3) Placental Metabolism Flashcards
When does the fastest growth of the placenta occur? Why?
- During the first half of pregnancy
- To prepare for the fetal growth spurt during the second half of pregnancy
What is the placenta?
The interface between the microcirculatory systems of the mother and fetus
What are functions of the placenta?
- Exchange of nutrients, respiratory gases, and metabolic waste
- Protection of the fetus from xenobiotics
- Acting as a source of hormones
When is there mixing of the maternal and fetal blood?
- There is NEVER any direct mixing of the maternal and fetal blood
- The placenta is composed of a maternal and fetal portion
Where does the majority of amniotic fluid come from?
The maternal blood via diffusion from the intervillus spaces of the placenta
What are functions of amniotic fluid?
- Acts as a shock absorber
- Prevents desiccation of the fetus
- Provides room for fetal movements
- Assists in body temperature regulation
The ________ plate forms the fetal surface of the placenta.
chorionic
______________ are cells from the placenta that connect the mother and fetus.
Cytotrophoblasts
What components form the large area for exchange of fetal and maternal material?
- Cytotrophoblastic shell
- Anchoring villi
Where does the exchange between maternal and fetal material occur?
Within the intervillus spaces, as maternal blood flows around the villi
What is the major functioning unit of the placenta?
Chorionic villus
What placental defects do IUGR infants display?
They have microscopically less branching of the villi
What is the function of the villi within the placenta?
Enhances the surface area, allowing for greater exchange of gases and nutrients
The placenta uses 50% of _______ and 65% of _______ from the maternal blood supply.
oxygen
glucose
What substances does the placenta synthesize for fetal use?
- Glycogen
- Lactate
- Cholesterol
What substances cannot cross the placental membrane?
Compounds possessing a large molecular weight
What substances are transported across the placental membrane via passive diffusion?
- Oxygen and carbon dioxide
- Fatty acids
- Steroids
- Electrolytes
- Fat-soluble vitamins
How does fetal hemoglobin differ from regular hemoglobin?
Fetal hemoglobin has a greater binding capacity for oxygen
How are fatty acids transported through the placental membrane?
- Passive diffusion
- Carrier-mediated transport for long-chain FAs (enhancement of PUFA transport)
- The fetus depends on a supply of EFAs
Of the substances that are transported via passive diffusion, there is a poor transfer of which one?
Fat-soluble vitamins
How are sugars transported through the placental membrane?
Carrier-mediated facilitated diffusion
What is the importance of glucose transporters within the placenta?
- Glycation is a mechanism of teratogenesis
- Glucose transporters are used to protect the fetus from high glucose levels
If a mother experiences hyperglycemia, is a fetus exposed to a hyperglycemic environment as well? Why or why not?
- No, the fetus experiences a lower glucose level
- Because of the use of glucose transporters
What substances require energy-dependent active transporters to cross the placental membrane?
- Amino acids
- Certain cations
- Water-soluble vitamins
What do iron and folate require to cross the placental membrane?
Pinocytosis
What do water and solutes use to cross the placental membrane?
Solvent drag
The fetal size is proportional to the _______ size.
placental
How may maternal malnutrition, such as iron deficiency, affect placental size and fetal growth retardation?
- Reduced blood volume expansion
- Decreases cardiac output and placental blood flow
- Decrease in placental size, reduced nutrient transfer, and subsequent fetal growth retardation
What conditions may decrease uterine blood flow and affect placental transport?
- Hypotension
- Renal disease
- Placental infarction
During the third trimester, how does the fetal weight and the placental weight change?
- The fetal weight more than doubles at the last 10 weeks
- The placental weight only increases by 50%
A lower rate of placental growth is a limiting factor for what?
For sufficient transfer of nutrients for fetal needs
What is partially responsible for the deceleration in fetal growth rate during the last 4 weeks of gestation?
A progressive decline in the quantity of nutrients transferred per unit of fetal body mass per unit of time
What mechanism often causes the failure of the placenta?
