BP is pressure of blood on the vessel wall and its generated by the pumping force of LV

BP & ISSUES:
BP is pressure of blood on the vessel wall and its generated by the pumping force of LV. So we need three things
Blood (intra vascular volume/ volume of blood )
Vessel wall in approximity to blood
Pumping force of LV.

BP can be increased or decreased by manipulating antic these factors.

BLOOD VOLUME & BP:
Renal failure causes HTN.
Diuretics, bleeding and dehydration reduce BP. Diuretics are one option to control BP.

VESSEL WALL & BP:
vasoconstriction brings blood and vessel wall together and cause high BP . Vasodilatation causes low BP. Sympathetic nerves cause stimulation of Alpha receptors on blood vessels cause smooth muscle contraction mediated by calcium. Hence smypatholytics, alpha blockers, calcium channel blockers, and direct vasodilators can all be used to reduce BP. Angiotensin II also cause vasoconstriction, hence ACEi or ARBs can can also be used.

LV OUTPUT & BP :
Beta 1 receptors on cardiac muscles increase force of contraction by calcium influx. Hence beta blockers. Calcium blockers can reduce BP by reducing cardiac output.

ESSENTIAL HTN:
Positive family history or HTN in old age are usually essential HTN.
However resistant HTN , malignant HTN, young age onset, associated weight Changes, or electrolyte abnormalities should alert secondary causes.

SECONDARY CAUSES of HTN:

Reno-vascular disease are common cause of secondary HTN. Hence first exclude renal causes. Renal failure, renal arterial stenosis, congenital renal disease like horse shoe kidney, single kidney, ectopic kidney etc needs exclusion.

Endocrine causes usually lead to weight changes with HTN. Or HTN with electrolyte abnormality ( K, Na,or Calcium).
Hypothyroid, Cushing , PCO, cause weight gain with HTN. Pheochromocytoma, hyperthyroid, acromegaly, cause weight loss and HTN. Hyper Aldosteronism causes HTN and hypo kalemia. Hyper Parathyroidism causes HTN & high calcium,
Addison’s, hypopitutrism etc cause low BP with weight loss. Obesity, hyperuricemia or metabolic syndrome etc often cause HTN as an association. Drugs like cocaine, amphetamine etc also cause vasoconstriction and HTN especially in young people.

Renin secreting tumours are rare but they do exist.
Vasculitis can cause HTN due to renal disease or vascular narrowing. Associated clinical features help.

WHAT DRUGS are BETTER?.
All the Drugs causing vasodilatation ( except ACEi/ARBs) are safe in pregnancy and renal disease both. Vasodilators also help treating peripheral vascular disease as well. So pregnancy, renal disease or PVD ,vasodilators are good choice. Vasodilators cause reflex tachycardia, so avoid in conditions where tachycardia is dangerous, but help in conditions where bradyarrhythmia are there. Alpha blockers also help treating BPH.

Beta blockers and ACEi/ARBs affect foetal kidney development by affecting renin. Diuretics cause hypovolemia and placental hypoperfusion. So avoid in pregnancy.

Calcium channel blockers can worsen systolic heart failure. So avoid in systolic heart failure.

Diuretics can help renal disease by reducing hypervolemia and BP. Beta blockers / cardiac calcium channel blockers can help control cardiac tachy arrhythmia/Ischemia etc but can worsen bradyarrhythmia.

If no co-existing condition then ACEi/ARB. Thiazides diuretics or beta blockers/ calcium channel blockers can be used to start with. Mono therapy is always good unless it’s not effective, not enough or causes side effects.