33-Hr Chick Embryo

EMBRYO. LAB. 4.3 DEVELOPMENT OF CHICK EMBRYO (Part 2 – 33 HR CHICK EMBRYO) (WHOLE MOUNT / WM)

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Main dev’tal advances of 33-Hr Chick: Brain & Heart Brain Regions: o Prosencephalon – forebrain; Telencephalon + Diencephalon o Mesencephalon – midbrain o Rhombencephalon – hindbrain; Metencephalon + Myelencephalon Heart Regions: (Anterior to posterior) o Truncus arteriosus o Ventricle o Atrium o Sinus venosus

1) Prosencephalon – forebrain - later divides into telencephalon (most anterior) and diencephalons - telencephalon and diencephalons later differentiates into: (HOT C) a. Hypothalamus b. Optic vesicles c. Thalamus d. Cerebral hemispheres 2) Optic Vesicles – paired - lateral evaginations @ sides of Prosencephalon - have opticoel 3) Infundibulum – ventral evagination of diencephalic floor - forms posterior of pituitary gland 4) Prosocoel – cavity of Prosencephalon - gives rise to Ventricles I to III 5) Mesencephalon – midbrain - cavity: Mesocoel (gives rise to Cerebral Aqueduct / Aqueduct of Sylvius)

6) Rhombencephalon – hindbrain - divided into: a. Metencephalon (more anterior) b. Myelencephalon (more posterior) 7) Metencephalon – anterior hindbrain subdivision - cavity: Metacoel (part of IV Ventricle) 8) Myelencephalon – posterior hindbrain subdivision - cavity: Myelocoel (part of IV Ventricle) 9) Spinal / Central Cord – part of neural tube posterior to myelencephalon 10) Sinus Rhomboidalis – rhomboid-shaped part of caudal region - where neural folds enclose primitive pit and Hensen’s node - later disintegrates

11) Notochord – rod-like - mesodermal - dorsal to gut - define anterior/posterior axis - for skeletal support 12) Nephrotome – a.k.a. Intermediate Mesoderm / Mesomere / Nephromere - stalk-like connection between somites and lateral plate mesoderm - (Anterior) forms Pronephros - (Posterior) forms Mesenchyme w/c becomes Mesonephros & Metanephros 13) Somites – 11 to 12 pairs 14) Anterior Intestinal Portal (AIP) – opening of foregut - moves posteriorly, becomes part of yolk stalk 15) Heart – single, tubular, S-shaped - bulges to the right

16) Area Pellucida (AP) – central part of blastodisc - where primitive streak forms - lies directly over subgeminal cavity - appears transluscent (due to thinness of blastoderm) - *Blastoderm – outer Epiblast (becomes ecto and mesoderm); inner Hypoblast

17) Area Opaca – peripheral part of blastodisc - surrounds area pellucida - in direct contact w/ yolk (gives opaque appearance) - 3 Zones: a. Margin of Growth (MoG) – peripheral; cells proliferate w/o adhering to yolk b. Zone Junction (ZJ) – intermediate region; cells cut free from yolk, then added to AP c. Germ Wall (GW) – inner; cells from ZJ, contains yolk granules; transition from opaca to pellucida - develops into 2 regions: 1. Area Opaca Vitellina – outer; initially lacks blood islands / blood vessels (BV) 2. Area Opaca Vasculosa a) Sinus Terminalis – vein encircling area vasculosa - gives rise to terminal BV of vitelline circulation b) Blood Islands – splanchnic mesoderm - form 1st RBC and BV - found in gut wall (amphibians) and yolk sac (amniotes) c) Proamnion – anterior to avian embryo, surrounds head - endoderm + ectoderm (later invaded by mesoderm) d) Subcephalic Pocket – cavity beneath head (as head fold forms)

Transverse Section (Thru Optic Nerve) 

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Optic vesicles – in this section, are lateral bulges of prosencephalon - precursors of retina - close to head ectoderm - induce ectoderm to invaginate, forming lens vesicle Extraembryonic germ layers are evident Mesoderm does NOT extend to the proamnion Proamnion – ectoderm + endoderm - pale staining in WM due to lack of mesoderm - disappears

1) Prosencephalon – forebrain - w/ median vesicle and lateral outpocketings 2) Anterior Neuropore – median cleft @ anterior tip of neural tube - indicates unfused neural folds 3) Prosocoel - cavity of Prosencephalon - gives rise to Ventricles I to III 4) Optic Vesicles - paired - lateral evaginations @ sides of Prosencephalon - have opticoel 5) Lens Placode – thickening of head ectoderm of optic vesicles - gives rise to eye lens 6) Infundibulum – shallow depression of prosencephalic floor @ posterior of optic vesicles 7) Amniotic Fold – fold of somatopleure - its fusion gives rise to amnion (inner) and chorion (outer) 8) Yolk Sac – an extraembryonic membrane - endoderm + splanchnic mesoderm (splanchnopleure) 9) Head Ectoderm - cuboidal cells (cuboidal in origin also); encloses head 10) Mesenchyme - loosely scattered cells - fill up spaces between foregut and neural plate

