Body Plan

Question 1

6 adaptations that allow mammalian embryo to survive inside another organism

Answer 1

Placenta, umbilical vein, ductus venous, foramen ovale, ductus arteriosus, umbilical arteries

Question 2

Internal iliac arteries

Answer 2

Umbilical arteries branch to form these and parts remain to supply the bladder

Question 3

Steps to embryonic development

Answer 3

1. Common organization (all embryos in this stage look alike)
2. The three germ layers (ectoderm, mesoderm, endoderm)
3. Embryonic folding (forms tubular organs and cavities)
4. Building blocks (epithelial, mesencymal, and blood cells)

Question 4

3 principal axes of body plan

Answer 4

Cranial-Caudal, Dorsal-Ventral, Left-Right

Question 5

Embryonic development stages

Answer 5

Zygote -> blastocyst -> baliminar disc ->trilaminar disc

Question 6

Mesoderm differentiation

Answer 6

Notochord, paraxial intermediate, and lateral mesoderm (lateral mesoderm will split into somatic and splanchnic mesoderm

Question 7

Cranial-caudal folding

Answer 7

Brings most cranial heart into thoracic (more caudal) position. Brings septum transversum caudal to heart (septum transversum is first division of embryonic coelom)

Question 8

Lateral folding

Answer 8

Closes the embryo and forms tubular organs like gut tube and heart. Incorporates extra embryonic coelom into the embryo thereby forming first intraembryonic body cavity (ie a coelomic cavity)

Question 9

Morphogenetic

Answer 9

Process of shaping body and its parts

Question 10

Gastrulation

Answer 10

Process of embryonic folding, transforms embryo into 3-d cylindrical shape and forms body cavities

Question 11

Embryogenesis

Answer 11

Choreographed interplay of cells and processes necessary in the development of the embryo

Question 12

Requirements to successfully complete embryonic development

Answer 12

1 survival
2 change (ie development)
3 prepare for birth

Question 13

Blood vessels fetus utilizes for nutrient and oxygen uptake

Answer 13

Umbilical vein and umbilical artery

Question 14

Placenta organ replacement

Answer 14

Placenta is lungs, kidneys and liver of developing fetus; contains tissues and vessels from both the embryo (chorionic plate) and mother (basal plate). Placenta mostly made of cells derived from trophoplast

Question 15

Respritory and digestive system adaptations for speeding up oxygen delivery to fetus

Answer 15

Foramen ovale and ductus arteriosus (respritory) and ductus venosus (digestive) provide short cuts for placental blood to get to fetus quickly by bypassing liver and lungs

Question 16

Ductus venosus

Answer 16

Placental blood is returned to fetus by 2 large umbilical veins that join as one when entering body at the navel, the single abdominal umbilical vein runs forward to penetrate liver and bypasses Hypatic circulation via the ductus venosus which tunnels through the liver joining caudal venacava

Question 17

Blood flow in placenta

Answer 17

Placental blood returns to fetus in 2 umbilical veins which become one in navel -> ductus venosus -> caudal vena cava (now mixes super oxygenated placental blood with deoxygenated blood returning from hind part of body) ->foramen ovale -> 2 branches
Branch one: foramen ovale -> right atrium -> right ventricle -> pulmonary trunk -> ductus arteriosus -> descending aorta -> umbilical artery -> placenta -> umbilical vein

Branch two: foramen ovale ->left atrium -> left ventricle -> aorta -> brain/ upper half of body -> umbilical artery -> placenta -> umbilical vein

Question 18

Umbilical arteries

Answer 18

Carry deoxygenated blood from descending aorta back to placenta for oxygenation. Umbilical arteries branch fo form internal iliac arteries

Question 19

Changes in circulation following birth

Answer 19

1. Removal of placenta -> drop in body temperature constricting and closing umbilical vein, change in resistance to blood flow (higher resistance) leads to no blood flowing in umbilical vein or ductus venosus which eventually closes
   2.first breath expands lung decreasing resistance to blood flow in lung dropping blood pressure in right atrium and right ventricle leading to close of foramen ovale
   Rise in oxygen level of the blood leads to smooth muscle contraction which closes ductus arteriosus.
   Loss of prostaglandin from removal of placenta leads to closing of umbilical arteries (distal part will become round ligament of bladder0, proximal part remains and supplies some blood to cranial part of bladder
   Stump of umbilical vein outside abdomen shrivels and intraabdominal part will transform to round ligament of the liver
   Ductus arteriosus- converted into fiborous structure known as ligamentum arteriosum

Question 20

Patent ductus arteriosus

Answer 20

If ductus arteriosus abnormally persists after birth and fails to close poorly oxygenated blood from right ventricle will enter systemic circulatory system without being oxygenated in the lungs. This is most common congenital cardiovascular birth defect in dogs.

