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Flashcards in Embryology Deck (139)
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1

What is the difference between embryological age and gestational age?

Embryological age is usually about 2 weeks less
Gestation starts after the beginning of the last menstrual period

2

What is oxygen tension at the third week?

3%

3

What embryological changes have occurred by the 3rd week?

- Formation of trilaminar disc (mesoderm)
- CNS formation
- Somite formation
- Blood vessel initiation

4

What placental changes have occurred by the 3rd week?

Initiation of placental villi

5

What embryological changes have occurred by the 4th week?

- Closure of neural tube
- Heart, face and arm initiated
- Umbilical cord

6

What placental changes have occurred by the 4th week?

- Elaboration of placental villi

7

What embryological changed have occurred by the 5th week?

Face and limbs continue

8

What embryological changed have occurred by the 6th week?

Face, ears, hands, feet, liver, bladder, gut, pancreas

9

What embryological changed have occurred by the 7th week?

Face, ears, fingers, toes

10

What embryological changed have occurred by the 8th week?

Lungs, liver, kidneys

11

What other changes have occurred by the 8th week?

- Placental elaboration continues, development of villi
- Placental endocrinology becomes dominant
- Cytotrophoblast plugs in spiral arteries lost over next 2 weeks

12

How does O2 tension change by week 10?

8%

13

What is the length of the foetus by the 3rd week?

3mm

14

What is the length of the foetus by the 4th week?

4mm

15

What is the length of the foetus by the 5th week?

5-8mm

16

What is the length of the foetus by the 6th week?

10-14mm

17

What is the length of the foetus by the 7th week?

17-22mm

18

What is the length of the foetus by the 8th week?

28-30mm

19

How does the weight of the foetus change over the three trimesters?

1st: 50g
2nd: 1050g
3rd: 2100g

20

Define blastocyst

Epiblast and hypoblast present at ~9 days (~0.1cm wide)

21

Define embryo

Small developing conceptus present at ~5-6 weeks (~1cm wide)
- Can include everything from day 1 onwards, baby and placenta

22

Define foetus

Developing conceptus present at ~3 months (~7cm wide)

23

Define conceptus

Anything derived from a fertilised egg

24

What are the 4 repeated processes which achieve embryology?

Proliferation
Movement
Differentiation
Cell loss

25

What is proliferation in response to in general?

GF, receptor expression, cell survival
All via para- or autocrine signalling

26

What is movement in response to in general?

Chemoattractants, cognate receptors, facilitated (via remodelling & proteases)

27

What is differentiation in response to in general?

Paracrine regulation, receptor expression, loss of proliferation

28

What is cell loss controlled by in general?

Programmed cell death controlled by mainly paracrine factors

29

What is concentration signalling?

The strongest signals are received by cells located closer to the source of the signalling molecules e.g. limb bud formation

30

What are HOX genes?

Establish A-P (anterior-posterior) axis, vertebral differences, CNS divisions, patterns in limbs

31

What activates HOX?

Retinoic acid (VitA derivative)

32

What is a blastocyst?

A bilaminar disc comprised of an epiblast and a hypoblast layer

33

What does gastrulation form?

A 3-layer conceptus comprised of the ectoderm, mesoderm and endoderm

34

Where does gastrulation occur?

Down the primitive streak

35

What are the three steps in gastrulation?

- Epiblast cells migrate towards the centre
- Epiblasts differentiate into mesoderm cells and move down into the new mesoderm layer
- Hypoblast cells apoptose and are replace by endoderm cells

36

What does the endoderm form?

Gut, liver and lungs

37

What does the mesoderm form?

Skeleton, muscles, kidneys, heart and blood

38

What does the ectoderm form?

Skin and CNS

39

What is formed after gastrulation?

Neural canal

40

How is the neural canal formed?

The ectoderm proliferates to form the neural plate, with no proliferation at the neural groove (negative stimulation of notochord)

41

What happens to the body cavity after day 21?

The body cavity closes

42

What happens to the yolk sac by day 28?

The yolk sac pinches off and becomes the umbilical cord (allantois)

43

What happens during the 2nd month of development?

The limbs develop (days 28-56)
Face develops
Internal tissues develop - heart, lungs & gut

44

When will the conceptus look human (foetal)?

Day 56

45

How does the CNS develop from days 22-23?

Tissues fuse down midline leaving anterior neuropore and posterior neuropore

46

When should the neuropores close by?

Days 25-28

47

What is spina bifida?

Failure to complete neurulation
- Doesn't fuse completely, can occur towards top or bottom of spine
- Can result in faulty neurology in lower body

48

Which type of spina bifida has a better prognosis; top or bottom?

Bottom

49

What is myelomeningocele?

Neural tissue is found in bulge

50

What is meningocele?

No neural tissue in bulge

51

What is spina bifida occulta?

Hair growth over area affected, no bulge

52

How are the vertebrae formed at the bulge?

