Embryo-4-Embryonic period (Weeks 3-8)

During the longitudinal folding of the head fold, part of the ENDODERM of the YOLK SAC is incorporated into the embryo as the _____________

foregut (primordium of pharynx, esophagus ....)

What does the intermediate mesoderm give rise to?

forms a longitudinal dorsal ridge known as the urogenital ridge, which is involved in the formation of the future kidneys and gonads.

During the TAIL FOLD, part of the ENDOdermal germ layer is incorporated into the embryo as the ___________. This ________ soon dilates slightly to form the ___________

hindgut (primordium of the descending colon), hindgut, cloaca (primordium of the urinary bladder and rectum)

Where is a Chordoma tumor usually found?

may be found either intracranially or in the sacral region.

The heart and great vessels form from _________ in the __________.

mesenchymal cells, cardiogenic area

The intermediate mesoderm connects the ______ and ______

paraxial mesoderm, lateral mesoderm

The notochordal process grows cranially between the ectoderm and endoderm until it reaches the _________

prechordal plate

As the primitive streak elongates by addition of cells to its caudal end, its cranial end proliferates to form a __________. At the same time, a narrow _________ develops in the primitive streak that is continuous with a small depression in the primitive node which is called the ________

primitive node, primitive groove, primitive pit

In the ______ fold, As the abdominal walls form, part of the ENDOderm germ layer is incorporated into the embryo as the MIDGUT (primordium of the small intestine)

tail

In which fold does the connecting stalk (primordium of the umblical cord) attach to the ventral surface of the embryo, and the allatois a diverticulum of the yolk sac is partially incorporated into the embryo.

tail

Which layer of the intraembryonic mesoderm does the Intraembryonic coelom form in?

the LATERAL MESODERM is a thin plate mesoderm in which the intraembryonic coelom forms, dividing the lateral mesoderm into two layers

What does the lateral mesoderm give rise to?

the connective tissues/muscles of the viscera and limbs, the serous membranes of pleura, perivardium and peritoneum blood and lymph cells, cardiovascular and lymphatic systems

What are the endocardial heart tubes? When do they develop and what do they do?

the endocardial heart tubes, are two tubes that develop during the third week and fuse to form a primitive heart tube. This tubular heart joins with blood vessels in the embryo, connecting stalk, chorion, and yolk sac to form a primordial cardiovascular system.

T/F As the notochord develops, the embryonic ectoderm over it thickens to form the neural plate, the neural plate gives rise to the Neural Tube which is the primordium of the CNS

true

T/F By the end of the third week, embryonic blood begins to flow slowly through the capillaries in the chorionic villi.

true

T/F Chordoma may be either benign or malignant.

true

T/F The first sign of gastrulation is the appearance of the PRIMITIVE STREAK at the CAUDAL end of the embryo, DORSALLY

true

T/F Week 3 is when the folding of the embryo occurs

true

The cells of the Epiblast of the primitive streak displace the hypoblast and epiblast as they proliferate and form the mesoderm. When they displace the hypoblast, the roof of the yolk sac is now known as the _________, And as they displace the epiblast, the epiblast is now known as the ________.

embryonic endoderm, embryonic ectoderm

All of the major organ systems begin to develop during the ________, which is week _____

embryonic, 3-8

The ectoderm, intraembryonic mesoderm, of the trilaminar embryonic disk are all derived from the ______.

epiblast, which is derived from the embryoblast (we called it future embryo for a reason)

What embryonic structures does the Ectoderm give rise to?

epidermis layer of the skin, CNS, PNS, lens, retina

What embryonic structures does the Endoderm give rise to?

epithelial linings of respiratory passages, GI tract (except oral cavity and endocrine glands), glandular cells of organs such as the liver, pancreas, and pharyngeal pouches

T/F The primitive heart tube develops in the Myocardium

false, As lateral folding occurs, these fuse to form the primitive heart tube, which develops into the endocardium. The myocardium and epicardium develop from mesoderm surrounding the primitive heart tube.

T/F The intraembryonic and extraembryonic mesoderm is formed during week 3 (gastrulation)

false, The term intraembronic mesoderm describes the germ layer that forms during week 3 (gastrulation) in contrast to the extraembryonic mesoderm, which formed during week 2.

T/F Gastrulation is first indicated by the formation of the primitive node, caused by a proliferation of hypoblast cells.

false, is first indicated by the formation of the PRIMITIVE STREAK caused by a proliferation of EPIBLAST cells.

T/F Chordoma occurs more commonly in male infants from birth to 6 months old

false, occurs more commonly in Men late in adult life (age 50).

