Embryo Lab Exercise 4

Embryo Lab Exercise 4 Development of the Frog Embryo

Characterized by the Presence of a: -

Tail

-

Neural tube

-

Notochord

-

Segmented mesoderm

-

Fin folds

Neural system differentiates into: (Has thickenings and constrictions) -

 foremost part

-

 middle part  hind part

Presence of -

-

Mid-dorsal evagination of the brain vesicle

Thickenings on lateral surface of head anterior

Evagination from Olfactory Placodes

o o

-

Olfactory pits are Cavities

Anterior to pits

-

: Ectoderm (paired thickenings of head ectoderm)

-

Evaginates to form the lens vesicle and then the eye lens in the future

-

Level of Rhombencephalon

-

In the form of a closed chamber

-

-

: evagination of the otic placode

Extends from midbrain to posterior end of body

o o

Found on each side of notochord Mesoderm subdivided into segments

-

Ectoderm Rudiment of mouth

-

: Invagination of antero-ventral ectoderm of head

-

In contact with anterior wall of the foregut

-

by an o

-

Separates endodermal foregut and stomodeum : Forms mouth when it ruptures

o

Ventrolateral to oral region : Ectodermal thickenings

o

-

Beneath the floor of the foregut

-

Anterior to yolk

-

-

Loose mesodermal cells; when organized forms the heart

Median posteroventrally directed diverticulum in the foregut

**Bulk of Body is filled with

 serves as nutrition for the growth and differentiation of

the embryo

-

Base of the tail Ectodermal invagination Breaks open in hind gut to be the

Study of Serial Section allows: -

Study of microscopic anatomy of embryo (internal anatomy of embryo)

-

Features that are not evident in the whole embryo

Serial sections -

Entire embryo sectioned into a certain plane

-

Serial cross sections o

Embryo sectioned perpendicularly to cranio-caudal axis from head to tail

o

Anterior most region of embryo 

o

Posterior most portion 

o

Located at the extreme left of uppermost row Last section of extreme right of bottom most row

Slides must be observed from left to right

-

Anterior of embryonic brain

-

: Prosocoel

-

Mesos – middle; Enchyma – infusion, something poured in **GREEK**

-

Embryonic Connective Tissue

-

-

-

 mesoderm and neural crest cells Forms in connective tissues Epithelial, muscular and nervous tissues

Fills spaces between presumptive epidermis (skin ectoderm) and walls of prosencephalon Mesoderm with additional cells of neural crest origin

Paired pigment invagination on either side of the prosocoel Found in head mesenchyme

-

Outermost skin layer

-

 Ectoderm

-

Portion of prosencephalon

-

Mesencephalon appears dorsal to the infundibulum

-

Develops as a depression in the floor of the prosecephalon

-

Precursor to the posterior portion of the pituitary gland

-

Ventral to infundibulum

-

Small knot of tissue

-

Ectoderm Develops as an inward growing cord of ectoderm from stomodeum

-

anterior portion of pituitary gland

-

Lateral to infundibulum

-

Lens vesicle present on left side

 of -

Ventral to infundibulum and hypohysis

-

Cavity

-

Has walls composed of endoderm

-

Mid region of developing embryonic brain with a thick roof

-

 mesocoel  midbrain

-

Cavity at cranial end of alimentary canal

-

Spherical in appearance

-

Thickened region

-

Cranial portion of the alimentary canal in contact with the ectoderm in head

-

 pharyngeal plate or oropharyngeal membrane

-

Ectoderm Ectodermal rudiment of mouth

-

 Invagination of the ectoderm At anteroventral region of head  (Hypo – under, beneath; Physis – growth)

-

Solid ingrowth or nodular aggregation of cells between oral and brain cavity

-

Hypophysis described in 2 ways:

-

May be used to describe portion of enveloping gland: : Invagination of stomodeum which fuses with the infundibulum to

o

form the pituitary gland o

-

Eg. Rathke’s pocket

May be used to describe a complete adult gland: o

Endocrine gland 

 An ingrowth from the stomodeum (Rathke’s pocket) and the infundibulum

-

-

: pituitary gland

Funnel like depression of prosencephalon Forms the posterior lobe of pituitary gland with the stomodeum Smaller, ventral component of diencephalon with thin roof and thick sides

