Mar 2, 2023
Day 0: Fertilization
Day 1- 5: Cleavage
● Series of rapid cell division (mitosis)
● Chromosomes copy and divide
● Egg cytoplasm just keeps getting divided into smaller blastomere cells
Day 6: Blastocyst (Blastula)
● (Cross section) - by Day 6 after fertilization - trophoblast will become the placenta
● Inner cell mass (ICM) - embryo will continue to develop from these cells
Gastrulation (Gastrula)
● 3 layers of derm: endoderm- (yell.), mesoderm (pink), ectoderm- (blue)
○ Endo = inside
○ Miso. = middle
○ Ecto: outside
● By the end of gastrulation, 3 embryo germ layers are fully formed, and body axes are
determined - cells will develop appropriately to where they are
● Ectoderm - derived
○ Nervous system Epidermis of skin
● Mesoderm-derived
○ Dermis of skin
○ Most major body system:
■ Skeletal
■ Circulatory
■ Lymphatic
■ Muscular
■ Excretory
■ Reproductive
● Endoderm- derived
○ Interior epithelia lining of:
■ Digestive tract
■ Respiratory tract
■ Reproductive tract
■ Urinary tract
■ Other entire organs and glands
Organogenesis
1. Notochord forms in the mesoderm
2. Notochord signals ectoderm to fold
3. Neural-tube formation is complete
4. Somites form (paired blocks of mesodermal tissue)
a. Surface view of somites
i. Neural tube
ii. Somites
b. Cross section of somites
, i. Ectoderm
ii. The neural tube (will become the brain and spinal cord)
iii. Somite
iv. Notochord (in vertebrates, this will go away)
1. Goes through programmed cell death (Apoptosis) as they are not
needed any longer
v. Endoderm
c. On each side of the neural tube, there are blocks of mesoderm called somites
i. Each section of cells in a somite receives different signals for cellular
differentiation- position determines fate!
1. Become muscles of the back
2. Become a dermal layer of skin
3. Become muscle in limbs
4. Become cells that build bone
ii. Remember once the cells get the signals and differentiate, there is no
going back! They cannot become anything else
Day 7-10: Implantation in uterine Wall
1. Placenta will develop now
2. Also, B-HCG (human beta chorionic gonadotropin) will be released - this is what a
pregnancy detects
Animal Form and Function
4 Main Types of Animal Tissue
1. Nervous - made of neurons
a. Most neurons have to last your whole life (although there is new evidence for
some limited adult neurogenesis)
b. Dendrites: messages moved from other cells - messages are processed in the
cell body (Soma), which sends out its own message down the axon
c. Information flows from dendrites to the axon (unidirectional) in neuron
2. Muscle (3 types) (unique to animals- dont find it in any other organism)
a. Skeletal (long cells)
i. Involved in voluntary movement (most muscles)
b. Cardiac (Branched cells)
i. Involuntary movement
ii. Cardiac = heart
c. Smooth (tapered cells
i. Involuntary movement (digestive tract)
● Most will last your whole life
3. Epithelial (2 different types) - lines outer and inner surfaces
GATEKEEPERS
a. Simple
i. Consists of a single layer of cells
Day 0: Fertilization
Day 1- 5: Cleavage
● Series of rapid cell division (mitosis)
● Chromosomes copy and divide
● Egg cytoplasm just keeps getting divided into smaller blastomere cells
Day 6: Blastocyst (Blastula)
● (Cross section) - by Day 6 after fertilization - trophoblast will become the placenta
● Inner cell mass (ICM) - embryo will continue to develop from these cells
Gastrulation (Gastrula)
● 3 layers of derm: endoderm- (yell.), mesoderm (pink), ectoderm- (blue)
○ Endo = inside
○ Miso. = middle
○ Ecto: outside
● By the end of gastrulation, 3 embryo germ layers are fully formed, and body axes are
determined - cells will develop appropriately to where they are
● Ectoderm - derived
○ Nervous system Epidermis of skin
● Mesoderm-derived
○ Dermis of skin
○ Most major body system:
■ Skeletal
■ Circulatory
■ Lymphatic
■ Muscular
■ Excretory
■ Reproductive
● Endoderm- derived
○ Interior epithelia lining of:
■ Digestive tract
■ Respiratory tract
■ Reproductive tract
■ Urinary tract
■ Other entire organs and glands
Organogenesis
1. Notochord forms in the mesoderm
2. Notochord signals ectoderm to fold
3. Neural-tube formation is complete
4. Somites form (paired blocks of mesodermal tissue)
a. Surface view of somites
i. Neural tube
ii. Somites
b. Cross section of somites
, i. Ectoderm
ii. The neural tube (will become the brain and spinal cord)
iii. Somite
iv. Notochord (in vertebrates, this will go away)
1. Goes through programmed cell death (Apoptosis) as they are not
needed any longer
v. Endoderm
c. On each side of the neural tube, there are blocks of mesoderm called somites
i. Each section of cells in a somite receives different signals for cellular
differentiation- position determines fate!
1. Become muscles of the back
2. Become a dermal layer of skin
3. Become muscle in limbs
4. Become cells that build bone
ii. Remember once the cells get the signals and differentiate, there is no
going back! They cannot become anything else
Day 7-10: Implantation in uterine Wall
1. Placenta will develop now
2. Also, B-HCG (human beta chorionic gonadotropin) will be released - this is what a
pregnancy detects
Animal Form and Function
4 Main Types of Animal Tissue
1. Nervous - made of neurons
a. Most neurons have to last your whole life (although there is new evidence for
some limited adult neurogenesis)
b. Dendrites: messages moved from other cells - messages are processed in the
cell body (Soma), which sends out its own message down the axon
c. Information flows from dendrites to the axon (unidirectional) in neuron
2. Muscle (3 types) (unique to animals- dont find it in any other organism)
a. Skeletal (long cells)
i. Involved in voluntary movement (most muscles)
b. Cardiac (Branched cells)
i. Involuntary movement
ii. Cardiac = heart
c. Smooth (tapered cells
i. Involuntary movement (digestive tract)
● Most will last your whole life
3. Epithelial (2 different types) - lines outer and inner surfaces
GATEKEEPERS
a. Simple
i. Consists of a single layer of cells
