don't know exactly how much to say,but, here it goes....
Coarctation of aorta= obstruction= increased blood pressure/volume in proximal parts of obstruction = blood needs to go somewhere = there is most commonly left subclavian artery.
This collateral circulation will develop mainly from the subclavian, scapular, internal thoracic,internal mammary and intercostal arteries.
Collateral circulation is divided into anterior and posterior systems
In the anterior system, the internal mammary arteries and the epigastric arteries join to form collaterals which supply the abdominal wall and the lower extremities.
In the posterior system, the parascapular arteries connect with the intercostal arteries to form collaterals which supply the distal aortic compartment and primarily the abdominal viscera.
The left subclavian may form collaterals through linkage to the IMA's and intercostals to give blood supply distally. The right subclavian will join with the vertebral, spinal, cervical, and scapular branches, and will eventually provide blood supply to the intercostal circuit.
bottom line, collaterals are basically important for diagnostic purpose. you will find a young adult with htn only on left side + on aortography you will see the coarctation plus the subclavian artery....not to mention the notching of left sided ribs( specially 6th-9th)
please read this responsibly...i dont claim that i cant be wrong.