33-hour Chick Reviewer 30285x

33-hour Chick: Whole Mount  

primary brain vesicles are already present fundamental regions of the heart have already formed

Prosencephalon  most anterior brain region  later divides into telencephalon (anterior) and diencephalon (posterior) o both further divide into cerebral hemispheres, thalamus, hypothalamus, and optic vesicles Prosocoel  cavity of the prosencephalon  will become ventricles I to III Optic Vesicle  paired lateral invaginations prosencephalon  opticoel - cavity of vesicle

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Infundibulum  ventral evagination on the floor of the diencephalon  forms the posterior lobe of pituitary gland Mesencephalon  midregion of the brain  cavity: mesocoel o fate of mesocoel is the aqueduct of Sylvius or the cerebral aqueduct Metencephalon  anterior portion of hindbrain  cavity: metacoel o metacoel is part of the IV ventricle Myelencephalon  posterior portion of hindbrain  cavity: myelocoel o myelocoel is part of the IV ventricle Spinal Cord  neural tube posterior to the hindbrain  cavity: central or spinal cord

Somites  11-12 pairs are present Anterior Intestinal Portal  opening of the foregut  as development progresses and the gut elongates, this opening will move to the posterior  will also eventually be part of the yolk stalk Heart  

single, tubular, S-shaped organ at right side of the body

Area pellucida  same as 24-hour chick Area vitellina  same as 24-hour chick Area opaca vasculosa  Sinus terminalis o vein that encircles the area vasculosa o gives rise to terminal blood vessel of vitelline circulation o  Blood islands o masses of splanchnic mesoderm o found in gut wall of amphibians and yolk sac of amniotes o form red blood cells and blood vessels Proamnion  region that is anterior to the developing avian embryo  surrounds the head  contains endoderm and ectoderm  will be invaded with mesoderm and become incorporated into the amnion Subcephalic pocket  cavity beneath the embryonic head as the head develops

Sinus Rhomboidalis  rhomboid-shaped region located on the caudal part of the embryo  this is the location of where the primitive pit and Hensen’s node are enclosed by unfused neural folds Notochord  rod-like structure that is dorsal to the gut  origin: mesoderm  function: defines anterior/posterior axis and provides skeletal for embryo Nephrotome  stalk-like connection between somites and lateral plate mesoderm  forms the pronephros (anterior) and mesenchyme (posterior) o mesenchyme will further differentiate into mesonephros and metanephros

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33-hour Chick: Transverse Section Level of Optic Nerve Optic Vesicles  lateral bulges of prosencephalon  forerunners of the portions of the eyes  will induce the head ectoderm to thicken, invaginate, and form the lens vesicles  cavity: opticoel Proamnion  region below the head fold  consists of ectoderm underlain with a layer of endoderm  will eventually be overgrown and disappear

Section through Oral Plate

Prosencephalon  forebrain that consists of median vesicle and a lateral outpocket on each side  cavity: prosocoel

Foregut  smile-shaped cavity  ventral to notochord  walls are derived from endoderm  middle portion of the foregut’s floor is slightly thickened

Anterior neuropore  median cleft at anterior tip of neural tube  presence of this opening means the neural folds have not fused yet Lens Placode  thickening of head ectoderm that surrounds the optic vessel  forerunner of eye lenses Infundibulum  shallow depression of prosencephalic floor  located at posterior border of optic vessels Amniotic fold  fold of somatopleure  arise at the head region, the sides, and the caudal end  fusion of amniotic folds will give rise to amnion (inner) and chorion (outer) Yolk sac  extra embryonic membrane  encloses and absorbs yolk of amniote embryos  endoderm + splanchnic mesoderm (splanchnopleure) Other structures to be noted (description in 24-hour chick)  Head ectoderm  Mesenchyme  Neural Crest  Subcephalic pocket  Area pellucida  Coelom  Area Vasculosa

Notochord  ventral to mesencephalon  mesoderm derived

Oral Plate  thickened area formed by the ventral ectoderm and the adjacent endodermal evagination of pharynx  ventral to the foregut  will form the mouth when it perforates Subcephalic Space Extraembryonic germ layers

below the head fold

Mesencephalon  oval-shaped brain vesicle  posterior to prosencephalon Anterior cardinal veins  paired blood vessels at the lateral sides of the mesencephalon Pharynx  region of foregut at this level Dorsal Aorta  large, paired blood vessels  dorsal to the pharynx Stomodeum  shallow midventral depression in the ectoderm  forerunner of buccal cavity Ventra Aorta  small paired blood vessels  located below the pharynx  one is at each side of a median depression in the floor of the foregut First Aortic Arches  connects the dorsal aorta with the ventral aorta  can be seen at the anterolateral region of the foregut

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Neural Crest  cells found at the edges of the neural plate and above the neural tube  will form ganglia, pigment cells, and parts of the gills Thyroid Gland  endocrine gland that functions for control of metabolism and growth  from ventral endoderm of pharynx  seen as a thickened shallow depression of the foregut at the region of the dorsal mesocardium Section at the level of the Heart: Posterior Sections Atrium  posterior level of the heart  located now at the middle of the pericardial cavity  becomes the future auricles Sinus venosus  caudal continuation of the atrium  dorsoventrally flattened tube in the midline Section at the level of the Heart: Anterior Section Ventral Aortae  fusion of ventral aorta from earlier  now a median, unpaired vessel Bulbus arteriosus  anterior chamber of heart embryo  connects ventricle to the ventral aorta Epimyocardium  outer, thicker layer of heart rudiment  arises from splanchnic mesoderm  fuses with the endocardium to form the heart’s wall  will give rise to: epicardium (outer covering of the heart) and myocardium (cardiac musculature)

Anterior Intestinal Portal  ventral opening of the gut into the yolk  future midgut Vitelline veins  paired, large vessels that enter the atrium via sinus venosus  at the caudal sections, these vessels will rise at the lateral part of the blastoderm Anterior cardinal veins  pair of small blood vessels above the dorsal aortae  also lies adjacent to the rhombencephalon

Isthmus  broad connection between heart and foregut  synonymous to dorsal mesocardium rhombencephalon by the time na mag-heart na

Section at the level of the Heart: Through the Ventricle Ventricle  bends to one side of the coelom  narrower dorsal mesocardium Rhombencephalon  posterior part of brain  level of future ventricle  possesses a thick wall Auditory Pits  ectodermal thickenings at hindbrain level  forerunners to the inner ears  syn: auditory placodes

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Section through the Sinus Rhomboidalis Neural Tube  neural groove has opened Hensen’s node  large mass of compactly arranged cells  displaces the notochordal tissue

Section through the Somites

Unsegmented mesoderm  somites are not yet divided at this section Omphalomesenteric vein  it is located far out in the splanchnopleure

Spinal Cord  elongated with elliptical cavity Notochord Somites Nephrotome

refer to the 24-hour chick description for these structures

Hypomere Dorsal Aortae  pair of large vessels between the endoderm and the somites  at more caudal sections, they continue laterally into the plexus of vessels -- emphalomesenteric arteries

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pictures are from: http://www.vcbio.science.ru.nl/images/embryology/c hicken-33hrs-dorsal-longitudinal-patten.gif http://nte-serveur.univlyon1.fr/nte/embryon/www.uoguelph.ca/zoology/devobio/33h rchck/33ckintr.htm https://embryology.med.unsw.edu.au/embryology/i mages/thumb/7/72/Patten028.jpg/600px-Patten028.jpg

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