Reproduction - The Human Edition

Reproduction - The Human Edition

Reproduction is the story of how you, me and 7.8 billion humans were born on the earth!

Humans undergo sexual reproduction where the sperm from the father fuses with the egg cell from the mother. This results in an offspring being born.

Male Reproductive System 🍆

Organ Function
Sperm The male reproductive gamete
Testes Produce sperm and testosterone
Scrotum A sac containing testes (outside body)
Sperm ducts Carries semen from testes to the urethra
Prostrate gland Produces semen; a liquid in which the sperm swim
Urethra Used to pass semen and urine at different occaisons
The male reproductive organ that is inserted into the
vagina during sexual intercourse

Female Reproductive System 🌺

Organ Function
Egg cell The Female Gamete
Ovaries Produce egg cells once in 4 weeks
Fallopian tubes
Connects the ovaries to the uterus
Uterus Has thick muscular walls that are occupied by the
developing baby during pregnancy
- Narrow muscular opening at the end of the uterus
which is guarded by muscles
- Leads to the vagina
Vagina Receives semen from the erect penis during sexual

A Comparison between male and Female Reproductive Gametes

Sperm Egg cell
Size Smaller than egg cells (~50μm) ~30 times larger than sperms
Structure Consists of:
1. Head
2. Tail (flagellum)
3. Acrosome (containing enzymes)
Consists of a deep layer of jelly
Ability to move (Mobility)
Can swim through the semen; extremely mobile Can move, but less mobile than sperms
Number(s) produced
Millions at a single ejaculation One in 4 weeks, from puberty till

Adaptive features of Sperm 💦

Adaptive Feature Function
Flagellum Generates swimming movements to
get to the Egg Cell
Mitochondria Releases energy needed to generate
swimming movements in the Flagellum
Enzymes in the Acrosome Helps dissolve the way through the Jelly
surrounding the Egg Cell

Adaptive features of Egg Cells 🥚

Adaptive Feature Function
Cytoplasm containing
energy stores
Provides energy to divide the Zygote
post fertilisation
Layer of Jelly that changes
during fertilisation
Forms an impregnable barrier to prevent
any more sperm cells from entering the Egg Cell

Fertilisation and Development

portraying sperm cells going into vagina
Definition: Fertilisation is defined as the fusion of the nuclei from a male gamete (sperm) and a female gamete (egg cell/ovum)
  • Once the sperms reach the egg cell, they begin to use enzymes in their vesicles to dissolve their way into the thick jelly layer. Only one sperm cell (in rare cases more than one) is able to do so.
  • The head containing the nucleus enters the egg cell; its tail remains outside it. The egg cell and the sperm cell fuse together. This is known as fertilisation. A zygote (diploid cell) is formed.

The Formation of An Embryo

The zygote continues to move slowly towards the uterus. As it proceeds it divides by mitosis. Soon a ball of cells called the embryo forms.


When the embryo reaches the uterus, it sinks into the uterus wall. This is known as Implantation.

The Formation of the Fetus and the Umbilical Cord

  • After implantation, the embryo begins to develop. The embryo’s cells begin to take up different functions. Some become skin cells, some muscle cells, some blood cells and so on.
  • 6 weeks post fertilisation is the time where the major organs begin to emerge. It begins to move when the muscles are developed when it is 8 weeks old.
  • 11 weeks post fertilisation; the organs are in their correct positions. The embryo develops into the Fetus
  • As this happens, an umbilical cord develops as well. The umbilical cord consists of 2 arteries and 1 vein. The arteries take blood from the Fetus into the placenta. The vein returns the blood to the Fetus.
  • Psst. I know this is a lot of information to take in all at once. Just wanted to say that you're doing great (like seriously), and don't forget to reward yourself with a few breaks here and there to let all this information sink in 😊.

The Placenta

  • As the embryo grows, a structure called the placenta also develops.
  • It is soft and dark and has finger like projections called the villi
  • The villi help connect the placenta to the uterus wall.

Functions of the Placenta

  • The placenta is the embryo’s life support system.
  • It is responsible in the exchange of substances between the embryo and the mother.
  • It separates the mother’s and the fetus’s blood and brings them close enough so that nutrients can diffuse across two different concentration gradients.
  • Oxygen and food materials diffuse across the placenta into the fetal blood.
  • Carbon dioxide and waste materials diffuse the other way, into the mother’s blood
  • It acts as a barrier to prevent the passage of some Toxins and Pathogens; Toxins such as Nicotine, and Pathogens such as Rubella can pass through the placenta and can affect the growth of the fetus.

Ante-natal care

Ante-natal (before birth) care is a routine care for the healthy pregnant woman.

Dietary Needs

The mother needs to take care of her diet as everything she will eat will diffuse across the placenta to her baby.

