LECOM Embryo 6 (Embronic and Fetal Periods)

Embryonic Period

The three cell layers undergo differentiation

A Period of Organogenesis

Age of embryo expressed by somites present

Derivatives of Ectoderm

Surface: Epidermis, mucosa, mamary glands, anterior pituitary

Neural: Neural Tube (CNS Pineal, Post Pituitary), Neural Crest (ganglia, optic nerves, chromaffin, endocardial)

Derivatives of Mesoderm

Paraxial: Sclerotome, Dermomyotome

Intermediate: Urogenital System (Kidneys, Ureter), Repro System

Lateral: Somatic, Splanchnic

Endoderm

Epithelium/parenchyma of GI, Liver, Pancreas, Trachea, Bronchi, Parathyroid

Tumor Classification in Epithelium

Mesoderm: vascular endothelium

-Benign tumors -angiomas

-Malignant tumors -sarcomas

Endoderm: Epithelium of structures derived from yolk

-Benign- papilloma/andenoma

-Malignant -carcinomas

Ectoderm: epidermis

-Benign- papilloa/adenomas

-Malignant -carcinomas

Tumor Classification CT

Mesoderm for torso and limbs

-Benign- fibroma + lipoma + chondroma + ossteoma

-Malignant- sarcomas

Neuroectoderm (neural crest) for head.

Tumor Classification Muscle

Mesoderm

Benign -myomas

Malignant -myosarcomas

Tumor Classification Nerve

Neuroectoderm

Teratoma more than one layer

Neurulation

Prechordal plate the ectoderm thickens and becomes knwon as the neural plate.

Day 20

Neural plate begins to fold inward forming neural groove and neural folds.

Neural folds

First make contact day 22 in the area of the four occipital somites and first cervical somite.

Fusion in both cranial and caudal directions.

Closing Dates

Cranial Neuropore: 24-26

Caudal Neuropore: 27-28

Neural Tube

Fusion of the neural folds results in this formation.

The neural tube exists as a hollow tube.

Neural Crest

During neurulation cells detach from neural plate and migrate through body.

Neural Crest Give Rise To

Ganglia: parasympathetic (3,7,9,10), sensory (5,7,8,9,10) and autonomic and dorsal root ganglia

Surface Ectoderm Give Rise To

Epidermis, hair, nails, cutaneous and mamary

Ant Pituitary gland

Enamel of teeth

Internal Ear

Lens of eye

Mesoderm Fate

Intraembryonic mesoderm condenses into rod and sheet like structures on both sides of the notochord.

Mesoderm lateral to notochord form cylindrical bodies called paraxial mesoderm, intermediate mesoderm, and lateral plate mesoderm.

Paraxial Mesoderm

Form axial skeleton (arms and legs) voluntary musculature and part of the dermis

Intermediate Mesoderm

Form urinary system and parts of the genital system

Lateral Plate Mesoderm

Will split into two layers: the splanchnic mesoderm associated with the endoderm and the somatiopleuric mesoderm associated with the ectoderm

Paraxial Mesoderm Continued

Forms somitomeres in a segmental fashion, most develop further into somites (structures in head and neck)

On about day 20 the 8th somitomere becomes the first somite and they form in succession so that by day 30 there are 42 and 44 somites, however the caudal most soon dissapear leaving 37 pairs.

Where Somites Form

First four in the occipital region and contribute to dev of the occipital part of the skull.

5-12 form the cervical region, next 12 in thoracic wall and ab

By week 4 somites differentiate into a sclerotome and dermomyotome

More Fates of Mesoderm

Sclerotome: Form rudiments of the vertebral arch and body cervical Ribs

Dermaomyotome: Dermis of neck and intrinsic back

Vasculature: Hermangioblasts rise to hemopoietic stem cells

Capillary Hemangiomas: tumor like collections of blood vessels

Endodermal Derivatives

Endoderm of embryo is contributed by yolk sac

Epithelium of respiratory tract, bladder, urethra, tympanic cavity and auditory tube

Parenchyma of thyroid, parathyroid, liver

Stroma of the tonsils and thymus

The Fetal Period

9th week to birth

External form of developing human and by the presence of all major organ systems

Time of rapid growth and further development

Fetus becomes viable during this period

Weeks 9-12

The Liver is site of erythropoiesis

Week 9 external genitalia can be distinguished as male or female

Weeks 13-16

Sites of ossification are evident

Eye movements and the eyes are facing forward

Week 17-20

Primary oocytes are formed

Testes are descending

Weeks 21-25

Surfactant is beginning to be secreted in the lungs

Weeks 26-29

Lungs now capable of breathing

CNS is capable of controlling breathing and body temp

Spleen is still making blood cells by 28 weeks blood formation shifts to bone marrow

Weeks 30-34

Fat and Pupillary light

Weeks 35-38

Finishing period-this involves the final preparations of tissues important in the transition to the outside world (Cardio and respiratory)

Blood Notes

First 12 weeks of development the yolk sac is major hemopoietic organ

12-30 liver is major hemopoietic organ

12-24 spleen functions in hempoiesis

By week 30, the bone marrow is the major hemopoietic organ

Amniocentesis

Sampling of amniotic fluid:

Mother is of advanced age

Downs Child

Chromosomal abnormal

X-linked carriers

History of neural tube defects

Parents have inborn errors of metabolisms

Layers traveresed to sample amniotic fluid

Perimetrium, myometrium, endometrium, chorion cavity (3 layers) amnion

Alpha-fetoprotein

Elevated with defects of embryonic body wall

Depreseed in maternal serum in downs and trisomy 18