Embryology Flashcards
How does the pancreas develop within the mesentery?
Tail in dorsal mesentery
Head in ventral mesentery
During development which part of the gut tube has both dorsal and ventral mesentery?
Foregut
When does lateral folding of the embryo occur during development?
Days 18-24
What name is given to the identical ball of cells formed before the blastocyst?
Morula
What are the 2 cell layers in a blastocyst?
Trophoblast and Embryoblast
When does implantation occur?
Day 6
When does the amniotic cavity form?
Day 8
What is the Syncitiotrophoblast?
Multinucleated cell, multiple cells fused together, surrounds embryo
Secretes enzymes to aid invasion of the endometrium by the forming embryo
When does the primary yolk sac form?
Day 9
What does the extraembryonic mesoderm consist of?
Cells, extracellular matrix, cavities (coelom)
What is formed by cavitation of extraembryonic mesoderm?
Chorionic cavity, fluid filled
At day 13, what structure is present which will form the future umbilicus?
Connecting stalk, made from extraembryonic mesoderm
At day 13, what cell laters form the bilayer disc?
Epiblast and hypoblast
When is the first time to notice that the menstrual period is late?
Day 15
What are the primitive streak and node?
Raised areas of ectoderm, significant cell division
Streak extends from cloaca to primitive node
What are primitive groove and pit?
Indentations of ectoderm in centre of streak and node
At day 15, what primitive forms of the mouth and anus are present?
Prochordal plate - mouth
Cloacal membrane - anus
What is Gastrulation?
Formation of 3 germ cell layers
Migration of epiblast cells from primitive streak towards hypoblast
During Gastrulation, which parts of the embryonic disc remain mesoderm free?
Buccopharyngeal and cloacal membranes
What does ectoderm develop into?
Skin and neural tissue
What does endoderm develop into?
Lining of gut tube, respiratory system and urinary system
What does mesoderm develop into?
Paraxial - somite (skeleton, muscle, dermis of skin)
Intermediate - genitourinary
Lateral plate - serous membranes
Muscle, bone, connective tissue, organs, body cavity linings (peritoneum)
What are somites?
Somites form axial skeleton, associated muscle & dermis of skin Appear sequentially between days 20 – 30
30-35 pairs formed by paraxial mesoderm
Each supplied by single spinal nerve and migrate to form parts of body
Explains dermatomal sensory mapping of the skin - migrate towards the anterior midline and pull spinal nerves with them
Which cavity is drawn around the disc during folding?
Amniotic cavity
What is reversal?
Longitudinal folding moves heart, brain, mouth & anus to adult position
At what point are tissues of the folding disc folded and reflected?
Umbilicus
What forms the dilated terminal portion of the gut tube?
Bladder
What does the urorectal septum separate?
Cloaca is separated into the bladder and rectum
What is the name of the point where the cloacal membrane meets the septum?
Perineal body
What process results in the gut tube having its adult disposition?
Herniation and rotation of the gut tube 270 degrees about the SMA
What is an Omphalocele?
Abdominal wall defect
Organs in sac outside abdomen
What is gastrocshisis?
Abdominal wall defect
Organs can protrude through umbilicus
What can happen if the gut rotates clockwise about the SMA?
Volvulus/obstruction as transverse colon is behind midgut and rotated on own mesentery which can cut off blood supply
What is a Meckels Diverticulum?
Remnant of vitellointestinal duct
If infected or inflamed, will present in similar way to appendicitis
What is an imperforate anus?
Abnormal urorectal septum formation
What developmental feature forms the neck and lower face?
Pharyngeal arches
What are pharyngeal arches innervated by?
Each arch is innervated by a cranial nerve and receives blood from an aortic arch artery
What features are formed by the pharyngeal arches?
Outer & middle ear Tongue Facial & neck muscle Larynx Thyroid, parathyroid & thymus gland Part of facial skeleton
Notocord forms within the mesoderm layer but what does it form?
Part of vertebral column
What can form from remnants of primitive streak tissue?
Sacrococcygeal teratoma
What folds to form the neural tube?
Neural plate
What is spina bifida?
Defective neural tube closure together with anomalies of covering tissues, non fusion of vertebral arch
What are the 4 types of spina bifida?
Spina bifida occulta - unfused vertebral arch
Meningocoele - dura mater and subarachnoid space protrude through
Meningomyelocoele - spinal cord protrudes through
Myeloschisis - neural tissue fails to migrate so remains at surface
What are migrating neural crest cells involved in?
Heart septation Face & skull connective tissues GI tract ganglia (Parasympathetic) Adrenal medulla Melanocytes Meninges (Arachnoid & pia) Dorsal root ganglia Autonomic nerve ganglia
What key events occur during week 1?
Fertilisation
Blastocyst formation
Implantation
What key events occur during week 2?
Implantation
Bi laminar disc formation
Amniotic and yolk sac formation
What key events occur during week 3?
First missed period Primitive streak formation Gastrulation Neural plate & groove formation & folding Somite formation
What key events occur during week 4?
Heart formation (beats) Eye and ear primordia Pharyngeal arches Neural tube formed & folds fused Upper limb growth begins
What key events occur during week 5?
Further eye development Feet and hand plates present Face begins to form Brain vesicles form Lower limb growth begins
What key events occur during week 6?
Oral & nasal cavities, & upper lip form
External acoustic meatus forms
Digits begin to appear
Gut rotation & return to abdo cavity
What key events occur during week 7?
Genital development starts
External ear forms
Palate formation
Gut rotation & return to abdo cavity
What is contained in the falciform ligament?
Ligamentum teres - remnant of umbilical vein
What is contained in the ventral mesentery?
Liver
Gallbladder
Pancreas
What is contained in the dorsal mesentery?
Spleen
Pancreas
