Reproduction in Plants and Animals | Biology Form 3

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Background information

All organisms are brought to being, live, and eventually they die. New organisms arise from existing organisms of the same kind thus ensuring continuity of species.

For example a maize plant will give rise to a new maize plant while a cat will give rise to a new cat.

The development of a new generation of organisms from existing generation is referred to as reproduction.

In form one we defined the term reproduction while in this topic we shall cover in details the process of reproduction in different organisms.

Objectives

By the end this topic you should be able to: -

  • Describe the location and appearance of chromosomes and chromosome movement during mitosis and meiosis.
  • Differentiate between mitosis and meiosis stating their significance in reproduction.
  • Describe asexual reproduction (binary fission, spore formation and budding) in living organisms.
  • Describe the process of fertilization in plants.
  • Differentiate between internal and external fertilization as exhibited by amphibians and mammals (humans).
  • Describe the role of hormones in human reproduction.
  • Identify and explain the methods of transmission and prevention of sexually transmitted infections.

REPRODUCTION IN PLANTS AND ANIMALS

Introduction

Reproduction is the process by which living organisms give rise to new organisms of the same kind. There are two types of reproduction depending on whether or not sex cells are involved.  These are: - sexual and asexual reproduction.
In this topic we shall cover the following areas: -

  • Cell division
  • Asexual reproduction in living organisms.
  • Fertilization in flowering plants
  • Reproduction in Amphibians
  • Fertilization, implantation and role of placenta in humans.
  • Gestation period
  • Role of hormones in reproduction in humans

The video clip below shows a bee landing on a flower to facilitate pollination and fertilization in frogs.Click on the play button to view the video clip.








Cell division

Reproduction, growth, repair and replacement of old cells involves the multiplication of cells. For cells to be able to multiply, they undergo cell division where one cell divides into two, two cells divide into four and so on. The resultant cells from these divisions are called daughter cells which are similar to the parent cells.

Play the animation below to see the cells dividing.

In order to understand the process of cell division, it is important that we discuss and understand chromosomes which are the vehicles of heredity. They determine characteristics of daughter cells and the organisms that develop from these cells.

Chromosomes

These are thread like structures found In the nucleus of a cell. Chromosomes remain invisible when a cell is not dividing. However, as a cell prepares to divide, the chromosome threads coil up forming a thicker, shorter and more compact structure. Each chromosome consists of two parallel strands called chromatids. The two chromatids are joined at one point called centromere. The chromatids, occurring in pairs are exact copies of one another, with the same length and shape. These pairs are called homologous pairs; each member of the homologous pair is called a homologous chromosome.

The illustration below shows two chromatids joined together at the centromere to form a chromosome.

Mitosis

In mitotic cell division, a cell divides into two daughter cells and each of the daughter cells have the same number of chromosomes as the parent cell i.e. the diploid number of chromosomes. The process of mitosis occurs in a sequence of stages, each of which is a continuation of the other. Each stage merges with one another without interfering with cellular activities. The stages of mitosis are: Interphase, Prophase, Metaphase, Anaphase and Telophase


The animation below shows the process of mitosis starting from interphase, prophase, metaphase, anaphase and telophase. Click on the play button to view the animation.


Interphase.

Often regarded as the resting stage. Cell has normal appearance as any non-dividing cell. Nucleolus is visible and chromosomes are not visible even under the light microscope.

During this phase;

  • Chromosomes replicate.
  • Organelles are synthesized through duplication.
  • There is a built-up of energy to be used during mitosis.

Early Prophase

  • Chromosomes become visible; nucleolus shrinks.
  • Centrioles move to opposite ends (poles) of the cell
  • Spindle fibers begin to form Centrioles

Late Prophase

  • Chromosomes become shorter and thicker
  • Each chromosome is seen to consist of a pair of chromatids joined at the centromere
  • Nucleolus disappears and nuclear membrane disintegrates.

Play the animation below to view, chromosomes becoming shorter and thicker, nucleolus shrinking, Centrioles moving to opposite poles of the cell and spindle fibers beginning to form.

Metaphase

  • Chromosomes arrange themselves on equator of the cells.
  • Homologous chromosomes do not associate
  • Chromosomes become attached to spindle fibres at the centromere

    This animation show chromosomes grouping themselves on equator of the cell and they become attached to the spindle fibres at the centromere.Click on the play button to see the animation.


    Anaphase

    • Contraction of spindle fibers causes the chromatids to separate and move to opposite poles of the cell.
    • The spindle apparatus begins to disappear.
    • In animal cells the cell membrane begins to constrict towards the end of anaphase.

