Embryology II Sem 1 Flashcards
What is teratogenesis?
Process by which congenital malformations are produced in an embryo or Fetus
Which period in development is the most susceptible to abnormal development ?
Embryonic period (weeks 3-8)
What effect would exposure to drugs have on the following periods of development?
- First 3 weeks
- Weeks 3-8
- After week 8
- ) most likely to kill embryo
- ) greatest risk as all major structures form
- ) most organs are well established so risk is low but different organs have different period of susceptibility
What are the 4 steps after implantation has occurred?
- Gastrulation
- Neurulation
- Segmentation
- Folding
Gastrulation:
A) what is it?
B) when does it occur?
C) purpose?
A) process by which 3 primary embryonic germ layers (ectoderm, mesoderm and endoderm) are formed.
B) 3rd week of development (start of embryonic period)
C) to ensure correct placement of precursor tissues
Outline the process of gastrulation
- begins with formation of primitive streak on surface of epic last
- streak consists of node and pit
- cells of epiblast MIGRATE towards streak and INVAGINATE: move beneath epiblast
- once invaginated:
1. some cells displace hypoblast—> creating the endoderm
2. Some cells lie between epiblast and endoderm —> form mesoderm
3. Cells remaining become the ectoderm
What are the Derivatives of the layers of the trilaminar disk?
- Ectoderm: outside
- organs and structures that maintain contact w outside world e.g. nervous system and epidermis - Mesoderm: middle
- supporting tissues e.g. muscle, cartilage, bone, vascular system - Endoderm: inside
- internal structures e.g. epithelial lining of GI tract, respiratory tract
How does body asymmetry form?
By the action of ciliates cells at the node- they send side specific signals
What is situs inversus? How is it formed?
Medical condition where the major visceral organs are mirrored from normal position
Due to immotile cilia
What is the notochord and what is its function?
Solid rod of cells running in the midline
It has a signalling role- releases signalling molecules that signal ectoderm to thicken and become the neural plate
What is neurulation?
Process?
- Formation of the neural tube
- The edges of the neural plate elevate out of the plane of the disk and curl towards each other creating the neural tube
What is segmentation?
Organisation of the mesoderm into:
- paraxial mesoderm
- somatic mesoderm (body)
- Splanchnic mesoderm (viscera)
What is the paraxial mesoderm organised into?
Somites
- first pair appear at day 20
- more appear in sequence- 3 pairs per day until 42-44 pairs are present by week 5
- some disappear and leav 31 in total —> basis of musculoskeletal system
What are the 3 components that somites differentiate into?
- Sclerotium: cartilage and bone component
- Myotome: muscle component
- Dermatome: dermis of skin component
A) what is folding
B) what are the types?
A) flat embryonic disk develops into a cylindrical structure like a C
B)
1. Cephalocaudal folding/flexion- in the longitudinal direction: head fold and tail fold
- Lateral folding: in the transversal direction- leads to formation of primitive gut
