L3 Kidney development (P1 Mid)

Study Notes

ILO 1: Identify the embryological origin of the urinary and genital systems.
ILO 2: Describe the stages of kidney development.
ILO 3: Memorize congenital anomalies of the kidney.

Polyhydramnios Case Study: A pregnant woman in her 10th week of gestation, during a routine examination, exhibited polyhydramnios, likely caused by an absent organ. Diagnosis is needed.

Embryonic Development: The urogenital system arises from the intraembryonic mesoderm.
Intermediate Mesoderm: After folding, the intermediate mesoderm forms the urogenital ridge on each side of the dorsal aorta.
Nephrogenic Cord: The part of the urogenital ridge that forms the urinary system is called the nephrogenic cord.

Structure: Transient, non-functional structures appearing in the 4th week.
Location: Cell clusters and tubular structures located in the neck region opposite the 7th to 14th somites.
Ducts: Open into the cloaca.
Fate: Degenerate.

Structure: Large, elongated excretory organs.
Development Time: Develop late in the 4th week and function as a transient kidney for roughly 4 weeks.
Location: Positioned below the pronephroi, opposite the 14th to 28th thoracic and upper lumbar somites.
Components: Glomeruli and mesonephric tubules.
Ducts: Open into the mesonephric ducts and the cloaca.
Fate: Degenerate toward the end of the first trimester.

Origin: Primordia of permanent kidneys.
Development Timing: Develop in the 5th week and start functioning about 4 weeks later.
Sources for Development The ureteric bud and metanephric mass (both mesodermal in origin).
Diverticulum: An outgrowth that grows from the mesonephric duct, forming the ureter, renal pelvis, calices, and collecting tubules.

Structure: Stem from the mesonephric ducts near the cloaca entrance.
Components: Ureter, renal pelvis, calices, and collecting tubules.
Function: Grows and penetrates the metanephric tissue.
Stalk: Become the ureter, and its expanded cranial end the renal pelvis.
Structure Change: Straight collecting tubules undergo repeated branching, generating tubules, major calices, and collecting tubules
Metanephric Tubules: Derived from the caudal part of the nephrogenic cord.
Metanephric Vesicles: Elongating and developing into metanephric tubules.

Structure: Mass of intermediate mesoderm.
Formation: Derived from the caudal part of the nephrogenic cord.
Stages: Develop into metanephric vesicles, then elongate into metanephric tubules.
Glomeruli: Invaginate the proximal ends of the tubules.
Filtration: Begins around the 9th fetal week and increases until week 32.
Nephron: Consists of the renal corpuscle (glomeruli and Bowman's capsule), proximal convoluted tubule, loop of Henle, and distal convoluted tubule.

Lobulation: Divided into lobes, which lessen as the fetus matures.
Nephron Number: At term, each kidney contains 800,000 to 1,000,000 nephrons.
Postnatal Growth: Kidney size increase is mainly due to growth in proximal convoluted tubule and interstitial tissue.
Maturation: Occurs after birth.

Initial Location: Lie close together in the pelvic region.
Movement: Move to abdominal position; farther apart, and attain their adult position by the 9th week.
Rotation: Rotate medially 90°.
Hilum: Faces anteromedially by the 9th week.

Development: Initially branches from common iliac and median sacral arteries.
Ascending Kidneys: Receive blood supply from the distal end of the aorta as they ascend.
Cranial Branches: Permanent renal arteries form from the abdominal aorta.
Suprarenal Glands: Contact with glands stop their upward movement at the 9th week.
Involution: Caudal branches undergo involution and disappear.

Cystic Kidney Disease:
- Polycystic Kidney: Autosomal disorder, diagnosed at birth by ultrasound, exhibiting many cysts in both kidneys, leading to kidney failure.
- Multi-Cystic Dysplastic Kidney Disease (MDK): Results from abnormal kidney development, and often leads to good outcomes. Infant death is possible soon after birth.
Horseshoe Kidney: Fusion of the caudal ends of the kidneys. Interconnecting bridge usually behind inferior mesenteric artery.
Ectopic Pelvic Kidney: Arrested development in an abnormal location (pelvic region).
Renal Agenesis: Absence of one or both kidneys. Unilateral agenesis is possible. Often asymptomatic, but bilateral agenesis can be associated with oligohydramnios.