help propel semen (and normally urine) through the urethra

Mediastinum

house rete testis (not in stallions)

Bulls and Rams. Boars do but it’s corkscrew-shaped

animals fibroelastic penis

stallion

animals with vascular penis

what animal has the largest ejaculate volume?

boar (225-400 mL). low concentration of sperm

what animal has the lowest ejaculate volume?

rams

sperm transport

seminiferous tubules → rete testis → efferent ductules → caput epididymis → corpus epididymis → cauda epididymis → vas deferens → ampulla → colliculus seminalis → urethra