ALTERNATIVE TO NORMAL FERTILIZATION
- Polyovulation wherein one or more oocyte released in a given ovarian cycle are fertilized by spermatozoa from male and another oocyte is fertilized by different male
- Female gamete can’t produce embryo w/o male gamete, occasionally the oocyte is activated w/o sperm.
- Shows multinucleated blastomeres
- Variable degree of degeneration
- Self-cleaning or spontaneous abortion wherein abnormal zygotes are lost during early stages w/o the mother being aware of it
UTERUS AT TIME OF IMPLANTATION
- 3 layers of uterus wall:
- Endometrium or mucosa lining the inside wall
- Myometrium, thick layer of smooth muscle
- Perimetrium, peritoneal covering lining the outside wall
- At time of implantation the mucosa of the uterus is in the secretory or progestational phase. It is caused by the progesterone secreted by corpus luteum.
- Signs: Uterine glands and arteries become coiled and the tissue become succulent, as a Result layers are recognized in the endometrium:
- Superficial compact layer
- Intermediate spongy layer
- Thin basal layer
- If oocyte is fertilized, the glands in the endometrium show increasing secretory activity and the arteries become tortuous and form a dense capillary bed beneath the surface. As a result the endometrium becomes highly edematous.
- If oocyte is not fertilized, the venules and sinusoidal spaces become gradually packed with blood cells and an extensive diapedesis of blood into the tissue is seen.
- Menstrual phase, blood from superficial arteries and small pieces of stroma and glands break away. During 3 or 4 days the compact and spongy layers are expelled and the basal layer is the only part retained in the endometrium.Basal layer is supplied by its own arteries, basal arteries, and functions as the regenerative layer in the rebuilding of glands and arteries in proliferative phase.
ABNORMAL IMPLANTATION SITES
- Human blastocyst usually implants along the posterior or anterior wall of the body of uterus. Sometimes implantation sites are found outside the uterus resulting in extrauterine orectopic preganancy.
- This may occur at any place in the abdominal cavity, ovary, uterine tube. Ectopic pregnancy usually leads to death of embryo and severe hemorrhaging during 2nd month.
- In the abdominal cavity the blastocyst most frequently attaches itself to the peritoneal lining of the rectouterine cavityor douglas’ pouch.
- Sometimes blastocyst develops in the ovary proper causing a primary ovarian pregnancy. More commonly at ectopic pregnancy is lodged in uterine tube (tubal pregnancy).
FETAL MEMBRANES AND PLACENTA
- Trophoblast – characterized by a great no. of secondary and tertiary villi giving it a radial appearance
- Villi – anchored in the mesoderm of the chorionic plate
- Attached peripherally to the maternal decidua via the cytotrophoblast shell
- Its surface is formed by the syncytium on a layer of cytotrophoblastic cells
- Cytotrophoblastic cell – cover a core of vascular mesoderm
- Formation of the extramembrane vascular system capillary system developing in the core of the villous stem comes in contact with capillaries of the chorionic plate and connecting stalk
- Numerous small extensions sprout from existing villous stems into the lacunar or intervillous spaces
- The syncytium and Endothelial wall of the blood vessels the only layers separate the maternal and fetal circulations
- Syncytial knots broken off pieces of syncytium a nuclei may break off into the intervillous Blood lakes enter maternal circulate degenerate without causing symptoms
- Disappearance of cytotrophoblastic cells progress from the smaller to larger villi some persist in large villa don’t participate in plate exchange
CHORION FRONDOSUM and DECIDUA BASALIS
- In the early weeks of development, villi cover the entire surface of the chorion
- Villi on embryonic pole will continue to grow and expand chorion frondosum (bushy chorion)
- Villi on the abembryonic pole degenerate 3rd month, it will become smooth chorion laevae
- The decidua, the functional layer of the endometrium is shed during parturition
- Decidua basalis decidua over the chorion frondosum a compact layer of the large cells
- deciduals cells with abundant amounts of lipid and glycogen
- Decidua plate – tightly connected to the chorion
- Decidua capsularis – decidual layer over the abembryonic pole will become stretched and later degenerates because of the increase in size of the chorionic vesicle
- Chorion laevae comes into contact with the uterine wall (decidua parietalis) on the Opposite side of the uterus fuse obliterate uterine lumen (only the portion of the chorion participating in exchange process is the chorion frondosum)
- Placenta – chorion frondosum + decidua basalis
- Amnochorionic membrane fusion of the amnion and chorion
- Ruptures during labor, breaking of the H20
STRUCTURES OF THE PLACENTA
- By 4th month placenta has:
- Fetal portion formed by the chorion frondosum
- Maternal portion decidua basalis
- Fetal side – border: chorionic plate
- Maternal side – border: decidua basalis of which the decidual late (most intimately incorporated into the placenta)
- Junctional zone – where the trophoblast and decidua cells intermingle characterized decidual and syncitial giant cells is rich in amorphous extracellular material
- Most of the cytotrophoblast have degenerated
- Intervillous space filled w/ maternal blood derived from lacunae in the syncitiotrophoblast lined with syncitium of fetal origin
- Villous trees grow into intervillous blood lakes
- 4th or 5th month, decidua forms a number of septa = decidual septa
- Decidual septa projects into the intervillous spaces but not reach the chorionic plate core: maternal tissue surface is covered by a layer of syncitial cells
- At all times a syncitial layer separates maternal blood in the intervillous lakes form fetal tissue Of the villi
- Placenta is divided into a number of com0artments or cotyledons
- Placenta enlarges and the uterus expand
- Its increase in the surface are parallels the uterus, covering 15-30%of internal surface of the uterus
- Increase of thickness is a result of arborization of existing villi and not further penetration
FULL TERM PLACENTA
- Discoid shape
- 15-25 cm diameter, 3 cm thick
- Weight: 500-600 gm
- Torn from the uterine wall 30 mins after birth of child it is expelled from the uterine cavity
- Maternal side viewed:
- 15-20 shortly bulging areas/cotyledons covered by a thin layer of decidua basalis.
