Reproduction is the story of how you, me and 7.4 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	Carry 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 times
Penis	The male reproductive organ that is inserted into the vagina during sexual intercourse

Female reproductive system

Organ	Function
Egg cell	Female gamete
Ovaries	Produce egg cells once in 4 months
Fallopian tubes (oviducts)	Connect the ovaries to the uterus
Uterus	Has thick muscular walls that are occupied by the developing baby during pregnancy
Cervix	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 intercourse.

A comparison between Male and Female reproductive gametes

	Sperm	Egg cell
Size	Smaller than egg cells	Larger than sperms
Structure	Consists of: Head Tail (flagellum) Vesicle (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 menopause

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.

	Adolescent Males	Adolescent Females
Sex Hormone	Testosterone	Oestrogen
Function	Development of secondary sexual characteristics	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 harder)	Breasts develop and grow bigger
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 and stronger	The pelvis (hip) widens
Testes begin sperm production	Menstruation begins

The Menstrual Cycle

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

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. 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 (in the brain)	Stimulate the developing follicle to keep secreting oestrogen
Luteinising Hormone (LH)	Pituitary Gland (in the brain)	Stimulate the developing follicle to keep secreting oestrogen
Oestrogen	Developing Follicle	Makes the uterus lining grow: thick spongy
Progesterone	Corpus Luteum	Keeps the uterus lining: Thick Spongy Well supplied with blood
Common misconception: Oestrogen makes the uterus wall develop into a thick and spongy layer; progesterone maintains the lining

The process of the menstrual cycle

Ovary	Pituitary Gland (In the Brain)
A follicle develops Secretes oestrogen Oestrogen concentrations in the blood increase Lining of the uterus grows thick and spongy	Secretes LH, FSH 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 fertilized

If the egg cell is not fertilized

Corpus Luteum doesn’t degenerate quickly
Secretes progesterone until the embryo sinks into uterus wall and a placenta develops
Placenta secretes progesterone throughout pregnancy
Keeps the uterus lining thick and spongy so that menstruation does not occur during pregnancy

Corpus Luteum gradually disappears

No more progesterone secreted

Uterus lining breaks down

A new follicle develops

Fertilisation and development

After ovulation, the egg cell is released out of the follicle.
It enters the fallopian tube (oviduct) and travels slowly through it.
If the egg cell is not fertilized within 8-24 hours, it degenerates and the uterus wall lining breaks down.

Sexual Intercourse

When the man is sexually excited, blood is pumped into his penis. This causes it to become erect.
Simultaneously, mucus is produced from the woman’s vagina to lubricate the passage of the penis
The erect penis is inserted into the woman’s vagina.
At a point, thrusting movements are made which stimulate the tip of the penis with the clitoris.
This results in a reflex action to take place:
The walls of the tubes containing the sperm contract rhythmically and sperm is ejaculated into the vagina.
This biological process is known as sexual intercourse and is the beginning of reproduction.

Ejaculation deposits the semen at the neck of the vagina (cervix).
The sperm cells begin the journey towards the egg cell. The journey of life…

Fertilisation

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

Implantation

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

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.
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 substances can diffuse.
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

The formation of a 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 fertilization 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.

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	Why needed
amino acids	Healthy growth and development of fetus
carbohydrates	To give the mother energy to walk around
calcium	Development of fetus’s bones
Iron	To make Haemoglobin

Exercise

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

Things to avoid

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

Birth

Giving birth to a child is what brings pleasure to every child’s parents. This is the final stage of reproduction.

The process of birth

Strong muscles in the wall of the uterus begin to contract
This is called labour
Contractions of the muscles slowly stretches the opening of the cervix
Simultaneously, the amniotic sac breaks
When the cervix is wide enough for the baby’s head to pass, the muscles of the uterus begin to push the baby outwards.
This stage is excruciatingly painful!
When the baby has been pushed out of the uterus, the placenta breaks away and passes out of the vagina.
This is called afterbirth
The baby is still connected with the umbilical cord, which is removed by cutting it just above the point where it joins the baby.
This leaves a mark at the stomach called the navel

Afterbirth Care

Though a baby develops for 9 months, it is extremely helpless at first. Both parents need to take special care with their child such as:

Mammals have a unique feature: lactation; mammary glands in the mother’s breasts begin to produce milk which is extremely nutritious and beneficial for the child.
The parents also need to support the child emotionally and physically till its adulthood
Parental care also includes teaching the child about how to take care of itself in the society

Breast feeding and Bottle feeding (Formula Milk)

	Advantages	Disadvantages
Breast feeding	Sterile Free of cost Improves bond between mother and baby Perfect composition of nutrients needed for the baby Composition of nutrients naturally changes according to baby’s growth Contains antibodies Gives baby passive immunity	Father is unable to bond and spend time with baby Sometimes the mother is unable to produce sufficient breast milk It can be difficult for mothers to breast feed babies in certain situations Keeps mother preoccupied
Bottle feeding (Formula milk)	Helps father to bond with baby Gives mother time to relax and do other jobs	Expensive Needs extra effort to maintain sterility Probability of getting infected is high

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, Mechanical and Surgical:

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

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)	Sometimes contains copper A similar device called as an IUS can be used. An IUS releases hormones that prevent implantation and development of any fertilized egg cell.
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 check ups 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 as well!

Mechanical 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.

Surgical Methods
How it works	Vasectomy	In a man the sperm ducts are cut and tied, thus preventing the passage of any sperms produced. In a woman the oviducts are cut or tied, sopping 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)

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 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 transmittion 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
Unsterilized 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 sure you aren’t!)

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Reproduction in humans