Human Reproduction

Introduction: 

As everyone is aware, the term reproduction means the production of offspring. Human reproduction is the process of producing offspring via sexual means. The male and female reproductive systems contribute to the process of Human Reproduction.

The concept of Human Reproduction is broad and vital. This concept includes Gametogenesis, menstruation cycle, fertilisation, followed by pregnancy and delivery of the foetus.

The Male Reproductive System

The male reproductive system includes accessory ducts, external genitalia, and testes. It is situated in the pelvic region. 

• Scrotum: It is a pouch-like structure outside the abdominal cavity where the testes are located. This helps to maintain the temperature between 2-2.5℃ of the testes, which is lower than the normal body temperature. The lower temperature of the testes is necessary for spermatogenesis. The testes are in an oval shape.
• Testicular lobules: In each testes, there are around 250 Testicular lobules, which are covered by a dense covering. Each testicular lobule contains 1-3 highly coiled seminiferous tubules where sperms are produced. Sertoli and Spermatogonia are lined on the inside of each seminiferous tubule.
• Interstitial Spaces: It is the outside region of seminiferous tubules that contains interstitial cells and small blood vessels. 
• The accessory ducts comprise vasa efferentia, rete testis, vas deferens, and epididymis. These ducts store and transport sperm from the testes to the outside through the urethra, which starts from the urinary bladder to the external opening known as the urethral meatus.
• Penis or male external genitalia is made up of particular tissue, which is covered by the foreskin (the loose fold of skin).
• The accessory gland comprises the prostate, paired seminal vesicles, and paired bulbourethral glands.

The Female Reproductive System

The female reproductive system includes a pair of ovaries, a pair of oviducts, vagina, uterus, external genitalia and cervix, which is positioned in the pelvic region. The female reproductive system and mammary glands are integrated to support different processes, namely ovulation, fertilisation, pregnancy, childbirth and child care.

• Ovum and Ovarian hormones are produced in the ovaries, which are situated on each side of the lower abdominal. Ovaries are connected to the uterus and pelvic wall by ligaments.
• Female accessory ducts consist of the fallopian tube, vagina and uterus.
• A fallopian tube extends from each ovary to the uterus and stores the ovum in the fimbriae, which leads to the ampulla and then to the isthmus.
• An isthmus has a narrow lumen that joins the uterus, also known as the womb. The uterus is supported by ligaments that are attached to the pelvic wall. The uterus opens into the vagina through the cervix. 
• The cervical wall, the cavity of the cervix, along the vagina forms the birth canal.
• The hymen is a membrane that partially covers the opening of the vagina. It is often torn during first intercourse, but it can also be torn during fall, active sports like horse riding, or during the tampon insertion.
• The mammary gland is paired breasts that consist of glandular tissue and fat. Glandular tissue is divided into 15-20 mammary lobes consisting of alveoli, which secrete milk.

Gametogenesis

• Gametogenesis is a process where gametes, i.e., sperm and ovum, are produced by the primary sex organs in men and women, respectively. 
• The spermatogonia produce sperms in the testis at puberty. Each spermatogonium consists of 46 chromosomes. 
• Spermiogenesis is a process where spermatids are transformed into sperms. Termination is a process where sperms are released from seminiferous tubules.
• Oogenesis is a process of the formation of mature female gametes. This process starts during the embryonic development, when millions of oogonia are produced within each ovary.
• Maximum no. of follicles degenerate before puberty, and each ovary is left with only 60000-80000 primary follicles.
• Primary follicles transform into secondary follicles, which change into tertiary follicles. The tertiary follicles further transform into Graafian follicles, and in the process of ovulation, Graafian follicles release secondary oocytes from the ovary.

Menstruation Cycle

• The menstrual cycle is a reproductive cycle in females, which begins at puberty and is known as menarche.
• Menstruation is repeated at an average interval of 28/29 days, and the interval between one menstruation to next is called the menstrual cycle. Between this period, one ovum is released. 
• The menstruation cycle starts with the menstrual phase and lasts for three to five days, and this process occurs when the ovum is not fertilised.
• Menopause generally occurs at the age of 50 in the female human.

Fertilisation and Implantation

Fertilisation is the process when the fusion of sperm with the ovum takes place. This process starts with intercourse when semen is released in the vagina by the penis. Sperms swim through the cervix, enter into the uterus and lastly reach the fallopian tube ampullary region.

Fertilisation only occurs if the ovum is also transported to the fallopian tube ampullary region.

During this process, sperm comes in contact with the zona pellucida layer of the ovum and blocks the entry of other sperms. A Sperm enters into the cytoplasm of the ovum with the help of acrosome, which induces the meiotic division of the secondary oocyte and further forms the ootid and second polar body. The sperm and ovum fuse to form a zygote, and at this stage, the sex of the got decided.

Implantation can be defined when the blastocyst, which transforms with the continuous division of the morula, is embedded in the endometrium of the uterus. Implantation leads to pregnancy.

Pregnancy and Embryonic Development

The human pregnancy is for 9 months, in which different developments take place in the foetus.

• During the first month, the embryo’s heart is formed, and before the start of the third month, the limbs and digits of the foetus are developed. At the end of the first trimester, major organs are developed.
• By the end of the second trimester, foetus eyelashes and eyelids are developed, and the body of the foetus is covered with fine hair.
• By the end of the third trimester, the foetus is fully developed and ready for delivery.

Parturition and Lactation

Human pregnancy’s average time period is about 9 months, and it is known as the gestation period.

Parturition is the process of childbirth after the vigorous contraction at the end of pregnancy. Lactation is the process that starts by the end of pregnancy by producing milk. This process helps the mother to feed the infant. Colostrum, the initial days of lactation, contains several antibodies for the development of the baby.

Conclusion

As we have studied the above about the process of Human Reproduction which is an essential part and process of human beings. Human Reproduction starts with the development of the reproductive system in the male and female, respectively. In female human reproduction, the process starts with Gametogenesis and menstruation and results in pregnancy and delivery.