FERTILIZATION AND IMPLANTATION:
· During copulation (coitus) semen is released by the penis into the vagina is called insemination.
· The motile sperm swim rapidly, pass through cervix, uterus and finally reach the junction of isthmus and ampulla (ampullary-isthmic junction).
· The ovum released from the ovary also transported to ampullary isthmic junction where fertilization takes place.
· Fertilization only takes place if both sperm and ovum reach ampullary – isthmic junction simultaneously.
· The process of fusion of a sperm and ovum is called fertilization.
· Acrosome of sperm secretes enzymes helps in penetration into the ovum.
· Once a sperm comes contact with the zona pellucida of ovum and induces the changes in the membrane that blocks the entry of additional sperms.
· That ensures monospermy and prevents polyspermy.
· Only one sperm fertilize with one ovum.
· Entry of sperm into the ovum induces the ovum to complete its second meiotic division of secondary oocyte.
· Meiosis-II is also unequal cytokinesis resulting production of one large ovum (ootid) and one small second polar body.
· Haploid nucleus of sperm fused with the haploid nucleus of ovum to form a diploid zygote.
· Sex of a baby has been decided during fertilization and in the zygote.
· Sex is determined by the sex-chromosomes present in gametes.
· Human female contain two XX chromosomes.
· Human male contain XY chromosomes.
· All the female gametes produced with only ‘X’ chromosome.
· Sperms produced by male, 50% with ‘X’ and 50 % with ‘Y’ chromosome.
· After fertilization zygote either carries XX or XY chromosomes.
· Zygote with XX chromosomes develop into female and with XY chromosome develops into male.
· Repeated mitotic division of the zygote without growth resulting a multicellular ball like embryo is called cleavage.
· Cleavage starts soon after fertilization.
· Daughter cells produced during cleavage are called blastomeres.
· The product of cleavage is called Morula, which is 8 to 16 celled.
· The morula continues to divide and grow and transformed into blastocyst.
· The blastomeres in blastocyst arranged into an outer layer called trophoblast and an inner mass of cells attached to trophoblast called inner cell mass.
· Trophoblast cells attached to the endometrium helps development of placenta.
· Inner cell mass gets differentiated into the embryo.
· After attachment the uterine cells divide rapidly and cover the blastocyst.
· Blastocyst completely embedded in the uterine endometrium. This is called implantation.
Pregnancy and embryonic development:
· After implantation, finger like projections appears on the trophoblast called chorionic villi.
· Chorionic villi surrounded by uterine tissue and maternal blood.
· Temporary association between the fetal tissue (chorionic villi) and maternal tissue (uterine endometrium) is called placenta.
Function of placenta:
· The embryo connected to the placenta by umbilical cord, which transports substances to and from the embryo.
· Facilitate transport of oxygen and nutrient from mother to embryo.
· Removes CO2 and waste material from the embryo.
· Acts as endocrine gland and produces several hormones like:
o Human chorionic gonadotrophins (hCG)
o Human placental lactogen (hPL)
o Relaxin produced from the ovary in the later stage of pregnancy.
· After implantation the inner cell mass of blastocyst differentiated into an outer layer called ectoderm and an inner layer called endoderm.
· Mesoderm differentiated in-between ectoderm and endoderm.
· The inner cell mass thus called stem cells, having potency to produce all types of cell, tissues and organs by differentiation.
· Formation of different organs in the embryo is called organogenesis.
· Human pregnancy lasts for 9 months.
· After one month of pregnancy heart is formed in the embryo.
· By the end of 2nd month the foetus develops limbs and digits.
· By the end of 12 weeks (first trimester) most of organ system is formed (limbs and external genitalia are well developed).
· First movement of foetus and appearance of hairs observed in 5th month.
· By the end of 24th week (2nd trimesters) the body is covered with fine hairs, eye-lids separate, and eyelashes are formed.
· By the end of 9 months the foetus is fully developed and is ready for delivery.
Reproductive health can be decided by applying proper strategies. Population explosion are the result of decreased MMR(Maternal Mortality Rate} and IMR(Infant Mortality Rate).
Birth control methods are adopted to reduce birth rate. Certain methods are adopted to reduce birth rate. Medical termination of pregnancy or induced abortion are another measure of birth control.
Diseases which are transmitted through sexual intercourse are known as sexually transmitted disease. Such are gonorrhea, syphilis, trichomoniasis, hepatitis B,AIDS.