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Embryology: Summer Semester > Unit 2.L1-Development of Limbs, Integumentary System, Body Cavities, Mesenteries & Diaphragm > Flashcards

Unit 2.L1-Development of Limbs, Integumentary System, Body Cavities, Mesenteries & Diaphragm Flashcards

1
Q

What are the 4 cellular processes that promote Limb formation?

A
  1. Cell divison promotes the growth of limb
  2. Cell migration causes cells to reach their correct location
  3. Cell Differentiation produces specialized cells, such as muscle cells
  4. Apoptosis eliminates cells in between fingers
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2
Q

By Day 26 & Day 28 respectively what appears and from where?

A

By Day 24, upper limb buds & Day 26 lower limb buds appears from the somatic lateral mesoderm.

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3
Q

What appears from the somatic lateral mesoderm by Day 26, Day 28?

A
  • Day 24→Upper limb buds
  • Day 26→Lower limb buds
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4
Q

What does the upper and lower limb buds contain? (2)

A

The bud has a mesenchyme core & outer epithelial ectoderm (comes from epiblast)

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5
Q

What migrates into the buds from the somites?

A

The muscle cells migrate into the bud from the somites.

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6
Q

What is present underneath the tip of the limb buds and what is its function?

A

Progress zone (PZ) (underneath the tip of the bud) has dividing & proliferating mesenchyme, which elongates the limb buds

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7
Q

What lays above the progress zone (PZ) and what is its function?

A

The epithelial Apical Ectodermal Ridge(AER) (lays above the progress zone) and initiates limb bud formation

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8
Q

Where does the Upper limb buds appear and what grows faster compared to it?

A

Upper limb buds appear low as the cranial half grows faster

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9
Q

Upper limb buds form opposite to what?

A

Upper limb buds form opposite to the caudal cervical segments

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10
Q

Lower limbs form opposite to what?

A

Lower limb buds form opposite to the lumbar/upper sacral segments

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11
Q

What are the 2 developmental fields/organizing centers that are formed in the early limb? And include their locations

A
  1. Apical Ectodermal Ridge (AER) at the limb bud tip (anterior)
  2. Zone of Polarizing Activity(ZPA) with 2 PZ (Progress Zones) at the posterior by aggregation/condensation of mesenchymal cells

Limb patterning is regulated by positioning information

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12
Q

What is the location and function of the Apical Ectodermal Ridge (AER)?

1 of 2 developmental fields/oganizing area

A

The AER at the distal border, induces proliferation of the underlying undifferentiated mesenchyme, elongating the limb bud

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13
Q

What is function of the Zone of Polarizing Activiy (ZPA)?

A

When this zone of proliferating cells (proliferating/progress zone; PZ) begin differentiation and condense into the cartilage precursors, initiation of limb bones begin

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14
Q

What are the 2 Progress zones of the Zone of Polarizing Activity (ZPA)?

A
  • The proximal PZ
  • The distal PZ (tip)
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15
Q

What does the Promixal PZ differenitate into?

Part of the Zone of Polarizing Activity (ZPA)

A

The proximal PZ differentiate into blood vessels & cartilage bone models

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16
Q

What does the distal PZ (tip) differentiate/flatten into?

Part of the Zone of Polarizing Activitiy (ZPA)

A

The distal PZ (tip) of the limb buds flatten into hand plates and foot plates

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17
Q

Upper limbs develop __________ than lower limbs

A

earlier

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18
Q

By Day 44 of hand formation, what condenses and what does it form?

Day 32-56, Wk 5-8

A

By Day 44, mesenchyme in the hand plates condense to form digital rays, forming fingers in the hand plates.

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19
Q

How are fingers in the the hand plate formed?

A

Mesenchyme in the hand plate condensing to form digital rays

Footplate develops in the same way

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20
Q

By day 48 of foot development, what condenses and what does it form?

A

By Day 48, mesenchyme in the foot plates condense to form digital rays, forming toes in the foot plates.

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21
Q

What is present at the tip of each digital ray (formed in the hand and foot plate) and what does it become?

A

At the tip of each digital ray, the AER induces the mesenchyme to become bone primordia (phalanges)

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22
Q

What induces mesenchyme (at the tip of each digital ray) to become bone primordia (phalanges)?

A

Apical Ectodermal Ridge (AER)

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23
Q

What happens to the mesenchyme between the digital rays and what is formed?

A

The mesenchyme between the digital rays apoptose and separate digits. This form fingers and toes by eighth week

Apoptose: death of cells that is normal

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24
Q

When are fingers and toes formed by in the developing fetus?

A

By the eight week

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25
Q

What forms bone models?

