[DEVBIOL LAB] LE 2

vitelline membrane, yolk, albumen, chalazae, shell membranes, shell made up of calcium carbonate ,area pellucida , primitve streak

parts of chick embryo

 Vitelline membrane

A transparent, protein-based membrane that encases

the egg cell and contains the yolk.



 Yolk

• The major part of the egg cell.

•  The _____ is a massive reserve of nutrients, including fats, proteins, vitamins, and minerals, required for embryonic development.

Albumen (egg white)



Secreted around the yolk as it passes through the magnum and isthmus, this is a protein-rich fluid that provides a watery medium for the embryo.

chalazae

 Opaque, rope-like structures of dense albumen that

anchor the yolk in the center of the egg.

Shell membranes

Two layers of transparent protein membranes are

added in the isthmus to protect against bacteria.

shell

 Composed of calcium carbonate, the outer shell is

formed in the uterus. It contains thousands of tiny

pores for gas and moisture exchange.

Area Pellucida

• center of blastodisc where primitive streak forms

•  lies over subgerminal cavity

•  appears transluscent (due to thinness of blastoderm)

epiblast - outer ( into ectoderm and mesoderm), hypoblast - inner (into endoderm)

blastoderm consists of

  Primitive Groove

location: A depression that forms within the primitive streak
function: It serves as the gateway through which most migrating cells pass into the deep layers of the embryo. It is homologous to the amphibian blastopore (gastrulation occurs here) 

  Primitive Ridges

margins of primitive streak @ sides of primitive groove

located at caudal end of embryo, converging bands 

Primitive Pit

location: A funnel-shaped depression found in the center of Hensen's node

function: It is the specific opening through which cells can enter the embryo to form the notochord and prechordal plate

  Hensen's Node

NOT PRESENT IN AMPHIBIAN

•  thickened area @ anterior end of primitive streak

•  thru it, cells invaginate, forming notochord

•  homologous to dorsal lip of blastopore of amphibians

• Cells migrating through this region form axial structures like the notochord

Proamnion 

• anterior to avian embryo

• that forms a pouch

  when the head sinks into it.

•  contains endoderm and ectoderm later involved with mesoderm, then with amnion

•  amnion is the membrane around the fetus

Neural Folds 

• precursor to brain and spinal cord

fate: about to fuse@ mid-dorsal region

function: source of migrating neural crest cells 

origin:  lateral edges of neural plate 

Neural Groove

• median longitudinal groove formed by rolling

  up neural plate

origin: neural plate → neural ectoderm; neural plate elevates to form neural fold and forms this 

function: Marks the midline of the forming nervous system during neurulation. 

• DEFINES ANTERIOR -POSTERIOR AXIS 

fate: temporary structure; neural tube → precursor of CNS (brain and spinal cord) 

Head Fold

- folded part of blastoderm

dark crescentic line (boundary of head)

Foregut

- 1st part of digestive tract

•  w/ definite floor

•  endodermal

• Dome-shaped

• lies inside the head

head mesenchyme

- loose network of cells found between

foregut and head's ectoderm

Anterior Border of Mesoderm

- faint line across area

pellucida

- @ level of anterior end of notochord

Thickened Splanchnic Mesoderm

- dark lines @ lateral

borders of anterior intestinal portal

• formed by delamination of lateral plate mesoderm

• becomes the heart, part of the circulatory system, etc

Unsegmented Mesoderm

- undivided part of mesoderm

• posterior to somite

area opaca 

(meaning 'non-transparent', outer marginal region) 

surrounds the central area pellucida and consists of extra-embryonic cells that contribute to the formation of the yolk sac and chorion, providing nutrients and driving expansion for the developing embryo

cranial neuropore 



= the opening at the front, or

cranial end, of the developing neural tube during

embryonic development

Segmental plate mesoderm

= a band of tissue on either side of the neural tube and notochord in the developing embryo's trunk region.

