34. The anatomy, histology and development of the testis, epididymis and ductus deferens.

The anatomy, histology and development of the testis, epididymis and ductus deferens.

Anatomy of Testis, Epididymis & Ductus Deferens

Scrotum:
cut pouch of thin pigmented skin and underlying tunica dartos, a facial layer cont w/ superficial penile fascia and superficial perineal fascia

Function:

• NO fat – to maintain temperature lower than rest of body
• contains testis and epididymis
• the dartos m. w/in tunica dartos attaches to the skin – it controls the wrinkling of skin of scrotum
  
  • contracted and wrinkled when cold (or sexually stimulated), bring testis in close contact w/ body to conserve heat
  • relaxed when warm and hence is flaccid and more pendulous to release and spread heat
  • By transferring the testicles into the scrotum a testicular temperature 2-3 ºC lower than body temperature is attained.  Lower temperature is necessary for producing sperm cells.

Structure

• divided into R & L compartments via scrotal septum (int) and scrotal raphe (ext)
• superficial dartos fascia – has no subcutaenous fat, like Scarpa’s fascia of the abdomen

Testis
* considered retroperitoneal

General Info:

• covered by visceral layer of tunica vaginalis testis – except where in contact w/ epididymis – covered by tunica albuginea
• attached to scrotum via gubernaculum testis –
  
  • remnant of embryonic caudal ligament
    
  • responsible for pulling down testis from ab cavity –> scrotum
  • analogous to round ligament in female

Function: produce spermatozoa (spermatogenesis) and secrete sex hormones

Spermatogenesis: production of spermatids, not mature sperm cells yet.  (spermiogenesis covered in next topic, w/ seminal vesicle and prostate)

Anim: http://highered.mcgraw-hill.com/olc/dl/120112/anim0043.swf

• Spermatogenesis is initiated in the male testis with the beginning of puberty. This comprises the entire development of the spermatogonia (former primordial germ cells) up to sperm cells. The gonadal cords that are solid up till then in the juvenile testis develop a lumen with the start of puberty. They then gradually transform themselves into spermatic canals They are termed convoluted seminiferous tubules (Tubuli seminiferi contorti) . They are coated by a germinal epithelium that exhibits two differing cell populations: some are sustentacular cells (= Sertoli’s cells) and the great majority are the germ cells in various stages of division and differentiation.
• development of the germ cells begins with the spermatogonia at the periphery of the seminiferous tubule and advances towards the lumen over spermatocytes I (primary spermatocytes), spermatocytes II (secondary spermatocytes), spermatids and finally to mature sperm cells.
• The Sertoli cell is essential for spermatogenesis as it provides support for the developing sperm cells – moving them towards the lumen of the semiferous tubule as they develop until maturity when they are released. The Sertoli cell also reduces motility and capacitation (initiation of the acrosome reaction) of the sperm cells so viability is maintained.
• Spermatozoa are produced in seminiferous tubules in the testes. They start off as spermatogonia , undergoing mitosis becoming a type A spermatogonium or a type B spermatogonium.
  • Type B spermatogonia become primary spermatocytes.
  • Primary spermatocytes go through a meiotic division to become secondary spermatocytes, which undergo another meiotic division to become spermatids.
  • Type A spermatogonia stay as spermatogonia, and do not change. They act as stem cells and will divide again producing more Type A and B cells.
• The primary spermatocytes contain twice the DNA of a normal body cell (2 × 2N).
  • Each primary spermatocyte divides into two secondary spermatocytes containing two sets of chromosomes (2 × 1N).
  • The secondary spermatocytes then divide into two spermatids, each containing just one set of chromosomes (1N), half the DNA needed to make a human being. (The other half will come from the ovum at fertilisation)

Tunica Vaginalis & processes vaginalis testis:

• fluid filled envelope
• testis attached to scrotum thru caudal lig of testis  & to peritoneum running above it
• During descent of testis, pertinoneum is pulled in to scrotal sac w/ testis = processes vaginalis testis –> become tunica vaginalis
• have a visceral and parietal layer, just like peritoneum

