The cardiovascular system The heart

RENAL-BODY FLUID CONTROL SYSTEM CARDIOVASCULAR SYSTEM HEART (PUMP) VESSELS (DISTRIBUTION SYSTEM) REGULATION AUTOREGULATION NEURAL HORMONAL

VEINS CAPACITY VESSELS HEART 80 mmHg 120 mmHg SYSTOLE DIASTOLE ARTERIES CAPILLARIES Work output External Kinetic

Functions of the Heart Generating blood pressure Routing blood –Heart separates pulmonary and systemic circulations Ensuring one-way blood flow –Heart valves ensure one-way flow Regulating blood supply –Changes in contraction rate and force match blood delivery to changing metabolic needs

Heart Wall Three layers of tissue –Epicardium: This serous membrane of smooth outer surface of heart –Myocardium: Middle layer composed of cardiac muscle cell and responsibility for heart contracting –Endocardium: Smooth inner surface of heart chambers

Cardiac muscle fibers arranged in a latticework is striated each cell has one nucleus has typical myofibrils that contain actin and myosin filaments functions as a Syncytium; intercalated discs and gap junctions autorhythmic cells and action potentials of longer duration and longer refractory period

STRIATED MUSCLE CARDIAC MUSCLE SKELETAL MUSCLE - Functional Syncytium - Automaticity - Motor Units - Stimulated by Motor Nerves

Unlike skeletal muscles, cardiac muscles have to contract in more than one direction. Cardiac muscle cells are striated, meaning they will only contract along their long axis. In order to get contraction in two axis, the fibres wrap around.

The function of valves

Cardiac cycle LATE DIASTOLE ATRIAL SYSTOLE ISOMETRIC VENTRICULAR CONTRACTION VENTRICULAR EJECTION ISOMETRIC VENTRICULAR RELAXATION DIASTOLE

Fick’s principle Right heart: 160 ml/l Left heart: 200 ml/l Thus, one liter of blood has to pass for 40 ml O 2 to be absorbed 200 ml of O 2 is absorbed every min (spirometry) FICK’S PRINCIPLE CO= VO 2 /( [O 2 ] a - [O 2 ] v ) = 5L/min Cardiac output=Oxygen absorbed per min/arteriovenous O 2 difference (ml/l)

CO= HR x SV SV = CO HR = 5 L/min 70 beats/min = L or 71.4 ml

Regulation of the Heart Intrinsic regulation: Results from normal functional characteristics, not on neural or hormonal regulation –Frank-Starling’s law of the heart Extrinsic regulation: Involves neural and hormonal control –Parasympathetic stimulation Supplied by vagus nerve, decreases heart rate, acetylcholine secreted –Sympathetic stimulation Supplied by cardiac nerves, increases heart rate and force of contraction, epinephrine and norepinephrine released

CARDIAC OUTPUT = STROKE VOLUME x HEART RATE Autoregulation (Frank-Starling “Law of the Heart”) Contractility Sympathetic Nervous System Parasympathetic Nervous System

Autonomic innervation

Reflexes in heart regulation Blood pressure Medulla Afferents: Bainbridge reflex

SARCOLEMMA 10% Mitochondria THICK MYOFILAMENT THIN MYOFILAMENT SR Ca ++ T-tubule 20% 80%

Effects of the autonomic nervous systems

TENSION MUSCLE LENGTH PASSIVE TENSION ACTIVE TENSION TOTAL TENSION CARDIAC MUSCLE

PRESSURE DIASTOLIC PRESSURE CURVE SYSTOLIC PRESSURE CURVE HEART End Diastolic Volume End Systolic Volume Isovolumetric Phase Isotonic (Ejection) Phase Stroke Volume Pre-load After-load

PRESSURE DIASTOLIC PRESSURE CURVE SYSTOLIC PRESSURE CURVE HEART End Diastolic Volume End Systolic Volume Isovolumetric Phase Isotonic (Ejection) Phase Stroke Volume Pre-load After-load INCREASED CONTRACTILITY

PRESSURE DIASTOLIC PRESSURE CURVE SYSTOLIC PRESSURE CURVE HEART End Diastolic Volume End Systolic Volume Isovolumetric Phase Isotonic (Ejection) Phase Stroke Volume Pre-load After-load DECREASED CONTRACTILITY

PRESSURE DIASTOLIC PRESSURE CURVE SYSTOLIC PRESSURE CURVE HEART End Diastolic Volume End Systolic Volume Isovolumetric Phase Isotonic (Ejection) Phase Stroke Volume Pre-load After-load INCREASED FILLING

CARDIAC FUNCTION CURVE STROKE VOLUME DIASTOLIC FILLING Cardiac Output = Stroke Volume x Heart Rate Constant If: Then:  CO reflects  SV Right Atrial Pressure (RAP) reflects Diastolic Filling

CARDIAC FUNCTION CURVE CARDIAC OUTPUT (L/min) RAP mmHg Volume Pressure THE FRANK- STARLING “LAW OF THE HEART”

CARDIAC FUNCTION CURVE CARDIAC OUTPUT (L/min) RAP mmHg THE FRANK- STARLING “LAW OF THE HEART” Increased Contractility