Related Experiment Video
Updated: Sep 20, 2026

Measuring Cardiac Autonomic Nervous System (ANS) Activity in Toddlers - Resting and Developmental Challenges
Published on: February 25, 2016
Relationship between maturity, electrolyte balance and the function of the renin-angiotensin-aldosterone system in
Abstract:
Simultaneous measurement of plasma renin activity (PRA), plasma aldosterone concentration (PA) and urinary aldosterone excretion (UAE) was made using the RIA method along with determination of Na and K balance in 1-week-old neonates with gestational age of 30-41 weeks (mean 35.9 weeks) and birth weight of 1,160-4,670 g (mean 2,680 g). It was demonstrated that PRA decreased from the value of 36.3 +/- 6.3 ng/ml/h (mean +/- SE) to a level of 10.2 +/- 2.1 ng/ml/h (p less than 0.001), PA did not change and UAE increased from 3.3 +/- 0.8 to 7.8 +/- 1.4 microgram/day (p less than 0.01) as the gestational age advanced from 30-32 to 39-41 weeks. There was no correlation between either PRA and PA and UAE. PRA showed a significant positive correlation with urinary Na excretion (p less than 0.001) and plasma K concentration (p less than 0.05), but it was negatively related to Na balance (p less than 0.001). Significant negative correlations were found between UAE and urinary Na excretion (p less than 0.05), urinary Na/K ratio (p less than 0.01 (and plasma K concentration (p less than 0.05); however, UAE positively correlated with Na balance (p less than 0.01). It is concluded that, in response to renal salt wasting and to the subsequent negative salt balance, premature infants can augment their PRA above values found for full-term infants. Their adrenals, however, failed to respond adequately to this stimulation.
Related Concept Videos
Hormonal Regulation
Introduction to Urinary System
The kidneys are bean-shaped organs located in the retroperitoneal space, on either side of the vertebral column, between the T12 and L3 vertebrae. They are partially protected by the rib cage and surrounded by perirenal fat, which provides cushioning. They are responsible for urine formation and play critical roles in regulating blood pressure, electrolyte levels, and hormone production. The ureters...
Renal Tubule and Collecting Duct
Proximal Convoluted Tubule (PCT):
The PCT is the initial segment of the renal tubule, extending from the Bowman's capsule that encloses the glomerulus. Its convoluted structure and microvilli-lined cells increase the surface area for reabsorption. The PCT reabsorbs glucose, amino acids, sodium, and water from the filtrate, ensuring essential...
Regulation of Sodium and Potassium
Sodium Regulation
Sodium ions make up approximately 90% of extracellular cations, with a normal blood plasma concentration of 136–148 mEq/L. A decrease in blood volume and pressure triggers the release of renin from granular cells in the juxtaglomerular complex (JGC), primarily in...
Renal Regulation of Acid-Base Balance
In the kidneys, cells within the proximal convoluted tubules (PCT) and the collecting ducts secrete hydrogen ions (H+) into the tubular fluid. Specifically, in the PCT, Na+/H+ antiporters secrete H+ while reabsorbing Na+.
However, the intercalated cells in...
Physiology of the Genitourinary System III: Urine Concentration and Dilution