Blood supply:
testicular a (ab aorta)
drained by v of pampiniform plexus –> become testicular v

Lymph vessels in area –> sup inguinal nodes & lumbar nodes

Epididymis:

• formed by the many twists and turns made by the 1 epididymal duct
• lies of post surface of testis, – only place where testis not covered by tunica vaginalis
• has head, body, tail
  
  • head – made up of 12-14 efferent ducts, leading from rete testis
  • body – duct of epididymis
  • tail – continous w/ ductus deferens

Ductus Deferens:

Function:

• continuation of epididymal duct
• carries spermatozoa from testis/epididymis to prostatic urethra
• unites w. duct of seminal vesicle to form ejaculatory duct
• Terminal portion = ampulla, med to seminal vesicle
• opens lat to seminal collicus on post wall of prostatic urethra

Pathway/Topography:

• begins in tail of epididymis –> asc w/ spermatic cord –> inguinal canal –> enter  retroperitoneal space @ deep inguinal ring –> desc to bladder
• int iliac a (DD runs in front)
• ureter (DD runs in front)
• no structure runs b/w peritoneum and DD

Blood supply: deferential a (usually inf vesicle a, sometimes sup vesicle a), joins testicular a w/in scrotum,

Veins = v run w/ a

Lymph Drainage = ext iliac lymph nodes

Nerve supply: inf hypogastric plexus
SNS – causes rapid contracting of musc during ejaculation

Spermatic Cord:

• develop from genital folds of embryo (analogous to labia majora)
• L & R  genital folds join to form scrotal raphe in midline of scrotal sac

Pathway:
Deep inguinal ring lat to lat umbilical fold (w/ inf epigastric a/v inside)
–> thru inguinal canal –> exit @ superficial inguinal ring –> scrotum @ post border of testis

Because the testis form in abdominal cavity, and then descends into scrotal sac, the layers of ab wall accompany this trip, and so the same layers can be seen in both spermatic cord, and scrotum

Layers of Ab wall are continuous w/ layer of Spermatic cord:

Contents of Spermatic cord:
1. Ductus deferens – originates from epididymis & carries spermatozoa

2. Arteries

1. Testicular a – paired visceral branches of ab aorta w/ pampiniform vein plexus = testis & epididymis
2. Deferential a (a of ductus deferens) – from inf vesicle artery = ductus deferens itself
3. Cremasteric a (from inf epigastric a) = cremasteric m

3. Pampiniform plexus – network of v around testicular a and ductus deferens –> ends as testicular v, cools down blood that enters testis

4. Nerves

• Genital br of genitofemoral n (lumbar plexus) = Cremaster m
• Autonomic fibers = regulate smooth m of ductus deferens and a/v (VM), and carry VS from testis
  • SNS regulates the a/v, and PNS regulates the DD itself
    

5. Lymph vessels –> sup inguinal nodes

Blood supply:

• int pudendal a (int iliac a)
• Ext pudendal a (femoral a)
• testicular a (ab aorta)
• cremasteric a
• all flow –> testicular v

Innervation:

• Ilioinguinal n
• pudendal n
• perineal br of post cut femoral n
• genital br of genitofemoral n

Histology of Testis, Epididymis & Ductus Deferens

Slide # 65 Testis & Epididymis

Structures to Identify:

• Sertoli cells (in semineferous tubules)
• Leydig cells
• Tunica Albuginea
• Epididymis
  
• CT septa
• Ductus Efferents
• Ductus epidymis
  
• Straight Tubules
• Rete Testis

General Info:

• covered by thick CT capsule = tunica albuginea
• just below tunica albuginea, is a layer of a/v =  tunica vaculosa
• on the posterior side of the testis, the tunica albuginea pushes into the testis to form the mediastiunum testis
• thin sheets come from the mediastinum testis to form septa between the 250 testicular lobules
• Each lobule has 1-4 seminiferous tubules, lined by stratified germinal epithelium (same epith like uterus)
  • Epith contains = germ cells, and Sertoli cells
• Between the seminiferous tubules, are fibroblasts, muscle like cells, a/v/n, and lymphvessels and Leydig cells
• Leydig cells = produce testosterone

