48 Hr Reviewer

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WHOLE MOUNT

 Cranial half : covered with head fold of amnion  Caudal part : does not show such covering

 Subcaudal pocket – separates from the underlying blastoderm

 Cephalization at the anterior portion (brain) → ventral flexion (bending) and dextral torsion (twisting)

 Heart becomes elongated (twisted itself) 

3 FETAL MEMBRANES

o amnion – encircles the anterior portion of embryo ; inner ectoderm & outer somatic mesoderm

o yolk sac – double-membraned on the left side; w/ blood vessels; endoderm & splanchnic mesoderm

o chorion – double-layered on the right side; close to amnion; outer ectoderm & inner somatic mesoderm



3 IRREGULAR WHITE LINES SEEN FROM HEART TOWARDS AUDITORY VESICLE o 1st_{branchial groove} o 2nd_{branchial groove} o 3rd_{branchial groove}  ARCHES o

1 st_{visceral arch – above 1}st_{branchial groove} o

2 nd_{visceral arch – between 1}st_{& 2}nd_{branchial groove} o

3 rd_{visceral arch – between 2}nd_{and 3}rd_{branchial groove} 

1 st_{visceral arch processes:}

o Maxillary process – ant. to stomodeum o Mandibular process – post. to stomodeum

 Myelencephalon – brain region where ganglia are associated

 Pharyngeal/ hyomandibular pouch & branchial groove – contribute to the formation of 1st branchial plate

 Rathke’s pouch & infundibulum – 2 structures that forms the hypophysis  3 pharyngeal pouch

 3 aortic arches  3 visceral arches

Structure Description Fate

TRANSVERSE SECTION SEC. THRU MESENCEPHALON mesencephalon

 Oval shaped

 1st_{cavity of the brain to be observed}

 Shows frontal section due to cranial flexure isthmus

 Constriction

 Partially separates the mesencephalon from hindbrain

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myelencephalon  Thin roof at the opposite end of mesencephalon

metencephalon  Underlined portion between myelencephalon and isthmus

mesenchyme  Loose connective tissue between brain and epidermis

fetal membranes  Amnion, chorion, & yolk sac extraembryonic

coelom

 Space bounded by mesoderm, between the chorion, yolk sac, amnion

SEC THRU DIENCEPHALON diencephalon  Lower cavity when the brain separates

 Replaces the position of mesencephalon velum transversum

 Depression found in the dorsal wall of the forebrain

 Demarcation between diencephalon & telencephalon

Metencephalon  Delimited by the isthmus at this section

Myelencephalon  Upper, larger cavity of all with thin roofs Posterior choroid plexus Semilunar ganglion  Ganglion of trigeminal (V) cranial nerve

 Dark cells closer to myelencephalon Jugular ganglion

 Ganglion of X cranial nerve  Lateral to myelencephalon  Above the anterior cardinal vein Anterior cardinal vein

syn: precardinal vein

 Space lined by thin wall along each side of myelencephalon

notochord

 Small, elongated mass of vacuolated cells  Between the myelencephalon &

diencephalon

 Separates into 2 (due to cranial flexure)

Disintegrate SEC THRU OTIC VESICLE

Otic vesicle syn: auditory vesicle

otocyst

 Paired vesicle each side of the myelencephalon

 Invagination of ectoderm Endolymphatic duct

Anterior cardinal vein  Pair on the ventro-lateral side of otic vesicle Acoustic-fascialis

ganglion

 Ganglia of VII & VIII cranial nerves

 Cells close (or attached) to otic vesicle & ant. cardinal vein

 Lateral to myelencephalon

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 Dark cells attached to myelencephalon Superior ganglion

 Ganglion of glossopharyngeal (IX) nerve  Cells on both sides of myelencephalon  Observed when otic vesicle is no longer

present or immediately posterior to the auditory vesicles

SEC TRHU OPTIC CUPS

Optic cup

 Double-walled structure on each side of diencephalon

 Derived from invagination of optic vesicle  Sensory retina – thicker, inner layer

 Presumptive retina – inner layer of cup

 Pigmented retina – thinner, outer layer  Presumptive pigmented epithelium –

outer layer of the cup Pigmented layer of retina Lens vesicle

 Little sac-like cavity nestled w/in the optic cups

 Arises as an invagination of ectoderm Optic stalk  Connects the optic cup with diencephalon

pharynx

 Cavity (triangular shape)

 1st pharyngeal pouch (arms of triangle) – hyomandibular pouch

 Invaginates to form 1st_branchial groove

 Double-layered formed is 1st_branchial plate

Pre-oral gut

 Anterior most part of the foregut

 Small circle or oval structure separated from the pharynx by oral plate

 Extends as a fingerlike diverticulum anterior to the future mouth

Carotid loop

 Extensions of the 1st_{aortic arches}

 Elongated spaces medial to ant. cardinal veins

Internal carotid arteries

 Paired vessels from the carotid loops to the optic cups

Dorsal aorta _ Blood vessels on either side of notochord Lies above the 1st_{pharyngeal pouch} 1st_{aortic arch}  Blood vessel beneath the 1st pharyngeal

pouches

Becomes located at mandibular process then

becomes continuous w/ ventral aorta

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syn: 1st_{visceral arch} _ _{Bears the 1}st_{aortic arch} Rathke’s pouch

