104 - Development 1

Question 1

Frequency of birth defects

Answer 1

~1:33 live births

Question 2

Most-common structural defects

Answer 2

Heart defects (~1:200)

Question 3

Rate of initial division of fertilised egg

Answer 3

Division every 24 hours

Question 4

Stage of development at 3 days

Answer 4

Morula (16 cells)

Question 5

Stage of development at 4 days

Answer 5

Blastocyst undergoes cavitation to form a blastocoele

Question 6

Where is the egg fertilised?

Answer 6

Fallopian tube

Question 7

Morula

Answer 7

16-cell stage, at around 3 days

Question 8

Arrangement of cells in a blastocyst

Answer 8

Two cell types: trophoblast (outer epithelial layer), inner cell mass (that becomes the embryo). Trophoblast forms a ring around the inner cell mass and the blastocoele

Question 9

What does the trophoblast do?

Answer 9

Forms some extraembryonic structures like the placenta.

Question 10

When does the blastocyst implant into the uterine wall?

Answer 10

5 - 10 days

Question 11

Formation of bilaminar disc 1 2 3

Answer 11

1) Inner cell mass splits into the epiblast and hypoblast. 2)Part of the epiblast becomes the embryo. 3) Hypoblast expands to line interior of trophoblast to form the yolk sac.

Question 12

Role of the yolk sac in humans

Answer 12

Not much. Doesn’t fill with yolk, embryo relies on maternal supply of nutrients.

Question 13

Gastrulation

Answer 13

Formation of endoderm, mesoderm and ectoderm from bilaminar disc (epiblast layer).

Question 14

Broad derivatives of ectoderm

Answer 14

Nervous system and epidermis

Question 15

Broad derivatives of mesoderm

Answer 15

Blood, heart, kidneys, gonads, most bones, connective tissues

Question 16

Broad definition of endoderm

Answer 16

Epithelium of gut and associated organs

Question 17

Neural tube formation 1 2 3 4

Answer 17

1) Notochord induces overlying ectoderm to form neural plate 2) Neural plate forms neural groove 3) Neural plate folds around groove to form neural tube 4) Neural tube is formed, with neural crest sandwiched between neural tube and epidermis

Question 18

Notochord

Answer 18

Formed from mesoderm. First structure to form in an embryo, runs down midline of developing embryo.

Question 19

Role of notochord

Answer 19

Organisation of embryo

Question 20

*Neural tube formation

Answer 20

Question 21

Neural crest derivatives

Answer 21

Largely PNS. • Dorsal root ganglia • Sympathetic and parasympathetic ganglia • Enteric ganglia • Schwann cells • Melanocytes • Dentine • Muscle, cartilage and bone of skull, jaws, face and pharynx

Question 22

Prevalence of cleft palate

Answer 22

1:1000 live births

Question 23

How does cleft palate come about?

Answer 23

Issue with migration of neural crest cells.

Question 24

Mesodermal derivatives

Answer 24

• Dermis • Muscles • Skeleton • Urogenital tract • Heart and blood vessels • Wall of gut and respiratory tract • Haemopoietic tissue • Pleura, peritoneum, pericardium

Question 25

Difference between mesoderm and mesenchyme

Answer 25

Mesoderm is one of the three germ layers. Mesenchyme refers to the shape and behaviour of cells. Used in contrast to epithelial cells (epithelial cells crowd together, form sheets, mesenchymal cells lose contact with one another, move independently, are motile).

Question 26

Divisions of mesoderm 1 2 3

Answer 26

1) Paraxial mesoderm (closest to midline) 2) Intermediate mesoderm 3) Lateral mesoderm (further from midline)

Question 27

Fate of paraxial mesoderm

Answer 27

• Dermis of skin • Axial skeleton • Axial and limb muscles

Question 28

Fate of intermediate mesoderm

Answer 28

Urogenital system

Question 29

Fate of lateral mesoderm

Answer 29

• Ventrolateral body wall • Limb skeleton • Visceral pleura, peritoneum • Blood vessels and blood forming tissue • Heart • Wall of gut and respiratory tissues

Question 30

Organisation of paraxial mesoderm

Answer 30

• Swellings (somitomeres) appear progressively down length of paraxial mesoderm • At the 20 somitomere stage, the eighth pair of somitomeres becomes an independent pair of somites • Somitomeres are replaced by somites from the 8th somite caudally.

Question 31

Somites

Answer 31

Somitomeres become independent from paraxial mesoderm from the 8th somitomeres caudally, become somites.

Question 32

Where is the 8th somitomere?

Answer 32

Equivalent of the neck. Above this becomes the head, below becomes the rest of the body

Question 33

*Development of somites 1 2

Answer 33

1) Somites split into sclerotome and dermomyotome.
2) Dermomyotome develops into dermatome and myotome.

Question 34

What do the divisions of somites become? 1 2 3

Answer 34

1) Sclerotome becomes axial skeleton 2) Dermatome becomes dermis of skin 3) Myotome becomes axial muscles, appendicular muscles

Question 35

What forms the axial skeleton and appendicular skeleton?

Answer 35

Sclerotome (from paraxial mesoderm) becomes axial skeleton. Lateral mesoderm becomes appendicular skeleton

Question 36

When does limb development begin?

Answer 36

End of fourth week of development

Question 37

What initiates limb development?

Answer 37

Mesoderm

Question 38

How do limb dermatomes come about?

Answer 38

When limb is budding, it pulls overlying ectoderm with it.

Question 39

How does the mesoderm form a limb? 1 2 3

Answer 39

1) Mesoderm forms a free limb patch, which will become a limb. 2) If free limb patch is removed, surrounding cells will compensate. 3) If whole patch is removed, no limb will develop

Question 40

Limb development 1 2 3

Answer 40

1) Mesoderm forms free limb patch, which begins limb development. 2) Overlying ectoderm forms apical ectodermal ridge, takes over limb development. 3) Damage to ectoderm can result in issues in limb development (EG: diplopodia). Ectoderm is fragile, relatively easy to mechanically injure.

Question 41

Name for developmental fusion of fingers

Answer 41

Syndactyly