11) Neural Crest - @ edges of neural plate - lies above neural tube - form ganglia, pigment cells, part of gill arches, etc. (by migration thru the embryo) 12) Subcephalic Pocket - cavity beneath head as head fold develops 13) Area Pellucida - center of blastodisc - where primitive streak forms - lies over subgerminal cavity - appears transluscent (due to thinness of blastoderm)  Blastoderm – consist of:  Epiblast – outer; differentiates into ectoderm and mesoderm  Hypoblast – inner 14) Coelom - cavity formed when somatic mesoderm and mesoderm separates 15) Area Opaca Vasculosa – inner part of area opaca - where splanchnic mesoderm thicken into blood islands 16) Proamnion - anterior to avian embryo - surrounds head - contains endoderm and ectoderm - later involved with mesoderm, then with amnion - amnion is the membrane around the fetus 17) Foregut - 1st part of digestive tract - w/ definite floor - endodermal - dome-shaped - lies inside the head

(Thru Oral Plate)   

Notochord – ventral to mesencephalon/midbrain Foregut – ventral to notochord; smile-shaped cavity delimited by endodermal walls Oral Plate – thickened ectoderm below foregut (specifically @ pharynx); forms mouth

1) Mesencephalon – oval; posterior to prosencephalon 2) Anterior Cardinal Veins (ACV) – paired BV @ lateral sides of mesencephalon 3) Pharynx – region of foregut at this level 4) Dorsal Aorta – large, paired BV - dorsal to pharynx 5) Stomodeum – shallow, midventral depression in ectoderm - becomes buccal cavity 6) Oral Plate – thickened area - formed by ventral head ectoderm + pharynx’ endodermal evagination 7) Ventral Aorta – small, paired BV - lies below pharynx, on sides of a median depression in the foregut floor 8) 1st Aortic Arches – BV connecting dorsal to ventral aorta

(Heart Level – Anterior) 1) Ventral Aortae – median, unpaired BV - formed by fusion of paired ventral aortae (See #7 of “Thru Oral Plate”) 2) Bulbus Arteriosus – a.k.a. Bulbus cordis / Conus arteriosus / Truncus arteriosus - anterior heart chamber; connects ventricle to ventral aorta

3) Epimyocardium – outer, thicker of heart rudiment - from splanchnic mesoderm - fuses w/ endocardium to form heart wall - gives rise to epicardium (outer heart covering) and myocardium (heart muscle) 4) Isthmus / Dorsal Mesocardium – connect heart and foregut

(Thru Future Ventricle) 1) Ventricle – heart region bending to 1 side of coelom - isthmus is narrower here 2) Rhombencephalon – hindbrain - characterized by thick wall 3) Auditory Pits / Auditory Placodes – paired ectodermal thickenings @ hindbrain - become inner ears 4) Neural Crest - @ edges of neural plate - lie above neural tube - form ganglia, pigment cells, parts of gill arches 5) Thyroid Gland – endocrine gland @ throat region - control metabolism and growth - formed from ventral sac of endoderm of pharynx - thickened, shallow depression of foregut @ region of isthmus

(Heart Level – Posterior) 1) Atrium – posterior level of heart @ middle part of pericardial cavity - future auricles 2) Sinus Venosus – caudal continuation of atrium - dorsoventrally flattened tube @ midline 3) Anterior Intestinal Portal (AIP) – opening of gut into yolk - floorless gut (midgut) 4) Vitelline Veins – paired, large vessels - enter atrium via sinus venosus - arise laterally onto blastoderm 5) Anterior Cardinal Veins (ACV) – pair of small BV - above dorsal aortae, adjacent to rhombencephalon

(Thru Somites) 1) Spinal Cord – cavity of neural tube @ level of somites - elliptical 2) Notochord - longitudinal band of cells - extends from neural folds to Hensen’s node 3) Somites - segmented mesodermal blocks - @ sides of spinal cord - arise from dorsal mesoderm

4) Nephrotome / Intermediate Mesoderm / Mesomere / Nephromere - stalk-like connection between somites and L - anteriorly forms pronephros - posteriorly forms mesenchyme w/c develops into mesonephros and metanephros 5) Hypomere - part of mesoderm distal to nephrotome - 2 layers: somatic and splanchnic mesoderm 6) Dorsal Aortae – pair of large vessels - between endoderm and somites - continue laterally to become Omphalomesenteric Arteries (network of interwoven vessels)

(Thru Sinus Rhomboidalis) 1) Neural Tube - @ this level, neural groove is open 2) Hensen’s Node – large, compact mass of cells - displace notochordal tissue 3) Unsegmented Mesoderm – undivided somites 4) Primitive Streak (PS) – neural groove has flattened and disappeared (remains of PS) 5) Omphalomesenteric Vein – far out in the splanchnopleure