 Small vesicle between infundibulum & pharynx

 Dorsal evagination of stomodeum

hypophysis Oral plate

syn: pharyngeal membrane

 Thin line (ectoderm & endoderm) separating stomodeum & pharynx

infundibulum  Evagination from diencephalon

 Will later evaginate post. lobe of hypophysis Diencephalon  More elongated in this section

stomodeum

 Slit-like space where Rathke’s pouch opens  Separates maxillary process & mandibular

process

SEC THRU THYROID RUDIMENT & 2ND_{AORTIC ARCH} Thyroid rudiment  Depression in the floor of the pharynx

2nd_{aortic arch}

 Lies beneath the 2nd_{pharyngeal pouches}

 Contained within 2nd_{visceral arches (hyoid}

arches)

 Will later become continuous with ventral aorta

2nd_{pharyngeal pouch} _ ₂nd_{outpocketing of pharynx}

Ventral aorta syn: aortic sac

 Blood vessel beneath the pharynx

 Starts where the bases of 1st_{aortic arches}

meet

 2 layers in its wall indicates beginning of

bulbus cordis

 Connected anteriorly: aortic arches (1,2,3)

 Connected posteriorly: bulbus cordis

SEC THRU 3RD_{AORTIC ARCH} 3rd_pharyngeal

pouches

 Large outpocketing of pharynx

 Together with pharynx, laterally oriented oral

cavity

3rd_{aortic arches}

 Beneath the 3rd_{pharyngeal pouch (not-so}

developed)

 Will later become continuous with ventral aorta

3rd_{visceral arch}

 Between 2nd_{& 3}rd_pouches

 Arches posterior to the hyoid arch = branchial

arches

Bulbus cordis

 1st_{heart cavity}

 Presence of endocardium & myocardium

(differentiates it from ventral aorta)

Dorsal mesocardium  Mesodermal stalk that attaches the stalk to the dorsal wall of coelom

Nasal placode  Thickened skin ectoderm lateral to the telencephalon

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1st_somite _ _{Cell masses lying lateral to myelencephalon}

dermatome  Darkly stained beneath the skin of ectoderm Dermis of skin

myotome  Lightly stained cell medial to dermatome muscle

Anterior cardinal veins

 Seprates into 2 vessels: postcardinal vein (dorsal) common cardinal vein (ventral)

SEC THRU ATRIUM AND VENTRICLE Spinal cord  Replaces the myelencephalon

Descending aorta  Fused dorsal aortae Dorsal

intersegmented arteries

 Small blood vessels arising at intervals from dorsal aorta & extending dorsally bet spinal cord & somite

Conus arteriosus

 Chamber of heart at the right side  Endocardium & myocardium are widely

separated Atrium

 Chamber at the left side

 Endocardium & myocardium are in close contact/ fused

auricle Ventricle  Large looped chamber of the heart

 Connects the conus and the atrium Laryngotracheal

groove

 Deep V-shaped depression in the floor of the foregut

Larynx, trachea, & lung bud Future esophagus  Dorsal portion of the gut

Cardinal veins

 Paired precardinals  Separates into 2 vessels:

postcardinal vein (dorsal) common cardinal vein (ventral)

SEC THRU SINUS VENOSUS

Sinus venosus  Portion of the heart attached to the foregut by dorsal mesocardium

Common cardinal vein

syn: duct of Cuvier

 To which sinus venosus is attached Pleuropericardial

membranes

 Mesenchyme enclosing the common cardinal vein (separates the pleural from pericardial) Lung buds  Slight evagination on the ventro-lateral

portions of the foregut into pleural cavities Pleural cavity  Paired, lateral to the developing lung buds &

continuous with pericardial cavity Transverse septum

 Mesenchyme surrounding the sinus venosus

 Connected with the pleuropericardial

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Cranial liver diverticulum syn: dorsal diverticulum

 Mass of cells on the dorsal side of sinus

venosus lying in the transverse septum ventral to the foregut

Caudal liver diverticulum syn: ventral diverticulum

 Branch/es on the ventral side of the cranial liver rudiment

duodenum  Continuous with the foregut posterior to the cranial liver diverticulum

SEC THRU ANTERIOR INTESTINAL PORTAL Anterior intestinal

portal  Opening of the foregut to the midgut Vitelline veins

syn:

omphalomesenteric vein

 Pair of blood vessels w/c are posterior extensions of sinus venosus

 Lie on each side of anterior intestinal portal  Left then right veins pass out onto the yolk Peritoneal cavity  Big space where internal organs are Paired mesonephric

duct

 Small tubules lateral to the descending aorta  Medial to mesonephtic tubules

 Formed by delamination from the nephrogenic cord (nephrotome)

SEC THRU LATERAL AMNIOTIC FOLDS Lateral amniotic folds

 Elevated & about to fuse folds

 Consist of somatopleure that forms inner amnion & outer chorion

Vitelline blood vessels

 Small blood vessel embedded within the splanchnic mesoderm

Paired dorsal aortae  Big pair of blood vessel below the notochord Mesonephric tubule

rudiments  Round cavity medial to mesonephric duct Nephrostome  Opening of the mesonephric tubule to the

coelom

Vitelline arteries  Posterior of dorsal aorta extending onto the yolk sac

SEC THRU TAIL BUD Tail bud

 Mass of mesenchymal cells at the caudal end

 Covered by skin ectoderm

Hindgut  Posterior portion of gut where it acquires floor

Allantoic rudiment  Endoderm lined cavity below tail bud Caudal intestinal

portal

 Space where the floor of the allantoic rudiment disappears

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