-

Cranial branchial arch o

-

-

-



caudal border of stomodeum



maxillary process cranial to stomodeum

: Paired Ectodermal thickenings in ventral surface Secrete adhesive mucus for attachment to floating objects  cement glands, mucous glands, oral suckers

: Evagination from the lateral wall of prosencephalon First indication of formation of eye : Walls give rise to ectodermal parts of eye (except lens and cornea)

Double-walled structure  Invagination of the distal portion of the optic vesicle

-

Inner layer thicker than outer layer

-

**what are the fates of the inner and outer layer of the optic cup? Idk manual asked

-

Connection of Optic Cup with Brain

Section through the Anterior Pharynx  (Gr. Rhombos – whirling, turning; Kephale – head) -

Most caudal of brain of developing embryo with a thin roof  Rhombocoel  hind brain

 (Gr. Noton – back; Gr. Chorde – guts, string) -

Mesoderm

-

Round structure from mesoderm and lying dorsal to gut and ventral to hindbrain

-

Defines anterior/posterior axis in developing embryo

-

Provides skeletal support in early devt

-

Region of foregut

-

Paired evagination corresponds to pharyngeal pouches

-

Paired invagination of of otic placode

-

Laterally located and ventral to brain

-

Separates from head ectoderm to form inner ear

-

Inner Ear

-

 auditory vesicle

-

 pericardial coelom

-

 dorsal mesocardium

-

Below the pharynx

-

Beneath enlarged foregut

-

Pericardium o

Delimits pericardial coelom

o

Thin layer of somatic mesoderm

o

Membrane enclosing the heart  migration of heart mesoderm to midventral region of the pericardial

o

cavity -

Loose mesenchymal cells o

Composition of heart

o

Thick mass of mesoderm

o

o

-



Mesenchymal cells organize into a continuous endothelial lining of the heart



Inner layer of heart



Lining of heart wall

Epimyocardium 

Form the muscle



Outer layer of heart

Paired bulges below horizontal level of notochord

-

Pronephric Tubules o

-

Endocardium

collectively may be called 

pronephros



pronephric kidney

Groove is the liver diverticulum (rudiment of liver) Section through the Pronephros

-

At a level caudal of the liver diverticulum

-

Foregut(pharynx) narrows into midgut

-

Presence of mass of yolky endoderm

-

Yolky endoderm o

-

Nutrient supply of developing embryo

Wedged between notochord and midgut, a small knot of cells can be identified that are part of the subnotochordal rod (omg review ano to ulit???)

o

Transient structure of endodermal origin

o

Unknown function that disappears later on

o

-

Char andyan na nga, mawawala pa. yan tayo eh

At base of tail, at level of proctodeum

: Ectodermal invagination that meets with the endoderm of the

o

hindgut o

: Ectoderm

o

Delicate strand of tissue between proctodeum and hindgut

o

Ecotdermal and endodermal plate

o

-

-

-

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

Flat extension of the body wall along dorsal midline of the trunk and tail Degenerates during metamorphosis of tadpole

Posterior most region of embryonic gut  cloaca, colon, small intestine, and rectum

Ectodermal invagination on ventral side of trunk at base breaks into hindgut forming anus  anal pit

Characterized with: -

Well – formed external gills

-

Functional heart

-

Embryo has changed shape and has become a

-

Elongated tail

-

o

Serve as a swimming organ

o

Provides lateral segmented somites and finfolds on ventral and dorsal side

Forebrain has further differentiation: o

Telencephalon (with 2 hemispheres)

o

Diencephalon

o

Deeply invaginated

o

Large pigmented cells surround this

o

Circular knob of cells separated from the brain

-

 underneath the brain extends up to the tail Head and trunk bloated

-

 can be identified

o

Persists as cloaca

o

Does not lose its cavity

o

Dorsal wall of hindgut becomes extended into the tail rudiment as the 

Post anal gut eventually breaks and disappears



Lahat nagbebreak at nawawala  gives rise to Urinary bladder

o



 Ventral Evagination



Transverse Section Level of the Telencephalon and Olfactory Pits o

Now visible lateral to ventral portion of prosencephalon

o

Began as two thickenings (placodes of ectoderm in 4mm frog) : Invaginated and lengthened to form pits

