Flashcards in Physiology Block 3 Week 16 16 Fetal and Neonatal Development Deck (35)
How does that placenta get most of the nutrition for the fetus?
Nutrients, waste products of metabolism, oxygen, and carbon dioxide pass through the placental membranes mainly by diffusion.
For the first few months after implantation, the placental membrane is thick and the surface area is small which limits diffusion. However, eventually the membranes thin and the surface area increases which greatly facilitates diffusion
How is oxygenated blood carried to the fetal heart?
By the umbilical vein
Un/semi-oxygenated fetus blood enters through two umbilical arteries and then flows through capillaries of the villi before returning through a single umbilical vein.
The mother’s blood enters through uterine arteries into maternal sinuses that surround the villi and then returns through the uterine veins.
Why for any PO2, the fetal blood has a higher content of oxygen?
There is a pressure different between the mother's blood in the placental sinuses and the fetal capillaries the provides difference for diffusion to occur
1. Fetal Hb has higher affinity than adult (Left shifted)
2. Concentration of Hb in fetus is much greater than adult
3. Double-Bohr effect
What is the Double Bohr effect?
Fetal blood entering the placenta has a high CO2 pressure; thus, as the CO2 diffuses into the maternal blood, the hemoglobin dissociation curve of the maternal blood shifts to the right. At the same time, the decrease in CO2 in the fetal blood shifts the dissociation curve of the fetus to the left.
How is fetal circulatory system different than newborn?
During 4th week of pregnancy, the fetus's heart begins to beat and pump blood through the placenta and through the fetus
1. oxygenated umbilical blood bypasses the liver through the ductus venosus into the inferior vena cava and the right atrium
2. (Bypass the Lungs) Most of this blood then passes directly into the left atrium through the foramen ovale and then to the left ventricle which distributes this blood primarily to the head and forelimbs.
3. (Bypass Lungs) Deoxygenated blood entering the fetal right atrium from the superior vena cava passes to the right ventricle to the pulmonary artery and then through the ductus arterious into the descending aorta to the umbilical arteries of the placenta for re- oxygenation.
***Placenta, not fetal lung, is organ of gas exchange
***L and R ventricles are parallel pumps
***pulmonary circulation has high resistance and low flow
When is the cortical surge and what does it do?
Cortisol is low for about 30 weeks, increased just before labor, and peaks after delivery
1. Facilitate lung maturation--activate sodium pump to clear lung fluid
2. Increased beta receptor density
3. Gut maturation (digestive enzymes)
4. Maturation of thyroid
5. Catecholamine release from adrenal glands
6. Maturation of glucose metabolism in liver
Helps adapt energy metabolism of glucose and fatty acids
Initiates thermogenesis from brown fat
Why does a baby lose body weight the first few days after birth?
the infant uses its stored fats and proteins for metabolism which results in a decrease in body weight for the first few days after birth until the mother’s milk provides the needed nutrients
As a fetus, was getting nutrients by diffusion
How does the lung clear fluid after birth?
The increase in cortisol, T4, and catecholamines at birth shut down the fluid secretion (critical for lung growth) and activate Na+, K+ and ATPase of airway epithelium to pump fluid into the interstitial space to be cleared by the vasculature or lymphatics
What happens if there is an operative delivery?
Can results in retained lung fluid often resulting in poor oxygenation and tachypnea
Preterm infants without maturation of the Na+ transport system to clear lung fluid may also experience same problems
Missing the cortical and catecholamine surge
What is the lung compliance like after birth?
The alveoli are collapsed at birth; thus, to counter the high surface tension, the first and second breaths require a high effort to inflate the collapsed lungs. However, by 40 minutes later, the compliance of the lung is nearly normal
over the first 30 minutes after birth, changes in the lungs and ventilatory control mechanisms change arterial blood gases and pH to near normal levels
How does the lung develop over the last 1/3 of gestation?
the lung rapidly grows forming millions of alveoli and numerous generations of airways.
Surfactant lipid and lipophilic proteins are formed such that by term, type II cells in the fetal lung contain more surfactant than the adult lung.
Surfactant secretion into the alveoli begins with labor under control of catecholamines which stimulate beta receptors
ATP and alveolar stretch probably also stimulate secretion early after birth particularly after operative delivery, but over the first few weeks after birth, the secretion decreases to adult levels.
What happens to arterial blood gasses and pH after birth?
the first few minutes after birth, arterial blood gases and pH change greatly to reach levels normal for neonates within 2 hours
the drop in pH after birth is due to an increase in lactic acid production (initially anaerobic state)
What are cardiovascular adaptation at birth?
Cortisol and catecholamine = inc BP
No longer have blood flowing thru placenta = increased vascualr and cardiac resistance
Pulmonary vascular resistance decreases = blood flow increases
Foramen ovale closed and ductus arteriosus and venosus obliterated = double in cardiac output (ventricular output now in series)
Why does pulmonary vascular resistance decrease and blood flow increase after birth?
a) the pulmonary vessels are no longer compressed by the fluid in the lungs
b) breathing increases PO2 which reduces vasoconstriction
c) local prostaglandins cause vasodilation.
What is important about the FRC in neonates?
The functional residual capacity (FRC) of the neonate is about 50% of the adult in relation to body weight.
it is a source (or store) of oxygen and it minimizes the cyclic variation in arterial blood gases.
As a result of the FRC in neonates, they will have large cyclic variations in blood gases particularly when breathing is low and also, they will have more airway and alveoli collapsing which requires greater effort to reopen
Why increases blood volume at birth?
Stripping the umbilical cord
The red cell count at birth is about 4 million/mm3 which transiently increases if the cord is stripped, but then the count decreases over the first 6.8 weeks of life
What will result due to the liver function being insufficient during the first few weeks?
Liver function is insufficient to prevent plasma proteins and glucose from falling.
liver poorly conjugates bilirubin with glururonic acid for excretion into the bile--can result in jaundice
Baby inherits Rh-positive red cells from the father while the mother is Rh-negative. The mother becomes immunized against the Rh-positive factor in the fetal blood and her antibodies destroy fetal red blood cells releasing large amounts of bilirubin in the fetus causing jaundice.
What results from the underdeveloped kidneys over the first few weeks?
acidosis, dehydration, and overhydration.
Compared to an adult, how is the metabolic rate? How does this effect temperature?
The metabolic rate of the neonate in relation to body size is twice that of the adult,
Because the body surface area in relation to body mass is higher in the neonate, body temperature decreases and then is unstable for several days
Brown adipose tissue generates heat by uncoupling oxidative metabolism from ATP synthesis in the mitochondria which results in release of heat.
Why is it important for babies to ingest milk?
the rapid ossification of bone requires adequate calcium from ingested milk and adequate vitamin D for calcium absorption from the gut.
What would happen if the mother did not have sufficient iron in her diet?
The neonate may have low store of iron leading to anemia
Why is ascorbic acid given?
Needed for formation of cartilage, bone, and other intercellular structures--not in milk
Are neonates born with their own antibodies?
No, for the first month, they inherit their mother's
Will form their own and by 12-20 months will be sufficient
What if the mother had above normal androgen levels?
Masculinization of feta sexual organs (hermaphroditism)
What if the mother had type I diabetes?
Leads to poor growth of the fetus and high rate of intrauterine and neonatal mortality
What if the mother had type II diabetes?
Would result in a large baby (GH stimulated by increase in glucose)
What if the mother had hyperthyroidism?
Neonate could have hypothyroidism leading to dwarfism