Overview
The lecture discusses passive transport in the circulatory system, focusing on blood pressure, capillary exchange, and cellular tonicity, including isotonic, hypertonic, and hypotonic solutions.
Blood Pressure and Capillary Exchange
- The heart creates pressure with each contraction (stroke), peaking at ~114 mm Hg and resting at ~75 mm Hg.
- Mean arterial pressure is calculated as 88 mm Hg using a specific formula.
- Blood pressure decreases as it travels through arteries to capillaries, from 55 mm Hg (arterial end) to 10 mm Hg (venous end).
- Osmotic pressure (~25 mm Hg) remains constant across the capillary membrane due to plasma proteins.
- At the arterial end, hydrostatic pressure causes filtration, pushing water, oxygen, and nutrients out to tissues.
- At the venous end, low blood pressure allows osmotic pressure to draw waste (CO2, urea) back into the capillary.
Cellular Anatomy and Tonicity
- Tonicity describes the effect of different extracellular solutions on cell volume.
- Isotonic solution: Electrolyte concentration is equal inside and outside; water movement is balanced and cells retain normal shape.
- Hypertonic solution: Higher electrolyte concentration outside the cell; water exits the cell, causing it to shrink.
- Hypotonic solution: Lower electrolyte concentration outside the cell; water enters the cell, causing it to swell.
Key Terms & Definitions
- Mean Arterial Pressure (MAP) — average pressure in arteries during one cardiac cycle.
- Osmotic Pressure — pressure exerted by solutes (mainly proteins) drawing water into blood vessels.
- Tonicity — the ability of an extracellular solution to change the volume of a cell by osmosis.
- Isotonic — equal solute concentrations inside and outside the cell; no net water movement.
- Hypertonic — higher solute concentration outside the cell; water moves out, causing cell shrinkage.
- Hypotonic — lower solute concentration outside the cell; water moves in, causing cell swelling.
Action Items / Next Steps
- Review textbook page 71 on passive transport and tonicity.
- Prepare to learn the calculation for mean arterial pressure in future classes.