Week 1- Embryology Flashcards
What happens between day 1-5?
Fertilisation to Blastocyst
Repeated mitotic divisions
Cells wrapped in zona pellucida
Day 3: Morula forms
Day 5: Blastocyst= x2 layers -> Trophoblast & Embryoblast
What forms on day 3?
Morula
What forms on day 5?
Blastocyst
(Trophoblast & Embryoblast= inner cell mass)
What happens on day 6?
Implantation
Blastocyst hatched out of zona pellucida to stick to uterine epithelium
What happens in Week 1 of embryology?
Fertilization
Repeated mitotic divisions
Day 3: Morula
Day 5: Blastocyst
Day 6: Implantation
What happens on Day 8?
Embryoblast —> Bilaminar disc: Epiblast & Hypoblast
Amniotic cavity forms within epiblast
Trophoblast —> Syncytiotrophoblast: Cytotrophoblast (single cell layer) & Syncytium (invasive outer later) containing digestive enzymes
Syncytiotrophoblast invades endometrium
What happens on Day 9?
KEY = Primary Yolk Sac Formation
Hypoblast forms Exocoelmoic membrane which lines the primary yolk sac
(Syncitiotrophoblast invading the uterine glands & blood vessels
(Sinusoids (maternal blood vessels) invade Lacunae (spaces in syncitiotrophoblast) –> Uteroplacentral circulation (Day 10-12) )
What happens on Day 12?
Embryo fully implanted
Extraembryonic mesoderm (cells & ECM) form layer between Bilaminar disk, yolk sac, amniotic cavity and trophoblast (Syncitio and cyto)
Extra-embryonic coelom appear (these will emerge to nearly surround the embryo forming the chorionic cavity)
Lacunae in trophoblast which communicate with maternal endometrial sinusoids deriving nutritional support
What happens on day 13?
Secondary yolk sac present (smaller than first on)
Amniotic sac present
Chorionic cavity formed by cavitation of extra embryonic mesoderm (extra-embryonic coelem)
Connecting stalk (to cytotrophoblast)= extra embryonic mesoderm & forms future umbilicus
Uterine epithelium reformed
What happens during week 2 of embryology including the important days
Day 8: Amniotic cavity formation
Syncitiotrophoblast invades endometrium
Bilaminar disc formation
Day 9: Primary Yolk sac formation
Day 12: Extra-embryonic mesoderm with coelom appearing
Trophoblastic lucunae
Day 13: Secondary Yolk sac formation
Chorionic cavity
Connecting stalk from extra-embryonic mesoderm
What happens during week 3 (brief)?
What is the significance of day 15?
Day 15 = first chance to notice mestrual cycle is late
Formation of Trilaminar disc!
Epiblast known as Ectoderm
Hypoblast known as Endoderm
Gastrulation: what happens in relation to buccopharyngeal & cloacal membrane?
Remain mesoderm free
Prochordal plate —> Buccopharyngeal membrane = membrane between mouth and pharynx
What is Gastrulation & what happens?
When does it happen?
Week 3
Formation of 3 germ cell layer
Primitive streak & node = Raised area of epiblast (rapid epipblast cell division)
Primative streak from cloaca to primitive node
Primative Groove (from streak) & Primative Pit (from node): Cells from ectoderm migrate down these and spread out laterally. Forming mesoderm.
[NOTE: Endoderm formed from migrating epiblastic cells displacing hypoblast]
Primative groove & pit = Indentations of ectoderm in centre of streak & node (cells migrating downwards)
Prochordal plate (mouth) & cloacal membrane (anus
What is the endoderm made from?
Cell that have migrated down the Primative Groove/ Pit and replaced the hypoblast
Gastrulation: How is the notochord formed?
Cells from the primitive node migrate towards buccopharyngeal membrane giving appearance of notochordal plate which folds to form solid cylinder= Notochord
What do the ectoderm, intra-embryonic mesoderm & endoderm form?
What day is this cross section showing and label the parts of the trilaminar disc
~ Day 19
Ectoderm = Skin & Neural tissue
Mesoderm:
- Paraxial:* Develop –> Somites which give rise to: Muscle, Dermis of Skin & Axial Skeleton
- Intermediate:* Genitourinary (Kidney/ Gonards)
- Lateral:* Serous membranes (peritoneum, pleura, pericardium)
Endoderm: GI & Respiratory Tract
Where do somites comes from?
What do they form?
Intra-embryonic mesoderm- paraxial
Axial skeleton (Skull, Vertebrae & Ribs)
Assoicated muscles & dermis of skin
Each supplied by single spinal nerve
Migrate to form parts of body pulling its nerve with it
Explains dermatomal sensory mapping of skin
When does disc folding occur in days & weeks?
How does it fold?
Days 18-24
Week 3 & 4
Longitudinal folding: Head to Tail
Lateral folding: Sides towards each other & meet in anterior midline
Disc folding pulls the amnion (membrane) & amniotic fluid with it
Label and state what happens at each stage of embryonic disc folding: lateral folding
Remember embryonic disc folding pulls the amnion & amniotic cavity with it!
