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Reproductive Systems > Reproductive Embryology > Flashcards

Reproductive Embryology Flashcards

1
Q

describe fertilisation: generalised acrosomal process

A
  1. sperm makes contact with egg
  2. acrosome reacts with zona pellucida
  3. acrosome reacts with perivitelline space
  4. plasma membranes of sperm and egg fuse
  5. sperm nucleus enters egg
  6. cortical granules fuse with egg plasma membrane, which renders the vitelline layer impenetrable to sperm
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2
Q

what happens during the first 5 days of embryo development?

A
  • day 1: formation of pronuclei
  • day 2: first cell division
  • day 3: cell division continues
  • day 4: formation of morula
  • day 5: blastocyst forms
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3
Q

how does hatching of the blastocyst occur?

A

trophoectoderm cells produce protease to dissolve the zona in preparation for implantation
- 5th day after fertilisation

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4
Q

what does the apposition step of implantation refer to?

A

first connection between blastocyst and endometrium, apposes to microvilli like structure called pinopodes expressed on receptive endometrium

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5
Q

what does the adhesion step of implantion refer to?

A

trophoblast of the blastocyst adheres to the epithelial layer of maternal endometrium, embryonic tissue starts to actively secrete hCG.

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6
Q

what does the invasion step of implantation refer to?

A

trophoblast proliferation, differentiation, crossing of the epithelial basement membrane and invasion of endometrial stroma to form the placenta. Uterine spiral arteries remodelled by the invasive trophoblast.

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7
Q

describe decidualisation that occurs prior to invasion of the blastocyst

A

Pre-requisite for trophoblast invasion and placentation involves transformation of stromal cells of maternal endometrium every month (during menstrual cycle, before pregnancy) under the effect of hormone progesterone.

Changes:
- Stromal cell differentiation (elongated fibroblast like cells) converted into decidual( rounded epithelial cells).
- Angiogenesis - new vessel formation, increase vascular permeability
- Increased macrophages, lymphocytes and decidual leukocytes(uterine natural killer cells) for maternal immune tolerance

These changes transform the endometrium into a vascular receptive tissue for blastocyst invasion.

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8
Q

the mature placenta is formed by which components

A

The mature placenta is formed by several components:
- chorionic villi
- intervillous space
- placental septae
- cotyledons (subunits of placenta)

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9
Q

what are the functions of the placenta?

A
  • Acts as an immunological barrier
  • Gas exchange
  • Nutrient exchange
  • Waste excretion
  • Endocrine functions
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10
Q

define embryogenesis

A

the first 8 weeks of embryo development post fertilisation
- beyond the endo of week 8, the ebryonic period ends and the foetal period begins.

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11
Q

Fertilised egg forms blastocyst on day 5 with two organised cell groups- what are these groups called?

A

inner cell mass (embryoblast) and trophoblast (outer cells)

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12
Q

what happens during weeks 2-3 of embryoblast development?

A
  • formation of bilaminar disc and development of amniotic sac, yolk sac, extraembryonic mesoderm and chorionic cavity.
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13
Q

what happens during weeks 3-4 of embryoblast development?

A

differentiation of bilaminar disc into trilaminar structure - three germ layers (endoderm, mesoderm and ectoderm) through process of gastrulation and neural tube formation.

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14
Q

what happens during weeks 5-8 of embryoblast development?

A

organogenesis

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15
Q

descibe the differentiation of the inner cell mass of a blastocyst

A

The inner cell mass differentiates into bilaminar epiblast (columnar epithelial cells) and thehypoblast (cuboidal epithelial cells). Hypoblast is the layer facing the blastocoel, while the epiblast is on the other side

Two cavities form, yolk sac on the side of the hypoblast and amniotic cavity on the side of epiblast

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16
Q

describe the process of epiblast differentiation/gastrulation

A
  • Epiblast differentiates into the three germ layers- ectoderm , mesoderm and endoderm in a process called gastrulation (D13 to 16 of embryo development)
  • Gastrulation starts with a groove appearing in the caudal end of epiblast called primitive streak
  • Epiblast cells migrate into the hypoblast layer displacing them- forming the endoderm
  • Further epiblast cells migrate through primitive streak between the epiblast and the hypoblast/endoderm to form the mesoderm
  • Remaining epiblast becomes the ectoderm
  • The newly formed trilaminar disc with three layers is called gastrula and forms the different organ systems
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17
Q

which structures are derived from the ectoderm?

A
  • epidermis
  • CNS
  • PNS
  • hair
  • nails
  • neuroendocrine organse (adrenal medulla, pituitary gland)
  • enamel of teeth
18
Q

which structures are derives from the mesoderm?

