Lecture 16: Fetal and Neonatal Physiology Flashcards
What week do nucleated RBC’s form in the yolk sac and mesothelium of placenta?
3rd week
When do the spleen and lymphoid tissue begin forming RBC’s?
9-12 weeks (3rd month)
When does renal function mature rapidly in the neonate; when does functional development of the kidney complete?
- Renal function matures rapidly in 3rd Trimester
- Kidneys are immature at birth
- Functional development complete around 1 month of life
What is the major hemoglobin of fetal life and how does it compare to that of an adult?
- Hb F (α2γ2)
- Oxygen binding affinity: fetal Hb > maternal Hb
Fetal urine accounts for what % of the amniotic fluid?
70-80%
What is the order of the 3 structures which begin hematopoiesis from earliest to latest?
1) Yolk sac
2) Liver
3) Bone Marrow
What is the ability of the fetal liver like in conjugation, protein/coagulation factor formation, and utilizing glucose; what does the infant use for metabolism until feeding from mother?
- Poor conjugation of bilirubin (hence neonatal jaundice)
- Deficiency in forming plasma proteins and coagulation factors
- Deficient blood glucose (levels the 1st day could be as low as 30-40 mg/dL of plasma)
- Infant uses its stored fats and proteins for metabolism until mother’s milk can be provided
What are the Ca2+ and Vit D needs like in a neonate; why is vitamin D so important for calcium?
- In stage of rapid ossification of their bones at birth, so need ready supply of calcium
- Can normally get adequate amount from diet of milk
- Absorption of calcium by the GI tract is poor in the absence of vitamin D —> can lead to rickets!
Where is iron stored in the infant and how much is typically stored in healthy infant?
Infants liver has stored enough iron to keep forming blood for about 6 months
If a mother does not have adequate iron in her diet during pregnancy what can this lead to?
Severe anemia is likely to occur in the infant
What are the nutritional needs of Vit C like in an infant; where do they get their Vit C from?
- Not stored in significant quantities in the fetal tissues
- Adequate amounts can usually be provided by the mother’s breast milk
- In some instances infants w/ Vit C deficiency need prescribed supplements
What is the immunitity of the neonate like at birth, at the end of the first month, and when do they start building up their immune system?
- Inherits great degree of immunity from the mother; not forming Ab’s of its own yet at birth
- By end of 1st month, there is a decrease in the baby’s gamma globulin (contains the Ab’s)
- Own immune system begins to form Ab’s and gamma globulin concentrations return to normal by age 12-20 months
Ab’s inherited from the mother protect the infant for how long?
6 months against major diseases
Ab’s inherited against what disease are normally insufficient in the neonate?
Whooping cough; require immunization within the 1st month or so of life
What secretes surfactant, what is its role, when is it formed?
- Secreted by type II alveolar epithelial cells
- Decreases surface tension
- Synthesis begins in the last trimester
How quick is breathing initiated at birth and what are the stimuli?
- Within seconds of birth
Stimuli:
- Asphyxiation during birth
- Sudden drop in ambient temperature and cooling of skin
What can cause delayed breathing at birth?
- Use of general anesthesia during delivery
- Prolonged labor
- Head trauma of infant during birth
What are 4 causes of hypoxia during delivery?
1) Compression of umbilical cord
2) Premature separation of placenta
3) Excessive uterine contractions
4) Excessive anesthesia of the mother (depressed maternal breathing)
What is the tolerance for hypoxia like in a neonate vs. an adult?
- Neonates have higher tolerance for hypoxia
- Adults: 4 min
- Neonates: 8-10 min
At birth, the alveoli are collapsed due to surface tension of amniotic fluid, how much pressure is needed to open them for first time and how much negative pressure is created and air brought in during the first breath?
- More than 25 mmHg negative inspiratory pressure is needed to overcome surface tension and to open the alveoli for the 1st time
- 1st inspiration capable of creating as much as 60 mmHg negative pressure in the intrapleural space
- 1st inspiratory movements bring in nearly 40 mL air
What happens to the ease of breathing after first breath and when does it normalize?
- Less effort needed after 1st breath, and so on..
