3: Embryology Flashcards
What are the cellular processes that happen in embryology?
They overall function the exact same as other cells
Everything also happens via
- proliferation
- differentiation
- reorganisation and
- apoptosis
What happes during the first two month of human development?
Mainly lay down of all important organs
After 8 Weeks: mainly growth and elaboration of the structures that develop during the first two months
What happens to the fertilised egg in the Preimplantation state?
Preimplantation about 6 days
- Serious of cleavage –> Every time doubeling the cell number
- Egg develops into a Morula (=ball of undifferentiated cells)
- Differentiates so outer cells differ from inner cells
- Develops into a Balastocyte
Explain the structure of a Blastocyst
structure that has an
outer layer of trophectoderm (surrounded by zona pellucida)
, an inner cell mass,
and a fluid-filled cavity.
When does implantation take place?
How does is happen?
The blastocyst seperates from outer zona pellucida and merges with the uterine lining (finished at day 10)
How does a Blastocyst differentate further (during implantation)?
The inner cell mass ot blastocyte becoms a bilayer disk, composed of
- hypoblast and
- epiblast cells
–> This bilayer disk gives rise to all the tissues of the human fetus
What is gastulation?
When does it occur?
14-18 days postfertilisation
which converts the bilayer of hypoblast and epiblast cells into a trilaminar embryo,
containing the three layers of Germ Cells
- (Ectoderm,
- Mesoderm and
- Endoderm),
Explain the process of gastrolation
- Epiblast cells proliferate and differentiate to form mesoderm cells
- These cells move to space between hypoblast and epiblast
- Mesoderm Cells differentiate and replace the hyoblast cells with endoderm cells
What kind of tissues to mesoderm cells differntiate?
muscles, blood, skeleton, heart and kidney
What kind of tissues to ectoderm cells differntiate to?
Skin and CNS
Which tissues to endoderm differentiate to?
Into
- Gut
- Lung
- Liver
But: Muscular and vascular tissue are generally of mesodermal origin, so tissues are normally a mixture of germ layer types (e.g. muscle in the skin and gut).
What is Neurolation
What is it controlled by?
It is formation of the Neural tube (Brain + Spinal Chord) controlled by the Notocord (in the mesoderm)
Explain the earyl process of neurolation
- Development of the neural plate
- It develops two folds
- They grow and meet over the neural groove
- to form the neural tube
When does the neural tube close?
Closing continues in Week four
- Cranial End about 22 days
- Rostral End about 23/24 days
Explain the process of embryological folding
When does this happen?
3-4 Weeks
- Tissues fold laterally and fuse in the ventral midline
- In anteroposterior direction
- Folds the primordial germ cells (PGCs) from caudal end into hindgut and heart progenitor cells under head of embryo
What is the state of the embryo at the End of Week 4?
Precursor of all internal organs have been laid down
External structures start to develop
As overview: what happens during Month 2 of embryological develompent?
Mostly elaborate the tissues formed in first weeks
- urogenital
- cardiac
- facial
- lung development
+
- Limbs
Summarist the embryological development of the limbs
Occurs over a number of weeks
- Forelimb bud appears at d27/8
- Hindlimb bud at d29
- Grow out from lateral plate mesoderm rapidly under control of special signalling regions (+rotation etc)
- Fully formed and patterned by d56.
- develop further (finger differentiation)
What controlls the pattern of digit development?
By the sonic Hedgehodge SHH protein in the:
The ZPA = Zone of Polarising activity
Explain the use of thalidomide (historically and present) and its complications
Historically: was used as treatment against morning sickenss in first trimester of pregnancy –> caused many deformations (not just limbs but also more organ systems)
- Now: As cancer treatment+ against leprosy
- it damages developing blood vessels, thus depriving the adjacent cells of nutrients and preventing their proper growth and development –> most seen in upper limb development
Summarist the development of the kidneys?
Closly interconected with genital formation
- Will develop from urogenital ridge in Mesoderm at around Week 4
- Pronephrons
- Week 4
- in cervical region of embryo
- get degraded around Week 6
- Mesonephrons
- develops caudally to pronephrons
- Month 2
- Metanephrons
- adult type of Kidney
- Apperars in 5th week of kidney, fully functional at 12th week
- Ascent from pelvic region to abdomen
- Pronephrons
–> Sequential development and degradation of pronephrons, mesonephrons and metanephrons
Summarise the development of the gonads
Develop from: The gonads arise from intermediate mesoderm within the urogenital ridges of the embryo
- The genital ducts arise from paired mesonephric and paramesonephric ducts (up to 7 Weeks: no differentiation)
- Differential development of the male reproductive system is dependent on the activity of sex-determining region Y (SRY) protein, coded for by the SRY gene on the Y chromosome.
