Sexual reproduction in humans

  • Sexual reproduction is process involving the fusion of haploid nuclei to form a diploid zygote and the production of genetically dissimilar offspring.
  • Reproduction in humans is when the male gamete (spermfuses together with the female gamete (ovum/egg).
  • The fertilized egg goes on to divide many times to form a ball of cells.  This grows into an embryo which eventually develops into a separate individual.
human-Male reproductive system
Male Reproductive System
  • Testes:produce sperm and testosterone
  • Scrotum: sack of skin which holds the testis.
  • Epididymis: sperm storage area that wraps around the superior and posterior edge of the testes.
  • Seminal vesicles:  produce a sugar-rich fluid (fructose) that provides sperm with a source of energy to help them move.
  • Vas deferens: transports mature sperm to the urethra, the tube that carries urine or sperm to outside of the body, in preparation for ejaculation.
  • Sperm ducts: carries sperm from testes to urethra.
  • Prostate gland: produce alkaline fluid to make semen
  • Urethra:urinate; pass semen and sperm through penis
  • Penis:become firm, inserted into vagina during sexual intercourse to transfer sperm.


Female reproductive system
Female reproductive system

Comparison between male and female gamete

Sperm Ova
Release in millions Release one at a time
Very small in size (0.05mm- of which around 80% is tail) Comparatively large ( 0.1mm in diameter)
Able to move / swim on their own by using their tail Unable to move on their own. Move by the action cilia and peristaltic contraction of oviduct.
Very small cytoplasm A lot of cytoplasm which contains nourishment for the zygote if the ovum is fertilized
Nucleus contain X or Y chromosomes Nucleus contains X chromosomes


The ovary

  • Human ovaries are a pair of almond shaped structures about 3cm long.
  • Each month, an ovary produces an egg that bursts from ovary during ovulation.
  • The egg develops inside a fluid filled structure called follicles.
  • Fluid pressure in the follicle increases to level the burst the follicle releasing the matured egg onto the surface of the ovary.

the ovary

Menstruation cycle

  • The cyclic changes that occur in the reproductive organs of primate females is called menstrual cycle
  • The cycle normally lasts about 28 days, although there is some variation from one woman to another.
  • If ovulation takes place and the egg isn’t fertilized, the lining of the uterus sheds through the vagina. This is a menstrual period.

menstrual cycle

The menstruation cycle take place as follow:

  • Beginning of the cycle. The pituitary secretes Follicle Stimulating Hormone (FSH) and a little Leutenizing Hormone (LH) into the bloodstream which cause the follicles to begin to mature.
  • The maturing follicles then release another hormone, As the follicles ripen over a period of about seven days, they secrete more and more estrogen into the bloodstream.
  • Estrogen causes the lining of the uterus to thicken. It causes the cervical mucus to change.
  • When the estrogen level reaches a certain point it causes the hypothalamus to release Leutenizing Hormone from the pituitary.
  • This surge of LH triggers the one most mature follicle to burst open and release an egg. This is called ovulation.
  • The follicle from which the egg burst becomes the corpus luteum (yellow body). It produces the hormones estrogen and, in larger amounts, progesterone which is necessary for the maintenance the uterus lining.
  • If the egg is not fertilized, the corpus luteum degenerates and no longer produces progesterone , the estrogen level decreases, the top layers of the lining break down and are shed, and menstrual bleeding occurs.

Changes that occur during menstruation cycle

changes during menstrual cycle

menstrual cycle2


  • Fertilizationis the union or joining of the egg and the sperm, resulting in a fertilized egg, otherwise known as a
  • The human female reproductive system working during reproduction and fertilization. The egg is released from the ovary and moves toward the oviduct.
  • During sexual intercourse, semen is expelled into the vagina, sperm swim through the cervix and uterus until they reach the Fallopian tubes
  • The sperm that reaches the egg will use an enzyme in its acrosomes to make an opening in the membrane of the egg.
  • Once one sperm enters the egg (only the head enters) the egg forms a membrane that prevents other sperm from entering.
  • The nucleus of the egg fuses with the nucleus of the egg. A diploid zygote forms.
  • The fused gamete, a zygote, undergoes cell division and the continued growth of the zygote will occur in the form of an embryo



  • Implantation is a process in which a developing embryo, moving as a blastocyst through a uterus, makes contact with the uterine wall and remains attached to it until birth.
  • The uterus has thick walls suitable for egg attachment and growth.
  • While the embryo is developing, structures form outside the embryo that support and nourish the embryo and fetus.
  • Two specialized membranes develop outside the embryo. One, called thechorion, combines with tissues created by the mother to become the
  • The other, called theamnion, surrounds the amniotic cavity, which fills with amniotic fluid that protects the developing embryo and fetus.
  • This fluid-filled sac helps to cushion the fetus during later development.



  • It’s a process of developing mass of cells moves inward, forming a ball of cells called agastrula.
  • It has 3 layers Each layer of cells in the gastrula eventually becomes a different type of tissue:
    Ectoderm: skin, nervous system
    : lining of gut and internal organs
    : muscles, bones, heart
  • After gastrulation, the specialized cells of the ectoderm, mesoderm, and endoderm begin migrating toward other cells with the same specialty.
  • This cellular migration is referred to asmorphogenesis because it gives the embryo a shape. As cells differentiate, organ systems begin to form.


