Embryology (MODULE 4) Flashcards
Mel/o
Limb/part
Pod/o
Limb/Foot
Apic/o
Peak/apex/tip
Dactyl/o
Digit (finger or tow)
Mer/o
Part or segment
Zon/o
Belt/Region
Proxim/o
Near/close to
Dist/o
Far/Away from
Styl/o
Pillar/Column
Pod/o
Limb/Foot
Zeug/o
Pair/Yoke
-ia/-al/-ous/-ic
Pertaining to
Hypoxial Muscles
Muscles derived from the hypomere, including subvertebral, lateral body wall, and ventral muscles.
Cartilaginous
Cartilaginous Stage: Phase of limb development where condensed mesenchymal cells differentiate into chondrocytes, forming a cartilage model of future bones.
Joint Cavitation
Joint Cavitation: Process of cell death and extracellular matrix remodeling that creates the joint cavity.
Mesenchymal stage
Mesenchymal Stage: Early stage of limb development consisting of a mesenchymal core covered by ectoderm.
Proximodistal principle
Proximodistal Principle: Developmental pattern where growth occurs from central parts of the body outward toward the extremities.
Apical Epidermal Ridge (AER)
Apical Epidermal Ridge (AER): A thickened ridge of ectoderm at the distal tip of the developing limb bud that promotes limb outgrowth.
What is the proximodistal principle?
The Proximodistal Principle refers to the developmental pattern in which growth occurs from the central parts of the
body (proximal) outward toward the extremities (distal).
• While this principle primarily describes patterns of physical growth and motor development, its context can also extend to skeletal and limb formation during embryogenesis.
What is the AER? (Apical epidermal ridge)
The Apical Epidermal Ridge (AER) is a thickened ridge of ectoderm located at the distal tip of the developing limb bud.
AER:
• Plays a central role in promoting and sustaining the outgrowth
of the limb along the proximodistal axis.
• This ridge exerts an inhibiting influence on adjacent
mesenchyme, causing it to remain as a population of
undifferentiated and rapidly proliferating cells (As the zone of
rapidly growing apical cells moves distally, the proximal end
begins to grow and differentiate d/t distance from and dilution
of the inhibiting effect of the undifferentiated zone at the ridge. • The GDFs there are less and less inhibited, and the proximal
end begins to undergo differentiation).
T or F
The paraxial mesoderm forms the somites
T
T or F
Myogenic progenitor cells originate in the hypoxial portion of somites and these cells migrate to the limb buds and form the future muscle tissue of the upper limb
T
Epaxial cells form what?
Hypoxia forms what?
Dorsal paraspinals (muscles along the back, specifically those associated with the vertebral column and spinal cord)
Forms all the muscle tissue in front of the spine and body wall, and upper extremities
Limb buds appear and grow out from the ventral lateral body wall at what time?
@ the end of the 4th week
What are the 4 stages of the upper limb skeletal development?
Early mesenchymal stage: Early structure consists of a mesenchymal core
derived from the lateral plate mesoderm covered by ectoderm projecting outwards. • This early limb development lays the groundwork for proximodistal growth, starting with the body’s core
and projecting outward.
Later Mesenchymal stage: These mesenchymal cells condense in the limb bud to form the precursors of skeletal structures. • Mesenchymal cells (derived from the mesoderm)
condense in the limb bud to form the precursors of
skeletal structures.
Cartilaginous stage: The condensed mesenchymal cells differentiate into chondrocytes, forming a cartilaginous model of the future bones. •Proximodistal growth can be observed as the cartilage extends outward from the central axis of the body.
Endochondrial stage: During this phase, the cartilaginous model is gradually replaced by bone through the process of endochondral ossification. •The growth continues outward, aligning with the proximodistal principle as bones elongate and mature.
Describe the stages of joint development (Undifferentiated interzone)
Mesenchymal Condensation:
• Mesenchymal cells aggregate in the limb bud
to form precursors of skeletal elements. • These cells differentiate into chondrocytes,
creating a continuous cartilaginous model of
the developing bones.
