41. Fetal and Neonatal Physiology Flashcards
Gestational age
Day 1 is last day of normal menstrual period
Fertilization age (aka embryonic age or fetal age)
Day 1 is fertilization
How do you calculate gestational age using fertilization age?
Gestational age = fertilization age + 2 weeks
Prenatal hematopoeisis takes place primarily in the _____ from fetal months 1-3
Yolk sac
[considered primitive erythropoiesis]
Prenatal hematopoeisis takes place primarily in the _____ from fetal months 3-7
Liver
Prenatal hematopoeisis takes place primarily in the _____ from fetal months 7-birth
Bone marrow
After ____ weeks gestation, hematopoietic progenitors are no longer detected in the yolk sac
7
The _____ serves as the primary source of red cells from the 9th to the 24th week of gestation
Liver
Liver is primary site of _____ transcription throughout fetal life
The _______ production of this factor increases throughout fetal life
EPO; kidney
________ becomes the major site of hematopoiesis after the 24th week of gestation and remains so throughout the remainder of fetal life
Bone marrow
Major hemoglobin of fetal life
HbF (alpha2gamma2)
[contrast with adult HbA (alpha2beta2)]
Normal adult levels of ____ are achieved by ~12 weeks of life (full term)
HbA2
Hyperbilirubinemia during first 2 weeks of life (full term) = ______ jaundice
Physiological
The mean hemoglobin level in cord blood at term is 16.8 g/dL, with 95% of the values falling between 13.7 and 20.1 g/dL
What accounts for this variation?
This variation reflects perinatal events, particularly asphyxia and also the amount of blood transferred from the placenta to the infant after delivery
What iatrogenic cause appears to heighten the occurrence of anemia at 2 months and to impair cardiopulmonary adaptation
Early cord clamping
[delay of cord clamping may increase the blood volume and red cell mass of the infant by as much as 55%, resulting in fewer transfusions and fewer days requiring oxygen and ventilation in preterm infants]
The serum ____ level in cord blood of the normal infant is elevated compared to normal levels
Iron
[the mean serum ferritin levels in iron-sufficient infants are high at birth, 160 mcg/L, rise further during the first month, and then fall toa mean of 30 mcg/L by 1 year of age]
Describe the amount of iron in the marrow at birth and how this changes up to 6 months of age
The amount of iron in marrow at birth is small but increases in both term and premature infants during the first weeks after birth
Marrow iron begins to decrease after 2 months and is gone by 4-6 months in term infants and earlier in premature infants
Iron is preferentially allocated to ________ if the availability of iron is limited
Erythropoisis
When does nephrogenesis occur and when is it completed
Begins at 8 wks getation and completed ~36 weeks
When does fetal urine production begin?
Begins as early as 10 weeks through 20 weeks gestation
________ accounts for 70-80% of amniotic fluid
Fetal urine
During what trimester of pregnancy does renal function mature rapidly? When does functional development complete?
3rd trimester — resulting in body fluid balance, acid-base balance, and electrolyte balance
Functional development completes closer to 1 month of age
Describe the fetal liver handling of bilirubin, plasma proteins and coagulation factors, and gluconeogenesis
Poor conjugation of bilirubin
Deficiency in forming plasma proteins and coagulation factors
Deficient gluconeogenesis (blood glucose levels the 1st day could be as low as 30-40 mg/dL of plasma)
Since the fetal liver has lacking gluconeogenesis ability, what does the infant use for metabolism?
Stored fats and proteins until mother’s milk can be provided
Since the neonate is in a stage of rapid ossification of its bones at birth, a ready supply of _____ throughout infancy is necessary
Normally the adequate amount can be supplied by the usual diet of ________
Calcium
Milk
Absorption of calcium by the GI tract is poor in the absence of ______
_____ can develop in infants who have this deficiency
Vitamin D
Rickets
The fetus has distinct goals in terms of Ca, Phosphorus, and bone homeostasis regulation. What are they
Fetus must actively pump calcium, phosphorus, and magnesium from maternal circulation against concentration gradients, maintain serum mineral concentrations at higher levels than in maternal circulation, rapidly mineralize the skeleton during the final quarter of gestation, and achieve overall positive mineral balance
The infant’s _____ has stored enough iron to keep forming blood for ____ months after birth — provided that the mother has provided adequate iron in her diet during pregnancy
Liver; 6
Describe iron content of breast milk vs. infant formula
Iron content is low, but bioavailability is high
Studies show that infants exclusively breastfed for first 6 months of life have normal iron status at 6 months, provided mother has adequate iron status
Iron content of infant formula is high because bioavailability is lower than breastmilk
If the mother has iron insufficiency in her diet, _______ is likely to occur in infant after 3 months of life
Severe anemia
What vitamin, necessary for appropriate formation of intercellular substances, especially the bone matrix and fibers of CT, is not stored in significant quantities in fetal tissues but can be provided by breastmilk?
