Embryology - Legends Flashcards

1
Q

When do the genitals first start developing?

A

Week 5-6

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2
Q

How do the genitals first appear?

A

As the genital or gonadal ridge. A thickening of the medial part of the mesonephros

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3
Q

What are the primitive sex cord?

A

Structures fromed from mesenchyme of Genital ridges.
They receive Germ cells from the yolk sac

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4
Q

How do germ cells reach the primitive sex cords?

A

In wk 6 germ cells migrate from the yolk sac –> Dorsal mesentery –> Primitive sex cords

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5
Q

What happens when germ cells migrate to the primitive sex chords?

A

They form a structure called the Indifferent Gonad

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6
Q

What happends after formation of the indifferent gonad?

A

Mesonephric epithelium invaginates to form the paramesonephric duct

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7
Q

Where is the paramesonephric duct found and where does it go?

A

Its lateral to the mesonephros and developing gonads.

The cranial end enters peritoneal cavity –> passes ventrally over mesonephric ducts –> enters dorsal wall of urogenital sinus

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8
Q

What happens to the indifferent Gonad?

A

Forms the testis

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9
Q

What happens to the mesonephric duct?

A

Forms:
- Epidydimis
- Vas Deferens
- Seminal Vescle

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10
Q

What happens to the paramesonephric duct?

A

Degenerates

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11
Q

What happens to the urogenital sinus?

A

Forms
Bladder
Urethra
Prostate

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12
Q

What gene is responsible for determining testes vs ovaries?

A

SRY (sex determing region Y) on the Y chromosome encodes for a protein called TDF (Testis determining factor) that triggers testes development

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13
Q

Describe the actions of SRY

A

Makes TDF –> Indifferent Gonad –> Testis

Found in Primordial Supporting Cells within the sex chords –> Sertoli cells

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14
Q

How are sertoli cells involved in development of the testes?

A

They’re created from Primordial Supporting Cells that express SRY

They secrete MIS (Mullerian Inhibiting Substance):
1) Paramesonephric duct degenerates
2) Mesenchymal cells between sex cords –> Leydig Cells

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15
Q

What do Leydig cells do to develop the individuals sex?

A

They produce testosterone –> masculine differentiation of mesonephric ducts and male external genitalia

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16
Q

So in wk 5 Primary sex cords, medulla and cortex of testes develop. Wk 6 germ cells are incorporated. Wk 7 TDF stimulates formation of seminiferous tubules.
What happens next?

A

Seminiferous tubules branch and the ends anastomose to form the rete testis

Tunica Albuginea replaces surface mesothelium

17
Q

What do the seminal vesicles develop from?

A

Caudal end of the mesonephric duct

18
Q

What does the prostate develop from?

A

The urethra, before that the urogenital sinus

19
Q

The gonads are required to descend, where do they originally form?

A

In the lumbar region

20
Q

Describe the descent of the testes?

A

Week 7 - T10

Week 12 - Deep inguinal ring

Week 39 (just before birth) - Enters scrotum

Testes are aided in their descent by the larger inguinal canal of males

21
Q

Whats the main developmental abnormality of the male genitalia?

A

Cryptorchidism aka testes absent from scrotum

22
Q

What are the possible reasons for cryptorchidism?

A

1) Undescended
2) Ectopic
3) Retractile testes
4) Absent testes

23
Q

What are the complications of cryptorchidism?

A

Infertility
Germ cell Tumours
Testicular Torsion

24
Q

How do we manage cryptorchidism?

A

Orchiopexy (surgically move the testes into the scrotum)