The Circulatory System Blood Flow Vessels Vessels are

The Circulatory System Blood Flow

Vessels • Vessels are a term for an object that contains or holds something else. – Circulatory system has its own set of vessels for the blood that flows through it, we have already discussed two of them, can you remember them?

Three Types of Vessels (covered in more detail later) • Arteries – caries blood away from the heart (oxygenated or deoxygenated? ) • Veins – carries blood back to the heart (oxygenated or deoxygenated? ) • Capillaries – Small vessels that normally only fit one red blood cell through them at a time…these release the oxygen in the red blood cell into the cells around it

Vessel Structure • Remember the doughnut…the inner most empty-space that the blood flows through is called the lumen • The rest of the layers are called tunics, meaning “cloaks. ”

The Tunics • Tunica Interna – Innermost layer of vessels. It is the most internal (remember). • Tunica Media – Middle layer of tunic. Smooth muscle cells determine whether lumen expands or contracts • Tunica Externa – Outermost layer. 3 Functions: – Protection – Reinforcement – Anchoring

How Vessels Affect Bloodflow • The tunics can do two things to affect the flow of blood: – Vasoconstriction – The tunica media flexes, making the lumen smaller, lowers blood flow, but making it flow at a higher pressure. – Vasodilation – The tunica media relaxes, causing an increase in lumen size, raising blood flow at a lower pressure.

What keeps blood vessels going? • On the outside of the tunica externa, there is a structure known as the vasa vasorum (the vessel of the vessels). This provides nourishment to the cells within tissues of the blood vessel.

Arteries • Different types of arteries –Conducting Arteries –Distributing Arteries –Arterioles

Conducting Arteries • Largest arteries with the greatest lumen area. • Move blood from heart to medium sized arteries. • Made of large amounts of elastin to help with expansion and contraction (review ? : what are these terms called? )

Muscular Arteries • These arteries deliver blood to specific organs within the body. • Have thickest tunica media of any arteries…why? • Function mostly in the actual act of vasoconstriction and vasodilation.

Arterioles • Smallest arteries. • Lead to capillaries. • Faucets of the body…this is where the most control over blood flow comes from. • Constriction of arterioles has blood bypass area while dilation greatly increases blood flow to that portion of the body.

Capillaries • These are the smallest blood vessels in the body. • Consist of three different types – Continuous Capillaries – Fenestrated Capillaries – Sinusoidal Capillaries

Continuous Capillaries • Appear most in skin and muscles • Called continuous because they provide an uninterrupted lining formed by “tight junctions” • This lining helps to exchange limited amounts of fluid and solutes in blood

Fenestrated Capillaries • Similar to continuous, but differ in the fact that there are pores within these capillaries • These pores give these capillaries much greater permeability • Usually found where absorption or filtration occurs (stomach & kidneys)

Sinusoidal Capillaries • “Leaky” capillaries found only in certain organs • Very few tight junctions, so largely porous • Allow large molecules to pass through • In cells that are involved in signaling and the immune system

Interweaving • Capillaries do not function individually…but the three types typically weave together to form a capillary bed

Venous System • The venous system returns blood back to the heart • Veins are composed of: – Venules – Veins – Venous valves

Venules • Venules – formed when capillaries unite. These are used after the blood has dropped off its supply of oxygen – Smallest called the postcapillary venule – Venules eventually run together to form veins

Veins • Veins are the large vessels that return blood to the heart, consisting of many venules • Veins have much thinner walls than arteries as the blood pressure in veins is much lower (remember lab) • House up to 65% of the body’s blood

Venous Valves • These are like the valves within the heart – Function to prevent backflow • Found in veins of the limbs as gravity prevents flow back to the heart – Giraffe – if valves did not exist, every time a giraffe would put its head down to drink, too much blood would flow into its head and it would die

Recap