Overview
This lecture explains how the body determines which tissues receive more or less blood at any given time, focusing on mechanisms of intrinsic (auto-regulation) and extrinsic control.
Blood Flow Distribution in the Body
- The body cannot fully supply all tissues with maximum blood flow simultaneously due to limited blood volume.
- The body adjusts blood flow based on current needs, such as during exercise or digestion.
- If all tissues received equal blood flow constantly, overall blood pressure would decrease.
Intrinsic Control (Auto-regulation)
- Intrinsic control means organs regulate their own blood supply based on their metabolic needs.
- It is driven by factors within the tissue, largely linked to cellular respiration (oxygen + glucose → ATP).
- When tissue metabolism increases (e.g., during muscle activity), local Oâ‚‚ decreases and COâ‚‚ increases.
- Low Oâ‚‚ or high COâ‚‚ prompts the endothelial lining to release nitric oxide (NO), causing vasodilation and increased blood flow.
- When there is excess Oâ‚‚ (e.g., after activity stops), endothelins are released, causing vasoconstriction and reduced blood flow.
- The brain also relies on auto-regulation to maintain constant supply; vasodilation occurs with low Oâ‚‚/high COâ‚‚, and vasoconstriction with high Oâ‚‚.
Extrinsic Control
- Extrinsic control refers to regulation from outside the organ, mainly by the nervous system and hormones.
- Nervous and hormonal inputs cause vasoconstriction in tissues needing less blood and vasodilation in tissues needing more.
- This mechanism allows prioritization of blood flow during situations like exercise or rest.
Key Terms & Definitions
- Intrinsic Control (Auto-regulation) — Regulation of blood flow by an organ in response to its own metabolic needs.
- Extrinsic Control — Regulation of blood flow by external factors such as nerves or hormones.
- Nitric Oxide (NO) — Molecule released by endothelial cells that causes blood vessels to dilate.
- Endothelins — Molecules released by endothelial cells that cause blood vessels to constrict.
- Vasodilation — Widening of blood vessels to increase blood flow.
- Vasoconstriction — Narrowing of blood vessels to decrease blood flow.
Action Items / Next Steps
- Review cellular respiration and its role in tissue metabolism.
- Prepare questions for the instructor if any concepts are unclear.