Overview
This lecture covers blood reservoirs, blood vessel diseases, blood pressure regulation, and factors affecting blood flow and resistance.
Blood Reservoirs and Sympathetic Nervous System
- Veins serve as blood reservoirs, holding extra deoxygenated blood.
- Sympathetic nervous system triggers venoconstriction to shift blood from veins to arteries during increased oxygen demand.
Blood Vessel Diseases and Disorders
- Atherosclerosis is plaque buildup (mainly cholesterol) in arteries.
- Arteriosclerosis is the resulting loss of vessel elasticity from atherosclerosis.
- Aneurysms are dangerous artery ballooning or weakening that may rupture without warning.
- Phlebitis is inflammation of veins, which can cause a clot (thrombophlebitis).
- Varicose veins develop when vein valves fail, causing blood to pool due to gravity.
- Compression stockings and movement help prevent blood pooling and edema in veins.
Blood Pressure Concepts
- Blood pressure is the mean pressure in large arteries; higher resistance or volume increases pressure.
- Blood moves from areas of high to low pressure, highest in arteries and lowest in veins.
- Standard blood pressure is 120/80 mmHg, but normal varies by individual.
- Systolic pressure: force from ventricular contraction; diastolic pressure: relaxation phase.
Regulation of Blood Pressure
- Cardiac output (blood leaving heart per minute) = heart rate × stroke volume.
- At rest, typical cardiac output is ~5 liters/minute, matching total blood volume.
- During exercise, cardiac output increases as heart rate rises; stroke volume may remain the same.
Resistance and Blood Flow
- Resistance is opposition to blood flow, caused by vessel contact and plaque buildup.
- Peripheral resistance increases with narrower vessels or higher viscosity (thickness) of blood.
- Viscous (thicker) blood, from dehydration or high cell/protein content, increases resistance and blood pressure.
Blood Pressure Control Mechanisms
- Cardiac output affects pressure via the Frank-Starling law: input to heart equals output.
- Neural control: sympathetic nervous system constricts, parasympathetic dilates vessels.
- Hormonal control: hormones like epinephrine raise blood pressure; erythropoietin increases blood cell production and viscosity.
- Emotions, body temperature, and exercise also influence blood pressure.
Key Terms & Definitions
- Blood Reservoir — extra blood stored mainly in veins.
- Atherosclerosis — plaque buildup in arteries.
- Arteriosclerosis — hardening and loss of elasticity of arteries.
- Aneurysm — abnormal ballooning/weakening of an artery.
- Phlebitis — vein inflammation.
- Thrombophlebitis — clot caused by vein inflammation.
- Varicose Veins — enlarged, twisted veins due to valve failure.
- Cardiac Output — amount of blood pumped by the heart per minute.
- Stroke Volume — amount of blood ejected per heartbeat.
- Peripheral Resistance — resistance to blood flow in small arteries and arterioles.
- Viscosity — the thickness of a fluid.
Action Items / Next Steps
- Review how to calculate cardiac output and blood pressure components.
- Read upcoming chapter on kidney regulation of blood pressure.
- Be familiar with factors that affect blood resistance and pressure for the next unit.