Week 1+2 Flashcards
Histology of the Uterus
Perimetrium - simple squamous & areolar connective tissue.
Myometrium - 3 layers
1. Outer longitudinal
2. Circular (thickest)
3. Inner longitudinal
Endometrium - 2 layers
1. Inner: simple columnar epithelium (ciliated & secretory cells)
2. Thick lamina propria: stratum functionalis & stratum basalis.
Capacitation
- Hyperactivation - activation of whiplash tail for greater motility.
- Acrosome reaction - interacts with ZP2/3 on zona pellucida, causing destablilisation of acrosomal head, allowing it to fuse with oocyte.
- Acrosome contains ACROSIN + HYALURONIDASE.
- Acrosin digests through Zona pellucida.
- Hyaluronidase used to digest through corona radiata.
Sperm need to go through capacitation to attain fertilizing properties.
Acrosome - head of the sperm.
Hyaluronidase - breaks down hyaluronic acid in the corona radiata.
Acrosin - digest through zona pellucida
What phase are primary and secondary oocyte arrested in?
Primary = Prophase I (Meiosis I)
Secondary = Metaphase II (Meiosis II)
LH surge stimulates resumption of Meiosis I
How is the egg activated?
When sperm binds it deposits C-phospholipase gamma = enzyme that starts signalling cascade that leads to calcium oscillations = resumption of metaphase II.
Cyclin B (component of Maturation Promoting Factor (MPF) complex)is destroyed in response to increased calcium levels.
MPF destroyed = initiation of meiosis in secondary oocyte.
How is polyspermia prevented?
Cortical granules move from the inside to the outside of the egg as the egg is underoing maturation.
Cortical granules exocytose in response to calcium flunctuations - releasing compounds that degrade the ZP2/3 glycoproteins to stop sperm from binding.
What is produced once Meiosis II is complete?
- Two polar bodies.
- One haploid ovum containing:
- female pronucleus
- Male pronucleus
Abnormal fertilisation
- Polyspermic - 3pn
- Digynic - 3pn
- Parthneogenetic - 1pn
Parthneogenetic - 1 female pronucleus
How is zygote formed?
Male and female pronuclei decondense, expand, and replicate their DNA in preparation for mitosis.
Pronuclei migrate towards each other, their nuclear enelops disintergrate and genetic material intermingles.
Morulla
16-32 flatten cells.
Cells called blastomeres.
What forms after the Morulla?
Day 5.
Blastocyst forms - blastocoel cavity and blastomeres (Totipotent cells).
Blastocoel cavity - liquid filled cavity.
Day 7: Blastocyst still. Totipotent cells (blastomeres) differentiate
- Trophoblasts/trophoectoderm = epithelium
- Pluroblasts/Inner cell mass = embryonic stem cells
Surrounded by glycoprotein (zona pellucida)
Conceptus
Developing embryo
How is corpus luteum maintained?
Conceptus has synchitiotrophoblasts (makes hCG - binds LH receptors) & progesterone production.
Progesterone production by Luteal cells in corpus luteum.
hCG decreases after first trimester.
Conceptus indepence
Independent of ovarian hormone production by week 6.
C19 androgens from foetal adrenal cortex.
Placenta aromatizes ANDROGENS to OESTRAGENS
Progesterone from conceptus produced from CHOLESTEROL.
hCG no longer need once embryo synthesises its own steroids.
Chorion & Amnion & Yolk Sac
Embryonic origins
Trophoblast and Mesoderm.
Epiblast and Mesoderm.
Hypoblast and Mesoderm.
Formation of trilaminar disc
from pluriblast
- Pluriblast > Epiblast + hypoblast (mesoderm inbetween)
- Mesoderm surrounds epiblast and hypoblast.
- Epiblast and hypoblast form cavities
i) Epiblast + meso = amniotic
ii) hypo + meso = yolk
iii) meso = coelom - Proembryonic disc - Epi, Meso, Hypo
- Trilaminar disc forms - Ectoderm, Mesoderm, Endoderm.
Monozygotic vs Dizygotic
Mono = early embryo splitting (own chorion & amnion). Fused mono-chorionic, diamniotic (1 chorion & own amnion). Mono-chorionic, mono-amniotic (split occurs in ICM, 1 chorion, 1 amnion). Embryonic disc split (occurs in trilaminar disc(1 & 1)).
Dizygotic = 2 Oocytes ovulated and fertilized at the same time.
IVF process
- Ovarian hyperstimulation - give GnRH antagonist (Ganirelix) to downregulate GnRH receptors.
- Inhibition of FSH and LH release. Preventing release of AMH so multiple follicles can develop.
- Stop Ganirelix. Give rFSH to maintain follicles and progress to 2nd oocytes.
