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Embryology > Lect. 5: Genitourinary System > Flashcards

Lect. 5: Genitourinary System Flashcards

1
Q

From what germ layer does the urinary system develop?

A

intermediate mesoderm (between paraxial mesoderm and lateral plate mesoderm)

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2
Q

What is the intermediate mesoderm called once it is arranged cranially to caudally?

A

urogenital ridge

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3
Q

From which portion of the urogenital ridge does the gonadal and genital system develop?

A

gonadal and genital system form from central and medial portion of the urogenital ridge

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4
Q

Kidneys develop in how many successive stages?

A

three

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5
Q

Name the three successive stages of kidney development.

A

1) pronephros
2) mesonephros
3) metanephros

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6
Q

What is the direction of kideny development?

A

renal development is cranial to caudal wave down intermediate mesoderm

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7
Q

Describe the pronephros. What is its lifespan?

A

Pronephros is the first stage of kidney that develops from the upper portion of the urogenital ridge in the first few days of the 4th week. It is non-functional (no filtration occurs) and disappears by the end of the 4th week. (2-4 day lifespan)

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8
Q

Describe the mesonephros. What is its lifespan?

A

Mesonephros is the second of the 3 kidneys. It develops from cranial to caudal as the pronephros is disappearing. Functional by 5th week and stays functional until around the 9th week when it regresses.

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9
Q

What are the two portions of the mesonephros?

A

1) basic nephron system (filtration)

2) mesonephric duct (on lateral side of urogenital ridge that drains into cloaca)

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10
Q

What is the metanephros? When does it begin to function?

A

Metanephros is the final of the 3 kindeys. (This is the kidney you are born with). It begins to function in the 2nd trimester (by 10th week).

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11
Q

What drains into the mesonephric duct?

A

all of the tiny mesonephros ductules

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12
Q

What is the other name of the mesonephric duct?

A

Wolffian duct

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13
Q

When does the metanephros develop?

A

begins to develop as mesonephros is functional (around the 5th week, the ureteric bud forms)

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14
Q

Describe the formation of the metanephros.

A

At the most distal end of the mesonephric duct, the ureteric bud develops and the metanephric mass (from intermediate mesoderm) develops as a cap over it.

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15
Q

What does the ureteric bud give rise to?

A

ureteric bud lengthens and subdivides to form the drainage system (“just the plumbing”): calyces, pelvis, ureter

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16
Q

Why is cross-induction important in the development of the kidney?

A

ureteric bud must meet up with metanephric blastema for a kidney to form–this will result in the lack of a kidney! (quite common and asymptomatic)

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17
Q

What is the most common defect of the ureteric bud?

A

double ureter

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18
Q

What are the symptoms of a double ureter?

A

Asymptomatic, simply a bifid or doubling of the ureteric bud. With a bifid ureter, one is usually smaller than another.

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19
Q

What is an ectopic ureter?

A

the ureter is formed and misdirects away from the bladder

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20
Q

What are the most common female ectopic sites for a ectopic ureter?

A

vagina, urethra, or into the vestibule

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21
Q

What are the most common male ectopic sites for an ectopic ureter?

A

prostatic urethra or neck of the bladder

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22
Q

What is the major problem with ectopic ureters?

A

incontinence

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23
Q

When does the metanephric mass begin to form? What does it eventually develop?

A

The metanephric blastema begins to form in the 5th week and forms the cortex/medullary portion of the kidney around the 8th-9th week (forms the nephrons and filtration system).

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24
Q

Where does the ureteric bud join with the metanephric mass?

A

distal ends of ureteric buds are collecting ducts that hook up to the distal convoluted tubule

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25
Q

What is a unilateral renal agenesis? IN whom and where is this most common?

A

missing a kidney (most common in males on LEFT side)

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26
Q

What is unilateral hypoplastic kidney? What are its symptoms?

A

kidney does not fully develop (never preceeds to develop all of necessary ductules and nephrons). It is asymptomatic.

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27
Q

What is a supernumerary kidney?

A

an extra kidney

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28
Q

What is polycystic kidney disease? What are the symptoms?

A

very severe autosomal genetic defect where the ends of collecting ducts dilate and form cysts (renal failure early after birth and quick fetal death)

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29
Q

What is bilateral renal agenesis?

A

bilateral loss of kidneys

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30
Q

Bilateral renal agenesis is the most common cause of what?

A

most common cause of oligohydramnios (low volume of amniotic fluid). Fetus consumes fluid but cannot excrete it. This reduces amount of amniotic fluid so fetus is not protected from external pressures

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31
Q

What is associated with bilateral renal agenesis?

A

Potter’s sequence (from oligohydramnios leading to external pressure)

1) Low set ears and flattened face
2) Club hand (short and stubby)
3) Hypoplastic lungs

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32
Q

What are the positional changes of the kidneys?