Failure of the uteroplacental blood vessels to deliver an increased uterine blood flow
How do essential fatty acid affect the placenta?
Deficiencies in EFAs cause defects in placental integrity and function
Low placental weight is found to be associated with lower plasma concentrations of which fatty acids?
- Arachidonic acid
- DHA
- Linoleic acid
What are reduced concentrations of AA, DHA, and LA associated with?
- Short gestation
- Small head circumference
The percent distribution of DHA is highest in which fetal structure?
The fetal brain, then liver and umbilical cord
70% of energy during fetal growth is devoted to what?
Brain development
______ form 50 to 60% of the structural matter of the brain.
Lipids
The brain is a structurally lipid-rich organ. What PUFAs does it use? Which ones in particular?
- 20- and 22-carbon PUFAs
- Arachidonic acid
- DHA
What kind of PUFA is arachidonic acid?
- 20:4 (n-6)
- Omega-6
What kind of PUFA is DHA?
- 22:6 (n-3)
- Omega-3
What is the function of hCG?
Maintains the corpus luteum, which secretes estrogen and progesterone
What secretes estrogen during the beginning of pregnancy? What structure replaces its secretion? When?
- The blastocyst secretes estrogen on day 7
- After implantation, hCG is produced by the placenta, allowing for the maintenance of the corpus luteum, which secretes estrogen
When does the peak of hCG occur? What happens after?
- The peak occurs at the 10th and 11th week of gestation
- After, hCG levels decline and remain low for the rest of pregnancy
What produces placental lactogen? When?
The placenta in late gestation
What is the function of placental lactogen?
Influences fat and carbohydrate metabolism (breakdown of maternal fats to provide fuel for the fetus)
What is a synonym for placental lactogen?
Human chorionic somatotrophin
What structures produce progesterone during pregnancy?
- Corpus luteum until the 10th week of gestation
- The placenta takes over afterwards
What are the functions of progesterone in supporting pregnancy?
- Inhibits the secretion of LH and FSH to prevent ovulation
- Supports the endometrium
How does progesterone prevent pre-term birth?
Suppresses contractility in uterine smooth muscle
Which hormone decreases and which hormone increases to facilitate parturition?
- Progesterone decreases
- Estrogen increases to increase contractility of the smooth muscles of the uterus
When is estrogen secreted maximally during pregnancy?
Towards the end of gestation
What are the functions of estrogen in pregnancy?
- Stimulates myometrium growth
- Antagonizes myometrial-suppression by progesterone
- Stimulates mammary gland development
Catabolism of which substances are controlled by the placenta?
- Glucocorticoids
- Insulin
- Thyroxin
How does the exposure to hormones vary if the placenta is underdeveloped?
The placenta developing inadequately decreases catabolism of these molecules, which may cause harm to the fetus
True or False: the placenta offers a substantial amount of protection against xenobiotics.
- False
- The placenta is highly permeable to a large variety of substances, and thus offers limited protection against xenobiotics
When does the majority of physiological adjustments during pregnancy occur? In most cases, how does physiological activity vary?
- During the first half of gestation
- In most cases, physiological activity increases
The physiological activity of which structures do not increase during pregnancy? Why?
- Smooth muscle function of the uterus (to prevent contractions)
- Smooth muscle function of the GI tract (to prevent heartburn)
What occurs to the kidney during pregnancy? Why?
- An increase in GFR and decrease in tubular reabsorption capacity
- Leading to an increased blood volume to facilitate the increased excretion of fetal waste products
What are the consequences of an increased blood volume during pregnancy?
An increase in renal losses of glucose, folate, iodine, and amino acids
What occurs to the stomach during pregnancy?
Depression of function due to a decreased secretion of pepsin and histamine
What does a decreased function of the stomach lead to?
Increased risk of heartburn due to the relaxation of the cardiac sphincter, causing a higher risk of regurgitation
What occurs to the gastrointestinal tract during pregnancy? Why?