A

Mesenchymal cellular condensation

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26
Q

What occurs to the bones model in the 5th week, 6th week, 7th week and 12th week of development?

  • 5th week: What centers appear?
  • 6th week: What is the limb skeleton made of?
  • 7th week: What begins in the primary ossification centers?
  • 12th week: What is present in all long bones?
A
  • 5th week: Chondrification centers appear.
  • 6th week (Day 42): The limb skeleton is cartilaginous
  • 7th week: Osteogenesis of long bones begins in the primary ossification centers.
  • 12th week: Ossification centers are present in all long bones
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27
Q

What occurs with the fingers and toes by day 52?

A
  • The fingers separate toes begin to separate.
  • Feet are fan shaped but toes have not separated.
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28
Q

What occurs to the fingers and toes by day 56? And what other features are visible?

A
  • Digits of the hands and feet are separated.
  • Elbows , Knees and distinct digits visible.

Rotation occurs during this time

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29
Q

How do the Upper limbs rotate? and where do the elbows point?

By day 56

A
  • Upper limbs rotate laterally by 90 degrees
  • Elbows come to point dorsally & point Caudally
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30
Q

How do Lower limbs rotate? And where do the knees point?

By day 56

A
  • Lower limbs rotate medially by 90 degrees
  • Knees come to face ventrally & point Cranially
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31
Q

Development of what by the 5th week provides innervation of the limb?

A

Development of the Dermatomal Patterns & Cutaneous Innervation of Limbs

From the Pre-axial mesoderm

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32
Q

What grows into the dorsal and ventral masses of the limb buds?

5th week

A

Motor axons & later Sensory axons (from the spinal cord) grow into the dorsal & ventral muscle masses of the limb buds

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33
Q

What type of cells do neural crest cells give rise to? and what does it form?

5th week

A

Neural crest cells give rise to Schwann cells, myelin sheath surround motor/sensory nerve fibers in the limbs and form the Neurolemma (aka Sheath of Schwann)

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34
Q

Where does every dermatome originate from? And has an areas of skin innervated by what?

5th week

A

Every dermatome originates from a single somite & has area of skin innervated by a single spinal nerve & its spinal ganglion

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35
Q

The dorsal dermatome is also called the? and which somites are present in the upper and lower limb?

5th week

A
  • Preaxial border
  • Upper Limb: Cervical somites C3-C6; Lower Limb: Lumbar somites L2-L4
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36
Q

The ventral dermatome is also called the? and which somites are present in the upper and lower limbs?

5th week

A
  • Postaxial border
  • Upper Limb: Cerivcal and Thoracic somites C7-T2
  • Lower Limb: Lumbar and Sacral somite L5-S3
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37
Q

What seperates the preaxial and postaxial borders in the upper and lower limbs?

5th week

A

Ventral axial line

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38
Q

What is caused by medial rotation of the lower limb?

5th wk

A

Original ventral surface of the lower limb goes to the back of the adult limb

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39
Q

Where does L5 and L2 (somites) of the lower limb rotate towards?

5th wk

A

L5 and L2: Rotated towards the posterior aspect

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40
Q

Where does S1, S2, and S3 (somites) of the lower limb move to?

5th wk

A

S1, S2, S3: Moves to the center at the ventral axis

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41
Q

Where does the developing blood supply to the upper limb start from?

A

Dorsal aorta

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42
Q

What does the dorsal aorta become before it enters the upper limb bud?

A

Intersegemental arteries

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43
Q

Where do intersegmental arteries go and what arteries do they become?

A

Intersegmental Arteries enter the upper limb bud and bifurcates into the Primary axial artery which becomes the Branchial artery (proximal arm)

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44
Q

What are the 4 branches of the brancial artery (proximal arm)?

A
  1. Ulnar
  2. Radial
  3. Medial
  4. Anterior Interosseous arteries
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45
Q

What does the Ulnar and Radial branches of the branchial artery form?

A

Palmer arches

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46
Q

Where does the developing blood supply to the lower limb start from?

A

Dorsal Aorta

(Umbilical, Common/External Iliac arteries)

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47
Q

What other important vessels that formed in the upper limbs? (2)

A
  • Deep Superficial palmar arch
  • Fine Capillary Network in limb mescenhyme & hand plate
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48
Q

What does the Dorsal Aorta bifurcate into in the Lower limbs? What does it give rise to?

A

The common Iliac artery which gives rise to the:
1. Primary axial artery
2. External Iliac artery

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49
Q

Which artery does the primary axial artery give rise to in the lower limb buds?