T/F Toward the end of the third week, the intermediate mesoderm differentiates and begins to divide intro paired cuboidal bodies, the somites.

false, paraxial mesoderm

T/F The last stage of chorionic villi (tertiary chorionic villi) cover the entire surface of the chorionic sac

false, secondary chorionic villi (which are formed when mesenchyme grows into the primary villi), cover the entire surface of the chorionic sac.

T/F The Paraxial mesoderm is part of the extraembryonic mesoderm

false, the INTRAembryonic mesoderm is divided into 3 parts: paraxial mesoderm, intermediate mesoderm, lateral mesoderm

T/F Week 4 is when the development of the cardiovascular system occurs

false, week 3

When is the organogenetic period?

Fourth to eight weeks

A genetic defect in the lack of/decreased synthesis of either the alpha-globin chain (alpha-thalassemia) or beta-globin chain (B-thalassemia) of hemoglobin alpha2 beta2 can result in what congenital abnormality?

Thalassemia syndromes

What is Angiogenesis? When does it occur? Where does it occur?

-Angiogenesis is blood vessel formation -Ocuurs at the beginning of the third week -angiogenesis, or blood vessel formation begins in the extraembryonic mesoderm of the yolk sac, connecting stalk and chorion.

What is the neural crest? What does it give rise to?

-As the neural folds fuse to form the neural tube, some NEUROECTODERMAL CELLS lying around the crest of each neural fold forms these Neural Crest (pic on pg.63) -give rise to the spinal ganglia (DRG), ganglia of the autonomic nervous system, and the ganglia of cranial nerves V, VII, IX, and X, pia matter, arachnoid matter, Schwann cells, cells of the suprarenal medulla/adrenal medulla, and several skeletal and muscular components of the head

When do the Primary chorionic villi appear? Where do they branch from?

-At the end of the second week -they begin to branch from cytotrophoblast cells produces cellular extensions that grow into the syncytiotrophoblast. These cellular projections from primary chorionic villi marks the first stage in the development of the chorionic villi of the placenta

What are somites? Are they bilateral to the Neural tube?

-By proliferation of ectoderm that gives rise to the neural tube, we have proliferation of different parts of mesoderm as well like SOMITES, which eventually give rise to different things such as bones, muscles, connective tissues etc. -yes

What is VATER and VACTERL? What congenital abnormality are these associated with

-Caudal dysplasia (in which there is absense of gastrulation so migration of the mesoderm is disturbed so a lot of things developing will be absent) -In VATER Caudal Dysplasia, it includes vertebral defects, anal atresia, tracheo-esophageal fistula, and renal defects -In VACTERL Caudal Dysplasia, its includes all the symptoms of VATER but in addition also induces cardiovascular defects and upper limb defects.

When do the Secondary chorionic villi appear? What happens to induce this formation?

-Early in the THIRD WEEK, Mesenchyme grows into the primary villi, forming a connective tissue. The villi at this stage is secondary chorionic villi, which cover the entire surface of the chorionic sac.

What are the important things that happen in the Fifth week? What does each thing give rise to?

-Enlargement of the head is caused mainly by the rapid development of the brain and facial prominences -The (hyoid) pharyngeal arch Upper limb buds lower limb buds -Mesonephric ridges indicates the site of the mesonephric kidneys (FUTURE KIDNEYS)

What is gastrulation? When does it occur?

-Gastrulation is when some cells start to proliferate from the epiblast, and then underneath the epiblast will be formation of other layer of cells which forms the Mesoderm. -the process that establishes the three definitive germ layers of embryo (ectoderm, intraembryonic mesoderm, and endoderm), thereby forming a trilaminar embryonic disk by day 21 of development -occurs in week 3 (by day 21)

What is the most severe form of alpha-thalassemia? What does it result in?

-Hydrops fetalis is the most severe form of alpha-thalassemia -causes severe pallor, generalized edema, massive hepatosplenomegaly, and invariably leads to intrauterine fetal death.

What are the MAIN differences between the 2nd and 3rd week of pregnancy?

-In 2nd week we have 2 layers, we have formation of extraembryonic mesoderm (future yolk sac)(exocelomic cavity) -In 3rd week we have 3 layers, we have formation of intraembryonic mesoderm

What does the intraembryonic mesoderm form? What does the extraembryonic mesoderm form?

-Intraembryonic mesoderm forms various tissues and organs found in the adult, whereas: -extraembryonic mesoderm is involved in placenta formation.

What are the important things that happen in the Seventh week? What does each thing give rise to?

-Notches between digital rays (Digital rays start to seperate) -The intestines enter the extraembryonic coelom in the proximal part of the umblical cord (now we can start to identify intestines)

What is the treatment for Chordoma?

-Since its near the brain and the spinal cord treatment is very difficult, so chemotherapy is not effective. Surgery is preferred. Best way is radiation in combination with surgery

What is the chorion and the chorionic sac? Whats in the chorionic sac?

