Question

describe how the vessels and hormones affect the blood pressure. Include prod and afterload as well as antidiuretuc hormone, aldosterone and the renin-angiotensin-aldesrerone system in your explanation.

Answer 1

First lets learn how hormones affect blood pressure.

1.via renin-angiotensin-aldosterone system(RAAS)

Main role in this mechanism is played by kidneys.when blood pressure falls,the glomerular filtration rate (gfr) falls.this is because blood is filtered by kidneys as you all know.

Fall in gfr leads to the activation of RAAS mechanism.Angiotensinogen produced by liver is acted upon by renin which is produced by kidneys to convert it into angiotensin 1.Angiotensin 1 is converted into angiotensin 2 by angiotensin converting enzyme(ACE) produced by lungs.

This angiotensin 2 acts by various mechanisms to elevate blood pressure which includes arteriolar vasoconstriction,release of aldosterone etc...

2.Aldosterone causes reabsorption of sodium ions and water from renal tubules which increases blood pressure

3.this also causes pituitary gland to release antidiuretic hormone or ADH which causes reabsorption of water from collecting duct,which increases blood pressure

So,these are the hormonal methods to regulate BP

Now, lets look at how the vessels or how preload and afterload affect BP

Preload is the volume of blood remaining in the ventricles at the end of diastole.left atrial pressure at the end of diastole will determine preload.the greater is the preload,greater will be the blood pressure.(frank starling law)

Resistance against which the left ventricle must pump blood is knoen as afterload.The lower the afterload, the more blood the heart will eject with each contraction.Therefore, if the systolic pressure is lower, the heart will be able to contract to a smaller volume at the end of systole. This will result in an improved stroke volume.