SEM_05_Organoge

116 Questions

During which period does organogenesis occur in humans?

First trimester

What is the etymological meaning of organogenesis?

Organ generation

What is an organ or tissue in its earliest recognizable stage of development referred to as?

Primordium

When are most major malformations produced during human development?

First trimester

During amniogenesis, the amnion is formed from which of the following?

Ectoderm and parietal (somatic) mesoderm

The amnion surrounds and protects the embryo by:

Bathing the embryo in amniotic fluid

Ancestors of reptiles, birds, and mammals shifted from an aquatic lifestyle to a fully terrestrial one, leading to:

Decreased dependence on water for development

In humans, amniogenesis takes place before gastrulation, and is referred to as:

Amniogenesis by cavitation

The amniotic folds rise up and surround the embryo in which region first?

Cephalic region

In horses, dogs, and cats, complete separation of the amnion and chorion occurs due to the degeneration of:

Amniotic raphe

The foetus is often born covered with the amnion in species where:

Complete separation of the amnion occurs

"Amniogenesis by cavitation" in humans accomplishes a similar result as:

"Amniogenesis by folding"

The primitive coelom is divided into intraembryonic and extraembryonic compartments that communicate through which structure?

Umbilical cord

Which structure is a major inductor during early organogenesis?

Notochord

What eventually replaces most of the notochord?

Vertebral column

Where do remnants of the notochord persist?

Intervertebral discs

Which structure plays a crucial role in inducing the formation of the neural plate during early embryonic development?

Notochord

During the early stages of embryonic development, what type of tissue is composed of loosely connected cells embedded in an extracellular matrix?

Mesoderm

Which fold forms first during the transformation of the flat embryo into a cylindrical structure?

Head fold

What does the mesoderm transform into during early embryonic development?

Mesenchyme

Which structure forms the foregut during the folding process of the early embryo?

Endoderm

What type of tissue forms structures and lines organs, vessels, and cavities during early embryonic development?

Epithelium

What is the function of the tail fold during early embryonic development?

Encloses part of the mesoderm and endoderm to form the hindgut

Which type of cells compose mesenchyme tissue during early embryonic development?

Loose cells connected by gap junctions

What does the folding process bring into their ventral positions during early embryonic development?

Mouth and heart

During early embryonic development, what undergoes a transformation from a flat to a cylindrical structure?

Embryo

What is the role of the lateral body folds during early embryonic development?

Encloses the underlying mesoderm and endoderm, forming the midgut

During early embryonic development, what tissue expands throughout the embryonic disc before formation of body walls?

Ectoderm

Which structure is responsible for the segmental partitioning of the body in metameres?

Somites

What do the sclerotomes give rise to?

Vertebrae and ribs

What is the precursor of the muscular cells that lead to the formation of skeletal muscles?

Myotomes

What is the dorsal portion of the somites that gives rise to the connective tissues of the back skin called?

Dermatomes

What is responsible for the formation of organs originated from the endoderm, such as the gut?

Visceral mesoderm

What does the parietal mesoderm contribute to the formation of?

Body wall and foetal membranes

What develops into part of the urogenital system and reproductive system?

Intermediate mesoderm

What is the space between the parietal and visceral mesoderm known as?

Coelom

Which structure stretches from the future neck region to the posterior part of the body?

Embryonic coelom

What forms a cavity for housing the lungs, heart, and abdominal organs?

Coelom

During embryonic development, which cells form temporary epithelia such as the somites and lateral mesoderm?

Primary mesenchymal cells

Which process leads to the formation of the neural tube from the embryonic ectoderm?

Neurulation

What results from the failure to close the anterior (rostral) neuropore during neural tube closure?

Anencephaly

Which cells contribute to the formation of peripheral nervous system and various structures outside the central nervous system?

Neural crest cells

What do the terms 'mesenchyme' and 'epithelium' primarily refer to in embryonic development?

Tissue organization

Which tissue organization can derive into mesenchyme, contrary to traditional understanding?

Ectoderm

What do the neural crest cells develop into during embryonic development?