The Embryo

  • At the end of the embryonic period, a human embryo is about an inch and a half long and has recognizable human body structures.
  • The initial formation of in gastrulation period major bodily areas, less essential characteristics begin to develop such as the eyes, ears and nose.
  • By the tenth week of pregnancy these facial characteristics become recognizable, and the overall figure of the embryo now resembles that of a human.
  • By the fourteenth week, all the major characteristics of the embryo have more or less developed, and possess all the requirements of a fully functional being.
  • From this time onwards, the embryo will continue to grow in size rather in complexity via cell division.


The development of the fetus

  • At the end of the embryonic period, a human embryo is about an inch and a half long and has recognizable human body structures.
  • It is the development of a fertilized egg that occurs early on in pregnancy.
  • Organs such as the heart develop and, after 8 weeks, the embryo is called a fetus.
  • Growth of the fetus requires a good supply of nutrients and O2. This is achieved through the link between the placenta and the mother’s blood supply in the uterus lining.
  • The placenta grows into the wall of the uterus and is joined to the fetus by the umbilical code.
  • Blood from the fetus passes through the umbilical cord in the umbilical artery to the placenta.
  • Transport O2 + nutrients from mother to fetus.
  • Transport CO2 + wastes from fetus to mother through umbilical vein.
  • The placenta has two important functions:
    * Passing oxygen and nutrients from the mother’s blood into the embryo or fetus.
    * Removing waste materials from the embryo or fetus.
  • Forty weeks later, nine months since fertilization, the embryo, now in the foetal stage is mature enough to enter the world.


Factors Affecting Fetal Development
  • Poor nutrition
  • Use of alcohol
  • Smoking
  • X-rays and other kinds of radiation
  • Illnesses such as AIDS, smallpox, , or severe flu



  • After nine months the baby is fully developed and ready to be born into the big wide world.
  • These days, if the pregnant female has difficulty with the pregnancy.
  • When the time is right, the cervix relaxes and muscles in the wall of the uterus contract. This contraction forces the baby through the cervix and vagina and out of the mother’s body.
  • The umbilical cord is cut by the doctor to separate the mom from the baby.




Nutritional needs of pregnant women


  • Good nutrition during pregnancy can help to keep you and your developing baby healthy.
  • Eating healthily during pregnancy will help your baby to develop and grow.
  • You don’t need to go on a special diet, but it’s important to eat a variety of different foods every day to get the right balance of nutrients that you and your baby need.
  • Daily you can these foods daily :
    • Fruit and vegetables. E.g. Apple, orange, banana.
    • Starchy foods (carbohydrates). E.g. bread, potatoes.
    • Protein. E.g. fish, egg.
    • Dairy. E.g. Milk, yogurt.
    • Foods those are high in sugar or fat. E.g. ice-cream, cake.




The advantages of breast milk compared with bottle milk


  • Breast milk is always available and free.
  • Breast milk contains active infection-fighting white blood cells and natural chemicals that give increased protection against infections in the first months, when these can be the most serious.
  • Breast milk contains the perfect proportion of nutrients that your baby needs, including protein, carbohydrates, fat, and calcium.
  • Breast milk is easily digestible.



Methods of Birth control

Birth control, also known as contraception, is designed to prevent pregnancy.

There are 5 main groups of birth control methods: natural, chemical, mechanical, hormonal and surgical.


  • Natural method
    1. Withdrawal Method

In this method the man is to withdraw his penis out of the vagina before ejaculation. This is not a reliable method as sperms may leak out early during intercourse

  1. Rhythm Method

This involved abstaining oneself from sexual intercourse during the fertile period of the menstrual cycle (between day 11 to day 15 after the first day of menstruation) .This is an unreliable method because it depends on the regularity of the menstrual period of the women

  • Chemical method
      1. Spermicide It contains a chemical that kills sperm. It comes in the form of foam, jelly, cream, or film that is placed inside the vagina before sex.


  • Mechanical method
    1. Intrauterine Device (IUD)

It is a small plastic or metal device placed in the uterus by a doctor .It prevents implantation of the fertilized ovum.

  1. Male CondomThe latex condom is the classic barrier method. It prevents sperm from entering the woman’s body, protecting against pregnancy and STDs.
  1. Female CondomThe female condom is a thin plastic pouch that lines the vagina and can be put in place up to 8 hours before sex. Users grasp a flexible, plastic ring at the closed end to guide it into position.


  • Hormonal method
    1. Oral contraceptive pills

It contains a combination of synthetic hormones (progesterone and oestrogen). One pill must be taken a day for 21 consecutive days beginning on the 5th day of menstruation. The hormones in the pills act to prevent the release of ovum from the ovary (ovulation).

  • Surgical method
    1. Tubal Ligation A surgeon closes off the fallopian tubes, preventing eggs from making their journey out of the ovaries.
  1. Vasectomy – Besides condoms, a vasectomy is the only birth control option available to men. It involves surgically closing the vas deferens – the tubes that carry sperm from the testes, through the reproductive system. This prevents the release of sperm but doesn’t interfere with ejaculation.