A
  • dermis
  • MSK structures
  • CVS
  • kidneys
  • ureters
  • trigone of bladder
  • gonads (not germ cells)
  • adrenal cortex
  • visceral and parietal linings (pleura, peritoneum, pericardium)
19
Q

which structures are derived from the endoderm?

A
  • lining of GI tract
  • parenchyma of liver
  • pancreas
  • thyroid
  • parathyroid
  • tonsils and thymus
  • bladder (excluding trigone)
  • urethra
20
Q

which mesoderm gives rise to the kidneys, ureter and gonads?

A

intermediate mesoderm

21
Q

list the causes for multiple pregnancy

A

Dizygotic:
- two or more eggs fertilising and implanting, non-identical

Monozygotic:
- one ebryo splitting, identical twins

22
Q

what happens if twins have a division day > 14 post fertilisation?

A
  • share placenta and amniotic sac
  • conjoined twins
23
Q

describe the devlopment of the indifferent gonad

A
  • The indifferent gonad develops in the gonadal ridge which is closely related to the mesonephros.
  • Primordial germ cells do not originate in the gonadal ridge but migrate to the gonads from endoderm lining of yolk sac via hindgut around 6 weeks of gestation
  • Epithelium of gonadal ridge forms primitive sex cords
  • Combination of germ cells and primitive sex cord forms the indifferent gonad which is capable of developing into a testis or ovary
24
Q

describe the process of gonad differentiation from indifferent gonads

A

The Y chromosome contains the SRY gene (sex-determining region Y)

SRY produces testis determining factor / SRY protein

This protein acts on the indifferent gonad to promote the formation of the testis

In rare cases, following a translocation error, a male can be born with a 46 XX Karyotype (1:20,000)

25
Q

detail the development of the ovary beginning with migrating germ cells

A
  • migrating germ cells enter the ovary
  • primitive sex cords extend into the medulla but degenerate
  • secondary sex cords (cortical cords) develop and surround the germ cells to form the ovarian primordial follicles
  • ovarian follicle pool (determining female ovarian reserve established at 20 weeks of gestation in foetal life)
26
Q

detail the development of the testis beginning with migrating germ cells

A

The migrating germ cells enter the testis

The primitive sex cords extend into medulla and form testis cords (medullary cords) which transform into future seminiferous tubules and rete testis

Sertoli cell are derived from surface epithelium under effect of AMH

Leydig cells are produced from intermediate mesoderm and produce testosterone from 8 week onwards

27
Q

describe testicular descent

A

The gonads originate in the posterior abdominal wall

The testes reach the deep inguinal ring by 7 months of pregnancy

By term 97% of male infants will have fully descended testes

Undescended testicle, also known as cryptorchidism requires early surgery for correction

28
Q

what are the two sets of genital ducts called?

A

mesonephric (Wolffian) duct next to the gonad
paramesonephric duct laterally

29
Q

the presence of what determines whether the mesonephric (Wolffian) or paramesonephric duct develops or regresses?

A

the presence or absence of AMH determines which develops and which regresses
- In the male the presence of AMH causes the paramesonephric ducts to regress and these do not form any part of the adult
- In the absence of AMH, the paramesonephric ducts continue to develop and the mesonephric ducts regress

30
Q

what do the mesonephric ducts go on to form?

A

In both males and females it forms the trigone part of the bladder

Rest of the duct only persists in the males under the effect of testosterone and forms the epididymis, vas deferens and seminal vesicles

31
Q

what do the paramesonephric ducts go on to form?

A

Paramesonephric ducts grow medially and fuse. The fused portions of the paramesonephric ducts canalises to form the uterus and upper 2/3 rd of vagina. The unfused portions give rise to the fallopian tubes

Paramesonephric ducts fuse with the urogenital sinus at the sinus tubercle and point of fusion forms the hymen

32
Q

which embryological structure forms the lower 1/3 of vagina?

A

urogenital sinus

33
Q

what does the genital tubercle give rise to in a male?

A

elongates to form the penis

34
Q

The urogenital folds fuse posterior to anteriorly to form what in males?

A

penile urethra (spongy urethra)

35
Q

In the female the urogenital folds form the ?

A

labia minora

36
Q

in the female the labioscrotal folds form the

A

labia majora

37
Q

in the female the genital tubercle forms the

A

clitoris

38
Q

what is the cause of a micropenis?

A

genital tubercle does not elongate fully

39
Q

what is hypospadias?

A

urethral development problem causing opening to be abnormally located

40
Q

the vas deferens can be absent due to which condition?

A

cystic fibrosis

Reproductive Systems (17 decks)

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