Developmental biology

Question 1

What is fertilisation (stage 1)

Answer 1

A sperm cell fertilizes an oocyte (egg), forming a zygote.
This is the highest level of developmental potency.

Question 2

What totipotent mean

Answer 2

cell has ability to become any cell type, including:
all embryonic tissues
all extraembryonic tissues (placenta, chorion, amnion)

Question 3

What is cleavage (stage 2)

Answer 3

• The zygote begins dividing rapidly without increasing in size.
• Early: blastomeres form
• later: becomes morula
• cells are still totipotent

Question 4

What is blastocyst formation (stage 3)

Answer 4

Fluid fills the morula, forming a cavity.
- forms blastocyst containing:
Inner Cell Mass
Trophoblast
These cells contribute only to extraembryonic structures (e.g., placenta).

Question 5

What is bilaminar disk formation (stage 4)

Answer 5

The Inner Cell Mass separates into two layers:
Epiblast (future embryo)
Hypoblast (contributes to the yolk sac)
Cells at this stage are now multipotent

Question 6

What does multipotent mean

Answer 6

cells can form many types of cells, but only within specific developmental pathways

Question 7

What is Gastrulation (stage 5)

Answer 7

The epiblast undergoes extensive cell movement.
Three primary germ layers form:
Ectoderm
Mesoderm
Endoderm
Cells at this stage are multipotent, now restricted to their germ layer.

Question 8

What does the ectoderm germ layer make

Answer 8

nervous system and skin

Question 9

What does the mesoderm germ layer make

Answer 9

blood, heart, muscle

Question 10

What does the endoderm layer make

Answer 10

pancreas, liver, gut and lungs

Question 11

What determines cell differentiation

Answer 11

cell-cell interaction (signalling molecules and growth factors)
cytoplasmic factors

Question 12

How can stem cells be repleanished

Answer 12

Stem cells
division of differentiated cells

Question 13

What is regeneration

Answer 13

process of replacing or restoring damaged or missing cells, tissues, organs, and even entire body parts to full function.

Question 14

What is Healing

Answer 14

Wound healing is restoring integrity of tissue to protect inside from outside

Question 15

What are the issues with mammalian regeneration

Answer 15

• cancer risk
• lost or altered genetic programme
• smaller stem cell pool

Question 16

How could inability to regenerate in mammals be down to lost or altered genetic programme

Answer 16

• We are long-lived organisms that have lots of mutations
• For regeneration blastima is a group of rapidly dividing undifferentiated cells (formed by dedifferentiation)
• If we combine these with mutations and we tumours
• So the reason we don’t form blastimas could be down to risks of forming tumours

Question 17

How can other organisms detect cell location for limb regeneration

Answer 17

• Gradient of pattern of proteins along the arm
• Higher at upped arm area and decreases as you move down the arm
• This concentration difference allows cells to identify where they are along the limb

Question 18

What are blastomeres

Answer 18

Individual totipotent cells produced during early cleavage

Question 19

What is a mordula

Answer 19

dense ball of totipotent cells formed during late cleavage

Question 20

What is the inner cell mass

Answer 20

These cells in the blastocyst are pluripotent, meaning they can form any cell of the embryo, but not extraembryonic tissues.

Question 21

What is a trophoblast

Answer 21

These cells in the blastocyst contribute only to extraembryonic structures (e.g., placenta).

Question 22

What are the stages of wound healing

Answer 22

1. Bleeding
2. Clotting - prevent entry of pathogens
3. Now a gap in epithelial tissue
4. Macrophages come and kill pathogens
   - A sterile environment has now been created for the regeneration of the tissue (restoring architecture and function)
5. Epithelial cells divide to rebuild epithelial tissues

Question 23

Why might inability for mammals to regenerate limbs be down to a smaller stem cell pool

Answer 23

As cells differentiate the stem cell availability decreases.