Session 6 - Placental Function & Dysfunction Flashcards
Which structure does the placenta come from?
Placenta is formed from the syncytiotrophoblast, in the week of 2s.
It is a specialisation of the chorionic membrane (outer)
When does implantation begin?
Day 6 trophoblast contacts endometrium.
Day 9 embedded in endometrium.
What happens to the yolk sac and chorionic cavity as the embryo continues to develop?
The yolk sac is no longer needed, so regresses.
The chorionic cavity reduces as the amniotic sac grows and ‘fills’ its space.
What does implantation of the embryo and the syncytiotrophoblast achieve?
- Exchange between the mother and embryo. (Villi) finger like projections of trophoblast.
- Anchors the placenta.
- establishment of maternal blood flow through structure.
What happens to the placental membrane as development progresses? Why is it important?
Membrane becomes thinner, ultimately one cell layer (trophoblast).
In order to reduce the diffusion pathway for higher rate of oxygen, and nutrient diffusion for an increased demand from the foetus.
How are the mother and foetal circulation separated?
At placenta by one layer of trophoblast, ensures circulations don’t mix.
What is a chorionic villus?
A finger like projection of the trophoblast with inner connective tissue core.
Has foetal vessels, for exchange with maternal blood.
What are two major implantation defects and their process? What are the risks?
Ectopic Pregnancy
- Implantation at site other than uterine body (most common Fallopian tube ampulla)
Risk: Bleeding into pelvic cavity
Placenta Praevia
- Implantation in the lower uterine segment (sometimes over birth canal)
Risk: Haemorrhage in pregnancy
(C-section)
In the presence of the embryo what happens to the endometrium of the uterus?
Becomes the decidua.
The uterine lining during pregnancy, promoted by progesterone
What is the decidual reaction?
The set of changes in endometrium in preparation for embryo implantation.
Embryo implantation may be unsuccessful without this reaction happening properly.
What are the cotyledons of the placenta?
The separations of the decidua containing a main stem of a chorionic villus and its branches, which form the placenta.
What is the structure of a chorionic villus?
- Main stem containing syncytiotrophoblast cells on the outer layer, and some cytotrophoblast cells deep to this.
- Has branches, and terminal branches, containing vessels with foetal blood.
Thin layer for diffusion.
How do nutrients and oxygen from maternal blood diffuse into the foetal circulation?
The chorionic villi of the foetal placenta are surrounded by flow of maternal blood.
Which vessels from the foetus carry blood too and from the placenta?
Two umbilical arteries: deoxygenated blood from foetus to placenta.
One umbilical vein: brings oxygenated blood back to foetus.
What is the function of human chorionic somatomammotrophin from the placenta?
Peptide hormone
- Has anti insulin properties in the mother, to reduce glucose use by mother.
- To allow higher glucose concentration and to be used more by the foetus.
What is an important endocrine function of the placenta?
Secretes progesterone and oestrogen.
Takes over from corpus luteum.
Important in preparation of pregnant state, increasing hunger (Progesterone maintaining endometrium)
- Increases breast size and preparation for lactation. (Oestrogen)
Where is Human chorionic gonadotropin secreted from? Why is its function?
- Secreted from syncytiotrophoblast of the placenta.
- Thus secreted in the pregnant state.
- Supports the secretory function of the corpus luteum.
Which hormone present in urine is used in pregnancy tests?
Human chorionic Gonadotrophin (hCG)
By which week do the placental hormones take over the corpus luteum?
11th week
What is the reason for limit of oxygen diffusion at the placenta?
Flow limited, not diffusion limited
How are molecules that aren’t passively diffused moved through the placenta into foetal blood stream?
By specific ‘transporters’ on the syncytiotrophoblast.
Amino acids, iron, vitamins
How is transfer of maternal immunity achieved to the foetus?
IgG from the mother are transported through a receptor mediated process. (Higher concentration in foetus than mother - against gradient)
Which dangerous substances can pass the placental barrier?
Teratogens
Name some harmful teratogens that can cross the placental membrane, and their effects.
Thalidomide
- Limb defects
Alcohol
- Foetal alcohol syndrome FAS, and ARND
- Anti-epileptic drugs
- Warfarin (can cause foetal bleeding)
- Drug abuse - can cause adiction
- Maternal smoking (placenta changes)
What are the effects of teratogens in the pre-embryonic, embryonic, and foetal stages.
Pre-embryonic
- Lethal effects, loss of pregnancy
Embryonic
- Most sensitive period
(Narrow window for some systems)
Foetal
- Not as sensitive, fewer denovo structures developing.
After embryonic period, low risk except CNS.
