Urogenital_system Wk9 - The Urinary System • • • •...

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Unformatted text preview: The Urinary System • • • • 1. Kidney 2. Ureter 3. Bladder 4. Urethra Kidneys • Pronephros – nonfunctional – fish • Mesonephros – functions briefly – amphibians • Metanephros – permanent Pronephros • 4th week • cell clusters and tubes in the cervical region Mesonephros • 4th week through 3rd trimester • consists of – glomeruli – mesonephric tubules • which will become effferent tubules – mesonephric duct Metanephros • 5th week • not functional until 9th week • urine is formed – excreted into the amniotic fluid • metanephric diverticulum • metanephric mass of intermediate mesoderm Metanephric diverticulum • • • • Ureter renal pelvis calices collecting tubules – branch • minor calices - 1st 4 branches • major calices - 2nd 4 branches Nephron • • • • Renal corpuscle proximal convoluted tubules loop of Henle distal convoluted tubules Uriniferous tubules • Nephron – metanephric mass • collecting tubule – metanephric diverticulum Miscellaneous • • • • Kidneys develop into lobes Nephron formation is complete at birth Functional maturation after birth Filtration by 9th week Ascent • 9th week • caudal grows quicker and away from the kidney Blood Supply • Originally from the common iliac Bladder • Urogenital sinus – vesical – pelvic – phallic • Trigone – from mesonephric ducts Bladder • Epithelia – endoderm of urogenital sinus • other layers are from splanchnic mesenchyme • Allantois-urachus median umbilical ligament • Enters pelvis by age six Urethra • Epithelia – endoderm of urogenital sinus • connective tissue and muscle are from splanchnic mesenchyme Suprarenal glands • Cortex – mesoderm – 6th week • Medulla – neural crest cells Cortex • Fetal abdominal mesothelium • Zones (late in fetus) – glomerulusa – fascicuata (androgens, glucocorticoids) – reticularis (androgens) • becomes small Gonads • Mesothelium • mesenchyme • germ cells from yolk sac Indifferent Gonads • Week 5 • primary sex cords – cortex - ovaries – medulla - testes Primordial germ cells • 4th week • by week 6, they become incorporated into the sex cords Sex Determination • Week 7 • short arm of the y chromosome • 2 X’s are needed for proper female phenotype • Testosterone determines maleness • Femaleness is not dependent on hormones • Male – primary sex cords become seminiferous tubules • Female – absence of y chromosomes causes ovaries to form Male • Testosterone stimulates mesonephric ducts to become male genital ducts • Mullerian inhibiting substance (MIS) causes degeneration of the mullerian ducts • mesonephric ducts degenerate, some become efferent tubules Male • Seminal vesicals are outpockets from mesonephric ducts • Prostrate gland – endoderm and mesenchyme • Bulbourethral gland – spongy urethra – mesenchyme Female • Uterine tube – arms of the fused paramesonephric ducts • Vagina – endoderm of urogenital sinus – mesenchyme – sinovaginal bulbs • vaginal plate • center breaks down • Lumen of the vagina is separated from the urogenital sinus by the hymen, a fold of the posterior wall of the sinus • Urethral/paraurethral glands are equivalent to the prostrate • greater vestibular gland is equivalent to the bulbourethral Testes • Primary sex cords condenses to form the rete testes, and seminiferous tubules • connective tissue develops around Seminiferous tubules • Interstitial cells – produces androgen by week 8 • Sustentacular cells (Sertoli) – forms MIS • solid until puberty • spermatogonia Ovaries • 10 th week • secondary sex cords more prominent • 16th week follicles are present as cell clusters • active mitosis occurs • no oogonia form postnatally Ducts • Male – Wolffian • Female – paramesonephric • 5th/6th week they are indifferent • 8th week – testosterone causes formation of epididymis – paramesonephric ducts fuse in the middle, forming a “Y” External genitalia • 7th week • 12th week differentiated • genital tubercle – cranial end of cloaca • Labioscrotal swellings/Urogenital folds • genital tubercle elongates Masculinization • Induced by testosterone • urogenital folds fuse, forming the spongy urethra • terminal part of the urethra • 12th week prepuce formed from ectoderm • corpora cavernosa and spongiosum from mesenchyme • labioscrotal swellings fuse to form the scrotum (endoderm and mesenchyme) Feminization • Not clearly understood but estrogens are involved • phallic growth ceases, forming the clitoris • Urogenital folds do not fuse and form the labia minora • labioscrotal folds form the mons and labia majora Inguinal canals • Gubernaculum from gonad to labioscrotal swellings – creates pathway for inguinal canal • in females the gubernaculum becomes the ovarian ligament and round ligament Descent of the testes • Testes enlarge/mesonephros atrophy • 26th week the cranial part of the abdomen grows away from the caudal part • controlled by androgens • once in the scrotum the inguinal canal contracts • descending testes are surrounded by fascia – internal spermatic fascia – cremasteric muscle – external spermatic fascia • paramesonephric ducts atrophy • enlargement of vaginal process ...
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