Anatomy and Physiology of Children and Adolescents - M. R. Sapin 2007

Urogenital System
Urinary (Excretory) System
Urethra - Age-Related Features of the Urinary System Organs

In newborns and infants, the Kidney is rounded and lobulated in appearance due to its lobular Structure. This lobular Organization persists until 2–3 years of age. At birth, the kidney is approximately 4 cm long and weighs 12 g. During infancy, its size increases by about 1.5 times, and its weight reaches 37 g. In early childhood, the average kidney length is 8 cm and its weight is 56 g. By adolescence, the length reaches 10 cm and the weight increases to 120 g. Between the ages of 5–9 years, and especially from 16–19 years, renal dimensions increase primarily due to the growth of the cortical substance, whereas the growth of the medulla ceases by age 12. The mass of the renal cortex increases As a result of the elongation and broadening of the convoluted tubules and the ascending limbs of the nephron loops. Compared to newborns, the thickness of the cortex in adults increases approximately fourfold, while the medulla doubles in thickness. The fibrous capsule of the kidney becomes distinct by 5 years of age. The adipose capsule begins to form only during early childhood and subsequently undergoes gradual thickening. By 40–50 years of age, the renal adipose capsule reaches its maximum thickness, but in elderly and senile individuals, it thins out and may even disappear altogether.

The Topography of the Kidneys changes with age. In newborns, the upper pole of the kidney is projected at the level of the upper border of the 12th thoracic vertebra, whereas in infants (under 1 year of age), it is located at the level of the middle of the 12th thoracic vertebra due to the rapid growth of THE Vertebral Column. After 5–7 years of age, THE POSITION OF the kidneys relative to the spine approaches that of an adult.

Over the age of 50, particularly in elderly or emaciated individuals, the kidneys may lie lower than in youth. Throughout all stages of life, the right kidney is situated slightly lower than the left.

In newborns, the Ureters have a tortuous course. The length of the Ureter is 5–7 cm, increasing to 15 cm by 4 years of age. The muscular coat is poorly developed in early childhood.

The Urinary Bladder is spindle-shaped in newborns, pear-shaped in toddlers, and assumes the adult configuration by adolescence. The bladder capacity in newborns is 50–80 ml. By age 5, it holds 180 ml of urine, and after 13 years, 250 ml. In newborn infants, the circular Muscle layer in the bladder wall is weakly expressed, whereas the mucous membrane is well developed and possesses folds.

The apex of the urinary bladder in newborns reaches halfway between the umbilicus and the Pubic Symphysis; consequently, at this age, the bladder does not come into contact with the Vagina in girls or the rectum in boys. Between 1 and 3 years of age, the Cytology/practical/108.html">Fundus of the bladder lies at the level of the upper margin of the pubic symphysis. In adolescents, it is located at the level of the middle of the pubic symphysis, and in young adults, at the level of its lower margin. Subsequently, the fundus of the bladder descends depending on the tone of the Muscles of the urogenital Diaphragm.

Review and Self-Assessment Questions:

1. Describe the various parts (regions) of the kidney.

2. Name the segments of the nephron. In which PARTS OF THE kidney are they located? What is The structure of the renal corpuscle?

3. What can you tell about the STRUCTURE OF THE renal calyces, the renal pelvis, and the ureter?

4. What is the forniceal apparatus of the kidney, and what Functions does it perform?

5. What anatomical parts are distinguished in the urinary bladder, what openings are present, and where are they located?

6. Describe how the Organs of the Urinary System change with age.