Question Answer
what happens at 24 days (3 wks) of gestational development? primitive lung bud appears
how does development continue? by single budding and irregular branching
what happens at 26-28 days? cartilage; lung bud divides into beginnings of two mainstem bronchi
what happens at 6 weeks? embryo has TBT w/ 18 segmental bronchi; pulm arteries/veins develop along w/ branching airways
what happens at 7 weeks? distinct rings in the trachea
what happens at 12 weeks? major lobes are differentiated
what happens at 16 weeks? conducting airways of the TBT are present in miniature form
what happens at 24 weeks? resp bronchioles, alveolar ducts, alveoli, pulm vessels, lymphatic vessels develop
what happens at 26 weeks? formation of alveolar-capillary unit sufficient to allow extrauterine life
what happens at 27-28 weeks? more alveolar sacs and more capillaries in contact with them (better gas-exchange)
what happens at 28-29 weeks? terminal air sacs are lined with mature type II cells from which surfactant is released
what happens at 30-33 weeks? new alveolar units appear rapidly
what happens at 34-36 weeks? mature alveolar structures are evident
growth in the number of alveoli is usually completed by __ years of age, the alveoli increase in size until adulthood. 8
when do the first 4 stages of lung development occur? during intrauterine life
when does the 5th stage occur? continues into adulthood
what does the intrauterine stages consist of? embryonic period, pseudoglandular period, canalicular period, terminal air sac period
when is the embryonic period and what is developed? 4-6 wks; development of proximal airways, ends with appearance of segmental bronchi
when is the pseudoglandular period and what is developed? 7-16 wks; conducting airways, lungs w/ glandular appearance, cilia, cartilage, glands
when is the canalicular period and what is developed? 17-24 wks; acinus (gas-exchange portion of the lung), connective tissue decreases and lungs become more vascularized
when is the terminal air sac period and what is developed? 24 weeks-birth; gas-exchange units (alveolar duct system, alveolar surface area increases)
at birth, the lungs contain approximately ___ million alveoli with a surface area of approximately ___ square meters. 55; 10
when is the postnatal stage and what happens? birth-8 years: increase in number and size of alveoli; 8 years-adulthood: increase in alveolar size
the adult lungs contain approximately ___ million alveoli with a surface area of ___ square meters. 300; 70
what is pulmonary surfactants? mixture of phospholipids and proteins and are responsible for altering surface tension at alveolar level
what are these surfactants secreted by? Type II alveolar cells (Type II pneumocytes)
what is the major surfactant? phosphatidyl choline (lecithin)
what happens with a lack of surfactant? atelectasis; makes lungs stiff and noncompliant
what is it called to have an occurance of noncompliant lungs caused by immature surfaction production in the newborn? hyaline membrane disease or resp distress syndrome
what are 2 surfactants produced by the fetus and secreted into the amniotic fluid? lecithin and sphingomyelin
when does sphingomyelin begin and peak? when does lecithin begin and peak? 18 wks, 30 wks; 18 wks, 38 wks
what are the ways to obtain L and S? amniocentesis, vaginal examination in mothers w/ premature rupture membrane, gastric aspirate from mouth of infant
what are 3 ways to determine lung maturity? L/S ratio (MOST COMMON), shake test, direct measurement of level of saturated phosphatidylcholine in amniotic fluid
what are the good and bad levels of L/S ratio? >2.0 – mature lungs, no resp distress; <1.0 – severe lung immaturity, resp distress; 1.0-2.0 – RDS may or may not develop
how does the shake test work? samples of amniotic fluid are mixed with alcohol and shakes, forming bubbles at surface; stability of the bubbles observed
what determines a L/S ratio of 2.0 or greater? a complete ring of bubbles at the surface after 15 mins (no bubbles – lung immaturity)
what conditions accelerate maturation of the lungs in the fetus who are less than 34 wks? toxemia, severe diabetes, maternal HTN, maternal infection, prolonged ruptured membranes, placental insufficiency
what conditions delay maturation of the lung? mild diabetes, fetal Rh disease, small identical twins in full term babies
what are variables may affect the accuracy of L/S ratio measurement? maternal bleeding in amniotic fluid, meconium in amniotic fluid (false pos or neg)
what can accelerate the maturation of the lungs? corticosteriods
what is given to be effective 48 hrs, not more than 7 days, before delivery? betamethasone, dexamethasone (30-32 wks most effective; only <34 wks given this)
the ________ is the nutrient, gas-exchange, and waste removal organ for the fetus. what does this provide? placenta; direct contact b/t circulation of the mother and fetus and keeps 2 blood supplies separate
what comprises the placenta? (KNOW) segments (cotyledons) that contain fetal vessels, chorionic villi, & intervillour space
the ________ _____ are fingerlike projections of tissue that invade the uterine wall at the site of implantation of the placenta. what do these contain and what are the spaces formed in the uterine by these surrounded by? chorionic villi; fetal capillaries, maternal blood
these blood-filled areas are the ____________ ______ and the site of exchange of nutrient, gaseous, and waste substances between the maternal and fetal blood. intervillous spaces
what is maternal blood supplied to the placenta by? uterine arteries and oxygenated blood from these arteries surrounds the villi
how does fetal blood enter the placenta? through TWO umbilical arteries in umbilical cord; vessels branch and terminate in capillaries within each villus
what happens after gas-exchange? fetal blood returns to fetus through ONE umbilical vein; maternal blood drains back into venous system
in the fetus, what carries the highest oxygen concentration? what is the avg O2 saturation in this? umbilical vein; 80% (PO2: 29 mmHg)
what is the O2 saturation in the inferior vena cava from mixing of oxygenated blood from the umbilical vein and deoxygenated blood from the tissues? 67%
how is blood from the inferior vena cava diverted from the RA to the LA? foramen ovale
what does blood that is relatively rich in O2 supply? brain and heart of fetus (organs that use the most O2)
