15 - Fetal and Neonatal Physiology Flashcards
After fertilization, what occurs before implantation? Where does the blastocyst get it’s nutrition?
Multiple cell divisions and 4-5 days after fertilization is implantation.
Before implantation, blastocyst obtains nutrition from endometrial secretions.
How does the ovum get nutrients after implantation but before total penetration?
Trophoblasts surrounding the ovum digest the endometrium to provide nutrition for several weeks of pregnancy.
How is HCG made and what effect does it have after fertilization?
HCG is secreted by trophoblasts about 9 days after ovulation.
Stimulates corpus luteum to continue secretions of progesterone and estrogens which prevent menstruation.
Stimulates decidual cell growth in endometrium to provide embryo nutrition.
How do HCG levels change during pregnancy?
It peaks around week 8 and decreases and levels off around week 20.
What secretes progesterone and estrogen during embryonic development? What effect does this have?
Syncytial trophoblast cells of the placenta.
Progesterone: proliferative function on repro organs of mom
Estrogen: Important for mom and baby nutrition before and after birth
How do levels of progesterone and estrogen levels change during pregnancy?
They increase throughout and peak at the end (week 40)
Besides progesterone and estrogen, what does the placenta secrete? What is their function?
HCG and somatomammotropin (aka human placental lactogen) which is important for breast development in mom.
HPL also have a growth-like effect on the fetus and decreases mom’s glucose u
How does placental membrane conductivity change during pregnancy? What is the function of this?
It increases to enable diffusion to provide an increasingly greater amount of nutrition to the fetus.
What results in the formation of the placenta? When does this occur?
Trophoblast activity.
It develops rapidly so by 10 weeks most of the fetal nutrition is by diffusion from the placenta.
How does blood get from the mom to the fetus and back?
Fetal blood enters through two umbilical arteries and flows through capillaries of the villi before returning through the uterine vein.
What passes through the placenta? How?
Nutrients, waste products of metabolism, O2 and CO2 via diffusion.
Describe the fetal oxyhemoglobin dissociation curve compared to that of an adult? Why is this the case?
Fetal curve is shifter to the left such that at low PO2 levels the fetal Hb can carry more oxygen (20-25%) than the maternal Hb.
Describe the difference in maternal PO2 and fetal PO2? What purpose does this serve?
Maternal: 50 mmHg
Fetal: 30 mmHg
Allows for diffusion of oxygen to the fetus.
Even at a PO2 of 30 mmHg, the fetal O2 transport to tissues is nearly as large as that of the mother to her tissues. What three factors make this possible?
Fetal Hb affinity for O2 is greater than that of an adult.
Concentration of Hb is nearly 50% higher in the fetus.
Double bohr effect in placental circulation?
What is the double bohr effect?
Fetal blood entering placenta has high PCO2; thus as CO2 diffuses into maternal blood, the Hb dissociation curve of the maternal blood shifts right.
This decrease in CO2 in the fetus shifts the fetal dissociation curve to the left.
These shifts increase the gradient for diffusion of oxygen from mom to fetus.
In the late stage of pregnancy, how is glucose transported to the fetus?
Facilitated diffusion by carriers in the trophoblasts of the placental membrane.
What happens when the fetal heart begins to beat and pump blood through the placenta at week 4?
Minimal blood is pumped to the liver and lungs because they aren’t functional.
Fetal circulation is different than adult circulation because of this.
Describe the three differences in fetal circulation?
- Oxygenated umbilical blood bypasses the liver via the ductus venosus in the IVC.
- Most blood passes from R atrium to the L atrium through the foramen ovale and to L ventricle.
- Partially deoxygenated blood enters the SVC, goes to the R atrium, R ventricle, and pulm a. where it goes through the ductus arteriosus into the descending aorta to the umbilical arteries of placenta for reoxygenation.
Where does fetal gas exchange occur?
The placenta; thus oxygen content is higher in the umbilical vein than the umbilical artery.
What are the three structures in the fetus that allow the bypass of blood?
Foramen ovale, ductus arteriosus, ductus venosus.
The fetal L and R ventricles work as two ________ pumps.
Parallel.
What are normal adaptations that occur as the fetus transitions from intrauterine to extra-uterine life?
