EMBRYONIC DEVELOPMENT & STEM CELL COMPENDIUM
EMBRYONIC DEVELOPMENT & STEM CELL COMPENDIUM
94. The Urinary or Excretory System: The Definitive Kidney
Review of MEDICAL EMBRYOLOGY Book by BEN PANSKY, Ph.D, M.D.
- The definitive kidney
- BY MONTH 3, THE NEPHRONS already formed are anatomically and histologically identical to those of the adult kidney, and at this stage of development, the kidney begins to make urine, even though it has not acquired as yet its total number of approximately one million functional units
- The functional units grow, in number, by concentric layers throughout the prenatal life and are laid down until about term
- No nephrons usually are developed after birth, except in premature infants, but existing nephrons complete their differentiation during infancy and increase in size until adulthood
- Thus, the increase in kidney size is due to hypertrophy and not to an increase in the number of nephrons after birth
- THE FETAL KIDNEY normally has a polylobar appearance due to the manner of development of the ureteric bud in the metanephric blastema
- The lobular form diminishes at birth by means of progressive filling in of the interlobular grooves
- Although the adult kidney is smooth and regular, the prenatal appearance sometimes persists, and we refer to a polylobed kidney or fetal-like kidney
- CHANGES IN KIDNEY POSITION: the metanephros initially is located in the pelvic region but shifts later to a more cranial position in the abdomen
- This so-called "ascent" of the kidney is probably due to a diminution of the body curvature as well as growth of the body in the lumbar and sacral regions
- The kidney hilum initially faces ventrally, but ascent and rotation of 90? turn the hilum so that it faces medially
- VASCULAR SUPPLY
- In the pelvis, the metanephros receives its arterial supply from the pelvic branches of the aorta
- During ascent to the abdomen, the kidney is vascularized by arteries that originate from the aorta at continuously higher levels
- The lower vessels usually degenerate, except for vascular variations and anomalies