- Grooves between cotyledons are formed by deciduals septa
- Much of the decidua remains temporarily in the uterus and is expelled w/ subsequent uterine bleedings
- Fetal surface viewed:
- Covered by chorionic plate
- Chorionic vessels – large arteries and veins converging toward the umbilical cord
- Chorion is covered by amnion
- Attachment of the umbilical cord usually is eccentric and occasionally even marginal
- Rarely in velamentous insertion
- Insertion into chorionic membranes outside the placenta
CIRCULATION of THE PLACENTA
- Cotyledons receive their blood supply via 80-100 spiral arteries piercing the decidual plate and entering the intervillous spaced at regular intervals
- Lumen of spiral artery is narrow an increased blood pressure when entering the intervillous pace
- This pressure forces the blood deep into the intervillous space and bathe the small villi of the villous tree in oxygenated blood
- As pressure decrease the blood flows back form the chorionic plate toward decidua and enter the endometrial veins
- Blood from the intervillous lakes drain into the maternal circulation through endometrial veins.
- Intervillous spaces of a mature placenta contain approximately 150 ml of blood that is Replenished abt 3-4 times /minute.
- Placental exchange does not take place in all villi, only those in which fetal vessels are in Intimate contact with the covering syncytial membrane – these villi have brush border Surfaces with numerous microvilli greatly increasing the surface area and exchange rate between maternal and fetal circulation.
- Placental membrane separates maternal and fetal blood composed of 4 layers:
- endothelial lining of fetal vessels
- connective tissue in the virus core
- cytotrophoblastic layer
- From the 4rt month on the placenta membranes become thinner since the endothelial living of the vessel comes in intimate contact with the syncytial membrane. Increasing rate of exchange.
- Placental barrier = not a true barrier since many substances pass thru it freely = hemochonial type
FUNCTIONS OF THE PLACENTA
- Exchange of metabolic & gaseous products between maternal & fetal blood stream.
- Production of hormones
- Exchange of gases O2, CO2, CO Simple diffusion Fetus extracts 20-30 ml of O2 per minute.Placenta blood flow is critical to O2 supply. Amount of O2 reaching fetus dependent on delivery not diffusion
- Exchange of nutrients & electrolytes Amino acids, free patty acids carbohydrates & Vitamins Rapid Increases as pregnancy advances
- Transmission of maternal antibodies maternal antibodies taken up by pinocytosis by syncytiotrophobast & transported to fetal capillaries. Fetus acquires maternal antibodies of IgG is diptheria, measels, small pox Passive immunity important because fetus has little capacity to produce own RH Incompatibility Related to erythrocyte antigens Fetus (Rh +) is mother (Rh-) Fetal RBC invading maternal blood stream may elicit an antibody response in the mother Hemolytic disease of the newborn of fetal RBC – intra urine death Rh Ig given to mother
- Hormone production By end of 4th month, placenta produces progesterone to maintain pregnancy All hormones are synthesized in the syncytial trophoblast Produce increasing amounts of estrogenic hormones = estriol until just before the end of pregnancy – stimulate uterine growth and development of mammary gland Produce gonadotropins (hCG) Hormones are indicators of pregnancy. Somatomammotropin – a growth hormone like substance that gives the fetus priorityon maternal blood glucose & makes mother diabetogenic
AMNION & UMBILICAL CORD
- Primitive umbilical ring – omnivectodermal junction– oval in shape
- At 5th week the following:
- Connecting stalk – contain allantois and the umbllical vessels consisting of 2 arteries & 1 vein
- Yolk stalk /vittelineduct – accompanied by vitlelineduct vessels.
