Exercise 4 Frog Embryo 4mm 7mm 10mm

8/18/2019 Exercise 4 Frog Embryo 4mm 7mm 10mm

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Comparative Vertebrate Embryology SY 2014-2015

1 Sacha Pajarillo 4Bio2

DEVELOPMENT OF THE FROG EMBRYO

4MM FROG EMBRYO

WHOLE MOUNT

characterized by the presence of tail , neural tube, notochord , and segmented mesoderm and fin folds

neural system: prosencephalon – foremost part, mesencephalon – middle part, rhombencephalon – hind part

epiphysis – slight mid-dorsal evagination of the brain vesicle, will become the pineal body in adult

olfactory placodes

thickenings on the lateral surface of the head anterior

have cavities known as olfactory pits

lens placode

paired thickenings of the head endoderm

will evaginate to form the lens vesicle, then eye lens

notochord

extends from the midbrain up to the posterior end of

the body somites – subdivided mesoderm that flanks the

notochord on each side

TRANSVERSE SECTION

Level of Prosencephalon and Nasal Rudiments

prosencephalon

anterior part of the embryonic brain

cavity is prosocoel

mesenchyme

embryonic connective tissue

mesoderm and neural crest cell derived

later forms predominantly connective tissues

head mesenchyme

fills the spaces between the presumptive epidermis and walls of prosencephalon

olfactory placodes

paired pigment invaginations on either sides of prosocoel

epidermis

outermost skin layer

ectoderm derived

Level of Mesencephalon and Optic Cups

mesencephalon

appears dorsal to portion of prosencephalon called infundibulum

mid-region of the developing embryonic brain with thick roof

mesocoel – brain cavity

also known as midbrain


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oral cavity

cavity at the cranial end of alimentary canal

more or less spherical in appearance

stomodeum

ectodermal rudiment of mouth

formed by invagination of ectoderm at anteroventral region of head

hypophysis

small knot of tissue ventral to infundibulum, develops as an inward growing cord of ectoderm from

stomodeum, will form anterior portion of pituitary gland

solid ingrowth or nodular aggregation of cells lying between the oral and brain cavity

may be used to describe:

o invagination of the stomodeum which fuses with the infundibulum to form pituitary gland

o endocrine gland formed from an ingrowth from the stomodeum (Rathke’s pocket ) and infundibulum

also known as pituitary gland

infundibulum

funnel-like depression of prosencephalon, part of which forms the posterior lobe of pituitary gland together withstomodeum

seen as smaller, ventral component of diencephalon with thin roof and thick sides

mandibular arch

most cranial branchial arch

forming the caudal border of stomodeum

maxillary process cranial to stomodeum

adhesive glands

paired ectodermal thickenings found in ventral surface of anuran embryos

secrete adhesive mucus for attachment to floating objects

also known as cement glands, mucous glands, oral suckers

optic vesicle

evagination from lateral wall of prosencephalon

first indication of formation of eye

its walls will give rise to various ectodermal parts of eye, except lens and cornea

optic cup

double-walled structure formed by invagination of distal portion of optic vesicle

inner layer should be thicker than outer layer

optic stalk

connection of optic cup with the brain

Level of Rhombencephalon

Section through the anterior pharynx

rhombencephalon

most caudal region of the brain of developing embryo with a thin roof

rhombocoel – cavity

also known as hindbrain


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notochord

round structure originating from mesoderm

lying dorsal to gut and ventral to hindbrain

defines the anterior/posterior axis in developing embryo

provides skeletal support during early development

pharynx broad region of foregut

paired evagination corresponds to pharyngeal pouches

otic

paired invagination of otic placode

laterally located and slightly ventral to brain

when separated from head ectoderm, will form inner ear

also known as auditory vesicle

Section through the embryonic heart

heart

located beneath enlarged foregut appears suspended within pericardial coelom by dorsal mesocardium

pericardial coelom delimited by thin layer of somatic mesoderm called pericardium (membrane enclosing the

heart)

pericardium – formation is brought about by migration of heart mesoderm to midventral region of pericardial

cavity

two layers of the heart

o endocardium – inner endothelial layer of heart, will form the lining of heart wall

