Vein Anatomy

Venous Reserve

Your veinsBlood vessels that return deoxygenated blood to the heart (except pulmonary veins, which carry oxyge hold 60 percent of your blood. The largest veins can be called capacitance vessels because they act as reservoirs. If you nick your femoral artery and blood gushes out, your veins react by mobilizing their reservoir. The systemic veins constrict as much as possible in response to the loss in blood volume. This abnormal constriction pushes blood back to the heart, which redistributes it into arteriesBlood vessels that carry oxygenated blood away from the heart (except pulmonary arteries, which carr.

It’s not just veins that mobilize blood. Veins in organs like the liverA large organ that produces bile, detoxifies blood, and stores nutrients., skinThe body’s largest organ, providing protection and regulation., and lungs hold the most blood and act as significant reservoirs. When mobilized, they push blood into circulation. This explains why someone who is bleeding heavily, either externally or internally, might appear pale. Blood is drawn from the skin’s reservoir.

Venules

As the capillariesThe smallest blood vessels where gas, nutrient, and waste exchange occurs between blood and tissues. come together and leave the capillary bed, they form a venule. Venules are still exchanging with the tissue around them because they are reasonably porous. Venules then come together to form veins.  Veins can be classified as medium or large veins.  Veins still hold about 60 percent of the blood in your body. This is interesting because, even when veins hold a lot of your blood, they’re not even full. They’re like half full most of the time.  In this picture of a medium sized vein, the lumenThe inside space of a hollow organ or structure. is collapsed. This is compared to the open circle of the lumen of an artery.

Vascular Anastomoses

Look at the back of your hand. You will see veins draining blood from the capillary networks in your fingers. They also drain from the networks in your palm. You can see the vessels coming together and interconnecting in structures called anastomosesConnections between blood vessels that allow blood to bypass capillary networks, ensuring circulatio. There is only one route via an artery to a capillary bed. There are many routes out of the bed. You have more veins than arteries.  These interconnections are very common around articulations like the elbow and the knee. As you bend your elbow or knee, you squeeze blood vessels. This action requires your blood to take alternate routes to the capillary beds. When you are dehydrated, these vessels and their interconnections are usually quite pronounced on the back of your hand. If you are well watered or well hydrated they are less obvious. Look at the back of your hand. You will see veins draining blood from the capillary networks in your fingers. They also drain from the networks in your palm. You can see the vessels coming together and interconnecting in structures called anastomoses. Although there is only one route via an artery to a capillary bed, there are many routes out of the bed.  You have more veins than arteries.  These interconnections are very common around articulations like the elbow and the knee. As you bend your elbow or knee, you squeeze blood vessels. This action requires your blood to take alternate routes to the capillary bets. When you are dehydrated, these vessels and their interconnections are usually quite pronounced on the back of your hand. If you are well watered or well hydrated they are less obvious.

Pressure in Veins

By the time the blood reaches the venous system, there is not enough pressureThe force exerted by gases in the respiratory system, affecting airflow and gas exchange.. This lack of pressure prevents the blood from returning to the heart. Veins have several modifications that help them get the blood to flow back to the heart. First, veins have valves, which prevent blood from flowing backwards. Secondly, more skeletal muscle activity increases the efficiency of venous return. As the skeletal muscles surrounding the deepAway from the surface of the body. veins contract and relax, they move blood toward the heart. This is called the muscular pump. In addition to this, the pressure changes in the thoracic cavityThe body cavity housing the heart and lungs. during breathing help facilitate venous return. This is called the respiratory pump. Of the two, the skeletal muscle pump is the more important.

Veins

The lumen of a vein appears collapsed, like a frown. Medium and large veins have very little smooth muscle with a slight hint of elastic in them.  Some of the large veins have no smooth muscle.  The tunica externaThe outermost layer of a blood vessel, made of connective tissue, providing support and anchoring. can be pretty thick on the largest of veins.  The largest of veins, such as the vena cava, is extremely thick. It needs its own blood supply, just like any other organ.  The little blood vessels that vascularizeTo invade a tissue with blood capillaries. these large veins are called the vaso vasorumSmall blood vessels that supply the outer layers of large blood vessels with nutrients and oxygen. which means “vessels of the vessels.”

Venous Valves

Veins have valves, which are infoldings of the tunica intimaThe innermost layer of a blood vessel, consisting of endothelium and a thin connective tissue layer.. These infoldings prevent backflow.  Blood returning to the heart in the large veins of your legs needs these valves to prevent backflow with gravity.  If you spend a lifetime on your feet, such as, oh I don’t know, maybe teaching and nursing?!?!?!, these valves can blow out. Retail, too.  They don’t close fully anymore, allowing blood to pool in your lower extremities.  This causes varicose veins. What’s the solutionA homogeneous mixture of two or more substances. to this? Wear compression socks. Don’t wait until after 20 years of working on your feet to start wearing them.  Start now.  Seriously. If you want surgery for varicose veins, you will need to wear compression socks for a long time. This is required before you’re eligible for the procedure.  I could teach an entire class on compression stockings and constipation.  I bet half of you would sing up for it! If we throw in incontinence, I bet I could get another 25% of you!