The Questions of Developmental Biology

These buds eventually separate from the nephric duct to become the ureters that take the
urine to the bladder. When the ureteric buds emerge from the nephric duct, they enter the
metanephrogenic mesenchyme. The ureteric buds induce this mesenchymal tissue to condense
around them and differentiate into the nephrons of the mammalian kidney. As this mesenchyme
differentiates, it tells the ureter bud to branch and grow.
Reciprocal interaction of kidney tissues
Thus, the two intermediate mesodermal tissues the ureteric bud and the
metanephrogenic mesenchyme interact and reciprocally induce each other to form the kidney
(Figure 14.19). The metanephrogenic mesenchyme causes the ureteric bud to elongate and
branch. The tips of these branches induce the loose mesenchyme cells to form epithelial
aggregates.
Each aggregated
nodule of about 20 cells will
proliferate and differentiate
into the intricate structure of
the renal nephron.
Each nodule first elongates
into a "comma" shape and
then forms a characteristic
S-shaped tube.
Soon afterward, the cells of
this epithelial structure begin
to differentiate into regionally
specific cell types, including
the capsule cells, the podocytes,
and the distal and proximal
tubule cells.