REPRODUCTION & GROWTH

REPRODUCTION & GROWTH4.3 Early Development of a Human ZygoteOvulationthe release of ovum into the Fallopian tube1st sperm that reaches the ovum will penetrate it

FertilisationOccurs when the nucleus of the sperm that penetrates the mature ovum in the Fallopian tube fuses with the ovum nucleusMiddle piece & the tail of the sperm are left outside

FertilisationZygote forms fertilisation membrane around itselfTo prevent other sperms from penetrating it again

Early Development of a Zygote

36 hours after fertilization, zygote begins to divide repeatedly by mitosis as it travels along the Fallopian tube towards the uterus

The first division forms a two-celled EMBRYOFurther division result in the formation of a solid mass of cells known as a MORULA

5th day, morula is a ball of about 100 cells known as blastocyst

Blastocyst outer layer (trophoblast); inner cells (inner cell mass)Trophoblast develop into placentaInner cell mass dev into embryo

Implantation :7th day after fertilisationBlastocysts firmly embedded into endometrium

The Formation of Twins

TwinsTwo individuals born to the same mother at almost the same time after the same period of pregnancy

Divided into 2 types:Identical (monozygotic twins)Fraternal (dizygotic twins)Identical TwinsOne ovum + one sperm = two foetusesIncomplete division produced Siamese twins

Identical TwinsIdentical twins:Same sexShare one placentaGenetically identicalAlmost identical physical featuresSame blood group

Conjoined Twins

Non Identical Twins (Fraternal Twins)Two ova + two sperm = two fetusesEach with its own placenta

Non Identical Twins (Fraternal Twins)Genetically differentSame / different sexDifferent physical characteristics

The functions of the placenta in foetal development

Placenta

PlacentaTemporary organ of embryonic tissue origin Develop in the endometrium Forms a selective barrier between mothers blood & foetal bloodUmbilical cord connects the foetus to the placentaFunctions of PlacentaAllows the attachment of the embryo or foetus to the mothers uterine wallTransport nutrients such as glucose, mineral salts, amino acids, vitamins, fatty acid & glycerol from the mothers blood to the blood of the foetusFunctions of PlacentaRemoves excretory wastes from the blood of the foetusTransport hormones & antibodies from the mothers blood to the foetusActs as an endocrine gland that secretes estrogen & progesterone

UMBILICAL ARTERIES :Carry deoxygenated blood from the foetus to the placentaUMBILICAL VEIN :Carries oxygenated blood from the placenta to the foetusThe advantages of having separate foetal & maternal circulatory systemThe Advantages Of Having Separate Foetal & Maternal Circulatory SystemPrevents the mixing of blood groups of the mother and the foetus which may be incompatibleEnsure that the fine blood vessels of the foetus do not burst as a result of high pressure caused by the flow of the mothers bloodThe Advantages Of Having Separate Foetal & Maternal Circulatory SystemPrevents certain harmful bacteria and their toxins from entering the foetusPrevents the action of chemicals in the mothers blood from harming the developing foetus