A

kidneys form very low down in the trunk (lower lumbar pelvic region) and they must “ascend” by undergoing a positional change where they come to rest in the dorsal abdominal wall of T11-12 through L1-L2 vertebral levels.

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33
Q

Do the kidneys really ascend?

A

As kidneys form, the pelvis and lower trunk grows inferiorly under the kidnays so that the kidneys don’t really move upward all that much.

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34
Q

What is a pelvic kidney?

A

one kidney is left behind and held in the pelvis (the other kidney ends up in the right spot). This is asymptomatic unless it rotates and the ureter gets twisted

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35
Q

What is a horse-shoe kidney? What does it get stuck on?

A

both kidneys stay in pelvis and the lower poles meet in midline and fuse (when they try to ascend they get caught under the inferior mesenteric artery)

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36
Q

Where does the urogenital sinus come from?

A

the urorectal septum divides the cloaca into the anorectal canal (dorsal) and urogenital sinus (ventral)

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37
Q

What does the urogenital sinus form?

A

bladder, urethra, prostate gland, and lower vagina/vestibule

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38
Q

How do the male and female urethras differ?

A

most of male, but ectoderm forms most distal end of the penile urethra

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39
Q

What is the origin of the relationship between the ureter and vas deferens?

A

In development, the 2 mesonephric ducts and the ureteric buds get absorbed into the posterior wall of the bladder. Ureters raise up in higher position as mesonephric ducts move caudally towards the urethra (so it is looped over the ureter)

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40
Q

What is the relationship between the developed ureter and vas deferens?

A

in males, the mesonephric duct is the vas deferens and it loops superior to the ureter and drops down and drains into the prostatic urethra

41
Q

From what do the gonads develop?

A

gonad develops from the medial side/central part of the intermediate mesoderm

42
Q

What are transported into the gonads around the 4th-6th weeks?

A

primordial germ cells (fore-runners of male and female gametes) must be moved into the developing gonads

43
Q

Where do the primordial germ cells originate?

A

yolk sac (from extraembryonic mesoderm)

44
Q

Where is extraembryonic mesoderm?

A

cells that line yolk sac posteriorly around the allantois

45
Q

How long does it take the primordial germ cells to travel to the gonads?

A

takes around 2 weeks for PGCs to travel from yolk sac through the dorsal body wall through the connecting stalk and migrate bilaterally into the gonads (at urogenital ridge)

46
Q

What do the PCGs do when they arrive in the female gonad (ovary)?

A

PGCs immediately go through meiosis I

47
Q

What do the PCGs do when they arrive in the male gonad (testis)?

A

PCGs go dormant and do not perform meiosis until puberty, then they undergo meiosis

48
Q

What is an indifferent gonad?

A

from 4th-7th week, you cannot tell whether the gonad will be a male or female structure

49
Q

What are the 3 basic components of the indifferent gonad?

A

1) primordial germ cells
2) Primary sex cords (CT bands growing out of surface epithelium)
3) Two duct system

50
Q

Describe the definitive development of sex cords.

A

sex cords have definitive development
Male: testosterone gives signal to become seminiferous tubules
Female: primordial follicles (lack of testosterone causes the follicles NOT to elongate, regress and break up into segments

51
Q

What are the two ducts of the two duct systems?

A

1) Mesonephric (Wolffian) Duct: male genital tract–originally from second kidney duct system
2) Paramesonephric (Mullerian) Duct: female genital tract–from first kidney duct system

52
Q

What happens to the Wolffian Duct in females?

A

it degrades

53
Q

What happens to the indifferent gonad at week 7-9 if the Y-chromosome is present?

A

there is a critical series of events that must occur to form a male:

1) Y chromosome releases protein called Testis Determining Factor (TDF)
2) Leydig (secrete testosterone) and Sertoli cells (secretes Mullerian-Inhibiting Factor) developed by 8th-9th week
3) DHT released

54
Q

What is the function of testosterone?

A

Testosterone drives male system development

55
Q

What is the function of MIF?

A

MIF shuts down Mullerian Duct so that males do not develop female genital tract

56
Q

What is required to convert testosterone to DHT?

A

5 alpha-reductase 2 enzyme

57
Q

What is the role of DHT?

A

formation of external genitalia

58
Q

Are male or female newborn genital defects more common?

A

male (due to lack of 5a-reductase 2 enzyme, low levels of MIF, etc.)

59
Q

What happens to the indifferent gonad at week 7-9 if the Y-chromosome is absent?

A

No TDF, so ovarian development (much easier to make ovary than testis)

60
Q

What all happens with female gonad development?

A

Regression of mesonephric, break down of sex cords into follicles (with oocytes), and the Mullerian Duct is retained

61
Q

What will occur if male has low levels of MIF?

A

you will get a male with some female characteristics (ex. clitoris, rudimentary vagina, etc)

62
Q

What happens if you do not have enough 5alpha-reductase 2 enzyme?

