Early development

Embryonic period

Fetal period

Fertilization

Implantation

Formation of trilaminar embryo

Placental formation

Determination of body axes

What are the functions of all the preliminary (pre-spermatocyte) products of gametogenesis shown? What kind of divisions are they undergoing?

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Dark - "reserve" cells

Pale - actively dividing

Type B - actively giving rise to spermatocytes

They are undergoing mitotic division

Nuclear condensation

Loss of cytoplasm

Formation of an acrosome

Neck and tail formation

Identify the types of follicles shown

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Primordial

Primary

Graafian

Sperm penetrates corona radiata

Sperm binds to zona pellucida

Plasma membranes of sperm and oocyte fuse

Oocyte releases lysosomal enzymes, inducing the zona reaction (causes binding sites on the zona pellucida to change)

Both replicate their DNA

Final polar body released by meiotic division

Blastocyst.

Defining feature: the cavity

"Stone baby" - calcified embryo.

Pelvic/abdominal CT scan most likely to reveal it.

Epiblast: outside layer, high columnar cells adjacent to amniotic cavity

Hypoblast: inside layer, small cuboidal cells adjacent to blastocyst cavity

What 2 cavities are formed in the second week of development?

Amnion and yolk sac

What two layers does the extraembryonic mesoderm split into?

Somatopleure and Splanchnopleure

What layer within the embryoblast forms the amniotic cavity?

Epiblast

Both the _________ and the _________ of amniotic fluid is critical to proper development?

Volume, Makeup

What is polyhydramnios, and what kind of developmental problems might it indicate?

Too much amniotic fluid, may indicate problem with GI system

What is oligohydramnios? What kind of developmental problems might it indicate? Result in?

Not enough amniotic fluid. May indicate problem with urinary system. May result in poor limb development

Define the green and blue structures. What is the lining indicated by the yellow arrows? 

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Trophoblast

Epiblast

Extraembryonic endoderm

What is indicated by the red arrows in this picture? When does this occur?

[image]

Separation forming between cytotrophoblast and hypoblast.

This occurs in week 2

What large cavity surrounds the embryoblast and fills the trophoblast?

Chorionic cavity

What structure is indicated by the red arrow?

Somatopleuric layer of extraembryonic mesoderm

What layer of the extraembryonic mesoderm covers the yolk sac/embryoblast?

Splanchnopleuric

What is the function of the syncytiotrophoblast?

Invade endometrium

Erode maternal tissue

Secrete hCG

What is the name of the cavities that form in the syncytiotrophoblast? What are they there for?

Trophoblastic lacunae, which accept blood being "dumped" in from maternal sinusoids

What are primary stem villi?

Cellular columns originating from the embryo, penetrating into and surrounded by the syncytium

At what point do primary stem villi become secondary stem villi?

Day 16, when the extraembryonic mesoderm extends into them

At what point do secondary stem villi become tertiary stem villi?

End of week 3, when they have formed blood vessels that connect to forming fetal blood vessels

In this graphical illustration of a tertiary stem villi, what colors represent what structures?

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Syncytiotrophoblast

Cytotrophoblast

Connective tissue

Maternal artery

Which parent's genome contributes more to the formation of the trophoblast?

Father's

Define genomic imprinting

Differential modification and/or expression of homologous alleles or chromosome regions depending upon the parent from whom it was derived

A patient presents with nausea and vaginal bleeding in her first trimester of pregnancy. Physical examination reveals a uterus that is enlarged for her gestational age, and bloodwork shows abnormally high levels of hCG. What condition should be expected?

Hydatidiform mole

What causes a hydatidiform mole, and what abnormal developmental morphology arises as a result?

Caused by fertilization of an empty oocyte. Zygote begins to develop, but never forms embryoblast (just trophoblast)

What does the primitive pit indicate?

Midline of body

What three layers are indicated by the blue, red, and yellow cells in this picture? When does this occur?

Ectoderm

Mesoderm

What morphologically characterizes the prechordal/cloacal plate, and what do these sites indicate?

Ectoderm and endoderm in direct contact with each other, no mesoderm. These sites indicate the location of development of the mouth and the anus, respectively

What are the 4 important characteristics of the notochord for development?

Anatomic midline

CNS development

Vertebral column development

Nucleus pulposis formation

What disorder causes an organ or organs to be formed outside the body? What development error causes this?

Gastroschisis - caused by anterior wall defect (failure to completely enclose splanchnic/somatic mesoderm)

Define situs inversus

One or more organs on the opposite site of the body from "normal"

Failure in producing proper midline for facial structure results in:

Holoprosencephaly (can be mild, moderate, or severe)

What is sirenomelia, and what is it caused by?

Called "mermaid syndrome", caudal dysgenesis - not enough mesoderm to make lower extremeties. Caused by oligohydramnios

What disorder is present in this picture? 