A

Deep artery of the thigh (profunda femoris)

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50
Q

Which arteries does the External Iliac artery of the lower limb give rise to? (2)

A

Femoral artery→Popliteal artery

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51
Q

Which arteries does the Popliteal artery (from the ext. iliac artery) in the lower limbs give rise to? (3)

A
  1. Fibular artery
  2. Anterior tibial artery
  3. Posterior tibial artery
  • Lateral Planter Artery
  • Medical Planter Artery
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52
Q

What are the foot & toe capillaries and where do they arise from?

A
  • Lateral Planter Artery
  • Medial Planter Artery
  • Arise from the Posterior tibial artery
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53
Q

When do limb defects occur in fetuses and how often?

A
  • D24 -36: Limb defects occur during the most critical period of limb development.
  • Common: 1:500 neonates

Causes include genetics, environmental (tabacoo, alcohol)

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54
Q

Birth Defect of the Limbs

What is Quadruple Amelia and what causes it?

A
  • Quadruple Amelia means all four limbs are missing
  • Cause was Thalidomide (teratogen) that is most potent at 3-5 week stage

  • Amelia: Absense of limbs
  • Thalidomide a medication from Europe that helped treat morning sickness
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55
Q

Birth Defect of the Limbs

What is Meromelia?

A

Partial limb formation

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56
Q

Birth Defect of the Limbs

What is Sironomelia (Mermaid Syndrome)? and is cause known?

A
  • Caudal dysgenesis: lower limbs fused; appears like a mermaid’s tail
  • Exact cause unknown; sporadic!
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57
Q

Birth Defect of the Limbs

What are some examples (5) of split hand/foot malformations (SMFMs) and what is the cause?

A
  • Bifurcated (forked) hand
  • Cleft foot
  • Absence of one or more central digits
  • Fingers missing
  • Toes missing
  • Cause: Failure of development of one or more digital rays
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58
Q

Birth Defect of the Limbs

What is Brachydactyl and what type of genetic trait is it? What clinical manifestation is seen?

A
  • Shortness of the digits (fingers or toes) due to reduction in the length of the phalanges
  • Dominant inherited trait
  • Shortness of body or overall short stature
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59
Q

Birth Defect of the Limbs

What is Polydactylyl and what type of gentetic trait is it?

A
  • Shows more than five digits on the hands or feet.
  • Extra digits are called “supernumerary digits”
  • Dominant inherited trait.
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60
Q

Birth Defect of the Limbs

What are the extra digits caused by Polydactylyl called?

A

Supernumerary digits

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61
Q

Birth Defect of the Limbs

What are the two types of Syndactyly?

A
  1. Cutaneous Syndactylyl
  2. Osseous Syndactylyl
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62
Q

Birth Defect of the Limbs

What is Cutaneous Syndacytyl? Where is it more frequent? And what causes it?

A
  • Simple webbing between digits is called “cutaneous syndactyly” . It is seen more frequently in the foot than in the hand.
  • Cause: Failure of the webs to degenerate between two or more digits due to blockade of cell apoptosis; thus, the digits do not separate
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63
Q

Birth Defect of the Limbs

What is Osseous Syndactyly and what causes it? Where is it seen frequently?

A
  • Fusion of bones (synostosis).
  • Cause: Notches between the digital rays fail to develop & digits do not separate. Seen frequently between the third and fourth fingers and between the second and third toes
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64
Q
  • What is Talipes equinovarus aka Clubfoot?
  • How common is it and what is the cause?
  • Explain the characteristics present (What is the position of the foot and what does it cause? Where is the sole of the foot turned? The foot is what? How is it seen in 50% of the cases? Who gets affected more?)
  • What is the treatment?
A
  • Talipes equinovarus (Latin talus (ankle) + pes (foot)) or clubfoot is a common birth defect with musculoskeletal deformation
  • 1:1000 births
  • Cause: Multifactorial inheritance

Characteristics

  • Abnormal position of the foot does not allow normal weight bearing
  • The sole of the foot is turned medially
  • The foot is inverted (incurving)
  • Seen bilaterally in 50% of cases
  • Occurs twice as frequently in males
  • Treatment: Casting or taping & physiotherapy
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65
Q

Limb buds appear _______ of gestation as ________ on the __________.

A

Limb buds appear 24-28th day of gestation as slight bulges on the ventrolateral body wall

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66
Q

Upper limbs develop _______ of lower limbs from ___________ and _________.

A

Upper limb buds develop 2 days ahead of lower limb buds from mesoderm + ectoderm.

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67
Q

The limb buds elongate by ________ of the __________.

A

The limb buds elongate by proliferation of the mesenchyme

68
Q

_________ degenerates tissues in the ________ between the digital rays.

A

Cell apoptosis degenerates tissues in the notches between the digital rays

69
Q

_______ are derived from mesenchyme (myogenic precursor cells;myoblast) originating in the ___________. ________ convert to ________ to form mature muscles.

