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Flashcards in Module 10: Special Senses Deck (313)
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Neonatal Physiology

• Switch from intrauterine life to extrauterine life
• “Immaturity” of systems
• Higher metabolic needs (anabolism)
• Rapid period of growth and development


At Birth...

• Loss of placental support
• Needs own source of nourishment
• Changes in respiratory function


Onset of Breathing

• Begins to breathe within seconds
• Normal respiratory rate within 1 min
• Initiated by sudden exposure to the outside world:
- Slightly asphyxiated state
- Cooled skin


Delayed or abnormal breathing at birth (Risk for Hypoxia)

• Causes: 1) Umbilical cord compression, 2) Premature separation of the placenta, 3) Excessive contraction of the uterus, 4) Excessive anesthesia
• Can be tolerated by the neonate up to 10 minutes
• 4 minutes ONLY in the adult
• Permanent brain damage may occur after at least 8 minutes


Expansion of lungs at birth

• Need to overcome the surface tension from the viscid fluid that fills the lungs


Changes in Fetal Circulation After Birth

• Closure of the Foramen Ovale (right to left atrium)
• Closure of the Ductus Arteriosus (connection between aortic arch)
• Closure of the Ductus Venosus (at the liver)


Neonatal Nutrition

• Blood glucose concentration frequently falls the first day = 30 to 40 mg/dl of plasma (less than half the normal value)
• Has stored fats and proteins for metabolism until mother's milk can be provided 2 to 3 days later
• Special problems: adequate fluid supply to the neonate because the infant's rate of body fluid turnover averages seven times that of an adult, and the mother's milk supply requires several days to develop.
• Physiologic weight loss = decrease of 5 -10 % (as much as 20%) within the first 2 to 3 days of life due to fluid loss


Special Functional Problems in the Neonate
Due to:

• Instability of various hormonal and neurogenic control systems
• Immaturity of the organ systems
• Ongoing adjustments to extrauterine life


Respiratory System (Neonates)

• Normal Respiratory Rate = 40 breaths per minute
• Tidal Volume = 16 mL
• Total Minute Respiratory Volume = 640 ml/min, (about twice as great in relation to the body weight as that of an adult)
• The functional residual capacity of the infant's lungs is only one-half that of an adult in relation to body weight
• Causes excessive cyclical increases and decreases in the newborn baby's blood gas concentrations if the respiratory rate becomes slowed because it is the residual air in the lungs that smoothes out the blood gas variations


Circulatory System (Neonates)

• Blood Volume = about 300 mL
• Additional 75mL if the infant is left attached to the placenta for a few minutes after birth or if the umbilical cord is milked (RBCs are valuable to the neonate)
• Next few hours, fluid is lost into the neonate's tissue spaces
- increased hematocrit
- eventually returns to the normal value of about 300 milliliters


Circulatory System (Neonates) 2

• Cardiac output = averages 500 ml/min (twice as much in relation to body weight as in the adult)

• Arterial Pressure
- First day after birth: ave. 70/50 mmHg
- Increases slowly during the next several months to about 90/60
- Much slower rise during the subsequent years until the adult pressure of 115/70 is attained at adolescence


Blood Characteristics (Neonates)

• RBC count = 4M per cubic millimeter
• If blood is stripped from the cord into the infant, RBC count increases to 0.5-0.75 million during the first few hours of life
• Few new RBCs are formed in the infant during the first few weeks of life, presumably because the hypoxic stimulus of fetal life is no longer present to stimulate red cell production.
• Physiology Anemia = at 6-8 weeks of age, less than 4 M per cubic millimeter ; returns to normal within 2-3 mos.
• WBC count = 45,000 per cubic millimeter, which is about five times as great as that of the normal adult


Liver Function in the Neonate

• Liver functions poorly in the first week of life
• Incapable of conjugating bilirubin with glucuronic acid for excretion in the bile
• Conjugates bilirubin with glucuronic acid poorly and therefore excretes bilirubin only slightly during the first few days of life
• Deficient in forming plasma proteins (15 – 20% less than that for older children); may develop hypoproteinemic edema
• Incapable of effective gluconeogenesis results in low glucose levels
• Forms too little of the blood factors needed for normal blood coagulation


Physiological Hyperbilirubinemia vs Pathologic Jaundice

• Physiological Hyperbilirubinemia - the plasma bilirubin concentration rises from a normal value of less than 1 mg/dl to an average of 5 mg/dl during the first 3 days of life and then gradually falls back to normal as the liver becomes functional.
• Associated with mild jaundice (yellowness) of the infant's skin and especially of the sclerae of its eyes for a week or two (physiologic jaundice)
• Vs. Pathologic Jaundice – appears within the 1st 24 hours of life


Fluid Balance, Acid-Base Balance, and Renal Function (Neonates)

• The rate of fluid intake and fluid excretion in the newborn infant is 7x as great in relation to weight as in the adult
• The rate of metabolism in the infant is 2x as great in relation to body mass as in the adult; tendency toward acidosis in the infant
• Functional development of the kidneys is not complete until the end of about the first month of life; can concentrate urine to only 1.5 times the osmolality of the plasma
• Most important problems of infancy: acidosis, dehydration, and, more rarely, overhydration


