EMBRYOLOGY-5

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Questions and Answers

What is the significance of bilateral symmetry in the evolution of organisms?

It allows for enhanced reproductive capabilities.

It facilitates efficient motility and food seeking. (correct)

It enables stronger limb development.

It enhances sensory organ development.

During which weeks does the organogenetic period occur?

9th to 12th week

4th to 8th week (correct)

13th to 16th week

1st to 3rd week

What role does the cardiovascular system play during the organogenetic period?

It is responsible for the heartbeat before any other system.

It is the first fully developed system.

It has significant organ function compared to others.

It carries nutrients and is crucial despite others having minimal function. (correct)

What was the consequence of thalidomide use in pregnant women?

Defects in the limbs of newborns. (B) Signup and view all the answers

At the end of which week does the human embryo reach the phylotypic stage?

4th week (B) Signup and view all the answers

In which region does segmentation primarily take place?

Trunk region (A) Signup and view all the answers

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

Folding and segmentation (B) Signup and view all the answers

What is the primary consequence of calcium spikes during the organogenetic period?

They facilitate muscle contractions. (A) Signup and view all the answers

Which of the following networks connects the embryo to the placenta?

Umbilical network (A) Signup and view all the answers

What type of blood is carried by the umbilical veins?

Richly oxygenated blood (A) Signup and view all the answers

During the early development of the embryo, what is the primary role of the liver?

Erythropoiesis (D) Signup and view all the answers

Which vessels are responsible for bringing blood from the heart to the periphery?

Arteries (C) Signup and view all the answers

What does the term 'vasculogenesis' refer to?

Formation of blood vessels (C) Signup and view all the answers

What is the characteristic feature of fetal hemoglobin compared to adult hemoglobin?

Higher affinity for oxygen (B) Signup and view all the answers

Which type of blood disorder is associated with problems in hemoglobin genes?

Thalassemia (C) Signup and view all the answers

Which arteries supply blood to the yolk sac and primitive intestine?

Vitelline arteries (D) Signup and view all the answers

What anatomical structure is positioned caudal to the heart and contributes to the future diaphragm?

Septum transversum (B) Signup and view all the answers

What is the primary role of the pericardial-peritoneal canals?

Allow communication between thoracic and abdominal cavity (A) Signup and view all the answers

What major developmental defect is associated with congenital diaphragmatic hernia (CDH)?

Inhibition of lung development due to cavity communication (A) Signup and view all the answers

Which nerve is responsible for innervating the diaphragm?

Phrenic nerve (A) Signup and view all the answers

Which condition is the most common cause of pulmonary hypoplasia linked to diaphragmatic issues?

Bochdalek hernia (A) Signup and view all the answers

From which germ layer do the first blood vessels develop during the third week of embryonic development?

Mesoderm (D) Signup and view all the answers

Which structure separates the thoracic compartment from the abdominal cavity in development?

Septum transversum (C) Signup and view all the answers

What role does the vitelline duct and body stalk play during development?

Create the umbilical cord (C) Signup and view all the answers

What is the role of Hox genes in segmentation?

They guide cranio-caudal segmentation and organ development. (A) Signup and view all the answers

Which section of the body undergoes somitogenesis?

Only the trunk region. (C) Signup and view all the answers

What is the reason that the most rostral somites (1-7) do not contribute to somite formation?

They form the mesoderm of the branchial arches. (B) Signup and view all the answers

What is the significance of the meeting of retinoic acid and FGF8 gradients in somite formation?

They facilitate somite formation. (B) Signup and view all the answers

How many somites typically remain by the end of somitogenesis?

35-37 somites. (D) Signup and view all the answers

What model explains the process of somite formation?

The clock and wavefront model. (C) Signup and view all the answers

At what embryonic stage does somitogenesis begin?

Around day 20. (B) Signup and view all the answers

In what manner does somitogenesis progress along the body axis?

From rostral to caudal. (D) Signup and view all the answers

What does the somatopleura consist of?

Parietal layer and overlying ectoderm (C) Signup and view all the answers

What region develops into the pericardial cavity during embryonic development?

Rostral part of the intrambryonic coelom (C) Signup and view all the answers

When does the heart begin to beat during embryonic development?

22nd day of gestation (C) Signup and view all the answers

What structure connects the endocardial heart tubes to the aortic system?

