DEV Flashcards
What is the rate of children born a ‘birth defect’?
1:33 babies have a “birth defect” which must be treated/managed
(this is live births only- many more case miscarriage)
What is hypospadia?
A misplaced urethral opening in males
Where does fertilization occur in the FT?
The most distal region
What are the 5 stages of embryonic development
- Early Blastocyst Formation
- Blastocyst Split
- Two Germ layer Stage
- Three Germ Layer Stage
- Extra-embryonic tissue
What occurs during early blastocyst development?
- Egg fertilized -> uterus [dividing on the way 1 division/24 hours]
- Morula = Ball of cells = -> 16 cell stage after 3 days
- Blastocyst = Cell Mass -> at 4 days.
- On 4th day Blastocyst undergoes cavitation to form a cavity -> Blastocoele
- Blasotcyst is asymmetrical with more cells up the top.
- Called the ‘ Inner cell mass’
What are the two types of cell in the blastocyst?
Outer epithelial layer (trophoblast)
- Forms extra embryonic structures like placenta.
Inner cell mass
- Forms embryo
At what stage of development does the blastocyst implant into the uterine wall?
Between days 5 and 10
What happens during the two germ layer stage?
- Inner cell mass splits to form the:
- Bilaminar Disk = Epiblast above and Hypoblast below
- Embryo forms from part of the epiblast
- Rest of the epiblast and all of the primitive hypoblast give rise to extra-embryonic tissues
What does the hypoblast from?
It bgins to surround the blastocoele - it is called the yolk sac though it does not have any yolk in humans
What does the epiblast form?
- Forms a cavity called the Amniotic Sac.
- Upper cells form the roof
- Lower cells will form the embryo
- Embryo will form at the point of overlap b/w Yolk Sac and Amniotic Sac
What are three germ layers and what do they form?
Ectoderm - nervous system and epidermis
Endoderm - epithelium of gut and associated organs
Mesoderm - blood, hear, kidneys, gonads, most bones, muscles and CT, urinary tract, haemopoetic tissue, pleura, peritoneum, pericardium and NOTOCHORD
How does the Notochord form and what does it do?
The notochord forms in the mid-line (the location of the vertebral column). The notochord runs the length of the embryo and gives it its axis. its used as a landmark for other structures and produces chemical signals do drive development in the surrounding structures.
The Notochord induces the overlying ectoderm to form the neural plate which in turn forms the neural groove which folds in on itself to give the neural tube. The neural tube runs the length of the embryo and become the brain and spinal cord.
What is the neural crest?
The cells at the top of the neural tube form the neural crest. These are ectodermal cells which migrate away from the neural tube to contribute to a wide range of structures. The first thing they do is separate the neural tube from the ectoderm
What are the neural crest derivatives and what happens if these cell fail to migrate properly?
Dorsal root ganglia • Sympathetic and parasympathetic ganglia • Enteric ganglia • Schwann cells • Melanocytes • Dentine • Muscle, cartilage and bone of skull, jaws, face and pharynx
Cells are heading for the midline of the face, they come from the back (of the face) and migrate around. Failure to do so properly can cause cleft lip and palate (1:1000)
This occurs in the 4-5th week of life when too few cell end up in the midline
What is the difference between mesoderm and mesenchyme?
Mesoderm
• Mesoderm is one of the three embryonic tissue types (origin)
Mesenchyme
• Mesenchyme refers to the shape and behavior of the cells
• Can be of ANY origin, but often mesodermal origin
• If Cells are MESENCHYMAL they lose contact with one another and move independently and alone
• If Cells are EPITHELIAL they are closely bound together.
- Cancer is a conversion to a mesnechymal cell (i.e. which allows metastasis)
What are the three types of mesoderm?
1) Paraxial
2) Intermediate
3) Lateral
What does paraxial mesoderm from?
Closest to Midline
(i) Dermis of skin
(ii) Axial skeleton
(iii) Axial and limb buds
What does intermediate mesoderm from?
In Between
• Urogenital system (kidneys + tubes)
What does lateral mesoderm from?
Closest to the Edge
1) Ventrolateral body wall
2) Visceral pleura, peritoneum
3) Blood vessels and blood forming tissue
4) Heart
5) Wall of gut and respiratory tissue
What are somites and how do they form?
- Somitomeres -> Swellings appear progressively down length of paraxial mesoderm, on either side of the Neural Tube.
- At the 20 somitomere stage, the 8th pair of somitomeres becomes an independent pair of somites.
- Somite is a free somitomere.
What happens to the somitomeres above and below 8?
- After the 8th changes, the 9th then changes etc…
- Region above 8th somitomere never forms somites.
- Region above 8th is the head and neck.
- Thus below that is C1 Vertebra and down
What do somites become?
sclerotome and dermomyotome
Where is the sclerotome and what does it form?
The sclerotome is in the inner region of the somite.
Medial Scleretome forms:
Vertebral body
IV disk
Proximal ribs
Lateral Sceretome forms:
Vertebral arch
Pedicle of vertebra
Distal ribs
What are the sub-branches of the Dermomyotome?
Myotome
Dermatome
Where is the myotome and what does it form?
Myotome is in the middle of the somite
It forms the back muscles
Medial myotome (extensors) 1. Intrinsic back muscle
Lateral myotome (flexors)
- Limb muscles (after migration)
- Muscles of ventrolateral body wall
- Intrinsic back muscles
What does the lateral mesodermal plate give rise to?
Appendicular skeleton (arms and legs) Body wall musculature
Where does the axial skeleton come from?
The sclerotome