Phys Chapter 83
Fetal Metabolism and Nutrient Storage and Accumulation
 Weight of fetus is proportional to cube of length, and length is directly proportional to age
 Fetal kidneys begin to excrete urine during second trimester, and fetal urine accounts for about 70-80% of
amniotic fluid
o Abnormal kidney development or severe impairment of kidney function can cause oligohydramnios and
can further lead to fetal death
o Renal control systems for regulating fetal extracellular fluid volume and electrolyte balances, especially
acid-base balance, are almost nonexistent until late fetal life and do not reach full development until a
few months after birth
 Fetus uses mainly glucose for energy and has high capability to store fat and protein
o Much if not most of fat is synthesized from glucose rather than being absorbed directly from mother’s
blood
 Metabolism of calcium and phosphate – accumulate 22.5 g Ca and 13.5 g PO4 during gestation, about half of
which is during last 4 weeks of gestation (during rapid ossification of fetal bones and rapid weight gain of fetus)
o Rarely any ossification at all until 4 months of pregnancy
o Minimal drain from mother of these substances during pregnancy – much greater drain comes from
lactation
 Accumulation of iron – accumulates even more rapidly than calcium or phosphate
o Mostly in form of hemoglobin, which begins to be formed from 3rd week on
o Small amounts concentrated in mother’s uterine progestational endometrium even before implantation
of ovum – this iron ingested intro embryo by trophoblastic cells and used to form very early RBC’s
o About 1/3 of iron in fully developed fetus stored in liver – can be used several months after birth for
formation of additional hemoglobin as necessary
 Utilization and storage of vitamins
o B vitamins, especially B12 and folic acid, necessary for formation of RBC’s and nervous tissue, as well as
overall growth of fetus
o Vitamin C – necessary for appropriate formation of intercellular substance, especially bone matrix and
fibers of connective tissue
o Vitamin D – necessary for bone growth in fetus
 Mother needs it for adequate absorption of calcium from GI tract
 If mother has plenty of vitamin D in her body fluids, large quantities of the vitamin will be stored
by fetal liver to be used for several months after birth
o Vitamin E – necessary for normal development of early embryo (absence can result in spontaneous
abortion during early stage of pregnancy)
o Vitamin K – used by fetal liver for formation of Factor VII, prothrombin, and several other blood
coagulation factors
 Insufficient vitamin K in other results in Factor VII and prothrombin deficit in fetus and mother
 Because most vitamin K is formed by bacterial action in mother’s colon, neonate has no
adequate source of vitamin K for first week or so of life after birth until normal colonic bacterial
flora become established in newborn – therefore prenatal storage in fetal liver of at least small
amounts of vitamin K derived from mother is helpful in preventing fetal hemorrhage,
particularly in the brain when head is traumatized by squeezing through birth canal
Breathing Adjustments of Infant to Extrauterine Life
 Onset of breathing – after normal delivery from mother who has not been depressed by anesthetics, child
ordinarily begins to breathe within seconds and has a normal respiratory rhythm within less than a minute after
birth
o Breathing is initiated by sudden exposure to exterior world, probably resulting from slightly asphyxiated
state incident to birth process and sensory impulses that originate on suddenly cooled skin
o In infant who does not breathe immediately, body becomes progressively more hypoxic and
hypercapnic, which provides additional stimulus to respiratory center and usually causes breathing
within an additional minute after birth

If mother has been depressed by general anesthetic during delivery, which at least partially anesthetizes fetus as
well, onset of respiration is likely to be delayed for several minutes – important to use as little anesthesia as
possible
 Many infants who have head trauma during delivery or who undergo prolonged delivery are slow to breathe or
sometimes do not breathe at all – can result from 2 effects
o Intracranial hemorrhage or brain contusion causes concussion syndrome with greatly depressed
respiratory center
o Prolonged fetal hypoxia during delivery can cause serious depression of respiratory center
 Hypoxia can occur during delivery because of
o Compression of umbilical cord
o Premature separation of placenta
o Excessive contraction of uterus, which can cut off mother’s blood flow to placenta
o Excessive anesthesia of mother, which depresses oxygenation of her blood
 Neonate can survive as long as 10 minutes of failure to breathe after birth
o Permanent and serious brain impairment often ensues if breathing delayed more than 8-10 minutes
