Reproduction 18 Flashcards
When is the endometrium most receptive?
Mid-luteal phase of menstrual cycle-
secretory activity peaks- endometrium rich in glycogena and lipids
Glands increase in size and number,
maintained by high progesterone and oestrogen levels
Change in endothelial surface- pinopode formation
Describe implantation
Implantation window = microvillus epithelium swell up and form more elaborate and dimpled to have greater surface area, preventing cilia beating off the implanting blastocyst. Allows strong surface for implantation
Embryo attachment and penetration of the endometrium and maternal circulatory system to form the placenta
Apposition- blastocyst loosely associates with the uterine wall followed by attachment
Invasion- attachment triggers enzyme production that degrades the wall and invades the glycogen rich endometrial stroma. Provides nutritional support
Describe decidualisation of the endometrium
Oedema, changes in ECM, angiogenesis, leucocyte infiltration (uterine natural killer cells)
Stromal fibroblasts change to polygonal morphology
Store glycogen and lipids and secrete decidual proteins eg. prolactin, IGFBP-1, tissue factor, VEGF, PIGF, IL-15
The decidua completely surrounds the blastocyst by day 10
Describe the placenta
Placenta funciton is: Transport, metabolism, endocrine and immune privelage
Human placenta is haemochoroidal- the chorion is in direct contact with the blood (Other types include endotheliochoroidal in cats and dogs- the maternal blood endothelium comes in to contact with the chorion Epitheliochoroidal in cows and pigs, most primitive- the maternal epithelium of the uterus come into direct contact with chorion)
Myometrium-> Decidua basilisa basalis containing maternal spiral arteries-> cytotrophoblastic shell with placental septum between villi-> villi containing fetal blood vessels
Describe the development of the placenta
Trophectoderm gives rise to three main types of trophoblast
Cytotrophblast-> Syncytiotrophoblast- forms by fusion of villous cytotrophoblast (syncytialisation)- multinucleated, terminally differentiated syncytium, forms continuously throughout placental development covering the entire villious tree
Extravillious cytotrophoblast- interstitial and endovascualr (For immune regulation)
Lacunae form within the syncytiotrophoblast, which invades and erodes the maternal capillaries, these anastomose with the lacunae to form sinusoids, intervillous space develops
Primary villi- day 11-13, swellings of cytotrophoblast extend into syncytiotrophoblast layer and form finger-like projections in the decidua
Secondary Villi- extra embryonic mesoderm invades the core of the primary villous. Mesoderm covers the entire surface. VIlli continue to extend into the decidua between the blood filled lacunae
Tertiary villi - Mesodermal cells diffrentiate to form endotheial and other cells types. Blood vessels form an arterior capillary netwrok in the villi. Vessels fuse with developing vessels in the stalk to link the fetal blood system to the umbilical cord
Describe the structure of the mature placental villi
Stem villi- basal part of the villi, attached to chorionic plate
Branch/intermediate villi- project from the sides of the stem villi
Terminal villi- swellings at the tips of the branch villi contain terminal vessels, form convoluted knots where the majority of exchange occurs. The cytotrophoblast layer becomes very thin, but remains mostly intact- 80% coverage in full term placenta
Describe the remodeling of maternal blood vessels
Critical to establish low resistance, high flow blood supply to the intervillous space
Spiral arteries- resistance vessels supplying the endometrium, coiled appearence, 150 vessels transformed, diameter is increased 10x (200um to 2mm)
Extravillous Trophoblasts (EVT)- plug developing spiral arteries and create a low oxygen environment which might protect the embryo from oxidative stress, plugs breakdown initiating blood flow to the intervillious space around week 14 EVTs help remodelling, leading to loss of vascualr cells, remodelling of the ECM and endovascular trophoblasts taking over the walls of vessels
List substances that transported across the placenta
Parabiotic relationship (fetus is dependant on maternal provision of nutrition)
Diffusion- Oxygen, carbon dioxide (fetal haemoglobin has higher affinity for oxygen) Na Urea (foetus regulates maternal AA metabolism trhough progesterone) Fatty acids (lipids broken down by lipases found on the brush border on the syncytiotrophoblast, cellular transport by FABP) Sugars- facilitated diffusion (Uptake by insulin insensitive hexose transporters- maternaltissues show insulin inenstivity due to hPL) non-conjugated steroids, thyroxine (T4)
Active transport - Iron (By transferrin increase absorption in 3rd trimester to cover blood loss during partuition), Ca (needed for fetal ossification in 3rd trimester), folic acid and vit B12 cocaine, alcohol, caffeine, tetracycline
Non-transported- conjugated steriods, nucleotides, most bacteria
Virsus (Rubella), bacteria (spirochetes) and prtozoa (toxoplasma) can cross the placenta
Describe blood supply from mother to the foetus
Uterine blood flow increases 20x during pregnancy, CO increases by 30-40%, 25% to placenta, increased blood volume 40%
Placenta- 3-4 layers separates the maternal and fetal circulations
Syncytiotrophoblast, Cytotrophoblast, Connective tissue, Capillary endothelium
Fetal blood flow - Umbilical arteries (deoxygenated)–> Fetal capillaries (Stem villi->intermediate villi->terminal villi)–> Umbilical Vein (oxygenated)
Describe the consequences of poor EVT infiltration
Significant loss of placental function
Shallow invasion- early onset pre-eclampsia, intra-uterine growth restriction (AA transport severly compromised, reduced fatty acid ion transport, acidosis and reduced bonemineralisation)
Premature loss of plug- miscarriage
