Development of kidney in vertebrates

1. SYED MUHAMMAD KHAN (BS HONS. ZOOLOGY)
pg. 1
Development of Kidney In Vertebrates
Organogenesis is a process in which the three germ layers formed from gastrulation,
ectoderm, endoderm, and mesoderm form the internal organs of the organism. It is the
phase of embryonic development that starts at the end of gastrulation and goes until
birth.
 The endoderm gives rise to gastrointestinal and respiratory organs.
 The mesoderm forms the blood, heart, kidney, muscles, and connective tissues.
 The ectoderm forms epidermis, the brain, and the nervous system.
The urogenital system (kidneys, gonads, and their respective duct systems) is
generated by the intermediate mesoderm. The human kidney is an incredible organ
whose importance cannot be overestimated. Its functional unit, the nephron, contains
more than 10,000 cells and at least 12 different cell types, each cell type having a
specific function and being located in a particular place in relation to the others along
the length of the nephron.
Stages of Kidney Development
Mammalian kidney development progresses through three major stages. The first two
stages are temporary; only the third and last persists as a functional kidney.
Stage# 1 – Pronephros:
Early in development, the pronephric duct arises in the intermediate mesoderm. The
anterior region of the duct induces the adjacent mesenchyme to form the pronephros, or
tubules of the initial kidney. The pronephric tubules form functioning kidneys in fish and
amphibian larvae, but they are not believed to be active in amniotes. In mammals, the
pronephric tubules and the anterior portion of the pronephric duct degenerate, but the
more caudal portions of the pronephric duct persist and serve as the central component

2. SYED MUHAMMAD KHAN (BS HONS. ZOOLOGY)
pg. 2
of the excretory system throughout development. This remaining duct is often referred
to as the Nephric duct / Wolffian duct.
Stage# 2 – Mesonephros:
As the pronephric tubules degenerate, the middle portion of the nephric duct induces a
new set of kidney tubules in the adjacent mesenchyme. This set of tubules constitutes
the mesonephros / mesonephric kidney. In some mammalian species, the mesonephros
functions briefly in urine filtration, but in mice and rats, it does not function as a working
kidney. Human mesonephros filters blood and makes urine. In humans, as more tubules
are induced caudally, the anterior mesonephric tubules are destroyed through
apoptosis. Human mesonephros also provides important developmental functions
during its brief existence:
 First, it is one of the main sources of the hematopoietic stem cells necessary for
blood cell development.
 Second, in male mammals, some of the mesonephric tubules persist to become the
tubes that transport the sperm from the testes to the urethra (the epididymis and vas
deferens).
Stage# 3 – Metanephros:
The permanent kidney of amniotes, the metanephros, is generated by some of the
same components as the earlier, transient kidney types. It is thought to originate
through a complex set of interactions between epithelial and mesenchymal components
of the intermediate mesoderm. In the first steps, the metanephrogenic mesenchyme is
committed and forms in the posterior regions of the intermediate mesoderm, where it
induces the formation of epithelial branches, called ureteric buds. These buds
eventually become the collecting ducts and ureters that take the urine to the bladder.
The ureteric buds induce the mesenchymal tissue (of metanephrogenic mesenchyme)

3. SYED MUHAMMAD KHAN (BS HONS. ZOOLOGY)
pg. 3
to form the nephrons of the mammalian kidney. As the mesenchyme differentiates, it
tells the ureteric bud to branch and grow.
Figure: General scheme of development in the vertebrate kidney. (A) Pronephros. (B)
Mesonephros. (C) Metanephros.
Reciprocal Interactions of Developing Kidney Tissues
The two intermediate mesodermal tissues (the ureteric bud and the metanephrogenic
mesenchyme) interact and reciprocally induce each other to form the kidney.
 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 which form the structure of a renal nephron.

4. SYED MUHAMMAD KHAN (BS HONS. ZOOLOGY)
pg. 4
While this transformation is happening, the epithelializing nodules fuse with the ureteric
bud ducts. This fusion creates a connection between the ureteric bud and the newly
formed tubule, allowing material to pass from one into the other. These tubules, derived
from the mesenchyme form the secretory nephrons of the functioning kidney, and the
branched ureteric bud gives rise to the renal collecting ducts and to the ureter, which
drains the urine from the kidney.