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Karan - MBBS Year 1: Principles Week 1 > Introduction to Embryology > Flashcards

Introduction to Embryology Flashcards

1
Q

Define embryology

A

Study of formation and development of embryo and fetus

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2
Q

Define embryo

A
  • Organism in process of development
  • From 2nd to 8th week after fertilisation
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3
Q

Define fetus

A
  • Developmental period from week 9 post-conception
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4
Q

Define embryogenesis

A

Progression from a single cell by establishing organ primordia

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5
Q

Why is embryology important?

A
  • Prenatal diagnosis
  • Preventing birth defects
  • Fertility assistance
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6
Q

What has human genome sequencing allowed scientists to do while studying embryology?

A
  • Cell lineage tracing
  • Roles of individual genes and environmental factors in development
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7
Q

What are the three steps of Week 1?

A

OVULATION
FERTILISATION
MITOSIS AND IMPLANTATION

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8
Q

Describe ovulation in Week 1. PART 1

A
  • Increased production of LH and FSH from anterior pituitary - follicle maturation
  • Graafian folic matures - oocyte completes Meiosis I and initiates Meiosis II
  • LH causes contraction. Ovarian wall ruptures - oocyte released.
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9
Q

Describe ovulation in Week 1. PART 2

A
  • Fimbriae pass oocyte into fallopian tube which contracts (along with mucosal cilia) moving oocyte towards the uterus
  • At site of rupture, corpus luteum forms - secretes progesterone.
  • Uterus prepared for pregnancy
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10
Q

Describe fertilisation in Week 1.

A
  • Occurs in ampulla of fallopian tube
  • Penetration of corona radiata and then zone pellucida
  • Fusion of sperm and oocyte membranes
  • Zygote forms
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11
Q

What occurs during cleavage?

A
  • Rapid cell division following fertilisation
  • Day 1: Single cell zygote
  • Day 2: Two cell stage
  • Days 3-4: Eight cell stage (early morula)
  • By Day 4: 16-cell stage (late morula). Zone pellucida disappears
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12
Q

What is each cell formed during cleavage known as?

A

Blastomere

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13
Q

By day 4, morula cells separate into 2 cell masses. What are these masses called and what is the consequence of their formation?

A
  • EMBRYOBLAST - Inner mass
  • TROPHOBLAST - Outer mass
  • Blastocele forms and embryo now a blastocyst
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14
Q

What is the embryoblast and what happens to it during development?

A
  • Future embryo
  • Different into epiblast, hypoblast and AVE and organise themselves
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15
Q

What is the trophoblast and what happens to it during development?

A
  • Future placenta
  • Invaginate into endometrium of uterus
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16
Q

What is Week 2 of development characterised by?

A
  • Bilaminar disc formation
  • Cell differentiation
17
Q

What occurs in the trophoblasts during cell differentiation in Week 2?

A
  • Differentiate into cyto/syncytiotrophoblasts
  • Holes (trophoblastic lacunae) form
18
Q

What occurs in the embryoblasts during Week 2?

A
  • Epiblast cell mass separates to form amniotic cavity
  • Hypoblast cells extend to form exocoelomic membrane which surrounds exocoelomic cavity (primitive yolk sac)
19
Q

What has happened by the end of Week 2 (Day 13)? PART 1

A
  • Presence of extra embryonic cavity separating trophoblasts and embryo
  • Primary yolk sac becomes secondary yolk sac
  • Bilaminar sac forms
20
Q

What has happened by the end of Week 2 (Day 13)? PART 2

A
  • Amniotic cavity is present and a primitive placenta exists
21
Q

What occurs in Week 3 of development?

A
  • Gastrulation
  • Epiblasts become ectoderm
  • Epiblasts that invaginate through primitive streak form the mesoderm
  • Hypoblast cells become endoderm
  • Cephalo-caudal and left-right axes established
22
Q

What occurs during Weeks 4-8 of development?

A
  • Endoderm differentiates to form tubes e.g airways, the gut
  • Mesoderm differentiates to form connective tissue, muscle and blood vessels
  • Ectoderm forms skin, neural tissue
23
Q

What occurs from Week 9 to birth (the fetal period)?

A
  • Organ maturation
  • Placental development
  • Increase in weight (particuarly in last 2 months) and length( particularly 3rd-5th month)
  • Slowdown in head growth
  • Full term 40 weeks after onset of last menstruation (38 weeks from
    conception)
24
Q

How can genomes influence embryonic development?

A
  • Genes transcribed to form proteins which can regulate gene expression
  • Proteins can also acts as signalling molecules
25
Q

What is induction?

A
  • Group of cells and tissues causes change in activity of another group of cells/tissues
26
Q

What does induction depend on?

A
  • The competence of cells to respond to induction usually through cell signalling
27
Q

Describe the Sonic Hedgehog Pathway.

A
  • Responsible for vasculature and neural development
  • Left-right axis formation
28
Q

In detail, what occurs in the Sonic Hedgehog Pathway.

A
  • SHH proteins binds to Patched (Ptc) protein receptor
  • Binding stops Ptc inhibited of smoothened proteins
  • Once activated, these proteins up regulate the GLI transcription factors which regulate expression of target genes
29
Q

What is the Notch pathway needed for?

A
  • Apoptosis
  • Cell proliferation
  • CVS and neural system development
30
Q

In detail, describe the Notch pathway. PART 1

A
  • Notch transmembrane receptors bind to DSL ligands
  • Binding cleaves off the Notch intracellular domain (NICD)
31
Q

In detail, describe the Notch pathway. PART 1

A
  • NICD enters nucleus and binds to DNA binding protein inhibiting transcription of Notch target genes
  • Binding of Notch removes inhibition so target genes can be transcribed.
32
Q

Describe the the planar cell polarity pathway.

A
  • Controls cell reorganisation within tissues
  • Causes convergent extension - tissues become longer and narrower
33
Q

In detail, outline what happens in the PCP pathway.

A
  • Wnt proteins bind to Frizzles receptor.
  • Wnt, along with CELSR and VANGL transmembrane proteins activate DVL protein
  • DVL regulates kinase signalling causing cytoskeletal changes.
34
Q

What are the consequences of abnormal PCP pathways?

A
  • Neural tube defects
  • Congenital heart disease

Karan - MBBS Year 1: Principles Week 1 (14 decks)

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