A

you will not get DHT, so you will have male born with microgenitalia (small penis/scrotum) or indifferent genitalia

63
Q

Do males completely get rid of the Mullerian duct?

A

no, there are tiny remnants (ex. utriculus prostaticus)

64
Q

What all forms from the mesonephric ducts?

A

epididymis, vas deferens, serminal vesicle

65
Q

What all forms from the paramesonephric ducts (mesoderm)?

A

uterine tube, uterus, upper portion of vagina

66
Q

What structures of the female genitalia form from the urogenital sinus (endoderm)? What drives this development?

A

labia, clitoris, lower portion of vagina/hymen (estrogen drives this development)

67
Q

Why is the vagina a “dual developed structure”?

A

upper portion formed by mesoderm, lower portion formed by endoderm

68
Q

Name 2 examples of Wolffian ducts in females.

A

1) Epoophoron (in broad ligament)

2) Gartner’s cyst (close to vaginal wall)

69
Q

Describe the formation of structures from the paramesonephric ducts.

A

Paramesonephric ducts descend and fuse (forming primordial uterus, cervix and upper vagina)

70
Q

What is the tubercle of the vagina?

A

lower portion of vagina that is formed by the endoderm

71
Q

What is the most common uterine abnormality?

A

bicornate uterus (2 paramesonephric ducts that stayed separate distally)

72
Q

When is the indifferent stage in the external genitalia?

A

takes around 11-12 weeks to be sure of the gender of the child

73
Q

What are the 3 components to the indifferent stage of external genitalia?

A

1) genital tubercle
2) genital swellings
3) urethral groove

74
Q

What do the genital swellings form in males?

A

scrotum (fused at midline raphe because swellings fuse at midline)

75
Q

What does the genital tubercle form in males?

A

glans and part of the shaft

76
Q

What completes the formation of the ventral shaft of the penis?

A

fusion of the genital folds

77
Q

What does the genital tubercle form in females?

A

clitoris

78
Q

What do the genital swellings form in females?

A

labia majora (DO NOT fuse in midline)

79
Q

What do the urogenital folds form in females?

A

labia minora (DO NOT FUSE IN MIDLINE)

80
Q

What is the most common male newborn external genitalia defect?

A

failure of urogenital folds to fuse (urethra not closed off so opens in weird places along the midline of VENTRAL shaft or scrotum)

81
Q

Are dorsal defects of the penis common? What is this called?

A

NO, very rare. This is called epispadias

82
Q

What often accompanies epispadias?

A

exstrosphy of the bladder (failure of lateral body folds to fuse causes an “open bladder” so the lumen of the bladder is protruding out of the stomach)

83
Q

When does testis/ovary descent occur?

A

in 3rd trimester

84
Q

Where does testis descend?

A

goes through lateral body wall, through inguinal canal, and into the scrotum

85
Q

What two events precede testicular descent?

A

1) an extension of the parietal peritoneum (processus vaginalis) and gubernaculum travel ahead of the testis
2) processus obliterates and forms a postnatal peritoneal remnant in the scrotum called to tunica vaginalis

86
Q

What is the gubernaculum?

A

a CT band that descends from testes into peritoneum (acts like GPS of testes, and testes follows its track)

87
Q

Describe the formation of the tunica vaginalis.

A

processus vaginalis is patent until around the 8-9th month when it scars down and a piece of it (double wall inclosure) is grabbed by the testis (and this tunica vaginalis is a serous membrane that reduces friction!!)

88
Q

What can occur when a newborn has a patent processus vaginalis?

A

congenital indirect inguinal hernia

89
Q

What happens in male if tunica vaginalis starts accumulating fluid?

A

hydrocele

90
Q

What is female intersexuality? What commonly causes it?

A

Female pseudohermaphroditism (congenital adrenal hyperplasia causes too much androgen release and females have masculinization of the external genitalia)

91
Q

What is the genotype of a person with female intersexuality? Describe their internal genitalia.

A

These are 46, XX women with ovarian internal genitalia

92
Q

What is male intersexuality? What commonly causes it?

A

male pseudohermaphroditism most commonly caused by inadequate production of testosterone, MIF, and 5alpha-reductase deficiency. These men have various stages of stunted development of male external genitalia (female-like external genitalia)

93
Q

What is the genotype of a person with male intersexuality? Describe their internal genitalia.

A

46, XY with testicular internal genitalia

94
Q

What is another name for testicular feminization syndrome?

A

androgen insensitivity

95
Q

What external genitalia are found in individuals with androgen insensitivity?

A

female external genitalia with rudimentary vagina

96
Q

What is the genotype of a person with androgen insensitivity?

A

46, XY

97
Q

What internal genitalia are found in individuals with androgen insensitivity?

A

develops testes that are located in labia majora or inguinal canal (these must be removed or they will become carcinomic)

98
Q

What is the external appearance of a person with androgen insensitivity?

A

normal-appearing female appearance and psychosocial orientation if female despite their genotype

Embryology (6 decks)

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