Undifferentiated Interzone Formation:
• A distinct region, the Interzone, forms at the
future joint site. • The Interzone consists of undifferentiated,
flattened, densely packed mesenchymal cells.
Describe the stages of joint development: (Synovial, Cartilaginous, Fibrous)
Synovial
• Central interzone cells undergo apoptosis, forming the joint cavity
→ outer fibrous and inner synovial membranes • Peripheral interzone cells differentiate into articular cartilage,
synovial membrane, and joint capsule. • Free-moving Synovial joints of the body
Cartilaginous • Interzone cells differentiate into hyaline cartilage or fibrocartilage • Synchondroses of IVD, Symphysis, Costochondral joints.
Fibrous • Interzone cells differentiate into dense fibrous connective tissue
(dense regular CT) to link adjacent bones • Syndesmoses like the distal tib/fib, sutures of the skull
INTERZONE: Subject to inductive signals (GDFs, genetics, fetal movements ) → Differentiation of Interzone mesenchyme
15
Explain joint cavitation and differentiation of joint tissues.
Joint Cavitation:
• Within the Interzone, cell death (apoptosis)
and extracellular matrix remodeling create a joint cavity.
• Synovial fluid is produced, providing
lubrication for the joint.
Differentiation of Joint Tissues:
• Articular Cartilage: Develops from
mesenchymal cells at the joint surfaces. • Joint Capsule and Ligaments: Arise from the
surrounding mesenchyme. • Synovial Membrane: Forms from the inner
layer of the joint capsule.
Development of the limb buds happens in a ______________ ___________
Proximodistal manner
In segmentation of the UE what are the 3 components of limb formation and structures they turn into?
3 components are formed:
1) Stylopod (humerus and femur) distal end)
2) Zeugopod (radius/ulna and tibia/fibula)
3) Autopod (carpals, metacarpals, tarsals, metatarsals)
What is the autopod? When does this formation take place?
Autopod (carpals, metacarpals, tarsals, metatarsals) Fingers and toes are formed due to cell death (apoptosis) in hand and foot plates, separates the plates into five parts
Takes place at 48 days/51 days
What does the developmental anomaly Amelia involve?
Amelia:
1. Definition: Complete absence of one or both upper limbs.
2. Cause: Early failure in limb bud formation, often due to genetic mutations (e.g., TBX5 gene defects) or teratogenic exposures (e.g., thalidomide).
3. Timing: Occurs during the 4th week of embryogenesis.
What does the developmental anomaly Meromelia involve?
Meromelia:
1. Definition: Partial absence of a limb, where some structures (e.g., hand, forearm) are missing. 2. Cause: Disruption in proximodistal growth, often related to impaired
function of the apical ectodermal ridge (AER) or FGF signaling
pathways. 3. Timing: Develops later than amelia, typically during the 5th or 6th week
of gestation. 19
What does the developmental anomaly brachydactyly involve?
Brachydactyly: Shortening of fingers or toes due to underdeveloped or missing phalanges.
What does the developmental anomaly syndactyly involve?
Syndactyly: Definition: Fusion of two or more fingers or toes resulting from failure of interdigital apoptosis during development.
What does the developmental anomaly polydactyly involve?
Polydactyly: Definition: Presence of extra fingers or toes.
Where does the sclerotomal and dermatomal portions migrate during axial development?
Sclerotomal portion of the somite have migrated around the notochord for axial skeletal development
Dermatomal portion of the somite has also migrated posteriorly to differentiate into the skin of the dorsal surface of myotome the developing embryo
Dorsomedial muscle cells = ?
Forms what?
Epimere
Paraspinal muscles
Ventral lateral muscle cells = ?
And migrate to form what?
Hypomere, migrates to form the hypoxia muscles:
- Sub vertebral, or on the ventral side) muscles 2. 4 layered lateral body wall muscles
- Supracostal or outermost muscles
- External muscles
- Middle muscles
- Innermost muscles 3. Ventral muscles 24
What are the contributions to limb bud formation?