o Lesions can develop mainly in thalamus, inferior colliculi, and other brain stem areas, permanently
affecting many motor functions of the body if too long hypoxic
 At birth, walls of alveoli are at first collapsed because of surface tension of viscid fluid that fills them – more than
25 mm Hg of negative inspiratory pressure in lungs usually required to oppose effects of surface tension and
open alveoli for first time
o Once alveoli do open, further respiration can be effected with relatively weak respiratory movements
 First inspirations of normal neonates are extremely powerful – usually capable of creating as much as 60 mm Hg
negative pressure in intrapleural space
 Hyaline membrane disease – small number of infants, especially premature infants and infants born to diabetic
mothers, develop severe respiratory distress in early hours to first several days after birth, and some die within
the next day or so because of alveoli that contain large quantities of proteinaceous fluid (almost as if pure
plasma had leaked out of capillaries into alveoli)
o Fluid also contains desquamated alveolar epithelial cells
o Material filling alveoli looks like a hyaline membrane on histologic slides
 Respiratory distress syndrome – respiratory epithelium secretes insufficient surfactant
o Type II alveolar epithelial cells do not begin to secrete surfactant until last 1-3 months of gestation, so
many premature babies can experience this
o Insufficient surfactant causes collapse of alveoli and development of pulmonary edema
Circulatory Readjustments at Birth
 Circulatory adjustments during first few hours of life cause more and more blood flow through baby’s liver,
which has had little blood flow courtesy ductus venosus
 55% of blood goes through placental circuit, leaving only 45% to pass through all tissues of fetus
 Primary changes in circulation at birth are
o Loss of tremendous blood flow through placenta, which doubles systemic vascular resistance at birth,
increasing aortic pressure and pressures on left side of heart
o Pulmonary vascular resistance greatly decreases as a result of expansion of the lungs
 In unexpanded fetal lungs, blood vessels are compressed because of small volume of lungs –
immediately on expansion, these vessels no longer compressed and resistance to blood flow
decreases several-fold
 Hypoxia of lungs causes considerable tonic vasoconstriction of lung blood vessels, but
vasodilation takes place when aeration of lungs eliminates hypoxia
o Pulmonary arterial pressure decrease causes right side of heart pressures to decrease
 Low right atrial pressure and high left atrial pressure cause blood to attempt to flow backward through foramen
ovale (from left atrium to right atrium), causing the small valve that lies over foramen ovale on left side of atrial
septum to close over the opening, preventing further flow through the foramen ovale
o In most people, the valve becomes adherent over the foramen ovale and forms permanent closure over
the next few months to years
o
Even if permanent closure does not occur, left atrial pressure throughout life normally remains greater
than right atrial pressure and backpressure keeps valve closed
 Ductus arteriosus closes because increased systemic resistance elevates aortic pressure while decreased
pulmonary resistance reduces pulmonary arterial pressure
o After birth, blood begins to flow backward from aorta into pulmonary artery through ductus arteriosus
o After a few hours, muscle wall of ductus arteriosus (reacts to PO2 in blood stream) constricts markedly
and within 1-8 days, constriction is sufficient to stop all blood flow (functional closure of DA)
o During next 1-4 months, DA ordinarily becomes anatomically occluded by growth of fibrous tissue into
its lumen
o Patent DA thought to result from excessive ductus dilation caused by vasodilating prostaglandins in
ductus wall, and administering indomethacin (blocks synthesis of prostaglandins) usually results in
closure
 Ductus venosus closes – immediately after birth, blood flow through umbilical vein ceases, but most of portal
blood still flows through ductus venosus, with only small amount passing through channels of liver
o Within 1-3 hours, muscle wall of ductus venosus contracts strongly and closes the flow, increasing portal
venous pressure enough to force portal venous blood to flow through liver sinuses
Nutrition of Neonate
 Before birth, fetus derives almost all its energy from glucose obtained from mother’s blood
 After birth, amount of glucose stored in infant’s body in form of liver and muscle glycogen is sufficient to supply
infant’s needs for only a few hours
 Liver of neonate is still far from functionally adequate at birth, which prevents significant gluconeogenesis, and
therefore infant’s blood glucose concentration frequently falls first day to as low as 30-40 mg/dL
o Appropriate mechanisms allow infant to use its stored fats and proteins for metabolism until mother’s