- Becomes normal about 40 min after birth
What is the branching, oxygen content, and location of the umbilical arteries?
- Branch repeatedly under the amnion
- Form dense capillary networks at terminal villi
- Return deoxygenated blood
What is the function of the umbilical vein and what shunt does this blood pass through?
- Returns oxygenated blood to fetus from placenta
- Blood enters the ductus venosus
What is the liver bypass shunt and where does blood go?
- Ductus venosus
- Causes bypass of the largely non-functional liver
- Direct route from umbilical vein –> IVC
What is the third major shunt after fetal blood passes through the ductus venosus and into the IVC?
- Foramen Ovale
- Hole in the septum diving the right and left atria
- Blood enter the right atrium and then crosses through foramen ovale to enter left atrium (right to left atrial shunt)
Why is the Foramen Ovale so imporant and what organs are supplied?
- Allows blood with the highest O2 (PO2 = 27 mmHg) content to enter right through into the left ventricle from the IVC
- About 27% of blood entering right atrium will be shunted through foramen ovale
- Supplies the carotid and brain
What happens to the remainder of the blood not shunted through the foramen ovale; which ventricle has the highest PO2?
- Enter the right ventricle and mixes w/ deoxygenated blood from the superior vena cava and coronary vessels w/ oxygenated blood
- Blood from the superior vena cava is not shunted through the foramen ovalec
- PO2 LV > RV
- Blood from the right ventricle enter the trunk of the pulmonary artery
What is the fourth major shunt and where is blood directed?
- Ductus Arteriosus
- Another right –> left shunt
- Directs blood from the pulmonary artery —> aorta
How and why does pulmonary vascular resistance change at birth?
- Pulmonary vascular resistance decreases due to lung expansion
- Vasodilation due to aeration of lungs eliminating hypoxia (local prostaglandins)
- Reduced pulmonary arterial pressure, right ventricular pressure, and right atrial pressure
What causes closure of the foramne ovale and what are 2 important changes in fetal circulation cause this?
- Reversal of the pressure gradient across the atrial septum, pushes foramen ovale’s “valve” shut
1) Increases venous return to the left atrium and elevated left atrial pressure
2) Decrease in right atrial pressure
*As the flap of the foramen ovale pushes against the septum, blood flow from left to right atrium is prevented
What changes in fetal circulation cause the ductus arteriosus to close?
- As aortic pressure exceeds the pressure of pulmonary artery, blood flow through the ducuts ateriosus reverses (now from the aorta into the pulmonary artery)
- Well-oxygenated aortic blood now flows through the ductus arteriosus into the pulmonary artery
What changes occur physiologically that contribute to the closure of the ducutus arteriosus (i.e., PO2, hormones..); what is the timeline for closure?
- High PO2 causes vasoconstriction, which functionally closes the ductus arteriosus within a few hours
- Falling prostaglandin levels contribute to the rapid closure
- Within 1-8 days, the constriction is usually sufficient to stop all blood flow through the ducuts
- Within 1-4 months, becomes anatomically occluded
Closure of what establishes the separate right and left circulatory systems?
1) Foramen Ovale
2) Ductus Arteriosus
What is a patent foramen ovale (PFO) and what can cause this?
- Unsealed flap can open if right-sided pressures become elevated
- Sustained pulmonary HTN or even transient increases in right-sided pressures (i.e., during bowel movement, coughing, or sneezing) can produce brief periods of right-to-left shunting
A patent ductus arteriosus (PDA) can be heard how; what happens to the blood flow and what problems can it cause?
- Heart murmur that can be heard w/ a stethoscope
- Opening allows oxygen-rich blood from the aorta to mix with oxygen-poor blood from the pulmonary artery
- Can put strain on the heart and increase BP in the lung arteries
What are the changes in RBC count and serum bilirubin like in the first 16 weeks of life; contribute to what?
- Physical anemia at 6-12 weeks (RBC count drops)
- Physiological hyperbilirubinemia during the first 2 weeks of life
What is the order for major sites of hematopoiesis throughout fetal development and what trimester does each correlate with?
First Trimester = Yolk sac
Second Trimester = Liver
Third Trimester = Bone marrow
