Previous lecture discussed arteries and arterioles.
Current lecture focuses on capillaries, the smallest and thinnest blood vessels.
Arterioles slow down blood flow before it enters capillaries.
Structure of Capillaries
Capillary Walls
Extremely thin: one cell thick endothelium.
This thinness allows for efficient exchange of substances.
Lumen
Very narrow, approximately 7 micrometers in diameter.
Size is comparable to the diameter of a red blood cell.
Red blood cells pass through in single file due to the narrow lumen.
Gaps in Walls
Capillary walls have tiny gaps between endothelial cells.
These gaps will be important in the discussion of tissue fluid.
Function of Capillaries
Exchange of Substances
Allow exchange between blood and body cells, e.g., neurons.
Neurons require oxygen for aerobic respiration.
Oxygen Transport
Oxygen is carried by red blood cells in the blood.
Arterioles slow blood to allow time for oxygen exchange in capillaries.
Importance of Capillary Structure
Thin Walls
Minimize diffusion distance, facilitating easier diffusion of oxygen.
Narrow Lumen
Ensures proximity of red blood cells to body cells, enhancing diffusion.
Comparison of Blood Vessels
Thick Walls (Arterioles)
Prevent diffusion due to the long diffusion path.
Wide Lumen (Inefficient Capillaries)
Red blood cells are too far from body cells, hindering diffusion.
Thin Walls & Narrow Lumen (Efficient Capillaries)
Optimal for diffusion: thin walls and narrow lumen force proximity.
Oxygen diffuses efficiently into body cells, and carbon dioxide diffuses back into blood.
Summary
Capillaries are crucial for effective exchange of gases and nutrients.
Highlights of capillary structure include one-cell thick walls and narrow lumens, which jointly minimize diffusion distances, facilitating rapid and efficient substance exchange between blood and body cells.