Embryology Flashcards

1
Q

What occurs during the first trimester ?

A
  • 0-13 weeks
  • embryonic development
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2
Q

What occurs during the 2nd & 3rd trimester ?

A
  • 2nd =14-26 weeks
  • 3rd = 27-40 weeks
  • foetal development
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3
Q

Describe Germ Cells

A
  • contain 1 copy of each chromosome
  • this is because the nuclei of 2 germ cells will fuse at fertilisation to produce a 2n zygote
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4
Q

What are germ cells derived from?

A
  • they’re derived from diploid cells called primordial germ cells (PGCs) which are produced by the embryo
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5
Q

When do PGCs commence meiosis in males?

A
  • after puberty
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6
Q

Describe when PGCs begin meiosis in females

A
  • PGCs begin meiosis before birth in order to form a primary follicle
  • these are then held in an arrested state mid-meiosis till after puberty
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7
Q

When is meiosis arrested during female development ?

A
  • during prophase of the 1st division
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8
Q

What happens to the primary follies during the menstrual cycle ?

A
  • 5-12 primary follicles resume development
  • eventually a single oocyte becomes dominant & completes development
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9
Q

Define oocyte

A

egg

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10
Q

What happens when the primary follicle matures?

A
  • called a Graafian follicle
  • contains a fluid-filled cavity = antrum
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11
Q

What happens to the oocyte on day 13/14 of menstruation ?

A
  • it resumes meiosis & completes it
  • creating a polar body
  • beings meiosis II but it arrested midway - will remain this way till after fertilisation
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12
Q

What happens to the follicle at ovulation ?

A
  • it ruptures to release the oocyte into the Fallopian tube
  • the oocyte is carried to the womb by flow created by beating cilia
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13
Q

What happens to the ruptured follicle ?

A
  • it forms the corpus luteum which acts as an endocrine organ
  • signals the endometrium
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14
Q

What hormones are released by the corpus luteum ?

A
  • oestrogen
  • progesterone
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15
Q

What hormones are released by the pituitary gland during menstrual cycle?

A
  • follicle stimulating hormone
  • Luetenising hormone
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16
Q

What is the term for male germ cell production ?

A

Spermatogenesis

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17
Q

Describe what happens to dormant male PCGs after puberty

A
  • proliferate via mitosis to form spermatogonia
  • spermatogonia undergo both rounds of meiosis concurrently
  • this produces spermatocytes –> haploid spermatids
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18
Q

What happens when spermatids mature ?

A
  • maturation produces mature spermatozoa
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19
Q

What are the 3 anatomical regions of Spermatozoa ?

A
  1. Head = contains condensed nucleus & acrosome
  2. midpiece = contains mito.
  3. tail = contains microtubules for propulsion
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20
Q

What is an acrosome ?

A

a vesicle containing hydrolytic enzymes

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21
Q

Describe the process of fertilisation

A
  • multiple sperm are attracted to the oocytes & penetrate the cumulus cell layer
  • sperm bind to glycoprotein receptor called ZP2
  • binding triggers enzymes to digest ZP
  • sperm membrane fuses with oocyte
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22
Q

Define Polyspermy

A
  • fertilisation by more than 1 sperm
23
Q

How is Polyspermy prevented ?

A
  • via changes triggered by the membrane fusion including generation of calcium wave & release of cortisol granules
24
Q

Define Zygote

A
  • fertilised egg
  • single cell from which all other cells of the body are derived from
25
What are the major stages of embryo development ?
- Day 0 = fertilisation - Day 2-4 = cleavage - Day 5 = Blastula - Day 8-9 = Implantation
26
Describe the Cleavage Stage of embryo development
- Day 2-4 - large oocyte is divided into smaller cells - results in an undifferentiated ball of cells called a Morula
27
Describe the Blastula stage of embryo development
- Day 5 embryo becomes a Blastula - specific structures & regional differences can be seen - coelum (cavity) forms inside morula - 2 types of cells = inner cell mass & trophoblasts
28
Describe the implantation stage of embryo development
- embryo attaches then embed into wall of the endometrium - trophoblasts differentiates to form the placenta - endometrium is induced to differentiate to produce blood vessels
29
Describe the Development of the Placenta
- begins at implantation when trophoblasts invade maternal endometrium - maturation reached at 2nd trimester
30
Describe the role of the placenta
- mediates essential communication between embryo/mother via close contact between maternal & foetal blood vessels - mediates uptake of nutrition & oxygen - endocrine & immune functions
31
Describe the Gastrula Stage of embryo development
- Day 14-21 - Gastrulation is one of the most important stages - 3 major events occur during ; 1. cells become fate-restricted 2. cells become motile 3. embryo is patterned
32
Describe what happens when cells become fate-restricted during gastrulation
- they-re fate restricted to become one of the three germ layers - Ectoderm, mesoderm or endoderm
33
Describe what happens when the embryo is patterned during gastrulation
- forms the major axes which will determine the body plan
34
Describe the Neurula stage of embryo development
- Days 21-28 - immediately after gastrulation, neuralisation begins - nervous system is formed as flat plate on embryo surface and later this plate folds/rolls to form a neural tube
35
How is the CNS built from the neural tube ?
- Brain is formed by expansion of part of neural tube followed by tube folding
36
What are the 3 morphological divisions of the brain that can be seen from early stages of development ?
1. Forebrain 2. Midbrain 3. Hindbrain
37
What are the 2 fundamental processes occurring during development ?
- differentiation - morphogenesis
38
Define differentiation
the process of producing mature cells with a define function
39
Define morphogenesis
- the acquisition of shape and form - new cells must be precisely organised to form tissues & organs
40
How does differentiation occur ?
- embryo contains stem cells which remain undifferentiated & repeatedly divide - cell will stop dividing and begins differentiation to acquire mature form
41
How does morphogenesis occur ?
- cells communicate with each other - embryos contain patterning centres which release signals that organise & pattern the body
42
How are tissues and organs developed in the 2nd stage of embryogenesis ?
- fields of precursor cells are first patterned - - they receive/respond to signals which give them an identity --> this tells cells where they are and where they need to be - this information its used to build tissues/organs
43
What are the 2 key properties of stem cells?
1. replicate indefinitely in undifferentiated state 2. under correct conditions they can differentiates into mature cell types
44
What is potency ?
- the ability of a stem cell to differentiate into 1 or more different cell types
45
What are the 4 different levels of potency ?
- decreasing in potency 1. totipotency 2. pluripotency 3. multipotency 4. unipotency
46
Define Totipotency
- ability to differentiate into any cell both within the body & within the placenta - maintained through cleavage stage but lost when embryo becomes a blastula
47
What level of potency does a zygote have ?
totipotency
48
What level of potency do blastulas have?
- pluripotency --> this is because they contain 2 distinct cell types 1. trophoblasts 2. embryonic stem cells
49
How were pluripotent stem cells orginally obtained ?
- from the inner mass of blastula embryos - embryos from IVF clinic can be used but this raises ethical concerns
50
Describe multipotent stem cells
- mid-range potential and can differentiate into a limited number of cell fates - examples = mesenchymal stem cells which can form adipocytes, chondrocytes or osteocytes
51
Describe unipotent stem cells
can propagate indefinitely in an undifferentiated state but when they differentiate they can only adopt a single fate
52
Describe the concept of cell fate
- it describes the differentiated state a cell adopts at the end of development - fate specification is the process by which cells choose what fate they will adopt
53
Define Cell Fate Determination
- describes the state of being irreversibly committed to adopting a particular cell fate
54
How is a stem cells differentiation potential reduced during development ?
- its reduced because certain regions of the genome are silenced