- Aspirate Oocyte via transvaginal ultra sound.
- Sperm and Oocyte co-incubated for 24hrs.
- Fertilized egg allowed to grow in medium for 48hrs.
- 2 embryos transferred to patient uterus via catheter.
If fertilized doesnt occur, can use Intracytoplasmic sperm injection (ICSI) to inject sperm directly into the Oocyte.
Sperm extraction methods
PESA - percutaneous epididymal sperm aspiration.
TESE - testicular sperm extraction.
TESA - testicular sperm aspiration.
MESA - microepididymal sperm aspiration.
azoospermia = no sperm
First trimeseter fetal development
Fertilization.
Implantation.
Initial development.
Placentation.
Mother experiences weight gain and nausea.
Second trimester fetal development
Nervous system.
Spine straightens.
Hair.
Ability to feel pain.
Proportion changes
Mother experiences, fundus rising, hypervolemia, cardiac remodelling, breast remodelling, placental growth.
Third trimester fetal development
Growth.
Fat deposition.
Brain growth.
Blood cells ( gamma chains replaced by beta chains).
Lung development.
Mother experiences Braxton-Hicks contractions (fake contractions), tired, restricted breathing, lactation.
Implantation process
- Blastocyst ZP and Glycocalyx is lost.
- Uterine epithelium produces LIF (Leukaemia Inhibitory Factor) to locally mediate implantation.
- Villous trophectoderm interdigitate (interlock) with villi on epithelium.
- Nuclei of epithelial cells of uterus move to basal pole of cell.
- Trophoblast cells invade uterine epithelium.
- Primary decidua is locally destroyed by trophoblast with proteases.
- Endometrial epithelium seals over the blastocyst in endometrial wall.
- Trophoblasts turn into Synctial trophoblasts and form Syncytium (one cytoplasmic mass w/ many nuclei) around inner layer of trophoblasts > turns into Cytotrophoblasts.
- Fragments of maternal capillaries engulfed by Syncytium.
- Trophoblastic lacunae fill with materal blood and are precursors of intervillos spaces of the placenta.
- Maternal capillaries expand to form sinusoids that anastomose with the trophoblastic lacunae.
What is Decidualisation?
Process that results in significant changes to cells of the endometrium in preparation for pregnancy and during pregnancy.
Decidua basalis (primary decidua) - between placenta and myometrium.
Decidua capsularis - encapsulates chorion.
Decidua parietalis - lines myometrium where there is no basalis.
Deciduous spiral arteries.
Endometrial blood supply remodelling to form Placenta
- Stem villi form from Syncytiotrophoblast and extend into the intervillous space within syncytium.
- Small villi form from the stem villus to create a network of terminal villi (site of gas exchange).
- Villi developed in 3 stages:
i) Primary - composed of syncytium
ii) Secondary - mesoderm invades villous core
iii) Tertiary - Blood vessels developed from mesoderm - Spiral arteries remodelled by replacement of smooth muscle and endothelium w/ trophoblast todrop pressure and increase volume (allows blood to pool) - deciduous spiral arteries.
- Deciduous spiral arteries expand to form sinusoids that enter intervillous spaces (Lacunae) & bathe foetal villi in oxygenated blood.
- Deoxygenated blood flows back to mother through endometrial veins.
- Umbilical vein carries blood away from the villi.
- Umbilical vessels from fetus enter Cytotrophoblast layer to form Chorionic vessels which supply villi.
placenta formed by week 12.
Fetal Lobule
Intervillous space (lacunae) supplied by a villus (many terminating branches), deciduous spiral arteries, and endometrial veins.
Villi development in placenta
- Primary stem villi formed from Synctiotrophoblasts - solid core.
- Mesoderm invades core to form secondary villi.
- Mesoderm develops to form blood vessels & connective tissue - tertiary villi.
- Tertiary villi carry on developing:
a) Mesenchymal villi - tertiary villi lengthen.
b) Immature intermediate tertiary villi - tertiary villi reach maxium lengths.
c) Mature intermediate tertiay villi - produce small nodule like secondary branches - Terminal villi - Terminal villi formed - final structure of the villus tree.
Endocrine function of the placenta
hCG - maintains corpus luteum until Synctiotrophoblast are mature enough to produce enough progesterone to maintain the uterine lining.
Oestrogen - Conceptus adrenal cortex synthesis androgens which are converted to estrogens via androgen aromatase.
Progesterone.
Somatomammotropin.
Estrogens role: proliferative effect on mother, relax pelvic ligaments and increase elasticity of pubic symphysis.
Progesterone role: causes decidualisation, increases uterine secretions, reduces uterine contractions.