Embryology Introduction Flashcards by Mai Alkari

Pre-embryonic phase

0-3 weeks

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Embryonic phase

4-8 weeks

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Foetal phase

9-40 weeks

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Spermatogenesis

Production of 4 sperm from spermatogonium, only starts after puberty

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Oogenesis

Production of 1 ovum from oogonium, meiosis I when embryo, meiosis II after puberty

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Product of fertilisation

Zygote

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Fertilisation

Pro-nucleus of sperm enters and fuses with the pro-nucleus of ovum

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Week 1

Zygote formed and divides to from blastocyst, moves through uterine time to reach uterine cavity

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Zygote divides to form a solid ball of cells called the

Morula

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Mitochondria are passed on from the

Mother

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What is formed once the number and size of cells of morula increase

Blastocystic cavity - blastocyst

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In blastocystic cavity, cells accumulate at one end to form an

Inner cells mass

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The outer lining of cells of blastocystic cavity is called the

Trophoblast

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Cell lining Fallopian tube to help with movement

Ciliated epithelium

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What could occur if cilia function in fallopian tube is abnormal

Ectopic pregnancy (fertilised egg implants itself in Fallopian tube)

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Blastocysts in implanted in the

Uterine cavity

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Week 2

Implantation occurs, placenta begins to develop, bilaminar disc is formed, sacs membranes and cord start to form

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Trophoblast divides to form

Chorion

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Chorionic villi

Finger like processes of chorion

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Chorion function

Implantation, forms part of placenta, secretes human chorionic gonadotropin (HCG)

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Decidua basalis

Part if endometrium deep to the implanted conceptus

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HCG

Maintains endometrium

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Cells of inner cell mass form a 2-layered disc called the

Bilaminar disc

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2 cavities formed by bilaminar disc

Amniotic cavity and yolk sac

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2 cell layers forming bilaminar disc

Epiblast and hypoblast

Function of yolk sac

Provide nutrition

Allantonic cavity

Accumulates waste material

Chorionic cavity

Holds embryo

Functions of placenta

Foetal nutrition, transport of waste and gases, immune

Foetal part of placenta

Smooth with foetal blood vessels and end of umbilical cord

Maternal part of placenta

Decidua basalis, rough and has maternal blood vessels

The placenta matures by

18-20 weeks

Fraternal (dizygotic) twins

2 ova, sperm and zygotes

Identical (monozygotic) twins

1 ovum, sperm and zygote, divides into 2 and each cell develops into a different embryo

Week 3

Gastrulation, neurulation, development of somites, early development of cardio vascular system

Gastrulation

Formation of germ layers

Neurulation

Formation of neural tube

Primitive streak

Little groove in the midline of the epiblast formed by the invagination of cells

What is formed once the primitive streak it formed

The axis of the embryo

3 germ layers formed by epiblast cells during granulation

Ectoderm Mesoderm Endoderm

What is formed at the end of granulation

Trilaminar disc

Notochord

Solid tube of cells formed from primitive streak of ectoderm

Function of notochord

Induce ectodermal cells in the midline to form a neural tube

Neural plate sinks down to form a

Neural tube

Neural tube effect on mesoderm

Induces it to thicken

Mesoderm separates into 3 parts called

Paraxial mesoderm Intermediate mesoderm Lateral mesoderm

Lateral plate mesoderm splits to form

A somatic and splanchnic mesoderm

Space formed in between somatic and splanchnic mesoderm

Intraembryonic coelom

Segmentation of paraxial mesoderm to from

Somites

3 somites formed

Dermatome Myotome Sclerotome

Dermatome

Forms dermis of skin

Myotome

Forms muscles

Sclerotome

Forms bones including vertebrae

Neural tube forms

Forebrain, midbrain, hindbrain and spinal cord

What day does the heart start to beat

Day 24

Endoderm forms

Gut

Intermediate mesoderm forms

Urogenital system (kidneys and reproductive)

Lateral plate mesoderm forms

Body cavities, peritoneum and pleura

How many somites from in the paraxial mesoderm

43 pairs

When does lateral folding of the mesoderm into a tube occur

Week 4

Teratology

Study of when things go wrong during development

Teratogens

Environmental factors that cause abnormal development

Drug that caused malformed limbs in babies

Thalidomide

Causes of abnormal development

Environmental, genetic, multifactorial and 60% unknown

Environmental factors that causes abnormal development

``` Dugs Alcohol Tobacco Infectious agents (transfer through placenta) Radiation ```

Genetic factors that cause abnormal development

Too many/few chromosomes | Structural changes

When is the period of greatest sensitivity to teratogens

Weeks 3-8

The risk posed by teratogen depends on 3 factors that are

Exposure during critical periods of development Dosage of drug/chemical/factor Genetic constitution of embryo

Methods of diagnosis prenatally

Blood Ultrasound scan Invasive tests

Methods of diagnosis postnatally

Hip stability Testes Fingers and toes Hearing