Growth 3 - Body size and shape

Question 1

What is foetal transfusion syndrome ?

Answer 1

When one twin is getting most of the blood / nutrients and the other is getting less

Question 2

Explain the growth hormone pathway

Answer 2

• pituitary gland releases growth hormone
• local tissues receive this
• these tissues release IGFI and IGFII

Question 3

What is IGF?

Answer 3

insulin like growth factor

Question 4

What will happen if there is more or less growth hormone?

Answer 4

more -> larger
less -> smaller

Question 5

What do pituitary tumours cause?

Answer 5

gigantism

Question 6

What is a major determinate of size in dogs?

Answer 6

• mutations controlling expression of non-coding RNA that modulate IGF

Question 7

What is the effect of growth hormone on the tissues in the body?

Answer 7

• muscle - directly affects
• other tissues - indirectly affects

Question 8

Explain the Rabbit leg experiment

Answer 8

• inhibit the growth of one leg by limiting the blood flow
• other leg grows normally
• legs therefore do not communicate with each other
• release inhibition
• leg catches up - has a faster growth than the other leg
• leg knows how big it has to be

Question 9

What determines the size of a limb?

Answer 9

the bone
- soft tissues are still proportionate to the bone

Question 10

What is the structure of the growth plate?

Answer 10

Going from top to bottom of the growth plate:

• zone of proliferation - stem cells
• cell enlargement
• cartilage matures (calcifies)
• cartilage cells die
• replacement with bone cells

Question 11

How is the growth plate maintained by external signals?

Answer 11

• IGFI controls rate of cell proliferation
• as cells mature they send a signal up the growth plate telling younger cells to mature to replace them
• these cells that are about to mature then send a signal to younger cells to increase proliferation
• this signal works by Indian hedgehog (IHH) signals to bone sheath (periosteum) which then releases a signal called PTHrP to the stem cells

Question 12

How does bone growth then stop?

Answer 12

• when the bone is small, it is near the edge
• when the bone is larger, it is much further away
• signalling loop then stops working and limb reaches maximum size

Question 13

Explain achondroplasia

Answer 13

• a mutation in FGFR3
• FGF signalling through FGFR£ usually inhibits proliferation and differentiation of chondrocytes
• this receptor is always active in achondroplasia
• proliferation happens slowly and growth plate is shut down too early

Question 14

What is achondroplasia?

Answer 14

leads to short limbs

Question 15

What does FGFR3 stand for?

Answer 15

fibroblast growth factor receptor III

Question 16

What are chrondrocyctes?

Answer 16

• the only cells in cartilage and they make it

Question 17

what happens if you knock out FGFR3?

Answer 17

• very long libs
• nothing to inhibit proliferation of chondrocytes

Question 18

Where is FGFR3 important?

Answer 18

• only in the limbs