Vitamin C
T/F: the neonate does not form antibodies of its own to a significant extend, requiring dependence on mother
True
By the end of ____ month, there is a decrease in the baby’s gamma globulins (contain the antibodies)
1st
The baby’s own immune system begins to form Abs and gamma globulin concentration returns to normal by the age of _____
12-20 mos
Antibodies inherited from the mother protect the infant for about ____ months against most major diseases.
However, inherited antibodies against ________ are normally insufficient to protect the neonate - so they require immunization against this illness within the ~1st month of life
6
Whooping cough
T/F: other than whooping cough, immunization against most other diseases is usually not necessary before 6 months of age
True
Since most maternal-fetal iron transfer occurs in the 3rd trimester, low birth weight pre-term infants are at higher risk of what condition?
Iron-deficient anemia
Respiratory consequences of preterm birth
Respiration is usually underdeveloped; respiratory distress syndrome is common cause of death
GI consequences of premature birth
Poor ingestion and absorption of food
Complications of premature birth include mmaturity of liver, kidneys, blood forming mechanism of the bone marrow, as well as depressed formation of _____ by the lymphoid system
They also struggle with instability of different homeostatic control systems.
Gamma globulin
Why is the neonate particularly susceptible to stress?
Underdeveloped HPA axis lacks synaptic maturity in the hypothalamus and related brain centers
Neonatal glucocorticoid response (cortisol level) is blunted because GC’s are toxic to developing nervous system
Neonatal glucocorticoid response (cortisol level) is blunted because GC’s are toxic to developing nervous system
Buffering to this response is maintained by what?
A consistent caregiver relationship with an adult (e.g., the mother)
Consequences of “toxic stress” experienced by the neonate in critical period of development
Increased risk of psychological disorders, physiological dysregulation, and chronic pain in adulthood
The fetal lungs develop slowly and there is no true respiration during fetal life. However, some respiratory movements will occur over the last ___-____ months of gestation
What is the purpose of inhibited respirations?
3-4
Inhibited respiratory development prevents lungs from filling with fluid and debris
Small amounts of fluid are secreted into the lungs by the _____ ____ up until birth
Alveolar epithelium
What occurs in weeks 4-5 of respiratory development?
Week 4: respiratory diverticulum forms
Week 4-5: respiratory diverticulum branches into left and right bronchial buds; stem of diverticulum will differentiate into trachea and larynx
What happens in weeks 5-7 of respiratory development
Branching yields secondary bronchial buds, which represent future lung lobes
Closer to week 7, branching yields tertiary bronchial buds, which represent future bronchopulmonary segmens
When in respiratory development do terminal bronchioles form? Is the next step after this?
Week 16
Week 16-36 respiratory bronchioles form, surrounding mesenchyme becomes highly vascular; first terminal sacs (primitive alveoli) form
From week 36 to birth, ________ ____ begin to differentiate into mature alveoli. Alveoli continue to form through the ___ year
Terminal sacs; 8th
Function of surfactant
Decreases surface tension
Surfactant is secreted by what cell type
Type II alveolar epithelial cells
When does surfactant production begin
Synthesis begins in last trimester
T/F: once alveoli open, it is harder to close them when exhaling without surfactant
True
Breathing initiates within seconds of birth. What are the stimuli for this?
Asphyxiation during birth
Sudden drop in temperature/cooling of skin
What might cause delayed breathing upon birth?
Use of general anesthesia during delivery
Prolonged labor
Head trauma
Describe the alveoli at birth
Alveoli are collapsed, amniotic fluid fills them
More than _____ mm Hg negative inspiratory pressure is needed to overcome surface tension and open alveoli at birth
The 1st inspiration — infant capable of ______ mm Hg
The 1st inspiratory movements — brings in nearly ____ mL air
25
-60
40
Deflation of lungs after birth requires strong _____ pressure to overcome viscous resistance of fluid in bronchioles
Positive
How long after birth does breathing normalize? What is the respiratory rate at that point?
~40 mins
Settles into 40 breaths per minute with a tidal volume of 6-10 mL/kg
Causes of hypoxia during delivery
Compression of umbilical cord
Premature separation of placenta
Excessive uterine contractions
Excessive anesthesia of the mother (depressed maternal breathing)
T/F: Neonates have a lower tolerance for hypoxia than adults
False: they have higher tolerance
Adults tolerate for 4 mins while neonates tolerate for 8-10 mins
Failure to secrete adequate amounts of surfactant resulting in collapsed alveoli and development of pulmonary edema
Respiratory distress syndrome
RDS is common in premature infants and infants born to mothers with _____
Diabetes
Common sign of RDS
Pulmonary edema
The heart begins to beat during the ____ week after fertilization with an intial HR of ___ bpm
This increases steadily to _____ bpm pre-birth
4th
65
The fetal heart does not pump much blood through the lungs or liver, but does through the ________
Placenta
Four unique shunts for fetal blood flow
- Placenta
- Ductus venosus
- Foramen ovale
- Ductus arteriosus
Massive blood flow to the placenta shunts blood away from what body region?