milk can be provided 2-3 days later
 Infant’s rate of body fluid turnover averages 7x greater than adults, and mother’s milk supply requires several
days to develop
 Infants drop 5-10% of body weight in first 2-3 days of life, most of it fluid loss rather than body solids
Special Functional Problems in Neonate
 Various hormonal and neurogenic control systems are unstable, partly from immature development of different
organs of body and partly from fact that control systems simply have not become adjusted to new way of life
 Normal rate of respiration is about 40 per minute, and tidal air averages 16 mL (total minute respiratory volume
is about 640 mL/min, 2x that of adult per body weight)
o Functional residual capacity of infant’s lungs is only ½ that of adult in relation to body weight
o Causes excessive cyclical increases and decreases in blood gas concentrations if respiratory rate
becomes slowed because it is residual air in lungs that smoothes out blood gas variations
 Blood volume of neonate immediately after birth averages 300 mL, but if infant is left attached to placenta for a
few minutes after birth or if umbilical cord is stripped to force blood out of its vessels into baby, an additional 75
mL of blood enters infant, totaling 375 mL
o During ensuing few hours, fluid is lost into neonate’s tissue spaces from blood, which increases
hematocrit but returns blood volume to normal value of 300 mL
o Stripping the cord could lead to some degree of respiratory distress, but the baby needs the extra RBC’s
 Cardiac output of neonate averages 500 mL/min (about twice what adult is) – child can have especially low
cardiac output caused by hemorrhage of much of its blood volume from placenta at birth
 Arterial pressure during first day after birth averages 70/50, which increases slowly during next several months
to about 90/60 – doesn’t reach adult levels until adolescence (about 115/70)
 Blood characteristics
o RBC count averages 4 million/mm3 – if blood is stripped from cord into infant, RBC count rises 0.5-0.75
million during first few hours of life
 Subsequent to this, few new RBC’s formed in first few weeks of life, presumably because
hypoxic stimulus of fetal life is no longer present to stimulate RBC production
 RBC count falls below 4 million by 6-8 weeks of age, and from that time on, increasing activity by
baby provides appropriate stimulus for returning RBC count to normal within 2-3 months
o Immediately after birth, WBC count is about 45,000/mm3 (about 5x that of adult)

Bilirubin formed in fetus can cross placenta into mother and be excreted through her liver, but immediately
after birth, the only means for ridding the neonate of bilirubin is through its own liver, which for the first week
or so of life, functions poorly and is incapable of conjugating significant quantities of bilirubin with glucuronic
acid for excretion into bile
o Plasma bilirubin rises from normal value of less than 1 mg/dL to an average of 5 mg/dL during first 3
days of life, then gradually falls back to normal as liver becomes functional
o Called physiological hyperbilirubinemia and can be associated with mild jaundice of infant’s skin and
sclerae for a week or two
 Erythroblastosis fetalis – baby is Rh+ and mother is Rh-, so mother becomes immunized against Rh+ factor in
fetus’s blood cells, and her antibodies destroy fetal RBC’s and can cause fetal death for lack of adequate RBC’s –
can cause neonatal jaundice if baby survives pregnancy
Fluid Balance, Acid-Base Balance, and Renal Function
 Rate of fluid intake and fluid excretion in newborn infant is 7x as great in relation to weight as adult, which
means that even slight percentage alteration of fluid intake or output can cause rapidly developing
abnormalities
 Rate of metabolism in infant is twice adult, meaning twice as much acid is formed, creating tendency toward
acidosis in infant
 Functional development of kidneys not complete until end of 1st month of life
 Because of immaturity of kidneys and marked fluid turnover and rapid formation of acid, most important
problems of newborns are acidosis, dehydration, and (rarely) overhydration
Liver Function
 Liver of neonate conjugates bilirubin with glucuronic acid poorly and excretes very little bilirubin during first few
days of life
 Liver deficient in forming plasma proteins, so plasma protein concentration falls during first weeks of life to 1520% less than older children – can occasionally develop hypoproteinemic edema because of this
 Gluconeogenesis function of liver deficient and, as a result, blood glucose level of unfed neonate falls to about
30-40 mg/dL, and infant must depend mainly on stored fats for energy until sufficient feeding can occur
 Liver usually forms too little of blood factors needed for normal blood coagulation
Digestion, Absorption, and Metabolism of Energy Foods and Nutrition
 Ability of neonate to digest, absorb, and metabolize foods is no different from older child except
