Reproductive System

Reproduction is one of the features of living beings and produces offspring to continue the race. Human reproduction is sexual and fertilization is internal.

In humans, male and female are different and distinct with sexual dimorphism. The organs taking part in reproduction are reproductive organs which remain interconnected and form the reproductive system.

Male Reproductive System

It is involved in the production of gametes and the transportation of them to the appropriate region of the female reproductive part to ensure fertilization.

The male reproductive system includes the following organs:

Organs of the Male Reproductive System (Diagram Summary)

• Urinary bladder
• Vas deferens
• Bulbourethral (Cowper's) gland
• Epididymis
• Right testis
• Scrotum
• Seminal vesicle
• Ejaculatory duct
• Prostate gland
• Prostatic urethra
• Membranous urethra
• Penile urethra
• Penis
• Glans penis

1) Testis

• One pair of oval whitish testes is located in a skin pouch called the Scrotum, which has darker pigmentation and thin hairs.
• The testes are located outside of the body cavity in the scrotum to maintain a temperature of 35°C, which is required for the production and maturation of sperm.
• Each testis is 4 cm long and 2.5 cm in thickness, with a weight of about 10-14g.
• The left testis is slightly lower than the right testis to avoid collision between the thighs.
• The testes' interior surface remains attached with muscles called Cremaster muscles, which at the other end remain attached to the body wall. These muscles regulate the movement of the testes and bring them near the body wall to provide warmth during winter seasons.

Histology of Testis

[Diagram Summary: Outer layer is Tunica Vaginalis, followed by a fluid-filled space called Hydrocoel, then Tunica Albuginea. Internally, there are Seminiferous tubules containing Spermatogenic cells and Sertoli cells. Between tubules are Interstitial (Leydig) cells.]

• Each testis has 2 layers: outer tunica vaginalis and inner tunica albuginea. Between them is a fluid called hydrocoelwhich absorbs mechanical shocks.
• Internally, the testis contains 200-250 lobes called seminiferous tubules. Each seminiferous tubule has 2 kinds of cells: spermatogenic cells and Sertoli cells.
• Spermatogenic cells: Produce sperm by the process called spermatogenesis.
• Sertoli cells: Irregular cells that nourish the sperm.
• Between seminiferous tubules are interstitial cells or Leydig cells which synthesize male sex hormones like testosterone and androgen.

2) Duct System

It includes tubes of different sizes that transport sperms from the testis to the appropriate region of the female reproductive part. It includes the following ducts:

• a) Epididymis: It lies on the posterior surface of each testis and is comma-shaped, having a head, body, and tail. It receives sperms from the testis for maturation. It is about 6m in length but is highly coiled.
• b) Vas deferens: Continuous from the posterior surface of the epididymis as a narrow tube called vas deferens, which is about 45 cm in length. The vas deferens runs upward to the pelvic cavity, makes a loop around the ureter on its sides. It transports sperms during sexual arousal.
• c) Ejaculatory duct: The vas deferens receives the seminal vesicle at its side and forms a duct called the ejaculatory duct, which is 2 cm in length. Two ejaculatory ducts, one on either side of the urethra, eject sperm into the urethra.
• d) Urethra: Below the urinary bladder is a tube called the urethra, which is about 20 cm in length and is a common passage for both urine and semen. Based on location, the urethra is classified as Prostatic urethra, Membranous urethra, and Penile urethra.
  • The part of the urethra below the urinary bladder is the prostatic urethra, which remains surrounded by the prostate gland and is about 4-5 cm in length.
  • The prostatic urethra is followed by a 2 cm long part called the membranous urethra.
  • The terminal part of the urethra is called the penile urethra, which opens out through an opening called the urethral orifice. It is about 10 to 14 cm in length.

3) Copulatory Organ

• The organ which helps in discharging semen to the appropriate region of the female reproductive system is called the copulatory organ, which is the penis in males.
• Structurally, the penis is composed of three erectile muscles. Among them, the median one is called Corpus spongiosum, while the two on either side contain Corpus cavernosa. These sets of muscles are externally covered with loose skin which allows for extension of the muscles during sexual arousal.
• The terminal end of the penis is called the glans penis, which is sensitive to touch and has an opening called the urethral orifice. The glans penis is partly covered with a skin called fore-skin (prepuce).

