4: Placenta, metabolism, birth weight Flashcards
At what point of the pregnancy is the “placental growth spurt”? “Fetal growth spurt”?
Placentas growth spurt is in the first half of pregnancy, fetus is in the last trimester.
Which comes first- embryonic or placental growth?
Embryonic then placental growth.
What are some of the main functions of the placenta?
Exchange of nutrients, respiratory gases, and metabolic waste. Protects growth and is a source of hormones.
Is there mixing of the fetal and maternal blood?
No direct mixing.
What does the amniotic sac enclose?
The embryo, amniotic fluid, and forms the epithelial covering of the umbilical cord.
What is the source of most of the amniotic fluid?
Maternal blood (diffusion)
What is the function of the amniotic fluid?
Shock absorption, prevents desiccation (dryness), allows room for fetal movements, assists in regulation of fetal temperature.
What is the fetal surface of the placenta called?
Chorionic plate.
What cells connect the placenta to the uterus and provide an area where materials can be exchanged?
Cytotrophoblasts. Act tumour-like to invade mothers uterus and establish blood flow to fetus.
What is the space called that the maternal blood enters (major functional unit of the placenta)?
Chorionic villus
When does the fetus begin to excrete urine into the amniotic cavity?
First trimester.
What are some examples of products that are synthesized by the placenta for the fetus?
Glycogen, lactate, cholesterol.
Does the fetal affinity for oxygen differ from the mothers?
Yes, the fetus has a greater affinity for oxygen due to the greater binding capacity of fetal hemoglobin.
Is there a difference in glucose levels between maternal and fetal blood during hyperglycemia? Why?
Glucose levels are lower for the fetus than the mother. Protects fetus from glycstion, which can be teratogenic.
What substances are transported to the fetus by passive diffusion?
Oxygen, carbon dioxide, fatty acids, steroids, electrolytes, fat soluble vitamins (generally poor transfer tho)
What substances are transported to the fetus by active transport?
Amino acids, cations, water soluble vitamins
What substances are transferred to the fetus by facilitated diffusion?
Sugars, long chain PUFA
How does the size of the placenta relate to the size of the fetus?
The fetus size is directly proportional to the placental size.
Does blood flow through the placenta stay constant through the duration of the pregnancy?
No, to compensate for the increased fetal needs later in the pregnancy, placental blood flow increases in the last trimester. Also compensates for the lower rate of placental growth compared to the fetal growth.
What partially accounts for the deceleration of fetal growth rate in the last 4 weeks of gestation?
Decline in the quantity of nutrients transferred per g fetal mass per unit time. Fetus increasing size so much, limited by size of placenta and amount of blood that can flow through the placenta.
What are lower concentrations of essential fatty acids in maternal and fetal blood associated with?
Lower birth weight, short gestation (preterm), and small head circumference.
How does the fetal levels of DHA relate to the mothers?
Fetus will have higher levels, through a process of bio magnification (selective transfer). Highest levels will be found in the fetal brain (much higher than what is found in the maternal blood.
What percentage of energy to the fetus is used for brain development?
70%!
What is human chorionic gonadotropin? Where is it secreted from throughout the pregnancy?
Maintains the corpus luteum, which is needed for secretion of estrogen and progesterone to support the first trimester of pregnancy. Secreted by the blastocyst preimplantation, then by the placenta for the rest of pregnancy (peak levels at wks 10-11).
What is human chorionic somatotropin? What is it also known as? Where is it produced?
Influences fat and carb metabolism, might be responsible for insulin resistance observed in pregnancy, also breaks down maternal fat to fuel the fetus. Aka placental lactogen. Produced by placenta later in gestation.
What is progesterones function? Where is it produced?
Prevents ovulation from occurring during pregnancy, supports endometrium, suppresses contraction of the uterine smooth muscle at the end of gestation. Corpus luteum produces until 10 weeks, then placenta takes over.
What is estrogens function during pregnancy?