Somatic mesoderm = hypaxial portion
Lateral plate mesoderm = provides connective tissue scaffolding, guiding muscle organization and attachments
Briefly name the steps and timeline of the muscle formation in the upper limbs.
- Migration (4th-5th week): Myoblasts migrate from cervical and upper thoracic somites (C5–T1 regions) into the developing upper limb bud. o Molecular growth and differentiation factors (GDFs) cue and direct migration
- Aggregation and compartmentalization (5th-6th week): Migrating myoblasts aggregate to form two primary muscle masses:
—>Dorsal Mass: Becomes extensors and supinators of the upper limb (e.g., triceps brachii, extensors of the forearm).
—>Ventral Mass: Becomes flexors and pronators of the upper limb (e.g., biceps brachii, flexors of the forearm). - Differentiation (6th - 8th week): Myoblasts differentiate into myotubes, which eventually
mature into skeletal muscle fibers. o Myogenic regulatory GDFs drive the differentiation
process - Patterning and Innervation (7th-8th week): Muscle patterning is directed by surrounding connective tissue from the lateral plate mesoderm. o Motor innervation arises from the brachial plexus (C5–T1), with nerve fibers guiding the segregation and functional organization of muscle groups.
- Maturation (fetal period): Muscle fibers grow and attach to bones via tendons, completing functional units. o Muscles refine their innervation and vascular supply.
For key upper limb muscle groups: the Dorsal Mass Derivatives make up what muscles?
- Shoulder muscles: Deltoid, supraspinatus, infraspinatus.
- Posterior arm: Triceps brachii.
- Posterior forearm: Extensors.
For key upper limb muscle groups: the Ventral Mass Derivatives make up what muscles?
- Anterior arm: Biceps brachii, brachialis.
- Anterior forearm: Flexors, pronators.
- Intrinsic hand muscles.
What is the annexation process?
The annexation of the outermost body wall and head muscles by the superior limb refers to the evolutionary and developmental processes where limb musculature integrates contributions from axial and cranial structures.
Function implications of limb:
- Limb muscles are derived primarily from somites, with additional contributions from nearby body wall and cranial musculature
- This annexation allows for a wide range of upper limb movements, integrating axial stability with appendicular dexterity.
- The interplay between axial muscles (e.g., trapezius) and limb muscles (e.g., deltoid) enables coordinated movements like lifting, pushing, and pulling.
- The annexation of the outermost body wall and head muscles into the superior limb reflects an evolutionary adaptation, enabling the complexity and functionality of the human upper limb.
What is retrogrowth in head muscle contributions?
Refers to the developmental process where these muscles (Trap, SCM) originating from the limb bud mesenchyme, extend and “grow back” to anchor themselves to the axial skeleton. This phenomenon is critical for establishing their functional role as proximal stabilizers and movers of the limb.
Retrogrowth in limb-specific modifications: a Proximodistal exception. (Rule breakers!!)
Retrogrowth: Refers to the developmental process where these muscles, originating from the limb bud mesenchyme, extend and “grow back” to anchor themselves to the axial skeleton. This phenomenon is critical for establishing their functional role as proximal stabilizers and movers of the limb.
• Pectoralis major, latissimus dorsi, and the Teres major muscles arise from
the Somitic mesoderm in the developing limb bud near the intertubercular groove.
• Myogenic precursor cells migrate from somites to form the muscle masses of
Proximal attachments:
• Pectoralis major: Anchors to the clavicle, sternum, and costal
the limb. • Retrogrowth: These muscles elongate and extend proximally toward the axial
skeleton during development. Connective tissue from the lateral plate
mesoderm guides this extension, ensuring the muscles attach appropriately to
the axial skeleton.
cartilages, forming a large, fan-shaped muscle. • Latissimus dorsi: Anchors to the spinous processes of the lower
thoracic and lumbar vertebrae, as well as the iliac crest. • Teres major attaches to the scapula (appendicular skeleton), while
pectoralis major and latissimus dorsi anchor to the axial skeleton.