4) Accessory Glands

• a) Seminal Vesicle: Below the urinary bladder, one on either side of the urethra, is a whitish fibro-muscular organ available and called the seminal vesicle. It is about 5 cm in length and produces fructose which nourishes sperm.
• b) Prostate Gland: Below the urinary bladder, around the urethra, is a whitish structure called the prostate gland. It is about 4 cm in length and produces an alkaline fluid which provides a medium for sperm to swim. The fluid with sperm is called semen.
• c) Bulbourethral Gland (Cowper's Gland): It is also called Cowper's gland and is about oval in shape. It is located at the base of the penis and produces an alkaline fluid which passes out before the discharge of semen. It neutralizes the acidic nature of the penile urethra and lubricates the glans penis. It assists in the penetration of the vagina and protects the glans penis from friction with the vaginal wall.

Female Reproductive System

The female reproductive system is well developed and has the following functions:

1. To produce ova.
2. To transport ova to the appropriate region.
3. To receive the penis during coitus and collect semen.
4. To ensure fertilization, development of embryo, and parturition.
5. To feed the baby.

The female reproductive system has the following parts:

Internal Parts of the Female Reproductive System (Diagram Summary)

• Ovary and Ovarian Ligaments
• Fallopian tube (Infundibulum, Fimbriae, Ampulla, Isthmus)
• Uterus (Fundus, Body, Cervix)
• Uterine wall (Perimetrium, Myometrium, Endometrium)
• Vagina and Vaginal rugae

1) Ovary

• A pair of almond-shaped ovaries lies one on either side of the uterus. It is the female gonad, located in the pelvic cavity and held in position with the help of several ligaments like the mesovarium.
• Each ovary is 3.5 cm long, 2 cm width, and 1 cm thick. It is pinkish at an early age and becomes darker at a later age.
• Histology: Each ovary has an outer germinal epithelium and inner tunica vaginalis. The space occupied by the inner tunica albuginea is called stroma. The stroma is differentiated into the peripheral cortex and central medulla.
• The cortex contains many small cells called Graafian follicles. A few Graafian follicles mature at each menstrual cycle and become primary oocytes. Out of many, one primary oocyte becomes a secondary oocyte. The secondary oocyte, when mature enough, is called an ovum, and others are ruptured to form a yellowish fluid-filled body called corpus luteum.
• The ovum ejects out of the ovary by the process called ovulation, which occurs at the 14th day of the menstrual cycle.

2) Duct System

• The duct system in females is represented by the uterine tube or Fallopian tube, which has 3 parts: infundibulum, ampulla, and isthmus.
• The terminal end of the uterine tube which lies over the ovary is called the infundibulum, which is encircled with finger-like projections called fimbriae. They capture the ovum.
• The wider path of the uterine tube is called the ampulla, where fertilization takes place. The ampulla posteriorly narrows and is called the isthmus, which opens into the uterus.

3) Uterus

• The hollow muscular and inverted pear-shaped structure is called the uterus. It is also called the womb, where the fetus grows. It is about 7 cm long, 5 cm width, and 2.5 cm thick, but it is extended many times during pregnancy.
• Structurally, the uterus has 3 parts: fundus, body, and cervix. The part above the opening of the isthmus is called the fundus. The middle widest part is called the body, and the lower narrow part is called the cervix, which has a canal called the cervical canal.
• Histology: The uterine wall has 3 layers. The outer is called perimetrium, the middle is called myometrium, and the inner is called endometrium. The endometrium is eroded as vaginal fluid during menstruation.

4) Vagina

• It is the female copulatory organ and is tubular in shape. It measures 8-10 cm in length and has ridges on the dorsal surface. These ridges are called vaginal rugae and help in distension during coitus (sexual intercourse).
• The inner wall of the vagina has Bartholin's glands which secrete an alkaline fluid that keeps the vagina lubricated. The opening of the vaginal orifice at an early stage remains covered with a thin membrane called the hymen. The hymen is later ruptured.

