what affect does anti-diurectics have on the nephrons and blood pressure?

Your body makes one, ADH, which increases the permeability of the nephrons and collecting duct in the kidneys. This allows the body to either uptake water directly, or passively uptake water by directly uptaking salts. Since water tends to effortlessly diffuse TOWARD salts, this passively reabsorbs water.

The increase in water volume in the blood stream increases blood pressure as the volume has now gone up. Aldosterone is another hormone like ADH which has this effect.

Anti-diuretics hormones speeds up the rate of re-absorption of water in your blood.

When water potential of your blood plasma is low, your pituitary gland in your brain detects it & secretes the anti-diuretic hormone so that your nephrons will reabsorb more water through the blood capillary allowing your water potential of blood return to normal level & vice versa.

Blood pressure is involved in this process because ultrafiltration occurs at the bowman capsule(part of nephron) which allows water to pass through the membrane of the blood capillaries in glomerulus into the bowman capsule

Anti- diuretics don't allow your kidneys to release water outside of the body. They higher the blood pressure because water is not being let out.