    Play the animation to see contraction of spindle fibers causing the chromatids to separate and move to opposite poles of the cell.


    Telophase

    • The chromatids arrive at their respective poles.
    • Spindle fibres disappears completely.
    • A nuclear membrane forms around each set of chromatids which are now called chromosomes.
    • Cytoplasm divides into two, leading to the formation of two daughter cells.

    The animation shows spindle apparatus beginning to disappear and the cell membrane constricting to form two new cells in an animal cell.


    Importance of mitosis

    • Brings about growth since more new cells are formed
      Replacement of old or damaged cells
      Preserves the number of chromosomes as in the parent cell.

    Importance of mitosis

      Brings about growth since more new cells are formed
      Replacement of old or damaged cells
      Preserves the number of chromosomes as in the parent cell.

    MEIOSIS

    - Meiosis takes place during gamete formation. The number of chromosomes in daughter cells is haploid meaning that they are half of those in parent cell.

    - Occurs in two successive stages, each stage going through the same series of events. Hence the terms meiosis I and Meiosis II.

    - The parent cell first divides into two, and then the two daughter cells divide to give a total of four daughter cells.

    - The first meiotic division separates homologous chromosomes from one another; hence called reduction stage while the second meiotic division separates the chromatids in a chromosome from each other; this is mitotic stage.

    - The phases are the same as in mitosis. They are however indicated as I or II to indicate the stage in meiotic division.

     


    Play the animation below to see the process of first and second meiotic division.


    FIRST MEIOTIC DIVISION

    This is the first phase of Meiosis. It involves halving or reduction of the number of chromosomes.It comprises Interphase I, Prophase I, Metaphase I ,Anaphase I and Telophase I.

    Interphase I

    During Interphase I,

    • Chromosomes replicate.
    • Organelles are synthesized through duplication.
    • There is a build-up of energy to be used during meiosis.

    Prophase I

    During this phase,

    • Centrioles collect at the opposite ends of the cell.
    • Nucleolus disappears.
    • Homologous chromosomes lie side by side forming units called bivalents.
    • Chromosomes shorten and thicken, becoming visible.
    • Chromatids of homologous chromosomes may coil around each other; and at times remain joined at certain points that are called chiasmata (chiasma). At these points, some important genetic exchanges may occur.

    The animation shows appearance of two pairs of chromosomes, formation of chiasmata, crossing over of chromatids and the Centrioles migrating to the opposite sides of the nucleus. Click on the play button to view the animation.

    Note

    It is common for one or both of the chromatids of the two homologous chromosomes to break at the chiasmata and join up with the chromatids of another chromosome in the bivalent. During this stage, genetic materials are exchanged, a process called crossing over.


    The animation shows appearance of two pairs of chromosomes, formation of chiasmata, crossing over of chromatids and the Centrioles migrating to the opposite sides of the nucleus. Click on the play button to view the animation.

    Note

    • It is common for one or both of the chromatids of the two homologous chromosomes to break at the chiasmata and join up with the chromatids of another chromosome in the bivalent.
    • During this stage, genetic materials are exchanged, a process called crossing over.

    Metaphase I

    During metaphase I,

    • Spindle fibres are fully formed and attach to the chromosomes at the centromere.
    • The homologous chromosomes which are still paired up as bivalents move to the equator of the cell.
    • At this stage, some chromosomes have already exchanged portions during crossing over.

    Anaphase I

    • Homologous chromosomes separate.
    • They migrate to opposite poles with their centromere leading.
    • Cell membrane begins to constrict around the middle.

    Telophase I

    • Spindle apparatus disappear.
    • Nuclear membranes reform around the two sets of chromosomes.
    • Once the chromosomes reach the poles, the cell divides into two new cells, each with half the number of chromosomes as the parent cell.

    Play this animation to see homologous pairs of chromosomes aligning themselves on the equator of spindle fibers, homologous chromosomes separating and migrating to the opposite side along the spindle fibres and formation of new cells when the cell membrane constrict at the middle. Each cell has half number of chromosome.

    Note

    Separation of Homologous chromosomes into two daughter cells has been achieved in the first meiotic cell division. The second meiotic division will separate the chromatids from one another.


    SECOND MEIOTIC DIVISION

    After the first meiotic division, the daughter cells should proceed to Interphase. However the nuclear membranes sometimes fail to form around the two sets of chromosomes at the poles and the cell proceeds directly to prophase II of meiotic II. During second meiotic division, the chromatids separate resulting into four haploid daughter cells. Four stages prophase II, metaphase II, Anaphase II and Telophase II are involved.

