8_Development in 10 mm Frog Larva

Telencephalon

This is derived from the forebrain (prosencencephalon) which is the anterior region of the primitive brain.

Ependymal layer

It is a once-cell thick lining and the innermost layer of the neurocoel.

Mantle layer

It is the broad layer adjacent to the ependymal layer which becomes the gray matter of the central nervous system (CNS).

Marginal layer

It is the outermost fibrous layer which becomes the white matter of the CNS.

Ependymal, Mantle, Marginal

Brain wall. This is composed of different layers:

Buccal cavity

The spacious chamber lined with a flat epithelium into which the mouth and the nasal passageways open. It is derived from stomaderm.

stomaderm

Buccal cavity is derived from _____

Melanophores

They are light brown stellate cells over the dorsolateral surface of the brain and lateral to the nasal organs.

Cartilages

They are small masses of hyaline cartilages, the prechordal or trabecular types, seen beneath the telencephalic hemisphere.

Mesenchyme

A loose reticulum of mesodermal cells which are stellate in appearance and migratory in behavior found in the spaces between the epidermis and the other organs mentioned.

Epidermis

It is the outermost two-cell layer of the skin derived from the ectoderm.

Diencephalon

It is the median, vertically elongated brain vesicle posterior to the telencephalon.

Infundibulum

It is a funnel-like invagination of the floor of diencephalon which, along with hypophysis, will give rise to pituitary gland of adult.

Eyes

They are well-developed structures at this stage with the following prominent parts: Cornea, Lens, Retina

Cornea, Lens, Retina

Eyes are well-developed structures at this stage with the following prominent parts:

Cornea

It is the superficial covering of the eye.

Lens

It is the spherical body, arising as vesicle and is partly enclosed by the optic cup.

Retina

It is the thick layer of the optic cup.

Pharynx

It is a flat and broad gut at this level.

Hypobranchial cartilage

It is a mass of long bar of cartilage below the floor of the foregut which supports the pharynx.

Myelencephalon

It is a large brain vesicle with thick floor (basal plates) and thin roof, the latter becomes the posterior choroid plexus.

Ear (auditory vesicle)

Irregular hollow organ to each side of the myelencephalon.

Endolymphatic duct

It is a thick-walled tube lying against the medulla which marks the course of the invagination of the auditory vesicle from the ectoderm.

Utriculus

It is the large chamber of the auditory vesicle.

Semi-circular canals

They are the sacculations of the utriculus in the anterior, horizontal and posterior parts.

Sacculus

The outer and ventral portion of the inner ear from which cochlea, the organ for hearing, arises.

Auditory (acoustic) ganglion

It is a dense mass located at the medial surface of the auditory vesicle

Notochord

The sagittal skeletal rod beneath the hindbrain.

Ear (auditory vesicle), Endolymphatic duct., Utriculus, Semi-circular canals, Sacculus, Auditory (acoustic) ganglion

Structures at the level of the myelencephalon and ears:

Notochord

The sagittal skeletal rod beneath the hindbrain.

Pericardial cavity

It is a coelomic space that encloses the heart.

Conus (bulbus)

It is the anteriormost chamber of the heart connected to the ventral aorta.

Ventricle

It is the chamber next to the conus as it is connected to the latter at the right side.

Atrium

It is a large thin-walled chamber which is dorsally situated.

Gill chambers (opercular cavities)

They are large paired chambers continuous to the cavity of the gut which are found on both sides of the heart. They contain folded internal gills that bear blood vessels.

Dorsal Aorta

They are paired vessels, one above each gill chamber.

Aortic arches

They are embryonic vessels encircling the pharynx.

Pronephros

They are paired larval excretory organs in the dorsolateral angle of the body cavity.

Mytomes

They are segmented blocks of skeletal muscles flanking the notochord.

Pleuroperitoneal cavity

It is the large coelomic cavity in which all visceral organs, except the heart, are suspended.

Esophagus

It is a tube with folded endodermal lining just below the notochord.

Dorsal Aorta

They are paired blood vessels between the gut and chorda.

Stomach

It is a ventrally, large thick-walled structure with deep invaginations of the endodermal lining to form the rudiments of the gastric glands.

Liver

It is an organ to the right of the midline of loose organization of liver cords interspersed with sinusoids.

Pancreas

It is an organ to the right of the liver and bile duct.

Lung-buds

They are thick-walled ovals on each side of the esophagus.

Dorsal fin, Notochord, Proctodeum, Spinal cord, Ventral fin

Structures at the level of the tail region:

Dorsal fin

This structure is derived from the ectodermal layer and is located above the spinal cord.

Notochord

It is the primary structure in initiating the formation of the central nervous system (CNS). This extends at the caudal portion of the embryo.

