ANATOMY 3.1 (Body and Coelom Formation)

Question 1

Evolution of extra-embryonic of fetal membranes:

Answer 1

-permitted reptiles, mammals, and birds to move away from aquatic environment and to evolve on land

Question 2

Early gastrulation: embryonic disc/epiblast

Answer 2

-becomes covered by the extra-embryonic membranes as a result of body folding

Question 3

Function of extra-embryoinc membranes:

Answer 3

-supply/store nutrients
-gas exchange
-excretion of wastes
-mechanical protection
-immune protection
-hormone protection (mammals)

Question 4

Extra-embryonic membranes:

Answer 4

-chorion
-amnion
-yolk sac
-allantois

Question 5

Yolk sac:

Answer 5

-first to be formed
-mediates nutrition in developing birds and reptiles (egg-laying vertebrates)
-becomes connected to midgut by yolk-duct (yolk duct wall continuous with gut)
*splanchonopleure (yolk sac wall)

Question 6

Splanchonopleure (yolk sac wall)

Answer 6

-endoderm and the visceral mesoderm (sphlanchnic)

Question 7

Yolk sac in higher mammals:

Answer 7

-does NOT contain yolk
-important as first hematopoietic organ (blood cell formation) in mammals
-first source of primordial germ cells (stem cells)

Question 8

Chorion:

Answer 8

-derived from trophectoderm, near embryonic disc AND somatic mesoderm
-called somatopleure
-outermost extra-embryonic membrane and functions in gas exchange, respiration, etc.
-in reptiles and birds, it would be up against the egg shell

Question 9

Body folding: cranial to caudal:

Answer 9

*around 2nd week
-somatopleure (chorion) pushes over top of embryo and creates chorioamniotic folds
-splanchopleure (yolk sac wall): pinches in under the embryo

Question 10

Amnion:

Answer 10

-most evolutionary significant membrane to form
-surround embryo proper
-provides and aquatic microenvironment which permits embryogenesis in water analogous to evolutionary ancestors
-amniotic cavity

Question 11

Important of having an aquatic microenvironment:

Answer 11

-preventing desiccation (no drying out)
-acting on a shock absorber (protect from physical forces)

Question 12

Amniotic cavity:

Answer 12

-formed by the fusion of the somatopleure around the embryo

Question 13

Mesamnion:

Answer 13

-chorioamniotic raphe
-little space between the chorioamniotic folds
>not maintained in horses and carnivores
>maintained in pigs and ruminants

Question 14

NO mesamnion in horses and carnivores:

Answer 14

-chorioamniotic folds came together
-connection of chorion and amnion is LOST (just have space in between)
-allantosis surrounds the whole fetus

Question 15

Mesamnion in pigs and ruminants:

Answer 15

-maintained
-allantois can not get in between (can’t go completely around the fetus)
>larger anchor shape

Question 16

Allantois:

Answer 16

-acts to store urinary wastes from embryo’s developing urinary system and mediate gas exchange

Question 17

Reptiles and birds allantois:

Answer 17

-can become quite large apposed to chorion
-keeping toxic by-products of metabolism away from the embryo

Question 18

Mammals allantois:

Answer 18

-size depends on how well nitrogenous wastes are removed by chorionic placenta
-it can fill the entire extra-embryonic coelom

Question 19

Cardiogenic field:

Answer 19

-important for surrounding the heart and the lungs

Question 20

Lateral body folding:

Answer 20

-lateral plate mesoderm pushes down ventrally on either side
-somatopleure are going to move up to the top of the embryo (chorioamniotic folds begin)
-splanchopleure will start pinching in
*completed by 3rd week

Question 21

Splanchnopleure folding lateral:

Answer 21

-get the future gut and soon to regress yolk sac
-left and right intraembryonic coelom develop

Question 22

Intra-embryonic cavity:

Answer 22

-lateral plate mesoderm creates clefts of spaces along the side of the embryo
-eventually fuse into the intraembryonic coelomic cavities on the right and left side of the embryo
-often extend cranially in front of the neural plate

Question 23

Following cranial, caudal, and lateral body folding:

Answer 23

-more cranial portion of the horseshoe-shaped coelom will be ventral to foregut and developing heart

Question 24

Initially developing heart and lungs are surrounded by:

Answer 24

-left and right segments of pleuro-pericardial cavity
-heart will eventually be suspended in one pericardial cavity when ventral and dorsal mesocardium are lost=single pericardial cavity
>suspended within the cavity via blood vessels leaving and entering the heart