    Prophase II

    • New spindle fibres are formed

    Metaphase II

    • Centrioles replicate and a new spindle is formed in each new cell
    • Chromosomes collect around the equator of the cell and attach to the spindle fibres at their centromeres
    • Chromosomes orientate themselves towards the opposite poles.

    Anaphase II

    • Sister Chromatids are pulled by contraction of spindle fibers towards opposite poles and become separated.

    The animation shows the formation of spindle fibers in each of the haploid daughter cells, aligning of individual chromosomes onto the equator of spindle fibers and the sister chromatids separating at the centromere and migrating to the opposite poles in each daughter cell.

    Click on the play button to view the animations.


    Telophase II

    • Spindle apparatus disappear
    • Nucleolus and nuclear membranes are reformed
    • Chromatids at the opposite poles are now the chromosomes
    • Cells constrict along the middle, giving a total of four daughter cells, often called a tetrad
    • Each cell has half the number of chromosomes meaning its haploid (n)
    • The chromosomes uncoil and become thin and invisible.

    Play the animation below to see the formation of four haploid daughter cells.

    Significance of Meiosis

    • It helps in restoring a constant diploid number of chromosomes in organisms after fertilization.
    • It brings about genetic variation among members of a species during chiasmata formation and subsequent crossing over.

    Comparison between Mitosis and Meiosis

    Similarities.

    • They both occur in plant and animal cells.
    • They both involve division of cells.

    Differences.

    • In mitosis the homologous chromosomes do not associate with one another while they pair up/lie side by side in meiosis.
    • In mitosis there is no crossing over while in meiosis chiasma formation leads to crossing over.

    • In mitosis unpaired chromosomes align on the equator of spindle fibres during metaphase while in meiosis paired chromosomes align on the equator during metaphase I.
    • Mitosis takes place in a single nuclear division while meiosis takes place in two nuclear divisions each with four stages.
    • Mitosis produces two daughter cells while meiosis produces four daughter cells.
    • Mitosis produces diploid daughter cells (2n) while meiosis produces haploid daughter cells ( n).
    • Mitosis takes place in somatic (body) cells while meiosis takes place in sex cells (gonads) leading to formation of gametes.

    ASEXUAL REPRODUCTION

    Asexual reproduction involves formation of new individuals from a single parent without the formation of gametes. Meiosis is not involved and the offsprings are genetically identical to the parents.

    In this lesson we shall discuss three types of asexual reproduction.

    • Binary fission in amoeba.
    • Spore formation in rhizopus.
    • Budding in yeast.

    The animation below show examples of offsprings resulting from asexual reproduction. These include:-rhizopus, amoeba and yeast

    Binary fission in amoeba

    In the Amoeba a mature cell becomes stationary when conditions are favorable. The nucleus starts to divide into two .The cytoplasm divides into two portions and forms two daughter cells that separate from each other and are identical.

    The animation below shows binary fission in amoeba. Click on the play button to view the animation


    Spore formation in rhizopus

    In the saprophytic mould e.g. Rhizopus that grow on bread, spores are carried by the wind from the sporangium. The spores germinate and form the mycelium with many branches. Some of the hyphae grow vertically and are called sporangiophore. At the tip it swells to form the sporangium which bears the spores. When fully mature it burst to release the spores which are dispersed by wind.

    Play the animation below to see spore formation in rhizopus.


    Budding in yeast.

    Yeast is usually found in sugar and minerals. When conditions are favorable a small area of the cell-wall of a mature parent cell softens and forms a projection of bud which bulges outwardly. The nucleus divides into two and one of the nuclei moves into the new bud. The bud then grows in size and separates off. When budding occurs rapidly the individuals do not separate at once and there results a short chain of cells.

    Play the animation below to view the process of budding in yeast


    Sexual reproduction in flowering plants.

    Sexual reproduction is a type of reproduction in which male and female gametes are involved to form a new cell which develops into a new organism. In flowering plants the flower is the sexual reproductive organ. The flower may have both male and female parts that produce gametes or the two can be on different flowers.

    The diagram below shows the male and the female parts of flowers.

      The male and female gametes fuse to form a zygote through a process called fertilization. The zygote then develops into a new organism. The offspring show genetic variation from the parents. The animation shows the male and female gametes fusing to form a zygote. The zygote develops into a new organism which is different from the parents showing genetic variation. Click the play button to view the animation.