Peripheral nervous system and craniofacial mesenchymal derivatives

What is the origin of the entire nervous system during embryonic development?

Neural plate

What are the three primary brain vesicles that differentiate into five secondary brain vesicles during brain development?

(Rhombencephalon, metencephalon, and prosencephalon)

Which process results in two temporal openings during neural tube closure?

(Neurulation)

'Spina bifida' is a congenital condition that results from the failure to close which part of the neural tube?

(Posterior) neuropore

'Anencephaly' is a congenital condition that results from the failure to close which part of the neural tube?

(Anterior) neuropore

During which period does organogenesis occur in humans?

Second month of gestation

What is the etymological meaning of organogenesis?

Organ generation

What are the three primary brain vesicles that differentiate into five secondary brain vesicles during brain development?

Telencephalon, diencephalon, mesencephalon

What is the precursor of the muscular cells that lead to the formation of skeletal muscles?

Myotome

Which structure plays a crucial role in inducing the formation of the neural plate during early embryonic development?

Notochord

What is responsible for the formation of organs originated from the endoderm, such as the gut?

Foregut diverticulum

During the early stages of embryonic development, what type of tissue is composed of loosely connected cells embedded in an extracellular matrix?

Mesenchyme

What is the precursor of the muscular cells that lead to the formation of skeletal muscles?

Paraxial mesoderm

What does the folding process bring into their ventral positions during early embryonic development?

Gut and heart

'Anencephaly' is a congenital condition that results from the failure to close which part of the neural tube?

Anterior neuropore

'Spina bifida' is a congenital condition that results from the failure to close which part of the neural tube?

Posterior neuropore

'Amniogenesis by cavitation' in humans accomplishes a similar result as:

'Extra-embryonic coelom' formation

'Amniogenesis takes place before gastrulation and is referred to as:

'Amnion formation'

During which period does organogenesis occur in humans?

Embryonic period

What are the three primary brain vesicles that differentiate into five secondary brain vesicles during brain development?

Telencephalon, diencephalon, mesencephalon, metencephalon, myelencephalon

When are most major malformations produced during human development?

Embryonic period

Which of the following accurately describes the origin of the amnion?

Arises from ectoderm and parietal mesoderm

What is the primary function of the amniotic fluid within the amniotic cavity?

Serves as a protective cushion for the embryo

In humans, what process leads to the formation of the amniotic cavity?

Cavitation resulting in a primordial cavity that grows into the amniotic cavity

What is the fate of the notochord during embryonic development?

It degenerates before being replaced by the vertebral column

How is the primitive coelom divided in amniotes?

Into intra-embryonic and extra-embryonic compartments through the umbilical cord

What role does the notochord play in embryonic development?

Contributing to body folding and organ development

What is responsible for the formation of the amniotic folds in most amniotes?

Cavitation leading to folding of extra-embryonic membranes

In humans, what type of morphogenetic process leads to amniogenesis?

Cavitation

What does the paraxial mesoderm give rise to during embryonic development?

Axial skeleton and ribs

Which mesoderm layer is located between the paraxial and lateral plate mesoderm?

Intermediate mesoderm

What is the precursor of muscle cells that leads to the formation of skeletal muscles?

Myotomes

What is the dorsal portion of somites that gives rise to the connective tissues of the back skin called?

Dermatomes

Which mesoderm layer develops into the body wall and some fetal membranes?

Lateral plate mesoderm

What event results in segmental partitioning of the body into metameres?

Formation of somites

To what does the coelom give rise during embryonic development?

Cavities of the body

What do sclerotomes form around and give rise to in embryonic development?

Notochord

Which structure forms a cavity for housing the lungs, heart, and abdominal organs?

Coelom

From which cells do the urogenital system and reproductive structures develop during embryonic development?

Intermediate mesoderm

During early embryonic development, what does the folding process bring into their ventral positions?

Notochord

What replaces most of the notochord during embryonic development?

Axial skeleton

What gives rise to the primitive gut during embryonic development?

