The Cardiovascular System: Heart and Blood Vessels – Study Guide

Chapter

• • Isovolumetric relaxation: All valves closed, pressure falls.

• End diastolic volume (EDV): Volume in ventricle at end of filling.

• End systolic volume (ESV): Volume remaining after contraction.

Heart Sounds

• "Lub" (S1): Closure of AV valves at start of ventricular systole.

• "Dub" (S2): Closure of SL valves at start of ventricular diastole.

Cardiac Output, Stroke Volume, and Heart Rate

• Cardiac Output (CO): Volume of blood pumped per minute.

  • Formula: $CO = SV \times HR$

• Stroke Volume (SV): Volume pumped per beat.

  • Formula: $SV = EDV - ESV$

• Cardiac Reserve: Difference between resting and maximal CO.

Regulation of Stroke Volume and Heart Rate

• Stroke Volume: Influenced by preload (venous return), contractility, afterload (arterial pressure).

• Heart Rate: Influenced by autonomic nervous system, hormones, ions, age, gender, fitness, temperature.

Autonomic Nervous System and Heart Rate

• Sympathetic stimulation: Increases heart rate and contractility.

• Parasympathetic (vagal) stimulation: Decreases heart rate (vagal tone).

• Homeostatic imbalances: Tachycardia (fast HR), bradycardia (slow HR), arrhythmias.

Chapter 19: The Cardiovascular System – Blood Vessels

Blood Vessel Wall Structure

Most blood vessels have three layers (tunics), each with specific functions.

• Tunica intima: Endothelial lining; reduces friction.

• Tunica media: Smooth muscle and elastic fibers; controls vasoconstriction and vasodilation.

• Tunica externa (adventitia): Connective tissue; protects and anchors vessel.

Vasoconstriction and Vasodilation

• Vasoconstriction: Narrowing of blood vessel diameter due to smooth muscle contraction.

• Vasodilation: Widening of vessel diameter due to smooth muscle relaxation.

Types of Arteries

• Elastic arteries: Largest, near heart (e.g., aorta); pressure reservoirs.

• Muscular arteries: Distribute blood to organs (e.g., brachial artery); distributing arteries.

• Arterioles: Smallest; control flow into capillary beds; resistance arteries.

Capillary Beds and Capillary Types

• Capillary bed: Network of capillaries for exchange between blood and tissues.

• Types of capillaries:

  • Continuous: Most common; tight junctions; found in skin, muscle, brain.

  • Fenestrated: Pores for increased permeability; found in kidneys, intestines.

  • Sinusoidal: Large gaps; found in liver, bone marrow, spleen.

• Regulation: Arterioles and precapillary sphincters control blood flow into beds.

Veins: Structure and Function

• Structure: Thinner walls, larger lumens, less smooth muscle than arteries; contain valves to prevent backflow.

• Function: Return blood to heart; act as blood reservoirs.

Vascular Anastomoses

• Definition: Interconnections between blood vessels.

• Importance: Provide alternate pathways for blood flow (collateral circulation).

Blood Flow, Blood Pressure, and Resistance

• Blood flow (F): Volume of blood flowing through a vessel per unit time.

• Blood pressure (P): Force per unit area exerted on vessel wall by blood.

• Resistance (R): Opposition to flow; mainly from vessel diameter, length, and blood viscosity.

• Relationship: $F = \frac{\Delta P}{R}$

Sources of Peripheral Resistance

• Blood viscosity: Thickness of blood.

• Vessel length: Longer vessels increase resistance.

• Vessel diameter: Most important; small changes greatly affect resistance.

Blood Pressure in Different Vessels

• Arteries: Highest pressure; steepest drop in arterioles.

• Capillaries: Low pressure to prevent damage and allow exchange.

• Veins: Lowest pressure; aided by muscular and respiratory pumps for return.

• Systolic pressure: Peak during ventricular contraction.

• Diastolic pressure: Lowest during relaxation.

• Pulse pressure: Difference between systolic and diastolic.

• Mean arterial pressure (MAP): Average pressure driving blood to tissues.

  • Formula: $MAP = \text{Diastolic Pressure} + \frac{1}{3}(\text{Pulse Pressure})$

Velocity of Blood Flow and Vasomotion

• Velocity: Fastest in arteries, slowest in capillaries, increases in veins.

• Vasomotion: Intermittent flow through capillaries due to precapillary sphincter activity.

• Cross-sectional area: Highest in capillaries, causing slowest flow for exchange.

Regulation of Blood Pressure

• Main factors: Cardiac output, peripheral resistance, blood volume.

• Factors increasing MAP: Increased heart rate, stroke volume, blood viscosity, vessel length, vasoconstriction, blood volume.

Capillary Exchange and Bulk Flow

• Capillary exchange: Movement of substances via diffusion, filtration, and reabsorption.

• Bulk flow: Movement of fluid driven by pressure differences.

• Hydrostatic pressure: Pushes fluid out of capillaries (filtration).

• Colloid osmotic pressure: Pulls fluid into capillaries (reabsorption).

• Filtration: Predominant at arterial end; Reabsorption: Predominant at venous end.

Vessel Type	Pressure	Velocity	Cross-sectional Area
Arteries	High	Fast	Low
Capillaries	Low	Slow	High
Veins	Lowest	Intermediate	Low

Example: The aorta (an elastic artery) acts as a pressure reservoir, maintaining blood flow during diastole. Capillaries in the kidneys are fenestrated to allow rapid filtration of blood plasma.