Blood Vessels and Their Roles PDF

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This lecture was led by Jennifer Mansfield-Jones and covers the topics of Blood Vessels and Their Roles...

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Blood Vessels and Their Roles The Blood Travel Guide ● Following the left ventricular output: ○ Large arteries (conducting arteries) ○ Smaller arteries (distributing arteries) ○ Arterioles (resistance) ○ Capillaries (thinnest walls and allows exchanges) ○ Venules and veins (venules - small veins) ○ Right atrium of the heart ● Volume is NOT equal on each side of the heart ○ AT REST most of the blood volume is on the venous side (roughly ⅔ of the systemic blood volume is here)

Vessel Layers ● 1) Tunica Interna - The innermost layer ○ Endothelial cells with a basement membrane ● 2) Tunica Media - Middle layer ○ Smooth muscle layers, collagen, and some elastic tissue ● 3) Tunica Externa - Outermost layer ○ Collagen fiber layer with some elastic tissue (in veins) ● In determining an artery vs a vein in microscope slide - The artery has a round Lumen in the middle of the structure

Systolic and Diastolic Pressure ● Systolic Pressure - Measures the force your heart exerts on the walls of your arteries each time its beats ● Diastolic Pressure - Measures the force your heart exerts on the walls of your arteries between beats ● In areas that have a high systolic pressure, the tunica externa need to have a thick layer of tough fibrous connective tissue and a good supply of vitamin c

Conducting (Large) Arteries ● Found in the aorta and the carotid and is springy and tough ● From inside to outside: ○ Lumen - The “hole” or open part of the artery, the innermost structure ○ Tunica Interna - The structure that touches the blood ■ Made from endothelium ■ Is the only part of the artery that touches blood (cannot come into contact

with collagen or will form a clot) ○ Basement Membrane - Part of the Tunica Interna, separates it from Tunica Media ○ Tunica Media - The structure that allows the aorta to “spring back” ■ Is made of elastic connective tissue ■ Some smooth muscle is found here for controlling the size of the artery, but it’s not it’s main job (must stay large for blood flow and high pressure) ○ Tunica Externa - The outermost structure ■ Made from tough fibrous connective tissue (helps the aorta and other large arteries from failing because of the high systolic pressure) ■ A vitamin c deficiency is life threatening - fibrous connective tissue is maintained by vitamin c ■ High pressure = stronger need to be constantly repaired

Distributing Arteries ● Have an adjustable diameter and are also called muscular arteries ● From inside to outside: ○ Tunica Interna - Is the same as the tunica interna found in the conducting arteries ■ Contains a basement membrane and is made from endothelium ○ Tunica Media - Is vastly different and contains elastic lamina (internal and external) ■ Is elastic connective tissue found wrapped around the basement membrane and in between the tunica media and tunica externa ■ Is mostly made of smooth muscle to control where blood flow goes or how concentrated it is ○ Tunica Externa - Same tunica externa structure as the conducting arteries ■ Still needs tough connective tissue to keep it operating under high pressure ■ Still needs vitamin c for repairs

Arterioles ● Are numerous but small ● Contribute to distribution/control ○ Has a regional role: Blood distribution ■ Is not responsible for limb/organ control because they're too small ○ Has another important job: Has a strong resistance ■ This makes it harder for blood to pass through and has a very noticeable drop in pressure ● Is considered the last “muscular step” before the capillaries ● From inside to outside: ○ Tunica Interna - Consists of the basement membrane and endothelial cells ○ Tunica Media - Is made completely of smooth muscle and is very thin

○ Tunica Externa - Is very minimal and cannot handle high pressure

Capillaries ● Blood/tissue exchange of material ○ Exchange Zone: Very thin walls that allow exchanging of material (wastes, oxygen, etc.) ● Capillaries only have a tunica intima that can be one cell thick ● Capillaries are not always carrying blood ○ There are too many capillaries in the body to match the blood flow ○ The body controls which ones need blood ● Precapillary Sphincters - Control where blood is distributed ○ Controlled by smooth muscle cells under autonomic motor and local controls ■ Local controls: hormones, local chemical factors, other oddball factors ● Exchange across walls only happens in capillaries: ○ Continuous Capillary - The majority type of capillary in the body ■ Water, gases, and glucose get in and out easily ■ Have small holes for transfer of materials ■ In the central nervous system they are regulated by glial cells to increase tightness of endothelial cells ● AKA “Blood Brain Barrier” ○ Fenestrated Capillary - The “leakier” capillaries ■ Bigger molecules like hormones can cross easily (to and from) ■ Located in areas we need dissolved solutes such as the kidneys filtration system ○ Discontinuous Capillaries/ Sinusoids - Are the “leakiest” capillaries ■ Have big windows and large gaps between endothelial cells ■ Can be found in the liver and bone marrow ■ Large holes between cells let plasma proteins in and out along with red blood cells

Veins ● Valves prevent backflow ○ Valves help to keep the blood flowing “uphill” and moving in the right direction ● Veins can adjust in size ● Capacitance of vessels (~64% of blood volume here) ● Have the lowest pressure inside ● Veins have: ○ Tunica Media - Controls diameter ○ Tunica Externa - Controls some adjustment to the diameter ● In a vein transplant direction absolutely matters

○ The placement of the valve and the direction it opens matters ■ Must know the correct orientation of the vein during transplant...