1. Obstruction of flow within vessels :

a.Arteriosclerosis (Atherosclerosis) :

It is group of disease in which arteries are thickened and lose their elasticity. This can also be called as “hardening of arteries”. The most important type of arteriosclerosis is atherosclerosis. In atherosclerosis, fatty material (bad cholesterol) and fibrous tissue accumulate inside the arterial walls. The diameter of artery decreases, leading to reduced flow of blood supply to the tissue. This is called stenosis.

If this narrowing happens in an artery leading to heart, you experience pain in chest that is one of initial symptom of heart attack. Blood flow then reduces and tissues slowly begin to die due to lack of oxygen. The heart stops beating and person dies.

However if arteries in the upper and lower limbs (arms/legs), narrows person experiences pain after exercise/work (claudication) or even at rest (rest pain). In case of complete blockage of blood flow to limbs the tissues will die to loss of oxygen and is called gangrene. This eventually leads to amputation (cutting of dead tissues/gangrene) of arm/leg to save patients life.

Similarly if vessels supplying to brain is reduced or narrows, small portion of brain tissue dies leading to brain attack/stroke/paralysis.

b.Thrombosis :

It describes the presence of blood clot (thrombus) attached to inner (intima)wall of vessels (arteries/veins).which leads to complete blockage of blood flow to supplying body tissue and creates similar problems described above.

c.Embolism :

Blood flow of vessels is sometimes obstructed by small particles (embolus) of fat, air, blood clot and is called as embolism.

Important- the point of obstruction can be very far from where the embolus originates. For example: thrombus formed in leg veins can travels to lungs creating life threatening situation or clot can travels from heart or major blood vessels (Aorta) to leg, completely blocking artery and leading to gangrene.

2.Dilatation of blood vessels

Blood vessels are constructed in layers made up of tissues, strengthening and preserving integrity of vessels.

Certain conditions such as hypertension, atherosclerosis, trauma or infection can disrupt the integrity of vessels. As a result vessels wall gets weak and vessels bulges out this is called as aneurysm. As age advances this aneurysms are enlarged in size and leads to vessels rupture leaking blood out of vessels (hemorrhage).This affect blood flow to important body organs and tissues creating life threatening problems.