o epimyocardium – outer layer, will form the muscle

Section through the liver diverticulum

mesomeres

paired bulges of tissue just below the horizontal level of notochord have begun to develop pronephric tubules

may be called pronephros or pronephric kidney

liver diverticulum

extremely deep groove at the floor of the pharynx

rudiment of the liver

Section through the pronephros

spinal cord

cavity that replaces the hindbrain

smaller than the hindbrain

thick lateral sides almost touches at the roof part

pronephros

paired structure located on lateral side of specimen

appear as spherical/elongated structures clustered together

initial organ found in developing vertebrate embryos

functional in larval amphibians and fish

degenerates and is replaced by mesonephric kidney in adults


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somites

segmented mesodermal blocks located on either side of spinal cord

arise from dorsal mesoderm

will differentiate into:

o sclerotome – located above the neural tube and notochord, forms part of the axial skeleton

o myotome – forms muscle

o

dermatome – forms the dermal layer of skin

Section though the midgut

spinal cord

gradually tapers off in diameter form rhombencephalon to caudal end

diameter approximates that of notochord

subnotochordal rod

small knot of cells wedged between notochord and midgut

transient structure of endodermal origin

unknown function, will later disappear

Section through the hindgutproctodeum

ectodermal invagination that meets with the endoderm of the hindgut

cloacal membrane (ectodermal and endodermal plate)

delicate strands of tissue between proctodeum and hindgut

will become perforated to form the posterior opening of the digestive tract

dorsal fin

flat extension of the body wall along the dorsal midline of the trunk and tail

degenerates during the metamorphosis of tadpole

hindgut

posterior most region of embryonic gut

will form cloaca, colon, small intestine, and rectum

proctodeum

ectodermal invagination on the ventral side of the trunk at the base

later breaks into the hindgut forming the anus

also known as anal pit


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7MM FROG EMBRYO

WHOLE MOUNT

well-formed external gills and a functional heart

embryo has changed its shape and has become a tadpole

tail – serves as a powerful swimming organ, provided with lateral segmented somites and finfolds on the dorsal

ventral sides

forebrain – has further differentiated into telencephalon (two hemispheres) and diencephalon stomodeum – deeply invaginated

olfactory pit – surrounded by large

pigmented cells

epiphysis – formed by circular knob of cells

that are separated from the brain

notochord extends up to tail, head and

trunk are bloated, midgut is excluded

hindgut does not lose its cavity but persists

as cloaca

dorsal wall of hindgut becomes extended

into tail rudiment as post anal gut , which

later is broken down and will disappear in amphibians, hindgut gives rise to ventral

evagination, urinary bladder

TRANSVERSE SECTION

Level of the Telencephalon and Olfactory Pits

large indentation on the ventral surface of the embryo marks the beginning of the oral cavity

oral plate has become perforated

embryo now has an open mouth

telencephalon

paired hemispheres occupying the anterior region of forebrain

diencephalon

posterior division of the prosencephalon

olfactory pit

will subsequently develop into nasal passages with olfactory receptors

appears as a cavity on the lateral surface of the head

epiphysis

slight middorsal evagination of the brain vesicle

will become the pineal body in the adult

head mesenchyme

loose mesenchymal cells formed between the head ectoderm and the brain


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Level of the Diencephalon and Optic Cups

oral cavity is visible surrounded by presumptive jaw cartilages

diencephalon

posterior half of forebrain

appears as deep, laterally compressed region

optic stalks, infundibulum, and epiphysis are attached

mesencephalon

part of brain located posterior to the eye

center for reflexes associated with vision, hearing, and movement of head

optic cup

seen lateral to the brain

outer pigmented layer and inner retinal portion of the optic cup can be distinguished

lens vesicle – lies in its concavity

pharynx

large and more rounded clustered mass of cells on each side will give rise to mandibular arch (posterior border of stomodeum)

stomodeum

appears as deep invagination of the pigmented, midventral ectoderm at the anterior end of pharynx

adhesive glands

paired ectodermal thickenings found on ventral surface of head

secrete adhesive mucus for attachment to floating objects

also known as cement glands, mucous glands, oral suckers

Level of the Rhombencephalon

Section through the thyroid below mesencephalon, small portion of the wall f infundibulum is evident

lateral to floor of mesencephalon, developing cranial nerve ganglion can be observed

cranial nerve ganglion – part of the peripheral nervous system, derived from neural crest cells

shape of pharynx – width of pharyngeal cavity greatly exceeds the height

thyroid – arises as an invagination of the endodermal cells from pharyngeal floor

