The Embryonic Period Flashcards by Adrian Tiglao

Embryonic period

Period of organogénesis

How well did you know this?

Not at all

Perfectly

The embryonic period occurs from the __ of development.

Third to the eighth weeks

How well did you know this?

Not at all

Perfectly

It is the time when each of the three germ layers, ectoderm, mesoderm, and endoderm, gives rise to a number of specific tissues and organs.

Embryonic period

How well did you know this?

Not at all

Perfectly

It is formed when the 💡notochord and 💡prechordal mesoderm induces the overlying ectoderm to thicken.

Neural plate

How well did you know this?

Not at all

Perfectly

It is the 💡cells that make up the neural plate.

Neuroectoderm

How well did you know this?

Not at all

Perfectly

It promotes a neural pathway by an unknown mechanism while it represses 💡BMP transcription and upregulates expression of 💡💡CHORDIN and 💡NOGGIN

Fibroblast growth factor (FGF)

How well did you know this?

Not at all

Perfectly

They are up regulated by the 💡FGF, which inhibit 💡BMP activity.

They 💡neuralize ectoderm by inhibiting BMP and cause 💡mesoderm to become 💡notochord and 💡paraxial mesoderm (dorsalizes mesoderm).

They induce only 💡forebrain and 💡midbrain types of tissues.

CHORDIN and NOGGIN (+ Follistatin)

How well did you know this?

Not at all

Perfectly

It 💡permeates the mesoderm and ectoderm of the gastrulating embryo, ectoderm is induced to form epidermis, and mesoderm forms intermediate and lateral plate mesoderm.

Bone Morphogenetic Protein 4 (BMP4)

How well did you know this?

Not at all

Perfectly

These are secreted proteins that induces 💡caudal neural plate structures (hindbrain and spinal cord)

WNT3a and FGF

How well did you know this?

Not at all

Perfectly

It play a role in organizing the 💡cranial-to-caudal axis because it can cause 💡respecification of cranial segments into more caudal ones by regulating expression of 💡homeobox genes

Retinoic acid (RA)

How well did you know this?

Not at all

Perfectly

It is the process whereby the 💡neural plate forms the 💡neural tube.

Formation of 💡neural folds and 💡neural groove.

Neurulation

How well did you know this?

Not at all

Perfectly

What is the key events in neurulation?

Lengthening of the neural plate and body axis

How well did you know this?

Not at all

Perfectly

It is a phenomenon whereby there is a 💡lateral to medial movement of cells in the plane of the ectoderm and mesoderm.

The process is regulated by signaling through the 💡planar cell polarity pathway and is essential for 💡neural tube development.

Convergent extension

How well did you know this?

Not at all

Perfectly

Fusion of neural folds begins in the __ and proceeds cranially and caudally

Cervical region (fifth somite)

How well did you know this?

Not at all

Perfectly

It is the result of the 💡fusion of neural folds as they approach each other in the midline

Neural tube

How well did you know this?

Not at all

Perfectly

The cephalic and caudal ends of the neural tube communicate with the amniotic cavity by way of the __ and __.

Anterior and posterior neuropores

How well did you know this?

Not at all

Perfectly

Closure of the cranial neuropore occurs at approximately at what day?

Day 25 (18- to 20-somite stage)

How well did you know this?

Not at all

Perfectly

The posterior neuropore closes at what day?

day 28 (25-somite stage)

How well did you know this?

Not at all

Perfectly

When neurulation is completed, the CNS is represented by __, the spinal cord, and a much broader cephalic portion is characterized by a number of dilations which is called __?

Closed tubular structure with a narrow caudal portion

Brain vesicles

How well did you know this?

Not at all

Perfectly

As the neural folds elevate and fuse, cells at the lateral border or crest of the neuroectoderm begin to dissociate from their neighbors.

They also form and migrate from cranial neural folds, leaving the neural tube before closure in this region

Neural Crest Cells

How well did you know this?

Not at all

Perfectly

As neural crest cells leaves the neuroectoderm by active migration and displacement to enter the underlying mesoderm they undergo what kind of transition?

Epithelial-to-mesenchymal transition

How well did you know this?

Not at all

Perfectly

It refers to 💡cells derived from the 💡epiblast and 💡extraembryonic tissues.

Mesoderm

How well did you know this?

Not at all

Perfectly

It refers to 💡loosely organized embryonic connective tissue regardless of origin.

Mesenchyme

How well did you know this?