Some of the nutrients that are necessary for the mother and her baby are:

Nutrient Function
Amino acids Healthy growth and development of fetus
Carbohydrates To give the mother energy for day-to-day
Calcium Development of fetus’s bones
Iron To make Haemoglobin


  • Gentle exercise (swimming or walking)
  • Special exercises (that will prepare the mother when giving birth to the baby)

Substances to Avoid 💨

Substance/ Disease Effect(s)
(nicotine and carbon monoxide)
Restricts growth of baby
Alcohol consumption May be risky to the baby’s life
Illnesses (such as Rubella) - Produces rash and fever
- Baby may be born deaf
Drugs May be risky to the baby’s life

Birth 👶

The process of Being Born- described in scientific terms below:

  1. First, the Amniotic Sac breaks.
  2. This is followed by the contraction of the muscles in the uterus wall, which dilates (stretches out) the opening of the cervix.
  3. Next, the baby passes through the vagina.
  4. After which the Umbilical Cord is tied and cut.
  5. And finally, the afterbirth is delivered

Note: The Afterbirth is the breaking of the placenta from the Uterus walls, which is then taken out after the baby has come out.

Breast Feeding Vs Bottle Feeding using Formula Milk

Advantages Disadvantages
Breast Feeding 1. Sterile
2. Free of cost
3. Improves bond between mother and baby
4. Perfect composition of nutrients needed
for the baby
5. Composition of nutrients naturally changes
according to baby’s growth
6. Contains antibodies
7. Gives the baby passive immunity
1. The father is unable to bond and spend time
with the baby
2. Sometimes the mother is unable to produce
sufficient breast milk
3. It can be difficult for mothers to breast feed
babies in certain situations
4. Keeps the mother preoccupied
Bottle Feeding
(Formula Milk)
1. Helps father to bond with baby
2. Gives mother time to relax and do other jobs
1. Expensive
2. Needs extra effort to maintain sterility
3. Probability of getting infected is high
4. Does not give the baby passive immunity

Puberty 👨‌

The point in a person’s life where sexual maturity is reached is defined as puberty or adolescence. Puberty prepares a boy or a girl for adulthood and reproduction.

When a person reaches puberty:

  • Sperm production begins in a boy
  • Ovulation begins in a girl

Along with these, the secondary sexual characteristics develop as well during this time. These all are caused by certain sex hormones.

Sex Hormone Function
Adolescent Males Testosterone - Development of secondary sexual characteristics
Adolescent Females Oestrogen - Development of secondary sexual characteristics
- Making the uterus lining thick and spongy
during menstruation

Secondary Sexual Characteristics

Secondary sexual characteristics in Males Secondary sexual characteristics in Females
Voice breaks (Becomes deeper) 🗣 Breasts Develop 🍈
Penis begins to grow 🍆 Vagina becomes larger and wider 🌸
Facial hair, pubic hair, hair in armpits emerge Hairs emerge in armpits and in pubic areas
Body becomes more muscular 💪 The pelvis (hip) widens 🦵
Testes begin sperm production 🍒 Menstruation begins 🩸

The Menstrual Cycle 🩸

Tampons on Unsplash

When a girl reaches puberty (adolescence), she begins menstruating. As explained before, this is the indication that the girl is physically ready for reproduction.

By definition, Menstruation is the loss of the uterus lining through the vagina.

The menstrual cycle in women is a continuous process in which the lining of the uterus thickens and gets prepared for pregnancy; the woman does not get pregnant, the lining is shed at menstruation.

In most women, the cycle lasts about 28 days. During this time, the woman (or teenage girl) experience mood fluctuations due to the hormonal changes in the body.

Hormones in the Menstrual cycle

Hormone Site of secretion Function
Follicle Stimulating
Hormone (FSH)
Pituitary Gland Stimulates the developing follicle to keep secreting Oestrogen
Hormone (LH)
Pituitary Gland
Oestrogen Developing Follicle Makes the uterus lining grow thick and spongy
Progesterone Corpus Luteum Keeps the uterus lining thick, spongy and well supplied with blood
Common Misconception: Oestrogen makes the uterus wall develop into a thick and spongy layer; Progesterone maintains the lining.

Steps in the Menstrual Cycle

Ovary Pituitary Gland (In the Brain)
1. A follicle develops
2. Secretes Oestrogen
3. Oestrogen concentrations in the blood
increase ⏫
4. Lining of the uterus grows thick
and spongy
1. Secretes LH, FSH
2. Stimulates follicle to secrete Oestrogen.
When the follicle is fully developed, there is a surge in the levels of:
- LH at a greater extent ⏫
- FSH at a smaller extent 🔼
Ovulation occurs and the follicle releases the egg cell
- Empty follicle stops secreting oestrogen
- It is now called as a Corpus Luteum
Levels of LH and FSH fall in the blood ⤵️
If the Egg cell is fertilised 🐣 If the Egg cell is not fertilised 🩸
1. Corpus Luteum doesn’t degenerate quickly 1. Corpus Luteum gradually disappears
2. Secretes progesterone until the embryo sinks
into uterus wall and a placenta develops
2. No more progesterone is secreted
3. Placenta secretes progesterone throughout
the pregnancy
3. Uterus lining breaks down
4. Keeps the uterus lining thick and spongy so
that menstruation does not occur during pregnancy
4. A new follicle develops

Birth Control

Birth control is important in order to keep families small and limit the increase of the human population exponentially.