Clinical relevance annexation and retrogrowth: Nerve injuries
Nerve Injuries: Damage to nerves like the Spinal Accessory
Nerve (SAN) affecting trapezius highlights the integration of
cranial and limb innervation.
• Surgery: The nerve can be injured during neck
surgeries, such as lymph node biopsies, carotid or
internal jugular vein surgeries, or neck dissection. • Trauma: Blunt or penetrating trauma to the neck or
shoulder can injure the nerve
Limb rotations overview:
To attain an adult anatomical position, the upper and lower limbs rotate in opposite directions and to different degrees, resulting in the adult elbow pointing posteriorly and the adult knee pointing anteriorly.
Aspect Pre-limb Rotation Post-limb Rotation
**refer to slide 40 to cover the chart information
What is the primary function of the Apical Epidermal Ridge (AER)?
A. To initiate joint formation
B. To form the skin of the limb
C. To differentiate into muscle tissue
D. To form the bones of the limb
E. To promote and sustain limb outgrowth along the proximodistal axis
E
Which of the following structures is formed by the stylopod?
A. Phalanges
B. Carpals and metacarpals
C. Radius and ulna
D. Scapula
E. Humerus
E
Which developmental principle describes the pattern of limb growth from central parts of the body outward?
A. Proximodistal principle
B. Craniocaudal principle
C. Mediolateral principle
D. Anteroposterior principle
A
What is the term for the fusion of two or more fingers or toes?
A. Amelia
B. Polydactyly
C. Brachydactyly
D. Syndactyly
E. Meromelia
D
What is the term for the fusion of two or more fingers or toes?
A. Amelia
B. Polydactyly
C. Brachydactyly
D. Syndactyly
E. Meromelia
D
Which of the following is NOT a component of the autopod?
A. Carpals
B. Metatarsals
C. Metacarpals
D. Radius
E. Tarsals
D
During which stage of limb development do mesenchymal cells condense to form precursors of skeletal structures?
A. Early mesenchymal stage
B. Cartilaginous stage
C. Osteogenic stage
D. Endochondral stage
E. Late mesenchymal stage
E
Match the following embryonic structures with their derivatives:
A. Dorsomedial muscle cells derived from the somite
B. Ventral lateral muscle cells derived from the somite
C. Portion of the somite that forms skeletal muscle
D. Portion of the somite that forms the dermis
E. Portion of the somite that forms the vertebrae
Epimere -
Dermatome -
Sclerotome -
Myotome -
Hypomere -
Epimere - A
Dermatome - D
Sclerotome - E
Myotome - C
Hypomere - B
Match the following embryonic structures with their derivatives:
A. Intermediate mesoderm
B. Lateral plate mesoderm
C. Surface ectoderm
D. Neural crest cells
E. Paraxial mesoderm
Not directly involved in limb formation
Forms the peripheral nervous system of the limbs
Forms the skeletal muscles of the limbs
Gives rise to the limb bones and connective tissue
Develops into the skin and its appendages
A- Not directly involved in limb formation
D- Forms the peripheral nervous system of the limbs
E- Forms the skeletal muscles of the limbs
B - Gives rise to the limb bones and connective tissue
C- Develops into the skin and its appendages
Match the following stages of upper limb development with their timing:
Limb bud appearance -
Cartilage model formation -
Ednochondral ossifcaiotn begins -
Full skeletal maturity-
Digital rays’ appearance in hand plate-
Limb bud appearance - week 4
Cartilage model formation - week 7
Endochondral ossifcaiotn begins - week 8
Full skeletal maturity- Adolescence or early adulthood
Digital rays’ appearance in hand plate- week 6
Match the following stages of upper limb development with their timing:
Limb bud appearance -
Cartilage model formation -
Ednochondral ossifcaiotn begins -
Full skeletal maturity-
Digital rays’ appearance in hand plate-
Limb bud appearance - week 4
Cartilage model formation - week 7
Endochondral ossifcaiotn begins - week 8
Full skeletal maturity- Adolescence or early adulthood
Digital rays’ appearance in hand plate- week 6
