MICROANATOMY

Detailed explanation-1: -Left ventricular stroke volume also falls because of reduced pulmonary venous return (decreased left ventricular preload). This causes cardiac output (CO) and mean arterial pressure (MAP) to fall. If arterial pressure falls appreciably upon standing, this is termed orthostatic or postural hypotension.

Detailed explanation-2: -Increased pulmonary venous return to the left atrium leads to increased filling (preload) of the left ventricle, which increases left ventricular stroke volume by the Frank-Starling mechanism. In this way, an increase in venous return to the heart leads to an equivalent increase in cardiac output.

Detailed explanation-3: -The left ventricle experiences an increase in pulmonary venous return, which in turn increases left ventricular preload and stroke volume by the Frank–Starling mechanism. In this way, an increase in venous return can lead to a matched increase in cardiac output.

Detailed explanation-4: -Limiting venous return leads to reduced cardiac output and mean arterial blood pressure. An inactive person standing still is subject to the full hydrostatic pressure gradient in the venous system, and pressure in the foot veins will be  90 mmHg.

Detailed explanation-5: -The reason for these changes is that venous dilation, by reducing right atrial pressure, decreases right ventricular preload, which decreases stroke volume and cardiac output by the Frank-Starling mechanism.