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Anatomy & Physiology > Embryology > Flashcards

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
Q

What are the major stages of embryo development ?

A
  • Day 0 = fertilisation
  • Day 2-4 = cleavage
  • Day 5 = Blastula
  • Day 8-9 = Implantation
26
Q

Describe the Cleavage Stage of embryo development

A
  • Day 2-4
  • large oocyte is divided into smaller cells
  • results in an undifferentiated ball of cells called a Morula
27
Q

Describe the Blastula stage of embryo development

A
  • 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
Q

Describe the implantation stage of embryo development

A
  • 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
Q

Describe the Development of the Placenta

A
  • begins at implantation when trophoblasts invade maternal endometrium
  • maturation reached at 2nd trimester
30
Q

Describe the role of the placenta

A
  • mediates essential communication between embryo/mother via close contact between maternal & foetal blood vessels
  • mediates uptake of nutrition & oxygen
  • endocrine & immune functions
31
Q

Describe the Gastrula Stage of embryo development

A
  • 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
Q

Describe what happens when cells become fate-restricted during gastrulation

A
  • they-re fate restricted to become one of the three germ layers
  • Ectoderm, mesoderm or endoderm
33
Q

Describe what happens when the embryo is patterned during gastrulation

A
  • forms the major axes which will determine the body plan
34
Q

Describe the Neurula stage of embryo development

A
  • 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
Q

How is the CNS built from the neural tube ?

A
  • Brain is formed by expansion of part of neural tube followed by tube folding
36
Q

What are the 3 morphological divisions of the brain that can be seen from early stages of development ?

A
  1. Forebrain
  2. Midbrain
  3. Hindbrain
37
Q

What are the 2 fundamental processes occurring during development ?

A
  • differentiation
  • morphogenesis
38
Q

Define differentiation

A

the process of producing mature cells with a define function

39
Q

Define morphogenesis

A
  • the acquisition of shape and form
  • new cells must be precisely organised to form tissues & organs
40
Q

How does differentiation occur ?

A
  • embryo contains stem cells which remain undifferentiated & repeatedly divide
  • cell will stop dividing and begins differentiation to acquire mature form
41
Q

How does morphogenesis occur ?

A
  • cells communicate with each other
  • embryos contain patterning centres which release signals that organise & pattern the body
42
Q

How are tissues and organs developed in the 2nd stage of embryogenesis ?

A
  • 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
Q

What are the 2 key properties of stem cells?

A
  1. replicate indefinitely in undifferentiated state
  2. under correct conditions they can differentiates into mature cell types
44
Q

What is potency ?

A
  • the ability of a stem cell to differentiate into 1 or more different cell types
45
Q

What are the 4 different levels of potency ?

A
  • decreasing in potency
    1. totipotency
    2. pluripotency
    3. multipotency
    4. unipotency
46
Q

Define Totipotency

A
  • 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
Q

What level of potency does a zygote have ?

A

totipotency

48
Q

What level of potency do blastulas have?

A
  • pluripotency –> this is because they contain 2 distinct cell types
    1. trophoblasts
    2. embryonic stem cells
49
Q

How were pluripotent stem cells orginally obtained ?

A
  • from the inner mass of blastula embryos
  • embryos from IVF clinic can be used but this raises ethical concerns
50
Q

Describe multipotent stem cells

A
  • 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
Q

Describe unipotent stem cells

A

can propagate indefinitely in an undifferentiated state but when they differentiate they can only adopt a single fate

52
Q

Describe the concept of cell fate

A
  • 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
Q

Define Cell Fate Determination

A
  • describes the state of being irreversibly committed to adopting a particular cell fate
54
Q

How is a stem cells differentiation potential reduced during development ?

A
  • its reduced because certain regions of the genome are silenced

Anatomy & Physiology (15 decks)

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