- Decrease in motility to slow down transit time
- Leads to an increased efficiency of absorption of certain nutrients (vitamin B12, iron, calcium)
What is a possible consequence of the decrease in motility of the GI tract? In what situation?
Constipation, if combined with a lack of sufficient fluid intake
What occurs to the heart during pregnancy? Why?
- Cardiac hypertrophy, which increases cardiac output to allow a larger blood volume to circulate
- Improves blood flow to the placenta and fetus
What occurs to the lungs during pregnancy? Why?
Increased ventilation to accommodate for increased oxygen demands by the fetus, placenta, and maternal tissues
How does BMR vary during pregnancy? Why?
- BMR increases by 15 to 20% due to an increase in oxygen consumption
- BMR returns to normal a week after the baby is born
How do plasma lipid profiles vary during pregnancy? Why?
- Increased levels of plasma lipids (triacylglycerols and cholesterol)
- Since the maternal system is preferentially using lipids to conserve glucose for the fetus
How do blood glucose levels vary during pregnancy, specifically during the third trimester?
- The fetus’ glucose demands are increased, which causes maternal blood glucose to fall
- Increased lipolysis and ketosis compensates for the decrease in glucose
What occurs to hepatic gluconeogenesis during pregnancy? Why?
Impaired hepatic gluconeogenesis due to a decreased availability of alanine
What is the decreased availability of alanine during pregnancy due to?
To a decrease in muscle breakdown and an increase in placental uptake of alanine
What other physiological adjustments occur during pregnancy?
- Altered appetite and thirst
- Altered digestion and assimilation of food
- Hemodilution
The first half of pregnancy is the (anabolic/catabolic) phase, while the second half of pregnancy is the (anabolic/catabolic) phase.
anabolic
catabolic
What occurs to carbohydrates during the anabolic phase of pregnancy?
Excess carbohydrates are stored as glycogen or converted to fat, due to the sharp rise in blood insulin after meals
What occurs to fats during the anabolic phase of pregnancy?
- Rapidly synthesized into TGs
- Decreased rate of lipolysis to conserve fat stores for the second half of pregnancy
What occurs to proteins during the anabolic phase of pregnancy?
Increase in maternal protein synthesis, particularly in RBCs and the placenta
What is the preferred form of energy of the fetus?
- Glucose
- The fetus requires a quick source of energy for rapid growth
What occurs to fats during the catabolic phase of pregnancy? What is the result?
- Fat is mobilized to conserve glucose for the fetus
- Results in an increase in ketones and blood cholesterol
What occurs to insulin during the catabolic phase of pregnancy? What is the result?
- The action of insulin is blunted by estrogen, progesterone, and placental lactogen
- Catabolism of maternal fat, glycogen, and protein
What occurs to glucose levels after a meal during the catabolic phase of pregnancy? Why?
- Glucose levels rise sharply given the blunted insulin response
- Results in a greater uptake of glucose by the placenta
Does the placenta rely on insulin for absorption of glucose?
No
Prior to conception, a woman should possess __% body weight fat.
22
What is the average weight gain during pregnancy?
12.5 kg
How does the expected weight gain during pregnancy of underweight women compare to overweight women?
Underweight women need to gain more weight
What weight gain is recommended for adolescents?
28 to 40 pounds
What weight gain is recommended for twins?
35 to 45 pounds
What are the patterns of weight gain expected during the first 10 weeks of pregnancy, and the rest of the pregnancy?
- First 10 weeks: 3 to 4 pounds per week
- Rest of pregnancy: 1 pound per week
Gaining over ___ kg per week during pregnancy is a cause of concern.
one
What is the likely causes for gaining over a kilogram per week during pregnancy? What are possible risk factors?
- The presence of excessive edema, causing a risk for pre-eclampsia
- Increased risk for placental abruption, stillbirth, decreased blood flow to the placenta, and low-birth weight
What are the sources of obligatory fetal weight gain?
The growing presence of the fetus, placenta, and amnionic fluid
What are the sources of obligatory maternal weight gain?
