Ib 131 Lec 2: Embryology

Front 1

[Week 1 of Embryonic Period]

name the 5 stages of first week

Back 1

1. Zygote
2. 4-cell
3. Morula solid cluster of 12–16 cells
4. Early blastocyst
5. Late blastocyst (implants at this stage)

Front 2

Fertilization occurs in the ___

Back 2

uterine tube/ uterus tube

Front 3

Blastocyst has two parts they are? and they forms to what?

Back 3

• Inner cell mass—forms embryo
• Trophoblast—helps form placenta

Front 4

Day 7-- how does implantations begins?

Back 4

**Day 7: Implantation begins as trophoblast invades into
uterine wall

Front 5

[Week 2]

Day 9:
Implantation continues; inner
cell mass forms _____

Back 5

bilaminar disc

Front 6

• Bilaminar embryonic disc—inner cell mass divided into two sheets _____ and ________

Back 6

Epiblast and hypoblast

Front 7

Day 11: Implantation is complete, what forms?

Back 7

amniotic sac and yolk sac form

Front 8

[Week 3-The Three-Layered Embryo]

Primitive streak—

Back 8

raised groove on the
dorsal surface of the epiblast

Front 9

Gastrulation

Back 9

a process of the embryo
growing from a two-layered disc (with
epiblast and hypoblast layers) to a three layered disc with three germ layers (endoderm, mesoderm, & ectoderm) which are all derived from the epiblast

Front 10

Week 3-The Three-Layered Embryo with three primary germ layers:

Back 10

endoderm, mesoderm, and ectoderm

Front 11

Germ layers begin to form at about day 14 -15 when a raised groove called the _______ appears on the
dorsal surface of the epiblast

Back 11

primitive streak

Front 12

Which germ layers appear first?

Back 12

endoderm, mesoderm, ectoderm

Front 13

Endoderm—formed from

Back 13

migrating cells that replace the hypoblast

Front 14

Mesoderm—formed

Back 14

between epiblast and endoderm

Front 15

Ectoderm—formed from

Back 15

epiblast cells that
stay on dorsal surface

Front 16

[Week 3: The Notochord]


Primitive node—

Back 16

a swelling at one end of
primitive streak

Front 17

Notochord rod appears on day 16 and develops from

Back 17

primitive node

Front 18

Notochord rod is made up
primarily

Back 18

mesodermal cells as well as some endodermal cells

Front 19

Notochord

Back 19

defines body axis and forms the midline that divides the left and right sides of the body

Front 20

Notocord extends the length of the body and is
the future site of the

Back 20

vertebral column

Front 21

[Week 3: Neurulation]

Neurulation—as the notochord develops, it signals the

Back 21

as the notochord develops, it
signals... the surrounding ectoderm to start forming
brain and spinal cord

Front 22

Neurulation consist of the

Back 22

Neural plate and Neural groove

Front 23

how is the Neural groove form?

Back 23

ectoderm of neural plate folds
inward until a hollow neural tube is pinched off
into the body

Front 24

how is the Neural plate form?

Back 24

ectoderm in the dorsal midline
thickens to form neural plate

Front 25

Induction

Back 25

Ability of one group of cells to influence developmental
direction of other cells

e.g Notochord signals which stimulate the surrounding
ectoderm to start forming brain and spinal cord is an
example of induction

Front 26

Week 3: Neurulation:


Neural tube

Back 26

a hollow tube

Front 27

Cranial part of the neural tube becomes the

Back 27

the
brain and the rest becomes the spinal cord

Front 28

Closure of the neural tube begins at end of

Back 28

week 3 and is complete by the end of week 4

Front 29

Maternal folic acid deficiency can cause

Back 29

fetal neural tube defects

Front 30

how is the Neural crest made?

Back 30

Cells originate from ectodermal cells on the lateral ridges of the neural plate

Front 31

Neural crest forms

Back 31

sensory nerve cells which are
positioned just external to the closed
neural tube

Front 32

[Week 3: Mesoderm Differentiation]

Somites: In the developing vertebrate embryo, somites are

Back 32

are masses of mesoderm
distributed along the two sides of the neural tube

**our first body segments

Front 33

somites will eventually become

Back 33

eventually become dermis
(dermatome), skeletal muscle (myotome), and vertebrae (sclerotome)

Front 34

Paraxial mesoderm

Back 34

Somites —our first body segments
– Paraxial mesoderm: area of the mesoderm
that forms just lateral to the neural tube on both
sides
– Paraxial mesoderm: starting cranially and
proceeding caudally, the paraxial mesoderm
divides into the series of blocks called somites
– Somites are the first body segments and about
40 pairs form by the end of the 4th week
– The somites are visible in surface view as a row
of subepidermal bulges on each side of the
back

Front 35

[Week 3: The Mesoderm Begins to Differentiate]

Intermediate mesoderm

Back 35

• Intermediate mesoderm—begins as a
continuous strip of tissue just lateral to the
paraxial mesoderm
–Each segment of intermediate mesoderm
is attached to a somite (Fig 3.7b)
– Influenced by the segmentation of
somites

Front 36

Week 3: Mesoderm Differentiation

• Lateral plate

Back 36

plate—most lateral part of the mesoderm
splits into two layers (somatic mesoderm &
splanchnic mesoderm) which have a wedge of
space in between them called a coelom

Front 37

Coelom becomes serous body cavities for the

Back 37

peritoneal (abdominal), pericardial (cardiac), and
pleural (lung) cavities

Front 38

Two layers develop from the lateral plate

Back 38

Somatic mesoderm—next to ectoderm
• Splanchnic mesoderm—next to endoderm

Front 39

[Week 4: Body shape develops]

Back 39

The embryo folds laterally

Front 40

at the head and tail ________ bulges upward

Back 40

Embryonic disc

Front 41

Lateral folding is a result of the

Back 41

the fast growing
of somites

Front 42

The folding at the head and tail is caused by

Back 42

expansion of the brain and the lengthening of the spinal cord

Front 43

“Tadpole shape” by Day

Back 43

Day 24 after conception

Front 44

Primitive gut emerges: site of future...

