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501340725-Unit-2-Fertilization-impantation-development-of-placenta-and-its-function-abnormality (1).pptx
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- 2. Pregnancy • What happensto an egg after fertilisation ? • How does a baby develop in the uterus ?
- 3. Fertilization •The union ofovum and spermatozoa is called fertilisation or •Fertilization is the process of fusion of the spermatozoon with the mature ovum. •Fertilization occurs in the outer third of the fallopian tube – the ampullar portion. •other terms are conception, impregnation, or fecundation. •The critical time span during which fertilization may occur is about 72 hours.
- 4. The mature ovum -It is a large oval cell that varies from 117–142µ in diameter. It has two membranes; the inner thin one is the vitelline membrane and the outer one is the zona pellucida. - The corona radiata is two or three layers of cells surrounding the zona pellucida externally when the ovum is shed from the follicle.
- 6. The sperm Drawing showingthe main parts of the human sperm (X1250). The head, composed mostly of the nucleus, is partly covered by the cap like acrosome (an organelle containing enzymes). The tail of the sperm consists of three regions: The middle piece, principal piece, and an end piece.
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- 8. At the timeof intercourse about 60-120 million spermatozoa are deposited in the posterior vagina reaches the cervix of uterus within 90 seconds after deposition and to the outer end of the fallopian tube in 5 minutes. The functional life of spermatozoa is 48 hours
- 9. During the journeythrough the uterus, more sperm die, only thousands reach the tube, where they meet the ovum usually in the ampulla. After this sperm mature and become capable of releasing an enzyme called hyaluronidase, which allows penetration of zona pellucida and the cell membrane surrounding the ovum. Many sperm are tried for this but only one will enter the ovum.
- 11. After this, themembrane is sealed to prevent entry of any further sperm.
- 12. After penetration, thechromosomal material of the ovum and spermatozoa fuse and the structure is called zygote. Sperm (23) + Egg (23) = Fertilized Cell (46)
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- 14. Morula After thezygote formation, typical mitotic division starts. The two cell stage is reached approximately 30 hours after fertilization. Each contains equal cytoplasmic volume and chromosome numbers. Fertilized ovum multiply into 4, 8, 16 cell stage until a cluster of cells is formed and is called morula, resembling a mulberry.
- 17. As thezona pellucida remains intact, the morula after spending about 3 days in the uterine tube enters the uterine cavity. The transport is a slow process and is controlled by muscular contraction and movement of the cilia. The central cell of the morula is known as inner cell mass which forms the embryo, amnion, umbilical cord and peripheral cells are called outer cell mass (trophoblast) which will form protective and nutritive membrane (Chorion and placenta).
- 19. Blastocyst While themorula remains free in the uterine cavity on the 4th and 5th day. Due to enlargement of cell zona pellucida become stretched, thinned and gradually disappears and it is covered by a film of mucus. Now its termed as a blastocyst. This process is called zona hatching.
- 20. Implantation •Occurs on theseventh day after fertilization •Is the contact between the growing structure and the uterine endometrium. •Another name of implantation is Nidation. •Implantation occurs through four stages, e.g. apposition, adhesion, penetration and invasion.
- 22. Development of thefertilized ovum The Trophoblast: Small projections begin to appear all over the surface of the trophoblast. These trophoblastic cells differentiate into three layers- outer syncytiotrophoblast, inner cytotrophoblast and mesoderm.
- 25. The syncytiotrophoblasterodes the walls of the blood vessels of the endometrium, to make the nutrients in the maternal blood accessible to the developing embryo. The cytotrophoblast, which is a well-defined single layer of cells, produces a hormone known as HCG. This hormone is responsible for maintaining of oestrogen and progesterone and continue of pregnancy.
- 26. Mesenchyme develops tochorionic vesicle and membrane chorion. While the trophoblast develops to form the placenta, which will nourish the fetus, the inner cell mass develops to form the fetus itself. The cells differentiate into 3 layers- ectoderm, endoderm and mesoderm. The ectoderm develops into the central and peripheral nervous system, epidermis.
- 27. The endodermforms the dermis, the skeleton, the connective tissue, vascular and the urogenital systems and most skeletal and smooth muscles. The mesoderm forms internal organs such as the heart and blood vessels, liver, pancreas and also the bones and the muscles. As the development continues two cavities appear. These are termed as amniotic cavity and other is yolk sac. Amniotic cavity enlarge in size and its filled in water. Its called amniotic fluid. Yolk sac provides nourishment for the embryo until its completely attached to endometrium.
- 30. Chorionic villi andplacental development At the beginning of the 3rd week, the syncytiotrophoblast produces irregular finger like projection which is called primary stem villi. This primary stem villi after sometime renamed as chorionic villi. On 16th day, from primary chorionic villi, secondary chorionic villi are formed. This villi starts connecting with blood cells and vessels and now its called as tertiary villi.
- 31. The villi invadethe walls of maternal blood vessels as they penetrate the endometrium, opening them up to form a lake of maternal blood in which they float. The maternal blood circulate slowly, enabling the villi to absorb food and oxygen and excrete waste. These are known as nutritive villi. The placenta is completely formed and function from 16th weeks after fertilisation. In its early stages it is relatively loose structure, but become more compact as its mature.
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- 36. The placenta Theplacenta, at term, is almost a circular disc with a diameter of 15-20 cm and thickness of about 3 cm at its centre. It feels spongy and weighs about 500gm, the proportion to the 1/6th weight of the baby. It present two surface, fetal and maternal.
- 37. Fetal surface Fetal surfaceis covered by the smooth and glistening amnion with the umbilical cord attached at or near its centre. Branches of the umbilical vessels are visible beneath the amnion as they radiate from the insertion of the cord.
