Cells and Development

Question 1

Prophase

Answer 1

• The spindle fibers radiating out of the centriols can serve different purposes
• Some form asters, anchoring to the cell membrane
• Others extend towards the middle of the cell.
• These spindle fibers attach directly to chromosomes
  
  • More precisely, the spindle fibers attached to at protein structires called kinetochores on the chromosomes centromere.

Question 2

Metaphase

Answer 2

• Bring chromosomes to the middle
• They key to this step is the spindle fibers that are attached to the chromosomes at the kinetochores
  
  • These kinetochore fibers interact with other spindle fibers to align the chromosomes at the metaphase equatorial plate in the center of the cell

Question 2

Metaphase

Answer 2

• Bring chromosomes to the middle
• They key to this step is the spindle fibers that are attached to the chromosomes at the kinetochores
  
  • These kinetochore fibers interact with other spindle fibers to align the chromosomes at the metaphase equatorial plate in the center of the cell

Question 3

Anaphase

Answer 3

• Kinetochore fibers progressively shorten, pulling the sister chromatids towards opposite poles of the cell

Question 4

Telepahse

Answer 4

• Fourth step of mitosis
• It is the termination of mitosis
• Spindle apparatus disappears, nuclear membrane reforms around each set of chromosomes, and the nucleoli reappear.
• Cytokinesis is the final cleaving step
  
  • It separates the cytoplasm and organelles
  • In snimal cells, a contractile actin-myosin ring pinches the one cell into two and now there are two daughter cells.

Question 5

Embryogenesis

Answer 5

• Starts off with a female cell called an oocyte
• When ovulation occurs, a second oocyte , which is the haploid cell that develops after a diploid primary oocyte undergoes its first meiotic division, is released from the ovary and travels into a nearby fallopian tube.
• Most of the time this is the site where the oocyte makes contact with a sperm cell
• The oocytes cell membrane is surrounded by a protein cote known as zona pelludica.
  
  • In order to penetrate this outer coat, the sperm releases digestive enzymes contained in its cap-like structure called acrosome once it makes contact
  • As that happens, the sperm generates a tube-like structure, also known as acrosomal process, that extends and fuses with the occyte’s cell membrane
  • Once fused, the pronucleus, which is just a fancy name for the nulecus of the sperm during fertilization can then enter the occyte.
  • This triggers a cortical reaction
    
    • Calcium ions are released, causing a release of cortical granules that make the zona pellucida impassable.
    • This is important because it prevents polyspermy, or fertilization of the egg by multiple sperms
    • Now this release of calcium also allows our secondary oocyte to undergo a second meiotic division to form a mature egg cell called an ovum.
      
      • This final haploid ovum them merges with the sperms pronucleus to form the zygote

Question 6

Two Zygotes

Answer 6

• It is possibel to form two zygotes
• What happens is two eggs enter the fallopian tubes during ovulation and becoem fertilized by two different sperms.
  
  • This is actually how we get Dizygotic (Fraternal Twins)

Question 7

Cleavage

Answer 7

• The zygote can not sit still it has to migrate from the fallopian tubes to eventually make its way to the uterus to implant
• While teh zygote is moving towards the uterus is begins a process cause cleave.
  
  • This is when it undergoes rapid mitotic division
  • Remember that the zygote is still surrounded by that hardened zona pellucida, so the volume of the zygote stays the same, but the individual daughter cells inside of it get smaller and smaller
  • These daughter cells are undifferentiated, which means they haven’t begun specializing yet; growing up to take on their own identities in the form of different cells that each have their own role in out bodies.
    
    • They are capable of developing into their own organism
  • If you known someone that is an identical twin that is what happened:
    
    • some cells in their zygote split off, and the two groups of cells began developing into two individual but identical babies

Question 8

Three Stages of Development

Answer 8

• My Baby Grows
  
  • Morula
  • Blastula
  • Gastrula

Question 9

Morula

Answer 9

• After many divisions, the embryo is a small solid ball of cells called a morula
• After reaching the morula phase, instead of cells just dividing as before, they start migrating to the outside of the zygote, forming a hollow ball.