A

Limb muscles are derived from mesenchyme (myogenic precursor cells; myoblast) originating in the somites. Myoblast convert to myotubes to form mature muscles.

70
Q

Myoblasts migrate and form ___________ and _________ muscle masses. __________ grow into these muscle masses.

A

Myoblasts migrate and form dorsal and ventral muscle masses. Nerves grow into these muscle masses.

71
Q

Blood vessel in the limb buds arise from the ____________.

A

Intersegmental arteries

72
Q

Many birth defects of the limb have ___________; may arise as a result of interaction of _____________.

A

Most birth defects of the limbs have hereditary influence; many arise as a result of interaction of genetic & environmental factors (multifactorial inheritance)

73
Q

What is the Integumentary System?

A

The Skin & Its appendages the protect humans

74
Q

How many layers does the skin has and where were they dervied?

A

Skin has two layers derived from two different germ layers:
1. Epidermis: Superficial epithelial tissue derived from surface ectoderm
2. Dermis: Deeper layer of connective tissue derived from mesoderm

75
Q

During the 4-5th week of development what is the epithelium of the surface ectoderm of the skin? what does it form?

A

The surface ectoderm of the skin is made of simple cuboidal epithelium and forms the primordium of the epidermis

76
Q

During the 7th week, What begins to happen to the simple cuboidal epithelial cells and what do they form?

A

The simple cuboidal epithelial cells start to proliferate and form TWO layers of squamous epithelium

77
Q

What are the 2 layers of the squamous epithelium? What occurs in each layer?

A
  • The 1st layer: The periderm→ keratinization→Desquamation (shedding)→Complete Exfoliation of peridermal cells forming part of vernix caseosa
  • The 2nd layer: The basal layer cells: replace the periderm and forms the “future stratum germinativum”
78
Q

What layer of skin is formed at 11 weeks and what does it contain and where is it located?

A

An intermediate layer, containing several cell layers, is interposed between the basal cells (future stratum germinativum) and the periderm

79
Q

Where do cells of the intermediate layers invade and what do they form?

A

Cells from this intermediate layer invade the dermis to form epidermal ridges, which form future fingerprints on digits

80
Q

What can be used for diagnosis of Chromosomal defects? (eg. Down Syndrome)

A

Abnormal and unique epidermal ridge pattern is used for diagnosis

81
Q

During the early fetal period, what is the epidermis invaded with? where are they derived from?

A

During the early fetal period the epidermis is invaded by melanoblasts, which are the cells derived from the neural crest cells in mesoderm

82
Q

Where do melanoblast move to and what do they differentiate into?

A

Melanoblasts move to dermoepidermal junction and differentiate into melanocytes (pigment-producing cells) between day 40-50 (late embryonic stage)

83
Q

What is involved in the differentiation of Melanoblasts into Melanocytes?

A
  • The formation of pigment granules (grain-like particles containing “Melanin” in “Melanosomes”)
84
Q

What are the unique type of melanin carried by the melanoblast/melanocytes and what is the outcome for each?

A
  • Eumelanins→Black/brown heads
  • Pheomelanins→Red heads

Some individuals can synthesis both
Phemelanins are more prone to skin cancer

85
Q

Where do Melanocytes reside and how does this affect skin color?

A
  • Melanocytes reside in epidermis with their dendrites
  • Dendrites carry melanosomes which secrete out the melanin which is taken up by kerationcytes into the epidermis/epithelial cells on top

How melanosomes are distrubuted determines skin color not how much is present

86
Q

What disappers and forms on the skin by the 21st week?

A
  • Periderm disappears
  • Multiple layers of the epidermis are formed by differing stages of keratinization
87
Q

What are the 5 layers of the epidermis?

A
  1. Stratum corneum (Horney top layer; dead corneocytes)
  2. Stratum lucidum (Smooth layer; Eleidin a product of Keratohyalin)
  3. Stratum granulosum (Granular layer)
  4. Stratum spinosum (Spinous polyhedral or prickle cell layer)
  5. Stratum basale (Stratum germinativum cell layer)

NOTE: At birth all adult epidermis layers are present

88
Q

What gives rise to two disctinct types of the epidermis and what are they?

A

Continuous inductive interactions with the dermis gives rise to the two distinct type of epidermis depending on its thickness
1. Thick skin
2. Thin skin

89
Q
  • Where does thick skin cover and what is present/not present there?
  • Where does thin skin cover and what is present/not present there?
A

Thick Skin

  • Covers the palms of the hands and soles of the feet.
  • Has sweat glands only
  • NO hair follicles or hair
  • NO arrector muscles of hairs
  • NO sebaceous glands

Thin Skin

  • Covers most of the rest of the body
  • It contains hair follicles, arrector muscles of hairs, sebaceous glands, and sweat glands.
90
Q

What type of cells is the dermis derived from?