    Pollination and fertilization in flowering plants

    In flowering plants pollination precedes fertilization.Pollination is the transfer of pollen grains from the anther to the stigma of a flower of the same species. The pollen grains from the anthers are transferred to the stigma by pollinating agents such as wind and insects. Play the video clip below to see pollination in an insect pollinated flower.


    When the bee lands on the flower it facilitates the transfer of pollen grains from the stamens to the pistils. The pollen grain on the stigma absorbs nutrients and germinates to form a pollen tube. The pollen tube has a tube nucleus and a generative nucleus which is also the male nucleus. The pollen tube grows down the style into the embryo sac with the tube nucleus leading. In the process, the generative nucleus divides into two male nuclei. The pollen tube enters the embryo sac through the micropyle and when it reaches the centre of the ovule it penetrates the wall of the embryo sac and burst open. The tube nucleus disintegrates and the two male nuclei enter the embryo sac. One of the male nuclei fuses with egg cell to form the zygote which develops into an embryo while the other fuses with the two polar nuclei within the embryo sac to form the triploid nucleus which is the primary endosperm nuclei. The zygote undergoes mitotic division and develops into an embryo which then develops into a seed. The ovary wall changes into fruit wall.

    On the animation below, the pollen grain on the stigma absorbs nutrients and germinates to form a pollen tube which has tube nucleus and a generative nucleus. The pollen tube grows down the style and enters the embryo sac through the micropyle facilitating fertilization.

    Click on the play button to see the process.



    Reproduction in amphibians

    Amphibians are animals that live both on land and in water. Examples of amphibians are frogs, toads, newts and salamanders.

    The photographs below show examples of amphibians such as frogs, toads, newts and salamanders.


    They exhibit external fertilization. Eggs are laid in water and sperms are shed over them resulting to the gametes fusing outside the body. Mating takes place in the water. The male attracts a female by emitting croaking sounds. It mounts on the receptive female and clings to her nuptial pads found on the underside of the digit of the fore legs. The male then holds on female as she lays the eggs into the water and sheds sperms over the eggs as they are laid. The eggs are enclosed in a transparent gelatinous substances in the water which swells up forming a thick jelly-like layer. Eggs float in water until they hatch into tadpoles which undergo changes in body form (metamorphosis) to become adults.

    On the video clip, the Male frog is mounting on the receptive female as she lays the eggs into the water and sheds sperms over them. Click on the play button to watch the video clip.






    FERTILIZATION IN HUMAN BEINGS

    Fertilization is the fusing of the sperm nucleus with the ovum nucleus to form a zygote. It takes places in the upper part of the oviduct. During copulation, seminal fluid is deposited into the vagina of the female and suction force draws up the fluid through the cervix into the uterus. The sperm then swims towards the egg along the oviduct where fertilization takes place.

    Play the animation below to see the movement of the sperm through the female reproductive system.

    The human sperm

    It is the male gamete. It has the following adaptations: -

    • Has a head that contains a large nucleus with little cytoplasm and an acrosome. Acrosome is a cap like sac near anterior part; it bursts during fertilization to release lytic enzymes that digest the outer membrane of ovum to allow the sperm to penetrate.
    • Middle piece contains numerous mitochondria that produce energy to the sperm as it moves up from the vagina to the oviduct.
    • Tail enables the sperm to swim towards the egg.

    The figure shows the human sperm.


    The human ovum

    • It is the female gamete. It is spherical in shape.
    • It has more cytoplasm and yolk granules.
    • It is surrounded by Vitelline membrane beneath which lies a plasma membrane.

    The diagram shows a human ovum

    Process of fertilization in human beings

    During sexual intercourse sperms are deposited into the vagina. Sperms move up the uterus by sunction force and swim towards the ovum in the oviduct due to chemical attractions released by the ovum. In a single ejaculation, millions of sperms can be released but only one will fertilize the egg.

    The Illustration shows a spermatozoon penetrating an ovum for fertilization to take place.


    When the sperm comes into contact with egg the acrosome bursts, releasing lytic enzymes which dissolves the egg membranes. The burst acrosome is modified to form a fine filament that is used to penetrate the egg. Head of sperm enters the ovum leaving the tail outside the ovum. Vitelline membrane undergoes modification to stop other sperms from entering the ovum. Bursting of the head of the sperm releases the male nucleus which fuses with female nucleus to form a zygote.

