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Cardiovascular System. Part II Blood Vessels. Blood Vessels. An efficient mode of transport for oxygen, nutrients, and waste products to and from body tissues. Heart is the mechanical pump that propels the blood through the vessels. Heart and blood vessels form a closed-loop system.
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Cardiovascular System Part IIBlood Vessels
Blood Vessels • An efficient mode of transport for oxygen, nutrients, and waste products to and from body tissues. • Heart is the mechanical pump that propels the blood through the vessels. • Heart and blood vessels form a closed-loop system. • Blood is continuously pumped to and from the tissues. • Are not rigid and immobile. • Can pulsate and change shape in accordance with the body’s needs.
Blood Vessels • Arteries • Carry blood away from ventricles of heart • Arterioles • Receive blood from arteries • Carry blood to capillaries • Capillaries • Sites of exchange of substances between blood and body cells • Venules • Receive blood from capillaries • Veins • Carry blood toward atrium of heart
Three Main Classes of Blood Vessels • Arteries become progressively smaller as they divide and get further from the heart. • Veins become progressively larger as they merge and get closer to the heart. • Anastomosis: Site where two or more vessels merge to supply the same body region. • arterial anastomoses: alternate route • Veins tend to form many more anastomoses than do arteries.
Three Main Classes of Blood Vessels • End arteries • Arteries that do not form anastomoses • Only one route • E.g.: renal artery, splenic artery • Functional end arteries • Have small anastomoses • E.g.: coronary arteries
Arteries • In the systemic circulation, carry oxygenated blood to the body tissues. • Pulmonary arteries carry deoxygenated blood to the lungs.
Capillaries • Contain only the tunica intima, but this layer consists of a basement membrane and endothelium only. • Allow gas and nutrient exchange between the blood and the body tissues to occur rapidly. • Smallest blood vessels, connect arterioles to venules. • Are called the functional units of the cardiovascular system. • A group of capillaries (10–100) functions together and forms a capillary bed.
Veins • Drain capillaries and return the blood to the heart. • Walls are relatively thin and the vein lumen is larger. • Systemic veins carry deoxygenated blood to the right atrium of the heart, while pulmonary veins carry oxygenated blood to the left atrium of the heart. • Blood pressure is substantially reduced by the time blood reaches the veins. • Hold about 60% of the body’s blood at rest. • Veins function as blood reservoirs.
From Venules to Veins • Venules merge to form veins. • Venule becomes a “vein” when its diameter is greater than 100 micrometers. • Blood pressure in veins is too low to overcome the forces of gravity. • To prevent blood from pooling in the limbs, most veins contain one-way numerous valves to prevent blood backflow in the veins. • As blood flows superiorly in the limbs, the valves close to prevent backflow. • Numerous valves along its length to assist in moving blood back to the heart.
From Venules to Veins Many deep veins pass between skeletal muscle groups. • As the skeletal muscles contract, veins are squeezed to help pump the blood toward the heart. • This process is called the skeletal muscle pump.
Venous flow occurs by:1. muscle contraction2. respiratory pump3. valve assistance4. Ventricular relaxation
Arteriole • smallest arterioles only have a few smooth muscle fibers • capillaries lack muscle fibers
Pulse • alternate expanding and recoiling of the arterial wall that can be felt
Venipuncture of the Upper Limb • Because of the prominence and accessibility of the superficial veins of the upper limb, they are commonly used for venipuncture • These veins may be embedded with the subcutaneous tissue (fat), making them difficult to see • By applying a tourniquet to the arm, the venous return is occluded and the veins distend and are usually visible and/or palpable.
Venipuncture of the Upper Limb • The median cubital vein is commonly used for venipuncture for: • Drawing blood • Inserting a catheter for right cardiac catheterization • The dorsal venous network and the cephalic and basilic veins arising from it are commonly used for intravenous feeding
Measuring Blood Pressure • Arterial blood pressure measurement using sphygmomanometer. • A cuff is placed around the arm and inflated with air until it compresses the brachial artery against the humerus and occludes it. • A stethoscope is placed over the artery in the cubital fossa, the pressure in the cuff is gradually released • The examiner detects the sound of blood beginning to spurt through the artery. • The first audible spurt indicates systolic blood pressure. • As the pressure is completely released, the point at which the pulse can no longer be heard is the diastolic blaod pressure.
Major Branches of the Aorta • Coronary arteries • Brachiocephalic • Left common carotid • Left subclavian • Celiac • Superior mesenteric artery • Renals • Ovarian / testicular • Inferior mesenteric
Cerebral Arterial Circle • Circle of Willis • formed by anterior and posterior cerebral arteries, which join the internal carotid arteries
Hepatic Portal System • A venous network that drains the GI tract and shunts the blood to the liver for processing and absorption of transported materials. • Blood exits the liver through hepatic veins that merge with the inferior vena cava. • Is needed because the GI tract absorbs digested nutrients, and these nutrients must be processed and/or stored in the liver.
