Week 1- Embryology Flashcards by Kim -

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

How well did you know this?

Not at all

Perfectly

What forms on day 3?

Morula

How well did you know this?

Not at all

Perfectly

What forms on day 5?

Blastocyst

(Trophoblast & Embryoblast= inner cell mass)

How well did you know this?

Not at all

Perfectly

What happens on day 6?

Implantation

Blastocyst hatched out of zona pellucida to stick to uterine epithelium

How well did you know this?

Not at all

Perfectly

What happens in Week 1 of embryology?

Fertilization

Repeated mitotic divisions

Day 3: Morula

Day 5: Blastocyst

Day 6: Implantation

How well did you know this?

Not at all

Perfectly

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

How well did you know this?

Not at all

Perfectly

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) )

How well did you know this?

Not at all

Perfectly

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

How well did you know this?

Not at all

Perfectly

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

How well did you know this?

Not at all

Perfectly

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

How well did you know this?

Not at all

Perfectly

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

How well did you know this?

Not at all

Perfectly

Gastrulation: what happens in relation to buccopharyngeal & cloacal membrane?

Remain mesoderm free

Prochordal plate —> Buccopharyngeal membrane = membrane between mouth and pharynx

How well did you know this?

Not at all

Perfectly

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

How well did you know this?

Not at all

Perfectly

What is the endoderm made from?

Cell that have migrated down the Primative Groove/ Pit and replaced the hypoblast

How well did you know this?

Not at all

Perfectly

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

How well did you know this?

Not at all

Perfectly

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

How well did you know this?

Not at all

Perfectly

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