what blood supplies the lower part of the body and umbilical arteries? blood from the ductus arteriosus
how much of the blood ejected from the RV passes into the pulmonary circulation? 10%
because PVR is HIGHER than SVR, blood takes the path of ______ resistance through the ductus arteriosus. lower
what must the newborn do in the first minutes of extrauterine life? activate central/autonomic nervous systems, replace liquid in lungs w/ air, establish pulm circulation, change dir of blood flow through heart and great vessels
when do respiratory movements occur? from 30%-65% of the time ONLY in the REM stage of sleep
factors that stimulate the infant to initiate respiration at birth are probably both…? chemical and sensory in nature
what results since the placenta provides for gas exchange? transient fetal asphyxia
what provides a strong stimulus to breathe? the chemical factors (hypoxia, hypercapnia, resp acidosis) – transient fetal asphyxia
__________ _______, which results in metabolic acidosis as well as in the previously listed chemical changes, tends to depress rather than to stimulate respiration. prolonged asphyxia
_________ _______ may also play an important role in the initiation of respiration. sensory stimuli (change in environment, temperature; handling the infant)
the lungs in utero is normally filled with ______. the volume is approximately ___ ml/kg of BW and equal to the FRC of the newborn. fluid; 30
what happens to the fluid prior to delivery? amount decreases, so that it can be replaced with air since the lungs replace the placenta as the organ of gas exchange
what are the 3 primary mechanisms by which fetal lung fluid is removed? 1. compression of thorax during delivery 2. absorption into the pulmonary capillaries 3. clearance by pulm lymphatic system
how much does each mechanism remove? approx 1/3
during vaginal delivery, fluid is squeezed out of infant; however, during C section it is not and has more difficulty removing fluid – what does this result in? transient tachypnea syndrome
how is this syndrome avoided? using the last 2 mechanisms of fluid removal
what is created because of the very negative pressures created in the pleural space during the first breaths? a pressure gradient from the alveoli to the interstitial space, favoring movement of fluid out of the alveoli
what happens after birth? chest cage recoils, introduces air into lungs
what happens as the infant receives stimuli from the chemical and sensory changes associated with birth? initiates nerve impulses to the muscles of the respiration, results in expansion of thoracic vol and decrease in intrathoracic pressure
to overcome the surface tension of the alveoli and the viscosity of the remaining lung fluid, the newborn infant must often generate a negative intrathoracic pressure of ___-___ cmH2O. 60-80
what is the avg volume of the first breath? 40 mL
how much remains in the lungs after the first inspiration as the infant begins to establish FRC? 20-30 mL
following the first breath, _______ pressure gradients are required to achieve alveolar filling. lower
when is a normal FRC established? within the first few hours after birth
what does clamping the umbilical cord, thus removing the infant from the placental circulation result in? less blood flow returning to the RA and decreases the pressure in the R side of heart
the placenta is a _____ pressure circuit; loss of this outlet results in…? low; increase pressure in the LEFT side of the heart
after birth, why does PVR fall? the increase in PaO2 and decrease in PACO2.
what happens as PVR decreases? pulm perfusion increases, larger vol of blood is returned to LA, increasing pressure in L side of heart
what results in the closure of the foramen ovale? the difference in pressure b/t the R and L sides (L pressures must be higher than R to close!)
what happens if the pressure in the R side becomes elevated? foramen ovale can reopen and allow shunting of blood from R to L without passing pulm circulation
what is the major event that alters pressure on the right side of the heart? pulmonary vascular resistance
what factors contribute to an elevated PVR? failure to remove lung fluid adequately; failure to inflate the lungs adequately; hypoxia; hypercapnia
what are the reasons for constriction and closure of ductus arteriosus? decrease in PVR allows more blood ejected from RV to enter pulm circulation, decreasing blood from ductus
what is the difference b/t DA and FO? DA doesn’t close immediately at birth (ductal blood flow continues; flow from L to R)
what happens to the ductus after several hours? it begins to constrict, primarily in response to elevated oxygen tensions
what causes vasoconstriction in the pulmonary vascular bed and in the ductus arteriosus? hypoxia; elevated O2
when does anatomic closure of the ductus arteriosus usually complete? by 3 wks of age
following complete constriction, what does the ductus arteriosus become? a ligament (ligamentum arteriosum)
what is responsible for keeping the ductus open during fetal life? prostaglandins E1 and E2
what is the enzyme complex responsible for the formation of prostaglandins called? prostaglandin synthetase
____________ is a prostaglandin synthetase inhibitor commonly used with good success in infants with a patent ductus arteriosus. indomethacin
when does the ductus venosus close anatomically? within 3-7 days after birth
how does fetal Hb differ from adult Hb? its affinity for oxygen
what is the relationship between O2 and Hb represented by? the oxyhemoglobin dissociation curve (relates partial pressure of O2 to the Hb saturation)
fetal Hb has a _______ affinity for O2 than does adult Hb; what does this mean? higher; at any give PO2, fetal Hb will have a higher O2 sat than adult Hb (left shift)
what is the normal adult P50? infant P50? 27 mmHg; 6-8 mmHg lower than adult P50
what is the major reason for the difference in the oxygen affinity in adult and fetal Hb? related to inorganic phosphate, 2,3-DPG
what does DPG-2,3 do when it binds to Hb? reduces the affinity of Hb for O2
why does fetal Hb have a greater affinity for O2? b/c it cannot bind 2,3-DPG as well as adult Hb can
what is the ability to bind and release O2 related to in the newborn? level of fetal Hb present and to the amount of 2,3-DPG in the blood
when does the P50 level increase to the adult level? by 6 months of age