What morphological changes occur during the embryonic period?

Ectoderm, mesoderm, endoderm all undergo differentiation

Organogenesis begins.

What is the significance of the neural ectoderm?

Signaled by the notochord to become the neural plate; forms the CNS

When do the cranial and caudal neuropores close?

Cranial: day 24-25; caudal: day 26-27

Is neuropore nonclosure viable?

Cranial is not, caudal is but causes various defects

What 3 major derivatives form from neural crest cells?

Parasympathetic ganglia of CN 3, 7, 9, 10

Sensory ganglia of CN 5, 7, 8, 9, 10

Autonomic and dorsal root ganglia

Surface ectoderm will give rise to what 5 major structures?

Epidermis

Anterior pituitary

Tooth enamel

Internal ear

Phakic lens

What are the 3 "rod and sheet-like" mesodermal derivates and what systems will they form?

Paraxial mesoderm - axial skeleton, skeletal muscle, part of the dermis

Intermediate mesoderm - urinary and part of genital system

Lateral plate mesoderm - gives rise to splanchnic and somatic mesoderm

What are the structures indicated in this picture? What is their developmental significance? 

Somites ("Bricks" of mesoderm), later form skeletal muscle

After what week of pregnancy can external genitalia be distinguished as male or female?

Week 9

What developmental milestones are reached in weeks 13-16?

Sites of ossification evident

Eye movements

During what weeks of pregnancy are primary ovarian follicles formed and testes descend?

Weeks 17-20

During what weeks of pregnancy is surfactant beginning to be secreted in the lungs?

Weeks 21-25

What significant developmental milestones are reached in weeks 26-29?

Lungs are capable of breathing

CNS capable of controlling breathing and body temperature

Hematopoeisis shifts to bone marrow (week 28)

What weeks of pregnancy are referred to as the "finishing period"? What happens during this time?

Weeks 35-38; final preparations of tissues important to transition to the outside world

What are the major sites of embryonic hematopoeisis during what time periods?

Weeks 1-12: yolk sac

Weeks 12-30: liver

Weeks 12-24: spleen

Week 30: bone marrow

What embryonic layers must be penetrated in order to perform an amniocentesis?

Chorion (syncytiotrophoblast, cytotrophoblast, extraembryonic mesoderm) and amniotic sac

An amniocentesis is performed in the third trimester of pregnancy, revealing elevated levels of alpha fetoprotein. What disorder might be the cause? Why? What causes this disorder?

7

Somites

Muscle

What is the structure shown before? What layers is it differentiating into? What directions will those layers migrate, and what structures will they eventually form?

 [image]

Somite

Dermomyotome - migrates dorsally, forms dermis and skeletal muscle

Sclerotome - migrates ventrally, surrounding notochord/neural tube. Forms vertebral columns.

4 occipital

8 cervical

12 thoracic

5 lumbar

5 sacral

What is being pictured below? What are the blue, yellow, and orange structures? What protrudes between the two visible segments?

[image]

Vertebral segments

Notochord

Sclerotome

Myotome

Nerves and muscles protrude between vertebrae

Notochord

Sclerotome

Myotome cells become myoblasts

Myoblasts elongate, migrate, and fuse, forming myotubes

Contractile filaments appear in cytoplasm-->Muscle fiber

One spinal cord level or segment innervating more than one muscle
Longitudinally - trapezius and sternocleidomastoid

Tangentially - intercostals and obliques 

Pseudostratified columnar

Apical end

Marginal layer - nerve fibers and oligodendrocytes

Mantle layer - cell bodies (nuclei) and astrocytes

Ventricular layer - surrounds central canal

Alar - sensory information

Basal - motor commands (skeletal and autonomic)

What are the structures circled in green, branching off of the spinal cord?

[image]

Dermatome

Segmental and overlapping

Pia and arachnoid - neural crest

Dura - mesoderm

Hemi

Scoliosis

What is the structure circled in red?

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Malignant tumor arising from notochord remnants. Invade bone

Base of skull and lumbar region

What is the diagnosis for the condition shown below? What is its etiology?

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Spinal dural sinus

Caudal neuropore nonclosure

Physical examination of a newborn reveals a cyst protruding through the lumbar region of the spine. Gestational history shows elevated alpha-fetoprotein levels.

What is the diagnosis? What two types of this disorder may occur?

Spina bifida cystica

Meningiocele - fluid only

Meningiomyelocele - fluid and CNS tissue

Intramembranous ossification - most flat bones of the skull, most of the clavicle

Endochondral ossification - most limb bones

Mesenchyme condenses and becomes highly vascular

Osteoblasts lay down a matrix

Calcium is deposited

Hyaline cartilage cells hypertrophy

Matrix becomes calcified and cells die

Thin layer of bone deposited under perichondrium (becomes periosteum)

Invading cells differentiate into hemopoietic cells