Embryogenesis of urinary system & reproductive duct
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Questions and Answers

What primarily drives the differentiation of embryonic structures into male external genitalia?

  • Progesterone
  • Testosterone and dihydrotestosterone (correct)
  • Follicle-stimulating hormone
  • Estrogen

    • Which embryonic structure differentiates into the glans penis in males?

  • Urogenital sinus
  • Urogenital folds
  • Labioscrotal swelling
  • Genital tubercle (correct)

    • What is the female equivalent of the bulbar urethral glands in males?

  • Bartholin glands
  • Greater vestibular glands (correct)
  • Urethral glands
  • Skene glands

    • During which weeks does the development of the urogenital sinus occur?

    <p>4-6 weeks</p> Signup and view all the answers

    What is the role of estradiol during the differentiation of external genitalia in females?

    <p>To drive the differentiation of female external genitalia</p> Signup and view all the answers

    What structures are formed in relation to the nephrogenic cord during embryo development?

    <p>Gonads and mesonephric duct</p> Signup and view all the answers

    Which embryonic structure is known as the first excretory organ in humans?

    <p>Pronephros</p> Signup and view all the answers

    At which stage of kidney development does the metanephros appear?

    <p>Final stage</p> Signup and view all the answers

    What divides the cloaca during embryonic development?

    <p>Urorectal septum</p> Signup and view all the answers

    Which part of the urogenital sinus is further subdivided into the vesicourethral canal?

    <p>Cranial part</p> Signup and view all the answers

    What is the fate of the pronephros as kidney development progresses?

    <p>It degenerates</p> Signup and view all the answers

    Which duct persists from the pronephros and is later integrated into the mesonephros?

    <p>Pronephric duct</p> Signup and view all the answers

    Where does the mesonephros arise during embryonic development?

    <p>Thoracolumbar region</p> Signup and view all the answers

    What is the initial location of the kidneys during development?

    <p>Pelvic region</p> Signup and view all the answers

    What happens to the original blood supply to the kidneys during their ascent?

    <p>It degenerates and is replaced by new vessels</p> Signup and view all the answers

    What type of kidney anomaly is characterized by an absence of kidney?

    <p>Agenesis</p> Signup and view all the answers

    From which embryological tissue does the adrenal cortex develop?

    <p>Intermediate mesoderm</p> Signup and view all the answers

    What are the characteristics of cystic kidney dysplasia?

    <p>Kidney with numerous cysts and enlargement</p> Signup and view all the answers

    What condition occurs when a kidney fails to ascend during embryonic development?

    <p>Pelvic kidney</p> Signup and view all the answers

    What determines the phenotypic sex during typical sex development?

    <p>Gonadal sex</p> Signup and view all the answers

    Which congenital anomaly results in the presence of an additional kidney?

    <p>Supernumerary kidney</p> Signup and view all the answers

    During which week of gestation does the first indication of primitive gonad development appear?

    <p>4th week</p> Signup and view all the answers

    What developmental change occurs to the ureters during bladder formation?

    <p>They move laterally and proximally</p> Signup and view all the answers

    What is primarily responsible for the differentiation of testes in male individuals?

    <p>SRY gene</p> Signup and view all the answers

    What do primordial germ cells (PGCs) eventually give rise to?

    <p>Gametes (sperm and oocyte)</p> Signup and view all the answers

    Which anomaly occurs when the ureteric bud crosses the central plane of the kidney?

    <p>Crossed ectopia</p> Signup and view all the answers

    What results from the secretion of Mullerian inhibitory factor (MIF)?

    <p>Suppression of paramesonephric duct differentiation</p> Signup and view all the answers

    Which type of kidney anomaly is characterized by a small size and underdeveloped structures?

    <p>Hypoplasia</p> Signup and view all the answers

    Where does the migration of primordial germ cells take place?

    <p>From the yolk sac to the urogenital ridge</p> Signup and view all the answers

    What are the undifferentiated gonads described as during the indifferent stage?

