Glossary for Blood Vessels

Blood Vessels & Circulation

• Anastomoses: Connections between blood vessels that allow blood to bypass capillary networks, ensuring circulation even if a vessel is blocked.
• Arteries: Blood vessels that carry oxygenated blood away from the heart (except pulmonary arteriesBlood vessels that carry oxygenated blood away from the heart (except pulmonary arteries, which carr, which carry deoxygenated blood).
• Arterioles: Small arteries that regulate blood flow into capillariesThe smallest blood vessels where gas, nutrient, and waste exchange occurs between blood and tissues. through vasoconstrictionThe narrowing of blood vessels due to contraction of smooth muscle, increasing blood pressure and re and vasodilationThe widening of blood vessels due to relaxation of smooth muscle, decreasing blood pressure and incr.
• Capillaries: The smallest blood vessels where gas, nutrient, and waste exchange occurs between blood and tissues.
• Veins: Blood vessels that return deoxygenated blood to the heart (except pulmonary veinsBlood vessels that return deoxygenated blood to the heart (except pulmonary veins, which carry oxyge, which carry oxygenated blood).
• Venules: Small veins that collect blood from capillaries and transport it to larger veins.

Blood Vessel Layers & Structure

• Endothelium: The innermost layer of blood vessels, composed of simple squamous epithelial cellsThe basic structural and functional units of life., which reduces friction and facilitates exchange.
• External elastic lamina: A layer of elastic fibers found in muscular arteries, providing flexibility and recoil.
• Internal elastic lamina: A layer of elastic fibers between the tunica intimaThe innermost layer of a blood vessel, consisting of endothelium and a thin connective tissue layer. and tunica mediaThe middle layer of a blood vessel, composed of smooth muscle and elastic tissue, responsible for va in arteries, allowing for stretch and recoil.
• Tunica externa: The outermost layer of a blood vessel, made of connective tissue, providing support and anchoring.
• Tunica intima: The innermost layer of a blood vessel, consisting of endotheliumThe innermost layer of blood vessels, composed of simple squamous epithelial cells, which reduces f and a thin connective tissue layer.
• Tunica media: The middle layer of a blood vessel, composed of smooth muscle and elastic tissue, responsible for vasoconstriction and vasodilation.
• Vaso vasorum: Small blood vessels that supply the outer layers of large blood vessels with nutrients and oxygen.

Types of Arteries & Capillaries

• Elastic artery: Large arteries (e.g., the aorta) with a high proportion of elastic fibers, allowing them to stretch and recoil with each heartbeat.
• Muscular artery: Medium-sized arteries with more smooth muscle, allowing them to regulate blood flow through vasoconstriction and vasodilation.
• Continuous capillary: A type of capillary with tightly connected endothelial cells, allowing only small moleculesGroups of atoms bonded together. to pass (found in muscles, lungs, and the brain).
• Fenestrated capillary: Capillaries with pores (fenestrations) that allow rapid exchange of fluids and small solutes (found in kidneys and intestines).
• Sinusoidal capillary: Large, leaky capillaries with wide gaps between endothelial cells, allowing passage of large molecules and cells (found in the liverA large organ that produces bile, detoxifies blood, and stores nutrients., spleen, and bone marrow).

Blood Flow, Pressure, & Resistance

• Blood viscosityThe thickness or resistance to flow in a fluid, such as blood.: The thickness of blood, which affects its ability to flow; higher viscosity increases resistanceThe opposition to airflow in the respiratory tract, influenced by airway diameter. and slows circulation.
• Colloid osmotic pressureThe force exerted by water moving across a membrane due to osmosis.: The pressureThe force exerted by gases in the respiratory system, affecting airflow and gas exchange. exerted by plasmaThe liquid component of blood. proteinsLarge molecules made of amino acids with various functions in the body. (mainly albuminA plasma protein that helps maintain osmotic pressure and transport substances.) that pulls waterThe universal solvent essential for life. into the blood vessels from the surrounding tissues.
• Filtration: The process by which fluid moves out of capillaries into surrounding tissues due to hydrostatic pressureThe force exerted by a fluid, such as the pressure of blood pushing against the walls of capillaries.
• Hydrostatic pressure: The pressure exerted by blood against the walls of capillaries, pushing fluid out into the surrounding tissues.
• Mean arterial pressure (MAP): The average pressure in the arteries during one cardiac cycle, ensuring adequate blood flow to organs. It is calculated as:
  MAP=Diastolic Pressure+13(Pulse Pressure)\text{MAP} = \text{Diastolic Pressure} + \frac{1}{3} (\text{Pulse Pressure})MAP=Diastolic Pressure+31​(Pulse Pressure)
• Net filtrationThe process by which fluid moves out of capillaries into surrounding tissues due to hydrostatic pre pressure (NFP): The difference between hydrostatic and colloidA mixture where small particles are dispersed but not dissolved in a liquid. osmotic pressures, determining whether fluid moves into or out of capillaries.
• Pulse pressure: The difference between systolic and diastolic blood pressure, indicating the force of each heartbeat.
• Reabsorption: The process of fluid moving back into capillaries from surrounding tissues due to colloid osmotic pressureThe pressure exerted by proteins (mainly albumin) in the blood that pulls water into the capillaries.
• Systemic circuit: The part of the circulatory system that carries oxygenated blood from the heart to the body and returns deoxygenated blood to the heart.
• Pulmonary circuit: The circulation of blood between the heart and the lungs, where blood is oxygenated.
• Tissue perfusion: The delivery of oxygen and nutrients to tissues via the blood supply.

Regulation of Blood Flow

• Precapillary sphincters: Rings of smooth muscle at the entrance of capillary beds that regulate blood flow based on tissue needs.
• Total peripheral resistance (TPR): The overall resistance of blood flow in the circulatory system, influenced by vessel diameter, blood viscosity, and vessel length.
• Turbulence: Irregular, chaotic blood flow that increases resistance and can contribute to clot formation.
• Vascular resistance: The resistance blood encounters as it flows through vessels, primarily determined by vessel diameter.
• Vasoconstriction: The narrowing of blood vessels due to contraction of smooth muscle, increasing blood pressure and reducing blood flow.
• Vasodilation: The widening of blood vessels due to relaxation of smooth muscle, decreasing blood pressure and increasing blood flow.