Session 9 : Early embryonic Flashcards by Nevan Senaratne

What section of the fetus is this showing?

Median section

How well did you know this?

Not at all

Perfectly

What section of the fetus is this showing?

Transverse section

How well did you know this?

Not at all

Perfectly

What section of the fetus is this showing?

Frontal (coronal) section

How well did you know this?

Not at all

Perfectly

What is the anatomical terminology for Front, Back, Superior, and Inferior?

Front = Ventral
Back = Dorsal
Superior = Cranial, cephalic
Inferior = Caudal

How well did you know this?

Not at all

Perfectly

What is the notochord?

Transient embryonic structure that acts as a center for signaling of adjacent tissues; later incorporated into the backbone

Crucial for maintaining left-right asymmetry
Notochord is ventral to neural tube
Defines axis of embryo

How well did you know this?

Not at all

Perfectly

What is the development of the notochordal process?

While the primitive streak regresses…

Forming Notochordal Process
- Group of epiblast cells migrate caudally from primitive node = left behind as ‘notochordal process’

moves cranially and forms a tube underneath ectoderm and above mesoderm

How well did you know this?

Not at all

Perfectly

What is neurulation?

Development of the nervous system

Formation of the neural tube structure as a result of lateral folding of neural folds

How well did you know this?

Not at all

Perfectly

What weeks does neurulation occur?

Week 3-4

How well did you know this?

Not at all

Perfectly

What happens during week 3 of neurulation?

ECTODERM FORMS NEURAL PLATE

Ectoderm thickening to form neural plate
Notochord elongates, neural plate extends to oropharyngeal membrane in cranial part of embryo
Day 18 = neural plate dips down (invaginates) centrally, forming neural groove
End of 3rd week = lateral edges of neural plate elevate, forming neural folds

How well did you know this?

Not at all

Perfectly

What happens at the end of week 3 (Neurulation)?

NEURAL PLATE FORMS NEURAL TUBE

Neural folds move together and fuse, converting the neural plate into the neural tube
Fusion begins in middle of embryo and progresses towards cranial and caudal ends in zip-like fashion

How well did you know this?

Not at all

Perfectly

What structures communicate with the amniotic cavity until fusion of neural folds is complete?

Cranial neuropore and caudal neuropore

How well did you know this?

Not at all

Perfectly

What day does closure of cranial neuropore occur on?

Day 25

How well did you know this?

Not at all

Perfectly

What day does closure of caudal neuropore occur on?

Day 28

How well did you know this?

Not at all

Perfectly

What marks the end of neurulation?

Closure of both cranial (day 25) and caudal (day 28) neuropores

How well did you know this?

Not at all

Perfectly

What structures are established upon the closure of the caudal neuropore?

1) Embryo establishes rudimentary spinal cord caudally
2) Embryo establishes brain vesicles cranially

How well did you know this?

Not at all

Perfectly

What is the neural tube?

The map of the entire CNS of the developing embryo

How well did you know this?

Not at all

Perfectly

What are neural crest cells?

Appearing at the end of Neurulation
Transient, migratory, multipotent cells that give rise to multiple derivatives

How well did you know this?

Not at all

Perfectly

When do Neural Tube Defects (NTDs) occur?

When the neural tube fails to completely close by 6 weeks

How well did you know this?

Not at all

Perfectly

What are the two types of NTDs?

1) Anencephaly
2) Spina bifida

How well did you know this?

Not at all

Perfectly

Anencephaly NTD occurs when neural tube fails to close in which region?

Cranial

How well did you know this?

Not at all

Perfectly

Spina bifida NTD occurs when the neural tube fails to close in which region?

Caudal

How well did you know this?

Not at all

Perfectly

What vitamin can prevent 50-70% of all NTDs in pregnant mothers?

Folic acid

How well did you know this?

Not at all

Perfectly

What do epiblast cells migrating at the central region of the primitive node form?

The notochord

How well did you know this?

Not at all

Perfectly

What do epiblast cells that migrate laterally form?

Paraxial, intermediate and lateral plate mesoderm

How well did you know this?

Not at all

Perfectly

What does the paraxial mesoderm form?

Somites → axial skeleton, voluntary muscles and dermis

What does the intermediate mesoderm form?

Urogenital system

What does the lateral plate mesoderm form?

Suprarenal, spleen, primordial heart ## Footnote Serous membranes: Pleura, pericardium, peritoneum

During the third week, the paraxial mesoderm is organised into segments called?

Somitomeres

At the end of the third week, somitomeres organize into what?

Somites

New somites appear in cranio-caudal sequence at a rate of how many pairs a day?

3 pairs a day until the end of the 5th week when there are 42-44 pairs present

What are the two main products of somite differentiation?

1) Sclerotome 2) Dermamyotome

What does the sclerotome give rise to?

Axial skeleton (ribs, vertebrae)

What does the dermamyotome consist of?

Dermatome = dermis on back Myotome = myoblasts which give rise to skeletal muscle

Dermic and connective tissue of the back arise from the?

Dermatome

Axial and appendicular skeletal muscle of the limbs arise from the?

Myotome

Axial skeleton arises from the?

Sclerotome

Why are somites important?

1) Transient structures that form basic developing body plan of vertebrates via segmentation, bone and muscle development, template of nervous system 2) Form different structures along different positions along the anterior-posterior axis 3) Somites are basis for multiple mature cell types in the body

What mature cell types do somites give rise to?