The External Visible Female Genitalia (Vulva)

Collectively called the vulva, which includes the following parts:

• Mons Pubis: Below the abdominal wall is a thick hump called the mons pubis, which is densely covered with pubic hair.
• Labia majorum: Inferior to the mons pubis is a pair of thick folds called labia majora, which are laterally covered with pubic hair.
• Labia minorum: Inner to each labia majora is a pair of thin folds called labia minora. The labia minora is uncovered with pubic hair and contains sebaceous and sweat glands that keep the vulvar region moist.
• Vestibule: Labia minora enclose a space called the vestibule. At the anterior end, a stimulating rod-shaped structure called the clitoris is available. It is homologous to the penis in males. Below the clitoris is an opening called the urethral orifice, which allows the release of urine. Below the urethral orifice is another opening called the vaginal orifice, which leads inwards into the vagina.

Breast (Mammary Glands)

[Diagram Summary: Mammary gland showing adipose tissue, areolar tissue, nipple, fluid lobules, and ducts.]

• Breasts are accessory reproductive glands. Prolactin hormone produces milk after the birth of a baby.
• A pair of globular mammary glands is located at the chest and is an accessory reproductive organ. Each breast has a terminal rod-shaped part called the nipple, which is followed by a colored region called the areola. The color is pinkish at an early stage and then gradually becomes dark.
• Posterior to the areola is a mass of adipose covered with skin. This adipose contains 15-25 chambers, and each chamber contains lobules which contain the cells that eject milk.
• Each lobule gives out a duct called the lactiferous duct, which unites with others and forms a common duct which opens at the surface of the nipple. The cells of the lobule eject milk under the influence of prolactin after the birth of the baby, when the baby suckles the nipple, the lobule ejects the milk.

Menstrual Cycle

• Menarche: The first menstruation.
• Menopause: The stoppage of menstruation, usually between 50-59 years.

The menstrual cycle consists of the following phases:

1. Menstrual phase: Bleeding phase (1 to 5 days). Often called the "weeping of the uterus" or "funeral of the ovum."
2. Follicular phase: (6th to 13th days). Pituitary gland secretes FSH, which stimulates follicles in the ovary to produce estrogen.
3. Ovulation: Occurs on the 14th day.
4. Luteal phase: (15th to 28th days).

In the human female, a cyclic change occurs in the reproductive parts. This biological phenomenon is called the menstrual cycle, which is of 28 days on an average. All the phases in the menstrual cycle are controlled and regulated by several hormones. The first menstruation is called menarche, which starts at the age of 12 years or beyond based on heredity, climate, diet, etc. It is continued up to the age of 52-55 years and then stoppage of menstruation is called menopause.

Phases in the Menstrual Cycle:

1. Menstrual Phase: This phase lasts for 3-5 days and is characterized with bleeding. The fluid discharged has mucus and unfertilized ovum. This phase is therefore also called the "weeping of the uterus" or "funeral of the un-fertilized ovum."
2. Follicular Phase: It extends from the 6th to the 13th day of the menstrual cycle. The pituitary gland secretes FSH (Follicle Stimulating Hormone), which stimulates follicles in the ovary. These follicles secret estrogen, which is increased in concentration at the 12th day. Simultaneously, LH (Luteinizing Hormone) is secreted. The stimulated follicles become primary oocytes. When estrogen and LH are at peak levels, the second oocyte ejects out of the ovary at the 14th day. This phenomenon is called ovulation.
3. Luteal Phase: Once the secondary oocyte (ovum) is ejected, the remaining primary oocytes are disintegrated and form progesterone, which prepares the uterus for anchorage of the fertilized zygote. The hormone adds a mucus layer on the surface of the endometrium and remains at a maximum in blood for 1 week. The fate of progesterone depends upon whether the ovum is fertilized.
   • If the ovum is fertilized, progesterone levels remain high in the blood until parturition.
   • When the ovum is not fertilized, the level of progesterone continuously declines, and the supply of blood to the overgrown tissues in the endometrium stops. At the 28th day, the overgrown endometrium is separated and discharged through the vagina, starting another menstrual cycle.