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Clin Sci IMS, Respiratory, Renal, Cardiovascular, Nutrition & Energy > Week 9 - Embryology > Flashcards

Week 9 - Embryology Flashcards

1
Q

What is a primordial germ cell?

A

Earliest recognised germ cell originates in epiblast close to the yolk sac - week 3 after conception
They migrate through the hind gut to the genital ridge day 24 post conception -m move along mesentery top genital ridge

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2
Q

Describe the male primordial germ cells in relation to sex chords

A

Association of somatic cells in gonadal region, male germ cells associated with chords and end up inside seminiferous tubules.
They enter presumptive seminiferous tubules with pro-sertoli cells, primordial germ cells settle on tubule wall first

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3
Q

Describe Sertoli cells maturation (males)

A

Form tight junctions and form the blood testes barrier, earliest germ cell outside this barrier

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4
Q

Describe male primordial germ cells

A

Proliferate via mitosis and develop gonocytes as testes are developing - pro-spermatogonia into spermatogonia by the end of the foetal stage

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5
Q

Describe the pre-pubertal phase in males

A

Some spermatogonia become stem cells and acquire self renewal - stem cell pool

  • Perinatal spermatogonia produces spermatocytes
  • All post stem cell donation is as synctiia until just before sperm cell release
  • Spermatocytes arrest at prophase pf 1st mitotic division
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6
Q

Give the 4 spermatocytes and there role

A
  1. Preleptotene - s’ phase
  2. Leptotenes - chromatin remodelling
  3. Zygotene - chromatin remodelling
  4. Packytene -transcription / translation
    Diplotene - enter mitosis
    1st mitotic division
    Secondary spermatocytes Second mitotic division
    SPERM
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7
Q

Describe spermatids

A

Development = spermigenesis

3 types - round, elongation, maturation

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8
Q

describe the second mitotic division and spermatids

A

Round spermatids, nucleus capable of division, nuclear histones replaced by transcription proteins

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9
Q

Describe elongation spermatids

A
  • Transcriptionally inactive
  • Transcription proteins replaced by protamines
  • Higher packing order and reduction of nuclear size
  • Cytoplasm shrinks to form droplet
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10
Q

Describe maturation of spermatids

A
  • Sheding? lumen of tubule age spermatination

- Cytoplasmic droplet phagocytksed by Sertoli cells

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11
Q

Describe oogenesis

A

Primordial germ cells - primary oocyte in prophase of meiosis 1

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12
Q

Describe diplotene

A

4th stage of meiosis where paired chromosomes separate into chromatids

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13
Q

Describe gametogenesis

A

Primordial cells give rise to oogonium therefore differentiate into 1st oocyte, surrounded bey granulose cells and germinal vesicle

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14
Q

Describe the 2nd follicle - antral follicle

A
  • Granulose cells proliferate and increase in follicle size
  • Secretion of follicular fluids- multi polysaccharides and serum = antrum fluid
  • Oocyte connected by stalk to thick granulose cell layer: cumulus oophorus
  • Gonadotrophin dependent synthesis of steroid
  • Thecal cell layer around glomerulosa cells
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15
Q

Describe the 3rd follicle - graafion follicle

A
  • Transient peak of LH stimulates ovulation
  • Breakdown of nuclear membrane, separation of chromosomes
  • Unequal division of cytoplasm, extrusion of 1st polar body
  • Separation of chromatids - metaphase plate - 2nd mitotic division
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16
Q

Describe ovulation

A
  • Disappearance of cytoplasmic processes
  • Synthesis of cortisol granules and new protein
  • Follicle 25mm from more fluid
  • Loosening’s of outer granulosa cell layers and increase in follicle blood supply
  • Steroid synthesis - progesterone, bulge in ovary wall shining of stigma
  • Rupture cilia on fimbriae sweep oocyte and cumulus cells - oviduct
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17
Q

Describe thecal cells

A

Smaller lutein cells - synthesise androgens, progesterone and inhibit

18
Q

Describe lukeolysis

A

Regression of corpus luteum - depends whether fertilisation has occurred

19
Q

Describe pulsatile secretion in males

A
  • GnRH diffuses to pituitary and causes release of gonadotropins - LH and FSH
  • GnRH reserves are replenished between pulsations
  • Overstimulation can cause depletion and deficiency as all GnRH is used up
  • Under stimulation = not stimulated enough to release
  • FSH acts on Sertoli cells, production of androgen binding protein for transport of testosterone around the bloodied direct germ cells via Sertoli cells producing inhibin - acting on leydig cells which produce testosterone
20
Q

Describe testosterone

A

Stimulates germ cells, bone, skin and hair
Testosterone to dihydrotestosterone effects on prostate and oestradiol - important in epiphysal closure and reproductive system

21
Q

Describe FSH Regulation

A

Negatively regulated by inhibin produced by Sertoli cells acts at pituitary to inhibit FSH
Positively regulated by actin and follistatin