-The chorion consists of the extraembryonic somatic mesoderm and the two layers of trophoblast -The chorion forms the wall of the CHORIONIC SAC (gestational sac), within which the embryo and its amniotic and yolk sacs suspended by the CONNECTING STALK.

When do the pharyngeal arches start to appear? What do these give rise to?

-The pharyngeal arches are visible in the FOURTH week. -The first arch gives rise to the mandible and the other arches give rise to maxillary tube, auditory tube/canal, auricle

What are the important things that happen in the Eigth week? What does each thing give rise to?

-The scalp vascular plexus appear and forms a characteristic band around the head. -Ossification begins in the lower limbs (femur) -The neck region is established and the eyelids are more obvious. -Sex differences exist in the appearance of the external genitalia

What are the important things that happen in the Sixth week? What does each thing give rise to?

-The upper limbs begin to show regional differentiation as the elbows and large hand plates develop. -Formation of Digit (Digital rays) which give rise to the future fingers -Several small swellings called AURICULAR HILLOCKS develop around the PHARYNGEAL GROOVE. This groove becomes the external acoustic meatus!

The capillaries in the TERTIARY chorionic villi fuse to form ____________. What do these do?

-arteriocapillary networks -They soon become connected with the embryonic heart through vessels that differentiate in the mesenchyme of the chorion and connecting stalk.

What is the most severe form of beta-thalassemia? What does it result in? Where in the world is it most common in?

-beta-Thalassemia major is the most severe form of B-thalassemia -causes a severe, transfusion-dependent anemia. -It is most common in Mediterranean countries and parts of Africa and Southeast Asia.

What is Sacrococcygeal teratoma? What does it result from? Is it more common in male or female infants?

-is a tumor that arises from remnants of the PRIMITIVE STREAK (which should be closed normally, but in this case remains open), which normally degenerates and disappears. -occurs more commonly in female infants.

What is contained in the Sacrococcygeal teratoma tumor and explain why its there? How is it treated after birth? What happens if its not treated?

-is derived from pluripotent cells of the primitive streak and often contains various types of tissue (e.g., bone, nerve, hair). -Primitive streak is the first step for formation of the mesoderm, and mesoderm gives rise to different tissues (bone, muscle, dermis etc.). Therefore, its logic that if the primitive streak remains open, these things will be present in the tumor -It usually becomes malignant during infancy and must be removed by age 6 months.

What is Caudal Dysplasia? What is it caused by?

-refers to a constellation of syndromes ranging from minor lesions of lower vertebrae to complete fusion of the lower limbs (pelvic cavity might be missing etc) -is caused by abnormal gastrulation, in which the migration of mesoderm is disturbed. (cuz gastrulation is important for bone and muscle development)

Which part of the intraembryonic mesoderm gets divided into two layers? What are they? what is the other name for them?

-the LATERAL MESODERM is a thin plate mesoderm in which the intraembryonic coelom forms, dividing the lateral mesoderm into two layers: -Intraembryonic somatic mesoderm (also called somatopleure) -Intraembryonic visceral mesoderm (also called visceropleure or splanchnopleure)

About the ____ day, the neural plate invaginates along its central axis to form a longitudinal median ________, which has __________ on each side.

18th, neural groove, neural folds

When does the heart begin to beat?

21st or 22nd day

Which part of the mesoderm forms a longitudinal dorsal ridge known as the urogenital ridge, which is involved in the formation of the future kidneys and gonads? A. intermediate mesoderm B. lateral mesoderm C. paraxial mesoderm D. none of the above, its formed from the epiblast E. none of the above, its formed from the hypoblast

A

The Notochord: A. is the future cardiogenic area B. is the future reproductive organs C. is the future vertebral body D. sends signals to the ectoderm to proliferate and develop CNS E. send signals to the endoderm to proliferate and develop CNS

A, C, D

The part of mesoderm that forms muscles, skeleton dermis of skin and connective tissue is the : A. intermediate mesoderm B. lateral mesoderm C. paraxial mesoderm D. none of the above, its formed from the epiblast E. none of the above, its formed from the hypoblast

C

Where do blood vessels develop from? When do they develop? When does Blood Formation begin?

Blood vessels Develop from the endothelial cells (hemocytoblasts) -the vessels develop in the walls of the yolk sac and allantois (connecting stalk) at the end of the third week -Blood formation does not begin in the embryo until the FIFTH WEEK

The ECTODERM of the NEURAL PLATE gives rise to what?

CNS, retina

__________ refers to a constellation of syndromes ranging from minor lesions of lower vertebrae to complete fusion of the lower limbs (mainly missing pelvic cavity)

Caudal dysplasia

What is the Craniocaudal folding caused by?

