72 Hr Reviewer

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[EMBRYO LAB]

WHOLE MOUNT  4 flexures: o Cranial/ cephalic flexure o Cervical/nuchal flexure (at the level of 1 st several somites) o Tail flexure flexure o Caudal flexure  Amnion and chorion – enclosed the entire embryo  Paired wing & lung bud – visible nut not sharply bounded  Allantois – sac-like structure encircled by the tail STRUCTURE

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DESCRIPTION TRANSVERSE SECtION Anterior part of the hindbrain w/ thicker walls than myelencephalon The roof undergoes enlargement

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Posterior part of the hindbrain Thin roof plate lying freely within the cavity

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Segmented enlargements in the walls of the myelecephalon & metencephalon 11 neuromeres Forebrain: 1st, 2nd, 3rd Midbrain: 4th and 5th Hindbrain: 6th – 11th Thin roof of myelencephalon which is folded in the myelocoell Where vascularization occurs Small, thick-walled oval structure that appears before the auditory vesicle (forerunner) Located at the level of 10th neuromere on each side of myelencephalon Bigger than endolymphatic duct Ganglia of VII (facial) & VIII (auditory) nerves Mass of cells lying against the cranial wall of auditory vesicles Spinal cord Central cavity of spinal cord Thin mid-dorsal wall of the spinal cord Mid-ventral wall of the spinal cord Lateral depression of the central canal about midway between the floor and roof plates Dorsolateral wings of the spinal cord Between sulcus limitans & roof plate

 Metencephalon

myelencephalon

Neuromeres

Posterior choroid plexus Endolymphatic duct Auditory vesicles syn: otic vesicle otocyts

Acoustic-facialis ganglia Central canal Roof plate Floor plate Sulcus limitans Alar plates

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cerebellum roof of the medulla & adjacent skin ectoderm

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Basal plates Marginal layer Ependymal layer Mantle layer

[EMBRYO LAB]

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Ventrolateral wings of the spinal cord Between sulcus limitans & floor plate Outer region of the neural tube Composed of several fibers & fewer nuclei Single, innermost layer of cells Adjacent to the central canal Cells capable of mitosis Wide heavily nucleated layer between marginal & ependymal

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Large mass anterior to the acoustic-facialis ganglion Subdivide into 3 branches

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(branches of trigeminal nerve): located w/in 1st branchial arch

Semilunar ganglion Maxillary branch - medial branch Ophthalmic branch – lateral branch closest to mesencephalon Mandibular branch – lateral branch above the ophthalmic branch

syn: gasserian ganglion

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Very small rounded accumulation of cells at the caudal side of auditory vesicle Glossopharyngeal nerves into 3rd branchial arch Cell mass lying immediately lateral to myelencephalon Small rounded region beneath the metencephalon & mesocoel Becomes continuous w/ metencephalon

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Cavity of mesencephalon

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Found @ mesencephalon Nerve fibers from the neural ectodermal cells appearing as a pair of streaks from the floor of mesencephalon Will innervate 4 pairs of extrinsic eye muscles

Superior ganglion Somite

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Mesencephalon mesocoel

Oculomotor nerve (III)

 Anterior cardinal vein

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syn: precardinal vein

notochord

Closing plates

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Found laterally situated in the mesenchyme of the floor of myelencephalon

Found between 2 regions of hindbrains or between spinal cord & hindbrain FOREGUT AND ASSOCIATED STRUCTURES  Double layered membranes formed by endoderm of pharyngeal pouches & ectoderm

Cerebral aqueduct/ Aqueduct of sylvius

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 Pharyngeal furrows  st

1 pharyngeal furrow and pouch nd

2 pharyngeal furrow and pouch

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Visceral arches Mandibular arch

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Maxillary arch Hyoid arch Symphysis of the lower jaw

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[EMBRYO LAB] of pharyngeal furrows Result of invagination of pharyngeal pouches that are projected lateral from pharynx to contact the adjacent region of skin ectoderm Endodermal evagination which soon become continuous with pharynx & open to the outside via 1st pharyngeal furrow Furrow – V-shaped ectodermal indentation Similar to 1st pharyngeal furrow & pouch but towards spinal cord Found between the adjacent pharyngeal furrows Greatly thickened & filled w/ mesenchymal cells Mass of mesenchyme anterior to the 1st furrow (towards mesencephalon) Lobe-like mass of mesenchyme anterior to stomodeum Found where mesencephalon is Mesenchyme between 1st (hyomandibular) pouch & furrow and 2nd furrow 2 arches fuse ventrally (posterior of mandibular arch) Paired structures w/c are cut frontally (foregut) Appear constricted into 2 parts of the level of 1st pharyngeal pouch

