Urogenital System Embryology PDF

Embryology of the Urogenital System  Gastrula Key structures for urogenital development at the folding stage:
Early Embryo – Gastrula  Development of the Urinary System The kidney develops from embryonic mesoderm in 3 successive forms from the ne...

Embryology of the Urogenital System  Gastrula Key structures for urogenital development at the folding stage:
Early Embryo – Gastrula  Development of the Urinary System The kidney develops from embryonic mesoderm in 3 successive forms from the nephrogenic cords as the cords elongate in a cranial-to- caudal direction. Early Development – 3 successive stages Pronephros - Most primitive Kidney Cervical nephrotomes - 5-7 pairs of small hollow balls of epithelium – connected to the primary nephric duct (pronephric duct) Non-functional in mammals Transient – nephrotomes degenerates by 24-25 days Primary nephric duct extends caudally to become the Mesonephric duct  Mesonephros Functional embryonic kidney Mesonephric tubules form in each segment Cranial to caudal sequence First 4-6 bud out from the primary nephric duct Remaining form in the intermediate mesoderm and connect with the Mesonephric duct Mesonephric tubule differentiates a cup-shaped Bowman’s capsule that wraps around the Glomerulus Glomerulus is a knot of capillaries Bowman’s capsule and Glomerulus make up the Renal Corpuscle Mesonephic tubules connect to Mesonephric duct (Wolffian duct) Mesonephros  Mesonephric Duct Initally a solid rod that grows caudally Diverges from intermediate mesoderm and fuses with the ventrolateral cloacal wall (future bladder) Mesonephric duct undergoes canalization – transformation from mesenchyme to epithelium Mesonephros is functional until 10 weeks Mesonephric Duct regression depends on sex (Genital Development) Mesonephric is also called the Wolffian duct Mesonephric Duct  Metanephros Ureteric Bud (Metanephric diverticulum) - outgrowth of the distal mesonephric duct Metanephric blastema is the mesenchyme surrounding the ureteric bud Ureteric bud – multiple events of elongation and bifurcation Bifurcation results in two ampulla each with its blastema Metanephros  Metanephric Blastema and Ureteric Bud Intermediate mesoderm in the pelvic region begin to differentiate into a structure called the metanephric blastema. Gives rise to the cells making up the nephrons. Releases growth factors that stimulate the development of an outpouching off the caudal portion of the mesonephric duct called the ureteric buds Ureteric buds grow toward and invade the metanephric blastema Elongating stalk of the ureteric bud develops into the ureter. Within the metanephric blastema, the ureteric buds undergo a series of branchings to form the: Renal pelvis, Major calyces, Minor calyces, Collecting tubules Growth, elongation, and division of the ureteric buds The Ureteric Bud Induces the Metanephric Blastema to Form Filtration Units
 Ascent of the kidney and changes in vascularization The kidneys are initially located in the pelvic region. As the caudal portion of the body grows downward, the relative location of the kidneys “ascends” into the upper quadrants of the abdomen (failure to ascend results in a pelvic kidney). As the kidneys ascend, the original blood supply degenerates. New vessels (higher up) develop off the aorta and invade the kidneys, becoming the mature renal arteries If the original vessels fail to regress, they may persist as additional renal arteries or veins.  Urogenital Sinus Urogenital sinus forms: Bladder Pelvic urethra Definitive urogenital sinus Males Females Pelvic Urethra Membranous & Urethra Prostatic Urethra Definitive Urogenital Penile Urethra Vagina Sinus  Development of the Bladder As the bladder grows and expands, the distal ends of the mesonephric ducts are absorbed into the wall of the bladder as the TRIGONE.  Development of the Suprarenal Glands Development of the adrenal cortex Arises mostly from intermediate mesoderm in the lumbar region of the embryo. Development of the adrenal medulla Trunk neural crest cells migrate into the center of the adrenal glands and develop into the chromaffin cells of the adrenal medulla. These cells are essentially postganglionic sympathetic neurons that release epinephrine or norepinephrine directly into the bloodstream as opposed to innervating a target organ.  