Not at all

Perfectly

Crest cells from the trunk region leave the neuroectoderm after closure of the neural tube and migrate along one of two pathways:

(1) A dorsal pathway through the dermis, where they will enter the ectoderm through holes in the basal lamina to form melanocytes in the skin and hair follicles
(2) A ventral pathway through the anterior half of each so- mite to become sensory ganglia, sympathetic and enteric neurons, Schwann cells, and cells of the adrenal medulla

How well did you know this?

Not at all

Perfectly

Neural crest cells contribute to the:

Craniofacial skeleton as well as neurons for cranial ganglia, glial cells, melanocytes

Fourth germ layer

Neural Crest Cells

The ectodermal germ layer gives rise to organs and structures that maintain contact with the outside world:

■ The central nervous system ■ The peripheral nervous system ■ The sensory epithelium of the ear, nose, and eye ■ The epidermis, including the hair and nails ``` In addition, it gives rise to the following: ■ The subcutaneous glands ■ The mammary glands ■ The pituitary gland ■ Enamel of the teeth ```

By approximately the 17th day, however, 💡mesodermal cells 💡close to the midline 💡proliferate and form a 💡thickened plate of tissue known as?

Paraxial mesoderm

More laterally, the 💡mesoderm layer remains thin and is known as the?

Lateral plate.

A layer continuous with mesoderm covering the 💡amnion, known as the?

Somatic or parietal mesoderm layer

A layer continuous with mesoderm covering the 💡yolk sac, known as the?

Splanchnic or visceral mesoderm layer

Together, these layers (somatic/splanchnic mesoderm layer) line a newly formed cavity, the __, which is continuous with the extraembryonic cavity on each side of the embryo.

Intraembryonic cavity

It 💡connects 💡paraxial and 💡lateral plate mesoderm

Intermediate mesoderm

It is a 💡paraxial mesoderm that is 💡organized into segments. They first appear in the 💡cephalic region of the embryo, and their formation proceeds cephalocaudally.

Somitomeres

💡Somitomeres in the 💡head region form in association with segmentation of the 💡neural plate.

Neuromeres

It is a process where 💡somites [exist as a ball of mesoderm (fibroblast- like) cells] 💡arrange themselves in a donut shape around a small lumen

Epithelization

💡Part of somite that will become the 💡tendón cartilage and bone component

Sclerotome

💡Part of somite that provides the segmental 💡muscle component

Myotome

💡Part of somite which forms the 💡dermis of the back.

Dermatome

They are produced by the 💡notochord and 💡floor plate of the neural tube, induce the 💡ventromedial portion of the somite to become 💡sclerotome.

NOGGIN genes and sonic hedgehog (SHH)

It initiates the 💡cascade of cartilage- and bone-forming genes for 💡vertebral formation.

PAXl

Regulates Expression of 💡PAX3 from the dorsal neural tube, marks the 💡dermomyotome región of the somite.

WNT proteins

WNT proteins from the 💡dorsal neural tube also target the 💡dorsomedial portion of the somite, causing it to initiate expression of the 💡muscle-specific gene to form 💡primaxial muscle precursors.

MYF5

It is a 💡muscle-specific gene that directs the formation of 💡primaxial and 💡abaxial muscle precursors.

MYOD

It is secreted by the 💡dorsal region of the neural tube that directs the 💡midportion of the dorsal epithelium to form 💡dermis.

Neurotrophin 3 (NT-3)

It 💡temporarily connects 💡paraxial mesoderm with the 💡lateral plate differentiates into 💡urogenital structures.

Intermediate mesoderm

💡Intermediate mesoderm that forms 💡segmental cell clusters in 💡cervical and 💡upper thoracic regions

Nephrotomes

💡Intermediate mesoderm that forms an 💡unsegmented mass of tissue caudally.

Nephrogenic cord

It splits into parietal (somatic) and visceral (splanchnic) layers, which line the intraembryonic cavity and surround the organs, respectively

Lateral Plate Mesoderm

These are 💡thin membranes formed by mesoderm cells of the parietal layer surrounding the intraembryonic cavity They will line the 💡peritoneal, 💡pleural, and 💡pericardial cavities and secrete 💡serous fluid

Mesothelial membranes, or serous membranes

Blood vessels form in two ways:

Vasculogenesis Angiogenesis

It a process of blood vessels formation whereby vessels arise from 💡blood island

Vasculogenesis

It a process of blood vessels formation which entails 💡sprouting from existing vessels

Angiogenesis

It is a 💡common precursor for 💡vessel and 💡blood cell formation.

