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UNSW Embryology

Development Week by Week

© Dr Mark Hill (2008)

Acknowledgements

Introduction

This page is organised to show week by week human development features and approximate timing of key events. The "weeks" refer to embryonic development and differ from clinical weeks (shown in brackets, from last menstrual period) and "stages" refer to Carnegie stages of development. The pull down menus below will take you to specific features and the small images are linked to pages with more specific information (More? week by week detail)

Week -2

(Clinical Week 1)

Day

Menstrual cycle

Event

1

Menstrual Phase


Menstrual cycle changes: Uterine endometrium (loss), Ovary (Follicle Development)

2

  

3

    

4

    

5

Proliferative Phase


Menstrual cycle changes: Uterine endometrium (proliferation), Ovary (Follicle Development)

6

7

    

Week -1

(Clinical Week 2)

Day

  

Event

8

Proliferative Phase

9

  


Mid proliferative

10

    

11

    

12

    

13

  


Late Proliferative

14

Ovulation

 Human Egg

Week 1

(Clinical Week 3)

Day

Stage

Event

1

Secretory Phase
Stage 1


Fertilization, Secretory Phase

2

Stage 2


Morula, Blastula

3

  

4

Stage 3

Blastocyst Hatching (zona pellucida lost)

5

  


Blastocyst (free floating)

6

Stage 4

Adplantation

7

Stage 5

Week 2

(Clinical Week 4)

Day

Stage

Event

8


Implantation

9

    

10

    

11

    

12

    

13

Stage 6

14

    

Week 3

(Clinical Week 5)

Day

Stage

Event

15

16

Stage 7

17

    

18

Stage 8

19

   Stage8sem

20

Stage 9

21

    

Week 4

(Clinical Week 6)

Day

Stage

Event

22

Stage 10

23

  

Heart tube "beating"

24

Stage 11

25

Stage 12

26

    

27

    

28

Stage 13

Week 5

(Clinical Week 7)

Day

Stage

Event

29

30

    

31

    

32

Stage 14

33

Stage 15

34

 

35

    

Week 6

(Clinical Week 8)

Day

Stage

Event

36

37

Stage 16

38

    

39

    

40

    

41

Stage 17

42

    

Week 7

(Clinical Week 9)

Day

Stage

Event

43

44

Stage 18

45

    

46

    

47

    

48

Stage 19

49

    

Week 8

(Clinical Week 10)

Day

Stage

Event

50

Stage 20

51

    

52

Stage 21

53

    

54

Stage 22

55

 

56

Stage 23

Week 9

(Clinical Week 11)

Day

Stage

Event

57

Fetal Period

58

    

59

 

60

    

61

 

62

    

63

 

Week 10

(Clinical Week 12)

Day

Stage

Event

64

Pancreas – insulin secretion begins.

65

    

66

 

67

    

68

 

69

    

70

 

Week 11

(Clinical Week 13)

Day

Stage

Event

71

Thyroid Gland - colloid appearance in thyroid follicles, iodine and thyroid hormone (TH) synthesis.

72

    

73

 

74

    

75

 

76

    

77

 

Second Trimester

(Clinical Week 14)

Week

Stage

Event

12

Clinical second trimester

13

    

14

15

  

Week 15 – glucagon detectable in fetal plasma

16

 

17

    

18

 

19

    

20

    

21

    

22

    

23

    

24

    

25

  

Respiratory - end month 6 alveolar cells type 2 appear and begin to secrete surfactant

Third Trimester

(Clinical Week 28)

Week

Stage

Event

26

Clinical third trimester

27

 

28

  

Respiratory - month 7 respiratory bronchioles proliferate and end in alveolar ducts and sacs

29

 

30

    

31

 

32

    

32

    

34

    

35

    

36

  

37

    

38

Birth

Clinical Week 40

Heart- pressure difference closes foramen ovale leaving a fossa ovalis

Glossary of Terms

A | B | C | D | E | F | G | H | I | J | K | L | M | N | O | P | Q | R | S | T | U | V | W | X | Y | Z

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UNSW Embryology ISBN: 978 0 7334 2609 4

UNSW CRICOS Provider Code No. 00098G