Proportion Flashcards
Causes of gigantism
Pituitary gland tumour that affects growth hormone
How is mammalian body size primarily regulated by?
Pituitary gland secreting growth hormone to local tissues, insulin-like growth factors to cells (protein structure similarity)
What does growth hormone affect?
Post-natal muscle growth directly but only other tissues indirectly
What did the rabbit leg experiment prove?
No communication between limbs for growth (different growth rates), once inhibition released faster growth rate therefore time not only factor
What is the original possible explanation for growth rate?
The ability of the growth plate of the long bone to respond to GH declines with the number of cell divisions it has made/ inherent sensitivity declines
What is the current explanation for growth rate?
Growth plate maintains itself using internal and external signals- dying cells signal for cells to mature, maturing cells signal via sheath of bone to proliferate new cells and insulin like growth factors also signal for proliferation
What is the structure of the growth plate?
Top to bottom: zone of proliferation, cell enlargement, cartilage matures/ calcifies, cartilage cells die, replacement with bone cell (conveyor belt)
Why does rate of growth fall away with size?
More growth= bigger distance from bone sheath= less efficient/ weaker signal so grows slower as less proliferation promoted
How is limb growth vulnerable?
Takes place rapidly hence high demand for oxygen- vascular system needs to grow very quickly into elongating limbs (impaired vascular growth)
How is Phocomelia caused?
Seal limb- thalidomide, impaired vascular growth vs anti cancer drug
What is Achondroplasia?
Activating mutation in FGFR3 (inhibited cartilage growth as proliferation declines/ premature closure of growth plates)- constant signal to reduce growth
What does Achondroplasia provide evidence for?
Independence of head and body growth, tissue growth not independent- hierarchy of bone growth
What is different about skin growth?
Growth unpredictable/ response to events such as pregnancy and obesity/ environmental factors not just genetically programmed/ cultural skin stretch therefore grows under tension
How do mechanically isolated organs grow?
Spleen- total mass= mass of one spleen (concentration in bloodstream?)
Thymus= all normal sized
So overall unclear
