Embryology Flashcards by Georgia Leggett

Recall the 4 cellular processes at work in embryological development

Proliferation: of epiblast cells
Differentiation: of epiblast cells to form mesoderm cells
Reorganisation: Mesoderm cells move into space between epiblast + hypoblast. Differentiate further to generate the endoderm, which replaces the hypoblast
Apoptosis: Loss of hypoblast cells due to replacement by endoderm

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Recall the 3 stages of renal development in utero

Pronephros
Mesonephros
Metanephros

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What is significant about the mesonephros pre-kidney structure?

Site of mesonephric + paramesonephric ducts development, that eventually differentiate into genital ducts

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Describe the arterial supply to the kidneys during embryonic development

Has to form, degenerate + reform as kidneys move up abdomen

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Where do the gonads originate from embryologically?

Intermediate mesoderm within urogenital ridges

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What do mesonephric and paramesonephric ducts give rise to?

Mesonephric = Male genital ducts (Wolffian system) 
Paramesonephric = Female genital ducts (Mullerian system)

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What influences differentiation of reproductive tracts after week 7 of development?

Presence or absence of SRY
+ : Male
- : Female

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What do the leydig and sertolli cells produce during male development?

Leydig: Testosterone (DHT), under stimulation of maternal hCG. Supports development of Wolffian ducts.
Sertolli: anti-Mullerian hormone (AMH), which causes regression of Mullerian (paramesonephric) ducts.

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In male embryos, what are the most common mal-developments a result of?

Inability to produce appropriate hormones (testosterone + AMH)
Inability of target tissues to respond to these hormones, normally due to defects in the cognate receptors.

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Where does heart development begin?

Outside the embryo proper, in a horseshoe pattern

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What happens at day 21 of heart development? What events occur after this?

2 tubes of horseshoe fuse to produce a single tube which can pump blood unidirectionally
Looping of heart + separation, giving rise to 4 chambered structure
Development of valves

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Where is the foramen ovale located?

Between atria

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What does the foramen ovale bypass in the foetus?

Right ventricle + therefore pulmonary circulation

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What is the purpose of ductus arteriosus?

Connects main artery from right ventricle to aorta, diverting blood that would normally go to lungs to arterial system

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What is the Tetralogy of Fallot?

4 structural abnormalities within the heart 
Pulmonary stenosis
RV thickening
Ventricular septal defect
Aorta overides septal defect

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How does transposition of the great arteries cause major issues?

Aorta is connected to RV + pulmonary artery to LV
Generates 2 separate blood flows; oxygenated blood is cycled through the left via the lungs; de-oxygenated blood through the right to the body.
Closure of foramen oval + ductus arteriosus at birth separates the blood flows
Infant becomes cyanotic
Treatment: prostaglandins to keep ductus arteriosus open, + perhaps opening of a link between the atria.

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When does lung production of surfactant begin? What does low levels result in? What can increase and accelerate production if preterm delivery is delayed?

Early in 3rd trimester
Low levels causes Respiratory Distress Syndrome
Glucocorticoids can increase + accelerate production

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What is a genetic mosaicism?

Meiotic non-disjunction causing different cells within the body to have non-identical genetic makeup

What is the most likely cause of spina bifida?

Folic acid deficiency

How does surgery effect spina bifida?

Can address anatomical problems to protect neural tissue

Can’t address functional problems; thus nerve damage results

When does the malformation occur in spina bifida and what is the problem?

~3 weeks

Incomplete fusion of the neural tube

What is a cleft palate?

Connection between the mouth+ nasal cavity

Recall 4 infectious agents that are common teratogens

Rubella
Syphilllis
HIV
HSV

What is ancephaly?

Compromised development of the head + skull

Similar aetiology to spina bifida, though results in a lack of closure of the anterior neuropore.

What are the 3 germ layers precursors of?

``` Endoderm = gut, liver + lungs Mesoderm= skeleton, muscle, kidney, heart + blood. Ectoderm = skin + CNS ```

List 3 developmental abnormalities of the kidneys

1. If retained in pelvis, rather than moving to abdomen 2. Retention of an extra artery may obstruct the ureter + cause enlargement of the renal pelvis. 3. Form separately, but may fuse to form a horseshoe; the extra tissue makes it impossible to move, so remains in the pelvis.

Give an example of male genital Mal-development

``` Androgen Insensitivity Syndrome Mutant androgen receptor No virilisation of external genitalia Internally lack Woolfian ducts AMH production is normal so no female structures ```

Give an example of female genital Mal-development

Congential Adrenal Hyperplasia Mutation in CYP450 21-hydroxylase enzyme, limiting cortisol production from fetal adrenals Lack of cortisol means theres no negative feedback on pituitary ACTH output, causes high ACTH, + over-stimulation of fetal adrenals, which make weak androgens. These cause partial virilisation of genitalia. Internal systems are female, as there is no SRY Female ducts develop (no AMH, as no Sertoli cells).

When are the terms conceptus, embryo, fetus and infant used?

Conceptus: everything resulting from the fertilised egg Embryo: up to week 8 of development Fetus: rest of pregnancy Infant: after delivery.

Summarise the key developmental events occurring in the first 2 months of pregnancy, week by week

2: Development of bilaminar disc 3: Formation of trilaminar disc (mesoderm), CNS + somites. Blood vessel initiation. Formation of placental villi. (3mm). 4: Closure of neural tube. Heart, Face, arm initiated. Umbilical cord. Elaboration of placental villi. (4mm) 5: Face + limbs continue. (5-8mm) 6: Face, ears, hands, feet, liver, bladder, gut, pancreas. (10-14mm) 7: Face, ears, fingers, toes. (17-22mm) 8: Lungs, liver, kidneys, (28-30mm)

Development of which structures continues beyond week 8?

Face Lungs Urinary + reproductive systems

What are the primary processes occurring in the second and third trimester?

Growth + Maturation | increased size + remodelling

In what pattern do primary structures of the face develop? How long does this pattern persist? How long does it take for this to change?

On the side of the head Persists until at least 5 weeks post-fertilisation Move over the next 5 weeks to expected position through tissues of the developing face

Describe the process of movement of pre-formed structures through the face

Repeated formation of clefts + filling in of the clefts leads to sequential loss of tissue from centre of the face + movement of tissues to correct places

What does the formation of the face from 2 separated halves result in if the process goes wrong?

Clefting in the lip or palate

Describe the usual appearance of cleft lip and cleft palate

Cleft lip: asymmetric, as only 1 of the 2 clefts does not function correctly Cleft palate: symmetric as the halves of the palate don’t meet + fuse correctly

Why is there usually little or no scarring after cleft correction surgery?

Rapid cell turnover in infants

What 4 steps occur in heart development?

Folding of embryo + heart tube fusion Heart looping Septation Outflow tracts divide

What should happen to the ductus arteriosus and foramen oval at birth?

They should close, allowing oxygenation within the lungs

What is polydactyly? What is Oligodactyly?

Polydactyly: > 5 digits per hand/ foot Oligodactyly: Loss of digits

What was Thalidomide marketed as? What did its use from 8 weeks of pregnancy cause?

Anti-morning sickness drug Interfered with blood vessel development in developing limb bud, leading to cell death + inhibition of growth Particularly effects upper limbs

In which conditions is Thalidomide currently used therapeutically?

Some cancers + leprosy

What is the mechanism of action of Thalidomide?

Damages developing blood vessels, thus depriving adjacent cells of nutrients + preventing proper growth + development.

What are Teratogens?

Factors affecting details of development, though primary structures will be present