    <p>Nonbinary and bipotent</p> Signup and view all the answers

    Which gene is associated with the development of ovaries in the absence of a Y chromosome?

    <p>WNT4 gene</p> Signup and view all the answers

    What are the structures called that are involved in the development before sex differentiation occurs?

    <p>Wolffian and Müllerian ducts</p> Signup and view all the answers

    What role does hormonal stimulation play in sex development?

    <p>Secretion of hormones by developing gonads</p> Signup and view all the answers

    What is a key function of the mesonephros during development?

    <p>Contributes to the male genital system</p> Signup and view all the answers

    At what stage does the metanephros begin to develop?

    <p>Starting in the 5th week of development</p> Signup and view all the answers

    What ultimately becomes the cells making up the nephrons in the metanephros?

    <p>Metanephric blastema</p> Signup and view all the answers

    Which structures are formed from the ureteric buds in the metanephros?

    <p>Renal pelvis and collecting tubules</p> Signup and view all the answers

    What is the primary process that allows the growth of metanephric mesoderm and metanephric blastema?

    <p>Reciprocal induction</p> Signup and view all the answers

    What occurs to the mesonephros by the end of the second month?

    <p>It undergoes complete degeneration</p> Signup and view all the answers

    Which of the following structures does NOT originate from the mesonephros?

    <p>Minor calyces</p> Signup and view all the answers

    What is the primary role of Bowman's capsules during the mesonephros phase?

    <p>To filter blood in the absence of other structures</p> Signup and view all the answers

    Which structure is associated with the degeneration of the mesonephros?

    <p>Allantois</p> Signup and view all the answers

    What is the first major interaction that occurs in the development of the metanephros?

    <p>Development of the ureteric bud</p> Signup and view all the answers

    What feature primarily facilitates the descent of the testes through the inguinal ring into the scrotum?

    <p>The gubernaculum</p> Signup and view all the answers

    Which of the following structures undergoes breakdown during male embryonic development, leading to the formation of the primitive urethral folds?

    <p>Urogenital membrane</p> Signup and view all the answers

    At what point in gestation is the descent of gonads expected to be complete?

    <p>Week 33</p> Signup and view all the answers

    What happens to the genital tubercle in male embryonic development?

    <p>It develops into the glans penis</p> Signup and view all the answers

    What structure do the right and left genital swellings fuse to form in males?

    <p>The scrotum</p> Signup and view all the answers

    What is the medial part of the urogenital ridge responsible for developing?

    <p>Genital system</p> Signup and view all the answers

    From which embryonic tissue does the urinary system primarily develop?

    <p>Intermediate mesoderm</p> Signup and view all the answers

    What is the term for the longitudinal elevation of mesoderm that forms along the dorsal body wall?

    <p>Urogenital ridge</p> Signup and view all the answers

    At what week of embryonic development does the formation of the urinary system begin?

    <p>4th week</p> Signup and view all the answers

    Which part of the urogenital ridge is responsible for the development of the urinary system?

    <p>Nephrogenic cord</p> Signup and view all the answers

    What do precursor cells migrate from during the formation of the urinary system?

    <p>Cranial to caudal end</p> Signup and view all the answers

    What structure further delineates the genital system from the urinary system in the urogenital ridge?

    <p>Nephrogenic cord</p> Signup and view all the answers

    What is the function of the kidneys as they develop and migrate?

    <p>To filter waste and produce urine</p> Signup and view all the answers

    What drives the differentiation of male internal organs from the mesonephric ducts?

    <p>Testosterone</p> Signup and view all the answers

    Which of the following ducts gives rise to the female internal sex organs?

    <p>Paramesonephric ducts</p> Signup and view all the answers

    What prevents the differentiation of the mesonephric ducts in female individuals?

    <p>Presence of testosterone</p> Signup and view all the answers

    Which hormone is primarily responsible for the differentiation of female external genitalia?

