what Is reproduction?
Reproduction is a biological process. It is seen in both plants and animals (unicellular and multicellular). It is the process of formation of a new offspring or organism similar to their parents.
The living organism has the capacity of reproduction, but the non-living organism has no ability for reproduction.
Sexual Reproduction
Sexual reproduction is commonly seen in multicellular organisms. During sexual reproduction, there is an involvement of two different sex is takes place (male and female), and these two opposite sexes are produced two different sex cell known as a gamete.
The males produce male gametes or sperm, and the female produces female gametes or ova. These two gametes are fuse to form a zygote which grows into a new individual.
The sperms are produced from the male sex organ testis, and the ova are produced from the female sex organ ovaries.
Male Reproductive System
Mammals are dioecious, that is, the sexes are separate. Both male and female sex possess reproductive organs. The primary reproductive organ of a male is the testes (singular – testis).
It also includes several accessory sex glands such as seminal vesicles, prostate glands, bulbourethral glands, and ducts. These include the epididymis, ejaculatory ducts, vas deferns, and urethra.
In a male, some supporting organ also presents these are the penis and scrotum, that produce sperm and secret hormones.
Organs Of male reproductive System
Testis Structure and Function
A pair of oval-shaped testes present in a pouch of skin called scrotum or scrotal sac, measuring about 2.5 cm in diameter, 5 cm long, and about 10-15 gm weight.
In the embryo, the testis is developed near the kidneys, near the posterior portion of the abdominal cavity.
But when the baby is born, the testes descend into the scrotum or scrotal sac through the inguinal canals, and the channel gets closed after the testes have descended down.
The testis is held in position within the scrotal sac by means of a compact cord called an inguinal cord or spermatic cord.
If the testis is failed to descend into the scrotal sac, this condition is called cryptorchidism.
If the inguinal canal failed to close or reopen due to some abnormal condition is called an inguinal hernia.
Structure and Function of Scrotum
The scrotum is a bag or pouch-like structure that consists of loose skin and is located just below the penis and hangs in between the two thighs.
Externally it looks like a single pouch, which separated into lateral portions by a median ridge known as raphe.
Internally, the scrotal septum divides the scrotal sac into two sacs, and each sac containing a single testis.
Generally, the scrotum has 2 – 3-degree celsius less temperature than the normal body temperature. It helps in the production and maturation of sperms.
Histological Structure of the testis
Each testis surrounded by a layer of a white fibrous capsule composed of dense irregular connective tissue called tunica albuginea.
The tunica albuginea extends inward that forming septa, which divide the testis into a series of internal compartment known as lobules.
Each compartment or lobules contain one or two or three tightly coiled long tubules called a seminiferous tubule.
Seminiferous tubules
The seminiferous tubules are internally lined with a single layer of germinal epithelium. The cells of seminiferous tubules produce spermatogonia (stem cell) from which sperm are formed.
The process of formation of sperm in the seminiferous tubules id known as spermatogenesis.
The seminiferous tubule contains spermatogenic cells (sperm forming cells) and sustentacular cells or Sertoli cells.
The Sertoli cells are present between the germinal epithelium cells and supply nourishment to the developing sperm.
In between the seminiferous tubules, Leydig cells or interstitial cells, nerve, and blood vessels are present.
The Leydig cells secrete male sex hormone, testosterone (androgen), it helps for the development of secondary sex organs, muscular development, and maintenance of accessory organs in males.
The seminiferous tubules are converged to the posterior part of the testis to form a network of small tubules called rete testis.
About 15 to 20 slender ducts called vasa efferentia of efferent ducts. The vasa efferentia arise from rete testis and merge into a single muscular duct called vas deferens or ductus deferens.
Epididymis
The epididymis is a comma-shaped organ that lies behind each testis. It is a long coil tubule about 20 feet or 6 m long, partially encircling the testis.
The epididymis is lined by pseudostratified columnar epithelium and encircled by layers of smooth muscle. It is also attached to the scrotal sac by a connective tissue called gubernaculum.
Stereocilia are the long, branching microvilli, lies on the free surface of the columnar cells of the epididymis. The stereocilia are increasing the surface area for the reabsorption of degenerated sperm.
The epididymis is differentiated into three different parts
- Capute epididymis (the top part connected with the seminiferous tubules).
- Corpus epididymis (middle part)
- Cauda epididymis (the bottom part connected with the vas deferens).
Function of Epididymis
- The epididymis is acting like a duct for the passage of sperms from the testis to vas deferens.
- In the epididymis, maturation of sperm takes place ( The process by which sperm acquire motility and the ability to fertilize on the ovum). It requires about 14 days.
- It propels sperm into vas deferens during sexual intercourse.
- It stores sperms, and the sperm that is not ejaculated by that time is again reabsorbed.
- Testis and epididymis together constitute the testicle.
Vas Deferens
It is a muscular tube that arises from the lower part of the globus minor (cauda epididymis) and leaves the scrotum through the inguinal canal into the abdominal cavity and joins with the duct of the seminal vesicle of its side.