- Enlarged uterine and breast tissue
- Expansion of blood volume
What are the sources of non-obligatory maternal weight gain?
Gain in adipose tissue, protein stores, and extracellular fluid
When does 50% of the increase in maternal blood peak? How does hemoglobin mass vary? What is the result?
- During the third trimester
- Lower increase in hemoglobin
- Hemodilution
How does the hematocrit vary during pregnancy?
The hematocrit decreases (hemodilution)
What are correlated outcomes associated with insufficient blood volume expansion?
- Stillbirths
- Low-birth weight
- Spontaneous abortions
Edema is commonly present in pregnancy. When is it not a cause for concern?
If it is gained gradually
When is the majority of the energy needed to support pregnancy deposited? What is it characterized by?
- In the first 20 weeks (anabolic phase)
- Characterized by an increase in subcutaneous fat in the abdominal and upper thigh areas
What comprises most of the weight gained during the second half of pregnancy?
Fetal tissues, placenta, and amniotic fluid
An increase in plasma volume and RBCs is directly related to what?
Fetal size
Describe the S-shaped curve of fetal weight.
- Little weight gain during the first trimester
- Rapid weight gain during gestational weeks 8 to 23
- Weight tapers off at weeks 37-38
What are the effects of weight maintenance and slight losses during the first trimester?
There is little effect on embryonic weight gain
What is the cause of morning sickness?
- Increase in estrogen and hCG
- Nausea and vomiting are a positive predictor of pregnancy outcome and decreased risk of fetal death, as it represents an adequate level of hormones
What are the effects of eating less during the first trimester?
- Does not substantially affect the growth of the fetus
- However, too many skipped meals may lead to ketosis and hypoglycemia (teratogenic risk)
What are the women recommended to eat in terms of meals?
Small, but frequent, high-fat, low-bulk meals
What are the three most important determinants of birth weight?
1) Gestational age
2) Maternal weight gain
3) Pre-conception weight
What is the best clinical indicator to judge pregnancy progress?
Maternal weight gain possesses the strongest influence on fetal weight gain
Mortality rates are lowest for infants of what weight range?
2.5 to 4 kg
What risks do dietary restrictions pose?
- Low-birth weight
- Hypertension
- Perinatal mortality
- IUGR
The highest perinatal mortality rates are in which type of women? What about the lowest perinatal mortality rates?
- Highest: underweight women who gain little weight during pregnancy
- Lowest: underweight women who gain an appropriate amount of weight
What are the risks of obese pregnant women?
- Pre-eclampsia
- Gestational diabetes
- Infection
- Cesarian
- Prolonged labor and complications during delivery (asphyxia, abnormal glucose regulation in infant)
What are the two main problems in pregnancy that are related to infants with a low-birth weight?
- Small for gestational age
- Prematurity
Define a preterm birth.
A preterm birth is below 37 weeks, while a term birth is above 37 weeks
What are the three criteria for IUGR?
- Below 2SDs in weight for gestational age
- Below the 10th percentile in weight for gestational age
- Below 2500 grams and gestational age above 37 weeks
If they survive birth, extremely premature infants are at a risk for severe morbidities, such as what?
- Retinopathy of prematurity
- Chronic lung disease
- Neurocognitive disease
What are the most severe morbidities of preterm infants?
- Cerebral palsy
- Mental retardation
- Seizure disorders
What are mildly preterm infants (32 to 36 weeks) at a risk for?
- Respiratory distress syndrome
- Infection
- Mortality
Define a low-birth weight.
Below 2500 grams
Define a small for gestational age infant.
Below the 10th percentile for gestational age
All infants who are (IUGR/SGA) are also (IUGR/SGA), but not all (IUGR/SGA) infants are (IUGR/SGA).
IUGR, SGA
SGA, IUGR
What are causes of preterm birth?