Section through the otic vesicle

rhombencephalon

roof composed of single layer of flat cells

third brain vesicle which expands anteriorly to form the IV ventricle

internal organization shows an unmistakable similarity to that of the spinal cord

will further differentiate into the metencephalon (anterior) and myelencephalon (posterior)

notochord


lying dorsal to gut and ventral to hindbrain

defines the anterior/posterior axis in the developing embryo



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otic vesicle

irregularly hallow organ on each side of hindbrain

closed chamber formed by invagination of the otic placode

will develop into inner ears

heart

lies beneath the pharynx truncus arteriosus – most anterior part, evident within pericardial coelom

has four subdivisions (anterior-posterior):

o truncus arteriosus

o ventricle

o atrium

o sinus venosus

blood flows through embryonic heart from posterior to anterior

bulbus cordis

most anterior heart chamber

pericardial coelom cavity that surrounds the heart

bounded by pericardium

Section through the heart

esophageal plug

mass of cells that temporarily blocks the esophagus before the amphibian larva begins to feed

atrium

chamber of the heart that receives blood from the sinus venosus and delivers blood to the ventricle

seen above the ventricle, observed as thin-walled chamber almost filled with blood

external gills

filamentous respiratory organ, has finger-like projections that protrude from sides of the head

arises from the branchial arches 3 to 6

replaced by internal gills

Level of the Spinal Cord

Section through the pronephros and midgut

glomus

two triangular-shaped structures seen ventral to dorsal aorta that hang down into the coelomic cavity

tufts of small blood vessels surrounded on their lateral and ventral surfaces by thin wall of coelom

functional components of pronephric kidney

where waste products are diffused from into the coelomic fluid

spinal cord

arises from the posterior most region of neural tube

somite

segmented mesodermal blocks located on either side of developing spinal cord

arises from dorsal mesoderm

will differentiate into: sclerotome (located above neural tube and notochord) which forms part of the axial

skeleton, myotome which forms muscle, and dermatome which forms the dermal layer of skin


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dorsal aorta

primitive, paired longitudinal arteries of the trunk

lying beneath notochord anterior to gut

pronephros

initial excretory organ found in developing vertebrate embryos

nitrogenous wastes are passed from pronephric tubules → pronephric ducts → hindgut (cloaca) → exterior functional in larval amphibians and fish

later replaced by mesonephric kidney

nephrostomes

funnel-shaped opening of pronephric tubules

where coelomic fluid is swept

midgut

middle part of gut with a small lumen and having a thick, yolky floor

derived from archenterons

will give rise to small intestine

Section through cloaca

dorsal fin

extension of body wall along mid-dorsal side of trunk and tail

degenerates in older specimens

cloaca

posteriormost chamber in the vertebrate digestive system

proctodeum

ectodermal invagination on the ventral side of the trunk at the base of the tail

will give rise to anus


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10MM FROG EMBRYO

WHOLE MOUNT

(same as whole mount 7mm)

TRANSVERSE SECTION

Level of the Telencephalon and Olfactory Organs

telencephalon

anterior division of the prosencephalon

is paired and each unit is roughly hemispherical but flattened at midline

each contains a cavity (lateral ventricle) formed by evagination of side of neural tube at the anterior end of

neurocoel

Layers of brain wall:

ependymal layer

o one-cell think, ciliated layer immediately surrounding the neurocoel

o cilia – aid in movement of cerebrospinal fluid in ventricles of brain and in central canal of the spinal cord

mantle layer

o broad layer adjacent to ependymal layer

o will form gray matter of central nervous system

marginal layer

o outermost layer

o contains neuroblasts from inner layers and fibers

o will form the white matter of central nervous system

nasal organ

found at the region of telencephalon and lying ventrolateral to it

tubular organ formed by invagination of ectoderm

olfactory nerve connecting the olfactory lobes to the brain arises from the olfactory epithelium

also known as olfactory organ

external naris

opening of the nasal cavity to the outside


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marks the point of original ectodermal invagination

internal naris

opening of the nasal cavity into the buccal region

also known as choana

frontal organ arises as an evagination of diencephalic roof together with epiphysis

beneath epidermis, migrates forward from region of diencephalon to region of telencephalon

contains photoreceptors and may function as a “third eye”