- Endocrine support
- Clearance of fetal lung fluid
- Surfactact secretion and spontaneous breathing
- Transition to neonatal circulation
- Decrease in pulm vascular resistance and increased pulm blood flow
What is the major regulatory hormone for terminal maturation of the fetus for neonatal adaptation at birth?
Cortisol; fetal levels continue to increase from ~5-10 mg/mL at week 30 to ~200 mg/mL after delivery.
What effects does the increase in cortisol have on the fetus?
- Lung maturation and increase in B receptor density in lung
- Activates sodium pump
- Matruation of thyroid axis
- Regulations catecholamine release
- Controls energy substrate metabolism
What is the role of catecholemines in adaptions at birth?
- Increase arterial BP
- Mobilize substrates for metabolism
- Stimulate thermogenesis from brown fat
- Contribute to surfactant production
What are five CV adjustments at birth?
- Cortisol and catecholamine functions
- Loss of low resistance placental circulation
- Large increase in pulm blood flow
- Two cardiac pumps in series
- Fetal vascular shunts close
What are changes in pulmonary circulation at birth due to?
Loss of compression by lung fluid, reduced hypoxic vasocontriction, prostaglandin vasodilation.
How do the three fetal shunts close after birth?
Foramen ovale: Left atrial valve closes due to greater L atrial pressure.
Ductus arteriosus: growth of msucle and fibrotic tissue closes lumen
Ductus venosus: contraction of muscle wall clases lumen
How is lung fluid cleared at birth?
Cortisol, catecholamines, and T4: terminate fluid secretion by airway epithelium and activate Na/K ATPase to clear fluid.
Increased abdominal and diaphragm activity forces fluid out of nose and mouth.
How is breathing initiated at birth? Why is the first breath difficult?
By the presence of placental supression and/or tactile, thermal, and blood gas stimuli.
Large effort is required to inflate collapsed alveoli on first breath.
What is the role of surfactant from alveolar type 2 cells? When is it produced and what controls it?
Begins in last month in fetus, increased with labor.
Under control of catecholamines, reduces surface tension.
Absence causes respiratory distress syndrome.
What happens in the absence of surfactant?
Alveoli have a high collapsing pressure.
How does arterial blood pH change after birth? What about arterial pCO2?
pH increases from ~7.3 to ~7.4
PCO2 decreases from ~60 to ~35 mmHg.
What are normal respiratory problems seen in a neonate?
Relatively low FRV causes:
- Reduced O2 store
- Large variations in blood gases
- Increased alveolar and airway collapse due to fluid in lungs
- Increased inspiratory work
What are normal circulatory problems seen in a neonate?
- Decrease in RBC count
- Low cardiac output due to placental hemorrhage
- Low blood pressure
Why is there a change in RBC count and bilirubin after birth?
Decrease in RBC count after birth due to loss of hypoxic stimulus
Increased bilirubin reflects immaturity of liver to conjugate bilirubin with glucuronic acid.
Describe the characteristics of low liver function seen in neonates?
Increased bilirubin from RBC breakdown.
Decreased formation of plasma proteins
Deficient gluconeogenesis (enzymes haven’t been induced yet)
Deficient coagulation factors.
How is body temperature controlled after birth?
Large ratio of body surface to metabolic rate favors heat loss.
Catecholamines initiate thermogenesis from brown fat.
Why due newborns have a high rate of acid production?
Because of metabolism and tissue formation.
Immature kidneys can’t filter as much.
What are some potential nutritional problems seen in neonates?
Deficient pancreatic amylase, fat absorption in GI, low/unstable glucose, and deficient calcium and vitamin D.
What does uncontrolled type 1 diabetes in mom cause? What about type 2? Thyroid deficiency?
Type 1: Poor growth and high mortality.
Type 2: large babies
Thyroid deficiency: dwarfism
What special problems are seem in preterm infants?
Depressed or absent surfactant causes collapsed alveoli.
poor ingestion/absorption
poor liver and kidney function
unstable homeostatic control mechanisms
What is respiratory distress syndrome (RDS) related to?
Male predominance, low gestational age, maternal diabetes, perinatal asphyxia.
Inversely related to gestational age.