- Genitourinary infection
- Multiple pregnancies
- Pregnancy-induced hypertension
- Low pre-pregnancy BMI
- Prior history of a preterm birth
- Smoking
- Strenuous physical labor
What are the two types of IUGR? How do they differ?
- Proportionate: infants with decreased growth potential or extreme fetal malnutrition
- Disproportionate: infants with maternal malnutrition
What are causes for decreased growth potential in proportionate IUGR infants?
- Congenital infection
- Genetic disorder
- Environmental toxins
What are the characteristics (length, weight, and head circumference) of proportionate IUGR infants?
- Length, weight, and head circumference are proportional, occurring within a similar percentile
- May also occur if the head is small relative to the body (microcephaly)
What are the characteristics (length, weight, and head circumference) of disproportionate IUGR infants?
The length and head circumference are closer to the expected percentiles for gestational age, but the weight is disproportionately small
What are causes of IUGR?
- Low-energy intake
- Low pre-pregnancy BMI
- Short maternal stature
- Pregnancy-induced hypertension
- Smoking
- Malaria
IUGR is a component of _____, a set of dysmorphic features
FAS
What are the effects of malaria in primiparous women? What has this been associated with?
- Major cause of anemia
- Associated with reduced birth weight and an increased risk of IUGR
What may severe IUGR lead to in the early neonatal period?
Hypoglycemia and hypocalcaemia
What adult diseases has IUGR been shown to be associated with?
- Hypertension
- Type II diabetes
- Cardiovascular diseases
The rapidly developing fetus is more susceptible to the permanent programming effects of malnutrition during which period of gestation?
Late gestation
What are the three abnormal patterns of fetal growth that are linked to adult diseases?
1) Symmetrical small babies of low-birth weight
2) Babies are thin at birth, but undergo catch-up during infancy
3) Average birth weight, but are abnormally small in proportion to their placental weight
What are risks of low-birth weight?
- Decreased lung capacity during childhood
- Twice the risk of cardiovascular disease
- Six times the risk of diabetes and impaired glucose metabolism
- Increased blood pressure risk, abnormally high TGs, insulin resistance, and low HDL
What is excessive birth weight (above 9 pounds) related to?
An increased risk of hormonally-related cancers
What advantageous mechanism occurs during undernutrition? Why?
- Maternal corticosteroid production increases as a stress response
- Increases fetal maturation of lungs and other organs
How is poverty associated with an increased nutritional risk for pregnancy?
Poor nutritional intake status, and increased smoking, in low-income groups are associated with twice the rate of low-body weight infants (down by 200 to 300 grams)
Define a short inter-conception interval.
Refers to a woman becoming pregnant shortly (less than one year) after giving birth
How is a short inter-conception interval associated with an increased nutritional risk for pregnancy?
High physiological and nutritional demand on the nutrient body stores of the mother, which increases the likelihood of deficiencies
What chronic illnesses may place heavy demands on nutritional intake?
Diabetes, chronic infection, cancer, alcoholism, and malabsorption
What unusual dietary patterns may place a woman at a higher risk of having an infant with a low-birth weight?
- Consuming microbiotics
- Dieting constantly
- Anorexia
- Pica
What is pica associated with, in terms of nutritional status?
- Low zinc and iron status
- Displacement of other nutritious foods
How is a history of anemia and/or obesity associated with an increased nutritional risk for pregnancy?
Indicates long-term imbalance or an inappropriate diet, which may adversely affect reproductive success
Why are teen pregnancies at a high-risk of low birth weight?
- Poor nutritional status
- Low pre-pregnancy weight
- High incidence of food fads
- Increased drug and alcohol use
- Decreased obstetric, nutritional, and social support
- Increased body image consciousness (insufficient maternal weight gain)
Why is there a greater risk of an infant with a low-birth weight in a younger adolescent mother?
- Due to immature endocrine and reproductive functioning
- 5 years post-menarche are required to foster a healthy pregnancy
What hormones are blunting the action of insulin during the catabolic phase of pregnancy?
Estrogen, progesterone, and placental lactogen
