PLACENTA DR.E. ZAREAN
Pregnancy: Level 1 • Fertilisation • Cell division Next slide
Fertilisation • Cell division • Wafted along Fallopean tube into uterus (or Oviduct)
This cleavage starts within 24 hours of fertilization and occurs nearly every 12 hours repeatedly The resultant 16 cells mass is called morulawhich reaches the uterine cavity after about 4 days from fertilization. Cleavage and blastocyst formation:
A cavity appears within the morula converting it into a cystic structure called blastocyst. The cells become arranged into an : Inner mass (embryoblast) which will form all the tissues of the embryo, and an Outer layer called trophoblastwhich invade the uterine wall. Cleavage and blastocyst formation:
The blastocyst remains free in the uterine cavity for 3-4 days, during which it is nourished by the secretion of the endometrium (uterine milk). Cleavage and blastocyst formation:
blastocyst Endometrium Next slide
Secretory duct Capillary Endometrium Trophoblast Uterine epithelium Yolk sack Blastocoel Embryo Blastocyst • Fertilisation • Cell division • Wafted along Fallopean tube • Implantation in uterine wall Next slide
Placenta formation Lacunae form within synctiotrophoblast--maternal blood fills these spaces Vili form with embryonic capillaries down middle
The decidua: • It is the thickened vascular endometrium of the pregnant uterus. • The glands become enlarged, tortuous and filled with secretion. • The stromal cells become large with small nuclei and clear cytoplasm, these are called decidual cells.
Chorion: After implantation, the trophoblast differentiates into 2 layers: a. An outer one calledsyncytium(syncytiotrophoblast)which is multinucleated cells without cell boundaries, b. An inner one called Langhan’s layer(Cytotrophoblast)which is cuboidal cells with simple cytoplasm. • A third layer of mesoderm appears inner to the cytotrophoblast.
Chorion: • The trophoblast and the lining mesoderm together form the chorion. • Mesodermal tissue ( connecting stalk) connects the inner cell mass to the chorion and will form the umbilical cord later on.
Chorion: • The outer syncytium and inner Langhan’s cells form buds surrounding the developing ovum called primary villi. • When the mesoderm invades the center of the primary villi they are called secondary villi. • When blood vessels (branches from the umbilical vessels) develop inside the mesodermal core, they are called tertiary villi.
Secondary villous Primary villous
Amnion: After implantation, 2 cavities appear in the inner cell mass; the amniotic cavity and yolk sac and in between these 2 cavities the mesoderm develops.
Fertilisation • Cell division • Wafted along Fallopean tube • Implantation in uterine wall • Formation of placenta Functions of the placenta • Supply oxygen and nutrients • Remove waste products and CO2 • Provide a barrier between mother and fetus who are • genetically and immunologically different • Endocrine organ (human chorionic gonadotrophin, • oestrogen and progesterone Next slide
Hormonal control of pregnancy • Phase 1 • Corpus luteum • Oestrogen and progesterone • Stimulated by luteinising hormone (LH) from pituitary Next slide
Hormonal control of pregnancy Phase 2 Trophoblast and early placenta Produces human chorionic gonadotrophin (hCG) This has LH like effects on corpus luteum hCG is a peptide hormone Basis of most pregnancy tests (antibody) (appears in urine) Responsible for “morning sickness” Also a growth hormone/prolactin analogue from trophoblast (human placental lactogen, hPL) Increases growth of many tissues and mammary glands Next slide
Hormonal control of pregnancy Phase 3 The placenta becomes the dominant source of oestrogen and progesterone Also secretes human chorionic gonadotrophin human placental lactogen Next slide
Progesterone hCG Oestrogen hPL End lastperiod 0 10 20 weeks 30 40 Parturition Blood levels of hormones during gestation, 40 weeks Blood concentration Next slide
hPL Progesterone hCG Oestrogen Blood concentration 0 10 20 weeks 30 40
Placenta formation Villi bathed in maternal blood in lacunae--exchange of nutrients, O2, CO2 After 13 weeks, full placenta--pancake-shaped organ.
Placental Abnormalities • Abnormalities of the Membranes • Umbilical cord Abnormalities
Normal placenta (term placenta ) • diameter : 30-70 cm • thickness : 2.0 ~ 2.5 cm • weights : approximately 470 g (about 1 lb). • Placental and fetal size and weight roughly correlate in a linear fashion • Fetal growth depends on placental weight which is less with small- -for- gestational age infants
Placental Abnormalities Placental calcification
Placental Abnormalities-Tumors of the Placenta- • Gestational Trophoblastic Disease • Chorioangioma(Hemangioma) • Tumors Metastatic to the Placenta • Embolic Fetal Brain Tissue
Placental Abnormalities-Tumors of the Placenta- Chorioangioma (Hemangioma) • The resemblance components to the blood vessels and stroma of the chrionic villus • Benign tumors of placenta • Incidence : 1% • Diagnosis : larger chorioangiomas – sonographic findings • Associated symptome - small growths : asymptomatic - large tumors : hydramnios or antepartum hemorrhage • Complication : associated with low birthweight : fetal death and malformations are uncommon
Abnormalities of the Membranes • Meconium Staining • Chorioamnionitis • Other Abnormalities