Definitions [7]
Reproduction is a process that results in the formation of new individuals of the same kind, though usually with slight genetic, structural and physiological variations.
Define the term puberty.
Puberty is the process of physical and hormonal changes by which a child’s body matures into an adult body capable of sexual reproduction to enable 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.
Define.
Fertilization
The formation of a zygote by the union of male and female gametes is known as fertilization.
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.
After nine months of pregnancy, the fully developed foetus is ready for delivery. The process of childbirth is called parturition.
or
Parturition is the act of expelling the full term foetus from the mother's uterus at the end of gestation.
The term lactation refers to the secretion and ejection of milk by the mammary glands.
Key Points
- Humans are sexually reproducing and viviparous (give birth to young ones, not eggs).
- 6 stages of reproduction in order: Gametogenesis → Insemination → Fertilisation → Implantation → Gestation → Parturition.
- Gametogenesis (gamete formation), Insemination (sperm transfer), Fertilisation (fusion → zygote), Implantation (blastocyst attaches to uterine wall), Gestation (embryo development), Parturition (delivery of baby).
- Sperm formation continues throughout a man's life; ovum formation ceases at around age fifty (menopause) in women.
- Testes (males) produce sperm; Ovaries (females) produce eggs; these are the primary reproductive organs (gonads).
- Features like beard (males) and breasts (females) are secondary sexual characters; they do not directly participate in 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.
- Parturition is the process of childbirth, i.e., the delivery of the foetus at the end of the gestation period.
- It is controlled by a neuro-endocrine mechanism involving signals from the fully developed foetus and placenta.
- Foetal signals trigger uterine contractions known as the foetal-ejection reflex (labour pain).
- Hormones like ACTH and corticosteroids from the foetus stimulate the release of oxytocin from the mother’s pituitary gland.
- Parturition occurs in three stages: dilation, expulsion of the baby, and after birth (placenta removal).
- Lactation is the process by which mammary glands produce milk at the end of pregnancy, under the influence of the hormone Prolactin.
- The first milk secreted soon after childbirth is called Colostrum - it is sticky, yellowish and rich in proteins, lactose and antibodies (IgA); fat content is low.
- Antibodies (especially IgA) in colostrum provide passive immunity to the newborn when its own immune system is not yet fully developed.
- Lactation helps the mother in feeding and nourishing the newborn baby, providing all essential nutrients required in early life.