    All these happen within the female reproductive system hence internal fertilization. The zygote undergoes a series of mitotic cell division to form a hollow ball of cells with a cavity which gets fluid filled through secretion of a fluid from the oviduct. This mass of cell is called blastocyst. The blastocyst moves down the oviduct towards the uterus aided by cilia movements and contraction of smooth muscles along the oviduct. This process takes about 7 days.

    On the animation, many sperms are swimming from the vagina through the uterus to the oviduct where fertilization takes place. Only one sperm penetrates the ovum and the two nuclei fuse to form a zygote. The zygote develops into a blastocyst as it moves towards the uterus for implantation.

    Click on the play button to view the animation.



    IMPLANTATION

    On reaching the uterus the blastocyst develops fingerlike projections from the outermost walls called chronic villi which grow into the soft wall of the uterus (endometrium).

    This embedding of the blastocyst into endometrium of the uterus is known as implantation. After this process the blastocyst is now called an embryo.

    The figure shows implantation in the human uterus.


    FORMATION OF THE PLACENTA

    Forms at the site where the embryo gets embedded into the uterine wall. During implantation the blastocyst differentiates into three layers: the chorion, the ammion and the allantois. The outermost layer is called the chorion and beneath it is the ammion which surrounds the embryo. Between these two membranes is a cavity called the amniotic cavity and is filled with a fluid called amniotic fluid secreted by the amnion.

    • The fluid acts as a shock absorber for the foetus protecting it from mechanical injury.
    • Amniotic fluid also suspends the foetus providing it with a fluid environment which supports the foetus.
    • It also allows free movement of foetus during growth.
    • It lubricates the foetus as it makes any movement.

    The chorionic villi, allantois and part of the endometrum tissues form the placenta.


    The illustration shows chorionic villi, allantois and part of the endometrum tissues forming the placenta.

    The allantois membrane contributes to the formation of umbilical artery and umbilical vein which branches into a network of blood capillaries. Some cells from the amnion and chorion form umbilical cord which is a tubular structure .The umbilical cord connect the embryo to the placenta. The umbilical cord increases in size as the embryo develops. On reaching the third month the embryo is now referred as foetus.

    Note that the maternal blood system has no direct connection with the foetal blood system to avoid bursting the delicate foetal blood vessels. Exchange of materials is through sinuses in the uterine wall and capillary systems of the foetus across the intercellular space by diffusion.

    ROLE OF THE PLACENTA

    It serves several functions in the development of the foetus.

    • It facilitates the transfer of nutrients needed for healthy growth and development.
    • Transfer of metabolic wastes products from the foetus to the mother.
    • Gaseous exchange : oxygen diffuses into the foetal blood stream from that of the mother and carbon IV oxide transported from the foetal blood stream to that of the mother.
    • Hormone : in early stage of development the hormone progesterone is secreted by the ovary. This role is take up by the placenta after the fourth month.
    • Protection: the foetus is protected from the maternal high blood pressure by the placenta since there is no direct link. The placenta filters harmful bacteria from reaching the foetus.
    • Antibodies from the mother pass through the blood stream of the foetus to build up natural immunity.

    Play the animation below to see the exchange of materials between the placenta and the embryo.

    Play the animation below to see the exchange of materials between the placenta and the embryo.


    Note: Some micro-organisms e.g. viruses and drugs such as alcohol and tobacco pass through the placenta and therefore can harm the foetus.


    Gestation period

    This is the period between implantation and birth. Various developmental changes take place and the period varies in different mammals e.g. in human it is about 278 days, while in mice it is about 25 days and in elephant it is about 640 days.

    Developmental stages between one to six months

    In human beings the following developmental stages occur:

    Between day seven up to 3 months:

  • Blood cells form and circulation of blood starts.
  • Heart muscles develop and rhythmic contraction thereafter.
  • Eyes develop.
  • Brain and spinal cord develop.
  • Skeleton develops and brains starts to function.
  • The stomach, liver, kidney and limbs begin to function.

  • The figure shows the foetus below three months

    Between 3rd month and 6th month

    • Genital organs develop.
    • Hair form on the head.
    • Baby grows in size rapidly and becomes fully formed.

    This figure shows the foetus between 3-6months.

    If this foetus leaves the womb before the six month, it will not survive and this is called miscarriage. If the foetus is forcefully expelled physically or chemically this condition is called abortion.


    Developmental stages between six to nine months and birth

    Premature birth is the birth of the baby after the seventh month but before the end of the nine months period. Premature babies are cared for in incubators.

