A Practical Approach, Second Edition=Ronald D. Ho.pdf

POSTNATAL DEVELOPMENTAL MILESTONES 1009in to four equal zones progressing from the outer to inner cores, and glomeruli were counted ineach. Results confirmed that nephrogenesis is still underway at the time of birth. Positive identificationof the differentiation of the primitive metanephric vesicle from the vascularized glomeruliwas not always possible since the glomeruli become more separated as the dog ages and tubuleselongate. In newborns, the glomeruli of the inner zone are larger than those in the outer zone, butthis difference gradually disappears as the kidney grows (21). A similar study showed that plasmaflow is an important factor in this process in maturing puppies (22).SheepNephrogenesis is complete in sheep at birth (23, 24).PrimatesNephrogenesis is complete in monkeys at birth (23, 24).RabbitsNephrogenesis is completed 2 – 3 weeks postnatally in rabbits (24). Maturation of the loop ofHenle has been studied in rabbits, with regard to succinic dehydrogenase and acid phosphataseactivity, and carbonic anhydrase IV activity (18). Succinic dehydrogenase and acid phosphatasehave high levels of activity in the neonate and decrease to adult levels by about postnatal day 28in the rabbit. Neonatal loops of Henle are relatively short loops without thin ascending limbs. Asmaturation occurs, apoptic deletion of thick ascending cells and transformation into thin ascendinglimb cells yields a well-defined boundary between inner and outer medullas. The expression ofcarbonic anhydrase IV has been correlated with this maturation process in the rabbit (18).Functional DevelopmentCompared to the adult renal function, the human infant has decreased renal blood flow, glomerularfiltration rate, tubular secretion, and a more acidic urinary pH (7). Urine production begins duringthe 10 th week of gestation (6, 2). Maturation of glomerular filtration, concentrating ability, acidbaseequilibrium, and urine volume control are described below.Glomerular FiltrationHumansThe primary function of the glomeruli is to act as a filter before plasma reaches the proximal tubule.Glomerular filtration rate (GFR) continues to increase after birth and reaches adult levels at 1 – 2years of age. After one month of age, creatinine clearance is used to measure GFR; however, GFRis commonly estimated in units of ml/min/1.73m 2 , based on the formula K L/S Cr , where K is aconstant*, L is length (or height in cm) and S Cr is serum creatinine (mg/dl). Serum creatinine levelsduring the postnatal days 1 and 2 reflect maternal values and decrease to 0.2 – 0.4 mg/dl by 3months. An increase in creatinine level indicates a decrease in GFR regardless of gestational age(2). Normal values for GFR are presented in the following table.* The K constant is 0.55 in children and adolescent girls, 0.70 in adolescent boys, 0.45 in term neonates, and 0.33 inpreterm infants.© 2006 by Taylor & Francis Group, LLC