Growth 3 - Body size and shape Flashcards
What is foetal transfusion syndrome ?
When one twin is getting most of the blood / nutrients and the other is getting less
Explain the growth hormone pathway
- pituitary gland releases growth hormone
- local tissues receive this
- these tissues release IGFI and IGFII
What is IGF?
insulin like growth factor
What will happen if there is more or less growth hormone?
more -> larger
less -> smaller
What do pituitary tumours cause?
gigantism
What is a major determinate of size in dogs?
- mutations controlling expression of non-coding RNA that modulate IGF
What is the effect of growth hormone on the tissues in the body?
- muscle - directly affects
- other tissues - indirectly affects
Explain the Rabbit leg experiment
- 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
What determines the size of a limb?
the bone
- soft tissues are still proportionate to the bone
What is the structure of the growth plate?
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
How is the growth plate maintained by external signals?
- 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
How does bone growth then stop?
- 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
Explain achondroplasia
- 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
What is achondroplasia?
leads to short limbs
What does FGFR3 stand for?
fibroblast growth factor receptor III
What are chrondrocyctes?
- the only cells in cartilage and they make it
what happens if you knock out FGFR3?
- very long libs
- nothing to inhibit proliferation of chondrocytes
Where is FGFR3 important?
- only in the limbs