Jacobson’s organ

saccular structure formed by evagination of nasal organ

may function in picking up the smell of food from buccal region

also known as vomeronasal organ

buccal cavity

region where nasal cavity and mouth opens

lined with epithelium and is derived from stomodeum jaws are tipped with horny material and tooth germs

oral papillae – lobose structures external to jaws

prechordal cartilage

hyaline cartilage beneath telencephalon

will form cartilaginous cranium (chondrocranium)

also known as trabecular cartilage

melanocytes

stellate cells scattered over dorsolateral region of brain and lateral to nasal organs

fine granules of melanin – light brown individually, black in aggregate

mesenchyme

stellate, mesodermal cells filling up the space between organs and epidermis

form a loose reticulum, with outermost cells forming the dermis of integument

epidermis

outer layer of skin composed of two strata of ectodermal cells

Level of the Diencephalon and the Eye

diencephalon

posterior subdivision of prosencephalon

ventrally elongated and possesses a cavity ( III ventricle)

infundibulum

funnel-like evagination of diencephalic floor

subsequently evaginates posterior or neural lobe of pituitary together with stomodeum

in more posterior sections, seen as smaller, ventral component with thin roof and thick sides

mesencephalon

middle region of brain dorsal to diencephalons

bears 3rd

and 4th

cranial nerves


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possesses a cavity known as cerebral aqueduct

pituitary body

oval mass beneath the thin floor of infundibulum

endocrine gland derived from infundibulum and solid ingrowth from stomodeum

also known as hypophysis

Structures of eye:

optic cup

o retina – thick inner layer of optic cup, differentiated into following layers:

layer of ganglian cells – innermost sublayer of retina, axons of nerve cells in this sublayer form the optic

nerve, optic chiasma is the region where optic nerves cross in the floor of diencephalon

layer of bipolar neurons – middle layer of cells that will synapse the receptor and ganglian cells

rods and cones – outermost sublayer of retina where photoreceptoral process is formed

o pigmented epithelium – outer wall of optic cup formed from medial half of optic vesicle, forms iris of the eye

lens – spherical body, partly enclosed by optic cup is formed by thickenings of inner wall of lens vesicle

o lens epithelium – one-cell thick outer layer

o lens fibers – columnar cells at the core of lens, will become long fibers arranged in layers

cornea – superficial covering of eye formed by assembly of ectodermal and mesodermal cells between ectodermand lens

choroid and sclera – outer investments of optic cup, represented by mesodermal cells aggregating outside the

pigmented epithelium

pharynx

broad gut

lined by endodermal cells

hypobranchial cartilages

long masses of cartilages under the floor of foregut

make up parts of visceral skeleton and support the pharynx

thyroid

pair of small endocrine bodies associated with pharynx

located beneath hypobranchial cartilages

skeletal muscle

mesodermal masses lying on lateral and ventral side of pharynx

oral suckers

pair of glandular structures on ventral surface of tadpole

composed of elongated columnar cells

produce a sticky slime for attachment to floating objects

also known as cement glands, mucous glands, adhesive glands

Level of the Myelencephalon and Auditory Vesicle

myelencephalon

most posterior region of brain with a thick floor (basal plates)

thin roof becomes vascularized to form posterior choroids plexus

cavity is the IV ventricle

auditory vesicle – completely hallow organ on each side of medulla


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endolymphatic duct – thick-walled tube between medulla and ear vesicle, marks the course of invagination of

auditory vesicle form ectoderm

utriculus – large dorsal chamber of ear vesicle

semicircular canals – three mutually perpendicular folds of auditory vesicle, sensory epithelium is the thickened

horizontal canal

sacculus – ill-defined ventral chamber of auditory vesicle, forms the lagena in lower invertebrates, gives rise to

cochlea in higher vertebrates

auditory capsule

mesenchymal cells surrounding the auditory vesicle

will form the cartilaginous ear capsule that surrounds and protects the inner ear

