Male Reproduction

 Introduction

In embryonic stage determination of sex can be done at the time of fertilization although the gonads do not acquire differential characteristic until the 7th week of devlopment .Gonads appear initially as longitudinal ridges,also known as genital or gonadal ridges 

These ridges are result of proliferation of the epithelium and condensation of mesenchyme  lying deep of epithelium lining. Germ cell usually appear after 6th week of development in the genital ridges 

PRIMORDIAL GERM CELLS 

During development primordial gem cells appear in the wall of yolk sac close to the allantois and migrate along the dorsal mesentary of the hind gut by an ameboid movement . These germ cells reach the primitive gonads by 5th week and stars invading in genital ridge  by 6th week 

If they fail to reach the genital ridges,honads do not form so the primordial germ cells have an inductive influence on devlopment of the gonads.Primordial germ cells have an inductive influence on devlopment of the gonads 

At rhe stage gonads are known as the indifferent gonads  

DEVELOPMENT OF TESTIS 

In the male embryo, the primordial germ cells have XY chromosome.The y chromosome has SRY gene ,which encodes an important factor known as the testis - determining factor, this factor promotes the proliferation of primitive sex cords and help them to penetrate deep into the medulla to form the testis or medullary cords. At the hilium of the gland, these cords break up into a channel of cell strands, which forms the tubulus of the testis. During the development, a fibrus connective tissue layer, the tunica albuginea, forms between the medullary cords of testis and the surface epithelium. By the fourth mounth of these testis cords become u shaped, and their terminal ends are the connected with the rate testis 

The testicular cords near composed of 

* Migrated primitive germ cells 

* Sertoli cells derived from the surface epithelium 

INTERSTITIAL CELLS OF LEYDIG 

The mesenchyme in the gonadal ridge, which is present between the developing testis cords, forms the Leydig cells. They develop in the mesenchyme after the onset of proliferation and differentiation of testis cords. By the 8th week of development.  Leydig cells start secretion of testosterone. This testosterone influence the sexual differentiation of the genital ducts and external genitalia Testis cords remainsolid until puberty, when they acquire a lumen, they known as the seminiferous tubules.

Thus the structural components of Testis are derived from three source 

*intermediate mesoderm ( mesenchyme) that forms the urogenital rtidges on the pisterior abdominal waal, giving rise to Leydig cells ( interistial cells) and myoid cells (peritubular contractile cells)  

* Mesodermal epithelium (surface epithelium of coelom) that lines the urogenital ridges and gives rise to sertoli cells 

*Primordial germ cells that migrate from the yolk sac into developing gonads, where they divide and differentiate into spermatogonia 

* FACTORS REGULATING DEVELOPMENT 

 The  components of developing genital system are 

* Gonads and primative sex gland 

* Genital 

* External genitalia 

All these components are initially in an indifferent stage in which they may devlop inti either a male or female genital system. The SRY gene on the Y chromosome encodes the testis determining factor which regulate ,male sexual development. SRY gene also influence the genes encoding steroidogenesis factor (SFI)and SOX9 that stimulate differentiation of sertoli and Leydig cells in the testes 

The SRY gene induce the 

* Devlopment of the testis ( medullary) cord 

* Formation of the tunica albuginea 

The SRY gene inhabits  the 

* Decvloopment of cortical (ovarian) cords

if the expression of the SRY gene is absent ,another gene DAXI, down regulate the steroidogenesis factor (SFI) , and along with that the  expression of gene WNT4 in the gonadal ridge, induce the formationn of ovaries with formation of epithelial cord in cortical part of gonads, instead of medullary cord 

ANATOMY AND FUNCTION OF MALE REPRODUCTIVE SYSTEM 

( INCLUDING ACCESSORY ORGAN SYSTEM AND FUNCTION)

The male reproductive system consists of the 

* Spermatic cord 

* Scrotum

* Testes

* Genital-excurrent duct 

* Accessory sex glands and penis 

Spermatic Cord 

During development, the testis traverses and abdominal wall and reaches into the scrotum ; and carries its vessels, nerve and ductile part with it. All these form the spermatic cord, which suspend the testis in the scrotum. The spermatic cord has coverings.Which are form by the layers of the abdominal wall. The spermatic cord contains ;

* Vas deferens 

* Artery to the vas deferens

* Testicular artery and veins 

* Cremasteric artery 

* Cremasteric nerve and the sympathetic components of the testicular plexus 

* Genital branch of the genitofemoral nerve 

* Lymph vessels draining the testis 

All of these structures are conjoined by loose connective tissue.

Scrotum

The scrotum is a fibromuscular sac covered by skin, containing the testes and part of the spermatic cords. It consist of 

* Skin 

* Dartos muscle 

* External spermatic 

* Cremasteric and internal spermatic fasciae  

The scrotum is devided into right and left mhalves by a cutaneous raphe, which continues ventrally to the inferior penile surface and dorsally along the midline of the perineum to the anus.

Testis 

Testis is a male gonad and importent component of reproductive system. The adult testis are paired ovoid organ that lie within the scrotum. Testis are connected by the spermatic cord to the abdominal wall and tethered to the scrotam by scrotal ligaments, the remnants of the gubernaculum. The testis devlop on the posterior wall  of the abdomen and latter on they dexcend into the scrotum 

Structure of testes 

Each testis is covered by a      thick connective tissue capsule, the tunica albuginea. The inner part of this capsulwe is a loose connective tissue that  contains blood vessels and known as the tunica vasculosa. This tunica vasculosa form deeper separation in testis, which devide the each testis into approximately 250 lobules. Along the posterior surface of testis , the tunica albuginea thickens and projects inward as the mediastinum testis.Blood vessels, lymphatic vessels and the genital ex current duct pass through the mediastinum  

Epididymis 

It is the first part of genital excurrent duct system. The epididymis lays posterio-lateral to the testis, and the vas deferens lies along its medial side. It has an expended head known as globulus major, a body and a tail

Paradidymis 

The paradidymis is a smalln collection nof convoluted tubules. It is present anteriorly in the spermatic cord above the epididymal head.

Vas Deferens 

The vas deferens is the distal continuation of the epididymis, starting as a muscular tube at the epididymis, starting as a muscular tube at he epididymal tail. It is 45 cm long and convey sperm to the ejaculatory duct 

Ejaculatory Ducts 

The ejaculatory ducts are formed by the union of ducts of the seminal vessicle and the terminbal part of the vas deferens.

Seminal vessicles 

The two seminal vesicles are sacculated tube located between the bladder and rectum 

Bulbourethral Glands 

The two bulbouretharal glands are small rounded, somewhat lobulated mass of approximately 1 cm diameter. 

Penis 

The penis consist of 

Root 

Free and pendulous Body 

The Root of the penis 

The root of penis consist of erectile tissue in the urogenital triangle, namely the two crura and the bulb, which are firmly attached to the pubic arch and perineal membrane respectively.

The Main Body of the Penis 

Body of the penis consists of the three masses of erectile tissue, the right and left corpora cavernosa, and the median corpus spongiosum, which are continuations of the crura and the bulb of the penis of root respectively. They become engoredn with blood during penile erection.