Endoderm

Which layer wraps the endodermal epithelium of the gut tube and gives rise to intestinal vasculature and connective tissues?

Mesoderm

What structure initially communicates with the yolk sac and becomes long and narrow as development proceeds?

Vitelline duct

Which part of the embryo incorporates the midline endoderm during folding, resulting in its incorporation inside the embryo?

Endoderm

What is the main source of nutrition for non-placental embryos until hatching?

The yolk sac

In mammals, what extra-embryonic membrane encloses the vitellus or yolk?

The yolk sac

Which extra-embryonic membrane develops inside the embryo and grows toward the exterior through the umbilical cord?

The allantois

In birds, what carries the allantoic blood vessels essential for respiration and nutrition?

The allantoic membrane

In mammals, what expands in the extra-embryonic coelom and joins the chorion to form the foundation of the placenta?

The allantois

In horses and dogs, what expands between the amnion and chorion, forming a temporary choriovitelline placenta?

The allantois

In ruminants and pigs, what floats within the coelom and eventually degenerates into the umbilical cord?

The allantoic sac

What plays a critical role in embryonic development by serving functions such as the first site for blood cell and vessel formation, endocrine, metabolic, and immunological functions?

The yolk sac

In mammals with what does development of yolk sac vary?

Placental

Which is a late extra-embryonic membrane responsible for waste product reservoir?

Allantois

What is the embryonic origin of the mesentery that suspends the intestinal tube within the body cavity?

Mesoderm

During early embryonic development, what is the fate of the lower part of the endoderm when the body is folded?

Pinched off outside the embryo

What does the midgut communicate with by a connecting stalk called vitelline duct?

Yolk sac

Which mesodermal layer wraps the endodermal epithelium of the gut tube and gives rise to intestinal vasculature and connective tissues?

Splanchnic mesoderm

Which embryonic membrane encloses the vitellus or yolk, serving as the main source of nutrition for non-placental embryos until hatching?

Yolk sac

In mammals, which extra-embryonic membrane varies in development and fate depending on the type of placenta?

Allantois

What is the function of the allantoic blood vessels in birds during embryonic development?

Respiration and nutrition

In mammals, which embryonic membrane expands in the extra-embryonic coelom and joins the chorion to form the foundation of the placenta?

Allantois

Which embryonic membrane remains connected to the embryo by an allantoic duct or urachus in mammals?

Allantois

In horses and dogs, which embryonic membrane expands between the amnion and chorion, forming a temporary choriovitelline placenta?

Allantois

In ruminants and pigs, what happens to the allantoic sac during gestation?

It degenerates into the umbilical cord

Which extra-embryonic membrane acts as a reservoir for waste products and a site for gas exchange in its original function?

Allantois

What is the first fetal membrane to form and enclose the vitellus or yolk in non-placental embryos?

Yolk sac

In mammals, what role does the yolk sac play in embryonic development apart from serving as a nutrition source?

Formation of blood cell and vessel

In birds, what structure carries essential blood vessels for respiration and nutrition during embryonic development?

Allantoic membrane

Which embryonic membrane arises from the posterior part of the primitive gut (hindgut) as a tubular diverticulum?