    Between the 6th to 9th months

    The baby gains full growth. To grow, protein, iron, calcium and phosphorus must be supplied in the right proportions from the mothers circulatory system.

    At the 9th month

    • There is a reduced level of progesterone in the blood of the mother.
    • Posterior lobe of pituitary gland releases oxytocin.
    • Oxytocin removes the inhibitory effect on contractions of the endometrium whose muscles start contracting.
    • Dilation of cervix
    • Rupture of the ammion and chorion releasing the amniotic fluid through the cervix.
    • Contraction of the uterine wall pushing the foetus downwards head first through the cervix.
    • Baby is born.
    • Newborn takes first breath due to changes in pressure and Carbon IV oxide concentration and the lungs expand and become functional.
    • Ligature of the umbilical cord and then cutting to separate the baby from the placenta.
    • Expulsion of the placenta as afterbirth from the womb.




    ROLE OF HORMONES IN HUMAN REPRODUCTION

    Hormones play a crucial role in the development and control of physiological, physical and emotional changes in both males and females. The hormones are responsible for secondary sexual characteristics observed in both males and females after puberty. During puberty an individual attains sexual maturity.


    Role of hormones in development of secondary sexual characteristics.

    In males.

    Hormones that control secondary sexual characteristics in males are known as androgens. Androgens are secreted by testes. Secretion of androgens increases at around the average age of 13-14 years.

    At this stage they are responsible for the following.

      Deepening of the voice.
      Growth of hair in pubic and armpits, and on the chin.
      Body becomes more masculine.
      Production of gametes (sperms).

    The Illustration shows growth of hair in armpits, pubic region and beards in males.


    In females

    Hormones that control secondary sexual characteristics are known as oestrogens. Production of oestrogen begins as early as age 10 yearas.

    Depending on the individual, they bring about the following changes:

      Development of mammary glands.
      Enlargement of pelvic girdle and widening of hips.
      Growth of hair in the pubic and armpit region.
      Body becomes more feminine.
      Brings about maturity of the ovaries.
      Onset of menstruation


    The Illustration shows the difference between the pelvic girdle of a young girl of 6 years and that of an adolescent girl of 15years. It also illustrates growth of pubic and armpit hair of an adolescent girl.

    Role of hormones in menstrual cycle

    The hormones that control the menstrual cycle are produced by the pituitary gland and the ovary.

    They are:

    • Follicle Stimulating Hormone,
    • oestrogen,
    • Luteinizing hormone and
    • progesterone.

    The role of Follicle Stimulating Hormone (FSH)

    • Causes graafian follicle to develop in the ovary.
    • Stimulates tissues of the ovary to secrete oestrogen.

    The Illustration below shows the flow of follicle stimulating hormone (FSH) from the pituitary glands in the brain to the ovaries where it leads to development of graafian follicles and stimulate secretion of oestrogen.

    The role of Oestrogen

    • After menstruation, it causes, healing, repair and growth of endometrium.
    • High concentration of oestrogen in blood inhibits production of FSH. This prevents ripening and growth of more follicles in the ovary.
    • High concentration of oestrogen stimulates the pituitary gland to secrete luteinizing hormone.

    The role of Luteinizing hormone

    • Causes ovulation - this is the release of a mature ovum from the ovary.
    • Causes formation of corpus luteum from a mature follicle cells.
    • stimulates corpus luteum to secrete progesterone.

    Play the animation to see the development of graafian follicle in the ovary, release of the egg into the fallopian tube and the change of the graafian follicle to corpus luteum.

    Role of Progesterone

    • Stimulates the thickening and increased, blood supply to the endometrium.
    • Inhibits secretion of both FSH and Luteinizing hormone
    • Maintains pregnancy incase fertilization took place.

    If fertilization does not occur the corpus luteum disintegrates. The disintegration of the corpus luteum stops the production of progesterone which is necessary for preparing endometrium for implantation. The thickened endometrium sloughs off and is discharged out of the uterus as blood and tissue debris; this is menses. This process is known as menstruation. The menstrual cycle starts with development of graafian follicles, ovulation and ends with menstruation. The cycle lasts for 28 days.


    SEXUALLY TRANSMITTED INFECTIONS

    These are diseases transmitted through sexual intercourse.

    The diseases include gonorrhea, syphilis, Hepatitis, candidiasis, HIV/AIDS, Herpes, and Trichomoniasis.

    Signs and symptoms

    Play the video clips below to see the signs and symptoms.

    Prevention, control and treatment

    Play the video clips below to view the prevention, control and treatment.

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