A

The dermis is derived from the mesenchyme (mesoderm/dermatomes) underlying the surface ectoderm (epidermis)

91
Q

What are the two origins of the skin mesenchyme of the dermis?

A
  1. Most from Somatic layer of the Lateral mesoderm
  2. Some from Dermatomes of the somites (fibroblasts)
92
Q
  • What type of tissue fibers are being produced by the mesenchymal cells at the 11th week?
  • What is the dermis made up of at birth?
A
  • At 11th week: the mesenchymal cells begin to produce collagenous and elastic connective tissue fibers
  • At birth: the dermis is made up of 2-layers (two mesodermal layers)
    1. The papillary layer
    2. The reticular layer
93
Q

What does the dermis (specifically the papillary layer) form and where?

A

Between the descending epidermal ridges, the dermis (the papillary layer) interdigitate upward and forms the dermal papillae (finger prints)

94
Q

What develops and what invades the dermal papillae?

A
  • Sensory nerve endings develop and invade into these papillae.
  • Capillary loops of blood vessels also simultaneously invade the dermis and provide nourishment
95
Q

At 5-6 weeks what develops concerning hair?

A

Hair bud develops by 5-6 weeks, but the hair is visible only later by 20th week

96
Q

How are hair buds developed? (Epidermal cells proliferate inwards, giving rise to what? And invades what? )

What happens to the hair buds at 16 weeks?

  • What does the root of the hair bud become? What does it form?
  • What does the hair bud get filled by?
  • Where does the hair shaft grow from?
A
  • After 14 wks: Epidermal cells proliferate inwards, giving rise to hair buds that invade into the underlying dermis
  • 16 wks: The root of the hair bud becomes cup-shaped, forming a hair bulb with a hair shaft
  • 16 wks: The hair bulb gets filled by mesenchymal “hair papilla” (some melanocytes are also present)
  • 16 wks: The hair shaft grows from the central epithelial cells of the hair bulb.
97
Q

Where does the hair shaft invade at the 20th week?

A

20 wks: The hair shaft invades upwards into the epidermis and protrudes out of the skin

98
Q

What does the peripheral cells of the hair bulb form?

A

The peripheral cells of the hair bulb form the epidermal(secondary epithelial layer)/dermal (muscle layer) root sheath

  • Epidermal root sheath forms INTO the mesodermal cells
  • Dermal root sheat forms FROM the mesodermal cells
99
Q

What do the cells of the epithelial sheath form?

A

Laterally, the cells of the epithelial root sheath proliferate to form a sebaceous gland bud (Sebum)

Formed in the same gland that hair is growing

100
Q

What is formed from the mesenchymal cells that differenitate into the dermal sheath?

A

The arrector pili muscle (for goose bumps, sebum) differentiates from the surrounding mesenchyme.

The more the arrector pilli contracts the more oil will come out

101
Q

What cells migrate into the hair bulb and what is there function?

A
  • Melanoblasts migrate into the hair bulb and differentiate into melanocytes to provide hair color
  • Capillaries/blood vessels come in to provide the hair bulb with nourishments

Some epithelial cells and mesenchymal stem cells present near the bulb get nourished all the time

102
Q

When and how do sweat glands develop in the skin? What do they start as?

A
  • Sweat glands develop by ~20th wk.
  • Starts as solid growth of epidermal cells invading the dermis by 16th wk
103
Q

For the Sweat Glands:

  • The terminal parts coils and forms what?
  • The central cells degenerates and forms what?
  • The peripheral cells differeniate into what?
A
  • Its terminal part coils & forms “body of the gland” by 20th wk
  • The central cells degenerate to form the lumen of the gland (sweat duct)
  • The peripheral epithelial cells differentiate into:
    1. Secretory cells (sweat)
    2. Contractile myoepithelial cell

Contractile myoepithelial cell contract as sweat comes out (Sympathetic)

104
Q

What are mammary glands?

A

Mammary glands are modified & highly specialized types of sweat glands

105
Q

By the 4th week, where do Mammary Crests (ridge) develop? Where do they eventually proliferate at?

A
  • By 4th wk Mammary Crests (ridges) develop along each side of the ventral surface of the embryo.
  • Mammary Crests spans the axillary region (armpit) to the inguinal region
  • Eventually, the Crest regress in most locations & proliferate around pectoral muscles
106
Q

What gives rise to the lactiferous ducts of the mammary glands?

A

The down-growth of epidermis/epithelial tissue continues to proliferate into 16-24 solid out-buddings which give rise to the lactiferous ducts (milk)

107
Q

What does the fibrous connective tissue form in the mammary gland?