No vertebral formation at bulge
Suggests bone growth dependent on neural tissue growth

53

What is the incidence of spina bifida?

1-2 per 1000

54

Does surgery help the anatomical and functional problems of spina bifida?

Anatomical not functional

55

What can be taken very early in pregnancy to prevent spina bifida and anencephaly?

Folic acid

56

What is anencephaly?

Reduced brain development
(Literally, lack of head)

57

What is the incidence of anencephaly?

1-8 per 10,000 births
F more than M

58

What is the embryological cause of anencephaly?

Failure of the anterior neuropore to close

59

What happens by day 21 in the development of the heart?

The two endocardial tubes fuse into a primitive heart tube

60

What layer do the endocardial tubes develop from?

Mesoderm

61

What is MacDonald's arc shape?

The horseshoe shape formed by the joining of the primitive heart tube at the cranial end

62

What happens to the heart development between days 23-28?

Undergoes turning action (anti-clockwise) and the 4 chambers form

63

When does blood flow begin?

Day 22

64

How do the atria and arteries rotate around each other?

Atria rotate behind the arteries

65

What happens to the heart development between days 17-28?

Head-tail folding -> aids heart rotation and heart movement more internally

66

What physiological changes result from the pressure of the folding head of the heart?

- Pushes the heart to the centre of the body
-Squashes the atria (less muscular than ventricles)

67

What heart changes occur at birth?

The ductus arteriosus and the foramen ovale close

68

What is the ductus arteriosus between?

Pulmonary artery and descending aorta

69

What is the foramen ovale between?

The right and left atria

70

When does the forelimb bud appear?

Day 27/28

71

When does the hind limb bud appear?

Day 29

72

Which layer do the limb buds grow from?

Lateral plate mesoderm

73

By what day are the limbs fully formed and patterned?

Day 56

74

What is achondroplasia?

FGF23 gain of function mutation, which stops conversion of cartilage to bone
Concerns limb elongation not primary formation, so detail is there but the limbs aren't very long

75

What was thalidomide used to treat?

Morning sickness

76

What did thalidomide affect in foetus'?

Limbs, eyes, heart, alimentary/urinary tracts, blindness, deafness

77

How many infants were affected?

~10,000 infants affected with a 50% survival rate

78

What is thalidomide currently used to treat?

Leprosy and other cancers

79

What genes regulate limb development?

Shh - Sonic Hedgehog protein - zone of polarising activity
FGF8 - fibroblast-like growth factor 8 - apical ectodermal ridge

80

How does thalidomide cause negative effects?

Interferes with blood vessel development which led to apoptosis and death of developing cells

81

What is amelia?

"Prolonged exposure" to thalidomide
Complete lack of limb growth

82

What is phocomelia?

"Short exposure" to thalidomide
Limbs are a lot shorter but hands and feet still develop

83

What is polydactyly?

Increased number of fingers or toes

84

What is the pronephros?

The first part of the urogenital system to develop
-Has no excretory function, solely developmental, degenerates as the mesonephros forms

85

What is the mesonephros?

Connects to the cloaca, has limited excretory function

86

What is the metanephros?

Definitive kidney

87

What happens after the mesonephros has formed?

-Metanephric ducts grow out of the cloaca and begin to form kidneys
- Mesonephric ducts begin to differentiate into testes/apoptose in F

88

How does the blood supply of the kidneys change as they develop?

Vascular buds initially grow from kidney and invade common illiac arteries
As the kidneys move cranially, form new vessels then induce regression of old vessels

89

What layer does the bladder form from?

Endoderm, apart from trigone (mesodermal) which forms from mesonephric duct

90

What is the trigone?

Signals filling of the bladder

91

What kidney developmental errors can occur?

- Renal agenesis (degeneration of ureteric bud): unilateral (1:1000, L > R); bilateral ("Potter's syndrome", oligohydramnios)
- Abnormal shaped kidneys
- Abnormal ureter - bifid ureter, double kidneys, supernumerary kidneys (extra kidney)
- Pelvic or horseshoe-shaped kidney - kidney doesn't ascend or kidneys fuse caudally to horseshoe shape
-Bladder exstrophy - protrusion of bladder through abdominal wall

92

What is the paramesonephric duct?

Mullerian ducts -> female ductal systems

93

What is the mesonephric duct?

Wolffian duct -> male ductal systems

94

How do the cells that make gametes develop?

Primordial germ cells found outside the embryo in the yolk sac -> move into embryo -> move into developing genital ridges

95

What is the difference between early male and female genital development?

Gonads are identical in both sexes and indifferent before primordial germ cells move in (week 7)

96

When does the urogenital ductal system develop?

Week 7

97

What gene causes the male ductal system to form?

SRY gene

98

What happens to the mesonephric tubes in males and females?

M - become the testes
F - not connected to the ovaries and develops separately

99

What do the gonads arise from?