Question 21

Location of structure in adult and embryonic body should be described in relation to the

Answer 21

CNS

Question 22

Establishment of axes

Answer 22

Originates just after fertilization
First axis to be established- Cranioventral-caudal
2nd to be established- dorso-ventral
3rd axis to be established - left-right

Question 23

Left right axis is critical to

Answer 23

Formation of heart and gastrointestinal tract
Heart on left
Stomach on left
Spleen on left
Liver on right
Vasculature inflow of heart on right, outflow on left

Question 24

Amnion

Answer 24

Water sac, allows embryo to float in fluid environment that protects it from shock an desiccation

Question 25

Yolk sac

Answer 25

Membrane derived from the embryo, enables nutrient uptake, development of circulatory system

Question 26

Allantois

Answer 26

Stores waste product, developers at caudal end of embryo

Question 27

Chorion

Answer 27

Forms the placenta, contains blood vessels that exchange gases with outside enviornment

Question 28

Blastocyst

Answer 28

Fluid filled sphere steps: Zygote becomes morula (ball of cells) (consists of small group of inner cells surrounded by large group of outer cells) Outer cell layer forms trophoblast which secretes fluid into morula making fluid filled cavity Inner cells become positioned on one side of the ring of trophoblast cells to form aggregate of inner cell mass These steps form blastocyst

Question 29

Inner cell mass vs trophoblast

Answer 29

Cells in inner cell mass will become embryo cells in trophoblast will become placenta

Question 30

Hypoblast

Answer 30

Separation of some of the cells in inner cell mass form this layer. The cells of hypoblast line the fluid-filled cavity where they give rise to extra embryonic endoderm which forms yolk sac

Question 31

Epiblast

Answer 31

Remaining inner cell mass tissue above hypoblast; the embryo will come entirely from the epiblast

Question 32

Amniotic cavity

Answer 32

Epiblast cell layer will split into embryonic epiblast and other epiblast cells which will line amniotic cavity. Once amnion is fully lined it fills with amniotic fluid

Question 33

Epiblast and hypoblast

Answer 33

Together they are referred to as the bilaminar disc (ie bilaminar embryonic disc). The two layers are sandwiched between other two layers of the disc the yolk sac and the amniotic cavity

Question 34

Trilaminar disc

Answer 34

Cells of epiblast give rise to three germ layers endoderm, mesoderm, and ectoderm. Formation begins with the primitive streak (depression in epiblast) which will define major body axes of the embryo as it extends in cranial caudal direction and divides the embryo into a left and right half. Epiblast cells migrate dorsal to ventral

Question 35

Endoderm formation

Answer 35

After the formation of the primitive streak first epiblast cells migrate and displace hypoblast cells of yolk sac

Question 36

Mesoderm formation

Answer 36

Epiblast cells that follow cells becoming endoderm become mesoderm

Question 37

Ectoderm formation

Answer 37

Remaining epiblast cells after primitive streak formation and endoderm and mesoderm cells migrate in formation of 3 germ layers

Question 38

Notochord formation

Answer 38

Central region of the trunk mesoderm forms the notochord. Major functions of notochord: establishing crainial caudal body axis and inducing and patterning future neural tube (which becomes adult CNS)

Question 39

Paraxial mesoderm formation

Answer 39

This flanks the notochord on both sides cells in this region form somites which are mesodermal blocks that will form the vertebrea

Question 40

Intermediate mesoderm

Answer 40

Further from midline than paraxial mesoderm, this will form urogenital system including kidneys, gonads, and associated ducts

Question 41

Lateral mesoderm

Answer 41

Furthest from the notochord. This will further separate into splanchnic mesoderm and somatic mesoderm

Question 42

Splanchinic mesoderm

Answer 42

Deepest lateral mesoderm layer, adjacent to endoderm. Forms smooth muscles and connective tissues of digestive and respiratory organs and also forms the heart

Question 43

Somatic mesoderm

Answer 43

Superfical layer of lateral mesoderm, adjacent to ectoderm and closer to body wall. Participates in development of body wall tissues

Question 44

Spanchopleure

Answer 44

Double layer formed by association of splanchinic mesoderm with endoderm

Question 45

Somatopleure

Answer 45

Double layer formed by association of somatic mesoderm with the ectoderm (body wall)

Question 46

Splanchopleure and somatopleure

Answer 46

Splanchnopleure (surrounds gut and heart) somatopleure forms body wall; together these form first body cavity (space in between them)

Question 47

Embryonic folding

Answer 47

Fold trilaminar flat embryo into mos or less of a cylindrical tube, closes initially flat embryo and closes initially flat organ primordial giving rise to tubular organs. Folding also forms body cavities which are more tubes

Question 48

Extraembryonic membranes in embryonic folding

Answer 48

Body cavities are formed during folding which is acomplished by segregating embryo from extraembryonic membranes, two water balloons are either obliterated (yolk sac and placenta) or incorporated (like coelom which is origin of body cavities) into embryo