Surrounding meschyme

A

Fat or adipose tissue of the mammary gland

108
Q

How is the mammary pit formed? And what happens to it after birth?

A
  • Epithelial lactiferous ducts at first open into a small mammary pit.
  • After birth, the nipples rise from the mammary pits because of proliferation/pushing of the surrounding connective tissue mesenchyme below the “Areola”, which surrounds the nipples.

The depressed nipple is d/t apoptosis

109
Q

When and how do fingernails and toenails develop?

A
  • 10th Wk: Toenails and fingernails develop as thickened areas of the epidermis (nail fields) at the tips of the digits
  • By 32 weeks the fingernails formed
  • By 36 weeks the toenail formed
110
Q

Where does the nail field extend and what eventually grows over it and what does it form?

A
  • The nail fields extend to the dorsal surface and is surrounded by the lateral nail folds
  • Cells from the proximal nail fold grow over the nail field and form keratinized nail plate, the primordium of the nail, which grows toward the tip of the finger.
111
Q

What are the 2 parts of the Keratinized Nail Plate?

A
  1. Eponychium (corneal layer of epidermis; proximal cuticle)
  2. Hyponychium (skin under the free margin of the nail)
112
Q

What are the five adult cavities? And how are the seperated?

A

Dorsal Cavity
1. Cranial Cavity
2. Vertebral Cavity

Ventral Cavity
3. Thoracic Cavity
4. Abdominal Cavity
5. Pelvic Cavity

  • Thoracic cavity: one pericardial; two pleural cavities
  • Abdomino-pelvic cavity: one larger peritoneal cavity
113
Q

How and when is the Intraembryonic cavity formed? (What is formed in the lateral mesoderm? What is formed by merging the vacuoles? What does the flat embryo split into and what is it surrounded by?)

A
  • Day 20: Vacuoles formed in the lateral mesoderm
  • Day 21: U- or Horse shoe-shaped body cavity forms by merging of vacuoles in the lateral mesoderm in the flat trilaminar disc (3-Somite stage).
  • “FLAT EMBRYO” splits →U-shaped cavity (Intraembryonic Coelom) surrounded by two layers:
    1. Somatopleure layer (Parietal layer;body wall)
    2. Splanchnopleure layer (Visceral layer; organs)
114
Q

What is formed by merging the vacuoles that formed in the lateral mesoderm?

A

U- or Horse shoe-shaped body cavity forms by merging of vacuoles in the lateral mesoderm in the flat trilaminar disc (3-Somite stage).

115
Q

When the “Flat Embryo” (flat trilaminar disc) splits what is formed?

A

U-shaped cavity (Intraembryonic Coelom) surrounded by two layers:
1. Somatopleure layer (Parietal layer;body wall)
2. Splanchnopleure layer (Visceral layer; organs)

116
Q

What are the two layers of the developing body cavity? And what do they cover/line?

A
  • Visceral (serous) layer – Covers organs (Sphanchnopleure)
  • Parietal (serous) layer – Lines the body wall (Somatopluere)

  • Visceral: Inner membrane
  • Parietial: Outer membrane
116
Q

What is the Pericardio-peritoneal canal?

A

Connection between the pericardial coelom and peritoneal coelom (cavity)

117
Q

What are serous membranes? And what is its function?

A
  • Single mesothelial cell layer (inner/outer)
  • Functions to preclude adhesions among organs so that organs can grow & move freely to be positioned & sculpted
118
Q

What are the Throacic membranes lining the cavity?

A
  • Visceral pleura
  • Parietal pleura
  • Visceral pericardium
  • Parietal pericardium

  • Pleura: lungs
  • Pericardium: heart
119
Q

What are the Abdominopelvic membranes lining the cavity?

A
  • Visceral peritoneum
  • Parietal peritoneum
  • Visceral perineum
  • Parietal perineum

  • Peritoneum: abdominal organs
  • Perineum: geneto-anal organs
120
Q

What does the “cranial bend” and lateral extensions (“limbs”) of the intraembryonic coelom each form?

A
  • The “cranial bend” in the intraembryonic coelom forms future pericardial cavity
  • The (lateral extensions; “limbs”) forms the future pleural and peritoneal cavities

Day 21-22

Continuity of Intraembryonic & Extra embryonic cavity at lateral edges

121
Q

How is the Pericardial cavity formed is the early heart?

A

Early heart growing and pushing into the 2 layer coelom (u-tube) which forms the visceral and parietal pericardium, between them is the formation of the pericardium (pericardial) cavity

122
Q

What makes up the extraembryonic splanchnopluere and somatopleure?

