The Placenta Anatomy, Physiology, Function Flashcards
What is Placenta Accreta?
What can incomplete invasion of the Conceptus lead to?
Invasion that is too deep
- Miscarriage
- Infertility
- Placental insufficiency (can lead to Pre-eclampsia)
The placenta is the first structure that begins to develop.
In what week does development occur?
What is the Placenta?
Week 2
A specialisation of an area of Fetal Membranes surrounding the fetus
Describe what happens as the Amniotic sac enlarges after implantation
(Amniotic sac is simply the Amniotic cavity, as is the Chorionic)
- Yolk sac disappears
- Chorionic sac is displaced
- Amniotic membrane fuses with chorionic membrane to produce a single amniotic cavity
What is “water breaking” in labour?
Amniochorionic membrane breaks and amniotic fluid leaks out
Initially, the outer surface of the Amniochorionic membrane has projections spread out over the entire surface.
How does this change as growth occurs?
Projections become concentrated into a single disc-like space, which goes on to become the placenta
What does Implantation achieve?
Describe this in stages
Establishes the basic unit of exchange from the Conceptus: Villi
- Primary Villi: Early finger-like projections of trophoblast
- Secondary Villi: Invasion of mesenchyme into core
- Tertiary Villi: Invasion of Mesenchyme core by fetal vessels
(They also anchor the placenta)
How do Tertiary Villi communicate with maternal blood flow?
Maternal vessels surround the villi
Describe the barrier between Fetal and Maternal blood and how it changes as pregnancy progresses
- Initially, thick barrier with full layer of Cyto- and Syncytiotrophoblast.
- Barrier becomes progressively thinner via reduction in no. of Cytotrophoblast
- Eventually only 1 Trophoblast layer thick, but Circulations never mix
Why does the Fetal-Maternal blood barrier thin as pregnancy progresses
Increased substance exchange, as fetal needs increase (mainly for brain development)
What are Decidua?
How do they carry out their function?
- Endometrial cells that specialise to regulate invasion of the Conceptus once it has implanted
- Via Decidualisation, balanced by factors that promote and inhibit the Decidual reaction
Why are Decidua clinically significant?
If implantation occurs where no Decidua are present (Ectopic pregnancy), no inhibition of Decidualisation occurs and Invasion is uncontrolled
What can happen if the Decidual Reaction is sub-optimal?
- Pregnancy not maintained (Miscarriage , Infertility)
- Placental insufficiency (Including Pre-eclampsia)
Name and describe the action of the maternal and fetal vessels
Maternal;
- Endometrial arteries + veins
- Bathe outside of the Villi
Fetal vessels;
- Bring waste to Villi via 2 Umbilical arteries
- Take O2+nutrients to fetus via 1 Umbilical vein
On which side of the Placenta will we see the shiny Amnion and Chorionic Vessel?
What do we see on the maternal aspect?
Fetal aspect (facing towards fetus)
- Cobblestone appearance
- Cotyledons (Functional units, contain chorionic villi)
Describe the Endocrine function of the Placenta
Protein hormones;
- Such as HCG, which sustains the Corpus Luteum in Trimester 1
Steroid hormones;
- After 1st Trimester, it takes over the role of the Corpus
- Produces Progesterone and Oestrogen (to keep HPG axis in a pregnancy state)
Why is HCG known to be pregnancy-specific?
How is this significant clinically?
Produced by Syncytiotrophoblast
- Can be analysed in urinary and serum testing
- Raised in Trophoblast disease
Describe the Maternal Metabolic changes caused by 3 Placental hormones
- Progesterone- Causes increase in appetite, diverts glucose to fat synthesis
- Oestrogen- Increase in PRL release
- Human Chorionic Somatommaotrophin/ Placental Lactogen (hCS/ hPL);
- Causes Insulin resistance in mother to direct glucose to fetus
What are 3 ways transport occurs at the placenta
Suggest substances transported via each way
Simple diffusion;
- Water, gas, electrolytes, Urea and Uric acid
Facilitated diffusion;
- Glucose
Active transport;
- Amino acids, Iron, Vitamins
Is Fetal-Maternal gas exchange flow limited or diffusion limited
Fetal O2 stores are small, what can happen if Uteroplacentalcirculation is inadequate?
Flow limited
‘Fetal distress’ (E.g Labour contractions-> Vessel contraction)
Describe transfer of Immunity from mother to fetus
- Antibodies can be transported across
- Only IgG immunoglobulin can cross
(Fetal Plasma [IgG] > Maternal Plasma [IgG])
When do Teratogen have their greatest effect?
Explain and describe the effects of Teratogens in the Fetal Period (weeks 9-36)
Embryonic period (weeks 3-8)
- Most symptoms have developed and only need to grow
- Effects tend to be less severe, other than in the CNS
Why is it significant that pregnancy is considered to be an Immunocompromised state for the mother?
Infections can have more serious consequences in pregnancy
Suggest an example of Physiological Teratogenesis and its effects
Blood group incompatibilities such as Rhesus disease;
- Maternal antigens cross barrier and attack Fetal RBCs
List 5 Teratogens
- Thalidomide (Limb defects)
- Alcohol (FAS, ARND)
- Smoking
- Medications (Warfarin, ACE Inhibitors, Anti-epileptics)
- Drugs of abuse (Dependency in Fetus and newborn)