Hypoblast = Endoderm forms exocoelomic membrane which lines yolk sac
Epipblast = Ectoderm lines the amniotic cavity
Mesdoerm: Lateral intra-embryonic mesoderm is continuous with extra embryonic coelam (mesoderm)
Extraembryonic coelom = Chorioic cavity
Blue= Ectoderm
Orange= Mesoderm (both intra & extra)
Yellow= Endoderm
Label the diagram of embryonic folding: Longitundial folding
Also state what happens during this process
Moves heart, brain, mouth & anus into adult position. Known as reversal
Prochordal plate becomes buccopharyngeal membrane
First diagram: Heart, Mouth, Brain
Second diagram: Nueroectoderm= brain grows so quick pushes itself forward
Label the diagram
Tissues of the folding disc are folded towards & reflected at future umbilicus
When is the gut tube formed?
What is its lining, where does it run from?
Label the diagram
Where does the respiratory system form?
Where does the bladder form from?
During embryonic folding- Week 3/4
Gut tube lining = endoderm
Gut tube from: Prochordal plate —> Cloacal membrane
Respiratory system forms from respiratory diverticulum of foregut
Bladder formed from dilated terminal portion of gut
At around week 6 what happens to the gut tube?
Growth causing
Herniated out the umbilicus
Rotation 270 degrees anticlockwise around SMA
What is omphalocele?
Gut tube has herniated out the umbilicus still covered in amniotic sac
What is Gastroschisis?
When the gut tube has herniated out at week 6 gone back in but then herniated out the abdominal wall
What happens if the gut tube rotates clockwise or mal-rotates?
Volvulus/ Obstruction
What is the Vitello-intestinal duct?
What can go wrong?
Initial communication between yolk sac & midgut
Normally the Vitelli-intestinal duct is obliterated but can remain in some people and behave like an appendix - stuff can get stuck here and cause pain in T10 dermatone region
What is the allantois? What does it become?
Unimportant structure in humans
This endodermal tube connects the primitive cloaca to the umbilicu
Becomes fibrous chord called Urachas (medial umbilical ligament)
What is an imperforate anus?
Anus is missing or blocked
Caused by: abnormal urorectal septum formation (normally meets the cloacal membrane) and anal membrane failing to break down- happens at week 7
When does this happen?
How does the cloaca become the bladder and rectum?
When the septum meets the ____ ____ it forms the ____ ____
What problem can occur if the urorectal septum does not form properly
About Week 6
Urorectal septum divides the cloaca into bladder & rectum
When the urorectal septum meets the cloacal membrane it forms the perineal body
Failure: Fistulars- between terminal hindgut, vagina, urethra or all three
Where does the notochord form in?
When does it happen?
What does it form?
In the mesoderm
Forms from primitive node and the cell migration downwards and towards the buccopharygneal membrane
Causes ectoderm to become neural in nature
Forms: Nuclei pulposi of IV discs
What does the neural tube become?
Brain & spinal cord
What forms if the priamtive streak remains?
Sacrococcygeal teratoma
Neuralation: What happens and what day is it completed by?
Day 19:
Neural plate folds to become to Neural Groove
Lateral edges of the ectoderm become more elevated = Neural folds
The dip in middle = Neural Groove
Area where neuroectoderm continuous with surface ectoderm= Neural Crest cells
Collectively= Neural Plate
Day 21:
Neural crest cells detach
Neural groove –> Neural tube
Completed by Day 25
Neuralation: What happens on day 25 & 27?
Cranial neuropore closes (day 25)
Caudal neuropore closes (day 27)
Neural crest cells: Which major organs/ body regions do they contribute to?
What conditions may arise with defective neural crest cell migration?
Heart- Ventricular Septum
Adrenal Glands
Dorsal root ganglion
Melanocytes
What happens if the neural tube fails to close?
Spina Bífida: defective neural tube closure (most often cuadally) with anomalies of covering tissues. Non-fusion of vertebral arch.
What are the types of the Spinda Bífida?
Spina Bidifa Oculta: Incomplete vertebral closure WITHOUT protrusion of spinal cord
Meningocoele: Meninges protrude between vertebrae posteriorly but spinal cord is undamaged
Meningomyelocoele: Portions of spinal cord remains unfused & protrudees posteiroly through opening between vertebrae in a sac formed by the meninges
Over many vertebral levels can lead to mereanencephaly (malformed cranial bones, median cranial defect & cranial protrusion)
Myeloschisis: Neural tissue in ectoderm
What do pharyngeal arches contribute to?
Formation of:
Neck
Lower face
Ear
How many pharyngeal arches form and develop?
What is in each pharyngeal arch?
6 form
5 Develop (1,2,3,4,6)
Innnervated by CN & received blood from aortic arch artery
They are like sausages whose free ends are attached fo the developing vertebral column
By what week have most of the major organ systems been formed?
Week 8