Proctodeum

it is an ectodermal pit in the region of the future cloaca. It appears as a ventral invagination anterior to the ventral fin.

Spinal cord

This is located anterior to the notochord.

Ventral fin

This is at the caudal end of the body. It is also derived from the ectoderm.

1. Fertilization

2. Cleavage

3. Blastula

4. Neurula

5. Gastrula

6. Organogenesis

Stages of Frog Early Embryology

MEROBLASTIC

Incomplete Cleavage

Superficial Meroblastic

Cleavage in centrolecithal eggs

Discoidal Meroblastic

Cleavage in discoidal eggs

HOLOBLASTIC

Complete Cleavage

Holoblastic Equal

Cleavage in microlecithal eggs

Holoblastic Unequal

Cleavage in mesolecithal eggs

Birds and Fish

Animals that undergo Meroblastic cleavage

Frogs and Mammals

Animals that undergo Holoblastic cleavage

blastocoel

As cleavage continues, the blastomeres become arranged around the outside, with a central fluid filled cavity, the ___

Epiboly

overgrowth of the ectoderm-forming regions AROUND the endoderm-forming regions

Emboly

invagination, the ingrowth of the endoderm forming zones UNDER the ectoderm-forming regions

2-layered

Early gastrula (____)

3-layered

Late gastrula (____)

blastopore

EARLY GASTRULA- formation of 2-layered gástrula (diploblastic) with opening called ____

Notochord • Mesoderm

Chordamesoderm differentiates into:

prosencephalon, mesencephalon and rhombencephalon

The embryonic brain vesicles are at first three in number (_______)

telencephalon, diencephalon, mesencephalon, metencephalon and myelencephalon

The embryonic brain vesicles are at first three in number (prosencephalon, mesencephalon and rhombencephalon) then five namely:

Prosencephalon (forebrain)

Divisions of vertebrate brain:

• Primary vesicles - ?

• Secondary vesicles - Telencephalon (divided into right and left vesicles)

• Cavities - Lateral ventricles (Ventricles I and II)

• Adult derivatives - Cerebrum

Divisions of vertebrate brain:

• Primary vesicles - Prosencephalon (forebrain)

• Secondary vesicles - ?

• Cavities - Lateral ventricles (Ventricles I and II)

• Adult derivatives - Cerebrum

Mesencephalon (midbrain)

Divisions of vertebrate brain:

• Primary vesicles - ?

• Secondary vesicles - Mesencephalon

• Cavities - Cerebral Aqueduct

• Adult derivatives - Optic lobes, etc

Rhombencephalon (hindbrain)

Divisions of vertebrate brain:

• Primary vesicles - ?

• Secondary vesicles - Metencephalon

• Cavities - IV ventricle

• Adult derivatives - Cerebellum

Metencephalon

Divisions of vertebrate brain:

• Primary vesicles - Rhombencephalon (hindbrain)

• Secondary vesicles - ?

• Cavities - IV ventricle

• Adult derivatives - Cerebellum

Organogenesis

Formation of body organs/systems from the three germ layers

ECTODERM

SKIN EPIDERMIS

❑ Hairs, feathers, scales, beaks

❑ Nails, Claws

❑Sebaceous, sweat, and mammary glands

❑Oral and anal lining

❑Tooth enamel

❑ Nasal epithelium

❑Lens of the eye

❑Inner ear

NERVOUS SYSTEM

❑ Brain and spinal cord, nerve cells and ganglia

❑ Retina

❑ Pigment cells

❑ External ear canal

❑ Medulla of adrenal gland

❑ Pituitary gland

MESODERM

EPIMERES

❑ Block-like segments (somites)

❑ Dermatome (inner skin layer)

❑ Myotome (axial muscles)

❑ Sclerotome ( supporting tissues)

❑ Connective Tissues

❑ Cartilage, Bone

❑ Subcutaneous tissues

MESOMERES

❑ Excretory Organs

❑ Reproductive OrganS

HYPOMERES

❑ Somatic layer

❑ Splanchnic layer

❑ Body wall

❑ Lining of somatic cavities

❑ Mesenteries (esophagus, stomach, intestines)

❑ Muscular layers of heart, arteries, and veins

ENDODERM

• Liver

• Gall bladder

• Pancreas

• Thyroid glands

• Thymus glands

• Parathyroid glands

• Palatine tonsils

• Middle ear

• Eustachian tube

• Urinary bladder

• Primordial germ cells

• Lining of all organs of the digestive and respiratory tracts

FATE MAPPING

experimental procedure to establish the ultimate fate of the three germ layers; use of a harmless dye to label specific cells and followed to a later stage of development