    <p>Estrogen</p> Signup and view all the answers

    What is the role of dihydrotestosterone in embryonic development?

    <p>Drives the differentiation of male external genitalia</p> Signup and view all the answers

    Which of the following structures degenerates in male individuals due to the influence of testosterone?

    <p>Paramesonephric ducts</p> Signup and view all the answers

    What begins the differentiation of sex organs in males starting from the 7th week?

    <p>Development of mesonephric ducts</p> Signup and view all the answers

    Which embryonic structure acts as the precursor to male internal sex organs?

    <p>Mesonephric ducts</p> Signup and view all the answers

    What is the primary differentiating factor for the development of internal organs in females?

    <p>Absence of MIF</p> Signup and view all the answers

    Which of the following statements is correct regarding the differentiation of sex organs?

    <p>Testosterone is essential for the differentiation of male internal organs.</p> Signup and view all the answers

    What is the role of the SRY gene during sex development?

    <p>It stimulates the differentiation of the testes in male individuals.</p> Signup and view all the answers

    Which embryonic structure gives rise to the primordial germ cells?

    <p>Yolk sac</p> Signup and view all the answers

    Which structure supports the development of the genital ridge?

    <p>Celomic epithelium</p> Signup and view all the answers

    What occurs during the differentiation of embryonic structures in male individuals?

    <p>Development of the prostate gland</p> Signup and view all the answers

    Which hormone is crucial for the differentiation of female external genitalia?

    <p>Estradiol</p> Signup and view all the answers

    What effect does Mullerian inhibitory factor (MIF) have during sex development?

    <p>Inhibits the differentiation of the paramesonephric ducts.</p> Signup and view all the answers

    What does the presence of the WNT4 gene indicate in sex development?

    <p>Differentiation into ovaries in females.</p> Signup and view all the answers

    Which structure develops into the bulbourethral glands in males?

    <p>Urogenital sinus</p> Signup and view all the answers

    Which component is responsible for the differentiation of bipotent gonads into either testes or ovaries?

    <p>Chromosomal sex present at fertilization</p> Signup and view all the answers

    What is the time frame for the start of differentiation of external genitalia?

    <p>Week 9</p> Signup and view all the answers

    Which embryonic structure gives rise to the glans penis in males?

    <p>Genital tubercle</p> Signup and view all the answers

    At what week does the first indication of primitive gonad development appear?

    <p>4 weeks</p> Signup and view all the answers

    The development of which female structure does the absence of dihydrotestosterone contribute to?

    <p>Labia majora</p> Signup and view all the answers

    What structures include the mesonephric ducts and paramesonephric ducts during early development?

    <p>Primitive urinary system</p> Signup and view all the answers

    Which of the following is an accurate sequence of embryonic development as it relates to sex differentiation?

    <p>Chromosomal sex → Gonadal sex → Phenotypic sex</p> Signup and view all the answers

    What is the fate of the urogenital folds during male differentiation?

    <p>Develop into the ventral penile shaft</p> Signup and view all the answers

    Which male external genitalia structure is formed under the influence of testosterone?

    <p>Scrotum</p> Signup and view all the answers

    What is the primary source from which gonads develop?

    <p>Intermediate mesoderm</p> Signup and view all the answers

    What does the urogenital sinus become in both sexes?

    <p>Bladder and urethra</p> Signup and view all the answers

    Which external genitalia structure is a derivative of the labioscrotal swelling in males?

    <p>Penile urethra</p> Signup and view all the answers

    Study Notes

    Urogenital Ridge Development

    • The nephrogenic cord, extending from the cervical to sacral region, forms several structures: excretory renal tubules (para-, meso-, and metanephric), the nephric duct (later mesonephric duct), the paramesonephric duct, and the gonad.
    • The cloaca, divided by the urorectal septum, forms the primitive rectum and the primitive urogenital sinus (subdivided into the vesicourethral canal and the definitive urogenital sinus).

