Embryology 5: 4th Week & Establishing Body Plan MCQ
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Questions and Answers

What structure develops at the caudal position relative to the heart during embryonic folding?

  • Septum transversum (correct)
  • Foregut
  • Ventricular wall
  • Primordial heart

Which of the following structures is formed from the oropharyngeal membrane breaking?

  • Umbilical cord
  • Cloacal membrane
  • Stomodeum
  • Esophagus (correct)

What is the relationship between the foregut and the heart during embryonic development?

  • The heart develops anterior to the foregut (correct)
  • The foregut develops into the heart
  • They develop next to each other
  • They are formed from the same embryonic layer

During which embryonic folding does the body stalk become ventral?

<p>Median plane fold (tail region) (D)</p> Signup and view all the answers

How does the midgut interact with the vitelline sac during development?

<p>It communicates with the vitelline sac through the vitelline duct (D)</p> Signup and view all the answers

What is a significant evolutionary benefit of bilateral symmetry?

<p>Improved mobility and food seeking (B)</p> Signup and view all the answers

During which weeks does the organogenetic period occur?

<p>4 to 8 weeks (B)</p> Signup and view all the answers

At what stage can the heartbeat of an embryo typically be detected by Doppler ultrasonography?

<p>5th week (A)</p> Signup and view all the answers

What was a major consequence of thalidomide when taken by pregnant women?

<p>Resulted in limb deformities (A)</p> Signup and view all the answers

What is the phylotypic stage of the embryo characterized by?

<p>Similarity to vertebrates' embryos (D)</p> Signup and view all the answers

Which process occurs in the paraxial mesoderm during development?

<p>Segmentation (C)</p> Signup and view all the answers

What two major events occur during the 4th week of development?

<p>Folding and segmentation (A)</p> Signup and view all the answers

What is the primary function of the cardiovascular system during the organogenetic period?

<p>Transporting nutrients (A)</p> Signup and view all the answers

What occurs when the concentrations of retinoic acid and FGF8 reach a reciprocal level?

<p>The paraxial mesoderm gets segmented. (C)</p> Signup and view all the answers

Which genes oscillate between permissive and non-permissive states during somitogenesis?

<p>Notch family genes (C)</p> Signup and view all the answers

What is the primary outcome of mesenchymal-to-epithelial transition during somitogenesis?

<p>Formation of somites (D)</p> Signup and view all the answers

Which structure will differentiate into the dermatome?

<p>Myotome (D)</p> Signup and view all the answers

Which part of the sclerotome forms the intervertebral disks?

<p>Arthrotome (A)</p> Signup and view all the answers

What does the medial sclerotome primarily differentiate into?

<p>Meninges and blood vessels (C)</p> Signup and view all the answers

What are the three main territories that each somite differentiates into?

<p>Sclerotome, dermatome, myotome (A)</p> Signup and view all the answers

What role does the central sclerotome play in development?

<p>Formation of proximal ribs and certain processes of vertebrae (A)</p> Signup and view all the answers

What is the primary function of the serosa in coelomic cavities?

<p>To allow organs to move and grow independently (C)</p> Signup and view all the answers

What layers constitute the serous membrane?

<p>Mesothelium and connective tissue (A)</p> Signup and view all the answers

What evolutionary advantage does the intraembryonic coelom provide to tripoblastic animals?

<p>Fluid-filled space for organ protection and movement (A)</p> Signup and view all the answers

What role does the serous space play in organ function?

<p>Cushions organs against shocks and allows free movement (C)</p> Signup and view all the answers

How does the presence of a true coelom benefit the circulatory system?

<p>It enables the formation of a more complex circulatory system (C)</p> Signup and view all the answers

What happens during the splitting of the lateral plate mesoderm?

<p>A true coelom is formed (A)</p> Signup and view all the answers

What is the relationship between the visceral layer and the organs?

<p>It covers the organs directly (C)</p> Signup and view all the answers

Which of the following is NOT an advantage of having a coelomic cavity?

<p>Enables direct attachment of organs to the body wall (C)</p> Signup and view all the answers

What type of bones do the somites primarily give rise to?

<p>Axial bones (C)</p> Signup and view all the answers

Which structure is responsible for guiding the cells of the ventral sclerotome to form vertebrae?

<p>Notochord (A)</p> Signup and view all the answers

What do epaxial muscles primarily develop from?

<p>Dorsal myotome (A)</p> Signup and view all the answers

The ventral muscle mass formed from myogenic cells gives rise to which types of muscles?

<p>Flexors and pronators (B)</p> Signup and view all the answers

How many vertebrae does one sclerotome form?

<p>Two vertebrae (D)</p> Signup and view all the answers

What is the primary origin of craniofacial bones?

<p>Mesoderm of the head and neural crest cells (D)</p> Signup and view all the answers

Which part of the myotome divides into epimere and hypomere?

