24 Questions
What is the result of lateral folding during embryonic development?
Pinching off part of the yolk sac to form the GI tract
What is the name of the curve exhibited by the spine during embryonic development?
Primary curvature
What is visible in the 5th week of development?
Growth of the head due to rapid growth of the brain
What is the result of cephalocaudal folding during embryonic development?
Shaping of the head and tail of the embryo
What is visible in the 7th week of development?
Upper limbs show regional development, especially elbows and wrists
What is the relationship between somites and the neural tube during embryonic development?
Somites closely associate with the neural tube, leading to specific spinal nerves and levels of the neural tube
What is visible in the 4th week of development?
Embryo is cylindrical in shape with a C-shaped curve
What is the significance of cephalocaudal and lateral folding during embryonic development?
They form the head, tail, and GI tract of the embryo
What is the main function of the endoderm layer during gastrulation?
Forms the lining of internal organ systems and specialized cells
What is the result of gastrulation in terms of germ cell layers?
The formation of three germ cell layers
What is the role of the primitive streak in gastrulation?
It is a groove in the midline of the epiblast where cells break off and migrate to form three new germ cell layers
What tissue does the mesoderm layer become during embryonic development?
Cardiac muscle, Skeletal muscle, Smooth muscle, connective tissue
During which week of embryonic development does gastrulation occur?
Third week
What is the result of cells migrating through the primitive streak during gastrulation?
The formation of the endoderm, mesoderm, and ectoderm layers
What is the role of the notochord in embryonic development?
A linear structure along the dorsal side of the embryo where the spine will form
Which layer becomes the external layer of the body during gastrulation?
Ectoderm
What is the primary function of the neural plate during neurulation?
To form the neural tube
What is the consequence of failed notochord development during embryogenesis?
Abnormalities in the vertebral column
Which of the following is NOT a component of somites?
Endoderm
During neurulation, what is the sequence of events that leads to the formation of the neural tube?
Neural plate → neural groove → neural fold → neural tube
What is the term for the organization of somites to form repeating structures?
Segmentation
What is the primary function of the sclerotome during embryogenesis?
To develop the vertebral column and ribs
During which week of embryogenesis does the neurulation process typically occur?
Week 4
What is the term for the blocks of mesoderm that form alongside the neural tube during embryogenesis?
Paraxial mesoderm
Study Notes
Embryology
- Somites are derived from the three components: Sclerotome (vertebrae + ribs), Myotome (skeletal muscle development), and Dermatome (Skin + Dermis)
- Somites closely associate with the neural tube, leading to specific spinal nerves and levels of the neural tube
- Cephalocaudal folding and lateral folding shape the trilaminar disk into an embryo
- Lateral folding forms a tube with ectoderm outside and endoderm inside, pinching off part of the yolk sac to form the embryo's GI tract
- Cephalocaudal folding creates the head and tail of the embryo
Primary Curvature
- The spine exhibits one continuous C-shaped curve
Developmental Stages
- 4th week: embryo is cylindrical C-shape
- 5th week: growth of head due to rapid growth of brain, branchial arches form mandible, and upper limb bud forms upper limb
- 6th week: limbs show regional development, especially upper limbs, with elbow and wrist identifiable
- 7th week: upper limbs bent at elbows, fingers and thumb are distinct but webbed
- 8th week: fingers and toes are distinct and separated, eyelids are evident, ears appear, and external genitalia start appearing
Gastrulation
- Gastrulation occurs in the third week, where the two-cell layers (bilayer) become three germ cell layers (trilaminar)
- The primitive streak forms a groove in the midline of the epiblast, and cells migrate towards it to form the three new germ cell layers: Endoderm, Mesoderm, Ectoderm
Germ Cell Layers
- Endoderm: forms the internal layer of the body, including the lining of internal organ systems and specialized cells (e.g. pancreas, liver, thyroid)
- Mesoderm: forms the supportive tissues of internal structures, including cardiac muscle, skeletal muscle, smooth muscle, and connective tissue
- Ectoderm: forms epidermal skin cells and neurons
Neurulation
- The notochord is a linear structure formed by the mesoderm layer, which induces thickening of the ectoderm and starts the process of neurulation
- The neural tube forms from the ectoderm and gives rise to the CNS
- Neurulation process: lateral edges of ectoderm elevate to form the neural fold, which then forms the neural plate, and eventually fuses to form the neural tube
- Failure of notochord development may cause vertebral column abnormalities (e.g. spina bifida, scoliosis)
This quiz covers the formation of somites into three components, their connection to the neural tube, and the folding process that shapes the embryo.
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