Hemangioblasts

It is a 💡site near the developing 💡mesonephric kidney

Aorta-gonad-mesonephros region (AGM)

It induces 💡blood island development from competent mesoderm cells that form hemangioblasts.

FGF2

Hemangioblasts are directed to form blood cells and vessels by __, which is secreted by surrounding mesoderm cells.

Vascular endothelial growth factor (VEGF)

It upregulates the 💡VEGF receptor FLKl

HOXB5

Hemangioblasts in the center of blood islands form the 💡precursors of all blood cells

Hematopoietic stem cells

It is 💡differentiated peripheral hemangioblasts The 💡precursors to blood vessels.

Angioblasts

💡Maturation and 💡modeling of the vasculature are regulated by other growth

Platelet-derived growth factor (PDGF) and TGF-beta

It is the 💡main organ system derived from the 💡endodermal germ layer.

Gastrointestinal tract

This germ layer 💡covers the ventral surface of the embryo and forms the 💡roof of the yolk sac

ENDODERMAL GERM LAYER

The tube is divided into three regions:

Foregut, midgut, and hindgut

It is a region of the tube which communicates with the yolk sac by way of a 💡broad stalk, the 💡vitelline (yolk sac) duct.

Midgut

It is a region of the tube where at its 💡cephalic end is 💡temporarily bounded by an 💡ectodermal-endodermal membrane called the 💡oropharyngeal membrane

Foregut

It separates the 💡stomodeum, the 💡primitive oral cavity derived from ectoderm, from the 💡pharynx, a part of the 💡foregut derived from endoderm. In the fourth week, it ruptures, establishing an open connection between the 💡oral cavity and the 💡primitive gut

Oropharyngeal membrane

It is a 💡region of the tube that also 💡terminates temporarily at an 💡ectodermal-endodermal membrane, the 💡cloacal membrane.

Hindgut

This membrane separates the 💡upper part of the anal canal, derived from endoderm, from the 💡lower part, called the 💡proctodeum, The membrane 💡breaks down in the seventh week to 💡create the opening for the anus.

Cloacal membrane

It is formed by an 💡invaginating pit lined by ectoderm. This membrane breaks down in the seventh week to create the 💡opening for the anus.

Proctodeum

During further development, endoderm gives rise to the following:

■ The epithelial lining of the respiratory tract ■ The parenchyma of the thyroid, parathyroid, liver, and pancreas ■ The reticular stroma of the tonsils and the thymus ■ The epithelial lining of the urinary bladder and the urethra ■ The epithelial lining of the tympanic cavity and auditory tube

These genes are known for their 💡homeodomain. They code for transcription factors that activate cascades of genes regulating phenomena such as segmentation and axis formation.

Homeobox genes

It is a 💡DNA-binding motif, the homeobox.

Homeodomain

It 💡collects homeobox genes

Homeotic clusters

It is a 💡homeotic gene complex from Drosophila which is important cluster of genes specifying the 💡craniocaudal axis.

Hom-C

It indicates the 💡age of the embryo because counting somites becomes difficult during the second month of development and expressed in millimeters. It is the measurement from the 💡vertex of the skull to the midpoint be- tween the apices of the 💡buttocks.

Crown-rump length (CRL)

Radial grooves They appear in the hand region first and shortly afterward in the foot, as the upper limb is slightly more advanced in development than the lower limb.

Rays

It result when neural tube closure fails to occur.

Neural tube defects (NTDs)

If the neural tube fails to dose in the cranial región, then most of the brain fails to form, and the defect is called?

Anencephaly

If closure fails anywhere from the cervical region caudally, then the defect is called?

Spina bifida

The most common site for spina bifida to occur is in the?

Lumbosacral region

These are 💡abnormally dense collections of 💡capillary blood vessels that form the most common tumors of infancy, occurring in approximately 10% of all births.

Capillary hemangiomas

It is highly expressed in the lesions and may be one factor promoting abnormal vessel growth.

INSULIN-LIKE GROWTH FACTOR 2

Most major organs and organ systems are formed during the __. the time when most gross structuralbirth defects are induced.

Third to eighth weeks

``` Crown-Rump Length (mm): 5-8 10-14 17-22 28-30 ```

``` Approximate Age (wk): 5 6 7 8 ```