<p>Ventral myotome (C)</p> Signup and view all the answers

The nucleus pulposus of intervertebral disks is primarily derived from which structure?

<p>Notochord (D)</p> Signup and view all the answers

What is the fate of the yolk sac during embryonic development?

<p>It degenerates and is no longer needed. (B)</p> Signup and view all the answers

What is formed from the cranial, caudal, and lateral margins of the disc during embryonic development?

<p>The ventral surface of the body. (B)</p> Signup and view all the answers

What roles do the splanchnic and somatic mesoderm play in embryonic development?

<p>The splanchnic mesoderm surrounds the gut tube, while somatic mesoderm forms the body wall. (B)</p> Signup and view all the answers

What distinguishes lateral folding from other forms of folding in embryonic development?

<p>It is driven by the folding of the amniotic sac. (A)</p> Signup and view all the answers

What happens to the vitelline sack during embryonic folding?

<p>It elongates and becomes part of the primitive intestinal tube. (C)</p> Signup and view all the answers

What structural formation occurs due to the folding concentrated in the outer rim of the embryonic disc?

<p>The transition from a trilaminar disc to a cylindrical embryo. (D)</p> Signup and view all the answers

What is necessary for the organs to be suspended in the coelomatic cavity during development?

<p>Both dorsal and ventral mesentery are essential. (A)</p> Signup and view all the answers

During the development process, what structure completely envelops the embryo in the rostral and caudal regions?

<p>The amniotic sac. (C)</p> Signup and view all the answers

Flashcards

Anterior-posterior axis

The imaginary line running from the head to the tail of an embryo during its development.

Dorsoventral axis

The imaginary line running from the back (dorsal) to the belly (ventral) of an embryo.

Bilateral symmetry

The body plan where an organism can be divided into two equal halves along a midline, resulting in mirror images.

Organogenetic period

The stage of embryonic development during weeks 4-8, where all major internal and external organs are formed.

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Teratogens

Substances that can cause birth defects during embryonic development.

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Phylotypic stage

The stage of embryonic development where embryos of different vertebrate species look remarkably similar.

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Folding of embryo

The process where the embryo bends and folds, creating body cavities.

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Segmentation

The process of dividing the body into repeating segments, primarily in the trunk region, not the head.

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Axial Bone Origin

Axial bones, like the vertebral column, develop from somites, segmented blocks of mesoderm.

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Limb Bone Origin

Limb bones, like those in your arms and legs, form from the lateral plate mesoderm.

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Craniofacial Bone Origin

Craniofacial bones, like those in your skull, originate from the mesoderm of the head and neural crest cells.

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Sclerotome Function

The ventral portion of each sclerotome migrates around the notochord to form vertebrae.

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Notochord's Role

The notochord forms the nucleus pulposus of intervertebral disks.

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Epimere Development

The epimere, or dorsal subdivision of the myotome, gives rise to epaxial muscles of the back.

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Hypomere Development

The hypomere, or ventral subdivision of the myotome, gives rise to hypaxial muscles of the lateral body wall and limbs.

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Limb Muscle Origin

Progenitor myogenic cells from the ventral myotome migrate into the limb bud to form limb muscles.

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Retinoic acid and FGF8

These signaling molecules play a crucial role in somitogenesis. Retinoic acid is more concentrated at the anterior (rostral) end, while FGF8 is more concentrated at the posterior (caudal) end. When their concentrations reach a specific balance (wavefront), the process of segmentation begins.

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Somitogenesis

The process of forming somites, which are blocks of mesoderm that give rise to vertebrae, ribs, and muscles. It's driven by a wavefront of signaling molecules.

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Notch Signaling

A key pathway involved in somite formation. Notch signaling genes oscillate between active and inactive states. Both genes need to be active for a somite to form at the wavefront.

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Mesenchymal-to-epithelial transition

Cells in the mesenchyme, a loosely organized tissue, change their characteristics to form a tightly packed epithelial layer during somite formation.

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Sclerotome

A portion of each somite that develops into bones and connective tissues.

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Dermatome

A portion of each somite that develops into the dermis, the deeper layer of skin.

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Myotome

A portion of each somite that develops into skeletal muscles.

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Arthrotome

A subdivision of the sclerotome that gives rise to intervertebral disks, vertebral joint surfaces, and proximal ribs.

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Folding in the Heart Tubes' Region

The two endocardial cavities within the developing embryo merge to form a single pericardial cavity, which encloses the heart.

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Septum Transversum Inversion

Due to the head fold, the septum transversum (future diaphragm) rotates 180 degrees, ending up caudally (below) the heart.

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Primitive Foregut Formation

The head fold incorporates a part of the vitelline sac, creating the foregut, which lies between the brain and heart.

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Oropharyngeal Membrane

A membrane separating the future mouth (stomodeum) from the foregut, it eventually breaks to establish a connection.

