Physiology of Pregnancy and Lactation Flashcards
What is implantation?
The fertilised ovum progressively divides and differentiates into a blastocyst as it moves from the site of fertilisation in the upper oviduct to the site of implantation in the uterus
What is a blastocyst?
a cluster of dividing cells made by a fertilized egg. It’s the early stage of an embryo.
Days 3-5 of implantation?
transport of the blastocyst into the uterus
Days 5-8 of implantation?
blastocyst attaches to the lining of the uterus
What do the inner cells of the blastocyst develop into?
The embryo
What do the outer cells of the blastocyst develop into?
Placenta
When the free-floating blastocyst adheres to the endometrial lining, cords of trophoblastic cells begin to penetrate the endometrium. True/false?
True
How does the blastocyst insert itself into the endometrial lining?
- Advancing cords of trophoblastic cells tunnel deeper into endometrium, carving out a hole for the blastocyst
- The boundaries between cells in the advancing trophoblastic tissue disintegrate
How does the placenta maintain pregnancy?
produces several hormones I.e. progesterone
What are trophoblasts (trophoblastic cells)?
cells forming the outer layer of a blastocyst, which provides nutrients to the embryo, and develops into a large part of the placenta
What is decidual tissue and it’s role?
Decidual tissue (decidua) has been known as maternal uterine tissue, which plays essential roles in protecting the embryo from being attacked by maternal immune cells and provides nutritional support for the developing embryo prior to placenta formation.
What is the placenta derived from?
trophoblast and decidual tissue
Trophoblast cells (chorion) differentiate into multinucleate cells
(syncytiotrophoblasts) which invade decidua and break down
capillaries to form cavities filled with maternal blood. True/false?
True
How is “placental villi” formed?
Developing embryo sends capillaries into the syncytiotrophoblast projections
What does each villus of the placenta contain?
contains fetal capillaries separated from maternal blood by a thin layer of tissue - no direct contact between fetal & maternal blood
What does the villi of the placenta aim to do?
Achieve a 2 way exchange of respiratory gases, nutrients, metabolites etc between mother and foetus, largely down diffusion gradient
Placenta (and foetal heart) functional by what week of pregnancy?
5th week of pregnancy
What signals the corpus luteum to continue secreting progesterone?
HCG
What stimulates decidual cells to concentrate glycogen, proteins, and lipids?
Progesterone
How does oxygen pass from maternal into foetal circulation?
- Oxygen diffuses from the maternal into the fetal circulation system
- Carbon dioxide follows a reversed gradient (elevated in fetal blood)
The supply of the fetus with oxygen is facilitated by what three factors?
- Fetal Hb - increased ability to carry O2
- Higher Hb concentration in fetal blood
- Bohr effect - fetal Hb can carry more O2 in low pCO2 than in high pCO2
Transport mechanisms for placental exchange?
The placental exchange processes occur via classic membranous transport mechanisms (passive transport, simple diffusion, osmosis, simplified transport, active transport)
Role of HCG?
Prevents involution (shrinkage) of corpus luteum (CL stimulates progesterone and oestrogen)
Does HCG have an effect on the testes of the male foetus?
Yes
Development of sex organs
In what cases is HCG used in clinical scenarios?
Useful to monitor changes to help diagnose:
- Ectopic pregnancy - static or slow rising
- Failing pregnancy - falling
- Ongoing viable pregnancy - doubling or >60% rise
What conditions can still show high HCG?
Multiple pregnancy (having more than 1 child at once) or molar pregnancy
At what point does HCG levels fall?
12-14 weeks
What is human placental lactogen and what is it’s role?
Human placental lactogen (hPL) is a hormone produced by the placenta during pregnancy.
It is a polypeptide that belongs to the somatotropin family and is similar to growth hormone and prolactin.
It helps prepare the body for breastfeeding, regulates metabolism and insulin sensitivity, and provides nutrients and oxygen to the foetus.
progesterone function in pregnancy?
- Development of decidual cells
- Decreases uterus contractility
- Preparation for lactation
oestrogen function in pregnancy?
- Enlargement of uterus
- Breast development
- Relaxation of ligaments
Cardiac output is decreased during pregnancy. true/false?
False
Cardiac output is increased in pregnancy due to demands of the uteroplacental circulation
How is cardiac output calculated?
HR x SV
Heart rate x stroke volume
Are the ranges for blood results during pregnancy different from typical ranges?
Yes
ALT, Urea, creatinine and albumin show different ranges.
During pregnancy, what changes are made to maternal coagulation?
Pregnancy is a hypercoagulable state
This reduces the risk of haemorrhage during and after delivery HOWEVER comes with increased risk of venous thromboembolism.
What is parturition?
Birth of baby
Underlying features that induce parturition (birth)?
Occurs towards end of pregnancy, when uterus becomes progressively more excitable.
Oestrogen: progesterone ratio alters, increasing excitability.
Oxytocin (from maternal posterior pituitary gland) increases contractibility and excitability.
Oestrogen inhibits contractility. true/false?
False
Oestrogen increases contractility
Progesterone inhibits contractility
What are Braxton Hicks contractions?
Braxton Hicks contractions are a tightening in the abdomen that comes and goes.
They are contractions of the uterus in preparation for giving birth. They tone the muscles in the uterus and may also help prepare the cervix for birth.
Cervical stretching also causes further oxytocin release. true/false?
true
What is lactation?
Production and release of milk
Oestrogen role in lactation?
Growth of ductile system
Progesterone role in lactation?
Development of lobule-alveolar system
Both oestrogen and progesterone induce milk production. True/false?
False
Oestrogen and progesterone inhibit milk production. At birth there is a sudden drop in these hormones.
What hormone stimulates milk production?
Prolactin - stimulates milk production with steady rise in levels from week 5 to birth.
1-7 days after birth, prolactin induces high milk production
Roles of oxytocin in pregnancy?
Oxytocin is a hormone that stimulates uterine contractions and facilitates labour and delivery.
Oxytocin receptors in the uterine muscle increase and become more sensitive during pregnancy, especially at term.
Oxytocin also reduces stress, calms pain, and promotes bonding with the baby before and after birth.
Oxytocin helps to expel the placenta and prevent bleeding after birth
