Anatomy- Somite Stages And Limb Buds

Front 1

What happens during the first 2 weeks of human development?

Back 1

1.formation of zygote
2. implantation
3. formation of bilaminar embryo

Front 2

What is the name of the period between weeks 3-8 in human development?

Back 2

embryological period

Front 3

What is the name of the period between weeks 9-38 in human development?

Back 3

fetal period

Front 4

What thickens to form the paraxial mesoderm and where is it located?

Back 4

intraembryonic mesoderm which is located on each side of the forming notocord and neural tube

Front 5

What does the paraxial mesoderm divide into and when does it do this?

Back 5

paired bodies called somites and this happens by the end of the 3rd week.

Front 6

What do the somites give rise to?

Back 6

1.axial skeleton (vertebrae, ribs)
2. associated musculature
3. adjacent dermis of skin

Front 7

Where does the 1st pair of somites develop and where do the rest develop in relation to the first?

Back 7

posterior to the cranial end of the notocord and the rest form caudally

Front 8

How many somites form and for what period do they form?

Back 8

around 42-44 pairs form from days 20-30

Front 9

How is somite development used as a tool?

Back 9

used to determine age of the embryo

Front 10

What does each somite become differentiated into and what arises from these structures?

Back 10

1.ventromedial sclerotome (vertebrae and ribs)
2. myotome (muscles)
3. dermatome (skin)

Front 11

By what week are the somites and neural tube well formed but is open at the rostral and caudal neuropores?

Back 11

beginning of 4th week

Front 12

When do upper limb buds become recognizable?

Back 12

during week 4 (day 26-27)

Front 13

When do the lower limb buds become recognizable?

Back 13

by the end of week 4 (day 28)

Front 14

Why do the upper limb buds appear low on the embryo?

Back 14

due to dominance of development of head and neck

Front 15

What do the upper and lower limb buds form opposite from?

Back 15

1. upper form opposite to the caudal cervical segments
2. lower form opposite to the lumbar and upper sacral segments

Front 16

What is the structure of the limb buds?

Back 16

1.consists of a mass of mesenchyme derived from the somatic mesoderm
2. covered by a layer of ectoderm
3. at the tip ectoderm cells form a apical ectodermal ridge

Front 17

What is the purpose of the apical ectodermal ridge?

Back 17

promotes growth and development of the limbs

Front 18

Activation of the fibroblast growth factors and T-box genes from the apical ectodermal ridge activates the mesenchymal cells which causes what?

Back 18

expression of the Sonic Hedgehog (Shh) gene which controls patterning of the limb along the anterior-posterior axis.

Front 19

Expression of Wnt-7 and EN-1 specifies dorsal-ventral patterning. Which one expresses which direction?

Back 19

Wnt7 expresses dorsal specificity
EN-1 expresses ventral specificity

Front 20

What happens during week 5?

Back 20

1. bones appear as mesenchymal condensation in the limb buds
2. upper limbs show regional differentiation with developing hand plates

Front 21

What happens during week 6 of human development?

Back 21

1. mesenchymal models of bones undergo chondrification to form hyaline cartilage
2. further differentiation in limb buds

Front 22

The clavicle develops by what process?

Back 22

intramembranous ossification

Front 23

Where do cartilage models form sooner?

Back 23

1.upper limb
2. proximodistal sequence

Front 24

What becomes identifiable in the upper limb buds during week 6?

Back 24

elbow and wrist regions

Front 25

The hand plates develop into what during week 6 and what does this eventually become?

Back 25

digital rays that eventually will become thumb and fingers

Front 26

What is contained at the tip of each digital ray?

Back 26

apical ectodermal ridge

Front 27

How is the development of the lower limb in relation to the upper limb?

Back 27

always slower by a few days

Front 28

What happens to the loose mesenchyme between the digital rays during week 7?

Back 28

breaks down and notches begin to appear between each ray

Front 29

What happens during week 7 of human development?

Back 29

1.notches appear between digital rays in hand
2. digital rays form in foot plate
3. ossification in long bones begins

Front 30

What are the primary centers of ossification of the long bones?

Back 30

diaphyses

Front 31

What forms the limb muscles?

Back 31

myogenic precursor cells that migrate into limb buds and become myoblasts

Front 32

Where are the myoblasts derived from and what genes are expressed there?

Back 32

dorsolateral muscle forming region of the somite which expresses MyoD and myf-5

Front 33

Expression of MyoD results from?

Back 33

influence of activating Wnt proteins and inhibitory BMP-4 proteins

Front 34

Originally (before rotation), how are the flexor and extensor muscles placed?

Back 34

flexor is ventral and extensor is dorsal

Front 35

After rotation, how are extensor muscles placed in the upper limb?

Back 35

rotated 90 degrees on the longitudinal axis so extensors lie lateral and posterior

Front 36

After rotation where are the extensor muscles in the lower limb?

Back 36

rotation is 90 degrees in the opposite direction of the upper limb and extensors face anteriorly

Front 37

The radius and ulna are homologous to what other bones in the lower limb (think due to rotation)?

Back 37

Radius is homologous to tibia
Ulna is homologous to fibula

Front 38

What is the last week of embryonic life?

Back 38

week 8

Front 39

What happens during the beginning of week 8 in human development?

Back 39

1.digits of hand are short and webbed
2. notches develop between the digital rays of the feet

Front 40

What happens during the end of week 8 in human development?

Back 40

1.apparent regions of the limbs, long fingers,and distinct toes

Front 41

What happens during weeks 9-12 of human development?

Back 41

1.short legs and small thighs form(week 9)
2. upper limbs have reached final relative length but lower limbs have not(end of week 12)
3. primary centers are present in all long bones

Front 42

Where are the secondary ossification centers formed?

Back 42

epiphyses

Front 43

Where are the first secondary ossification centers formed?

Back 43

distal end of femur and proximal end of tibia

Front 44

What intervenes between the diaphysis and epiphysis?

Back 44

epiphysial cartilage plate

Front 45

What is the area of skin innervated by a single spinal nerve and its dorsal root ganglion?

Back 45

dermatome

Front 46

Peripheral nerves grow from where into the mesenchyme of the limb buds during week 5?

Back 46

brachial and lumbar plexuses

Front 47

The limb buds are supplied by what to form the vasculature?

Back 47

branches of the intersegmental arteries from the aorta

Front 48

What initially supplies the limb bud with blood and what initially drains the limb bud?

Back 48

a primary axial artery and its branches supplies the limb bud and a peripheral marginal sinus drains it.