- Adipocytes - Chondrocytes - Osteocytes - Fibrocytes - Muscle cells - Nervous system cells

What is somite innervation?

Each myotome & dermatome retains its spinal nerve root innervation from its somite segment of origin, no matter where cell migrates

What do somites determine?

The migration pattern of neural crest cells and spinal nerve axons

What are dermotomes?

Areas of skin supplied by a single spinal nerve level ## Footnote Testing of dermotomes is the basis of the neurological examination.

What shape does the embryo take as folding of the flat tri-laminar embryo starts?

Cylindrical (double-tube body plan)

What isolates the embryo from the embryonic membranes?

The umbilical cord

In how many directions does embryo folding occur?

Simultaneously in two directions

What happens during cephalo-caudal flexion?

- Cranial rim folds ventrally = forming future face, neck, chest - Brings primordial heart into thoracic position

What happens during lateral flexion?

- Intraembryonic coelom formed - Ectoderm sheet fuses = ectoderm covers entire embryo

What are the consequences of embryo folding?

Establishes tube-within-tube body plan in which embryo consists of two main tubes: 1) Outer ectodermal tube that forms SKIN 2) Inner endodermal tube that forms GUT

What does the lateral plate mesodermal part of the mesoderm split to form?

Coelom

What does the lateral plate mesoderm split into during the third week?

Dorsal somatic mesoderm (somatopleure) and ventral splanchnic mesoderm (splanchnopleure)

What does the intraembryonic coelom give rise to?

1) Pericardial cavity 2) Pleural cavity 3) Peritoneal cavity

Which one of the following cells or structures are not derived from the neural crest cells? a) Teeth b) Ribs c) Enteric ganglia d) Facial bones e) Melanocytes

b) Ribs

What is the fate of the intermediate mesoderm?

Urogenital system

What is the fate of the somatic mesoderm?

Connective tissue of body wall and limbs

What is the fate of the paraxial mesoderm?

Somites

What is the fate of the splanchnic mesoderm?

Smooth muscle, connective tissue and vasculature of the gut

What is the fate of the myotome?

Skeletal muscle of back and body wall

What is the fate of the dermatome?

Dermis of skin; the skin of the back

What is the fate of the sclerotome?

Tendon and bone of spinal column

What disorder results from failure of closure in the caudal region, but without herniation of meninges or spinal cord?

Spina bifida occulta

What disorder results from a failure of closure in the cranial region?

Anencephaly

What disorder results from a failure of closure in the caudal region, with herniation of meninges or spinal cord?

Spina bifida cystica

Spina bifida occulta results from a defect in the formation of which region of a vertebra?

a) Vertebral arch

Which plane of folding is driven by growth of somites?

Transverse

Which plane of folding creates the body wall and gut tube?

Transverse

Which plane of folding is driven by growth in the cranial and caudal regions?

Longitudinal

Which plane of folding pulls the connecting stalk ventrally?

Longitudinal

Which plane of folding relocates the heart from the oral region to the thorax?

Longitudinal

Which plane of folding draws the amnion around the embryo?

Transverse

Match the image with the most appropriate description: Normal, meningocoele, myelomeningocoele, spina bifida occulta.

A = Normal B = Spina bifida occulta C = Meningocoele D = Myelomeningocoele

What is the fate of the lumen of the neural tube?

The central canal of the spinal cord and ventricular system of the brain

What is the fate of the neural tube?

The spinal cord

What is the fate of the neural crest cells?

Sympathetic chain ganglia

What is the fate of the notochord?

The nucleus pulposus of the spinal cord

What does the cephalic end of the neural tube develop into?

Primary cerebral vesicles, and ultimately the brain

What name is given to agents that cause birth defects?

Teratogens

Which of the following is NOT a teratogen? a) Folic acid b) Rubella virus c) Alcohol

a) Folic acid

What is given to agents that cause birth defects?

Teratogens

Which of the following is NOT a teratogen? a) Folic acid b) Rubella virus c) Alcohol d) Vitamin A e) Thalidomide

a) Folic acid

What is the most sensitive period of development with regard to teratogenesis?

a) Embryonic period

Based on the woman's diet, the GP suggests folic acid supplementation. Why is this beneficial?

Promotes neural tube closure

Signals emanating from the ___ signal to the overlying ectoderm to thicken and form the neural ___. This becomes raised at the margins, with the neural folds flanking a neural ___. The folds move medially, fusing initially in the ___ region.

Signals emanating from the notochord signal to the overlying ectoderm to thicken and form the neural plate. This becomes raised at the margins, with the neural folds flanking a neural groove. The folds move medially, fusing initially in the caudal region.

Epiblast cells migrating at the central and most cranial part of the primitive node form the ___

Notochord

Epiblast cells migrating laterally from the primitive node form the ___, ___ and ___ plate mesoderm

Epiblast cells migrating laterally from the primitive node form the paraxial, intermediate and lateral plate mesoderm

Differentiation of the mesoderm

During gastrulation, specific regions of the epiblast migrate through different parts of the node and primitive streak to form mesoderm

What is a meningocoele?

A meningocoele is a birth defect where there is a sac protruding from the spinal column. The sac includes spinal fluid, but does not contain neural tissue.

What is myelomeningocele?

Myelomeningocoele is a type of spina bifida. This is when the neural tube has failed to close and the neural tissue is exposed on the baby's back.