Fetal and neonatal physiology Flashcards
how do you calculate gestational age
fertilization age + 2 weeks
growth: hyperplasia and hypertrophy
hyperplasia: increase in cell number
hypertrophy: increase in cell size
___ is primary form of placental growth
hypertorphy
intrauterine growth restriction
- abnormality of fetal growth and development
- decreased placental reserve caused by insult
- mothers who smoke during pregnancy have small palcentas
what does the fetus use as its major energy source?
glucose
glucocorticoids do what to fetal liver
promote storage of glucose as glycogen
Insulin on fetal growth
causes glucose to be stored as glycogen,
uptake of aa’s
-lipogenesis
GH (postnatally)
binds GH receptors on liver causes production of somatomedin or IGF-1
-minimal effect on fetal growth bc fetal liver has few GH receptors
IGF-1 and IGF-2
mitogenic peptides, important for fetal growth
amt correlates with birth weight
thyroid hormones and fetal growth
most T4 in fetus is maternal (before second trimester)
- fetal TSH and T4 begin to increase in 2nd trimester
- hypothyroidism has adverse effects on fetal growth
when does the fetal heart begin to beat at how fast
- 4th week after fertilization
- 65 bpm, goes to 140 bpm just before birth
when do nucleated RBCs form in fetus and where
3rd week, yolk sac and mesothelium of placenta
when do non-nucleated RBCs form and where
4th-5th weeks, by fetal mesenchymal and endothelial cells of fetal blood vessels
what takes over blood cell formation at 6 weeks
liver
at 12 weeks the ___ and ___ start forming RBCs
spleen and lymphoid tissue
from 3rd month on _____ becomes principal source of RBCs
bone marrow
fetal erythrocytes and reticulocytes
fraction of erythrocytes that are reticulocytes is high in young fetus but decreases at term
-fetal erythrocytes live 80 days as compared to adult being 120
development of NS
by 3rd and 4th month after pregnacny most reflexes present
-cerebral cortex development continues after birth
fetal metabolism and iron
by week 12 gestation iron accumulates rapidly and 1/3 is stored in liver, available to use for Hb for months after birth
development of kidneys: when does urine excretion begin
2nd trimester and accounts for 70-80% of amniotic fluid
-renal control stystems don’t fully develop until few months after birth
what stimulates breathing at birth
- asphyxiation during birth
- sudden drop in ambient temp 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: depressed respiratory center
causes of hypoxia during delivery
CAPE
compression of umbillical cord, anesthesia (excessive, which depresses oxygen of even her blood), premature separation of placenta, excessive uterine contractions
how much negative inspiratory pressure is needed to overcome surface tension and open alveoli for 1st time
over 25mmHg
- air in lungs remains almost exactly zero until negative pressure reaches -40
- once gets to -60 then 40 mL of air comes into lungs
how much positive pressure does it take to deflate lungs on first breath
+40
is more or less effort required after first breath and when does breathing become completely normal
less, after 40 minutes
surfacant fnct and made by what
secreted by type II alveolar epithelial cells
- mainly phospholipid (phosphatidylcholine)
- syn begin last trimester
- harder to close aveoli with surfacant once open
Respiratory distress syndrome common in what and due to what
common in premature infants and infants born to diabetic mothers
-failure to secrete adequate amounts of surfactant resulting in collapsed alveoli and develop of pulmonary edem
4 unique shunts of fetal circulation
placenta
ductus venosus
foramen ovale
ductus arteriosus
placenta shunt
shunts blood away from lower trunk and lowers effective blood flow to all abdominal viscera including kidneys
blood from the umbilical vein returns ___ blood back to fetus from placenta and enters ___
oxygenated, ductus venosus
ductus venosus blood flow
blood from umbilical vein to the IVC, bypassing the liver
foramen ovale
-right to left shunt
blood goes from right atria to left atria
-of 69% combined CO that enters RA through IVC, 27% shunts into LA
formaen ovale blood that isn’t shunted to LA
rest of combined cardiac output that enters RA from IVC joins poor oxygenated blood from SVC and coronary vessels
- none of this shunts to LA
- instead goes through tricuspid to RV so PO2 here is lower than in LV
- blood from right ventricle then enters trunk of pulmonary artery
ductus arteriosus
directs blood from pulmonary artery to the aorta
- contains SM in vessel wall
- pateny of vessel is due to active relaxation of SM from PGE2
at birth there is a ____ pulmonary and ___ systemic vascular resistance
decreased pulm: due to lung expansion, vasodilation from prostaglandins
increased systemic: loss of blood flow from placenta increases this
-increases pressure in aorta, LA, and LV
what causes the foramen ovale to close
reversal of pressure gradient pushes valve on left side shut on septum which eventually seals
-due to increased venouse return to LA and elevated LA pressure
ductus arteriosus closing
now aortic pressure excedes pulmonary a pressure so blood flow reverses from aorta to pulmonary a
- high oxygen content from aorta causes vasoconstriction of DA
- also falling levels of prostaglandins cause closure
patent ductus arteriosus
ductus arteriosus remains open which allows O2 rich blood from aorta to mix with O2 poor blood in pulmonary a
-strain on heart and increase BP in lung arteries
ductus venosus closing
after birth blood flow through umbilical vein stops but portal blood flow still goes through
- muscle wall of ductus venosus contracts strongly and closes
- increase in portal venous pressure forces venous blood flow through liver sinuses
neonate: HR BP RR metab
HR: 100-150 bpm (even higher in prematures)
BP: 70/50 first day, 90/60 few months, 115/70 adolescence
RR: 40
metab: 2X adult
special feature of kidney neonate
- high fluid tunrover
- rapid acid formation, only concentrates urine/plasma 1.5X compared to 3-4X of adult
- problems with acidosis and dehydration
neonate phys and body temp
body temp falls easily
nutritional needs neonate
- calcium and vitamin D: bone ossification
- iron: for RBCs, withou = anemia
- vitamin C: not stored in enough quantitiy in fetal tissue
- can be provided in breast milk
