Male Reproductive System
Reproductive system is unique because it ensures the continuation of the species. The main difference between other systems like urinary system, cardiovascular system, respiratory system etc., and the reproductive system is that, other systems function for the survival of the individual but the function of reproductive system (producing offspring) is not necessary for the survival of the individual. An individual can live a long, healthy and happy life without reproducing offspring. However, continuation of the generation depends only on reproductive system.
Four processes execute the function of the reproductive system:
1 Production of egg and sperm
2 Transport and maintenance of egg and sperm
3 Nurturing of developing offspring
4 Secretion of male and female sex hormones.
The organs of the reproductive system can be divided into two portions namely internal reproductive organs and external genital organs. Gonads are the main organs which produce the gametes - sperm and egg or ovum. A pair of testes (singular - testis) produces sperms in males and a pair of ovaries produces ovum in females.
Normally, most of the animals including humans are either definite males or definite females. However, in some organisms like earthworms and snails, both sexes may be present in the same organism and this condition is known as hermaphroditism.
In humans and most of the higher animals, reproduction occurs sexually, i.e., by mating. However, there are some species like insects which can produce offspring without mating.
Male reproductive system includes the primary sex organs and accessory sex organs. Primary sex organs are testes and the accessory sex organs are seminal vesicles, prostate gland, urethra and penis which are situated on either side of prostate. Secretions of seminal vesicles are emptied into ampulla of vas deferens. The ampulla of the vas deferens is continued as ejaculatory duct, which passes through prostate to form internal urethra (see below).
° PROSTATE GLAND
Prostate gland is also an accessory sex organ. It is constituted by many secretory glands. Secretion from these glands is emptied into internal urethra through utriculus prostaticus.
Urethra has two parts namely, internal urethra and external urethra. Internal urethra is the continuation of ejaculatory duct. Internal urethra passes through penis as external urethra. Urethra contains mucus glands throughout its length, which are called glands of Littre. The bilateral bulbourethral glands also open into the urethra.
Penis is the male genital organ. Urethra passes through penis and opens to the exterior. Penis is formed by three erectile tissue masses, i.e. a paired corpora cavernosa and an unpaired corpus spongiosum. The corpus spongiosum surrounds the urethra and terminates distally to form glans penis.
NATURE OF SEMEN
Semen is a white or grey fluid that contains spermatozoa (sperms). It is the collection of fluids from testes, seminal vesicles, prostate gland and bulbourethral glands. Semen is discharged during sexual act and the process of discharge is called ejaculation.
Testes contribute sperms. The prostate secretion gives milky appearance to semen. And, the secretions from seminal vesicles and bulbourethral glands provide mucoid consistency to semen.
At the time of ejaculation, human semen is liquid in nature. Immediately, it coagulates and after some time it undergoes a secondary liquefaction.
The fibrinogen secreted from seminal vesicle is converted into a weak coagulum by the clotting enzymes secreted from prostate gland. The coagulum is liquefied after about 30 minutes, as it is lysed by fibrinolysin. Fibrinolysin is the activated form of profibrinolysin produced in prostate gland.
When semen is ejaculated, the sperms are non-motile due to the viscosity of coagulum. When the coagulum dissolves, the sperms become motile.
COMPOSITION OF SEMEN
Semen contains 10% sperms and 90% of fluid part which is called seminal plasma. The seminal plasma contains the products from seminal vesicle and prostate gland. It also has small amount of secretions from the mucus glands, particularly the bulbourethral glands.
The total count of sperm is about 100 to 150 million/ml of semen. Sterility occurs when the sperm count falls below 20 millions/ml.
Though the sperms can be stored in male genital tract for longer periods, after ejaculation the survival time is only about 24 to 48 hours at a temperature equivalent to body temperature.
The rate of motility of sperm in female genital tract is about 3 mm/minute. The sperms reach the fallopian tube in about 30 to 60 minutes after sexual intercourse. The uterine contractions during sexual act facilitate the movement of sperms.
Structure of Spermatozoon
Spermatozoon (pleural = spermatozoa) is the male reproductive cell, developed in the testis. It is also called the sperm. The matured spermatozoon is 60 µ long. Spermatozoa consists four parts:
Head of sperm is oval shaped (in front view), with a length of 3 to 5 µ and width of up to 3 µ. The anterior portion of head is thin.
The head is formed by a condensed nucleus, a thin cytoplasm and a thin cell membrane. The anterior two thirds of the head is like a thick cap and it is called acrosome (Galea capitis). Acrosome develops from Golgi apparatus and it is made up of mucopolysaccharide and acid phosphatase. It also contains hyaluronidase and proteolytic enzymes which are essential for the sperm to fertilize the ovum.
The head is connected to the body by a short neck. Its anterior end is formed by thick disc shaped anterior end knob, which is also called proximal centriole. The posterior end is formed by another similar structure known as posterior end knob. It gives rise to the axial filament of body.
Often, the neck and body of sperm are together called midpiece.
It is cylindrical with a length of 5 to 9 u and the thickness of 1 \L. The body of the sperm consists of a central core called axial filament the neck. After passing through the body, it passes through a perforated disc called end disc or end ring centriole. Finally, the axial filament reaches the tail as axial thread.
In the body, the axial filament is surrounded by a closely wound spiral filament consisting of mitochondria.
The tail of the sperm consists of two segments:
I. The chief or main piece of tail: It is enclosed by cytoplasmic capsule and has an axial thread. It is 40 to 50 µ long
II. The terminal or end piece of tail: It has only the axial filament.
QUALITIES OF SEMEN
The minimum required qualities of semen for fertility are:
- Volume of semen per ejaculation must be at least 2 ml
- Sperm count must be at least 20 millions /ml
- Number of sperms in each ejaculation must be at least 40 millions
- 75% of sperms per ejaculation must be alive
- 50% of sperms must be motile
- 30% of sperms must have normal shape and structure
- Sperms with head defect must be less than 35%
- Sperms with midpiece defect must be less than 20%
- Sperms with tail defect must be less than 20%.