Intermediate mesoderm within urogenital ridges

100

How does urogenital development proceed in SRY -ve?

Female path (~9th week onwards)

101

What do the gonads develop into?

Testis containing spermatogonia, Leydig cells, Sertoli cells

102

What do the Leydig cells produce?

Testosterone -> supports growth of mesonephric ducts (absence -> regression)

103

What happens to some of the testosterone produced?

Converted to DHT -> supports development of prostate, penis and scrotum

104

What do the Sertoli cells produce?

AMH (anti-Mullerian hormone)/MIS (mullerian inhibiting substance) -> induces regression of paramesonephric ducts (absence -> persistance of paramesonephric ducts)

105

What forms the ureters?

Ureteric bud

106

What do the mesonephric ducts form?

Rete testes, efferent ducts, epididymis, vas deferens, seminal vesicle, trigone of bladder
(testes and trigone)

107

What does the urogenital sinus form?

- Bladder, prostate gland, bulbourethral gland, urethra
- Bulbourethral glands, lower 2/3rd of vagina

108

How do the testes move inside the abdominal/pelvic cavity?

Testes arise in lumbar region and descend into pelvic cavity via inguinal canal

109

Why is there this movement?

The testes are tethered to the anterior body wall by the gubernaculum
The growth and elongation of the embryo and shortening of the gubernaculum pulls testes through body wall

110

What do gonads develop into in SRY -ve?

Develop into ovary containing oogonia and stromal cells

111

What do the paramesonephric ducts form?

Oviducts, uterus, upper 1/3rd of vagina

112

What is hCG?

Human chorionic gonadotrophin

113

When is the hCG peak? Why is this significant?

8 weeks after last menstrual period
Drives testosterone production

114

What are the complications of undescended testes?

Increased risk of cancer
Do not function normally

115

What is hypospadias?

Incomplete fusion of urethral folds -> urethra exits penis early

116

What can Mullerian duct anomalies result in?

Abnormal fusion of ducts e.g. two uteruses

117

What is persistant Mullerian duct syndrome?

Occurs in M with mutations in AMH/MIS or receptor
No inhibition so paramesonephric ducts persist
Testis either sit by ovaries or one/both can descend
Testosterone/DHT produced so normal external genitalia/ducts

118

What is androgen insensitivity syndrome?

Occurs in genetic (XY) M with mutations in androgen receptor
Lack of virilisation (androgens have no effect)
Normal F external genitalia but undescended testes
Mesonephric ducts rudimentary due to testosterone loss
Normal MIS production causes Mullerian duct regression so no oviducts, uterus or upper 1/3rd of vagina

119

What is congenital adrenal hyperplasia?

Occurs in genetic females with no 21-OH enzyme (no cortisol) -> overproduction of ACTH and overactive adrenal glands
Leads to increased weak androgen production (DHEAS) -> weak virilisation -> enlarged clitoris, partial or complete labia majora fusion
Internal genitalia all F - testes absent

120

When does the face develop?

Weeks 5-10

121

How does the face develop?

Grooves form
Mesenchyme apoptoses pulling eyes and nostrils towards midline
Grooves filled in by bulk tissue movement (clefting results if this doesn't happen)
Results in two different halves of face

122

When do the lungs start to develop?

Weeks 3-4

123

How many primary bronchi are there?

3 right and 2 left

124

When is surfactant produced?

From week 25

125

What are the stages of lung development?

Embryonic - weeks 3-4
Pseudoglandular - weeks 5-16
Canalicular - weeks 16-26
Saccular - week 26-birth
Alveolar - month 8-childhood

126

What happens during the embryonic and pseudoglandular stages of lung development?

- Formation of major airways
- Formation of bronchial tree and portions of respiratory parenchyma
- First formation of acinus

127

What happens during the canalicular stage of lung development?

- Last generations of lung periphery formed
- Epithelial differentiation
- Air-blood barrier formed by blood capillaries migrating closer to bronchioles

128

What happens during the saccular stage of lung development?

- Expansion of air spaces
- Surfactant detectable in amnionic fluid

129

What happens during the alveolar stage of lung development?

Secondary septation

130

What is respiratory distress syndrome?

Low physiological surfactant levels
Incidence ~1% of all births

131

How does premature birth affect RDS incidence?

24 weeks: 100%
26-28 weeks: 50%
30-31 weeks: 25%

132

What is surfactant composed of?

40-45% DPPC (reduces alveolar tension)
40-45% other phospholipids
5% other proteins
Trace cholesterol and other components

133

How can in utero production of surfactant be increased?

Glucocorticoid injection

134

What is the half-life of surfactant?

5-10 hours

135

What cells produce surfactant?

T2 pneumocytes

136

What is the function of surfactant?

Induce low surface tension in alveoli

137

What are teratogens?

Factors that dysregulate patterning

138

What can happen if teratogens are present earlier in development?

Major defects

139

When do most teratogens exert their main effects?

1st trimester of pregnancy