location: lateral to each neural fold, band of tissues extending from last pair of somites

anterior border of mesoderm / head mesoderm (18 hr)

function/ location: Faint line across area pellucida
fate: contribute to head region of embryo

hensen’s node (18 hr)

function/ location: gastrulation begins here; formation of 3 germ layers
fate: cells undergo epithelial to mesenchymal transformation

neural plate (18 hr)

function/ location: fold and fuse into neural tube at 33 hr; epiblast cells proliferate 
fate: develops into brain and spinal cord (CNS) 

Embryonal area (18 hr)

function/ location: turns into the 3 layers 
fate: from bilaminar to trilaminar disk 

proamnion

function: encases embryo and forms amniotic cavity

location: Anterior to head and forms pouch when head sinks into
fate: Helps head flexure and contributes to amniotic fold formation

origin: ICM

notochord 

origin: from mesodermal cells that ingress through hensen’s node 

function: axial support during early development to form neural tube
fate: vertebral column , the rest is: nucleus polpous

location: midline beneath neural tube  

area opaca

origin: hypoblast or outer region of blastoderm

function: Facilitates absorption of nutrients from the yolk into the embryo through the yolk sac circulation.

location: Non transparent outer marginal region
fate: Contributes to extraembryonic membranes and blood vessels and yolk sac

cranial neuropore (24 hr) 

function/ location: Opening at the rostral end of the neural tube

that allows neural folds to communicate with the amniotic cavity during closure.
fate: Closes to form the forebrain region of the neural tube.

skin ectoderm (24 hour)

function/ location: Outermost covering of the embryo, provides protection.
fate:Forms epidermis, feathers/scales, and associated glands.

origin: outermost layer of epiblast ( not part in neural induction) 

Neural fold (24 hour)

function/ location: Elevated lateral margins of neural plate that converge to form the neural tube.
fate: Fuse at midline to form neural tube (CNS).

lateral margin of foregut or foregut 

function/ location: Defines the sides of the developing anterior gut cavity.
fate: Contributes to foregut-derived organs (pharynx, esophagus, liver, pancreas).

origin: splanchnic mesoderm

posterior intestinal portal (24 hour)

function/ location: Caudal opening of the embryonic foregut.
fate: Marks the region where midgut will develop and close.

somites (in 24 hours 1-3 pairs, in 33 hours 8-10 pairs)

function/ location: segmented body plan 
fate: Differentiate into sclerotome (vertebrae, ribs), myotome (skeletal muscles), dermatome (dermis).

origin: ectoderm 

Segmented plate mesoderm

function/ location: Pre-somite mesoderm; precursor to somites.
fate: Differentiates into somites, then axial skeleton, muscle, dermis.

primitive streak

function: Site of gastrulation; cells ingress to form mesoderm and endoderm.

origin: formed by thickening of epiblast cell @ area pellucida
fate: Regresses after gastrulation; replaced by notochord and neural tube at midline

location: Extends from posterior to anterior along the midline of the area pellucida and ends at hensen’s node

amphibian equivalent: blastopore

Hensen’s node (24 hr)

function/ location: Organizer at anterior end of primitive streak
fate: Gives rise to notochord and prechordal plate mesoderm.

prosencephalon

function/ location: Anterior region of neural tube.
fate: Forms telencephalon (cerebrum) and diencephalon (thalamus, hypothalamus, retina).

foregut (24 hr)

function/ location: Anterior portion of developing gut tube.
fate: Forms pharynx, esophagus,stomach, liver, pancreas, lungs.

origin: splanchnic mesoderm 

head ectoderm (24 hour)

function: Ectoderm covering anterior head region

fate: Gives rise to lens placode, nasal placode, epidermis of head.

somatopleure (33 hr)

