Lecture 4 Embryology Urinary System PDF

Learning outcomes Describe the embryology of the urinary system by describing the development of the following: urogenital ridges pronephros, mesonephros, metanephros collecting system Chapter 15, Sixth Edition. Available excre...

Learning outcomes Describe the embryology of the urinary system by describing the development of the following: urogenital ridges pronephros, mesonephros, metanephros collecting system Chapter 15, Sixth Edition. Available excretory system on ClinicalKey bladder and urethra (through library databases) Objectives Describe the embryological development of the urogenital ridges of the urinary system Describe the embryological development of the pronephros, mesonephros, metanephros of the urinary system Describe the embryological development of the collecting system of the urinary system Describe the embryological development of the excretory system of the urinary system Describe the embryological development of the bladder and urethra of the urinary system  DEVELOPMENT OF THE URINARY SYSTEM OVERVIEW Overview https://www-clinicalkey-com.ez.sun.ac.za/#!/content/book/3-s2.0- B9780323696043000155 From intermediate mesoderm (nephrotome). Three successive nephric structures – increasing complexity: Pronephros (primitive, regress) Mesonephros (functional) & mesonephric duct Metanephros & ureters (definitive) Urogenital sinus (anterior part of cloaca) – bladder, urethra Clinical Case Bilateral renal agenesis. Oligohydramnios – little amniotic fluid. Absence of kidneys, ureters and bladder on fetal ultrasound scan. Incidence: 1 in 4000-4500 births. More common in males. Potter sequence of features. Mortality: pulmonary hypoplasia. Associated with genetic changes. https://healthjade.net/potter-syndrome/  Pronephros & mesonephric duct formation Formation of the pronephros & mesonephric duct “Epithelialization” of intermediate mesoderm along 5th – 7th cervical levels– forms duct (mesonephric). Develop in caudal directions – induces cells to convert from mesenchyme to epithelium at caudal tips. Adjacent mesoderm (ventromedial side) condenses into epithelial buds: hollow and form the pronephros. Form functional kidneys in lower vertebrates. Humans: regress around day 24/25.  More caudally, mesonephric buds formed (induced by the duct). Lumbar region: ducts grow towards & fuse with ventrolateral walls of cloaca (day 26) – will become posterior wall of future bladder.  As the ducts fuse with cloaca, they “cavitate” & form a lumen which progresses cranially. Caudal end induces the evagination of ureteric bud. Mesonephros formation  Formation of mesonephros 4th week: Mesonephric tubules (x40) form in mesonephric buds. Thoracic to lumbar region adjacent to the mesonephric duct. Craniocaudal succession within mesonephric mesenchyme. Also called urogenital ridge: gonads develop on medial side. End of 5th week: cranial mesonephri regress, leaving 20 pairs at 1-3 lumbar levels. Tubules differentiate into excretory units: Medial end – cup shaped Bowman’s capsule Wraps around capillaries (glomerus) – renal corpuscle. Formation of mesonephros Lateral parts of mesonephric tubules (cranial 6-7) fuse with mesonephric duct. Forms a passage from excretory units (mesonephros) to the cloaca. Functional between weeks 6-10. Regress in females. In males form efferent ductules. Mesonephric ducts also regress in female. In male: form part of male genital duct system. Metanephros formation  Formation of metanephros: ureteric buds & metanephric mesenchyme Formation of ureteric buds in the sacral intermediate mesoderm. Forms from the caudal end of each mesonephric duct (day 28). Penetrates part of sacral intermediate mesoderm (metanephric mesenchyme) Begins to bifurcate. Kidney = 2 functional Continues to branch. components Each tip (ureteric ampulla) gets a cap of Excretory portion mesenchyme (cap mesenchyme). Collecting portion By end of 16th week: 14-16 lobes formed Formation of metanephros: collecting system Form from ureteric bud. Initial expansion into metanephric mesenchyme: renal pelvis. Ureteric bud bifurcates (previous slide): 16; branches coalesce forming 2-4 major calyces. Next group of branches coalesce – form minor calyces. Next group: 1-3 million branches – collecting ducts.  Formation of metanephros: nephron Form from metanephric mesenchyme. Reciprocal inductive signals between the ureteric bud & cap mesenchyme. Form a renal vesicle next to the ureteric stalk. Also regulates the branching and growth of ureteric buds. Renal vesicle – comma shaped – S shaped. S-shaped fuses with ureteric stalk – lumens continuous. Forms uriniferous tubule – forms structures of nephron (see fig). Formation of metanephros: nephron S-shaped: forms outer layer of Bowmans capsule and the podocytes (glomerular epithelial cells). Uriniferous tubule forms proximal convoluted tubule, descending and ascending limbs of loop of Henle, distal convoluted tubule. Medulla of kidney forms. Nephrogenesis is completed by birth. Metanephroi functional during week 10 (embryogenesis). Fetal urine contributes to amniotic fluid (placenta removes waste). Recap: Metanephros forms kidney Relocation of kidneys  Relocation of kidneys Relocate to the lumbar region (from sacral): between 6th -9th weeks. Inferior to the suprarenal glands. Revascularised from dorsal aorta. Original renal artery in sacral region disappears. Right kidney is lower than left – liver. Formation of urinary bladder and urethra  Formation of urinary bladder and urethra (urogenital sinus) Animation here: https://www- clinicalkey- com.ez.sun.ac.za/#!/content/book/3- s2.0-B9780323696043000155 Cloaca of hindgut: partitioned into ventral urogenital sinus and dorsal anorectal canal.  Formation of urinary bladder and urethra (urogenital sinus) Urogenital sinus forms bladder (may also be formed from lower allantois), membranous and prostatic urethra in males, membranous urethra in females, phallic segment (below the genital tubercle). Phallic segment – penile urethra, vestibule of vagina. Caudal ends of mesonephric duct and ureteric ducts – form common duct connecting to posterior wall of bladder.  Formation of urinary bladder and urethra (urogenital sinus) Apoptosis of common duct – brings ureter progenitors in contact with urogenital sinus. Remodeling and expansion of bladder wall – ureteric openings shift laterally and superiorly. In males, the mesonephric duct shifts inferiorly to open into prostatic urethra. Smooth muscle of bladder wall – forms from splanchinic mesoderm in week 12. Recap  Summary Urinary system develops from intermediate mesoderm. Three successive nephric structures: Pronephros (primitive, regress), Mesonephros (functional) & mesonephric duct, Metanephros & ureters (definitive). Urogenital sinus (anterior part of cloaca) – bladder, urethra. THANK YOU FOR LISTENING 32