    Kidney Development Stages

    • Three successive kidneys develop from the nephrogenic cord: pronephros, mesonephros, and metanephros, with the metanephros becoming the permanent kidney.

    Pronephros

    • The first rudimentary embryonic excretory organ, arising in the cervical region during weeks 3-4.
    • Composed of a pronephric duct and nephric tubules; has temporary excretory function.
    • Degenerates as the mesonephros develops; its duct persists, becoming the mesonephric duct.

    Mesonephros

    • The second embryonic excretory organ, developing caudally to the pronephros.
    • Arises in the thoracolumbar region during the 4th week.
    • Consists of S-shaped tubules draining into the mesonephric duct (Wolffian duct), forming Bowman's capsule.
    • Most tubules disappear, some contributing to the male genital duct system (epididymis, ductus deferens, seminal vesicle, ejaculatory duct).
    • Functions until the end of the second month, then degenerates. Blood is filtered through glomerular capillaries in Bowman's capsule, traveling down the mesonephric tubule to the cloaca and allantois.

    Metanephros

    • The third embryonic excretory organ, developing caudally to the mesonephros and persisting as the permanent kidney.
    • Arises during the 5th week, canalization complete by the 10th week; matures until weeks 35-36.
    • Develops from the ureteric bud (outgrowth of the mesonephric duct) and the metanephric blastema (condensation of intermediate mesoderm). Reciprocal induction between these structures promotes growth via growth factors.
    • The metanephric blastema forms nephrons. The ureteric bud forms the ureter, renal pelvis, major and minor calyces, and collecting tubules.

    Urinary Bladder Development

    • Initially, the Wolffian ducts and ureteric buds enter the urinary bladder base.
    • Later, they become independent, with ureters moving laterally and proximally, and Wolffian ducts dorsally and caudally.
    • Specialized transitional epithelium develops from the urogenital sinus endoderm.

    Kidney Relocation and Vascularization

    • Kidneys initially are in the pelvic region; they ascend to the abdomen during development. Failure to ascend results in pelvic kidney.
    • The original blood supply degenerates as kidneys ascend; new vessels from the aorta become the mature renal arteries. Persistent original vessels may form additional renal arteries or veins.

    Congenital Anomalies

    • Agenesis (absence of kidney) – bilateral agenesis is incompatible with life.
    • Hypoplasia (underdeveloped kidney)
    • Supernumerary kidney
    • Double kidney
    • Renal dysplasia (aplastic kidney with no parenchyma or cystic kidney with many cysts)
    • Positional anomalies (pelvic kidney, crossed ectopia)

    Adrenal Gland Origin

    • The adrenal medulla derives from neural crest cells near the dorsal aorta.
    • The adrenal cortex develops from the intermediate mesoderm.

    Typical Sex Development Overview

    • Chromosomal sex determines gonadal sex, which determines phenotypic sex.
    • Up to 6 weeks, development is nonbinary: undifferentiated gonads, mesonephric (Wolffian) and paramesonephric (Müllerian) ducts, urogenital sinus, and genital tubercle, swellings, and folds.

    Indifferent Stage of Gonad Development

    • Gonads develop from intermediate mesoderm, coelomic epithelium, and primordial germ cells.
    • The genital ridge appears around week 4, formed by mesoderm condensation and coelomic epithelium proliferation.

    Primordial Germ Cells (PGCs)

    • Originate in the yolk sac, migrating through the vitelline duct to invade the urogenital ridge.
    • Give rise to sperm and oocytes.

    Genetic Influence on Gonad Differentiation

    • Genes at fertilization determine gonad differentiation (testes or ovaries).
    • The SRY gene on the Y chromosome encodes the testis-determining factor (TDF), stimulating testes differentiation.
    • Absence of SRY and the presence of WNT4 lead to ovary development.
    • Müllerian inhibitory factor (MIF), from Sertoli cells, suppresses paramesonephric duct differentiation in males.