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Folding of the Median Plane (Tail Region)

The body stalk and vitelline duct come together ventrally to form the base of the umbilical cord.

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Embryonic Folding

The process by which the trilaminar embryonic disc transforms into a cylindrical embryo.

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Amniotic Sac Role in Folding

The amniotic sac actively folds around the embryonic disc, driving the lateral folding process.

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Lateral Folding

The process of the embryonic disc folding sideways, bringing the lateral plate mesoderm and intraembryonic coelom downwards.

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Vitelline Sack Incorporation

The vitelline sack elongates and gets enclosed within the embryo, forming the primitive intestinal tube with its surrounding endoderm.

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Splanchnic Mesoderm

The visceral layer of the mesoderm that surrounds the gut tube.

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Somatic Mesoderm

The parietal layer of the mesoderm that forms the body wall.

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Dorsal Mesentery

A membrane connecting the gut tube to the dorsal body wall, containing vessels and nerves for the viscera.

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Ventral Mesentery Degeneration

The ventral mesentery, initially present, degenerates except for the region of the future stomach.

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Serosa

A thin membrane lining coelomic cavities and the organs within them, composed of mesothelium and connective tissue.

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Parietal Layer

The outer layer of serosa that lines the walls of the body cavity.

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Visceral Layer

The inner layer of serosa that lines the organs within the body cavity.

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Serous Space

The fluid-filled space between the parietal and visceral layers of serosa.

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Intraembryonic Coelom

The fluid-filled cavity that forms within the mesoderm of an embryo.

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Splitting of the Lateral Plate Mesoderm

The process by which the intraembryonic coelom forms, separating the mesoderm into parietal and visceral layers.

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Study Notes

Embryonic Development

  • Early Development (Weeks 1-3):
    • The anterior-posterior and dorsoventral axes form.
    • Three tissue layers develop.
    • Bilateral symmetry emerges, enabling movement and survival.
  • Organogenesis (Weeks 4-8):
    • All major internal and external structures are created.
    • Organ functions are minimal, except the cardiovascular system.
    • Heart starts beating around days 21-22.
    • Doppler ultrasonography can detect heartbeats in week 5.
    • Teratogens can cause major abnormalities during this period.
  • Thalidomide:
    • A drug previously used to alleviate pregnancy-related nausea and depression.
    • Was not tested on pregnant animals.
    • Administered to pregnant women, leading to limb defects (upper limbs with 4th week exposure, lower limbs with 5th week exposure).

Embryo Body Plan Development

  • Phylotypic Stage (4th Week):
    • The embryo resembles all other vertebrate embryos.
  • Evolution of Animal Body Plan:
    • Tissue formation
    • Bilateral symmetry
    • Development of body cavities (lined by serosa)
    • Segmentation (paraxial mesoderm, only in the trunk, not the head)

Segmentation

  • Occurs in the paraxial mesoderm of the trunk region (around embryonic day 20).
  • Proceeds from rostral to caudal.
  • Determined by gene expression and gradients.
  • Results in the formation of somitomers (35-37 somites).
  • Somites lead to the development of vertebrae.

Segmentation of the Neural Tube

  • The neural tube, adjacent to the somites, develops into functional segments.
  • Each segment innervates associated dermatomes, myotomes, and sclerotomes
  • Develop from adjacent somites

Folding and Development of Body Cavities

  • The embryonic disk folds laterally and rostrocaudally.
  • A tube develops within a tube
  • Development of the primitive intestine
  • Development of coelomic cavities, lined by serosa (membranes).
  • The coelomic cavities evolve in the embryo.

Formation of Somite Derivatives

  • Sclerotome—forms vertebrae, ribs, and parts of the skull
  • Myotome—forms skeletal muscles
  • Dermatome—forms the dermis
  • Syndetome—forms some tendons

Heart Development

  • Formation of the heart starts around day 22 (of gestation).
  • Endocardial heart tubes form in the primary heart field of the embryo.
  • Tubes merge, forming a single heart tube.

Primitive Circulation

  • Blood vessels form from the extraembryonic mesoderm.
  • Networks of vessels develop in the yolk sac, body stalk, chorion, and embryo.
  • Heart tube connects to vessels (vitelline, umbilical, and cardinal).
  • Vitelline veins carry poorly oxygenated blood from the yolk sac.
  • Umbilical veins carry oxygenated blood from placenta.

Additional Notes

  • Thalidomide use in pregnant women led to severe limb birth defects.
  • Congenital diaphragmatic hernia (CDH) is a condition.

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Embryology 5 - 4th Week Body Plan PDF

Description

Explore the stages of embryonic development from early formation to organogenesis. This quiz covers critical periods such as the phylotypic stage and the impact of teratogens like thalidomide on embryonic health. Test your knowledge on how these processes are crucial for the formation of a healthy organism.

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