PERIPHERAL CIRCULATION

• Aorta: The thickest blood vessel due to its structural strength to handle high pressure.
• Capillary: The thinnest blood vessel, allowing for efficient gas and nutrient exchange.
• Elastic Tissue: Found in blood vessels, allowing them to distend (stretch) to accommodate varying blood pressures.
• Smooth Muscle: Present in blood vessel walls, enabling them to contract and relax to regulate blood flow.

  • Arteries have more smooth muscle, giving them the ability to vasoconstrict (narrow) and vasodilate (widen).
  • Terminal Arterioles (smaller arteries before capillaries) also have smooth muscle and the ability to vasoconstrict.
• Vena Cava: Has the largest diameter, allowing a large volume of blood to return to the heart.
• Capillaries and Venules: These vessels are very thin to allow for the diffusion of oxygen and carbon dioxide between the blood and tissues.
• Tunica Media:

  • More prominent in arteries, as it contains smooth muscle and elastic fibers, allowing arteries to regulate blood flow and pressure.
• Tunica Adventitia:

  • The thickest layer in veins, providing structural support and containing collagen fibers.
• Vasa Vasorum:

  • Small vessels that supply blood to the walls of larger blood vessels, especially in the tunica adventitia and tunica media.
• Capillaries:

  • Only have a single layer of endothelial cells (tunica intima), enabling easy diffusion of gases, nutrients, and waste products.
• Arteries

  • The pumping action of the heart produces pulsatile blood flow and causes blood pressure to fluctuate in the arteries.
• Arteries are relatively elastic and stretch as blood pressure increases during ventricular contraction (systole). The maximum pressure following contraction is called the systolic pressure.
• During ventricular relaxation (diastole), arterial pressure decreases slowly. The stored energy in the distended elastic arteries is released and the recoil of their walls drives blood flow. The lowest pressure during ventricular relaxation is called the diastolic pressure.
• Blood flow in the arterial system during diastole is driven by elastic recoil of the major arteries. 
• Windkessel Efffect

  In a compliant artery: 

  • During systole: Semilunar valves open and blood from left ventricle is ejected through aortic valve going to aorta. 
  • During diastole: Semilunar valves close and blood flow CONTINUES despite no ejection of blood from the heart.
• Continuos blood flow to tissues despite diastole and systole because aorta is very compliant (has the capacity to have elastic recoil and store blood flow)
• When left ventricles contracts = blood goes to aorta but not all goes to systemic circulation

  • Since aorta expands it can stretch so that it has reserve volume of blood so that during diastole (closed aortic valve) there is still reserved volume of blood
• What will happen if the artery is noncompliant?

  • Discontinues supply of blood to tissues