L3 Kidney development (P1 Mid)

AL AZHAR UNIVERSITY, FACULTY OF MEDICINE - KIDNEY DEVELOPMENT

• Course: Anatomy & Embryology
• Module: Renal Module
• Academic Year: 2024/2025
• Course Code: IPM-07-20318
• Credit Hours: 5
• Lecturer: Dr. Amina Mohamed Tolba

Intended Learning Outcomes (ILOs)

• 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.

Development 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.

Development of the Urinary and Genital Systems

• 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.

I- Development of the Kidneys: The Pronephroi

• 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.

2- Development of the Kidneys: The Mesonephroi

• 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.

3- Development of the Kidneys: The Metanephroi

• 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.

Metanephric Diverticulum Development

• 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.

Metanephric Tubules (Primordia of Nephron) Development

• 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.

Fetal Kidneys

• 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.

Positional Changes of Kidneys

• 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.

Changes in Blood Supply of Kidneys

• 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.

Congenital Anomalies of the Kidney

• 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.