• which contributes to the body wall and amnion

function: Specifically in the limb fields, the somatopleural mesoderm undergoes an epithelial-mesenchymal transition (EMT) before the mesoderm in flank regions

fate: contributing mesenchymal cells to the limb bud

origin: somatic mesoderm + ectoderm

splanchopleure

function: It overlies the endoderm. Together with the endoderm

fate: walls of gut, yolk sac and allantoi; forms: digestive tract, heart parts, nutrient absorption and embryonic circulation

origin: lateral plate mesoderm → splanchnic mesoderm + endoderm

coelom (33 hr) (not in 24 hr)

function: to provide space for the internal organs to develop, move, and grow independently of the body wall. It also allows organ movement

description: the space created by the splitting of the lateral plate mesoderm is the body cavity, or coelom; formed between the somatic (dorsal) mesoderm and the splanchnic (ventral) mesoderm

fate: These mesodermal folds subdivide the coelom into

pleural - thorax

pericardial - heart

peritoneal cavities- gastrointestinal

Head ectoderm (24 hour)

function; Ectoderm covering anterior head region.

fate: Gives rise to lens placode, nasal placode, epidermis of head.

cranial intestinal portal

function: opening of foregut 

fate: becomes part of pharyngeal endoderm

Lateral extension of head fold

function: Overgrowth of ectoderm and mesoderm lateral to head.

fate: Contributes to head shaping and amnion formation

rhombomeres

periodic segmented swellings that temporarily divide the embryonic hindbrain (rhombencephalon). They function as distinct "territories" where cells are restricted from mixing with adjacent segments.

primitive folds (24 hr)

function: Raised edges flanking primitive streak

fate: Regress after gastrulation

blood islands (24 and 33 hr)

function: Aggregates of mesodermal cells in area vasculosa that initiate blood and vessel formation

fate: Form blood cells and endothelial lining of vessels

description: marks intial step in formation of blood vessels and corpuscles

primitve groove (24 hr)

function: Central depression of primitive streak where cells ingress

fate: Regresses after gastrulation; site of mesoderm and endoderm internalization

 subcephalic pocket (24 and 33 hr)

function: Defines posterior boundary beneath developing head; and separates foregut from yolk sac

fate: anterior body cavity;  Involved in foregut and head fold morphogenesis

origin: ectoderm and head endoderm

lateral plate mesoderm

function: Edge between mesodermal and non-mesodermal tissue

fate: Source of somatic and splanchnic mesoderm

Pericardial cavity 

function: Coelomic cavity portion near heart primordium

fate: pericardial sac

origin: somatic mesoderm from intraembryonic coelom

splanchnic mesoderm

function: Region of mesoderm associated with heart formation

fate: Forms heart tube and later cardiac structures

Body of embryo

function: Main embryonic mass where organogenesis occurs

fate: Gives rise to the definitive organism

Area vitellina

function: Yolk-rich region adjacent (next to) to area pellucida

fate: Provides nutrients and contributes to yolk sac

area vasculosa

function: Region with blood islands, vascularization around yolk

fate: Contributes to vitelline circulation

sinus terminalis (33 hour)

function: Collects blood from the vitelline capillaries of the yolk sac and directs it into the vitelline veins, which return blood to the embryonic heart.

fate: connects the vitelline veins and arteries of the yolk sac to the embryonic heart.

origin: splanchopleure @ area vasculosa 

Optic vesicle (present in 33 hr)

function: Outpocketing of diencephalon

fate: Forms retina, optic stalk, lens induction

origin: ectoderm

mesencephalon

part of the brain vesicles

function: Neural tube region controlling visual and motor reflexes.

fate: Forms optic tectum, tegmentum, midbrain nuclei

location: caudal to diencephalon, appearing as a thickened neural tube with central cavity

rhombencephalon

function: Posterior neural tube controlling balance, respiration, circulation.

fate: Forms metencephalon (pons,cerebellum) and myelencephalon

(medulla)

Metencephalon

function: Anterior hindbrain portion

fate: Forms pons and cerebellum

location: caudal to mesencephalon

Neuromeres

function: Segmented hindbrain regions

fate: Organize cranial nerve nuclei and hindbrain patterning

Caudal extent of the sub cephalic pocket

function: Posterior boundary of beneath head 

fate: Contributes to foregut extension

Diencephalon

function: Forebrain subdivision

fate: Forms thalamus, hypothalamus, optic vesicles

telencephalon

function: Most anterior forebrain

fate: Cerebral hemispheres, olfactory bulbs

ventricle

function: flows blood into conontruncus

fate: ventricle

origin: splanchnic mesoderm

Sinoatrial region

function: Acts as the pacemaker region of the embryonic heart, initiating rhythmic contractions even before neural control develops.