Question 10

Blastulation

Answer 10

• When the cell begins to release fluid which begins to accumulate in the centre of the ball.
• When this stage is completed, the embryo is known as a blastula or a blastocyst in mammalian organism
• When blastulation is complete the inner fluid-filled cavity is called a blastocoel.
  
  • Coel is the greak work for cavity.
• Not that there are two parts to the outer ball of cells
  
  • The outer layer of cells is called the trophoblast
    
    • Those cells will develop into the placenta, chorion, and amniotic sac that surround the baby as it develops
    • The small lump of cells protruding from the trophoblast on the inner side is known as the inner cell mass
      
      • If everything goes well, this tiny mass will develop into a healthy baby
    • The embryo will normally implant into the uterus during blastulation
      
      • This is critical because only the uterus can safetly sustain the pregnancy

Question 11

ectopic pregnancy

Answer 11

If the zygote implants anywhere else besides the uterus

Question 12

ectopic pregnancy

Answer 12

If the zygote implants anywhere else besides the uterus

Question 13

Gastrulation

Answer 13

• So far we have an inner cell mass of undifferentiated cells.
• These cells are specifically what we call pluripotent or embryonic stem cells, which can give rise to any type of cell.
• During gastrulation, the inner cell mass of the embryo develops into three primary germ layers that will be precursors for every differentiated cell in the body
  
  • The process begins with some cells moving into the fluid-filled blastocoel, forming a small invagination
    
    • This invagination from the innermost germ layer, called the endoderm

Question 14

Endoderm

Answer 14

• Gives rise to the digestive tract between the mouth and anus, and all the accessory organs attached to it, including the pancreas and the liver.
• It also forms the lungs as well as the bladder and distal urinary tract.

Question 15

Ectoderm

Answer 15

• The outer layer is known as the ECTOderm, you can think of it as the attachto-derm because it develops into things that might attach 1 organism to another at the surface level:
  
  • It forms the epidermis, the hair, the eyes, and the epithelium of the upper respiratory tract including the nose and mouth

Question 16

Mesoderm

Answer 16

• Between the endoderm and the ectoderm
• the middle layer
• Provides the means for moving things around
• It develops into the musculoskeletal system, which helps you to move around, and it also forms the system that move fluids through the body:
  
  • The lympahtic system, which includes the lymph nodes;
  • The circulatory system
  • genitourinary system
• Also forms the gonads and the adrenal cortex, as well as adipose tissue and connective tissue that support the digestive and respiratory system

Question 17

Neurrulation

Answer 17

• When the nervous system becomes fully intact
• Once the three germ layers have formed, a rod of mesodermal cells form a structure called the notochord, which will become the anterior party of the baby spinal column
  
  • Remember the spinal column is made up of bone which means it forms from cells in the mesoderm
• The notochord releases molecules that causes the ectodermal cells next to the notochord to fold inwards
• They form a groove running down the length of the embryo surface, called the neural groove
• These ectodermal cells continue to fold in until the overlaying surfaces re-fuse.
• These folded cells, which are now internalized, create a tube called the neural tube
  
  • The cells of the neural tube will ultimately develop into the central nervous system
• Again because this is the nervous system, its cells are derived from the ECTOderm
• On either side of the neural tube are residual cells from nearby neural folds.
  
  • These cells are the neural crest cells.
  • Just as the neural tube becomes the central nervous system, these ectoderm cells will become the peripheral nervous system, including the sensory and automatic ganglia
• They also form specialized cells like those found in the adrenal medulla, the calcitonin-producing cells in the thyroid, and melanocytes, the cells in the skin that produce pigments
• In a small percentage of babies the neural tube does not completely close, leading to a condition known as spina bifida.
  
  • The symptoms can rang from as little as an indentation or tuft of hair in the skin to significant motor and sensory deficits.
• Embryogenesis ends when neuralation is complete, at that point the embryo becomes the fetus and development continues as the fetus grows and the remainder of its organs develop