Lower trunk
Describe umbilical arteries
Branch repeatedly
Return deoxygenated blood
Dense capillary network at terminal villi
“Legs” connect to inferior vena cava
Describe umbilical vein
Returns oxygenated blood to fetus from placenta
PO2 = 30-35 mm Hg
Blood from the umbilical vein enters the ___ ____
Ductus venosus
The ductus venosus serves as the ____ bypass, since this organ is largely non-functional
Thus the ductus venosus is a direct route from umbilical vein to _____
Liver
IVC
Hole in septum dividing the atria, posterior aspect of right atrium
Foramen ovale
The foramen ovale is a ___ to ___ shunt
Right to left
The foramen ovale bypasses what heart region
Right ventricle
The foramen ovale allows blood at PO2 ~27 mm Hg (high) to pass right through to the _________ to supply the carotid arteries and brain
Left ventricle
T/F: of the blood entering the right atrium, almost all is shunted through the foramen ovale
False - about 27% is shunted through foramen ovale, the remainder enters the right ventricle
T/F: blood from the superior vena cava is not shunted through the foramen ovale
True
Is PO2 greater in left ventricle or right ventricle in fetus?
Greater in left ventricle. Blood from right ventricle enters the trunk of pulmonary artery
What serves as shunt from pulmonary artery to aorta?
Ductus arteriosus
The ductus arteriosus is a ____ to ____ shunt
Right to left
The ductus arteriosus is associated with a substantial amount of smooth muscle that is being dilated by _______
Prostaglandins (PGE2)
Blood flow changes upon birth include ______ pulmonary vascular resistance and ______ systemic vascular resistance
Decreased; increased
Describe reasoning for decreased pulmonary vascular resistance at birth
Lung expansion
Vasodilation due to aeration of lungs eliminating hypoxia (local prostaglandins)
Reduced pulmonary arterial pressure, right ventricular pressure, and right atrial pressure
Describe reasoning for increased systemic vascular resistance
Loss of blood flow from placenta doubles systemic vascular resistance
Increases aortic pressure, left ventricular pressure, and left atrial pressure
What causes closure of foramen ovale
Reversal of pressure gradient across atria which pushes foramen ovale’s “valve” shut
This is due to increased venous return to left atrium and elevated left atrial pressure, as well as reduced right atrial pressure
Eventually the flap seals
What causes closure of ductus arteriosus?
Aortic pressure rises above pulmonary artery pressure — blood flows the wrong way
Now well-oxygenated aortic blood flows through the ductus arteriosus; high PO2 —> vasoconstriction within a few hours, which when coupled with falling prostaglandin levels leads to sufficient constriction within 1-8 days, and full anatomical occlusion in 1-4 months
Closure of what 2 shunts establishes separate right and left circulatory systems?
Foramen ovale
Ductus arteriosus
What causes patent foramen ovale
Increased right atrial pressure can push flap open
Sustained pulmonary HTN or transient increases with BM, coughing, or sneezing
[occurs in 20% of individuals by 2 years of age]
Describe patent ductus arteriosus
Heart problem that occurs soon after birth
Can be heard as heart murmur with stethoscope
Oxygenated blood mixes with deoxygenated blood in pulmonary artery — puts strain on heart and increases pulmonary blood pressure
Immediately after birth, most portal blood flows through the __________
Describe closure of this structure
Ductus venosus
[within 1-3 hours, the muscle wall of ductus venosus contracts and closes; portal venous pressure rises, forcing venous blood through liver sinuses]
Neonatal HR
100-150 bpm (higher in premature neonate)
Neonatal BP
During 1st day after birth: 70/50
After few months increases to 90/60
Adult pressure is attained during adolescence 115/70
Neonatal respiratory rate
~40 breaths/min
Neonatal metabolism
2x adult
Neonatal kidneys
Immature — functional development is not complete until end of 1st month of life
High fluid turnover rate (rate of fluid intake and fluid excretion relative to weight is 7x greater than in adult)
Rapid acid formation — can only concentrate urine to only 1.5x osmolality of plasma (adult can concentrate urine to 3-4x plasma osmolality); problems with acidosis and dehydration
Erythropoiesis pathway
Multipotent hematopoietic stem cell
Common myeloid progenitor
Proerythroblast
Basophilic erythroblast
Polychromatic erythroblast
Orthochromatic erythroblast
Polychromatic erythrocyte
Erythrocyte (RBC)
