Placenta Flashcards
What are the parts of the placenta?
Fetal part
Maternal part
What type of an organ is the placenta?
Fetomaternal organ
What are the parts of the placenta derived from?
- Fetal part: from the chorionic sac (the outermost fetal membrane)
- Maternal part: from the endometrium (innermost layer of the uterine wall)
Outline implantation
- begins at day 6 of pregnancy
- trophoblast cells interact with endometrial lining of uterus after losing the Zona pellucida
- blastocyst embeds into the endometrium where it interacts with the increased vasculature + secretory glands in the endometrium
When does implantation begin?
Day 6 of pregnancy
What is decidualisation?
Process by which stromal cells differentiate into highly specialised secretory epitheleoid cells called decidual cells
Function of decidual cells
- Control depth of invasion of trophoblast
- protect conceptus from maternal immune rejection
When does decidualisation occur?
During the secretory phase
What happens if implantation occurs where there are no decidual cells?
No control over the extent of invasion or rejection from maternal immune system
What happens when implantation occurs in the correct place but the decidual reaction is suboptimal?
Complications in the pregnancy:
- not maintained (miscarriage or infertility)
- placental insufficiency e.g. pre eclampsia
Normal location of implantation
Upper posterior uterine wall
Normal invasion location
Within the stratum/decidual functionalis
Outline the attachment of the blastocyst
- trophoblastic cells have microvilli which attach to pinopodes on endometrium
- stronger connection made between integrins + receptors on endometrium
- blastocyst is attached to endometrium of uterus
What does the trophoblast differentiate into?
Cytotrophoblast
Syncytiotrophoblast
What produces hCG?
Syncytiotrophoblast
When does placenta formation start?
Second week of pregnancy
What happens in the case of a disease placenta or failed implantation of placenta?
Miscarriage
(Embryo isn’t provided nutrients and oxygen)
What part of the embryo becomes the placenta?
Trophoblast
Describe the layers of chorionic villia
- syncytiotrophoblast (outer layer)
- cytotrophoblast
- core of extra embryonic mesoderm with fetal vessels
Formation of the primary villus
- cytotrophoblast send projections through the syncytiotrophoblast
- intervillus space between the projections
- forms a cytotrophoblastic shell
Formation of secondary villus
- extra embryonic mesoderm invades into the primary villli
- this forms the 3 layered secondary villus
What happens at the same time as secondary villus formation?
The connecting stalk differentiates to form umbilical vessels
2 arteries + a vein
Formation of the tertiary villus
Chorionic vessels grow up into villus
What is a cotyledon?
Decidual cells of endometrium invaginate into placenta causing septae which separate tertiary villi into groups
How does the placenta change throughout pregnancy?
- initially, barrier between fetal and maternal blood is thick which a full layer of cytotrophoblast + syncytiotrophoblast
- as pregnancy progress, the barrier thins by reducing the cytotrophoblast cells to optimise transport
Changes in the embryonic spaces during pregnancy
- yolk sac disappear
- amniotic sac enlarges
- chorionic sac is occupied by expanding amniotic sac
Outline the umbilical vessels
- two umbilical arteries: deoxygenated blood + waste products from fetus to placenta
- one umbilical vein: oxygenated blood + nutrients from placenta to fetus
What conditions can occur due to implantation at incorrect site?
Ectopic pregnancy
Placenta praevia
What conditions occur if implantation is too shallow?
Placental insufficiency
Pre-eclampsia
What conditions occur if implantation is too deep?
Placenta accreta
Placenta increta
Placenta precreta
Increasing depth (alphabetic order)
Three functions of the placenta
Endocrine function
Metabolic changes
Transport function
Describe the endocrine function of the placenta
- syntiotrophoblasts produces human chorionic gonadotropin hCG
-
hCG sustains the corpus luteum in the 1st trimester
. - placenta also produces steroid hormones at the start of the 2nd trimester
- placenta takes over the role of the corpus luteum
- produces enough oestrogen + progesterone to keep the HPG axis in the ‘pregnancy state’
What hormones are produced by the placenta?
Human chorionic gonadotropin hCG
Oestrogen
Progesterone
Describe the metabolic function of the placenta
- progesterone increases maternal appetite > increased fat deposition to support the fetus + breastfeeding
- human placental lactose hPL creates diabetogenic state to cause insulin resistance in mother > increases glucose availability to fetus
What hormone is related to gestational diabetes?
Human placental lactogen hPL
What are the three ways transport occurs in the placenta?
Examples of substances for each
- Simple diffusion: e.g. water, gases, electrolytes
- Facilitated diffusion: e.g. glucose
- Active transport: e.g. amino acids
How is the rate of exchange in gas exchange limited between mother and baby?
What is needed?
Flow limited
Adequate uteroplacental circulation is needed
What specific immunoglobulin crosses the placenta?
IgG
What are teratogens?
Substances that cause congenital disorders in developing fetus
e.g. alcohol, drugs, medications
When do teratogens have the greatest effect?
- Early pregnancy
- Especially embryonic stage (3-8 weeks) as organs systems are most at risk of damage
Why is hCG pregnancy specific?
It is produced by the syncytiotrophoblast
What system is at a continual risk of damage by teratogens during development?
Central nervous system
Long development
Function of human placental lactogen
- Puts mother in diabetogenic state
- causes insulin resistance in mother
- increases glucose availability to fetus
What are TORCH infections?
Infections that can pass across the placenta
Toxoplasmosis
Other- syphilis, HIV
Rubella
Cytomegalovirus
Herpes simplex
What antibody can pass from the mother to the fetus?
By what process does this happen?
IgG
Receptor mediated endocytosis
How soon after fertilisation can hCG be detected reliably in maternal urine?
14 days