Dorsal aorte (D) Signup and view all the answers

Which structure forms an extension of the yolk sac in the body stalk?

Allantois (C) Signup and view all the answers

What is the temporality of the communication between the intrambryonic and extraembryonic coeloms?

It communicates for a brief period in the central region of the embryo. (C) Signup and view all the answers

How do the endocardial heart tubes develop during embryogenesis?

They form two tubes which later fuse into one. (D) Signup and view all the answers

What is the significance of the allantois in human development?

It plays a minor role functionally. (A) Signup and view all the answers

What happens to the yolk sac during embryonic development?

It remains still and is no longer needed. (B) Signup and view all the answers

Which structures are responsible for stiffening the dorsal axis of the embryo?

Notochord, neural tube, and somites. (A) Signup and view all the answers

What type of folding predominantly occurs in the thin flexible outer rim of the embryonic disc?

Medial/sagittal folding. (C) Signup and view all the answers

What is formed when the lateral plate mesoderm and the intraembryonic coelom are brought down during lateral folding?

Primitive gut tube. (A) Signup and view all the answers

Which layer surrounds the gut tube formed during embryonic development?

Splanchnic mesoderm. (C) Signup and view all the answers

What ultimately happens to the ventral mesentery during development?

It degenerates except from the region of the future stomach. (D) Signup and view all the answers

What does the complete envelopment of the embryo by the amniotic sac ensure?

Protection from environmental factors. (D) Signup and view all the answers

Where do the folds converge in the embryo during lateral folding?

In the region where the future umbilicus will be. (C) Signup and view all the answers

Study Notes

Early Embryonic Development

By week 3, the anterior-posterior and dorsoventral axes are formed, along with three tissue layers.
Bilateral symmetry emerges, enabling movement, mate finding, and predator avoidance.
The period from weeks 4-8 involves organogenesis with major structures established, though organ function is minimal apart from the cardiovascular system.
The heart starts beating between days 21-22 and is detectable by ultrasound.
Teratogens during this period can cause significant abnormalities.

Thalidomide and Birth Defects

Thalidomide, a drug used to treat pregnancy-related nausea and depression, proved teratogenic when administered to pregnant women.
Thalidomide exposure during weeks 4-6 led to upper limb defects, and exposure during week 5-7 led to lower limb defects in exposed children.
Critical note: Thalidomide was not tested on pregnant animals beforehand.

Phylotypic Stage

The human embryo reaches its phylotypic stage at the end of week 4.
At this stage, it resembles all other vertebrate embryos.

Embryonic Body Plan Development

Tissues form.
Bilateral symmetry is established.
Body cavities develop (lining by serosa).
Segmentation occurs within the paraxial mesoderm of the trunk.

Segmentation

Segmentation mainly occurs in the paraxial mesoderm of the trunk (not the head).
Development of segmented structures, including vertebrae, is driven by segmentation
Folding events happen during week 4 which delineate specific body cavities.

Somitogenesis

Somites develop in the trunk region (rostral to caudal starting roughly at Day 20).
Somitogenesis is guided by gradients of genes and factors in head-trunk region boundaries.
Somites ultimately give rise to many structures in the trunk.

Hox Genes and Clusters

Hox genes are crucial for establishing the head-tail axis in embryos
Different Hox gene clusters are responsible for different parts of the body, along the head/tail axis.
Mutations in these genes can lead to developmental abnormalities (like a condition called synpolydactyly)

Mesoderm Differentiation

Mesoderm develops three types of cells: sclerotome (bone), dermatome (skin), and myotome (muscle).
The sclerotome may be further divided into different compartments.

Coelom Development

The developing embryo forms a tube-within-a-tube structure.
Internal cavities (coelom) develop within the embryo, lined with serous membranes.

Primitive Circulation

Blood vessel formation, in the yolk sac, body stalk, and chorion begin around week 3.
Vasculogenesis (new vessel formation) and angiogenesis (sprouting of new vessels) are critical processes here.
Vessels connect to the circulatory systems of the embryo, yolk sac, and placenta, establishing circulation.

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Description

This quiz covers essential topics related to the organogenetic period in embryo development, including bilateral symmetry, cardiovascular roles, and critical events during the fourth week. Test your knowledge on crucial concepts like vasculogenesis, fetal hemoglobin, and the implications of thalidomide use.