Evolution is the process of change over time of living organisms. Humans have evolved from our apelike ancestors centuries ago. An organism is a living thing and biology is the study of organisms. Human beings are a species of mammals that live on planet Earth. Scientists and biologists study human beings from how they are conceived, to how they grow, develop, and up until death.
What happens during human reproduction?
Human beings are divided into two different genders, male and female. They are differentiated by their different reproductive systems. The male reproductive system contains a penis while the female reproductive system contains her vagina. Humans reproduce sexually via intercourse. For this to happen, the males penis gets erect and is inserted into the female’s vagina. Sexual intercourse takes place with back and forth motions from the penis and vagina until climax occurs and the male ejaculates sperm and semen into the vagina.
👉This articles describes the organs, both male and female, that are involved in human reproduction. The reproductive process itself is covered in other articles.📚
Sperm cells are produced in the males testes. Egg cells are produced in the female’s ovary. Fertilisation occurs in the fallopian tube when a sperm and egg cell meet. 500 million sperms are deposited into the vagina during sexual intercourse and swim up by chemotaxis which is attraction towards a chemical released by the egg. As the sperms travel up through the female reproductive system, more than half are killed by acidic vaginal secretions and others die on the journey (1-5hours). Using enzymes from the acrosome, one sperm penetrates the egg, leaving its body and tail behind. The nuclei of the sperm and egg fuse, forming a zygote.
Egg lives for 24-48 hours and sperm (in female cervical mucus) for 2-3 days. The fertile period is the period of time in the cycle when an egg can be fertilised (days 12-16).
Development up to implantation
After fertilisation the zygote divides by mitosis as it moves down the fallopian tube, by peristaltic contractions, until after 1 week it reaches the uterus and implantation occurs (day 7). The zygote first becomes a morula (solid ball of 32 cells). Eventually it forms into a hollow ball called the blastocyst, with a fluid filled cavity and inner mass that will become the embryo. The blastocyst implants and the outer cell layer of the blastocyst- the trophoblast – forms the chorion and the amnion that will surround the embryo. The amnion contains fluid to cushion the embryo and the chorion forms the villi of the placenta. Blood vessels from the villi converge in the umbilical cord, the lifeline between the placenta and the embryo.
Implantation is the attachment of the blastocyst to the endometrium.
Conception is fertilisation followed by successful implementation.
After conception the female is pregnant for usually around 40 weeks before going into labour and giving birth.
I will now explain the difference between sexual characteristics of males and females. Secondary sexual characteristics are the physical features that appear during puberty and adolescence. They have been induced by the sex hormones testosterone in males and oestrogen in females.
Males get a deeper voice or enlarged larynx, growth of public, underarm, facial, and body hair, a growth spurt, and increased muscular and bone development.
Females develop breasts, a widening of the pelvis, an increase of body fat, growth of underarm hair, and a growth spurt.
The male and female reproductive systems produce different hormones for males and females. Males produce testosterone, while females produce oestrogen and progesterone. These hormones work differently.
Testosterone is produced in the testes and causes the primary sex characteristics in early life such as growth of the penis and other reproductive parts. It also causes the production of sperm in the testes and testosterone is responsible for the male secondary sexual characteristics.
Oestrogen in females is produced in the ovary and causes endometrium to develop. High levels just before day 14 stimulate the production of LH by the pituitary gland. Oestrogen causes the development of secondary sexual characteristics in females.
Progesterone is also produced by the ovary. Its function is to keep endometrium built up and also stops the uterus from contracting.
A Female’s body goes through a series of changes every month which prepares her body for pregnancy. This is known as the menstrual cycle. This is what happens during the menstrual cycle: the ovaries in the female reproductive system produce hormones oestrogen and progesterone which causes a build up of the lining of the uterus or womb. This means that the built up lining of the womb makes it ready for a fertilised egg to attach to the womb and start developing. If there is no fertilised egg, the lining breaks down and starts to bleed which is known as a period. A female will go through a monthly process of what’s called the menstrual cycle. This is a series of changes in a woman’s body each month which is preparing her for pregnancy. Each month the ovaries release an egg. This is called ovulation. Hormones are preparing the woman for pregnancy. When a man’s sperm fertilises with a woman’s egg , this is when pregnancy happens. The menstrual cycle is a 28 day cycle in females. It brings on a series of changes in the woman’s uterus lining as it responds to the changing levels of hormones oestrogen and progesterone. It is hormones that control the menstrual cycle.