- Canal connecting the intraembrayonic & extraembryonic coelomic cavities
- The yolk sac proper occupies a spree in the chronic cavity With further development, the amniotic cavity enlarges rapidly at the expense of the Chrorionic cavity – amnion regins to envelop the connecting and yolk stalks – leading to formation of primitive umbilical cord
- Distally, the cord contains: the yolk sac stalk 2 umbilical vessels
- Proximally: intestinal loops: remnant of allantois
- The yolk sac is found in the chronic cavity.Connected to the umbilical cord via its stalk
- By 3rd month, the chorionic cavity is obliterated, yolk sac shrinks and is also gradually obliterated.
- Physiological hernia of the umbilicus Due to the intestinal loops extending into the extracoelomic space because of a Small abdominal cavity – loops are withdrawn by the end of the 3rd month – coelismic cavity is obliterated
- The remaining umbilical vessels and cord are surrounded by jelly of Wharton
- Wharton’s jelly –
- Tissue rich in proteoglycans-
- Function protective layer for blood vessels
- Walls of the vessels – arteries are muscular & contain many elastic Fibers –rapid construction.
- Amniotic bands
- Due to tearsin the amnion
- Encircle part of the fetus = digits & limbs
- Ring constrictions may result
PLACENTAL CHANGES AT THE END OF PREGNANCY
- Increase in fibrous tissue in the core of the villus
- Increase in the thickness of the basement membrane in fetal capillaries
- Obliterative changes in small capillaries of the villi
- Deposition of fibrinoid on the surface of the villi in the junctional zone & in the chorionic plate
- Excessive fibrinoid formation – infarction –cotyledon appear whitish
- At birth, umbilical cord is 2 cm in diameter & 50- 60 cm long – may produce false knots.
- Short cords – difficulty in delivery long cords –encircle neck
|Pregnant nerves||Blood vessel contained|
|Sciatic nerve||Branch of inferior gluteal artery|
|Optic nerve||Central retinal artery|
- Pregnant nerves- these are the nerves which carry a blood vessel in them.
- Nutrient artery to the tibia is the largest nutrient artery in the body
- Housemaid’s knee- Prepatellar bursitis
- Clergyman’s knee- Infrapatellar bursitis
- Amniotic cavity is filled with a dear watery fund
- Produce by amniotic cells but derived primarily from maternal blood
- Amount increases from 30ml at 10 wks gestation to 350ml at 20 wks, 800-1000ml at 37 wks
- Absorb jolt
- Prevent adherence of the embryo to the amnion
- Allow fetal movements
- Volume of fetal fund is replaced every 3 hors
- Fetus swallows its own amniotic fluid – drinking about 400 ml.day
- During childbirth, the amniochronic membrane forms a hydrostatic wedge that helps dilate The cervical canal.
- Oligohydramnios decreased amount <400ml of amniotic fluid can cause clubfoot & lung hypoplasia caused by renal agenesis
- hydramnios / poly hydramnios excess amniotic fluid caused by idiopathic causes, maternal diabetes congenital malformation, CIVS disorder, gastrointestinal defects.
FETAL MEMBRANE IN TWINS DIZYGOTIC TWINS / FRATERNAL
- Incidence increased with maternal age result from simultaneous shedding of 2 octets &fertilization by 2 different spermatozoa. Zygotes implant individually Develop own placenta, amnion, chorionic sac When too close together may fuse Possesses RBC of different types erythrocyte mosaicism)
- Develop from a single fertilized ovum Twining rate: 3-4 /1000 Result from splitting of zygote at various stages of development
- Earliest separation at 2 cells stage Blastocyst implant separately Each has own placenta & chorionic sac Strong resemblance in blood groups, fingerprints, sex and external appearance
- Splitting of zygote occurs at early blaslocyst stage Inner cell mass splits into 2 separate groups of cells within the same blastocyst cavity 2 embryos have a common placenta and a common chorionic cavity but have separate amniotic cavities
- Sometimes separation occurs at the bilaminar germ disc stage just before the appearance of the primitive streak – form 2 partners with single placenta, common chorionic & amnion sac have common placenta, blood supply is well balanced.
- Twin pregnancies have higher morbidity & a tendency toward preterm delivery Low birth weight Vanishing twin = death of one fetus
- Usually in 1st or early 2nd trimester & fetus papyraceus
- Twin transfusion syndrome > 1 twin is larger that the other
- Conjoined siamese twins > incompletely separated classified as:
- Thoracophagus > fastened