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