BY 124L - Lab 10: Development

Stages of Early Development

1. Fertilization (Zygote)

2. Cleavage

3. Blastulation

4. Gastrulation

5. Neurulation + Organogenesis

differentiation

cells of different tissue lineages will express different parts of their genome to fulfill their designated function

morphogensis

development of an organism's body plan and tissue organization

Zygote

• sperm meets egg in metaphase 2

• polar body is expelled + zygote completes metaphase 2, leading to a single diploid cell

• embryonic development

• has TWO poles

embryonic development of zygote

• single 2n cell has multicellularity via mitotic divisions and cell signaling

two poles of zygote

• Animal Pole: becomes the organism

• vegetal pole: feeds the animal pole

Cleavage

• the division of the single cell into multiple cells without an overall change in size

• Blastomere

• results in the morula

blastomere

a cell produced by cleavage events

morula

• result of cleavage

• consists of 16 to 32 blastomeres

cleavage events

• first 2 events: longitudinal (4 blastomeres present)

• third event: latitudinal (leads to 8 blastomeres)

blastulation

• forms the blastocoel

• cells apical to the blastocoel become ectoderm

• results in blastula

blastocoel

fluid filled spaced formed within the morula

blastula

• completion of the blastocoel

• has the dorsal lip of the blastopore

gastrulation

• cell begin migrating inward (invagination), destroying the blastocel, forming the archenteron (the precursor for mesoderm and endoderm)

• FIRST TIME the cells are differentiated

Neurulation

nervous tissue begins forming

organogensis

first two organs to develop are the neural tube ectoderm and the notochord form the mesoderm

neurulation and organogensis

• archenteron becomes the gut

• vegetal pole begins shrinking because it is used as fuel for this process

• archenteron moves to either end of the developing embryo to become the anus and mouth

ectoderm

becomes brain, spinal cord, and pituitary during last stage

mesoderm

becomes notochord, heart, liver, and skeletal muscle

endoderm

becomes anus, mouth, pharynx, and intestines

Muscle structural hierarchy

• sarcomere

• myofibril

• muscle fiber

• muscle

sarcomere

the fundamental functional and contractile unit of striated muscle, bounded by Z-lines and containing overlapping thin actin filaments and thick myosin filaments

myofibril

A long, repeating chain of sarcomeres lined end-to-end inside a muscle cell

Muscle Fiber

an individual, multinucleated muscle cell packed with myofibrils

Muscle

The complete muscle organ made up of thousands of bundled muscle fibers

Muscle Fiber types

• fast-twitch (light fibers)

• slow-twitch (dark fibers)

Fast-twitch fibers

• lower myoglobin content

• anaerobic

• fatigues quickly

• low mitochondria

• sprinting, jumping, weightlifting

Slow-Twitch fibers

• high myoglobin and blood supply

• slow

• high fatique (built for endurance)

• aerobic

• high mitochondria density

• long-distance running, cycling,