ANATOMY

Detailed explanation-1: -Most capillaries are only about 8 to 10 micrometers in diameter (a micrometer is 0.001 mm). They’re so tiny that red blood cells have to pass through in a single file line. Capillaries contain two layers of cells: Endothelial cells are inside the capillary.

Detailed explanation-2: -Red blood cells squeeze through narrow capillaries in single file. Haemoglobin molecules inside red blood cells pick up and carry the oxygen. These oxygen-rich cells travel in the blood vessels from the lungs to the left side of the heart. The blood is then pumped around the body.

Detailed explanation-3: -Capillaries: Arteries and veins are connected by blood capillaries, microscopically small tubes which form a network, the capillary bed in different tissues. The blood capillaries are so small that red blood cells can only move in single file through it. The exchange of all substances takes place in these capillaries.

Detailed explanation-4: -Red Blood Cells (erythrocytes) are approximately 0.01 mm, so only one can pass through the small capillary.

Detailed explanation-5: -The walls of capillaries are made up of a thin cell layer called endothelium that’s surrounded by another thin layer called a basement membrane.