Which region of the embryo does the connecting stalk and yolk sac duct attach to once the ventral body wall has formed?
The umbilical region
What are the 2 cell types found in the blastocyst, and what will each become?
- Embryoblast - the embryo proper
- Trophoblast - support tissue
Where are the cells that form the extraembryonic mesoderm derived from?
The primitive yolk sac
What structures arise from the mesoderm?
- Smooth muscle
- Connective tissue
- Vessels and tissues of organs
- Cardiovascular system
- Bone marrow and blood cells
- Skeletal muscle
- Reproductive organs
- Excretory organs
What are the 2 parts of the prosencephalon at 5 weeks?
What structures are formed by the liver growing into the mesenchyme of the septum transversum?
- It forms the lesser omentum between the oesophagus, stomach, duodenum and the liver
- It also forms the falciform ligament, extending from the liver to the ventral body wall
What layer of the embryo does the GIT develop from?
What is the lacunae stage of development of the trophoblast?
It is where vacuoles in the trophoblast fuse together to form large lacunae
What organs arise from the ectoderm?
What structure does the spleen primordium develop within?
The dorsal mesogastrium
What is found at the cephalic end of the primitive streak?
The primitive node, surrounded by the primitive pit
What makes up the lining of the exocoelomic cavity?
- The exocoelomic (Heuser's) membrane
What is the name of the congested, dilated maternal vessels that are eroded by the syncytiotrophoblast?
Where is the amniotic cavity in relation to the bilaminar disc?
It is found adjacent to the epiblast
What 3 reactions must occur for implantation?
- Decidual reaction - epithelium of uterus reacts to allow implantation
- Synctitiotrophoblast formation - trophoblastic cells merge together
- Embryoblast differentiation - embryo becomes epiblast and hypoblast
By the end of what week does the oesophagus finish elongating?
What is neurulation?
It is the process whereby the neural plate forms the neural tube
What causes anencephaly?
A failure of the crainal neuropore to close
What day does the caudal neuropore close?
The 28th day
What are the 3 regions of the gut?
Where is the ventral mesentery of the oesophagus, stomach and upper part of the duodenum derived from?
The septum transversum
What are the 2 layers of the inner cell mass at day 8?
What structure is formed at the beginning of gastrulation, and roughly what day is it produced?
- The primitive streak
- Day 14-15
What are the 2 parts of the rhombencephalon at 5 weeks?
Which 2 areas of the embryo have no mesoderm; they have direct contact of endoderm and ectoderm?
The buccopharyngeal membrane
The cloacal membrane
What are the primary villi of the developing embryo?
They are columns of cytotrophoblasts protruding into the syncytiotrophoblast
What structure does the greater omentum develop from?
The dorsal mesogastrium
What are exocoelomic cysts?
They are pockets of fluid that are formed when the exocoelomic membrane changes
What structure is the cloaca derived from?
What are the 3 layers that gastrulation produce?
Which border of the stomach grows the fastest, the dorsal or ventral?
Dorsal - forms the greater curvature
What are the cells called that are adjacent to the cytotrophoblast that line the amniotic cavity?
What is spina bifida?
It is a failure of the neural tube to close anywhere from the cervical region caudally, leaving a hole in the back
By what week does the epithelium filled lumen of the oesophagus clear?
How is an organ secondarily retroperitoneal?
The organ is originally covered by peritoneum, but it fuses with the posterior abdominal wall to become retroperitoneal; e.g. pancreas
How much does the stomach rotate around its longitudinal axis?
90 degress, causing the left side to face anteriorly and right face posteriorly
What is gastrulation?
It is the formation of the 3 germ layers of the embryo from the bilayer disc
What structure covers the defect of implantation by day 9?
The fibrin coagulum
What forms between the extracoelomic membrane and the trophoblastic cells?
The extraembryonic mesoderm
Which region of the gut communicates with the yolk sac via the vitelline duct?
What are the 3 dilations of the neural tube at the cranial end called?
The primary brain vesicles
- Prosencephalon - forebrain
- Mesencephalon - midbrain
- Rhombencephalon - hindbrain
What structures arise from the endoderm?
- Epithelia of the GIT and respiratory tract
- Glandular cells of associated organs such as liver and pancreas
The lengthening of what structure is responsible for the curving of the embryo?
The neural tube
The appearance of what structure induces ectoderm to thicken and form the neural plate?
Which week does neurulation begin?
The 3rd week
Which half of the embryo does the primitive streak form?
The caudal half
What happens to the blastocyst cavity at day 9?
It becomes larger and is called the exocoelomic cavity
What are the 2 directions neural crest cells travel after they dissociate from the neural tube, and what structure do they become?
- Dorsally; melanocytes in the skin and hair follicles
- Ventrally; sensory ganglia, sympathetic neurones, Schwann cells and cells of adrenal medulla
Which neuropore is the first to close, and on what day?
The cranial neuropore at day 25
How does the ventral body form?
The 2 lateral body walls fold and move ventrally to meet each other
What is the exocoelomic cavity/ primitive yolk sac referred to after the formation of the chorionic cavity?
Secondary yolk sac
Where does the fusion of the neural crests begin in the embryo?
It begins at the 5th somite, found in the cervical region
What is the chorionic plate?
It is the extraembryonic mesoderm that lines the inside of the cytotrophoblast
Which week of development does the stomach first appear?
Through what structures do the caudal and cephalic ends of the nerual tube communicate with the amniotic cavity once fusion of the tube has begun?
The cranial and caudal neuropores
After the formation of the chorionic cavity, how is the embryo connected to the surrounded cytotrophoblast?
It is connected by the connecting stalk