Blood Pressure and Flow

Systolic/Diastolic
Blood pressure is written as the pressure in the brachial artery as the ventricles contract (systolic) over the pressure when the ventricles relax (diastolic).

Pressure difference drives blood flow
BP is highest in the arteries, and is lowest in the veins. The pressure drop is caused by resistance as blood passes from the arteries through the capillaries. The difference in pressure is what drives blood flow (perfusion).

Factors of blood pressure 
BP is controlled by volume and flow resistance. If blood volume increases, so does cardiac output (L/min) and BP. Peripheral resistance can be caused by increased blood viscosity or vasoconstriction in the arteriolar level; the resulting backup of blood in the arteries causes BP to increase.

Sympathetic nerve innervation causes vasoconstriction in blood vessels (of certain organs) with vasoconstrictive receptors.

Factors of blood flow
Of the heart:
Cardiac output is influenced by contractile force, heart rate, and venous return to the heart. Increased venous return is dependent on increased: blood volume, dilation of arteries, differential pressure between arteries and veins, skeletal muscle contractions which move blood along veins.

Of the peripheral tissues:
Increased flow is dependent on increased: cardiac output (except in coronary arteries which feed to heart muscle - a systole also contracts these arteries, blocking some flow), blood volume, vessel dilation, time spent lying down.

Also see the Poiseuille equation for factors affecting flow (Q), noting what is directly or inversely proportional to Q.