11.13 Physiology of Pregnancy Flashcards
What are the critical periods of pregnancy?
- Periconceptual period, early pregnancy are critical that marternal health is good
- First 2 weeks of foetal life is where there is the most highest susceptibility to death
- Embryonic period weeks 3-8: risk of major formation abnormalities
- Foetal period (9 weeks onwards): risks for growth, function and physiological changes
What is the duration of pregnancy?
280 days (40 weeks) from last menstrualperiod
Which is actually 266 days (38 weeks) from fertilisation but this is a lot harder to measure
How do we estimate foetal age?
Length and ultrasound measurements of fetus
What are the physical signs of the establishment of pregnancy? [6]
- cessation of menstruation
- morning sickness (this has some impact on maternal nutrition)
- Increased frequency of urination
- Increased size of breasts (Developing in preparation to provide nutrition after birth)
- fatigue (due to energy use of physiological adaptations)
- darkening of areolae
Does the cessation of menstrual periods always mean pregnancy?
No
Many higher centres of the brain impact the HAO axis (eg. extreme stress can suppress ovulation and development of endometrium)
Other pathological sources can cause cessation of menstrual periods (eg. PCOS, drugs and alcohol, weight loss/gain, pituitary adenoma, thyroid, endocrine)
What is the gold standard biochemical marker for pregnancy?
How is it measured?
human chorionic gonadotropin (hCG)
- Measured in the urine
- Measured as a blood test (this is definitive for pregnancy)
(beta HCG can also be secreted as a result of some cancers)
Pregnancy adaptations occur in the mother during pregnancy, what body systems are involved and how do they change?
Dynamic process with maternal adaptations:
- Anatomy, physiology, biochemistry, metabolism
- Cardiovascular, blood, metabolic, renal, respiratory, endocrine
Why are these physiological changes in the mother necessary in pregnancy?
- Maintain uteroplacental perfusion
- Maintain fetal demands
What can impact or hinder the physiological changes that need to occur in the mother during pregnancy?
Pathological or already existing problems with these systems in the mother prior to conception (ie. chronic disease) undergo further stress during pregnancy and thus there can be failure or altered pregnancy development/adaptations
Describe the process of implantation
Trophoblast cells invade into the endometrium (which is secretory and nourishes the structure and process). And allows for the boundary to be continuous.
Once the blastocyst is implanted, the endometrium is called the dicidua of pregnancy
What are the major functions of the placenta?
An organ that connects the developing fetus to the uterine wall to allow nutrient uptake, waste elimination, and gas exchange via the mother’s blood supply, fight against internal infection and produce hormones to support pregnancy.
How is the placenta connected to the mother’s blood flow?
- The maternal artery takes blood to the maternal side of the placenta and the maternal veins take deoxygenated blood out.
Maternal blood bathes chorionic vessels (blood lakes - for maximal efficiency in transferring blood) that become the source and drainage point for the umblical vein and artery to connect with the placenta.
- The umbilical vein carries oxygenated blood from the mother.
- Deoxygenated blood is carried back to the mother from the foetus in the 2 umbilical arteries.
Why would the placenta structure contain the chorionic vessel/pool structure?
For maximal efficiency in transferring blood.
Another major reason is to prevent unwanted vessel constriction to occur to the foetus everytime there is a systemic peripheral change in maternal vasculature.
[Pathology: If invasion of placenta by the blastocyst is not appropriate then the plaecnta is exposed to peripheral vasoconstrictors then there is a problem with blood delivery to the foetus]
The placenta acts as a substitute for foetal organs. How does it substitute for foetal lung functioning and why is this necessary?
The lungs are liquid filled at this point in time because the baby is free floating in the amniotic sac. They are making foetal breathing movements (practicing) but there is no air there.
Thus the placenta acts to deliver O2 and remove CO2 from the foetus
The placenta acts as a substitute for foetal organs. How does it substitute for foetal kidney functioning and why is this necessary?
Amniotic fluid comes from liquid produced by foetal lungs and foetal urine.
The foetus is producing large volumes of dilute urine with amniotic fluid that is excreted into the amnioitic fluid.
It is thus important that this urine doesn’t contain waste products and toxic products normally found in urine. Thus the placenta filters out the bad stuff so it is not in the amniotic fluid
The placenta acts as a substitute for foetal organs. How does it substitute for foetal gastrointestinal functioning and why is this necessary?
Swallowing amniotic fluid to facilitate gastrointestinal functioning and development.
The placenta also provides all the nutrients the baby requires
What is the importance of the Human chorionic gonadotropin (hCG) hormone?
- Rescue” of corpus luteum
- Basis of pregnancy tests
hCG (not LH and FSH) maintain the corpus luteum of pregnancy. It rescues it and keeps it a functioning endocrine gland producing progesteron and oestrogen
What is human chorionic gonadotropin (hCG) hormone?
A hormone produced by the cells that surround the growing human embryo (syncitiotrophoblasts - the outer layer of trophoblasts) from the implanting conceptus.
These cells will eventually go on to form the placenta.
Human chorionic gonadotrophin can be detected in the urine from 7-9 days post-fertilisation as the embryo attaches and implants in the womb
The placenta produces Human placental lactogen (hPL)
What is this hormone responsible for?
Breast development and metabolic effects
The placenta as an endocrine organ also acts as a source for two major hormones important for pregnancy. What are they and what is their significance?
Estrogen and progesterone
- Pregnancy maintenance
- breast development
Note: Several additional hormones are produced – maternal adaptations of pregnancy (Facilitate adaptations of mother and communications to foetus.)
What are the 2 ways of multiple pregnancy?
Describe each one
Monozygotic
- genetically identical
- same sex
- single fertilised ovum (the ovum splits: started out as one individual)
Dizygotic
- 2 oocytes ovulated and fertilised by 2 separate sperm
- two completely separate individuals that are the same as being regular brothers/sisters
What are the four major steps in partuition?
Describe them
- Prior to labor
- Maturation of fetal organs
- Softening of the cervix (normally long thick and closed)
- Labor
- Rhythmic uterine contractions
- Once initiated sustained by positive feedback -no way of stopping it once it starts; always leads to delivery
- Cervical dilation
- Delivery of the baby
- Placental release and expulsion
- Important to avoid haemorrhage of the mother
What causes the onset of labour?
The Trigger complex & unknown
- Corticotrophin releasing hormone CRH
- Fetus
- Placenta role
- Stretch of cervix stimulus (eg. impact or baby’s head or breeching)
What hormone is heavily involved in labour?
Describe this
Oxytocin released from the posterior pituitary
Stretch increases the levels of oxytocin which causes release of prostaglandin release that causes contractions of the myometrium of the uterus to aid in labour and partiuition.
A Positive feedback loop (uterine contractions then induce stretch to induce more oxytocin release)