Allantois

Study Notes

Cells can transition from epithelial to mesenchymal tissue and back during embryonic development.
Gastrulation leads to the formation of primary mesenchymal cells from epiblast epithelial cells.
These primary mesenchymal cells form temporary epithelia such as the somites and lateral mesoderm.
Later, these temporary epithelia transform into mesenchyme, which ultimately forms muscle and connective tissue.
The terms "mesenchyme" and "epithelium" refer to tissue organization and not specific germ layers.
Ectoderm, primarily epithelial tissue, can derive into mesenchyme.
Neurulation is the process by which the neural tube forms from the embryonic ectoderm.
The neural plate, a thickened ectoderm in the midline, becomes the origin of the entire nervous system.
Neural tube closure begins at the center and progresses cranially and caudally, resulting in two temporal openings.
Failure to close the anterior (rostral) or posterior (caudal) neuropores results in congenital conditions anencephaly and spina bifida, respectively.
The neural tube becomes the central nervous system (brain and spinal cord) while neural crest cells form peripheral nervous system and contribute to various structures.
The neural crests, which form from cells that detach from the neural groove, develop into a wide range of structures including the peripheral nervous system, pigment cells, and craniofacial mesenchymal derivatives.
The brain develops from brain vesicles, which are dilations in the cranial region of the neural tube.
The three primary brain vesicles (rhombencephalon, metencephalon, and prosencephalon) differentiate into five secondary brain vesicles, which eventually develop into all functional adult brain structures.
Notochord serves as a major inductor, leading to neural plate formation and ultimately the neural tube (neurulation)
The early embryo transforms from flat to cylindrical structure, enclosing the first organs (gut, neural tube, notochord, etc.)
Head fold (cranial fold) develops first, forming the most cranial part of the embryo and pulling the cranial part of the embryonic disc ventrally
The folding process brings the mouth and heart into their ventral positions and forms a foregut
Lateral body folds enclose the underlying mesoderm and endoderm, forming the embryonic coelom and midgut
Tail fold (caudal fold) forms at the caudal end, enclosing part of the mesoderm and endoderm to form the hindgut
Embryonic and extra-embryonic tissues are clearly distinguished, with the ectoderm, mesoderm, and endoderm expanding throughout the embryonic disc before formation of the cranial, lateral, and ventral body walls
Intraembryonic tissues include epithelium and mesenchyme, with epithelium being a sheet of closely packed cells that forms structures and lines organs and vessels, and mesenchyme as a filling tissue composed of loose cells connected by gap junctions and embed in the extracellular matrix
The mesoderm can exist in both epithelial and mesenchymal forms and can transform between the two.

Further clarification:

