Revision: Reproduction >> Human Reproduction CUET (UG) Human Reproduction

The release of the ovum from the ovary is called ovulation.

The rhythmic series of changes in the sex organs throughout the reproductive life of a female primate (e.g., monkeys, apes, and human beings) from puberty to menopause is called the menstrual cycle (L. mensis = month, lunar month).

It is the stage when a girl menstruates for the first time.

The period from birth to the natural death of the organism represents its life span.

Gametogenesis is the process by which male and female primary sex organs produce gametes (sperms and ova).

or

Gametogenesis is the process by which male and female gametes are formed from germinal cells in the gonads through a series of developmental stages.

Spermiation is the process of releasing mature spermatozoa. In this, spermatozoa are shed into the lumen of the seminiferous tubule for transport.

After spermiogenesis, sperm heads become embeded in sertoli cells from which they obtain their nutrition and finally get released into the lumen of seminiferous tubules. This process of release of mature sperms from sertoli cells is called spermiation.

Spermiogenesis is the process of transforming spermatids into mature, flagellated spermatozoa (sperms).

The process of transformation of a circular spermatid to a spermatozoon is called spermiogenesis.

Gametogenesis is the process of formation of gametes i.e., sperms and ovary from the primary sex organs in all sexually reproducing organisms. Meiosis plays the most significant role in the process of gametogenesis.

The formation of a zygote by the union of male and female gametes is known as fertilization.

The fusion of the male gamete (sperm) and female gamete (ovum) to form a zygote is called fertilisation.

or

Formation of a zygote by the union of a sperm and an ovum is called fertilisation.

The process of the blastocyst embedding itself into the endometrial lining of the uterus about 5–7 days after ovulation is called implantation.

or

The process of fixing of the blastocyst to the wall of the uterus/endometrium is termed implantation.

• The menstrual cycle is a series of monthly changes in females of reproductive age.
• The beginning of the cycle is called menarche, and its permanent stop is called menopause (around 45–50 years).
• It occurs mainly in primates, including humans, and involves changes in the ovaries and uterus.
• The cycle is controlled by hormones (gonadotropins and ovarian hormones) and repeats every ~28 days.
• In the middle of the cycle, ovulation occurs, where an egg is released from one of the ovaries.

• Gametogenesis is the process of formation of male and female gametes in the reproductive organs.
• It occurs in the testes of males and ovaries of females.
• Spermatogenesis produces sperms, while oogenesis produces ova (eggs).
• In this process, diploid germ cells form haploid gametes for sexual reproduction.

• Fertilisation in humans is the fusion of male and female gametes (sperm and ovum) and is an internal process occurring in the oviduct, leading to the formation of a diploid zygote.
• During copulation, millions of sperms are released into the vagina, but only one sperm reaches the ovum due to selection and protective barriers around the egg.
• Before fertilisation, sperm undergo capacitation and move towards the ovum; interaction between sperm and egg involves recognition molecules like fertilizin (ovum) and antifertilizin (sperm).
• The sperm’s acrosome releases enzymes that help digest the egg coverings (corona radiata and zona pellucida), allowing sperm entry through the membrane.
• After entry, the sperm nucleus and the ovum nucleus fuse (syngamy), forming a zygote (2n); this process restores the diploid chromosome number (46 in humans).
• Fertilisation triggers completion of meiosis II in the oocyte, formation of the second polar body, and formation of the female pronucleus and male pronucleus.
• In humans, sperm carry 22+X or 22+Y chromosomes, while ova carry 22+X only, determining the genetic sex of the offspring.

• The zygote divides by mitosis (cleavage) while moving towards the uterus.
• It forms blastomeres, and the 8–16 cell stage is called morula.
• Morula develops into a blastocyst with trophoblast (outer layer) and inner cell mass.
• Trophoblast attaches to the uterine lining (endometrium), and the inner cell mass forms the embryo.
• Implantation is the embedding of the blastocyst into the endometrium, leading to pregnancy.