Back 44

digestive tube and respiratory structures

Front 45

What are the Derivatives of ectoderm?

Back 45

• Brain
• Spinal cord
• Epidermis of skin

Front 46

Epidermis of skin can later produce

Back 46

hair, fingernails, toenails, sweat glands, and skin oil glands

Front 47

Neural crest cells of the ectoderm give rise to

Back 47

sensory nerve cells, pigment producing cells in the skin (melanocytes), certain bones of the head, and certain blood vessels of the head

Front 48

What are the derivatives of endoderm?

Back 48

• Inner epithelial lining of the gut tube
and its derivatives: respiratory
tubes, digestive organs, and urinary
bladder
• Secretory cells of glands that
develop from gut-lining epithelium
e.g., the liver and pancreas

Front 49

[Mesoderm differentiation]

Mesoderm actively differentiates during

Back 49

4th week

Front 50

Derivatives of Mesoderm?

Back 50

• Somites
• intermediate mesoderm
• Lateral plate: somatic and splanchnic mesoderm
• Notocord

Front 51

[Mesoderm]

• Notochord:

Back 51

nucleous pulposus of ntervertebral discs

Front 52

Somites divide into: (3)

Back 52

1. Sclerotome ("hard piece")
2. Dermatome ("skin piece")
4. Myotome ("muscle piece")

Front 53

Sclerotome (“hard piece”):

Back 53

these cells migrate and
gather around the notochord and the neural tube and
form the vertebrae and ribs at the associated level

Front 54

Dermatome (“skin piece”):

Back 54

the most lateral part of
each somite; these cells migrate to form the dermis
(not epidermis) of the skin in the dorsal part of the
body

Front 55

Myotome (“muscle piece”):

Back 55

these cells form trunk
and limb muscle tissue

Front 56

Intermediate mesoderm forms:

Back 56

Kidneys and gonads

Front 57

Mesoderm from lateral plate (what are the two lateral plate?)

Back 57

– Splanchnic mesoderm
– Somatic mesoderm

Front 58

– Splanchnic mesoderm forms:

Back 58

• Forms musculature, connective tissues, and walls
(but not epithelial lining) of digestive and
respiratory tracts
• Visceral serosa of the digestive and respiratory
structures
• Heart and most blood vessels

Front 59

– Somatic mesoderm forms:

Back 59

• Just external to the coelom
• Parietal serosa
• Dermis (not epidermis) of ventral body region
• Bone, ligament, and dermis formation of limbs

Front 60

what is dermis?

Back 60

The lower or inner layer of the two main layers of cells that make up the skin.The dermis contains blood vessels, lymph vessels, hair follicles, and glands that produce sweat, which helps regulate body temperature, and sebum, an oily substance

Front 61

Embryonic development: week 4

Back 61

• 2 mm long embryo with C shape at
beginning of week 4 (Fig 10-9)
• Eyes began to form on head
• Inner ear development begins
• Pharyngeal arches develop in neck
area which will develop into jaws, ear
and other structure
• Heart forms and begins beating
• Tiny arm and leg buds develop

Front 62

What forms during week 4?

[Week 5-8 – The Second Month of Embryonic Development]

What is seen in this 2n months?

Back 62

• Limb buds form
• Embryo first looks recognizably human (week 8)
• Head is disproportionately large
• All major organs are in place

Front 63

Embryonic development: week 5

Back 63

• Rapid growth of brain
• Arm buds flatten and hands
become paddle shaped (Fig 10-9)
• 1 cm in length by end of week

Front 64

Embryonic development: week 6

Back 64

• Eyes become pigmented
• Exterior ears began to form (Fig 10-9)
• Head/brain continues to grow
• Leg bud becomes paddle shaped
• Hand rays indicate positions of digits
• Distinct tail is still present

Front 65

Embryonic development: week 7

Back 65

• Toe rays form indicating position of
digits (Fig 10-9)
• Rapid development of gut tube causes
intestines to protrude into the umbilical
cord to produce an umbilical herniation
• Tail is diminished

Front 66

Embryonic development: week 8

Back 66

• 1.25 inches long by the end of week 8
• Eyelids have grown to meet each other and fuse
so eyes are closed
• Fingers and toes can be clearly seen, however, a
thin sheet of webbing still exists between each
digit (Fig 10-9)
• Tail has disappeared
• Embryo now begins to look human
• Brain, spinal cord, and peripheral nerves are all
developed

Front 67

Fetal Period

Back 67

• By week nine there has been
sexual differentiation with
development of male or female
external genitalia
• Organ systems established in the embryonic period continue to develop and differentiate
• Period of rapid growth

Front 68

Fetal period: Week 12 (end of first trimester)

Back 68

• fetal heart rate can be heard with a
stethoscope
• Fetus can react to stimuli and fetal
movements begin, however mom can not
yet feel these movements

**(month 4-5 gestation)--> mom may began to feel fetus moving

Front 69

Fetal period: End of month 6 (2nd trimester)

Back 69

• Skin covered with protective layer of
fatty secretions called vernix caseosa
• Skin grows layer of downy hair (lanugo)

Front 70

Fetal period
• 3rd trimester (months 7, 8, & 9)

Back 70

• Fetus adds layers of fat and loses its
wrinkled appearance
• Lungs mature