auditory ganglion

mass of nerve cells in medial side of auditory vesicle

also known as acoustic ganglion

notochord


lying dorsal to gut and ventral to hindbrain defines the anterior/posterior axis in the developing embryo


mesenchymal cells will give rise to notochordal sheath

parachordals

cartilages flanking the notochord on each side

heart – lightly coiled tube twisted to the right

pericardial cavity – chamber enclosing the heart

conus arteriosus – most anterior region of heart connecting the ventricle with the ventral aorta, also known as

bulbus cordis

ventricle – heart chamber with thick muscular wall that follows and is connected to conus atrium – dorsal, thin-walled chamber that receives blood from sinus venosus and delivers it to ventricle

sinus venosus – most posterior chamber lying on the right, anterior to liver, receives venous blood and delivers it

to atrium

opercular cavity

paired chamber continuous with gut and lying on each side of the heart

contains internal gills with branchial blood vessels

also known as gill chamber

dorsal aorta

blood vessel located above each gill chamber

aortic arches

blood vessels lying within the branchial arches and encircling the pharynx

connect the dorsal aorta with ventral aorta

ganglia

facial ganglion (VII) – large mass of nerve cell bodies anterior to auditory ganglion, acoustico-facialis ganglion is

the body arising from fusion of facial and auditory ganglia, also known as geniculate ganglion


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trigeminal ganglion (V) – larger mass of nerve cell bodies anterior and dorsal to acoustico-facialis ganglion, also

known as semilunar ganglion

glossopharyngeal ganglion (IX) – mass of nerve cell bodies below each auditory vesicle

operculum

external wall of opercular cavity formed by body fold

metencephalon

anterior subdivision of rhombencephalon, lies behind optic lobes and medial to V ganglion

Level of the Pronephros and the First Spinal Ganglion

spinal cord

derived from posterior region of neural tube

neural canal

cavity that is laterally compressed by thick lateral walls of spinal cord

ependymal cells that line the central canal possess cilia and pigment granules

also known as central canal

gray matter

inner layer of spinal cord close to ependyma

composed of compact mass of neuroblast and neuroglia

white matter

peripheral layer of spinal cord

containing axons of neurons in gray matter

meninges

membranous covering of central nervous system

first spinal ganglia

masses of nerve cell bodies ventrolateral to spinal cord

myotomes

thickened primordial of skeletal muscles on each side of notochord

skeletal muscle fibers are arranged longitudinally

pleuroperitoneal cavity

coelomic cavity containing viscera except heart

pleural cavity that contains lungs and peritoneal cavity that contains digestive organs, associated glands, kidney,

and reproductive organs are still continuous

esophagus

tubular organ with folded mucosal lining located below notochord

dorsal aorta

paired blood vessel between notochord and esophagus

will fuse into a single blood vessel posteriorly

pronephros

paired excretory organs that arise from nephrotome


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located at ventrolateral region of body cavity

pronephric tubules

ducts of pronephros lined by cuboidal epithelium

posterior cardinal veins

blood vessels within pronephros supplies latter with blood

nephrostome

opening of pronephric tubules into coelom

nephric duct

lone duct observed at most caudal section of pronephros

moves medially and eventually joins cloaca where it empties its contents

glomus

two triangular-shaped structures seen ventrally to dorsal aorta that hang down into the coelomic cavity

tufts of small blood vessels surrounded on their lateral and ventral surfaces by thin wall of coelom functional components of pronephric kidney

where waste products are diffused from into the coelomic fluid

stomach

posterior continuation of esophagus with folded lining and thick muscular walls

evaginations of endodermal lining form rudiments of gastric glands

duodenum

region of gut between the pyloric end of stomach and intestine

represented in upper right corner of body cavity

intestine located posterior to duodenum

filled with abundant yolk platelets

liver

highly vascularized and enlarged organ to the right of midline

sinusoids – spaces

gall bladder

once-cell thick, large vesicle associated with liver

bile duct

thick-walled tube that appears in place of gall bladder

pancreas

large organ within curvature of stomach

located to the right of liver and bile duct

identified by presence of nest cells (alveoli) surrounding small ducts


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Exercise 4 Frog Embryo 4mm 7mm 10mm