Cardiovascular System: Heart, Circulations, and Cardiac Function

Cardiovascular system

Heart, blood vessels, and blood; transports substances and maintains homeostasis

Cardiovascular system function

Transport gases, nutrients, wastes; communication; defense; temperature regulation

Heart

Muscular pump that moves blood through body

Heart function

Pumps blood through pulmonary and systemic circuits

Heart chambers

Right atrium, right ventricle, left atrium, left ventricle

Atria

Receive blood returning to heart

Ventricles

Pump blood out of heart

Septum

Wall separating right and left sides of heart

Pulmonary circulation

Blood flow between heart and lungs

Systemic circulation

Blood flow between heart and rest of body

Portal system

Two capillary beds in series (ex: hepatic portal system)

Arteries

Carry blood away from heart; thick walls; high pressure

Veins

Carry blood toward heart; low pressure; contain valves

Capillaries

Sites of exchange; very thin walls

Blood pressure

Force exerted by blood on vessel walls

Driving pressure

Generated by ventricular contraction

Pressure gradient

Difference in pressure that drives flow

Blood flow direction

Flows from high pressure to low pressure

Flow (Q)

Volume of blood per unit time

Resistance (R)

Opposition to blood flow

Flow relationship

Flow is proportional to pressure gradient

Resistance relationship

Flow is inversely proportional to resistance

Flow equation

Flow ∝ ΔP / R

Vasodilation

Increase in vessel diameter; decreases resistance; increases flow

Vasoconstriction

Decrease in vessel diameter; increases resistance; decreases flow

Poiseuille's law

Describes factors affecting resistance in vessels

Length effect on resistance

Increased length increases resistance

Viscosity effect on resistance

Increased thickness increases resistance

Radius effect on resistance

Increased radius decreases resistance (most important factor)

Flow vs velocity

Flow = volume/time; velocity = distance/time; not the same

Mean arterial pressure (MAP)

Average arterial pressure

MAP relationship

MAP ∝ cardiac output × peripheral resistance

Cardiac output (CO)

Amount of blood pumped per minute

Peripheral resistance

Resistance in blood vessels

Myocardium

Muscle layer of heart responsible for contraction

Pericardium

Fluid-filled sac around heart that protects and reduces friction

Heart valves

Ensure one-way blood flow

Atrioventricular (AV) valves

Between atria and ventricles; tricuspid (right), mitral (left)

Semilunar valves

Between ventricles and arteries; aortic and pulmonary valves

Valve function during contraction

AV valves close; semilunar valves open

Valve function during relaxation

Semilunar valves close; AV valves open

Cardiac muscle

Muscle of heart; involuntary; striated; branched cells

Cardiac muscle characteristics

Single nucleus, branched, many mitochondria, intercalated discs

Intercalated discs

Connections between cardiac cells

Desmosomes

Provide structural support between cells

Gap junctions

Allow electrical signals to pass between cells

Autorhythmic cells

Pacemaker cells that generate spontaneous action potentials

Contractile cells

Produce force for pumping blood

Excitation-contraction coupling (cardiac)

Process linking electrical signal to contraction in heart

Steps of cardiac contraction

AP → Ca2+ enters (L-type channels) → triggers SR Ca2+ release → Ca2+ binds troponin → contraction

Calcium-induced calcium release (CICR)

Calcium entry triggers more calcium release from SR

Cardiac relaxation

Ca2+ pumped back into SR and removed from cell via Na+/Ca2+ exchanger

Calcium sparks

Small localized Ca2+ releases

Calcium signal

Summed Ca2+ sparks that trigger contraction

Cardiac action potential (contractile cells)

Na+ influx → Ca2+ plateau → K+ efflux

Plateau phase

Sustained depolarization due to Ca2+ influx; prevents tetanus

Repolarization

Return to resting potential due to K+ exiting cell

Tetanus in cardiac muscle

Does not occur due to long refractory period

Autorhythmic cell depolarization

Driven mainly by Ca2+ entry

Stroke volume

Amount of blood pumped per beat

Heart rate

Number of beats per minute

Muscle contraction in heart

Depends on Ca2+ availability

High-yield concept: pressure-flow

Flow increases with pressure difference

High-yield concept: resistance

Resistance mainly controlled by vessel radius

High-yield concept: MAP

MAP depends on cardiac output and resistance

High-yield concept: valves

Ensure one-way blood flow

High-yield concept: plateau phase

Prevents tetanus in cardiac muscle

High-yield concept: CICR

Calcium entry triggers more calcium release

Summary of cardiovascular system

Heart pumps blood through vessels; flow depends on pressure and resistance; calcium controls contraction