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reproductive system 2 > Embryology > Flashcards

Embryology Flashcards

1
Q

When is the organogenetic period?

A

Weeks 4-8

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2
Q

When does maturation of organ systems occur?

A

Week 9 onwards

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3
Q

When does organogenesis of the reproductive system occur?

A

Extends beyond week 8 and even beyond the post-natal period

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4
Q

What system is the reproductive system linked closely to?

A

Urinary system (it forms a template for the reproductive system)

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5
Q

How many sets of kidneys develop?

A

3 sets

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6
Q

What is the first set of kidneys to develop?

A

Pronephros is the cervical region. They are vestigal

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7
Q

What is the second set of kidneys to develop?

A

Mesonephros in the thoracolumbar region. They are briefly functional

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8
Q

What is the last set of kidneys to develop?

A

Metanephros in the pelvic region. They are functional

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9
Q

What does the cloaca divide to form?

A

Rectum posteriorly and the urogenital sinus anteriorly

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10
Q

What does the mesonephric duct drain into?

A

The urogenital sinus

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11
Q

What does the urogenital sinus form?

A

The urinary bladder and the caudal end forms the urethra

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12
Q

What happens to the mesopnephros at about 6 weeks?

A

It forms a long ovoid structure in association with the thoracic and upper lumbar vertebra

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13
Q

What happens to the medial part of the mesonephric ridge?

A

It becomes thickened to form a genital/gonadal ridge

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14
Q

How are the indifferent gonads formed?

A

During week 6 germ cells migrate from the yolk sac, via the dorsal mesentery and embed into the primitive sex cords formed from the mesenchyme of the genital ridge

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15
Q

When are no gonads formed?

A

When there is failure of migration of germ cells to the genital ridge

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16
Q

How is the para-mesonephric duct formed?

A

Epithelium of the mesonephros invaginates to form a tube

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17
Q

Where does the paramesonephric duct develop?

A

Lateral to the developing gonads and mesonephric duct

18
Q

What is the structure of the paramesonephric duct?

A
  • Funnel shaped cranial end opens into peritoneal cavity
  • Caudally, cross ventral to mesonephric ducts
  • This projects into dorsal wall of urogenital sinus
19
Q

What is the male reproductive system formed from?

A
  • Gonad forms testis
  • Mesonephric duct develops into epididymis, vas deferens, seminal vesicle
  • Urogenital sinus forms bladder, urethra and prostate
20
Q

What is the female reproductive system formed from?

A
  • Gonad forms the ovary
  • Paramesonephric duct forms fallopian tube, uterus, cervix part of vagina
  • Urogenital sinus forms bladder and lower part of vagina
21
Q

What happens to the paramesonephric duct in the male?

A

Degenerates

22
Q

What happens to the mesonephric duct in the female?

A

Degenerates

23
Q

How does the indifferent gonad know whether to develop into a testes or an ovary?

A
  • SRY gene is expressed in certain cells (such as the primordial supporting cells within the sex cord) and it encodes for a protein called TDF
  • TDF makes the indifferent gonad develop into a testis
24
Q

How does TDF produce male genitalia?

A
  • TDF transforms the primordial supporting cells into sertoli cells
  • Sertoli cells secret MIS (MUllerian inhibiting substance) which transforms mesenchymal cells between cords to form Leydig cells
  • Leydig cells produce testosterone leading to production of male external genitalia
  • MIS also leads to paramesonephric duct degeneration
25
Q

Describe the development of the testis.

A
  • Week 5: primary sex cords, medulla and cortex
  • Week 6: primordial germ cells incorporated into primary sex cords
  • Week 7: TDF stimulates primary sex cords > extend into medulla> seminiferous cords> tubules
  • Mesothelium lost when thick capsule forms
  • Mesenchyme between cords five rise to Leydig cells
  • Week 8: Leydig cells produce testosterone and other hormones which stimulate masculine differentiation
26
Q

What are the seminal vesicles embryologically ?

A

Outgrowths from the caudal end of the mesonephric duct

27
Q

What is the prostate embryologically?

A

Outgrowth from urethra (urogenital sinus)

28
Q

What is the male external genitalia formed under the influence of?

A

Testosterone

29
Q

How does the indifferent gonad develop into an ovary?

A

In a female foetus there is no SRY region and no TDF

-By default the indifferent gonad develops into an ovary

30
Q

Describe the development of the ovary.

A
  • Primary sex cords degenerate leaving the primordial germ cells
  • Week 10: secondary sex cords develop from surface epithelium
  • Primordial germ cells become incorporated into them
  • Week 16: Primordial germ cells then bud off with single surrounding layer of cortical cells to form primordial follicles
  • Active mitosis of these early primordial follicles to form additional follicles
  • All follicles formed by 7th month
  • Oocytes enter meiosis and arrested I prophase
31
Q

What postnatal ovarian development occurs?

A
  • ~2 million primordial follicles at birth
  • Many become atretic before puberty
  • After puberty, hormonal influences stimulate 12-15 follicles per 28 day cycle to develop
  • Only one follicles reaches maturity and ovulation normally
  • Continues until the menopause
32
Q

Where do the tubular components of the female reproductive system come from?

A
  • Absence of testosterone causes degeneration of mesonephros and mesonephric duct
  • Paramesonephric ducts develop to give rise to female genital tract
33
Q

What is the origin of the female genital tract?

A
  • Cranial (open funnel) end of the paramesonephric duct becomes associated with ovary
  • Caudal end of paramesonephric duct (uterovaginal primordium) becomes uterus and superior part of vagina
  • Inferior part of vagina from urogenital sinus
  • Mesonephric duct degenerates
34
Q

Where do the gonads initially form?

A

In the lumbar region

35
Q

Describe the descent of the testis.

A
  • Week7: At T10 (diaphragm undescended)
  • Week 12: level of the deep inguinal ring. Remain here until 7th month
  • Enters scrotum just prior to birth (39 weeks)
36
Q

Describe the descent of the ovaries.

A
  • Week 7: At T10
  • Week 12: Broad ligament
  • Round ligament drawn through inguinal canal to attach to labrum majorum
37
Q

What changes occur due to the descent of the gonads?

A
  • Formation of the larger inguinal canal in males

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

38
Q

What developmental defects can occur?

A
  • Undescended testis
  • Remnants (Gartner’s cysts)
  • Anomalies of the paramesonephric duct in the female
39
Q

What is cryptorchidism?

A

One or both testis fail to descend

40
Q

What are the types of crytochidisim?

A
  • Undescended
  • Ectopic
  • Retractile testes
  • Absent testes
41
Q

What are the possible complications of undescended testis?

A
  • Infertility
  • Malignant transformation (germ cell tumours)
  • Testicular torsion
42
Q

What anomalies can occur with the uterus?

A
  • Complete duplication
  • Bicornuate uterus
  • Arcuate uterus
  • Septate uterus

reproductive system 2 (35 decks)

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