Developmental Annomalies of the Urinary System 3-4% of all newborns have a developmental abnormality of the urinary tract - most do not cause problems. Renal agensis – unilateral or bilateral Supernumerary kidney Crossed ectopia – migration problem Horseshoe kidney – fusion of kidneys, fails to ascend Bifid ureter - bifurcation of the ureteric bud  Supernumerary Agenesis Kidney Complete Ureter Duplication Bifid Ureter Migration Anomalies: Pelvic Kidney and Crossed Ectopia HKidney Fusion at the inferior lobe Failedorseshoe migration Developmental Anamoly- Fused Kidneys In congenital polycystic kidney disease It may be inherited as an autosomal recessive or autosomal dominant disorder or may be caused by other factors. Autosomal recessive polycystic kidney disease which occurs in 1/5,000 births, is a progressive disorder in which cysts form from collecting ducts. The kidneys become very large, and renal failure occurs in infancy or childhood. In autosomal dominant polycystic kidney disease, cysts form from all segments of the nephron and usually do not cause renal failure until adulthood. The autosomal dominant disease is more common (1/500 to 1/1,000 births) but less progressive than the autosomal recessive disease. Polycystic Kidney Recessive form: 1:5000; cysts from collecting tubules; renal failure in infancy Dominant form: 1:500-1000: cysts from anywhere; renal failure in adulthood Duplications of the Ureters
Kidneys With Double Ureter  Duplication of the ureter Results from early splitting of the ureteric bud Splitting may be partial or complete, and metanephric tissue may be divided into two parts, each with its own renal pelvis and ureter. More frequently, however, the two parts have a number of lobes in common as a result of intermingling of collecting tubules. In rare cases, one ureter opens into the bladder, and the other is ectopic, entering the vagina, urethra, or vestibule. This abnormality results from development of two ureteric buds. One of the buds usually has a normal position, whereas the abnormal bud moves down together with the mesonephric duct. Thus it has a low, abnormal entrance in the bladder, urethra, vagina, or epididymal region. Possible Positions for Ectopic Ureters  Urachal fistula Persistence of the urachus. The urachus is known as the allantois earlier in development, and it connects to the bladder. Babies with a urachal fistula may leak urine from their umbilicus at birth. Ectopic Vesicae  Development of the Reproductive System  Overview Chromosomal sex → determines gonadal sex → determines phenotypic sex Up until 6 weeks of gestation, sex development is identical and nonbinary; developing structures include: Nonbinary, bipotent, undifferentiated gonads Mesonephric ducts (also known as wolffian ducts; also part of the primitive urinary system) Paramesonephric ducts (also known as müllerian ducts) Urogenital sinus The genital tubercle, genital swellings, and genital folds  Overview The genes present at fertilization will determine how the developing bipotent gonads differentiate (e.g., into a testis or an ovary). The developing gonads will then secrete hormones. The presence and/or absence of specific hormones will determine how the remaining structures differentiate. In general, female organs and structures are the “default” phenotype if specific genes and hormones are not present to stimulate male differentiation.  Development of the Gonads The development of the gonads is the “rate determining step” the embryogenesis of the reproductive system. Indifferent gonad is formed from the urogenital ridge; derived from mesoderm and germ cells (primordial germ cells PGC from yolk sac). Epithelium from the urogenital ridge penetrate the mesoderm and forms the primitive sex cords (PSC). PSC + PGC = Gonads Migrating PGC/Gonadogenesis Development of the Internal Male Genitalia Structures of the male reproductive system Development od the Testes Medullary sex cords of testes forms the seminiferous tubules  Development of the Testes Testosterone: Stimulates differentiation of the wolffian/mesonephric ducts into: Epididymis Vas deferens Seminal vesicles Ejaculatory ducts Is converted to dihydrotestosterone (DHT) by 5α-reductase → stimulates development of: The prostate from the urogenital sinus External male genitalia Development of the Internal Female Genitalia  Development of the Ovaries Cortical cords break up (3months), If no SRY gene is present, the surrounding each of the germ cells primitive sex cords with an epithelial layer, forming degenerate. them into primordial follicles (a No testosterone→ no precursor to oocytes or egg cells). development of the mesonephric ducts No MIF → Cell types: paramesonephric/müllerian Granulosa cells ducts persist Theca cells Produce estrogen → stimulate the Epithelium of the indifferent formation of the external female gonad develop into cortical genitalia cords.  