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Reproductive System > Embryology > Flashcards

Embryology Flashcards

1
Q

What happens in weeks 1 and 2 of gestation?

A

Blastocyst forming and implanting in the uterus, starts to form 3-layered embryo

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2
Q

What happens in week 3 of gestation?

A

Gastrulation
Neurulation
Somite formation

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3
Q

What happens in weeks 4-8 of gestation?

A

Organogenetic period

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4
Q

What happens from week 9 onwards of gestation?

A

Maturation of organ systems

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5
Q

What is the timeline of reproductive system organogenesis?

A

Reproductive system organogenesis occurs beyond 8 weeks and beyond the post-natal period, it is not complete when the child is born

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6
Q

What are the 3 initial sets of kidneys that develop in gestation?

A

Pronephros - first rudimentary kidney
Mesonephros - briefly functional kidney with ducts and primitive urethra
Metanephros - functional, in pelvic region

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7
Q

What does the cloaca divide to form?

A

Rectum and urogenital sinus

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8
Q

What does the mesonephric duct drain into?

A

Urogenital sinus

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9
Q

What does the urogenital sinus form later in development?

A

Urinary bladder, caudal end forms urethra

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10
Q

The epithelium of the mesonephros invaginates to form

A

a tube which then becomes the paramesonephric duct

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11
Q

What does the paramesonephric duct develop lateral to in development?

A

Developing gonads and mesonephric duct

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12
Q

Where does the cranial end of the paramesonephric duct open?

A

Into the peritoneal cavity

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13
Q

What happens to the mesonephros at week 6 of development?

A

Forms a long ovoid structure in association with the thoracic and upper lumbar vertebrae

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14
Q

The medial part of the mesonephric ridge thickens to form

A

a genital/gonadal ridge

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15
Q

At week 6, germ cells migrate from the yolk sax via the

A

dorsal mesentery, and embed into the primitive sex cords

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16
Q

What are the primitive sex cords formed from?

A

Mesenchyme of genital ridges

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17
Q

What is the indifferent gonad?

A

A gonad that has not developed into a definitive ovary or testis, there is no migration of germ cells at this stage and so no true gonads

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18
Q

What primitive structures are needed to form the reproductive system?

A 
Indifferent gonad 
Mesonephric duct (disappears in females)
Paramesonephric duct (disappears in males)
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19
Q

What happens to the indifferent gonad, mesonephric duct, paramesonephric duct and urogenital sinus in males?

A

Gonad forms testis
Mesonephric duct develops into the epididymis, vas deferens and seminal vesicle
Paramesonephric duct degenerates
Urogenital sinus forms bladder, urethra and prostate

20
Q

In the early stages of development, what is the only difference between the male and female embryo?

A

XY compared to XX

21
Q

What makes the indifferent gonad develop into a testis?

A

SRY on the sex-determining region of the Y chromosome encodes a protein called TDF (testis determining factor) which makes indifferent gonad develop into a testis

22
Q

What cells express the SRY gene?

A

Primordial sex cells within he sex cords of the indifferent gonad

23
Q

What do Sertoli cells secrete?

A

Mullerian Inhibiting Substance (MIS)

24
Q

What does MIS cause?

A

Paramesonephric duct to degenerate so only mesonephric duct remains
Also transorms mesenchymal cells between sex cords into Leydig cells which produce testosterone

25
Q

At what week of gestation does TDF stimulate the primary sex cords to extend into the medulla?

A

Week 7

26
Q

What gives rise to the interstitial cells of Leydig?

A

Mesenchyme between sex cords

27
Q

Male external genitalia is formed under the influence of what?

A

Testosterone

28
Q

In females, what happens to the indifferent gonad, mesonephric duct, paramesonephric duct and urogenital sinus?

A

Gonad forms ovary
Mesonephric duct degenerates
Paramesonephric duct forms Fallopian tube, uterus and cervix
Urogenital sinus forms bladder and lower part of vagina

29
Q

Why do females not express TDF?

A

Two X chromosomes so no SRY region (on Y chromosome) and no TDF

30
Q

How do the primordial follicles form?

A

Primordial germ cells bud off with a single surrounding layer of cortical cord cells

31
Q

How are additional follicles formed, once primordial follicles are formed?

A

Active mitosis of the primordial follicles

32
Q

By what month of development have all follicles formed?

A

7

33
Q

In what phase of meiosis are oocytes arrested in?

A

Prophase (first meiotic division)

34
Q

How many primordial follicles are present at birth?

A

2 million

35
Q

After puberty, how many follicles per cycle are developed?

A

12-15 follicles per 28 day cycle

36
Q

What causes the degeneration of the mesonephros and mesonephric duct?

A

Absence of testosterone

37
Q

What do the cranial and caudal ends of the paramesonephric duct become?

A

Cranial end becomes associated with the ovary

Caudal end becomes uterus and superior part of vagina

38
Q

In what region are gonads initially formed? What does this mean as development takes place?

A

Initially form in lumbar region

Positional changes occur as development takes place

39
Q

Where do the gonads descend to in the male and female?

A

Descend out of the abdomen through inguinal canal to the scrotum in males
Descend to pelvis in females

40
Q

What is the level of the testis at week 7 and week 12 of development?

A

Week 7 - level of T10

Week 12 - level of deep inguinal ring

41
Q

What is the level of the ovary at week 7 and week 12 of development?

A

Week 7 - level of T10

Week 12 - broad ligament

42
Q

What aspects of development are linked to the descent of the gonads?

A

Male - formation of the larger inguinal canal

Female - presence of round ligament and its passage through the inguinal canal

43
Q

What is cryptorchidism?

A

Absence of one or both of the testes from the scrotum

44
Q

What are the complications of cryptorchidism?

A

Infertility
Malignant transformation
Testicular torsion

45
Q

What is the treatment of cryptorchidism?

A

Orchiopexy

46
Q

What are the complications of remnants of the mesonephric duct in females?

A

Remnants can collect fluid which can compress the ovary (causing infertility) or interfere with implantation or childbirth

Reproductive System (33 decks)

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