Seminiferous Tubules

• 1-4 in each lobule
• triangular nucleus
• produce spermatids
• 1st layer = in epith of tubules = Sertoli cells *more later*
  
• Contain spermatogenic cells in 2nd layer – b/w sertolis cells and lumen
  • regularly replicating and differentiating
  • organized poorly into layers
• 3rd layer = Tunica Propria
  
  • also called peritubular tissue
  • myoid cells sit beneath the basal lamina of Sertoli cells = nursing cells
  • contraction of myoid cells create peristaltic movement
  • if thickens in early life —> Infertility
• Basal compartment = spermatogonia, primary spermacytes
• Lumen = mature spermacytes, spermatids
• surrounded by interstitial tissue

Interstitial Tissue

• a/v
• loose CT
• clusters of epithelial like cells of Leydig
  • eosinophillic, round nucleus
  • lipid droplets
  • crystal of Reifkle = Rectangular, crystal-like inclusions in the interstitial cells of the testis (Leydig cells) and hilus cells in the ovary.
  • elaborate Smooth ER for enzyme production
  • testosterone production
    • in early fetal life = help male gonads develop
    • in Puberty = sperm production, pubic hair growht
    • In Adult = maintenance of sex glands, spermatogenesis

Sertoli Cells = tall columnar, non replicating cells that rest on basal lamina, 5 functions

1. Supporting cells – processes for exchange of metabolic substances and waste
2. Phagocytes – junctional complexes, and spermatogonia cells that don’t complete differentiation
3. Endocrine – Androgen Binding Protein (ABP) – binds testosterone from Leydig cells for proper maturation of spermatozoa, secrete fluid for passing mature sperim
4. Exocrine – secrete hormones
   • Inhibin – inhibits FSH release
   • Transferrin – Fe transport
   • Plasminogen activators – stimulate proteolytic enzymes
5. Help form Blood Testis Barrier
   • fluid in seminiferous tubules different from plasma – i.e diff amino acids, ions, carbs
   • protect genetically differentiating cells from immune system
   • junctional barrier
   • The barrier is formed by layers of cells from the VASCULAR ENDOTHELIUM of the capillary BLOOD VESSELS, to the SEMINIFEROUS EPITHELIUM of the seminiferous tubules. TIGHT JUNCTIONS form between adjacent SERTOLI CELLS, as well as between the ENDOTHELIAL CELLS.

Sperm is made and modified through the testicular duct system

Pathway: Seminiferous tubules (convoluted/straight tubules) --> rete testis (in mediastinum testis) --> Efferent ducts --> Epididymis ducts (tail, body, then head) --> ductus deferens

Pathway: Seminiferous tubules (convoluted/straight tubules) –> rete testis (in mediastinum testis) –> Efferent ducts –> Epididymis ducts (tail, body, then head) –> ductus deferens

First 4 you can identify in this slide, each one has different epithelial lining and function

Straight tubules: short narrow ducts, with cuboidal lining epith , no spermatogenic cells

Rete Testis: @ mediastinum testis,

• network of tubules wth wide lumen
• epith goes from simple squamous to low cuboidal to low columnar.
• widen near the efferent ducts

Epididymis:

• include efferent ducts and ducts of epididymis
• 4-6 M long coiled structure
• newly produced sperm mature here –> gain motility and ability of fertilize female oocyte
• head of sperm modified by addition of depcacitation factor, containing  carb like fluid which inhibits a second fertilization of the egg – IMP for transfer of DNA content
• fluid is released during capacitation in female reproductive tract — IMP for binding to oocyte
• lined by  pseudo stratified columnar epith, with primary cells and basal cells that have stereociliae
• lymphocytes are also present
• resevoir of sperm
• when stimulated – contraction occurs, ejaculation occurs