Development of the fallopian tubes, uterus, and vagina Step 1: Fusion of the paramesonephric ducts The ducts fuse in the midline adjacent to the urogenital sinus. Fused paramesonephric ducts differentiate into: Uterus Cervix Upper vagina The lateral ends of the paramesonephric ducts remain “unfused” → these will differentiate into the fallopian tubes  Development of the fallopian tubes, uterus, and vagina Step 2: Connection of the fused paramesonephric ducts to the urogrnital sinus. A thickening grows out of the superior portion of the urogenital sinus called the sinovaginal bulbs. Sinovaginal bulbs: Located between the fused paramesonephric ducts and the urogenital sinus Thicken and grow into a solid structure called the vaginal plate Vaginal plate elongates, connects developing uterus (from the paramesonephric ducts) to the vestibule (opening to outside the body, originating from the urogenital sinus) Hymen = meeting point of the vaginal plate and urogenital sinus. Development of the fallopian tubes, uterus, and vagina Development of the fallopian tubes, uterus, and vagina  Development of the External Genitalia Identical until about the 9 week, developing in the th cloaca membrane. Mesenchymal stem cells migrate from the primitive streak to cloaca membrane to form: 2 cloacal folds which fuse to form the genital tubercle Urethral folds Genital swellings develop either side of the urethral folds.  The Male External Genitalia Testosterone drives the development. The genital tubercle grows rapidly, elongating to form the glans penis. The urethral folds are pulled with it, forming the shaft of the penis, and the two folds fuse at around 4 months of gestation to form the urethra. The genital swellings move caudally and fuse, becoming the scrotum.  The Female External Genitalia No rapid elongation of the genital tubercle, grows slightly to become the clitoris. Without the elongation of the genital tubercle, the urethral folds do not stretch and fuse, and go on to form the labia minora, mons pubis Genital swellings are static, develop into the labia majora.  The Gubernaculum A fibrous tissue that retracts the gonads from the lumbar region where they are formed to their correct position. It does this by having one end attached to the gonad, and the other to the genital swellings (precursors to the scrotum or the labia majora).  Gubernaculum in Males It guides the testes through the inguinal canal and into the scrotum. The testes retain their original blood and lymphatic drainage, through the descent. The testicular arteries insert into the abdominal aorta, drains into the para-aortic lymph nodes. The gubernaculum remains postnatally as the scrotal ligament.  Gubernaculum in Females Ovaries descend in similar path, retain their blood and lymphatic supply from their original position. Developing uterus prevents ovaries descending into the inguinal canal. Gubernaxulum fuses with the uterus and degenerates into 2 ligaments of the ovaries: The ovarian ligament, which attaches the ovary to the uterus. The round ligament, which connects the uterus to the labia majora.  Developmental Anomalies of the Reproductive System Genital Anomalies - Males Hypospadia – Ventral opening of urethra Cryptorchidism  Müllerian anomalies Abnormal fusion of the müllerian/paramesone phric ducts can result in a variety of uterine, cervical, and vaginal anomalies. Usually asyptomatic , may present with infertility and menstrual issues Hymen anomalies  Disorders of Sexual Development A group of conditions characterized by atypical sexual development in an individual, which may involve abnormalities in the structure and/or function of the internal reproductive organs and/or external genitalia. Congenital adrenal hyperplasia: Increased formation of male sexual hormones (androgens) with virilization of the external female genitals. Characterized by low levels of cortisol, high levels of ACTH, and adrenal hyperplasia. Androgrn sensititvity syndrome Aromatase deficiency  DSDs 5α-reductase deficiency Pure gonadal deficiency Klinefelter syndrome Turner syndrome Ovotesticular disorder of sex development (formerly called "true hermaphroditism")