Craniocaudal folding is caused by the growth of the central nervous system and the amnion.

What are the most important 3 layers of the embryo that are formed in week 3?

Ectoderm (from the epiblast), Mesoderm, and Endoderm (from the hypoblast)

What is Chordoma? What does it result from?

Its a tumor that arises from remnants of the Notochord

What does the paraxial mesoderm give rise to?

Its first part of mesoderm and forms trunk muscles, skeleton (except skull), dermis of skin, and connective tissue

What is the Lateral folding caused by?

Lateral folding is caused by the growth of the somites, amnion, and other components of the lateral body wall.

What embryonic structures does the Mesoderm give rise to?

Muscles, smooth muscular coats, connective tissues, vessels associated with the tissues and organs, dermis layer of the skin, bones, cardiovascular system, blood cells and bone marrow, skeleton, striated muscles, reproductive and excretory organs

What are the parts of the Intraembryonic mesoderm?

Paraxial mesoderm, Intermediate mesoderm, Lateral mesoderm

During the head fold of the embryo, ________________ move onto the ventral surface of the embryo.

Primordial heart, pericardial coelom, and oropharyngeal membrane

After formation of the mesoderm, we should have closure of the primitive streak. What congenital abnormality is associated with the primitive streak being abnormally open?

Sacrococcygeal teratoma

In which week do formation of the digital rays appear?

Sixth week!

What happens shortly after the primitive streak appears?

Some cells leave its deep surface and form a loose network of embryonic connective tissue called MESENCHYME or MESOBLAST. Some mesenchyme forms a layer known as the INTRAEMBRYONIC MESODERM..

How do the tertiary chorionic villi form?

Some mesenchymal cells in the secondary chorionic villi soon differentiate into capillaries and blood cells. When this happens, and blood vessels are visible in the villi, they are known as the tertiary chorionic villi.

What is the first organ in the embryo to reach a functional state?

The cardiovascular system

What changes the shape of the embryo from a two-dimensional disk to a three-dimensional cylinder?

The craniocaudal folding and lateral folding

Why is development of the notochord important? What does it give rise to?

The development of the notochord is important because: -it induces the formation of vertebral bodies, it forms the nucleus pulposus of each intervertebral disk in a newborn, -it induces the overlying embryonic ectoderm to thicken and form the neural plate (the primordium of CNS), -it is the future cardiogenic area

Why does Angiogenesis occur so early (around day 16)?

The early formation of the cardiovascular system is correlated with the absence of a significant amount of yolk in the ovum and yolk sac (which was used to nourish the baby in the first 2 weeks), and the consequent urgent need for blood vessels to bring oxygen and nourishment to the embryo from the maternal circulation through the placenta.

As the chorionic sac develops, what is the extraembryonic coelom now called?

The extraembryonic coelom is now called the CHORIONIC CAVITY

What are the important things that happen in the Fourth week? What does each thing give rise to?

The pharyngeal arches are visible. The first arch gives rise to the mandible and the other arches give rise to maxillary tube, auditory tube/canal, auricle -The upper and lower limb BUDS (which give rise to the upper and lower limbs) become recognizable by day 26 or 27 as small swellings on the ventrolateral body walls. -Otic pits (primordia of the inner ears) -Lens placods (future lens of the eye)

What does the primitive streak consist of?

The primitive streak consists of the primitive groove, primitive node, and primitive pit.

What does the Primitive streak result from? (what happens which makes the primitive streak form the way it does)

The primitive streak results from the proliferation and migration of cells of the epiblast to the median plane of the embryonic disc.

What are Thalassemia syndromes?

They are a heterogeneous group of genetic defects characterized by the lack of or decreased synthesis of either the ALPHA-GLOBIN (alpha-thalassemia) or BETA-GLOBIN chain (Beta-thalassemia) of hemoglobin alpha2 beta2.

How would you measure the chorionic (gestational) sac diameter?

Transvaginal ultrasound is used for measuring chorionic (gestational) sac diameter

What is tracheo-esophageal fistula

abnormal opening between trachea and esophagus, a major symptom of Caudal Dysplasia

Located caudal to the primitive streak is the future site of the _____, known as the __________. Are the epiblast and hypoblast fused at this site?

anus, cloacal membrane, yes

What does anal atresia?

atresia in general = part of that organ is missing, a major symptom of Caudal Dysplasia

When does the head fold occur?

by the beginning of the fourth week

Some cells from the primitive streak migrate cranially on each side of the notochordal process and around the prechordal plate (rmr this is where the notochord process ends). Here they meet cranially to form the __________ in the _________. This is where the _______ begins to develop at the end of the ______ week.

cardiogenic mesoderm, cardiogenic area, primordium of the heart, third

The embryo has distinct human appearance by the end of ____ of development.

week 8