Ductus efferentes

notice the star shaped lumen - efferent ducts

• star shaped lumen –> due to tall ciliated cells, and shorter non ciliated cells
• found nearer to mediastinum
• surrounded by CT
• form part of head of epididymis
• reabsorb fluid secreted from seminiferous tubules
• musc layer surrounds ducts to push sperm forward

Ductus epididymis

Epididymal ducts: PRINCIPAL CELLS, are elongated and located at the base. Another population of cells has a rounder nucleus and can be found mainly at the base (called BASAL CELLS)

• pseudostratified columnar epith
• one tube that is convoluted and twisted, so you are seeing mutliple cross sections of its lumen
• has tall columnar principal cells with non motile stero cilia, and small basal cells (circular and at base)
• smooth round lumen
• located towards the outside, away from the medistinum testis

Slide #67 Ductus Deferens in Spermatic Cord

Structures to identify:

• pseudostratified columnar epith w/ sterocilia
  
• all 3 layers of muscle – inner longitudinal, middle circular, outer longitudinal (like in ureter)
  
• a/v/n
• adventia
• smooth and skeletal m

*Slide easy to identify as you can also see many other structures with it, and also do not confuse with ureter or urethra, this does not have urothelium, and the urethra’s lumen is long, and thin and irregular. This lumen is wide, kinda circular, and irregular.

General Info:

• tiny narrow irregular lumen, with mucosal foldings into it = glandular diverticuli.
  
• thin mucosa – LP has collagen fibers, and elastic fibers
• THICK muscular layer
• no submucosa or musc mucosa
• adventia = no peritoneal relationship

Embryology of Testis, Epididymis & Ductus Deferens

Development of Testis, Epididymis, Ductus Deferens
Until week 6, the embryo does not show a particular gender at all
At week 7 till week 20, embryo under a series of changes until a male or female phenotype is recognized

Gonads become ovaries or, in the case of the male, the testis
The primary genital duct that develops in the male is Mesonephric duct (Think M= male)

Scrotum:
In 3rd week, mesenchyme cells in primitive streak –>go to cloacal membrane to form cloacal folds

• Cranial (towards the head side, ant) to the cloacal membrane, the cloacal folds form genital tubercle
• Caudally, cloacal folds become urethral folds ant, and anal folds post

On each side of urethral folds, genital swellings form –> later form scrotal swelling in male, labia majora in female

• genital swellings grow in inguinal region, move caudally
• each makes up one half of scrotum, separated by scrotal septum

Testis:

1. intermediate mesoderm forms longitudinal elevation along dorsal body wall = urogenital ridge
2. coelemic epith + underlying mesoderm cells proliferate = from gonadal ridge
3. Primary sex cords from gonadal ridge and absorb primordial germ cells from primitive yolk sac –> later regress, but do form seminiferous tubules, tubuli recti, rete testis
4. lose connection w/ surface epithelium as tunica albuginea forms there

In order for males to become males, they have a specific gene = TDF, or testis determining factor

Seminiferous cords have the primordial germ cells and Sertoli cells – that secret MIF (Mullerian inhibiting factor), that supresses the development of the primary genital duct in female = the paramesonephric duct or mullerian duct.

Mesoderm b/w seminiferous cords –> give Leydig cells that secrete testosterone
Mesoderm = Leydig, Sertoli cells, primordial germ cells, and CT stroma of testis

Seminiferious cords canalize and form into tubules during puberty

Descent of Testis:

• All of the above reactions occur w/in the abdominal cavity
• Testis have to descend into scrotal sac
• It is unknown what makes them do so – but it seems to be related to growth to ab viscera, the gubernaculum, and testosterone

gubernaculum descends w/ testis in inguinal canal, and remnants of it hold the testis w/in the scrotum in adult life

Peritoneum also follows testis into scrotal sac via inguinal canal, and form the tunica processus vaginalis –> become the parietal and visceral layers of tunica vaginalis

Genital Duct formation:
Paramesonephric duct starts to develop, but later regresses, due to MIF

Mesonephric duct forms = epididymis, ductus deferens, seminal vesicle, ejaculatory duct, efferent ducts of testis