- 38. Maternal surface Thematernal surface is rough and sponge. Maternal blood gives it a dull red colour. The maternal surface is mapped out into 15-20 lobes or cotyledons. Numerous small greyish spot are visible. These are due to deposition of calcium in the degenerated areas and are of no clinical significance. The placenta is usually attached to the upper part of the body of the uterus at fundus.
- 40. Function of placenta Themain functions of placenta are- Transfer of nutrients and waste products between the mother and fetus. In this respect it attributes to the following function: • Respiratory • Execratory • Nutritive Endocrine function- placenta is an endocrine gland. It produce hormone to maintain pregnancy. Barrier function Immunological function
- 41. Respiratory function: Respiration is a key function of the placenta. O2 and CO2 pass through the placental membrane. Excreatory function: In addition of CO2, urea, uric acid, bilirubin are readily transformed from fetus to mother for disposal. Nutritive function: Glucose, which is the principal source of energy is transformed to the fetus.
- 42. Lipids forgrowth and development are transferred across the fetal membrane or synthesis in the fetus. Triglycerides and fatty acids are directly transported from the mother to the fetus in early pregnancy. Amino acids are transferred. Fetal protein are synthesis from the transferred amino acids. Water and electrolytes such as Na, K, Cl cross through the fetal membrane. Other than this Ca, phosphorus, iron, water soluable vitamin also transport.
- 43. Hormone function: Insulin, steroids from adrenal gland, chorionic gonadotrophin (HCG) are closes through placenta. Enzymatic function: Neumerous enzyme are transferred through placenta like- Diamine oxidase, Oxytocinase etc.
- 44. 2. Endrocrine function: The placenta produce several hormone necessary for normal pregnancy. HCG is secreted from placenta, which maintain balance of oestrogen and progesterone in body. Progesterone is essential for normal pregnancy is also secreted from placenta. Human placental lactogen/ Human chorionic somatotrophin- helps in growth of fetus and maternal breast development.
- 45. 3. Barrier function: Fetal membrane has long been considered as a protective barrier to the fetus against noxious agents circulating in the maternal blood. Antigen and antibody can transfer selectively across placental barrier. Maternal infection during pregnancy by virus (e.g.- rubella, chiken pox) may be transmitted. Drug used in pregnancy can be cross the placental barrier may have teratogenic effect.
- 46. 4. Immunological function: Many of the immunoglobin or antibody are passed from mother to fetus through the placenta. This confers passive immunity to the fetus against disease to which the mother is immune.
- 48. Abnormality Larger andheavier than normal placenta are seen with excessively large foetuses, fetal syphilis and erythroblastosis fetalis. Smaller and lighter than normal placenta may occur with general systemic disease/ local uterine condition which causes undernourishment of the placenta. Colour of placental tissue markedly lighter. This condition may caused by fetal anemia.
- 50. Oedematous placentais mushy, thick, pale, fluid can squeezed from it. It may happened from maternal heart disease, DM, nephritis, severe erythroblastosis.
- 51. Excessive infractedplacenta- infraction of cotyledons happens due to disease process such as maternal HTN, severe pre-eclampsia, Eclampsia.
- 52. Succenturiate placenta/placenta succenturiata- one or more separate accessory lobes in the membranes at a variable distance away from the main placental mass. This accesary lobe are usually connected to the main placental mass. Incidence are only 3%. May cause PPH, subinvolution.
- 53. Circumvallate placenta/placenta circumvallate- The ring situated at a variable distance between the margin and centre of placenta. A double fold of both chorion and amnion with fibrin and decidua form this ring.
- 54. Battledore placenta- Umbilicalcord is inserted at the edge or margin of the placenta. Occur in 10% of cases. It associated with low implantation of placenta chace for cord compression.
- 55. Velamentous placenta-The cord is inserted into the membrane of some distance from the edge of the placenta. The umbilical vessel from the cord run through the membrane for a variable distance. May seen about 1% cases.
- 56. Vasa previa-It is a dangerous anomaly with a increase prenatal mortality if ruptures occurs. It refers to the blood vessles, covered only with amnion and which present at the cervical OS. It may cause anorexia to fetus during labour.
- 57. Umbilical cord The umbilicalcord forms connection link between fetus and the placenta through which the fetal blood flows from maternal endometrium. The constitute of umbilical cord when fully formed are as follows- Covering epithelium- Its lined by a single layer of amnion epithelium. Wharton’s jelly- It consists of elongated cells od gletanious fluid formed by mucoid degeneration
- 58. Blood vessel-Initially, there are 4 vessles- 2 artery and 2 veins. The artery are derived from the internal iliac arteries of the fetus and carry the deoxygenated blood from the fetus to placenta. Among two veins, one vein disappear after 4 months, carries oxygenated blood from placenta to fetus.
- 59. Characteristics of umbilicalcord It is about 40-50 cm in length with an unusual variation. Its diameter is 1.5 cm. Umbilical cord thickness is not uniform but present nodes or swelling at places due to local collection of Wharton’s gelly.
- 60. Abnormality of umbilicalcord Short cord is one that is short in length. Cord length less than 20 cm/ 8”. It may cause umbilical hernia and fetal distress. Long cord are more common than short cord. Long cord may become looped around fetal neck. Cord length more than equals to 100cm. A true knot occurs when the fetus has passed through a loop in the cord and a real knot has been created.
- 61. False knottingoccurs when the cord appears to be knotted, but instead has kinking of the blood vessels with in the cord or accumulation of Wharton’s jelly on the cord. Markedly reduced amount of Wharton’s jelly may be seen in malnourished and post mature newborn.