Venous system. Veins of systemic and pulmonary circulation

BLOOD VESSELS

Major Systemic Veins

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Major Systemic Veins Superior Vena Cava Inferior Vena Cava

Major Systemic Veins Lower Limb Dorsal venous arch Dorsalis pedis vein Great saphenous vein Dorsalis pedis vein ↓ Anterior tibial vein Popliteal vein Femoral vein External iliac vein Common iliac vein Inferior vena cava Small saphenous vein Plantar Arch ↓ plantar veins Posterior tibial vein Fibular (peroneal) vein

BLOOD VESSELS Arterioles Veinules

COMPARISON OF ARTERIES, CAPILLARIES, & VEINS Arteries & Arterioles Capillaries Veinules & Veins Tunica Media Tunica Intima *Arteries carry blood to smaller arterioles which in turn lead to capillaries. * Capillaries carry blood to veinules * which lead to veins which carry the blood back to the right atrium. * The tunica adventitia or tunica externa is the outermost covering of arteries, arterioles, veinules and veins. It is primarily composed of connective tissue which protects, supports and anchors the vessels to adjacent structures. Loosely woven collagen fibers are the primary components of the tunica adventitia along with nerve fibers, lymphatic vessels and elastic fibers. * The tunica media is the middle layer of arteries, arterioles, veinules and veins. It is primarily made up of smooth muscle cells arranged in a circular fashion around those vessels along with some elastin. The primary function of the tunica media is vasoconstriction and vasodilation to regulate blood pressure and maintain the continuous circulation of blood. * The tunica intima or tunica interna is primarily made of simple squamous epithelial cells which line the lumen of all blood vessels. It provides a smooth surface to reduce friction. Since capillaries lack the tunica media and tunica adventitia, they are much more permeable than other blood vessels. Thus it is only through the walls of capillaries that diffusion of O2 and nutrients from the blood * into the cells and tissues as well as the diffusion of wastes from the cells and tissues into the blood occurs. * (Blood) Tunica Adventitia

CAPILLARY BEDS Sphincters regulate the flow of blood into capillaries thus affecting the perfusion of capillaries & the amount of diffusion which occurs between the blood and the tissues.*

BLOOD PRESSURE

VENOUS PUMP

VENOUS PUMP 1. Valves - formed from folds of tunica intima prevent backflow of blood in veinules & veins. 2. Function like semilunar valves forcing blood to flow against gravity toward the heart. Blood pressure is highest in the arteries and drops off gradually as the blood flows through the circulatory system. By the time the blood has passed through the capillaries, the pressure has decreases to 20 mm Hg or less and continues to drop. This low pressure is insufficient to allow the blood to move against gravity to return to the heart. The venous pump in veinules and veins makes up for the lack of pressure. * The valves forming the venous pump are formed from folds in the tunica intima. * They act as one-way valves, only allowing the blood to move toward the heart. * The force to move the blood from valve to valve toward the heart is provided by skeletal muscles which press against the walls of veinules and veins as they contract forcing the blood through the next valve toward the heart. * When skeletal muscles relax, the distal valves close to prevent blood flow away from the heart. *

VENOUS PUMP 3. Skeletal muscles pressing against walls of veins provide force to move blood from one valve through the next toward the heart. 4. Skeletal muscles pressing against walls of veins provide force to move blood from one valve through the next toward the heart.

VARICOSE VEINS 1. Veins that are stretched, dilated & overfilled with blood due to incompetent valves 2. Contributing causes: Weak valves or veins - (heredity) Excessive weight Excessive standing, straining Inadequate exercise Increased intra-pelvic pressure - pregnancy, constipation Varicose veins * have been stretched, dilated or overfilled to the extent that the valves of the venous pump are not able to close properly to prevent the backflow of blood. Thus blood pools in the extremities further aggravating the situation. * Things that may contribute to the formation of varicose veins include: * weak valves or veins due to heredity, * excessive weight, * standing for long periods of time with little movement and straining, * inadequate exercise, * increased intra-pelvic pressure due to pregnancy, constipation, etc. *

