Overview
This lecture covers the structure, function, and flow dynamics of the blood vessels within the cardiovascular system, emphasizing how blood travels, exchanges nutrients, and returns to the heart.
Closed Circulatory System & Vessel Types
- Humans have a closed circulatory system; blood stays within vessels.
- Blood follows this path: arteries → arterioles → capillaries → venules → veins.
- Arteries carry blood away from the heart; veins carry blood toward the heart.
- Pulmonary arteries/veins are exceptions to the oxygenated/deoxygenated rule.
Structure of Blood Vessels
- All vessels have three layers: tunica intima (internal, endothelium), tunica media (middle, smooth muscle and elastin), tunica externa (external, collagen).
- Arteries: thick tunica media, high blood pressure, elastic, maintain shape.
- Veins: thinner walls, larger lumen, often collapsed, have valves to prevent backflow.
- Capillaries: single cell layer (endothelium) for exchange, contain fenestrations (pores).
Blood Flow, Pressure, and Exchange
- Blood pressure is highest in arteries, decreases through arterioles, lowest in veins.
- Arteries move blood fastest, veins slowest; velocity drops significantly in capillaries.
- Capillaries allow exchange of gases, nutrients, and wastes due to thin walls and slow flow.
Capillary Exchange
- Two pressures influence fluid movement: hydrostatic (blood) pressure and osmotic (water attracted to solute) pressure.
- At the arterial end, hydrostatic pressure forces fluid out (filtration).
- At the venous end, osmotic pressure draws fluid back in (reabsorption).
- Blood is hypertonic; plasma proteins maintain osmotic pressure.
- Filtration delivers oxygen/nutrients; reabsorption removes carbon dioxide/waste.
Special Cases and Regulation
- Capillary beds can be regulated by shunts and sphincters to prioritize blood flow.
- Edema (swelling) occurs when plasma proteins drop (e.g., starvation), reducing osmotic pull into capillaries.
- Venous return assisted by muscle movements, valves, breathing, and sympathetic constriction.
Vessel Comparison & Flow Summary
- Arteries: fastest flow, highest pressure, thick muscle wall.
- Arterioles: slower than arteries, still relatively high pressure.
- Capillaries: slowest flow, largest total area, site of exchange.
- Venules/Veins: low pressure, larger lumens, thin walls, need valves and muscle assistance.
Key Terms & Definitions
- Closed Circulatory System — blood is always contained within vessels.
- Artery — vessel carrying blood away from the heart.
- Vein — vessel carrying blood toward the heart.
- Capillary — smallest vessel; site of nutrient/gas exchange.
- Tunica Intima/Interna — inner vessel layer, endothelium.
- Tunica Media — middle layer, smooth muscle and elastin.
- Tunica Externa — outer layer, collagen fibers.
- Hydrostatic Pressure — pressure exerted by fluid in vessels (blood pressure).
- Osmotic Pressure — pressure drawing water into the blood due to solutes/proteins.
- Filtration — movement of fluid out of capillaries (arterial side).
- Reabsorption — movement of fluid into capillaries (venous side).
- Edema — tissue swelling from excess fluid.
Action Items / Next Steps
- Draw and label diagrams illustrating capillary exchange (using color codes for pressures).
- Review terms: hypertonic, hypotonic, hydrostatic, osmotic pressure.
- Study comparison charts of vessel types (arteries, arterioles, capillaries, venules, veins).
- Prepare for lab on vessel identification and structure.