o

: Ectoderm

o

 nasal passages with olfactory receptors

o

-

Large

 on the ventral surface of the embryo 

-

Marks the beginning of the oral cavity

Oral o

Has become perforated and embryo now has an open mouth

-

Paired hemispheres occupying anterior region of forebrain

-

Posterior division of prosencephalon

-

Appears as a cavity on lateral surface of head

-

Slight middorsal evagination of brain vesicle

-

 pineal gland in adult

-

Loose mesenchymal cells Formed between head ectoderm and brain Level of the Diencephalon and Optic Cups

-

Portion of mesencephalon and prosencephalon evident in this section with constriction between them

-

Optic cups seen in lateral to brain

-

Oral cavity is visible surrounded by presumptive jaw cartilages

-

Adhesive glands present on ventral surface of embryo

-

Posterior half of forebrain

-

Deep, laterally compressed region

o

Optic stalks

o

Infundibulum

o

Epiphysis

-

Brain located posterior to eye

-

Center for reflexes associated with vision, hearing and movement of the head

-

Outer pigmented layer and inner retinal portion of the optic cup can be distinguished at this level

-

Lens vesicle in concavity

-

Pharynx is large and more rounded

-

Clustered mass of cells on each side

-

Gives rise to o

the posterior border of the stomodeum

-

Deep invagination of pigmented midventral ectoderm at anterior end of pharynx

-

 Ectoderm

-

paired ectodermal thickenings

-

found at the ventral surface of head

-

secretes adhesive mucus for attachment to floating objects

-

 cement glands, mucous glands, oral suckers Level of Rhombencephalon Section through the Thyroid

What can be seen? -

Below mesencephalon

-

Small portion of wall of infundibulum evident

-

Lateral to floor of the mesencephalon o

Developing cranial nerve ganglion observed here 

Part of the peripheral nervous system



Derived from neural crest cells

-

Posterior portion of the optic cup may still be visible

-

As described previously

-

But pharynx is wider here

-

 evagination of endodermal cells

-

 Endoderm From pharyngeal floor Section through the Otic Vesicle

-

Sectioning through the hindbrain (rhombencephalon  of o

-

Composed of single layer of flattened cells

Notochord now visible ventral to rhombencephalon

-

-

o

Beneath the pharynx, most anterior portion of the heart

o

Evident within pericardial coelom

Heart has 4 subdivisions in anterior or posterior order o

Truncus arteriosus

o

Ventricle

o

Atrium

o

Sinus venosus

-

 through embryonic heart from o

-

Starts in sinus venosus ends at truncus arteriosus  visible within the section now  ectoderm

o o

 inner ears

-

Third brain vesicle which expands anterior to form the IV Ventricle

-

Internal organization similar to the spinal cord

-

metencephalon (anterior) and myelencephalon (posterior)

-

mesoderm

-

Lying dorsal to gut and ventral to hindbrain

-

Defines anterior/posterior axis in developing embryo

-

Provides skeletal support during early development

-

Irregularly hollow organ on each side of hindbrain

-

Closed chamber

-

 invagination of otic placode

-

Lies beneath the pharynx

-

Most anterior heart chamber

-

Cavity that surrounds the heart and is bounded by the pericardium Section through the Heart

-

Sectioning of external gills evident on outer surface of pharyngeal region

-

External gills o

-

Finger-like projections that protrude from sides of head

Heart-forming region o

Ventricle seen with atrium appearing above

-

Mass of cells  temporarily blocks esophagus before amphibian larva begins to feed  (atrium – hall)

-

Chamber of the heart

-

Receives blood from sinus venosus

-

Delivers blood to ventricle

-

Seen above the ventricle

-

Thin walled chamber almost filled with blood

-

Filamentous respiratory organ

-

 the branchial arches 3 to 6 Replaced by internal gills in later development