VARICOSE VEINS * The pictures show how varicose veins may appear. * They tend to occur most frequently in superficial veins where skeletal muscles do not completely surround the veins being affected. Because of the stagnation of blood in varicose veins, there is an increased risk of blood clot formation with the attendant risk of emboli. *

Major Systemic Veins Lower Limb Dorsal venous arch Great saphenous Femoral External iliac Common iliac Inferior vena cava Dorsal venous arch Great saphenous Small saphenous Dorsalis pedis Anterior tibial Popliteal Femoral External iliac Common iliac Inferior vena cava Plantar arch Plantar veins Posterior tibial Fibular Anterior tibial Popliteal Femoral External iliac Common iliac Inferior vena cava Dorsal venous arch Small saphenous Popliteal Femoral External iliac Common iliac Inferior vena cava

Major Systemic Veins Abdomen I N F E R I O R V E N A C A V A Hepatic veins Hepatic veins Left suprarenal vein Right suprarenal vein Renal vein Left gonadal vein Right gonadal vein Lumbar veins Lumbar veins

Major Systemic Veins Head and Neck Brachiocephalic vein Occipital vein ↓ Posterior arcuate vein External jugular vein Vertebral Facial Superficial temporal vein Subclavian vein Brachiocephalic vein Superior vena cava Internal jugular vein

Major Systemic Veins Head and Neck Occipital vein Posterior arcuate vein External jugular vein Subclavian vein Brachiocephalic vein Superior vena cava Facial vein Superficial temporal vein Internal jugular vein Brachiocephalic vein Superior vena cava Vertebral vein Subclavian vein Brachiocephalic vein Superior vena cava

Major Systemic Veins Upper Limb Axillary ↓ Subclavian Brachiocephalic Median antibrachial vein Ulnar vein Radial vein Basilic vein Brachial vein Cephalic Axillary ↓ Subclavian Brachiocephalic Superior vena cava Median cubital vein

Major Systemic Veins Upper Limb Ulnar vein Basilic vein Radial vein Brachial vein Axillary vein Subclavian vein Brachiocephalic vein Superior vena cava Basilic vein Brachial vein Axillary vein Subclavian vein Brachiocephalic vein Superior vena cava Cephalic vein Axillary vein Subclavian vein Brachiocephalic vein Superior vena cava

Posterior intercostal veins Major Systemic Veins Thorax Azygos System Posterior intercostal veins ↓ Ascending lumbar vein Accessory hemiazygos veins Hemiazygos vein Azygos vein Superior vena cava

Major Systemic Veins Thorax Azygos System Posterior intercostal veins Ascending lumbar vein Accessory hemiazygos veins Azygos vein Superior vena cava Posterior intercostal veins Ascending lumbar veins Hemiazygos vein Azygos vein Superior vena cava

Major Systemic Veins Hepatic Portal System Veins from Veins from distal large intestine ↓ Inferior mesenteric vein Veins from spleen ↓ Splenic vein Veins from small intestine, ascending and transverse colon ↓ Superior mesenteric vein Veins from digestive viscera, spleen, & pancreas ↓ Hepatic Portal vein Liver Hepatic veins Inferior vena cava Veins from lesser curvature of stomach ↓ Left gastric vein

Major Systemic Veins Hepatic Portal System Veins from distal large intestine Inferior mesenteric vein Veins from digestive viscera, spleen and pancreas Hepatic portal vein Liver Hepatic veins Inferior vena cava Veins from small intestine, ascending and transverse colon Superior mesenteric vein Veins from digestive viscera, spleen and pancreas Hepatic portal vein Liver Hepatic veins Inferior vena cava Veins from spleen Splenic vein Veins from digestive viscera, spleen and pancreas Hepatic portal vein Liver Hepatic veins Inferior vena cava Veins from lesser curvature of stomach Left gastric vein Liver Hepatic veins Inferior vena cava

Major Systemic Veins Hepatic Portal System