Stimulates growth of the middle layer of the uterus wall (myometrium), stimulates mammary gland development, and antagonizes progesterone which suppresses myometrium growth. Peaks towards the end of gestation.
Do glucocorticoids, insulin, and thyroxine pass on to the fetus?
Placenta metabolizes these to inactive forms so don’t effect fetus.
When do most physiological adjustments occur to accommodate the pregnancy?
In the first half of gestation.
Hoe does gastric emptying change during pregnancy?
Slows due to decreased histamine and pepsin secretion.
How is the globular filtration rate and tubular reabsorption change during pregnancy?
Increased and decreased, respectively. This allows to excrete fetal waste products in addition to the maternal waste products. Also causes increased renal losses of glucose, folate, iodine, and amino acids.
Why are plasma lipids seen at higher levels during pregnancy?
Lipids are used by maternal system to conserve glucose for fetal use (maternal lypolysis).
What part of pregnancy is the anabolic phase? What does this anabolism encompass?
First half of pregnancy. Extra carb converted to glycogen or fat, fats quickly synthesized to TGs, increase in maternal protein synthesis (RBCs and placenta mostly)
What part of pregnancy is the catabolic phase? What does the catabolism encompass?
Second half of pregnancy. Fat stores are mobilize to conserve glucose for fetus, see rise in blood cholesterol and ketones, hormones released by fetus oppose anabolic effect of insulin (uptake of glucose by the placenta doesn’t require insulin so don’t need insulin levels higher).
What is considered the minimum body fat percentage preconception?
About 22%
What is the rule of thumb for weight gain through pregnancy?
3-4 lbs for the first 10 weeks then 1 lb/week afterwards.
What health risks are associated with rapid and large weight gains?
Excessive edema, risk of preeclampsia, decrease blood flow to placenta (because increased risk of separation of placenta from the uterine wall).
What consists of obligatory weight gain during pregnancy?
Fetus, placenta, enlarged uterine and breast tissue, and expanded blood volume.
What is associated with insufficient blood volume expansion?
Stillbirth, LBW, spontaneous abortion
What is morning sickness associated with?
Increase in blood estrogen and HCG (usually starts 4 weeks after conception and lasts 6-8 wks). Morning sickness is actually a positive predictor of pregnancy.
What are the recommendations to deal with morning sickness?
Eat small frequent meals with high fat (calories) and low bulk. Avoid spicy foods. Avoid skipping meals because pose risk of ketosis and hypolycemia (teratogens).
What are the three biggest predictors of birth weight?
Gestational age, maternal weight gain, preconception weight.
What is considered a “preterm infant”? “Mildly preterm infant”?
Less than or equal to 37 weeks. 32-37 weeks is considered mild.
What two processes determine birth weight?
Duration of gestation and rate of fetal growth.
What is low birth weight defined as?
Less than 2500 g
What are some factors that cause preterm delivery?
Genitourinary infection, multiple pregnancies, preeclampsia, low pregnancy BMI, history of preterm births, cigarette smoking, strenuous physical activity.
What is intrauterine growth retardation defined as?
Greater than 2 standard deviation in weight for age OR less than 10th percentile in weight for age OR < 2500 g at >37 weeks gestation.
What can IUGR cause that leads to fetal malnutrition and hypoxia?
Hypoglycemia and hypocalcemia
What long term effects are a higher risk with low birth weight?
Decreased lung capacity, twice risk of CVD, 6x risk of diabetes and impaired glucose metabolism, increased blood pressure risk, abnormally high TGs, low HDL
What increased long term risks are associated with high birth weights?
Increased risk of hormonally related cancers (prostate, breast, ovary, testicle)
What effect does increased maternal corticosteroid production have on enhancing short term survival of the pregnancy?
Increases speed of maturation of lungs and other organs.
What long term health consequence is associated with cortisol exposure early in gestation?
High blood pressure
What is considered the optimal time to support a pregnancy?
5 years after first period.
What is “pica”?
Consumption of non food substances (clay, dirt, laundry starch, ice, gravel, hair, baking soda etc).
