How do the kidney and vascular diseases contribute to hypertension?

Primarily, it's the other way around. Hypertension contributes to kidney and vascular diseases!

The kidneys autoregulate blood flow by controlling the diameter of tiny blood vessels going into and out of each of the microscopic urine-making structures called the "nephrons". When the pressure is high, these blood vessels become stiff from overgrowth of the muscle walls used to resist the flow. The nephrons themselves are damaged from pressure, and the organ's microstructure is slowly replaced by scar.

High blood pressure also represents a challenge to the rest of the bodily blood vessels, which become thickened in response to the pressure, and which are prone to shearing injuries to the lining. This is especially true when the lining is infiltrated with cholesterol in the form of atherosclerotic plaques. As the blood vessels become thickened and stiff, the pulsations of flow hammer away at the walls, creating things like aneurysms (balloon-like dilations prone to rupture) and blockages where the atherosclerotic plaques rupture and clot. This latter mechanism is commonly the cause of heart attack and stroke, as well as other end-organ damage.

There is one particular phenomenon, however, that DOES relate to your exact question. There is a condition known as renovascular hypertension, and this is one of the forms of high blood pressure that can be traced back to a treatable cause, and can be "cured" by an intervention. Most often, of course, hypertension is considered to be "essential hypertension" which means that there is no specific cause identified, and the hypertension itself needs to be treated because of the risks it poses to the patient's health.

Renovascular hypertension is a problem that occurs in those people who develop flow limiting atherosclerotic plaques in the arteries leading off to the kidneys. When this happens, the flow to the kidneys is substantially decreased, and the kidneys are "fooled" into thinking that there is a problem of flow throughout the body. The kidneys react to a situation that, if the arteries to the kidneys were normal, would probably represent low circulating blood volume. Basically, the kidneys are unable to tell the difference between low flow because the arteries are bad, and low flow because the patient lost a lot of blood from an injury.

The response from the kidney suffering low flow comes in the form of a hormone. This hormone is called "renin" and it has one job. Renin circulates in the blood and it turns a protein called "angiotensinogen" into "angiotensin 1". Angiotensin 1 is a hormone that increases the tension in blood vessels, but more importantly, it is a precursor to "angiontensin 2", which is what it its turned into immediately after passing through the lungs. Angiotensin 2 is one of the most powerful vaso-constricting hormones we have. It increases the blood pressure dramatically.

Renovascular hypertension can be treated by procedures which open up the narrowed blood vessel, but the key is that the problem needs to be recognized first! Sometimes people with this problem go unrecognized for long periods of time.

I hope that helps!

if the kidney is not functioning well,, it will retain water which will increase the intravascular volume and increases the pressure

hypertension causes cascular disease and endothelial (cells lining the vessels) damage which will contribute to atherosclerotic plaque formation...