Placentas Flashcards
Define placenta
- Placenta: functional unit for maternal-foetal exchange
- Oxygen supply, waste removal, immune barrier, endocrine organ
- Umbilical cord attached to baby
- Maternal surface is stuck to the uterus
- Maternal blood percolates around chorionic villi
Discuss embryonic cells
- Peripheral layer of blastomeres -> trophoblast, with a mass of cells at one aspect, polar trophoblast, bulging into the central lumen -> inner cell mass. Zona pellucida disappears, and implantation occurs.
- Trophoblast forms two layers (inner cytotrophoblast layer and an outer syncytiotrophoblast layer).
- Syncytiotrophoblast develops finger-like projections into the endometrium. A third type of trophoblast known as intermediate trophoblast invades the endometrium.
- A sponge-like network of spaces (lacunae) develops within syncytiotrophoblast, invasion by intermediate trophoblast causes disintegration of endometrial capillaries with leakage of maternal blood into lacunae.
- Trophoblast envelops maternal capillaries, expanding the lacunar network and establishing an arterial supply and venous drainage system.
What are the main placental hormones?
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Sex Steroids
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Progestins:
- Supports endometrium – provides an environment conducive to fetal survival
- Suppression of contractility in uterine smooth muscle, “progesterone block”
- Inhibits secretion of pituitary gonadotropins luteinizing hormone and follicle-stimulating hormone
- Prevents ovulation during pregnancy
-
Estrogens (estriol):
- Stimulate the growth of myometrium and antagonize myometrial-suppressing activity of progesterone
- Stimulate mammary gland development
- Suppress gonadotropin secretion from the pituitary gland
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Progestins:
also hPL, hCG (made first)
List some other hormones produced by the placenta
- Human chorionic gonadotropin (hCG): binds to luteinizing hormone receptor on cells of corpus luteum-> prevents luteal regression. Thus, hCG serves as signal for maternal recognition of pregnancy
- Human placental lactogen (hPL)
- Chorionic adrenocorticotropin (cACTH)
- Parathyroid hormone-related protein (PTH-rP)
- Growth hormone (chorionic somatomammotropin)
- Prolactin
- Hypothalamic hormones-gonadotropin-releasing hormone (GnRH), corticotropin-releasing hormone (CRH), thyrotropin-releasing hormone (TRH), and growth hormone-releasing hormone (GHRH)
- Relaxin
- Cytokine Growth Factors (transforming growth factors a and ß (TGFa, TGFß), and epidermal growth factor (EGF))
- Activin and Inhibin
- Renin
- Calcitonin
What are the benefits of examining a placenta?
Why Examine a Placenta?
- Benefits:
1. Clarification of the pathophysiology of adverse outcomes – categorize various etiologies into acute and chronic and often severity e.g. infarcts and type and severity of infection
2. Improve management of subsequent pregnancies for those shown to have conditions that have recurrence risks and may be either treatable or preventable e.g. infection, chronic villitis, maternal floor infarction, infarcts
3. Understand antenatal and intrapartum events that contribute to long-term neurological and developmental sequelae – identify and institute early intervention to improve long-term outcomes e.g. 2 vessel cord or cord thrombosis meconium
4. Independent assessment of factors that may contribute to a poor outcome as a factual basis for resolving medico-legal issues eg. Placental infarcts, chronic villitis, stem vessel thrombosis, velamentous insertion of a cord
What are the indications for placenta assessment?
- Ultrasound
- All placentas: macroscopic assessment
- Delivery suite: midwife/registrar or O and G
- Some placentas (~15%): more detailed macroscopic and microscopic assessment +/- cytogenetics and microbiological culture
- Pathology: registrar and pathologist
What are the details included in a placenta report?