A
  • Splanchnopleure=Endoderm+splanchnic mesoderm
  • Somatopleure=Trophectoderm+somatic mesoderm
123
Q

What action brings the “limbs” of the coelom together? On what side of the embryo?

A

Horizontal folding brings the “limbs” of the coelom together on the ventral side of the embryo.

124
Q

What is the coelom lined with and where is it derived from?

A
  • The coelom is lined by the mesothelium (serous membrane)
  • Derived from the somatic mesoderm (parietal layer) and the splanchnic mesoderm (visceral layer)
125
Q

What does the junction of the somatic (parietal) and sphlanchic (visceral) layers of the mesoderm form dorsally and ventrally?

A
  • Dorsally→Dorsal Mesentery
  • Ventrally→Ventral Mesentery
126
Q

What is reduced when the dorsal and ventral mensentaries are being formed?

A

Reduced communication between the intra-embryonic & extra-embryonic coeloms

127
Q

The somatic mesoderm forms what?

A

The somatic mesoderm forms the parietal-peritoneum lining the abdominal wall

128
Q

The splanchnic mesoderm forms what?

A

The splanchnic mesoderm forms the visceral-peritoneum covering the organs

129
Q

Which mesentary disappears and what is formed?

A

Disappearance of the ventral mesentery & formation of the ventral body wall

130
Q

What moves dorsally and begins to split the thoraic and abdominal cavities?

A

Septum transversum moves dorsally and begins to split the thoracic and abdominal cavities

131
Q

What action brings the pericardial cavity to the ventral side of the foregut?

A

Cranial folding brings the pericardial cavity to the ventral side of the foregut

132
Q

The Pericardioperitoneal Canals:

  • Arises from?
  • Passes where?
  • Lies where?
  • Caudally, opens into what?
A
  • Arise from the dorsal wall of the pericardial cavity
  • Pass on each side of the foregut
  • Lie dorsal to septum transversum
  • Caudally, open into the peritoneal cavity
133
Q

What pathway does the dorsal mesentery eventually form?

A

Pathway for blood vessels, nerves and lymphatics to reach the gut tube

134
Q

Dorsal mesentary forms a pathway for blood vessels the the gut. Which artery provide blood to the 3 sections of the gut?

End of 4th week

A
  1. Celiac arterial trunk (foregut)
  2. Superior mesenteric artery (midgut)
  3. Inferior mesenteric artery (hindgut)

5 week embryo

135
Q

Embryonic cavities in a 5 week embryo

What is attached to the midgut? What remains seperated?

A
  • Umbilical cord is attached to the mid-gut.
  • Peritoneal cavities remain separated.
136
Q

Embryonic cavities in a 5 week embryo

What is the state of the peritoneal cavity in the hingut?

A

Peritoneal cavity is continuous

137
Q

What folds are formed?What canal is formed and what incompletely divides the cavity into two at Day 28? What does incomplete division allow for?

A
  • Pleuropericardial folds are formed.
  • Pericardio-peritoneal canals forms as the septum transversum incompletely divides the cavity into two:
    1. Thoracic cavity
    2. Abdominal (peritoneal) cavity
  • Incomplete division allows formation of continuous Pericardio- peritoneal canals bilaterally

Formation of the Pleuropericardial folds & Pericardioperitoneal canals

138
Q

What seperates the thoracic cavity? And what two distinct cavities are evident?

At 35 days (end of 5 weeks)

A
  • Pleuropericardial folds separate the thoracic cavity
  • Two distinct cavities are evident:
    1. Pericardial cavity
    2. Pleural cavities
139
Q

What does the Pleuropericaridal folds carry? How does the position of the heart change and what fuses? And what does the pleuropericardial folds eventually form?

At 35 days (end of 5 weeks)

A
  • The Pleuropericardial folds carry the phrenic nerves & common cardinal veins
  • The position of the heart changes inferiorly & the folds fuse.
  • The pleuropericardial folds then forms the fibrous pericardium
140
Q
  • The LUNGS grow __________ & expands the _____________
  • The heart moves _____________
A
  • The LUNGS grow inferiorly & expands the pleural cavities
  • The HEART moves inferiorly
141
Q

What is isolated when the Pleuropericardial fold fuse to form fibrous pericardium?

A

Pleuropericardial folds fuse to form fibrous pericardium, isolating the pericardial cavity

142
Q

What canals and cavity are continous by week 5?

A

The pericardio-peritoneal canals & the pericardial cavity are continuous

143
Q

6 weeks: Lung ________ & the pleural cavities ________ into the body wall & splits the __________

A

6 weeks: Lung grows & the pleural cavities expand into the body wall & splits the somatic mesoderm

144
Q

7 weeks: Pleural cavities expand ________ around the ________. ___________ fuse medially, ventral to __________.

