The Male Reproductive System

The male reproductive system is responsible for producing, maintaining, and delivering sperm (male sex cells) and male sex hormones like testosterone. It consists of both external and internal structures, each with specific functions that work together to facilitate reproduction. 

1.0Introduction

• The male reproductive system is located in the pelvis region. It includes a pair of testes along with accessory ducts, glands and the external genitalia. 
• The male sex accessory ducts include tubuli recti, rete testis, vasa efferentia, epididymis, vas deferens, ejaculatory duct and urethra. These ducts store and transport the sperms from the testis to the outside through urethra. 
• The male accessory glands include paired seminal vesicles, a prostate and paired bulbourethral glands.
• In man, one pair testes are the main or primary reproductive organ. Size 4-5 cm × 2-3cm and oval in shape 
• Both testes are located in a small bag-like structure situated below & outside the abdominal cavity called scrotum or scrotal sac. The temperature of scrotum is 2 – 2.5°C lesser than body temperature, necessary for spermatogenesis. 
• Internally, scrotum is lined by dartos muscle. Dartos muscle helps in regulation of the temperature within the scrotum. During the cold season, it becomes contracted & during the warm season, it becomes relaxed. 
• Each testis is attached to the wall of scrotum through a group of flexible fibers collectively called as Gubernaculum or Mesorchium. 
• Each testis is attached to the wall of the abdominal-cavity through a cord termed as the Spermatic cord. Spermatic cord passes through the inguinal canal. Cremaster muscle helps in the elevation of testes. Contents of the spermatic cord are vas deferens, gonadal veins, gonadal arteries, nerves and lymphatics. 
• Scrotum is connected to the abdominal cavity through a passage termed as inguinal-canal. Through this canal the testes descend down into the scrotal-sacs at the time of birth. When the testes do not descend to reach the scrotum but remain in the abdominal cavity at the time of birth this condition is called undescended testes or cryptorchidism. Such testis cannot develop and function properly and may develop malignancy. 
• Orchiopexy : When the undescended testes are brought into scrotal sac by surgical process during childhood this process is called as orchiopexy. 

2.0Internal Structure Of Testis

• Testis is covered by dense covering which consists of three coats. Outermost is tunica vaginalis. The middle coat is tunica albuginea & innermost is tunica vasculosa. 
• Tunica vaginalis has a parietal & visceral layer. It covers the whole testis except its posterior border from where the testicular vessels & nerves enter the testis. 
• Tunica albuginea is a dense, white fibrous coat covering the testis all around. The posterior border tunica albuginea is thickened to form a vertical septum called the Mediastinum testis. 
• Tunica vasculosa is the innermost vascular coat of the testis lining testicular lobules. 
• Each testis has about 250 compartments called testicular lobule 
• Each testicular lobule has 1 to 3 seminiferous tubules (in which sperms are produced hence its called functional unit of testes). 
• The total number of seminiferous tubules in each testis is about 750 to 1000. • Seminiferous tubules join together at the apices of lobule to form straight tubules or tubuli recti. 
• Here they form a network of tubules called rete testis. Rete testis fuse to form 10 to 20 efferent ducts called as vasa efferentia or ductuli efferentes. These ductules come out from the upper dorsal (posterior) surface of testis & open into common tubules, which get highly coiled to form epididymis or ductus epididymis. This epididymis is responsible for functional maturation of sperm. 
• Liberation of sperms from testes is called semination. 

Epididymis and Vas Deferens

Epididymis is responsible for functional maturation of sperm and can store sperm for up to 1 month. Epididymis has 3 parts : 

(i) Caput epididymis - Upper, highly coiled part 

(ii) Corpus epididymis - Middle part 

(iii) Cauda epididymis -Basal, least coiled part

• Vas deferens arise from cauda epididymis and enter inside the abdominal-cavity from the scrotal sac. The terminal dilated part of vas deferens is called ampulla. 
• The wall of epididymis and vas deferens is made up of 2 layers - outer circular muscle layer and inner epithelium. The sperms reach the abdomen due to the pulsations/contractions of the circular muscles. 
• Vas deferens run upward & enter the abdominal cavity. Both vas deferens coil around the ureter of their respective sides and then dilate to form ampulla.
• Ampulla of Vas deferens of each side receives the seminal vesicle of that side. The vas deferens now forms an ejaculatory duct and opens into the prostatic urethra. 1 pair of seminal vesicles are situated on the dorso-lateral side of urinary bladder. 
• The urethra originates from the urinary bladder and extends through the penis to its external opening called urethral meatus. 