Digestion, Absorption, and Metabolism of Energy and Food (Neonates)

• Secretion of pancreatic amylase in the neonate is deficient
- The neonate uses starches less adequately than do older children
• Absorption of fats from the gastrointestinal tract is somewhat less than that in the older child
- Milk with a high fat content, such as cow's milk, is frequently inadequately absorbed
• The glucose concentration in the blood is unstable and low


Increased Metabolic Rate (Neonates)

- The normal metabolic rate of the neonate in relation to body weight is about twice that of the adult:
- =2x cardiac output
- = 2x minute respiratory volume in relation to body weight in the infant


Poor Body Temperature Regulation (Neonates)

- Results from large body surface area in relation to body mass
- Heat is readily lost from the body
- The body temperature of the neonate, particularly of premature infants, falls easily


Need for Calcium and Vitamin D (Neonates)

- Rapid ossification of its bones at birth needing a ready supply of calcium throughout infancy is necessary
- Ordinarily supplied adequately by the usual diet of milk
- GIT absorb calcium less effectively (especially preterm infants) than those of normal infants; needs Vitamin D to facilitate absorption


Necessity for Iron in the Diet (Neonates)

- May have stored enough iron to keep forming blood cells for 4 to 6 months after birth
- If the mother had anemia, severe anemia is likely to occur in the infant after about 3 months of life
- May feed infant with egg yolk or give iron supplement by the second or third month of life


Vitamin C Deficiency in Infants

- Ascorbic Acid: Required for proper formation of cartilage, bone, and other intercellular structures of the infant
- Not stored in significant quantities in the fetal tissues
- Little amount only found in milk (human milk > cow’s milk)
- Orange juice or other sources of ascorbic acid are often prescribed by the third week of life


Immunity (Neonates)

• Passive Immunity from the mother
(through the placenta and colostrum in milk)
- Can protect the infant for about 6 months against most major childhood infectious diseases, including diphtheria, measles, and polio
- Decrease of antibodies to less than half at age 1 month
- Gradual return of gamma globulin concentration to normal by the age of 12 to 20 months


Allergy (Neonates)

• The newborn infant is seldom subject to allergy
• May become sensitive several months later,
• May result in serious eczema, gastrointestinal abnormalities, and even anaphylaxis
• As the child grows older and still higher degrees of immunity develop, these allergic manifestations usually disappear


Endocrine Problems: Neonates (1)

• Ordinarily, the endocrine system of the infant is highly developed at birth
• Special cases occur due to the exposure of the child to hormones coming from the mother:
- A female child exposed to androgenic hormone or if an androgenic tumor develops in the mother during pregnancy: high degree of masculinization of her sexual organs (a type of hermaphroditism)
- May cause the neonate's breasts to form milk during the first days of life


Endocrine Problems: Neonates (2)

• Infants born to diabetic mothers
- Hypertrophy and hyperfunction of pancreatic islets leading to low blood glucose levels
- Macrosomal babies (large babies) born to Type II DM mothers
*The high levels of insulin are believed to stimulate fetal growth and contribute to increased birth weight
* Increased supply of glucose and other nutrients to the fetus may also contribute to increased fetal growth

- In the mother with uncontrolled type I diabetes (caused by lack of insulin secretion), fetal growth may be stunted because of metabolic deficits in the mother and growth and tissue maturation of the neonate are often impaired.


Endocrine Problems: Neonates (3)

• Hypofunctional adrenal cortices, often resulting from agenesis of the adrenal glands or exhaustion atrophy, which can occur when the adrenal glands have been vastly overstimulated.

• Infant born to a hyperthyroid mother is most likely to be temporarily hypothyroid; reverse is true
- In a fetus lacking thyroid hormone secretion, the bones grow poorly and there is mental retardation (cretinism)


Immature Development of the Premature Infant

• FC And FRC are small in relation to size of infant
• Low FRC = Cheyne-strokes (breathing pattern)
• Decreased or absent surfactant = RDS (respiratory distress syndrome)

Gastrointestinal Function
• Poor absorption of fat
• Difficulty in absorbing Calcium

Function of other organs
• Immaturity of the Liver, Kidneys, bone marrow and lymphoid syste


Instability of the Homeostatic Control Systems in the Premature Infant

• Acid-base balance
• Protein concentration (hypoproteinemic edema)
• Calcium ion concentration
• Blood glucose concentration


Instability of Body temperature (Infants)

• Temperature approeaches that of surroundings
• Temp below 96F (35.5C) is associated with high incidence of death


Oxygenation in Prematurity

• Excessive oxygenation may cause Blindness
• Increased Oxygen stops growth of new blood vessels in the retina
• Once oxygenation is stopped increased blood vessel formation up to vitreous humor blocking light from pupil to retina. These Blood vessels are replaced with fibrous tissue hence further contributing to blindness.
• Retrolental fibroplasia