A

7 weeks: Pleural cavities expand ventrally around the heart. Pleuropericardial folds fuse medially, ventral to esophagus

145
Q

8 weeks: Lungs/pleural cavities expand and split mesoderm further into what? (2)

A
  1. Inner fibrous pericardium protecting/isolating the heart
  2. Outer thoracic wall protects the lungs/pleural cavity
146
Q

What is the primordial mediastinum and where does it extend?

8 wks

A

Primordial mediastinum (mesenchymal mass), extends from the sternum to the vertebral column.

147
Q

What are the four components that the diaphragm develops from?

A
  1. Septum transversum
  2. Dorsal mesentery of esophagus
  3. Pleuroperitoneal folds
  4. Muscular ingrowth from lateral body walls
148
Q

What is the state of the developing diaphragm in:

  • 5 weeks:
  • 6 weeks:
  • 12 weeks:
A
  • 5 weeks: Unfused pleuroperitoneal folds
  • 6 weeks: Migration of myoblasts fuse the pleuro-peritoneal folds with septum transversum & esophageal mesentery
  • 12-weeks: Muscular ingrowth from the body wall (4th component).
149
Q

In the neonate diaphragm what does the septum transversum form? And what thickens?

A
  • Septum transversum forms the Central tendon of diaphragm
  • Muscular ingrowth thickens
150
Q

What is the crura of the diaphragm and where does it extend?

A

Crura of the diaphragm: Two tendinous structures (left right & crus; leg like structure), extends below the diaphragm to the vertebral column

151
Q

After the fusion of the 4 components of the diaphragm what invades the other parts forming the diaphragm and what does it give rise to?

A

After the fusion of the 4 components of the diaphragm, the myoblasts from the pleuroperitineal folds and the lateral body wall invade into the other parts forming the diaphragm & give rise to the muscles of the diaphragm

152
Q

What innervates the muscles of the diaphragm?

A

During development the phrenic nerve descends from spinal nerves (C3, C4, C5) & passes through the pleuropericardial membranes/folds and innervates the muscles of diaphragm

153
Q

What is Congential diaphragmatic hernia (CDH)? Where does it occur and what clincial manifestations are common?

Also called Posterolateral Defect of Diaphragm

A
  • CDH occurs commonly through a posterolateral defect in diaphragm (1: 2200 neonates)
  • Occurs mostly on left side.
  • Left lung hypoplasia is common
  • Herniation of abdominal contents
154
Q

What causes Eventration of the Diaphragm?

A

Because of defective musculature development of the diaphragm the abdominal viscera are displaced in the thorax within a pouch of diaphragmatic tissue

155
Q

What is Congential Hiatal Hernia?

A

Herniation of part of the fetal stomach may occur through an excessively large esophageal hiatus

156
Q

The __________ splits to form the __________. (Day 21)

A

The lateral mesoderm splits to form the intraembryonic coelom (Day 21)

157
Q

_____________ circles ________ to form a ________ in the ____________ by day 28

A

Intraembryonic coelom circles cranially to form a U-shaped cavity in the cardiogenic mesoderm by day 28

158
Q

Cranially, the coelom forms the ___________ and laterally, future ________ and ___________ cavities.

A

Cranially, the coelom forms the pericardial cavity and laterally, future pleural and peritoneal cavities.

159
Q

___________ parts of the Intraembryonic coelom move _______ towards the _________ aspects and merge to form the _________.

A

Lateral parts of the intraembryonic coelom move medially towards the ventral aspect and merge to form the peritoneal cavity

160
Q

The ________ of mesoderm enclose the ________ and suspends it from the _________ by a ____________ (made of splanchnic & somatic layer)

A

The splanchnic layer of mesoderm encloses the primordial gut and suspends it from the dorsal body wall by a double-layered dorsal mesentery (made of splanchnic & somatic layer)

161
Q

Fusion of the __________ during formation of the _________, seperates the ________ from the _________.

A

Fusion of the caudal pleuroperitoneal folds during formation of the diaphragm separates the pleural cavities from the peritoneal cavity

162
Q

The diaphragm develops from:
(i)
(ii)
(iii)
(iv)

A

The diaphragm develops from the (i) septum transversum, (ii) mesentery of the esophagus, (iii) pleuroperitoneal folds & (iv) muscular outgrowth from the body wall

163
Q

The diaphrgam divides the body cavity into ______ and _______.

A

The diaphragm divides the body cavity into thoracic and peritoneal cavities

164
Q

A birth defect (opening) in the pleuroperitoneal membrane on the left side causes what?

A

CDH (Congential diaphragmatic hernia)

Embryology: Summer Semester (10 decks)

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