The walls of both arteries and veins are made up of three main layers – a tough outer coating, a wall of muscle, and a smooth, inner lining. Arteries have a thicker middle layer of muscle to control the flow, or pressure, of blood. Pressure needs to be high enough to push blood around the system, but not so strong that it damages delicate capillaries.
Wall of muscle
Arteries’ muscular walls stretch to cope with the high-pressure pulses of blood pumped out by the heart. The muscle contracts to make the artery narrower and reduce blood flow, and relaxes to widen it and allow blood to flow more freely.
Artery:
Blood
Blood is made up of three types of cells floating in yellowish liquid called plasma. Arterial blood has just passed through the lungs and is ready to boost oxygen to sustain the peripheral organs.
Inner layer
The smooth inner lining lets blood flow easily. The innermost layer, the tunica intima (also called tunica interna), is simple squamous epithelium surrounded by a connective tissue basement membrane with elastic fibers.
Membrane
A thin, protective covering surrounds the inner layer. The vascular basement membrane is a dynamic, self-assembled layer of proteins, glycoproteins, and proteoglycans formed by and enveloping endothelial cells and pericytes of blood vessels.
Muscle layer
Muscular arteries contain more smooth muscle cells in the tunica media layer than the elastic arteries.
Elastic layer
Elastic arteries are those nearest the heart (aorta and pulmonary arteries) that contain much more elastic tissue in the tunica media than muscular arteries. These layers allow the artery to stretch and bounce back into shape.
Capillaries
Capillaries, the smallest and most numerous of the blood vessels, form the connection between the vessels that carry blood away from the heart (arteries) and the vessels that return blood to the heart (veins). The walls of capillaries are only one layer of cells thick, enabling gases to pass easily through them.
Outer layer
The artery wall is made of tough but flexible collagen. This layer is connective tissue with varying amounts of elastic and collagenous fibers.
Vein:
Valve
Valves in the veins make sure the blood flows one way only. Valves also help blood travel back to the heart against the force of gravity.
Muscle layer
The layer of muscle is thinner than an artery’s.
Picture Credit : Google