- Macroscopic: weight/measurements
- Weight/size
- With membranes and umbilical cord = 600g
- Just disc = 450-550g
- Ratio of placenta and foetus is close in first trimester, but by term the foetus weighs 7x the placenta
- Shape (normally oval)
- Complete
- Chorionic villous branching
- Weight/size
- Microscopic
- Maturation
- Infarction
- Athetosis
- Inflammation/infection
- Haematomas/thrombi
- Macroscopic and microscopic: umbilical cord, membranes
and disc and abnormalities - Commentary on relation with the clinical situation and
recurrence risk
What is the normal size of placenta? Provide examples of abnormal placenta in different trimesters with common causes
Main change in diameter in first and second trimester.
Main change to thickness in 3rd trimester.
- Normal: 500g, diameter: 200 mm, thickness: 35-50 mm
- Abnormal 1st-2nd trimester: 500g (“cupcake”)
- doesn’t reach maximum diameter
- thicker thannormal
- common in pre-eclampsia
- Abnormal 3rd trimester: 400g (“pancake”)
- placenta does not reach normal thickness, so weighs less
- common in infarction, chronic villitis (autoimmune disease), leading to growth restriction
- Abnormal entire pregnancy: 250g (“pikelet”)
- common in chromsomal abnormalities, viral infections, chronic intervilusitis, leading to growth restriction
Note: diabetes or high BMI can cause very large placenta
Describe chorionic vascular branching
- Determined by 14 weeks gestation - if placenta doesn’t have a complex appearance, then there is a problem
- Will influence placental efficiency
- Primary branches off the cord insertion
- Secondary branches off primary branches
- % coverage of disk area
- Normal: complex-complex >90%
- Complex-simple: late first/early second trimester pathology
- Simple-simple: uncompensated pathology
List issues of the placental disc
- villous maturation
- feto-maternal circulation
- infarction
- villitis
Describe villous maturation
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First Trimester:
- Chorionic villi of placenta are large and covered by two layers of cells-cytotrophoblast and syncytiotrophoblast. Blood vessels in villi are not prominent.-
Second Trimester:
- Villi become smaller and more vascular – immature intermediate villi.
- Syncytiotrophoblast cell layer draws up into “syncytial knots” which are small clusters of cells, leaving a single cytotrophoblast layer. Clumps of pink fibrin begin to appear.
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Third Trimester:
- Small and highly vascularized chorionic villi (1-6 vessels) to support blood gas and nutrient exchange of maternal-fetal circulation. Syncytial knots and intervillous fibrin are prominent. Blood vessels sit right against BM of cytotrophoblast layer
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Second Trimester:
Discuss an issue of feto-maternal circulation
- Atherosis: foamy macrophages in maternal blood vessels can cause change due to hypertension
* Trophoblasts invade through maternal blood vessels to reduce resistance - higher resistance can set up a cascade that can cause fibrinoid necrosis of vessels and infiltration of macrophages
Describe infarct formation
- Intervilus thrombus: breakage between villus tissue and maternal tissue causing massive foetal blood loss into maternal circulation
- Early infarct will have some preservation because villus tree has some areas of supply from other branches
Describe villitis
- Chronic villitis: intravenous mononuclear infiltrate, which is usually associated with areas of perivillous fibrin deposition
- Chronic intervillositis: intervillous infiltrate of mononuclear cells (inflammatory cells) which is usually associated with intervillous fibrin deposition
- Idiopathic villitis (VUE): major cause of growth restriction and still birth
- Currently thought to be due to a maternal immune response to unknown placental/foetal antigen - pregnancy should be a time of immune tolerance but sometimes this can start to fail
- Normal pregnancy: foetus is protected by immune deviation ∴ TH2 response prevails over TH1 (more B cells, less T cells)
- Currently thought to be due to a maternal immune response to unknown placental/foetal antigen - pregnancy should be a time of immune tolerance but sometimes this can start to fail
- VUE: TH1 response (delayed hypersensitivity response) causes influx in mother’s T cells (CD8)
- Recruits foetal and maternal monocytes and macrophages → attack foetal fibrovascular stroma of placental vili
- B cells (plasma cells) are not prominent feature → this is prominent in CMV)
What is the normal number of vessels in the umbilical cord?
- Number of vessels - should be 3 vessels, 2 arteries and 1 vein which carries oxygenated blood