o Secretion of pancreatic amylase is deficient, so neonate uses starches less adequately than do older
children
o Absorption of fats from GI tract somewhat less than that in older child, so fat in milk is frequently
inadequately absorbed
o Glucose concentration in blood is unstable and low
 Neonate capable of synthesizing and storing proteins – with an adequate diet, up to 90% of ingested amino
acids used for formation of body proteins (much higher than adults)
 Because body SA is large in relation to mass, heat is readily lost from body and, as a result, body temperature of
neonate, particularly premature infants, falls easily, often several degrees during first few hours after birth
o Body temperature returns to normal in about 7-10 hours, but body temp regulatory mechanisms remain
poor during early days of life, allowing for marked deviations in temperature that gradually stabilize
about 15-20 days after birth
 At birth, neonate is usually in complete nutritional balance, provided mother has had an adequate diet
o Function of GI system is usually more than adequate to digest and assimilate all nutritional needs of
infant if appropriate nutrients provided in diet
 Need for calcium and vitamin D – neonate is in a stage of rapid ossification of its bones at birth, so ready supply
of calcium throughout infancy is necessary and need vitamin D to absorb it
o Absence of vitamin D results in rickets in only a few weeks, particularly in premature babies because GI
tracts absorb calcium less effectively than normal infants
 Need for iron in diet – if mother has adequate amounts of iron in her diet, liver of infant usually has stored
enough iron to keep forming blood cells for 4-6 months after birth – without adequate iron in mother’s diet,
infant is likely to be anemic within 3 months
o To prevent anemia in babies, they can be fed egg yolk
 Need vitamin C (ascorbic acid) – not stored in significant quantities in fetal tissues, but needed for proper
formation of cartilage, bone, and other intercellular structures of infant
o Milk provides only small supplies of ascorbic acid, so orange juice or other sources of ascorbic acid often
prescribed by third week of life
Immunity
 Neonate inherits much immunity from mother because many protein antibodies diffuse from mother’s blood
through placenta into fetus, but neonate does not form antibodies of its own to a significant extent
o By end of 1st month, baby’s gamma globulins, which contain antibodies, have decreased to less than half
original level, with corresponding decrease in immunity
 Baby’s own immunity system begins to form antibodies and gamma globulin concentration returns to normal by
12-20 months of age
 Antibodies inherited from mother protect infant for about 6 months against most major childhood infections
(diphtheria, measles, and polio) – immunization against these diseases before age 6 months is unnecessary
 Inherited antibodies against whooping cough are insufficient to protect neonate, so they require immunization
against this disease within first month or so of life
 Newborn infants seldom subject to allergy – several months later, when the infant’s own antibodies first begin
to form, extreme allergic states can develop, resulting in serious eczema, GI abnormalities, and anaphylaxis
o As child grows and still higher degrees of immunity develop, these allergic manifestations usually
disappear
Endocrine Problems
 Endocrine system of infant is highly developed at birth, and infant seldom exhibits any immediate endocrine
abnormalities
 Only exceptions are
o If pregnant mother bearing female child is treated with androgenic hormone or if androgenic tumor
develops during pregnancy, daughter will be born with high degree of masculinization of her sexual
organs, resulting in a type of hermaphroditism
o Sex hormones secreted by placenta and mother’s glands during pregnancy occasionally cause neonate’s
breasts to form milk during first days of life – some can become inflamed from this or develop infectious
mastitis
o Infant born of untreated diabetic mother will have considerable hypertrophy and hyperfunction of islets
of Langerhans, so baby’s blood glucose may drop below 20 mg/dL shortly after birth
 Insulin shock or coma, even with this low blood level, rarely develops in neonates
 Maternal type II diabetes is most common cause of large babies – high levels of insulin stimulate
fetal growth and contribute to increased birth weight
 Increased supply of glucose and other nutrients to fetus may also contribute to
increased fetal growth – most of which is due to increased body fat
 Usually little increase in body length, although there may be some organomegaly (large
organs)
 In mother with uncontrolled type I diabetes, fetal growth may be stunted because of metabolic
deficits in mother and growth and tissue maturation of neonate are often impaired
 High rate of intrauterine mortality