3.0Accessory Reproductive Glands

The substances secreted by the accessory reproductive glands do not form gametes but help in reproduction, these are – 

1. Seminal Vesicle :- Internally, it is lined by glandular epithelium which secretes seminal fluid. This is a lubricating, transparent and jelly like substance, which makes 60–70% part of semen. It is slightly alkaline. Fructose is found in seminal fluid, it acts as fuel to sperm. This fluid also contains fibrinogen, prostaglandins, etc. 
2. Prostate Gland :- This gland is located below the urinary bladder. It is unpaired and made up of 5 lobes in man. Each lobe opens into the prostatic urethra through many fine apertures. It secretes slightly alkaline prostatic fluid which is milky, thick, sticky or jelly like. It makes about 30% part of semen and helps in sperm activation. The secretion of the prostate gland has calcium, clotting enzymes, profibrinolysin, etc. 
3. Cowper's Gland :- It is a pair of glands found on lateral sides of urethra. It is also called the bulbourethral gland. It is situated in the membranous part of urethra & opens into penile urethra. It secretes transparent, slimy, jelly-like fluid. This destroys the acidity of the urethra and cleans it for the movement of sperms. It also helps in the lubrication of the penis.

4.0Semen

• Semen = Sperm + Accessory reproductive gland fluid Volume = 3 to 4 ml. 
• pH = 7.3 
• Normal sperm count is 20 to 120 million/ml.
• Oligospermia sperm count & less than 20 million/ml.  
• Azoospermia – either absence or near absence of sperms.  
• Asthenospermia – reduced motility of sperms in semen 
• Teratospermia – sperms with abnormal morphology 

Note :- The human male ejaculates about 200 to 300 million sperms during a coitus of which, for normal fertility, at least 60 per cent sperms must have normal shape and size and at least 40 percent of them must show vigorous motility. 

5.0Histology Of Seminiferous Tubules

• The outer surface of seminiferous tubules is composed of white fibrous connective tissues called tunica propria while the inner surface is of cuboidal germinal epithelium. This epithelium is made up of spermatogenic cells which form sperm by spermatogenesis. 
• Some columnar cells are found in between the layer of germinal epithelium called as Sertoli cells (these occur in mammals).

Functions of Sertoli cells

• Provide nutrition to germ cells, so they are also called sustentacular or nurse cells. 
• Phagocyte the injured or dead sperm cells. 
• They are the basis of blood testis barrier.  
• Produce inhibin and Anti Mullerian Hormone. o FSH acts on the Sertoli cells and stimulates secretion of some factors which help in the process of spermiogenesis. 
• Produce Androgen Binding Protein (ABP) that concentrates testosterone.
• Some endocrine cells are found between seminiferous tubules in intertubular space, these are called interstitial or Leydig cells. 
• These cells secrete androgens (testosterone). 
• The testosterone from Leydig's cells enter the seminiferous tubules by diffusion under the effect of ABP & promotes spermatogenesis.
• Other immunologically competent cells are also present in the interstitial space. 

6.0Penis

• The penis is the male external genitalia and an erectile copulatory / intromittent organ (Organ of copulation), made up of special tissue (Erectile tissue). 
• The root of the penis contains a muscle called crura muscle. 

Body of Penis 

• It is composed of three longitudinal cylindrical masses of erectile tissue. 
• These masses are, the right and left corpora cavernosa and a median corpus spongiosum. The two corpora cavernosa do not reach the end of the penis. Each of them terminates under cover of the glans penis. 
• The corpus spongiosum continues further, its terminal part is expanded to form a conical enlargement called the glans penis. Throughout its whole length it is traversed by the urethra.  
• The glans penis is covered by a loose fold of skin called prepuce or foreskin. A special type of sebaceous gland is found on the prepuce called preputial gland which secretes oily secretion called smegma. Removal of prepuce by surgery is called circumcision. 
• External opening of penis is called penile/urethral meatus.

Erection of Penis 

• Erection of penis is a purely vascular phenomenon and is controlled by the Parasympathetic nervous system. 
• It occurs due to increase of blood supply, due to dilation of penile arteries causing enlargement and hardening of penis.

Ejaculation 

• Liberation of sperm from the body of male is called ejaculation. 
• The sympathetic nervous system is responsible for ejaculation. After ejaculation, penis becomes flaccid.