4. MECHANISMS OF DISEASE III: DURING EMBRYOGENESIS Flashcards
1
Q
What are the two main periods of embryogenesis?
A
- EMBRYONIC PERIOD - First 8 weeks, when most of the organogenesis occurs
- FOETAL PERIOD - The remaining period iin utero which involves growth & modelling
2
Q
What are the 7 processes of human development?
A
- FERTILISATION
- CLEAVAGE
- BLASTULATION
- GASTRULATION
5, NEURULATION - SOMITOGENESIS
- ORGANOGENESIS
3
Q
What is cleavage?
A
- Cleavage refers to a series of mitotoc divisions without growth
- Zygote - 2 cell -> 4 cell -> Morula
- The zygote undergoes many cleavages as it travels through the uterine tube to the uterus before it implants at around 10 days
4
Q
What is blastulation?
A
- Blastulation refers to the fromation of a blastocyst
- The Morula undergoes a process of compaction where the cells rearrange, getting closer to from a blastocyst
- Blastocyst consists of 32 - 46 cells at around day 4/5
5
Q
What are the two cell layers of the blastocyst?
A
- Outer trophoblast
2. Inner embryoblast - gives rise to the inner cell mass
6
Q
What is the blastocoele?
A
- The blastocoele is a fluid filled cavity which is located between the trophoblast & the embryoblast
- The trophoblast cells secrete fluid into cavity
- The blastocoele displaces the inner cell mass to one side
7
Q
What two cell layers does the inner cell mass give rise to?
A
- Inner cell mass differentiates into:
1. EPIBLAST
2. HYPOBLAST
8
Q
What is the bilaminar disc?
A
- The epiblast & hypoblast form the bilaminar disc
- The epiblast is located above the hypoblast
- Cells of the epiblast rearrange to from the amniotic cavity which is located in between the epiblast & hypoblast
9
Q
What is gastrulation?
A
- Gastrualtion refers to the formation of the three germ layers
- The blastocyst/blastula is rearranged into a gastrula
10
Q
What are the three germ layers?
A
- ECTODERM
- ENDODERM
- MESODERM
11
Q
What is the primitive streak & how does it form?
A
- The primitive streak originates at teh caudal end of the epiblast & grows cranially
12
Q
What is the primitive groove?
A
- The primitive groove is a shallow depression within the primitive streak
13
Q
What happens during invagination of the epiblast?
A
- Cells of the epiblast ingress/invaginate through the primitive groove into the underlying hypblast
- The ingressing epiblast cells dipslace the hypoblast to give rise to the endoderm & primitive mesoderm
14
Q
What two germ layers arise from the hypoblast?
A
- ENDODERM
2. MESODERM
15
Q
What germ layer does the epiblast give rise to?
A
- ECTODERM
16
Q
What is the trilaminar disc?
A
- Once the three germ layers have formed, the bilaminar disc becomes the trilaminar disc
17
Q
What is neurualtion?
A
- Neurulation is the process by which the neural plate folds back on itself to form the neural tube beneath the ectoderm
18
Q
How does the notochord form?
A
- Once the primitive streak has extended towards the cranial end, it begins regressing
- As the primitive streak regresses it lays down a chord like structure known as the NOTOCHORD underneath the ectoderm within the mesoderm
19
Q
How does the neural plate from?
A
- The notochord releases extracellualr signals which causes the overlying ectoderm to form the NEURAL PLATE
- The neural plate is a thickening of the ectoderm
20
Q
How does the neural plate become the neural tube?
A
- The neural folds of the neural palte fuse to form a ring which is the neural tube
- The neural tube begins by closing in the middle first, between the hindgut & spinal cord
- It then continues anteriorly & posteriorly until teh whole tube is fused
21
Q
What is somitogenesis & which germ layer is involved in somitogenesis
A
- Somitogenesis is the process by which somites from
- The cells of the mesoderm differentiate into somites
- Somites are precursors of muscle & bones
22
Q
What are neural crest cells?
A
- Neural crest cells are cells of the ectoderm which invaginate into the mesoderm
23
Q
What is the puprose of body/embryonic folding?
A
- Embryonic folding allows organs to be enclosed
- Mesoderm & endoderm give ris to oragns which need to be enclosed
24
Q
Waht two planes does embryonic folding occur on?
A
- HORIZONTAL PLANE
2. MEDIAN PLANE
25
What folds are produced through embryonic folding on the horizontal & median plane?
- Horizontal plane = two lateral folds
| - Median palne = cranial & caudal body folds
26
What main structure does the endoderm differentiate into?
- Endoderm differentiates into Gi tract
- As embryonic folding occur, teh endoderm moves towards the midline & fuses to form the primitive gut tube
- The primitve gut tube forms the foregut, midgut & hindgut
27
What are the main events of embryonic folding?
- Heart & septum move from margin to centre
- Yolk sac, allantois & stalk make umbilical cord
- Prochordal & cloaclal paltes form gut tube
28
What are the 5 main events organogenesis?
- Organogenesis refers to teh development of organs
1. Development of somitic derivatives - bone, muscle
2. Development of sensory structures - eyes, ears
3. Limb formation - forelimbs then hindimbs
4. Formation of face structures - jaw, nose, tongue, palate
5. Formation of genital structure
29
What type of diseases can occur due to defects in embryogenesis?
- Congenital malformations or diseases
| - If the defects occur earlier on, the resulting diseases will be more severe
30
What are 4 causes of disease?
1. SINGLE GENE MUTATIONS - one gene mutation produces a characteristic effect (Mendelian disease)
2. CHROMOSOMAL ANOMALIES - Abnormalities with chromosome number due to rearrangement e.g trisomy
3. POLYGENIC DISORDER - several genes causing disease
4. ENVIRONMENTAL - diet, infection, toxic compounds
31
What is multi-factorial aetiology?
- Congenital diseases have a multifactorial aetiology, meanining it's caused by a combination of intrinsic & extrinsic causes
32
What are the desirable characteristics of a model organism to study embryogenesis?
- It would be unethical to study embryogenesis with a human embryo so other models need to be used
1. Represenattive/relevant
2. Accessibility/availability
3. Experimental manipulation
4. Gentics of organism are known
5. Cost/space
33
What model organisms can be used to study disease during embryogenesis?
1. Drosophila
2. Flat worms
3. Vertebraes
4. Zebrafish
34
What properties of zebrafish make it an ideal organism for study?
+ Embryos of zebrafish are transparent amking it easy to study changes
+ Cheap & easy to maintain
+ 70% of zebrafish genes are homologous with humans & 84% of disease genes