fate:   Forms sinoatrial node and pacemaker region

origin: from the posterior end of the embryonic heart tube; from splanchnic mesoderm 

intestinal portal

function: Openings marking gut closure

fate: contributes to definitive midgut and hindgut 

Conontruncus

function: blood from ventricle → aortic arch 

fate: Divides into ventral aorta and aortic arch 

origin: splanchnic mesoderm 

function:

fate:

function:

fate:

function:

fate:

function:

fate:

neural folds first and processes to cephalon and caudal 

formation of neural parts in 24 hour

neural ectoderm 

thicker si ____ than skin ectoerm 

paired optic vesicles.

located laterally, as a rounded bulging out packeting of the neuroepithelium projecting toward the surface of the

ectoderm, forms optic cap priomdial 

ectoderm

The outermost layer is the ectoderm of the head.

It is a thin sheet of cells forming embryos protective

covering and contributing to the future epidermis

and neural structures.

Prosocoel

- which represents the cavity within the

developing forebrain vesicle.

Lined with: neuroepithelium

Forms: part of the brain ventricles

Optocoel

located laterally to forebrain; the cavity within the early optic vesicle.

This outpacketing marks the beginning of eye development.

Endoderm

- forming the line of the primitive gut.

it lies just beneath the mesenchymal layer and will

eventually Give rise: to the epithelial lining of the

pharynx and related organs.

splanchnic mesoderm

- related to endoderm; lies adjacent to the endoderm

Fate: smooth muscle, blood vessel, and connective tissue of the gut.

somatic mesoderm

- positioned closer to the ectoderm

Fate: contribute to the body wall structures.

Yolk

- serving as the nutrient reservoir that supports rapid cellular growth during early development.

1. early neurulation

2. neural folds visible but not fused yet

3. only 1-3 somites pairs present

4. optic vesicles beginning

5. otic placode absent

6. head fold beginning to rise

7. primitive streak still noticeable at posterior end

8. coelom not yet formed

chick is in 24 hours if its:

1. active neurulation 

2. neural tube closed anteriorly; open posteriorly

3. 8-10 somite pairs

4. optic vesicle are large and visible on sides 

5. otic placode at behind hindbrain 

6. heart tube is visible and begin to loop 

7. head fold more elevated and distinct brain divisions 

8. primitve streak present but shorter and fading at posterior end 

chick is in 33 hours if its: 

paired dorsal aorta

These vessels lie just lateral to the foregut and carry blood posteriorly from the developing heart region.

ventral aorta

located ventrally,  which represents the outflow tract of the early tubular heart

fate: aortic trunk and pulmonary arteries

function: flows blood from heart → aortic arch

origin: continous with truncus arteriosus and connects to aortic arch

truncus arteriosus and aortic arches

- continuous with ventral aorta

oral membrane

- thin bilaminar region temporarily separates the primitive mouth or the stomodeum from the foregut cavity until it ruptures to open the connection between the mouth and the pharynx.

Mesocoel

@ level of neural tube, the cavity of the developing midbrain, surrounded by neuroepithelium

differentiate into: brain tissue.

anterior cardinal vein

- an early venous channel that trains blood from the cranial region toward the heart

somatopleure, splanchopleure

two tissues from lateral plate mesoderm that is located along the body wall

extraembryonic coelom

- Separating these layers; a cavity that will eventually surround the embryo and participate in the development of the extraembryonic

membranes.

dorsal mesocardium

@ coelomic space,  connecting the developing heart tube to the dorsal body wall; a mesodermal sheet that temporarily suspend the heart in the pericardial cavity before breaking down to allow heart looping.

myocardium

• the muscular wall of the heart

function: produces cardiac jelly and for heart contraction and pumping blood

fate: muscular wall of heart

origin: splanchnic mesoderm