Dorsal aorta

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1st aortic arch

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Lies within mandibular process

2nd, 3rd, & 4th aortic arches

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Extend from the dorsal aortae into 2nd, 3rd, & 4th branchial arches Continuous with 1st aortic arches (separate vessels) Ventral ends of 2nd & 3rd also unite in ventral aorta Result from the fusion of paired aortae Posterior to 3rd pharyngeal pouch Narrower vessel arises as a cranial extension of dorsal aorta Located medial to ant cardinal vein Derived from group of neural crest cells Lying posterior to IX nerve Fades out w/in 4th branchial arch Arise from the floor of pharynx as a median diverticula/ depression bet. 1st and 2nd pair of

 Ventral aorta syn: aortic sac Descending aorta Internal carotid artery Jugular ganglion Thyroid rudiments

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jaws

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Oral plate syn:pharyngeal membrane

Pre-oral gut stomodeum

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Rathke’s pouch Laryngotracheal groove Trachea

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Lung buds

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[EMBRYO LAB] pharyngeal pouches Constituted by apposition of pharyngeal endoderm & stomodeal ectoderm Separates stomodeum from foregut Ruptures to form mouth opening Located cranial to the pharyngeal membrane Less conspicuous after rupture of oral plate Slitlike space lined by ectoderm Lies bet 2 visceral masses next to foregut Cavity lined with cuboidal epithelium opens in more posterior sections into the stomodeum Serves as rudiment of ant. pituitary gland V-shaped ventralmost part of foregut (post.) Seen at the level of 4th pharyngeal pouch Arises with the lung buds as ventrocaudal diverticulum of pharynx Paired bilateral expansion of laryngotracheal groove Doughnut-like structure (when cut off from laryngotracheal groove)

Pleural cavities

Esophagus

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Coelomic cavities lateral to lung buds Continuous w/ pericardial cavities

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Rounded part of foregut Contained w/in a thick mesentery of splanchnic mesoderm Whole mesenchymal mass where esophagus & lung buds are embedded Includes dorsal mesentery (mesoesophagus) and ventral mesentery (dorsal mesocardium)

 Mediastinum

Bulbus cordis

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Endocardium & myocardium (present) indicates the beginning of bulbus cordis

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Large chamber lying to the left and caudally to bulbus cordis Has blood corpuscles in it On the dorsal part of atrium Attached to foregut by dorsal mesocardium Separated from atrium by slight constriction Continuous with common cardinal vein Regions of heart where left and right fused Thick wall

syn: conus arteriosus

Atrium

Sinus venosus

Ventricle

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Ant. pituitary gland

bronchi

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Trabeculae Pericardial cavity Common cardinal vein syn:duct of Cuvier Pleuropericardial membrane syn: lateral mesocardium

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Irregular projections of myocardium Numerous in ventricular walls Coelom surrounding the heart

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Found continuous to sinus venosus Lower vessel

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Bridge of mesenchyme through which common cardinal vein passes

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Mesenchyme incompletely separates the pericardial cavity from peritoneal cavity Encloses the veins that enter the heart Body cavity posterior to transverse septum Continuous w/ pleural and pericardial cavity Replaces the mesencephalon Laterally compressed w/ thin walls Posterior to oculomotor nerves Long ventral outpocketing of diencephalon Formed by invagination of optic vesicles Inner layer of optic cup Differentiates into:  Sensory retina – thick layer of optic cup next to lens vesicle  Pigmented retina – thin external layer of optic cup Formed by ventral invagination of optic cups & optic stalks Seen as ventral gap in optic cup Lens become freed from superficial skin ectoderm 2 regions:  Elongated & centrally located – will form lens fibers  Outer & narrower cells – will become lens epithelium Single layer of epithelial tissue covering the lens of the eye

Transverse septum Peritoneal cavity Diencephalon Infundibulum Optic cup

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Retina

Optic fissure syn: choroid fissure

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Lens vesicle

Corneal epithelium

[EMBRYO LAB]