There are many birth control methods practiced by people worldwide. These birth control methods usually come into 4 categories: Natural, Chemical, Barrier, and Surgical.

1. Natural Methods

How they work Abstinence Woman avoids sexual intercourse completely 🙅‍♀️
Other Methods - Woman keeps track of her body temperature
(that rises at ovulation) and doesn’t have sex
during this period 🌡
- Woman checks if the mucus produced in her
vagina has become slippery or not
Advantages Useful for couples who don’t want to use other measures of birth
control for religious or other reasons 🛐
Disadvantages It is never possible to be 100% certain about ovulation period

2. Chemical Methods

How they Work Spermicides - Spermicides can be used to kill sperm that enter
the vagina 💀
- They can be effectively used in combination with
another method: a diaphragm
Contraceptive Pills 💊 - Contraceptive pills containing sex hormones can
be taken by the woman; this stops the production
of egg cells in the ovaries
IUD (Intra-Uterine-Device) - An IUS releases hormones that prevent implantation
and development of any fertilised egg cell.
- Sometimes contains Copper (Cu).
- A similar device called as an IUS can be used.
Advantages - A very effective method only when contraceptive pills are taken at the right time.
- The IUS and IUD lasts till 10 years 🕰.
Disadvantages - It is important to have regular checks by a doctor 👩‍⚕️ as some women do experience side
effects of contraceptive pills.
- Contraceptive pills play a vicious part in river pollution and cause some male fish to
change gender.

‌ 3. Barrier Methods

How they Work Condom ☔️ - A condom is a piece of rubber sheath
- A condom is placed upon the erect penis
and acts as a barrier between the sperm
and the vagina.
Femidom - A Femidom is a female version of a condom
and is used similarly
Diaphragm (or cap) 🧢 - A diaphragm is a circular and slightly domed
piece of rubber- Inserted into the vagina on
the top of the cervix
- Diaphragms are often used with spermicide
for the best results
Advantages - Condom is a very safe method of contraception only if it is used correctly.
- Condom helps in the prevention of HIV and gonorrhoea 🦠
- Diaphragm is also a very safe and reliable method IF used with spermicide
Disadvantages - Care must be taken when using a condom or a femidom; no sperm
should escape through it. 💦

4. Surgical Methods

How it works Vasectomy The sperm ducts are cut and tied, thus preventing
the passage of any sperms produced.
Female Sterilisation The oviducts are cut or tied, stopping egg cells from
travelling down the oviduct.
Advantages - Extremely reliable and sure method of contraception. 💯
- Have no side effects.🌞
Disadvantages - The tubes cannot be often opened. 🔒
- Not suitable for young couples who may wish to have children later.

Sexually Transmitted Infections (STI)

🎗Condoms can protect against HIV/AIDS and other sexually transmitted infections (STI/STD). Femidoms too, by the way. Stay safe → talk to each other.

An infection that is transmitted through body fluids via sexual contact is called as a sexually transmitted infection (STI). Till date, the most treacherous STI has been the Human Immunodeficiency Virus (HIV)

HIV and the Immune System

HIV reproduces by infecting a particular type of lymphocytes called the T-cells. Slowly and steadily, it destroys the person’s T-cells and hence, the person’s immune system becomes more vulnerable to diseases in the environment.

The person may develop cancer as well because one function of the immune system is to destroy cancerous tumours. They may also develop AIDS (Acquired Immune Deficiency Syndrome) within 10 years if proper treatment is not given.

There is no cure for AIDS. Research is being conducted worldwide to produce a vaccine that can kill the virus without infecting body cells...

...But still there is a ray of hope- HIV cannot be cured; it can be prevented.

HIV transmission methods

  • Unprotected sexual intercourse with infected people
  • Drug usage involving sharing needle used by infected people
  • Transfusion of infected blood
  • Infected mother to baby through placenta
  • Feeding a baby with breast milk from an infected mother
  • Unsterilised surgical instruments

Preventing HIV

  • Never have more than one sexual partner
  • Use condoms
  • Never have unprotected sexual intercourse
  • Always sterilise needles before injecting drugs into your blood
  • Screen blood for HIV when donating blood
  • Always wear protective clothing when dealing with road accidents, if you are a policeman or a paramedic (I’m almost sure you aren’t!)‌‌

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