The notochord plays a crucial role during the early stages of embryonic development by inducing the formation of the neural plate, which ultimately forms the neural tube (neurulation).
The early embryo undergoes a transformation from a flat to a cylindrical structure to enclose the first organs (gut, neural tube, notochord, etc.) inside the body.
The head fold, or cranial fold, is the first to form and pulls the cranial part of the embryonic disc ventrally, bringing the mouth and heart into their ventral positions and forming the foregut.
The lateral body folds enclose the mesoderm and endoderm, forming the embryonic coelom and midgut.
The tail fold, or caudal fold, forms at the caudal end of the embryo and encloses part of the mesoderm and endoderm to form the hindgut.
During the early stages of embryonic development, cells can be arranged in two types of tissues: epithelium and mesenchyme. Epithelium is a sheet of closely packed cells that forms structures and lines organs, vessels, and cavities. Mesenchyme is a filling tissue composed of loose cells connected by gap junctions and embedded in a mesh of proteins and fluid called the extracellular matrix.
The mesoderm can exist in both epithelial and mesenchymal forms during development and can transform between the two.
The embryonic structures called somites are formed from the paraxial mesoderm, located on either side of the neural tube.
Somites appear simultaneously on both sides of the neural tube, but formation occurs sequentially from head to tail.
Somites differentiate into three distinct cell populations: sclerotomes, myotomes, and dermatomes.
Sclerotomes form around the notochord and give rise to the axial skeleton, including vertebrae and ribs.
Myotomes are the precursors of muscle cells, leading to the formation of skeletal muscles.
Dermatomes are the dorsal portion of somites and give rise to the connective tissues of the back skin.
Intermediate mesoderm is a mesoderm layer located between the paraxial and lateral plate mesoderm, eventually developing into the urogenital system and reproductive structures.
Lateral plate mesoderm is another mesoderm layer that develops into the body wall and some fetal membranes.
The coelom is a cavity that forms between the parietal and visceral mesoderm and eventually gives rise to the cavities of the body, including the pleural, pericardial, and peritoneal cavities.
Sclerotomes, myotomes, and dermatomes are embryonic structures that develop into various tissues and contribute to the metameric organization of the embryo.
The urogenital system, reproductive structures, body wall, and fetal membranes all develop from different mesoderm layers.
The coelom is a cavity that forms between the parietal and visceral mesoderm and eventually leads to the formation of the cavities of the body.
The endoderm of the primitive gut gives rise to the epithelial lining of the gastrointestinal and respiratory tracts, as well as various organs derived from the pharynx and caudal parts of the urogenital system.
The yolk sac, an extra-embryonic membrane, is the first foetal membrane to form and encloses the vitellus or yolk, which is the main source of nutrition for non-placental embryos until hatching.
In mammals, the development and fate of the yolk sac vary depending on the type of placenta. Some mammals, such as horses and dogs, have a choriovitelline placenta where the yolk sac supports the embryo and forms functional blood vessels.
The allantois is a late extra-embryonic membrane that develops inside the embryo and grows toward the exterior through the umbilical cord. Originally, it acted as a reservoir for waste products and a site for gas exchange.
The allantois arises from the posterior part of the primitive gut (hindgut) as a tubular diverticulum and grows outside the embryo, becoming the allantoic sac. It remains connected to the embryo by an allantoic duct or urachus.
In birds, the allantoic membrane carries the allantoic blood vessels, which are essential for respiration and nutrition. Oxygen and carbon dioxide exchange occurs through the eggshell, and nutritive materials are absorbed by the allantoic circulation.
In mammals, the allantois also expands in the extra-embryonic coelom and joins the chorion to form the mammalian allantochorion, which is the foundation of the placenta.
In horses and dogs, the allantois expands between the amnion and chorion, forming a temporary choriovitelline placenta. Eventually, it also expands ventrally to form the definitive chorioallantoic placenta.
In ruminants and pigs, the chorioamniotic raphe or mesoamnion persists throughout gestation, and the allantoic sac is not attached to the chorion. Instead, it floats within the coelom and eventually degenerates into the umbilical cord.
In all animals, the yolk sac plays a critical role in embryonic development, serving functions such as the first site for blood cell and vessel formation, endocrine, metabolic, and immunological functions.
The endoderm of the primitive gut gives rise to the epithelial lining of the gastrointestinal and respiratory tracts, as well as various organs derived from the pharynx and caudal parts of the urogenital system.
The yolk sac, an extra-embryonic membrane, is the first foetal membrane to form and encloses the vitellus or yolk, which is the main source of nutrition for non-placental embryos until hatching.
In mammals, the development and fate of the yolk sac vary depending on the type of placenta. Some mammals, such as horses and dogs, have a choriovitelline placenta where the yolk sac supports the embryo and forms functional blood vessels.
The allantois is a late extra-embryonic membrane that develops inside the embryo and grows toward the exterior through the umbilical cord. Originally, it acted as a reservoir for waste products and a site for gas exchange.
The allantois arises from the posterior part of the primitive gut (hindgut) as a tubular diverticulum and grows outside the embryo, becoming the allantoic sac. It remains connected to the embryo by an allantoic duct or urachus.
In birds, the allantoic membrane carries the allantoic blood vessels, which are essential for respiration and nutrition. Oxygen and carbon dioxide exchange occurs through the eggshell, and nutritive materials are absorbed by the allantoic circulation.
In mammals, the allantois also expands in the extra-embryonic coelom and joins the chorion to form the mammalian allantochorion, which is the foundation of the placenta.
In horses and dogs, the allantois expands between the amnion and chorion, forming a temporary choriovitelline placenta. Eventually, it also expands ventrally to form the definitive chorioallantoic placenta.
In ruminants and pigs, the chorioamniotic raphe or mesoamnion persists throughout gestation, and the allantoic sac is not attached to the chorion. Instead, it floats within the coelom and eventually degenerates into the umbilical cord.
In all animals, the yolk sac plays a critical role in embryonic development, serving functions such as the first site for blood cell and vessel formation, endocrine, metabolic, and immunological functions.

Test your knowledge on the transformation of cells during gastrulation, from epithelial to mesenchymal and back again. Understand how cells change their characteristics and organization during this critical stage of embryonic development.

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