Question 25

Developing lungs:

Answer 25

-will grow into pleural cavities -expand into pleuro-peritoneal canals -visceral pleura: the mesothelium in direct contact with the developing lungs

Question 26

Parietal pleura (developing lungs):

Answer 26

-mesothelium that is in contact with the wall of pleural cavity

Question 27

Folds of mesoderm:

Answer 27

-pleuro-pericardial folds grow medially into left and right parts of pleuro-pericardial cavity eventually fusing to separate the pleural from the pericardial cavity >pleural cavities: dorsally >pericardial cavities: ventrally

Question 28

Mediastinal space:

Answer 28

-all structures in thoracic cavity except lungs, caudal vena cava and right phrenic nerve are in it -extends from the developing vertebral column to the developing sternum

Question 29

As diaphragm forms:

Answer 29

-it separates the pleuro-pericardial cavity from the developing peritoneal cavity

Question 30

Closure of space between pleural cavities and peritoneal cavity:

Answer 30

-occurs due to growth of pleuro-peritoneal folds from the lateral body wall to fuse with the septum transversum and the mesothelial fold suspending the esophagus (mesoesophagus) *primordial diaphragm results

Question 31

Septum transversum:

Answer 31

-mesodermal structure -partly separates the developing thoracic and abdominal cavities, which communicate with each other via the pleuro-peritoneal canals

Question 32

Musculature of diaphragm derives from:

Answer 32

-myoblasts which originate in cervical and thoraco-abdominal somites

Question 33

Congenital anomalies of the diaphragm happen when:

Answer 33

-components of it do not fuse and completely partition the abdominal from the thoracic cavities

Question 34

Diaphragmatic hernia:

Answer 34

-when fusion fails, there is a persistent opening between the thoracic and abdominal cavities

Question 35

Congenital diaphragmatic herniation:

Answer 35

-when abdominal viscera pass through this opening into thoracic cavity -2 types in domestic animals 1. Pleuro-peritoneal herniation 2. Peritoneal-pericardial herniation

Question 36

Pleuro-peritoneal herniation:

Answer 36

-failure of one or both pleuro-peritoneal folds to develop or fuse with mesoesophagus and septum transversum -usually occurs on left side -most common in humans

Question 37

Pleuro-peritoneal herniation in humans:

Answer 37

-viscera (ex. stomach and intestines) present in pleural cavity

Question 38

Peritoneal-pericardial herniation:

Answer 38

-domestic animals, particularly dogs and cats -results of defect in development of septum transversum leading to improper communication between peritoneal and pericardial cavities -herniation of viscera (liver, pyloric region of stomach and intestines) into the pericardial cavity

Question 39

Lateral body folding results in:

Answer 39

-left and right coeloms surrounding the developing gut -intra- and extra-embryonic regions

Question 40

Gut:

Answer 40

-suspended by folds of splanchnic mesoderm between the coelomic cavities lined by mesothelium (future peritoneum)

Question 41

Later in development, ventral mesentery:

Answer 41

-caudal to duodenum, and cranial to rectum ATROPIES -gut is now suspended only by dorsal mesentery >allows it to grow in length and rotate *a single peritoneal cavity is now present in this region

Question 42

Schistosomus reflexus:

Answer 42

-congenital fatal anomaly -primarily observed during embryonic development in ruminants -leads to significant dystocia (difficulty giving birth) that is less difficult in large ruminants compared to smaller ones

Question 43

Schistosomus reflexus dystocia;

Answer 43

-malformed calves are unable to pass through the birth canal -fetus must be removed by caesarean section or fetotomy (removing it in pieces) >leads to recovery of the cow for later breeding

Question 44

Presentation of schistosomus reflexus:

Answer 44

-head, limbs, and tail are in close proximity resembling a distinctive ventral convex curvature >result of acute angulations of spinal column -limb fusion/stiffness *failure to close all or most of the ventral wall of the fetal body resulting in exteriorized viscera

Question 45

Gastroschisis:

Answer 45

-failure of ventral body wall to close in the abdominal region -can lead to movement of abdominal contents Ex. intestines outside of the body cavity through a fissure between umbilicus and sternum

Question 46

Congenital umbilical hernias:

Answer 46

-associated with the kind of abdominal ventral body wall defect -protrusion of viscera occurs around the umbilicus due to lack of muscular body wall in that region -found in small animals, pigs and cattle >one of the most common developmental defects in pigs >common in calves (Holstein Friesian cattle) with frequency of 4-15% *maybe a genetic component?