REPRODUCTIVE SYSTEM: MALE REPRODUCTIVE TRACT

Organs of male reproductive system

Testes, a system of ducts (epididymis, ductus deferens, ejaculatory ducts, and urethra), accessory sex glands (seminal vesicles, prostate, and bulbourethral (Cowper’s) glands), and several supporting structures such as scrotum and penis

Semen

Sperm + secretions provided by the accessory sex glands
10% sperm, 60% seminal vesicle fluid, 30% prostatic fluid, other secretion contribute small amounts
pH ~7.5 with 2.5 mL per ejaculate w/ ~20 million sperm/mL

Function of testes

Produce sperm and androgens 

Testes

Develop near kidneys in posterior portion of abdomen
Descend into scrotum through inguinal canals during late 7th month of foetal development

Cryptorchidism

Failure of testes to descend
3% of male babies & result in infertility

Orchidectomy

Removal of a testis

Tunica vaginalis

Serous membrane derived from peritoneum and forms during descent of tests
Partially covers testes

Hydrocele

Collection of serous fluid in tunica vaginalis cause by injury to testes or inflammation of epididymis 

Tunica albuginea

White fibrous capsule composed of dense irregular CT
Extends inwards to form septa that divides testis into lobules

Seminiferous tubules

1 - 3 tightly coiled tubules in lobules
Produces sperm via spermatogenesis 
Contains spermatogenic cells and sustentacular (Sertoli) cells

Spermatogenic cells

Spermatogonia (2n) → 1^o spermatocyte (2n) → 2^o spermatocyte (n) → spermatid (n) → sperm cell (n)

Mitotic divisions

Spermatogonia differentiates via mitosis, one daughter cell remains undifferentiated and the others continues to divide
Occur in basal compartment of seminiferous tubules
On completion, spermatogonia move between adjacent Sertoli cells to adluminal compartment of seminiferous tubules

Meiotic division

Spermatogonia cells in adluminal compartments are labelled 1^o spermatocytes
They undergo meiosis I to produce 2 x 2^o spermatocytes
2^o spermatocytes undergoes meiosis II rapidly to produce 4 x spermatids

Spermiogenesis

Round spermatids differentiate their shape and become sperm (spermatozoa)
Sperm moves into lumen, forming a tail and head
Excess cytoplasm of spermatid lost into a structure called residual body, cleaned up by Sertoli cells

Structure of sperm

Head contains DNA in nucleus and covered by acrosome
Tail is divided into a neck, mid piece, principle piece, and end piece
Neck just behind head contains centrioles that from microtubules that make up rest of tail
Mid piece has high mitochondria arranged in a spiral for energy
Principle piece is the longest portion
End piece is tapering portion  

Spermiation

Sperm are related from their connections to Sertoli cells

Acrosome

Compartment filled w/ enzymes (hyaluronidase & protease) required for egg penetration

Primordial germ cells

Arise from yolk salt and enter testes during 5th week of development 
Differentiate into spermatogonia, which remain dormant until puberty

Sertoli cells

Among spermatogenic cell in seminiferous tubules
Extend from BM to lumen of tubule
Tight junctions join Sertoli cells together to form blood-testis barrier

Function of Sertoli cells

Nourish spermatocytes, spermatids, and sperm
Phagocytise excess spermatid cytoplasm
Control movements of spermatogenic cells and release of sperm into lumen
Produce fluid for sperm transport and androgen binding protein
Regulates effects of testosterone and FSH via secreting inhibin

Inhibin

A hormone that suppresses effects of FSH

Interstitial (Leydig) cells

Cluster of cells in the spaces between adjacent seminiferous tubules
Secrete testosterone by LH binding to surface receptors

Blood-testis barrier

Substances must past through Sertoli cells to reach developing sperm
Prevents immune response against spermatogenic cells
Spermatogonia cells are not included

Spermatogenesis

Occurs after puberty by reactivation of spermatogenic cells
300 - 600 sperm per gram of testis tissue per second
3 phases: Mitotic division, Meiotic division, Spermiogenesis
Takes 65 - 75 days
Cytokinesis is not completed = cytoplasmic bridges

Cytoplasmic bridges

Connects dividing cells through entire development
Half of sperm contain X chromy may carry genes needed for spermatogenesis
Other half contain Y chromy which may be lacking in those genes

Functions of system of ducts

Transport, store, and assist in maturation of sperm

Function of accessory sex galnds

Secrete most of liquid portion of semen

Function of penis

Contains the urethra for a passageway to the external environment, for both sperm and urine

Scrotum

Loose skin and underlying subcutaneous layer that hangs from the root of the penis
Externally separated by a median ridge called raphe 
Internally each testis is seperated by scrotal septum

Scrotal septum

Subcutaneous layer and muscle tissue called dartos muscle (bundles of smooth muscle fibres)
Dartos muscle also found in subcutaneous layer of scrotum

Cremaster muscle

Series of small bands of skeletal muscle descending as an extension of internal oblique muscle through spermatic cord to surround each testis

Function of scrotum

Location and contraction regulate temp. of testes
Normal sperm production is 2 - 3 ^oC below core body temp.
Maintained by being outside of pelvic cavity
Cold temps. → cremaster & dartos muscles contracting → testes closer to body to absorb heat → scrotum becomes tight and wrinkled to reduce heat loss

ABP

Androgen-binding protein is secreted by Sertoli cells into blood and lumen of seminiferous tubules & interstitial fluid around spermatogenic cells
Stimulated by FSH & test. acting synergistically
Transport protein for androgens (Binds to test. to keep conc. high)