22
Q

Describe LH regulation

A

Regulated by testosterone both at level of pituitary and hypothalamus

23
Q

Describe oestrogen effects in females during the menstrual cycle

A
  • Maintains bone mass
  • Effects CNS
  • Effects lipid metabolism
  • Effects on fat distribution
  • Promotes oestrogen secretion
  • Effects on blood clotting
24
Q

Describe effects of progesterone males during the menstrual cycle

A
  • Increase in body temperature
  • Changes to cervix lining - thickens + cervical mucous secreted
  • Exerts negative feedback control on the hypothalamus and pituitary
25
Q

Describe embryonic development

A 
Fertilisation 
Zygote 
Cleavage 
Morula 
Blastocyte 
Gastrulation - ectoderm, mesoderm and endoderm 
Orangogenesis
Foetal development
26
Q

Describe the implantation after fertilisation

A
  • Fertilised at ampulla region
  • Zona pellucida at first cleavage division
  • Blastocoel forms as fluid builds, hatching and naked blastocyst implants
27
Q

Describe zygote formation

A
  • Some unequal distribution of cellular products
  • Cleavage results in blastomeres - two cells
  • Rotational cleavage
  • 8 cell - Compaction flattening of blastomeres maximising cell - cell contacts tight junctions form
  • 16 cell
    Each cleavage occurs in an different plane / axis to ensure cells are in a spherical shape and compact
28
Q

Describe the zygote entering the uterine cavity - day 6

A
  • External polarised trophectoderm
  • Inner non polarised cells - inner cell mass
  • Trophectoderm to synctiotrophoblast - spreads around blastocyst
  • ICM to epiblast and hypoblast
    Epiblast - Embryonic embryo aminocytes, secrete fluid, embryo itself, bilaminer disc
    Hypoblast - Lines blastocoel and forms yolk sac
  • Trophectoderm forming around blastocoel/trophoblast, forms synctitium and invade uterine wall forming amniotic cavity
29
Q

Describe the synctiotrophoblast

A 
Day 9
3 germ layers - trilaminer disc
Ectoderm 
Mesoderm 
Endoderm 
Pattern formation - spacial and temporal pattern of cell activities is organised within the embryo
30
Q

Describe induction

A
  • Cell types under influence of different cell types

- Production of signals that bring about response in target cells

31
Q

Describe macrophogenesis

A

The achievement of developmental diversity by formation off different structures from the same initial structure e.g gastrulation, neurulation and limb formation
- Juxtacrine and paracrine signals lead to yes/no responses however can add variable result of modulation by interplay with other signals

32
Q

What is morphogen?

A

A signalling molecule that forms on the extra cellular concentration gradient

33
Q

Describe gastrulation

A

3 germ layers are formed, once committed to germ layer lineage cells don’t change path

  • Blastocyst around implantation, ICM differentiates into two layers forming bilaminer disc with amniotic cavity above and the blastocoel below
  • Reorganises the epiblast into a trilaminer disc
  • Initiated by organiser which is in the future dorsal posterior region
  • Formation if primitive streak and node in epiblast
  • Posterior extension streak, migration of epiblast cells through node - endoderm anterior notochord and precordial mesoderm
  • Migration of epiblast cells through streak - ventral and lateral mesoderm
  • Regression of streak and replacement of notochord
34
Q

Describe neurulation

A

Formation of neural tube - to spinal cord and brain - neural plate

  • Embryo is a trilaminer disc between amniotic cavity and yolk sac
  • Heart in position after cranio-caudal folding
  • Lateral plate mesoderm is splitting into the somatic and splanchic layers with intra embryonic coelom between
35
Q

Describe the organisers in mesodermal tissue during neurulation

A
  • Formation of neural plate and ectodermal layer
  • Changes in cell shape and surface properties
  • Folding of neural plate hinge regions, edge folds fuse
  • Failure to complete fusion = spinabifida - posterior or anencephaly - anterior
  • Tube separates sinks away from ectoderm
    Formation of neural tube and non neural ectoderm’s is covering
  • Neural crest cells migrate around spinal cord
36
Q

What can excessive egg overstimulation cause during assisted reproduction ?

A

Oedema in abdomen and increase thrombosis risk

37
Q

Describe implantation of fertilised egg into the uterus

A

Cleavage stage - most common don’t want to get growth arrest in culture - 3 days after fertilisation
blastocyst stage - allow selection of best quality embryo for success

38
Q

Describe grade A for day 3 blastomere implantation

A

Even blastomeres with no fragmentation

39
Q

Describe the expansion grade for blastocoel implantation

A
  1. Cavity of blastocoel less than 1/2 vol of embryo
  2. Blastocoel cavity more than 1/2 embryo vol
  3. Full blastocyst cavity larger than the embryo
  4. Expanded blastocyste cavity larger than the embryo with thinning of the shell
  5. hatching out of the shell
  6. Hatched out of cell
40
Q

Describe the ICM grade and trophectoderm grade of blastocoel implantation

A

ICM
A many tightly packed cells
B several loosely grouped cells

Trophectoderm
A Many cells form cohesive layer
B Few cells from cohesive layer
C Very few large cells

Clin Sci IMS, Respiratory, Renal, Cardiovascular, Nutrition & Energy (17 decks)

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