- The mesonephric ducts give rise to MALE genital ducts
- The paramesonephric ducts give rise to FEMALE genital ducts
Explain the formation of the male reproducitve system
- Primordial germ cells migrate to the genital ridge on the nephrogenic chord (intermediated mesoderm)
- Form gondads, attached to mesonephric duct (Wolffian)
- surrounded by paramesonephric duct
Up to this point: sex is indistinguishable
Then
- SRY+ (on y chromosome)
- Maternal hCG binds to leydig cells –> induction of production of testosterone and Anti-mullerian Hormone
- AMH= regression of mullerian (paramesonephric) + formation of wolffian (mesonephric) system
- External Genitalia: Tostesterone
Explain the formation of the Female reproductive system
- Primordial germ cells migrate to the genital ridge on the nephrogenic chord (intermediated mesoderm)
- Form gondads, attached to mesonephric duct (Wolffian)
- surrounded by paramesonephric duct (Müllerian system)
Up to this point: indistinguishable
- Absence of SRY- and Testosterone
- formation of female tract of the pararmesonephric ducts and female external genitalia
What are the main causes that might lead to abnormal development of the male reproductive system?
- inability to produce Testosterone/ AMH (anti-mullerian hormone)
- inability of tissues to respond to the stimmuli
Name examples of disorders of the reproductive system
- Androgen Insensitivity Syndrome Variable phenotypes
- genetic mutation in androgen receptor
- external genitalia: female
- Internal genitalia
- mesonephric (Woolffian) ducts are rudimentary/ lacking
- no descending of testicles
- But: AMH normal: no female structures possible
- Congenital Adrenal Hyperplasia
- enzyme deficiency (endo) of cortisol production
- high ACTH
- overstimmulation of adrenals
- androgen production
- Partial virilisation of the external genitalia
- Internal genitalia: female
- enzyme deficiency (endo) of cortisol production
Summarise the embryological development of the heart
- two heart tubes form which fuse to give rise to
- single heart tube (21 days post fertilisation)
- Complex Looping/Folding of Heart
4.
Explain the fetal circulation
Blood recieved from umbilical chord
goes through ductus venosus into IVC
to Right atrium
can go to left atrium via foramen ovale
Ductus arteriosum connects “pulmonary artery” directly to aorta
What are the most common cardiac abnormalities in developmen
Relativly common but can be severe
- often structual –> can be cured by surgery
- Most important: Septal defects
- But rare but might also occur: transposition of blood vessels
- e.g. aorta attached to right ventricle, pulmonary artery attahced to left ventricle
Explain the time and formation and risk factors of spina bifida
Defect in closing of neural tube (around day 21/22)
Occurs early in development
–> Many cases can be prevented with supply with folate acid
What is anencephaly?
When does this developmental defect originate?
No closure of the anterior neuropore
–> open skull and lack of part of the brain
Also at around 22 after fertilisation
Summarist the process and timing of embryological facial development
Most structures are formes in first 5 Weeks (bilaterally!
Migrate and meet in centre (over a period of about 5 Weeks)
- Movement thought to happen via
- Cleft formation and loss of tissue
- Filling of cleft with migrating tissue
Explain the formation of a cleft lip
- Usually unilateral upper lip and palate
- Might be bilaterally (cleft lip)
- Or symmetrical (palatine cleft)
- because of the way they come together (picture)
- Developmental Error about Week 10
Identify the five stages of lung development and Identify the changes in structure that occur in these stages.
- Embryonic
- Bronchi form
- Pseudoglandular
- Bronchioles and terminal bronchioles form
- Cannicular
- Respiratory bronchioles form
- Saccular
- alveolar ducts form
- Alveolar stage
- alveolar sacs form
When does surfactant production start?
What is its role in delivery and delivery of premature babies?
Production begins in early 3rd trimester of pregnancy and increases
- production needed for normal lung function at birth
- Can be accelerated by glucocorticoid injection
- ofte therefore: preterm babies suffer from lung complications (low surfactant production)
- might lead to Respiratory Destress syndrome
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- might lead to Respiratory Destress syndrome
