Congenital Development of Disease Symposium Flashcards
1
Q
What is Gastrulation?
A
- when the bilaminar disk of the embryo develops to form 3 distinct layers - usually around week 3
- ectoderm (from the epiblast)
- mesoderm (invading epiblast cells from the primary streak)
- endoderm (hypoblast replaced by epiblast cells)
2
Q
What happens during fertilization Day-1 ?
A
- Sperm and Ovum meet in Uterine Tube (usually in the ampulla) 12-24 hours after ovulation.
- Penetration of Corona radiate and Zona pellucida
- Fusion and 2nd meiotic division
- Acrosome reaction makes ovum impermeable to other sperm
- End- Zygote- has diploid (46 chromosomes)
3
Q
What happens in days 2-3 after fertilization?
A
- Cleavage occurs- this is the rapid process of mitotic divisions
- The first mitotic division occurs around 30 hours post-fertilization.
- By day 3 the fertilized ovum has become a 16 cell embryo
- Each cell is known as a blastomere.
- forming a solid sphere is known as a morula.
4
Q
What happens day 4-5 post-fertilization?
A
- Morula develops a cavity and becomes known as a blastocyst.
- The outer layer of the blastocyst thins out and becomes the trophoblast this helps form the placenta
- The rest of the cells move (are pushed up) to form the inner cell mass. This creates an embryonic pole.
- The blastocyst has now reached the uterine lumen and is ready for implantation.
5
Q
What happens day 6-7 post-fertilization?
A
- the Bilaminar Disc forms- As the embryo starts to implant it forms two layers.
- Inner cell mass differentiates into two layers: epiblast and hypoblast.
- These two layers are in contact.
- Hypoblast forms extraembryonic membranes
- Epiblast forms embryo
- the Amniotic cavity develops within the epiblast mass
6
Q
What happens day 6-8 post-fertilization?
A
- The Primary Yolk Sac is formed
- it is derived from the hypoblast is the exocoelomic membrane. (aka Extraembryonic hypoblast/membrane)
- The Yolk Sac contains nutrients that supply the embryo before the placenta functions.
7
Q
How has the embryo developed by week 4?
A
- the flat disc has to fold into 2 directions
- Longitudinal (cephalocaudal) (day 21) begins so that head and tail are brought closer.
- Lateral (transverse) (day 18) brings the amniotic cavity down, creating the future gut tube inside the peritoneal cavity.
8
Q
Describe the structure of the Mesoderm
A
- formed of three parts
- Paraxial mesoderm
- Lateral plate mesoderm
- Intermediate mesoderm
- these structures are either side of the notochord
- this is made from the mesoderm
- remains as the nucleus palposus, the inside part of the vertebrae throughout embryonic development
9
Q
Explain what happens to the Paraxial mesoderm and what its role is in the development
A
- Paraxial mesoderm undergoes further differentiation into paired blocks of tissue- somites
- 42-44 pairs eventually formed (prep for the vertebral arch)
- Somites undergo differentiation to form dermomyotomes and sclerotomes
- Dermomyotomes: form connective tissue and skeletal muscle
- Sclerotomes: form bone and cartilage- vertebral arch
- __the cells from the sclerotome come around the neural tube and form the boney arch (spinous process)
- if they don’t come around and join completely –> spinabifida
10
Q
Label the structures of this Somite
A
11
Q
What is the role of the Intermediate mesoderm?
A
- it gives rise to the urogenital system
- kidneys - from the pronephros then mesonephros then the metanephros
- gonads
- urogenital ducts and associated glands
- formed from the degenerating excretory tubules of the mesonephros and pronephros
12
Q
What is the role of the Lateral plate mesoderm?
A
- creates the parietal and visceral layers
- Continuous with the amniotic sac and yolk sac.
- Amniotic sac mesoderm–> Parietal or somatic layer
- Yolk sac mesoderm–> Splanchnic layer
- Mesodermal cells will become the membranes of the body (pericardium, pleura, peritoneum)
- all cavities are lined with lateral plate mesoderm to form tha parietal layer and the visceral layer
- this then begins to fold to form a horseshoe shape creating an Intraembryoinc cavity which is u shaped
- the bend in the U becomes the pericardial cavity
- limb of U becomes 2 cavities pericardioperitoneal (pleural) and peritoneal cavities.
13
Q
Give an overview of the development of the pharyngeal clefts and pouches
A
- Clefts separate the arches externally.
- First cleft is the only one that contributes towards the adult structures: external acoustic meatus
- The endoderm of the foregut grows and forms pouches which become: auditory tube, tonsils, thymus and parathyroid gland.
- 1-4 well developed, 5th absent
14
Q
Give an overview of the development of the face week 4-5
A
- Development begins in week 4 and forms from 5 swellings.
- Frontonasal
- Maxillary X2
- Mandibular X2
By week 5 two events occur:
- Maxillary prominences enlarge in the medial direction
- Nasal placodes appear and form medial and lateral processes
15
Q
Give an overview of the development of the face week 6-8
A
- Maxillary prominences enlarge in the medial direction
- the maxillary prominences fuse with the lateral and medial nasal processes to form the upper lip
- Nasal placodes appear and form medial and lateral processes
- medial nasal processes merge towards each other and form intermaxillary segments
16
Q
How is the Palate formed?
- consequences fo improper formation?
A
- Develops from the fusion of the primary and secondary palate
- Grows obliquely down and then elevates
- Fuses in the midline at palatine raphe
- At the same time frontonasal process and medial nasal processes form nasal septum
- if this doesn’t occur properly this results in a cleft palate/ lips
17
Q
Give an overview of Ear formation
A
- Eyes and ears arise from ectodermal placodes
- Placodes are thickened areas of ectoderm which have interacted with the neural tube.
- External and middle ear derived from first 2 pharyngeal arches and cleft and pouch
- Inner ear develops at day 22 into otic placode.
- Otic vesicle enlarges and forms 2 parts: Dorsal vestibular portion- semicircular canals and Ventral cochlear portion- cochlea
18
Q
Give an overview of Tongue formation
- anterior
- posterior (pharyngeal)
A
Anterior Tongue
- 3 tongue buds form from 1st arch
- The distal buds (lateral lingual swellings) expand and fuse and overgrow the median bud to form the anterior tongue.
Pharyngeal tongue (posterior)
- Two swellings from 2nd, 3rd & 4th arches.
- V-shaped line represents the line of fusion, with a midline depression (foramen caecum- the origin of the thyroid gland)
- Hence different innervation of the tongue
19
Q
What is the innervation for different parts of the tongue?
A
- CN V3 - oral sensation (1st arch) blue
- CN VII - oral taste (2nd arch) red
- CN IX - pharyngeal taste/sensation (3rd arch) green
26
Q
What is Intestinal Atresias?
- presentation/diagnosis
- managment/treatment
A
- Obstructruction of the intestinal tract
- Oesophageal atresia (with/out TO fistula)
- Duodenal atresia
- Jejunal / Ileal atresia
- (incomplete – stenosis)
- Polyhydramnios
- Intestinal obstruction
- Emergency that needs surgery