Prenatal development

Test. stimulates male pattern of development of reproductive system ducts and descent of testes
DHT stimulates development of external genitalia
Test. converted to oestrogens in brain for brain development  

Development of make sexual characteristics

Test. + DHT stimulate development and enlargement of male sex organs and secondary sexual characteristics

Development of sexual function

Androgens contribute to male sexual behaviour, spermatogenesis, libido (males and females)

Stimulation of anabolism

Androgens are anabolic hormones
Stimulate protein synthesis 

Male infertility

Reduce sperm count < 20 million/mL

Oligospermia

A reduced number of sperm count < 15 million/mL

Azoospermia

Obstructive azoospermia - blockages preventing sperm transport

Non-obstructive azoospermia - body not producing enough sperm

Immotile

Sperm can’t swim

IVF

In vitro fertilisation

Oocytes are harvested and fertilised outside of the body then replanted inside the uterus
Requires 50000 motile sperm

ICSI

Intracytoplasmic sperm injection

A single sperm is captured and injected into an oocyte
Can be immotile
Can be collected by biopsy of testes

Flow of ejaculate

Pressure generated by fluid secretion of Sertoli cells

Seminiferous tubules → Straight tubules → Rete testis → Coiled efferent ducts in epididymis → Vas deferens → Ejaculatory duct → Seminal vesicles → Prostate → Prostatic urethra → Intermediate membranous urethra → Penile urethra → External urethral orifice

Prostatic fluid → Sperm → Seminal vesicle fluid

Epididymis 

Where sperm acquire ability to be motile and fertilise 10 - 14 days
Reabsorbs liquid around sperm & old stored sperm (not ejaculated) to make it more concentrated
Mostly consists of tightly coiled ductus epididymis
Efferent ducts of testis join ductus epididymis at the head
Helps propel sperm into ductus deferens during sexual arousal by peristaltic contraction of smooth muscle

Head

Larger and superior protein of the epididymis

Body

Narrow mid portion of the epididymis

Tail

Smaller and inferior portion of the epididymis
Distal end continues as ductus (vas) deferens

Ductus epididymis

Lined w/ pseudostratified columnar epithelium, encircled by layers of smooth muscle
Free surfaces of columnar cells contain stereocilia

Stereocilia

Long & branching microvilli that increases surface area for the reabsorption of degenerated sperm

Ductus (vas) deferens

45 cm long and from the epididymis up and around the bladder then back down to join ejaculatory duct
Dilated terminal portion of ductus deferens is the ampulla
May store sperm for several months and reabsorb old sperm
Conveys sperm during sexual arousal from epididymis to urethra via peristaltic contractions 

Urethra 

Prostatic urethra long and passes through the prostate
Intermediate membranous urethra passes through deep muscles of perineum
Spongy urethra passes through the corpus spongiosoum of penis, ending at external urethral orifice

Seminal vesicles

Secretory glands that secrete an alkaline, mucoid (sticky) substance containing fructose, prostaglandins (induce contractions in FRS), and clotting proteins (Hold sperm in FMS)
Contents are emptied into ejaculatory duct directly after sperm is ejected from ductus deferens and washes sperm down the duct

Function of seminal vesicles

Neutralises acidity of male urethra and female reproductive system
Sperm motility and stimulate contractions in female reproductive tract
Coagulation after ejaculation

Prostate

Doughnut shaped organ (size of golf ball)
Secretes prostatic fluid into urethra ahead of sperm during ejaculation

Prostatic fluid

Slightly acidic (pH 6.5) & milky fluid containing citric acid/citrate, several proteolytic enzymes (prostate-specific antigen/PSA, pepsinogen, lysozyme, amylase, & hyaluronidase), acid phosphatase, seminalplasmin, phosphate, and calcium
Enzymes break down coagulant to inhibit sperm being stuck in FMS
Enter the prostatic urethra through many prostatic ducts

Function of prostatic fluid

ATP production via CAC
Break down clotting proteins from seminal vesicles
Acid phosphatase is unknown
Antibiotic that can destroy bacteria
Contribute to sperm motility and viability

Benign prostatic hyperplasia

Excess growth of the prostate that squeezes the urethra
Causes difficulty in voiding the bladder, weakening of bladder, urinary infections and/or kidney problems

Susceptibility increases w/ age

Treatments for BPH

Prostatectomy
Selective 5-α-reductase inhibitors (Finasteride, dutaseride, etc.) Stops prostate enlarging or shrinking it but requires long term therapy

Treatments for prostate cancer

PSA screening
Watchful waiting
Androgen depletion by 5-α-reductase inhibitors (Finasteride), castration, inhibitors of androgen synthesis
Inhibition of test. action (block androgen receptors)
Prostatectomy

Penis

Consists of body, glans penis, and root
Contains the urethra
Made up of erectile tissue

Body of penis

Composed of 3 cylindrical masses surround by tunica albuginea
Two dorsolateral masses called corpora cavernosa penis (main erectile tissues)
Smaller mid ventral mass called corpus spongiosum penis (prevents closing of urethra during erection)

Erectile tissue

Numerous blood sinuses lined by endothelial cells and surrounded by smooth muscle and elastic CT

Erection

Release of nitric oxide (NO) & prostaglandin E1 → smooth muscle of corpora cavernosa relaxes → blood fills cavernous space → engorgement of corpora reduces venous outflow

Relaxation requires cGMP as a secondary messenger
cGMP is broken down by phosphodiesterase

Viagra (Sildenafil)

Inhibits phosphodiesterase (type 5) → increased cGMP → relaxation of arteries supplying corpora cavernosa → erection