    Hormonal Stimulation in Gonad Development

    • Developing gonads secrete hormones influencing further development.

    External Genitalia Differentiation

    • Begins in week 9, driven by estradiol and dihydrotestosterone (DHT) presence or absence.
    • Testosterone converts to DHT (via 5α-reductase), differentiating male genitalia, glands.
    • Estradiol and absence of DHT differentiate female genitalia.

    External Genitalia Development Summary

    • The genital tubercle forms the glans penis/clitoris, corpus cavernosum/vestibular bulbs, and corpus spongiosum.
    • The urogenital sinus becomes the urethra, bladder, and distal vagina/vestibule.
    • Urogenital folds become the ventral penile shaft/labia minora.
    • Labioscrotal swellings form the scrotum/labia majora.

    Embryological Development of the Urogenital System

    • The urinary system develops from intermediate mesoderm and the primitive cloaca, beginning at the 4th week of embryonic development. Precursor cells migrate cranially to caudally.
    • The intermediate mesoderm forms the urogenital ridge after embryo folding. The medial part forms the genital ridge (genital system), and the lateral part forms the nephrogenic cord (urinary system).
    • Typical sex development follows a sequence: chromosomal sex determines gonadal sex, which determines phenotypic sex. Up to 6 weeks, development is identical and non-binary, including undifferentiated gonads, mesonephric (Wolffian) and paramesonephric (Müllerian) ducts, the urogenital sinus, and genital tubercle, swellings, and folds.

    Gonad Development

    • Gonads develop from intermediate mesoderm, coelomic epithelium, and primordial germ cells (PGCs).
    • PGCs, originating in the yolk sac, migrate through the vitelline duct to invade the urogenital ridge, forming gametes.
    • Gonadal differentiation depends on genetic factors: the presence of the SRY gene on the Y chromosome leads to testis differentiation; its absence, combined with the WNT4 gene, leads to ovary differentiation.

    Hormonal Influence on Sexual Differentiation

    • The SRY gene encodes a testis-determining factor (TDF).
    • The presence of testosterone (from Leydig cells) promotes mesonephric duct differentiation into male internal organs, and dihydrotestosterone leads to male external genitalia.
    • Müllerian inhibiting factor (MIF), produced by Sertoli cells, suppresses paramesonephric duct development in males.
    • In females, the absence of MIF allows paramesonephric duct development into female internal organs, and estrogen drives female external genitalia development.

    Ductal Sex Differentiation

    • Paramesonephric ducts develop into the fallopian tubes, uterus, and proximal vagina in females; they degenerate in males. Differentiation is driven by estrogens and suppressed by MIF.
    • Mesonephric ducts develop into male internal organs (seminal vesicles, ejaculatory ducts, epididymis, and ductus deferens) in males; they degenerate into vestigial remnants in females. Testosterone drives their differentiation.

    External Genitalia Differentiation (Week 9 Onwards)

    • Driven by the presence/absence of estradiol and dihydrotestosterone.
    • In males, testosterone converts to dihydrotestosterone (via 5α-reductase), leading to male external genitalia, bulbourethral glands, and prostate gland development.
    • In females, estradiol and the absence of dihydrotestosterone lead to female external genitalia.

    External Genitalia and Urogenital Structures

    • The genital tubercle forms the glans penis (male) or clitoris (female).
    • The urogenital sinus forms the bladder and urethra (both sexes), prostate gland (male), distal vagina and vestibule (female).
    • Urogenital folds form the ventral penile shaft and penile urethra (male) or labia minora (female).
    • Labioscrotal swellings form the scrotum (male) or labia majora (female).

    Descent of Gonads

    • Testes descend caudally from their initial retroperitoneal location through the inguinal ring into the scrotum.
    • Ovaries descend caudally to the pelvic rim. This descent, more prominent in males, is facilitated by the gubernaculum. Descent is generally complete by week 33.

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