The Placenta Flashcards
When does implantation occur
Implantation begins at day 6 when trophoblast cells interact with endometrial lining of uterus once zona pellucida is lost
What conditions are caused by implantation defects
Ectopic pregnancy - implantation at site other than uterine body. Can become life-threatening
Placenta priva - implantation in lower uterine segment that can cause haemorrhage during pregnancy. Can require C-section
Placental insufficiency
Pre-eclampsia
What does placenta develop from
Placenta develops from trophoblast cells to support pregnancy
What does implantation achieve
Establishes the chorionic villi
Anchors the placenta to the womb
Establishes maternal blood flow within the placenta
Describe the differences between the primary, secondary and tertiary villi
Pirmary - early, finger-like projections of trophoblast
Secondary - invasion of mesenchyme into core
Tertiary - invasion of mesenchyme core by foetal vessels
Describe the structure of chorionic villi and how they change with time
Villi are formed of an outer layer of syncytiotrophoblast and a core of CT where blood vessels develop
Cytotrophoblast expands with its cells merging with syncytiotrophoblast cells to enlarge the villus
In first trimester, barrier between maternal and foetal blood is thick as there is a full layer of cytotrophoblast cells but as pregnancy progresses, barrier becomes less thick as there is decreased number of cytotrophoblast cells for optimised transport
What is the decidua
Decidua is a group of cells in the endometrium that become specialised to modulate the degree of invasion of the conceptus once it has inplanted
What is the decidual reaction
Decidual reaction is the reaction between factors that promote and factors that inhibit decidualisation and how far the conceptus invades into the endometrium
How does blood exchange occur between maternal blood vessels and the foetal blood vessels
Maternal blood vessels bathe the outside of the chorionic villi in maternal blood for exchange to occur
Foetal vessels in the villi then absorb molecules/substance that are in the maternal blood
What are the functions of the placenta
Endocrine function
Metabolic function
Transport function
Immunity function
What are the endocrine functions of the placenta
Placenta produces protein hormones that act to increase glucose availability to the foetus and act to sustain the corpus luteum. E.g. hCG, hCS, hCT, hCC, hPL
Placenta produces steroid hormones to keep the HPG axis in a pregnant state and to increase appetite (progesterone)
What metabolic functions does the placenta have
Placental hormones have an impact on maternal metabolism
Progesterone increases appetite to increase fat deposistion to support foetus and breastfeeding later in pregnancy
Other hormone create a diabetogenic state to cause insulin resistance in mother to increase glucose availability to foetus
What are the transport functions of the placenta
Simple diffusion across concentration gradient - e.g. water, electrolytes, gases
Facilitated diffusion - e.g. glucose
Active transport - e.g. amino acid, iron, vitamins
What are the immunological functions of the placenta
Placenta transports antibodies across into foetal circulation to give the baby some defence against infection
Only IgG transported as transportation is via receptor mediated endocytosis - IgG is only Ig that can interact with receptor
What are teratogens
Agents that interfere with normal foetal developmental processes
