Age-related features of the kidney

In newborns and infants, the kidney is round, its surface is bumpy due to the lobular structure, which is associated with insufficient development of the cortex at this age. The lobular structure of the kidney is preserved up to 2-3 years. The length of the kidney in a newborn is 4.2 cm, and the weight is 12 g. In infancy, the size of the kidney increases by about 1.5 times, and the weight reaches 37 g.

During the period of early childhood, the length of the kidney is on average 7.9 cm, and the weight is 56 g. In adolescents, the length of the kidney already reaches 10.7 cm, and the weight of the kidney is 120 g.

In newborns, the thickness of the renal cortex is approximately 2 mm, and that of the medulla is 8 mm; their ratio is 1:4. The thickness of the cortex in an adult, compared to that of a newborn, increases approximately 4 times, and that of the medulla is only 2 times greater.

Kidney growth occurs mainly in the first year of a child's life. From 5 to 9 years of age and especially at 16 to 19 years of age, the kidney size increases due to the development of the cortex, which continues until the end of puberty; growth of the medulla ceases by the age of 12. The mass of the renal cortex increases due to the growth in length and width of the proximal and distal convoluted tubules and the ascending part of the nephron loop. The renal pelvis in a newborn is wide and ampullate.

The fibrous capsule of the kidney becomes clearly visible in the 5th year of the child's life, and by the age of 10-14 years, its structure is close to the fibrous capsule of an adult. The sheets of the renal fascia in a newborn are very thin, gradually thickening as the child ages. The fatty capsule is almost absent and begins to form only by the period of early childhood, later it gradually thickens. By the age of 40-50 years, the thickness of the fatty capsule of the kidney reaches its maximum values, and in old and senile age it becomes thinner, sometimes disappearing.

The topography of the kidneys changes with age due to their descent. In a newborn, the upper end of the kidney is projected at the level of the upper edge of the 12th thoracic vertebra, and in infancy (up to 1 year) - already at the level of the middle of the body of the 12th thoracic vertebra. The lower end of the kidney in a newborn is at the level of the lower edge of the 4th lumbar vertebra, in a one-year-old child - 1/2 vertebra higher, which is due to the rapid growth of the spinal column. After 5-7 years, the position of the kidney relative to the spine approaches that of an adult.

At the age of over 50, especially in old and emaciated people, the kidneys may be located lower than in young people. At all periods of a person's life, the right kidney is located slightly lower than the left.

In a newborn, both kidneys are in contact with the corresponding adrenal gland in the region of their upper end and anteromedial surface (almost to the renal hilum). The liver, cecum, and appendix are also adjacent to the right kidney. The spleen is adjacent to a small area of the left kidney; the tail of the pancreas is located medial to the hilum.

The longitudinal axis of each kidney in children up to 3-4 years old runs parallel to the spine, the renal hilum is directed slightly forward. By 5-6 years old, the longitudinal axes take an inclined (converging upward) direction.

As the human body grows, the position of the kidney and the relative length of its artery and vein, which make up the "renal pedicle," change. In a newborn, the "renal pedicle" is relatively long, the vessels are located obliquely: the beginning of the renal artery and the mouth of its vein are located above the renal hilum. Then the "renal pedicle" gradually assumes a horizontal position, and after 50 years, due to some downward displacement of the kidneys, the length of the "renal pedicle" increases and it is directed downwards.

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