 Among fetuses that come to term, there is a high mortality
 2/3 of infants who die succumb to respiratory distress syndrome
o Occasionally child born with hypofunctional adrenal cortices, often resulting from agenesis of adrenal
glands or exhaustion atrophy
o If pregnant woman has hyperthyroidism or is treated with excess thyroid hormone, infant is likely to be
born with temporarily hyposecreting thyroid gland
 If before pregnancy, a woman had her thyroid gland removed, her pituitary gland may secrete
great quantities of thyrotropin during gestation and child may be born with temporary
hyperthyroidism
o In fetus lacking thyroid hormone secretion, the bones grow poorly and there is mental retardation
(cretin dwarfism)
Special Problems of Prematurity
 All problems of neonatal life are severely exacerbated by prematurity
 Can be due to
o Immaturity of certain organ systems
o Instability of different homeostatic control systems
 Because of the above, premature babies seldom survive if they are born more than 3 months before term
 Respiratory system especially likely to be underdeveloped in premature infant – vital capacity and functional
residual capacity of lungs are especially small in relation to size of infant
o Surfactant secretion is depressed or absent
o Low functional residual capacity in premature infant is often associated with periodic breathing of
Cheyne-Stokes type
 Premature infant lacks ability to ingest and absorb adequate food – if more than 2 months premature, digestive
and absorptive systems almost always inadequate
o Premature infant must maintain a low-fat diet
o Has unusual difficulty in absorbing calcium and therefore can develop severe rickets before difficulty is
recognized – thus special attention must be paid to adequate calcium and vitamin D
 Other immature organs that frequently cause serious difficulties are
o Immaturity of liver, resulting in poor intermediary metabolism and often bleeding tendency as result of
poor formation of coagulation factors
o Immaturity of kidneys, which are particularly deficient in ability to rid body of acids, thereby
predisposing to acidosis and serious fluid balance abnormalities
o Immaturity of blood-forming mechanism of bone marrow, which allows rapid development of anemia
o Depressed formation of gamma globulin by lymphoid system, which often leads to serious infection
 Immaturity of different organ systems in premature infant creates high degree of instability in homeostatic
mechanisms of body
o Acid-base balance can vary tremendously, particularly when rate of food intake varies from time to time
o Blood protein concentration usually low because of immature liver development, often leading to
hypoproteinemic edema
o Inability to regulate calcium ion concentration may bring on hypocalcemic tetany
o Blood glucose concentration can vary between 20 and 100 mg/dL, depending on regularity of feeding
o Unable to maintain body temperature, so it tends to approach that of its surroundings (can stabilize in
80’s or 90’s F) – body temperature below 35.5o C (96o F) is associated with particularly high incidence of
death – thus incubator treatment for preemies is a must
 Because preemies frequently develop respiratory distress, oxygen therapy has often been used in treating them
o However, use of excess oxygen, especially in early prematurity, can lead to blindness because too much
oxygen stops growth of new blood vessels in retina, and then when oxygen therapy is stopped, blood
vessels try to make up for lost time and burst forth with great mass of vessels growing all through
vitreous humor, blocking light from pupil to retina
o Later, vessels are replaced with mass of fibrous tissue where eye’s clear vitreous humor should be –
called retrolental fibroplasias and cause permanent blindness
o Premature infants usually safe with up to 40% oxygen in air breathed
Growth and Development of Child
 Major physiologic problems of child beyond neonatal period related to special metabolic needs for growth
 Children of both genders are about equal in height until around age 11-13, when female estrogens begin to be
formed and cause rapid growth in height but early uniting of epiphyses of long bones around age 14-16
o Testosterone of male causes extra growth between age 13-17, and male undergoes more prolonged
growth because of delayed uniting of epiphyses
 Behavioral growth – principally a problem of maturity of nervous system
o Difficult to dissociate maturity of anatomical structures of nervous system from maturity caused by
training
o Certain major tracts in CNS not completely myelinated until end of first year of life
 Brain cortex and associated functions, such as vision, require several months after birth for final functional
development to occur

Brain reaches adult proportions by end of second year – associated with closure of fontanels and sutures of
skull, which allows only 20% additional growth of brain beyond first 2 years of life