Question 49

How does Embryonic folding happen

Answer 49

Embryonic folding is primarily achieved by differential rates of growth in different regions of the embryo. Because trilaminar embryo is flat have to make a closed tube by closing all directions so Cranio-caudal folding and lateral (ie left right) fold occur at approximately the same time

Question 50

Cranial-caudal folding

Answer 50

Happens at cranial and caudal edges of embryo. Cranial edge- we have repositioning (dropping from most cranial to more caudal position) of future opening of mouth, heart, primative thoracic cavity, and a wedge of mesoderm (septum transversum which forms diaphragm) Assures the following 1. Forms ventral surface of future face, neck, and chest 2. Assures heart within the thoracic cavity is below beck (brings heart from most cranial into thoracic position) 3. Repositioning of septum transversum divides for first time the coelom into two cavities, thoracic (includes pericardial and pleural) and peritoneal (abdominal) cavity Processes at caudal edge bring future urinary tract and gut openings into ventral position

Question 51

Lateral folding

Answer 51

AKA left right folding Accomplishes the following 1. Closes body wall (somatopleure) of embryo ventrally 2. Closes initially flat organ primordial (splanchnopleure) ventrally to form tubular organs 3. Forms first body cavity (coelom), flaps of mesoderm (splanchnopleure and somatopleure) fold toward ventral midline along with coelom and meet and merge. The coelom between them which had been extraembryonic is now incorporated in the embryo and is intraembryonic this single large cavity will later be subdivided into separate thoracic and peritoneal cavities

Question 52

Lateral folding at level of the navel

Answer 52

This closes the embryo at that level fuses midgut tube (forms the intestine) and forms the coelom that later becomes the abdominal cavity

Question 53

Lateral folding at level of future heart

Answer 53

Closes embryo at that level, fuses heart tube, forms coelom that will become the pericardial cavity This can also be referred to as lateral folding at level of the foregut

Question 54

Dorsal mesentery

Answer 54

“Neck” of splanchnic mesoderm which remains after folding of splanchnopleure and somatopleure this will suspend the gut tube from the dorsal body (abdominal) wall; the newly formed gut tube is suspended within the coelom from dorsal abdominal body wall by dorsal mesentery, this divides the coelom into left and right side

Question 55

Dorsal mesocardium

Answer 55

Connects heart tube to dorsal portion of the body (thoracic) wall

Question 56

Coelomic cavity divisions

Answer 56

Peritoneal cavity, pericardial cavity, pleural cavities. Initial coelom looks like a U, caudal region of U shaped coelom forms left and right peritoneal cavity. Cranial region of U-shaped coelom will become pericardial cavity.

Question 57

Septum transversum

Answer 57

Formation of this separates left and right peritoneal (abdominal) cavities from pericardial cavity, cranial caudal folding will eventually bring this initially cranial septum to a position caudal to the heart where it will form diaphragm *First cranial to caudal division of coelom*

Question 58

Thoracic cavity separation

Answer 58

Separates into pericardial and pleural cavities by growth of pleuropericardial folds. These communicate after separation via left and right pericardial-peritoneal canals

Question 59

Congenital diaphragmatic hernias

Answer 59

Closing of pericardial-peritoneal canals is acomplished by growth of pleuroperitoneal folds which fuse with septum transversum and seal left and right canals, left canal is larger than right canal and takes longer to close which is why more of these occur on the left side

Question 60

Three major cell types that make up embryo

Answer 60

Epithelial cells (majority of cells), mesenchymal cells, and endothelial cells

Question 61

Epithelial cells

Answer 61

These are super organized and the majority of cells. Usually form sheets or rows of cells with repeating shapes, these are very INVOLVED IN FOLDING Always found in big groups and fold together as a long sheet, tightly connected (cell cell adhesion), good for creating a barrier. These are polarized (asymmetrical) with apical structures like microvilli specialized for absorbtion and secretion, many have cillia, basal structures secrete matrix molecules that form a condensed tightly bound basement membrane

Question 62

Mesenchymal cells

Answer 62

Have random shape, love to hang out alone, migrate alone or in small groups, transiently touch each other, these are in connective tissue of embryo, indistinguishable from fibroblasts (which are found in adult mature tissues); these cells are surrounded on all sides by mesh work of extracellular matrix which contains high proportion of collagens . Can be stationary or highly motile. Can be invasive because have ability to penatrate ECM

Question 63

Can cells change type during develpment?

Answer 63

Yes epithelial cells can become mesenchymal cells and visa versa during development

Question 64

Epithelial cell and mesenchymal cell interactions

Answer 64

Are essential for develpment of both types of cells. If an epithelium doesn’t receive appropriate signals from adorning mesenchymal populations it will not continue to develpment and will usually denigrate, the opposite is true as well

Question 65

Stages of embryonic development

Answer 65

Zygot -> blastocyst -> bilaminar disc -> trilaminar disc

Question 66

Mediastinum formation

Answer 66

Formed internally by dorsal and ventral mesenteries of the esophagus