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Optic stalk

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Connects optic ups with diencephalon

Postcardinal vein Intersegmental vein

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Lies dorsal to mesonephros Appear as extensions of postcardinal vein Drain blood from the dorsal organs like somites,

corneal epithelium

Layer: sclera & choroid

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[EMBRYO LAB] notochord, neural tube

Stomach

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Lies medial to the pleural cavities

Dorsal mesogaster

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Mesentery dorsal to the stomach

Hepatogastric ligament

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Mesentery ventral to stomach

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Has become of sinus venosus Liver diverticula are embedded in it

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Lying above the ductus venosus

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Seen when ant. liver diverticulum becomes continuous with foregut

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Mesentery lying dorsal to duodenum

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Mesentery lying ventral to duodenum

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Lies beneath the ductus venosus & connecting duodenum

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Small tubes found ventrolateral to the dorsal aorta

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Drains blood from allantois

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Telencephalic vesicles – oval-shaped evagination Cavity of telencephalon:  Median telocoel (ventricle III) – connects posteriorly w/ diocoele  2 lateral diocoele (ventricles 1 & 2) – connect with the median telocoel thru foramen of Monro

syn:ventral mesogaster

Ductus venosus Anterior liver diverticulum syn: cranial liver diverticulum

duodenum Mesoduodenum Hepatoduodenal ligament syn:duodenohepatic ligament

Posterior liver diverticulum syn: caudal liver diverticulum Pronephros Allantoic veins syn:umbilical vein

 Telencephalon

Lamina terminalis

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Thin section of snterior telencephalic wall

Cerebral hemispheres

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Nasal placodes

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Thickened layer from skin ectoderm lateral to telencephalon

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Ectodermal invagination on each side of telencephalon

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2 big blood vessel on each side of cranial liver dicerticulum Level of gut

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Level of duodenum Ventral to ductus venosus

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Caudal to cranial intestinal portal Appear as conical bulges on each side of body Composed of somatic mesoderm covered by skin ectoderm Thickened as apical ectodermal ridge

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Small blood vessels continuous w/ dorsal aorta

syn: olfactory placode

Nasal pit syn: olfactory pit

Vitelline veins syn: omphalomesenteric vein

Cranial intestinal portal syn: anterior intestinal portal

Wing buds

Intersegmented arteries Mesonephric duct syn: Wolffian duct Mesonephric tubules Mesonephric ridge Subcardinal veins Leg buds Tail bud

Allantois

Chorio-allantoic membrane

[EMBRYO LAB]

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Yolk sac 

UROGENITAL SYSTEM Tiny duct w/ thin wall on each side Level of wing buds by cavitation of mesonephric duct rudiment Paired S-shaped tubules medial to mesonephric duct Rounded bulge of dorsal body wall into peritoneal cavity containing mesonephros Small blood vessel lying beneath each mesonephric kidney

Level of the posterior intestinal portal Remnants of primitive streak and Hensen’s node Large mass of undifferentiated cells Dark mass w/ large irregular sacculation located to the right of hindgut in extraembryonic coelom Formed from splachnopleure Store nitrogenous waste product Serves as embryonic respiratory organs for birds Lies beneath the inner shell membrane For respiration & absorption of calcium for shell Formed from splanchnopleure that overgrows yolk Endodermal cells of yolk sac digest yolk w/c are

External nares

Mesonephric kidneys

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Chorion

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Amnion

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Extraembryonic coelom

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syn: exocoel

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Hindgut Lateral body fold cloaca Cloacal membrane syn: anal plate

Caudal intestinal portal syn: posterior intestinal portal

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[EMBRYO LAB] transported to developing embryo via vitelline veins Outer wall of each amniotic fold Ectoderm on outside w/ adjacent layer of mesoderm inside Inner wall of each amniotic fold Consist of somatic mesoderm on outside and ectoderm on inside Somatic mesoderm lined cavity within each amniotic fold Continuous with intraembryonic coelom Endoderm line cavity Posterior region of the gut Forms the boundary bet. Embryonic & extraembryonic regions Posterior portion of hindgut w/c continuous ventrally w/ allantois & mesonephric ducts Double-layered membrane Ventral endoderm of cloaca fuses w/ ventral skin ectoderm Opening formed from hindgut into the subgerminal cavity

Upon rupture: anal opening