The dilated end part of the vas deferens is called the ampulla.
The muscles of vas deferens are composed of three layers of smooth muscle, and the mucosa of vas deferens consists of pseudostratified columnar epithelium and lamina propria.
Functionally the vas deferens ejaculate sperm during sexual intercourse from the epididymis towards the urethra by peristaltic contraction of its muscular coat. It also stores sperms for several months.
Cutting of vasa deferentia is called vasectomy (it is a method of male sterilization).
Ejaculatory duct
Ejaculatory ducts are two short ducts about 2 cm long and formed by the fusion or union of vas deferens (ampulla) and seminiferous vesicle.
The two ducts are present one each side. It enters into the prostate gland and finally opens into the urethra.
Urethra
The urethra is also called a shared terminal duct because it acts as a passageway for both semen and urine. It is about 20 cm long and passes through the prostate, the deep muscle of perineum, and the penis.
The urethra is different into three parts:
- The prostatic urethra (pass through the prostate)
- Intermediate urethra (passes through the perineum)
- Spongy urethra (passes through corpus sporangium of the penis).
Accessory sex organs of male reproductive system
Seminal vesicles
These are a pair of convoluted pouch about 5 cm in length located posterior to the urinary bladder and anterior to the rectum.
It secret an alkaline viscous yellow fluid, which constitutes about 60% of the semen.These alkaline viscous fluid contain nutrients like fructose, mucus, prostaglandins, vitamins, and clotting proteins.
The alkaline nature of this fluid helps neutralize the acidic environment of the male urethra and the female reproductive tract.
Fructose help in ATP production by sperm; prostaglandins help in providing nutrition and protection of sperm in the semen. It also helps in the contraction of smooth muscle within the female reproductive tract. The clotting protein helps in the coagulation of semen after ejaculation.
Prostate Gland
The prostate gland is a single, rigid, doughnut-shaped gland lies below the urethra or duct of the urinary bladder passes through the small hole of the prostate gland.
The size of the prostate gland increases slowly with the increase of age. Birth to puberty increase gradually, and after puberty expand its size rapidly until about age 30, after that its size remains stable until about age 45, enlargement may further occur.
The enlargement of the prostate gland in old persons constricts the urethra and obstructs urination.
The prostate gland secretes a thin, alkaline milky fluid (pH about 6.5) that neutralized the acidity in semen, urethra, and vagina.
Due to the alkaline nature of this fluid, it enhances the survival of sperms and increases the chance of fertilization with the ovum.
It contains nutrients like citric acid, several proteolytic enzymes, amylase, and hyaluronidase, acidic phosphate, seminal plasmin (it destroy bacteria).
It constitutes about 25% of the volume of semen and also increases sperm motility and viability.
Bulbourethral glands or Cowper’s glands
A pair of small pea-shaped bulbourethral glands or Cowper’s glands located below the prostate glands.
Short ducts of this gland open into the urethra at the base of the penis.
During sexual intercourse, it secret an alkaline fluid into the urethra, which protects the sperms by neutralizing acids from urine in the urethra.
The bulbourethral gland also secrets mucus, which lubricates the end of the penis and the lining of the urethra, which decreases the number of sperm damaged during ejaculation.
Semen
Semen is a mixture of sperm and seminal fluid. It is secreted from the seminiferous tubules, seminal vesicles, prostate gland, and bulbourethral glands.
In a typical ejaculation, about 2.5-5 milliliters with 50-150 million sperm per ml release. It is slightly alkaline due to higher pH(7.2 pH -7.7pH) and a larger volume of fluid from the seminal vesicles.
Structure and Function of penis
The penis is a cylindrical copulatory organ that releases sperms in the vagina of the female during sexual intercourse and excretes urine.
The body of the penis composed of three cylindrical masses of erectile tissue, two corpora cavernosa, and one corpus spongium, each enclosed by a fibrous covering, is called tunica albuginea.
From the corpus spongiosum, the urethra passes and acts as a passage for urine and semen.
The distal end of the penis is slightly enlarged (Acron-shaped region) called glans penis, and it is covered by a fold of skin known as prepuce.
At the time of sexual intercourse, the penis is become erect due to the dilation of the blood vessels carrying blood to the sinuses in the erectile tissues and the collection of blood there. As the erectile tissues are inflated, they constrict the veins inhibiting the flow of the blood out of the tissue.
During sexual intercourse, the erect penis is inserted into the women’s vagina. This leads to the contraction of the muscles present in the scrotum and raises the testis close to the body, epididymis, and vas deferens.
This short period of intense sexual excitement is called orgasm. As a result of an orgasm, the ejaculation of the semen takes place from the penis into the female reproductive tract.
Sperm path
Sperms (from the testis) –> Rete testis –>vasa efferentia –> Epididymis –> Vas deferens –> Ampulla –> Ejaculatory duct –> External urethra –> Internal urethra –> External urinary opening –> Vagina of Female.