UNSW Embryology

Placenta Development- Stage 22

© Dr Mark Hill (2009)

Acknowledgements

Introduction

In sections of the stage 22 embryo, only components of the placental cord and some membranes can be seen.

Stage 22 Embryo (Human)
A1	A2	A3	A4	A5	A6	A7
B1	B2	B3	B4	B5	B6	B7
C1	C2	C3	C4	C5	C6	C7
D1	D2	D3	D4	D5	D6	D7
E1	E2	E3	E4	E5	E6	E7
F1	F2	F3	F4	F5	F6	F7
G1	G2	G3	G4	G5	G6	G7

Glossary of Terms

A |B | C | D | E | F | G | H | I | J | K | L | M | N | O | P | Q | R | S | T | U | V | W |X | Y | Z

Placenta Development Terms

• anastomose-
• angiogenesis- the formation of blood vessels also called vasculogenesis in the embryo
• angioblasts- form clusters or blood islands on surface of yolk sac.
• capsularis-
• chorionic sac- fetal membrane that surrounds the developing embryo.
• cord knotting- umbilical cord knotting occurs in 1%, prevents the passage of placental blood. pseudoknots also occur usually with no effect.
• cotyledons- maternal side cobblestone appearance, originally placental septa formed grooves is covered with maternal decidua basalis.
• cytotrophoblast- extraembryonic cells of trophoblastic shell surrounding embryo, contribute to villi and placental membranes.
• decidua basalis reaction- occurs in maternal endometrium at site of, and following, blastocyst implantation. Seen as a deposition of glycogen and proliferation of blood vessels.
• endocrine- function of placenta:
  • Human chorionic gonadotrophin (hCG)- like leutenizing hormone, supports corpus luteum
  • Human chorionic somatommotropin (hCS)- or placental lactogen, stimulate mammary development
  • Human chorionic thyrotropin (hCT)
  • Human chorionic corticotropin (hCACTH)
  • progesterone and estrogens- support maternal endometrium
  • relaxin- role in parturition, softens ligaments
• fetal drug addiction- occurs when drugs used maternally cross the placental barrier and can establish addiction in the unborn fetus.
• fetal erythroblastosis- (Haemolytic Disease of the Newborn), an immune problem from fetus Rh+ /maternal Rh-, leakage from fetus causes anti-Rh antibodies, which is then dangerous for a 2nd child.
• frondosum-
• haemocytoblasts- stem cells for embryonic blood cell formation
• Haemolytic Disease of the Newborn- see fetal erythroblastosis.
• Human chorionic gonadotrophin- (hCG) like leutenizing hormone, supports corpus luteum
• Human chorionic somatommotropin- (hCS) or placental lactogen stimulate mammary development
• Human chorionic thyrotropin- (hCT) placental derived hormone equivilant to thyroid
• Human chorionic corticotropin- (hCACTH) placental derived hormone equivilant to corticotropin (ACTH) from the pituitary.
• maternal antibodies- antibodies from the mother's immune system that are capable of crossing placental barrier. They can provide immune protection to the embryo, but may also participate in immune disease (fetal erythroblastosis).
• maternal sinusoids- placental spaces around chorionic villi that are filled with maternal blood. Closest maternal/fetal exchange site.
• placenta- (Gk. plakuos= flat cake) describes its typical mature discoid shape (20cm diameter and 3 cm thick at term,weighs 500-600 gm).
• placenta accreta- abnormal, adherence with absence of decidua basalis.
• placental arteries- paired, carry deoxygenated blood and waste from the embryo (dorsal aorta->internal iliacs->PA)
• placental blood- blood found within the placental vessels. Obviously part of the fetal blood, but can be collected at birth for theraputic use containing blood stem cells (see cord blood banks).
• placental blood vessels- form initially in the connecting stalk (then umbilical cord), anastomose in chorioni and extend maternally toward chorionic villi, extend embryonically to the sinus venosus and dorsal aorta.
• placental layers- 4 layers separate maternal and fetal blood: syncitiotrophoblast, cytotrophoblast, villi connective tissue, and fetal capillary endothelium.
• placenta percreta- abnormal, villi penetrate myometrium.
• placenta previa- placenta overlies internal os of uterus, abnormal bleeding, may require cesarian delivery.
• placental veins- paired initially then usually only one left at end of embryonic period, carry oxygenated blood to the embryo (sinus venosus)
• primary villi- develop week 2, consist of trophoblastic shell cells both syncitiotrophoblasts and cytotrophoblasts. Form finger-like extensions into the maternal endometrium.
• protein hormone- usually a protein distributed in the blood that binds to membrane receptors on target cells in different tissues. Do not easliy cross placental barrier.
• relaxin- hormone.
• secondary villi- develop week 3, extraembryonic mesoderm grows into villi, initially covers entire surface of chorionic sac.
• sinus venosus- cavity into which all major embryonic paired veins supply (vitelline, placental, cardinal)
• syncitiotrophoblast- extraembryonic cells of trophoblastic shell surrounding embryo, outside the cytotrophoblast layer, involved with implantation of the blastocyst by eroding extracellular matrix surrounding maternal endometrial cells at site of implantation, also contribute to villi. (dark staining, multinucleated)
• tertiary villi- develop week 4, mesenchyme within secondary villi differentiates into blood vessels and cells, forms arteriocapillary network, fuse with placental vessels developing in connecting stalk.
• trophoblast-
• umbilical cord- fetal attachment cord 1-2 cm diameter, 30-90cm long, covered with amniotic attached to chorionic plate, umbilical vessels (artery, vein) branch into chorionic vessels. Vessels anastomose within the placenta.
• villi- initially outgrowth of the trophoblastic shell which involve other tissues with development. Develop in sequence (primary, secondary, tertiary) with mature villi being stem por branched type.
• virus- small infectious agent able to cross placental barrier. Can infect embryo and cause developmental abnormalities. (e.g. cytomegalovirus, rubella, measles)
• vitelline- Blood vessels cover entire surface of yolk sac and connect to embryo through yolk stalk
  • Arteries- arises from dorsal aorta and contribute to adult GIT arteries.
  • Veins- empties into sinus venosus and contribute to the adult portal system.
• waste products- products of cellular metabolism and cellular debris, e.g.- urea, uric acid, bilirubin

Quick Links

Placenta Pages:

Development Notes ----------------- Menstrual Cycle Week 1 Week 2 Week 3 Week 4 Placenta Serial Images Genes/DNA Molecular Dev Abnormal Dev Postnatal Dev Notes Index

System Notes ----------------- Heart/Cardiovascular Respiratory Coelomic cavity Gastrointestinal Tract Head and Neck Neural Neural Crest Eye Ear Nose Endocrine Urogenital Musculoskeletal Integumentary

Movies ----------------- Embryo Growth Ultrasound Week 1 Week 2 Week 3 Week 4 Stage 13/14 Stage 22 Neural Head and Neck Heart Vasculature Gastrointestinal Urogenital Other Embryos Larsen Internet

Other Embryos ----------------- Chicken Fly Frog Mouse Rabbit Rat Worm Zebrafish Guinea Pig

UNSW Embryology ISBN: 978 0 7334 2609 4

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