CVS

The Cardiovascular Systemy.s.y

The Cardiovascular System
A closed system of the heart and blood vessels The heart pumps blood Blood vessels allow blood to circulate to all parts of the body The function of the cardiovascular system is to deliver oxygen and nutrients and to remove carbon dioxide and other waste products

The Heart: Coverings

Pericardium – a double serous membraneVisceral pericardiumNext to heartParietal pericardiumOutside layerSerous fluid fills the space between the layers of pericardium

The Heart: Heart Wall

Three layers Epicardium Outside layer This layer is the parietal pericardium Connective tissue layer Myocardium Middle layer Mostly cardiac muscle Endocardium Inner layer Endothelium

External Heart Anatomy

The Heart: Chambers
Right and left side act as separate pumps Four chambers Atria Receiving chambers Right atrium Left atrium Ventricles Discharging chambers Right ventricle Left ventricle

The Heart: Valves

Allow blood to flow in only one directionFour valvesAtrioventricular valves – between atria and ventriclesBicuspid valve (left)Tricuspid valve (right) Semilunar valves between ventricle and arteryPulmonary valveAortic valve

The Heart: Valves

Valves open as blood is pumped throughHeld in place by chordae tendineae (“heart strings”)Close to prevent backflow

The Heart: Associated Great Vessels

Aorta Leaves left ventricle Pulmonary arteries Leave right ventricle Vena cava Enters right atrium Pulmonary veins (four) Enter left atrium

Coronary Circulation

Blood in the heart chambers does not nourish the myocardium The heart has its own nourishing circulatory system Coronary arteries Cardiac veins Blood empties into the right atrium via the coronary sinus

The Heart: Conduction System

Intrinsic conduction system (nodal system) Heart muscle cells contract, without nerve impulses, in a regular, continuous way

The Heart: Conduction System

Special tissue sets the pace Sinoatrial node Pacemaker Atrioventricular node Atrioventricular bundle Bundle branches Purkinje fibers

Heart Contractions

Contraction is initiated by the sinoatrial node Sequential stimulation occurs at other autorhythmic cells

Heart Contractions

Filling of Heart Chambers – the Cardiac Cycle

The Heart: Cardiac Cycle

Atria contract simultaneously Atria relax, then ventricles contract Systole = contraction Diastole = relaxation

The Heart: Cardiac Cycle

Cardiac cycle – events of one complete heart beatMid-to-late diastole – blood flows into ventriclesVentricular systole – blood pressure builds before ventricle contracts, pushing out bloodEarly diastole – atria finish re-filling, ventricular pressure is low

The Heart: Cardiac Output

Cardiac output (CO) Amount of blood pumped by each side of the heart in one minute CO = (heart rate [HR]) x (stroke volume [SV]) Stroke volume Volume of blood pumped by each ventricle in one contraction



Cardiac Output Regulation

The Heart: Regulation of Heart Rate

Stroke volume usually remains relatively constantStarling’s law of the heart – the more that the cardiac muscle is stretched, the stronger the contractionChanging heart rate is the most common way to change cardiac output

The Heart: Regulation of Heart Rate

Increased heart rate Sympathetic nervous system Crisis Low blood pressure Hormones Epinephrine Thyroxine Exercise Decreased blood volume

The Heart: Regulation of Heart Rate

Decreased heart rate Parasympathetic nervous system High blood pressure or blood volume Dereased venous return

Blood Vessels: The Vascular System

Taking blood to the tissues and back Arteries Arterioles Capillaries Venules Veins

Differences Between Blood Vessel Types

Walls of arteries are the thickestLumens of veins are largerSkeletal muscle “milks” blood in veins toward the heartWalls of capillaries are only one cell layer thick to allow for exchanges between blood and tissue


The Vascular System

Blood Vessels: Anatomy

Three layers (tunics) Tunic intima Endothelium Tunic media Smooth muscle Controlled by sympathetic nervous system Tunic externa Mostly fibrous connective tissue

Movement of Blood Through Vessels

Most arterial blood is pumped by the heart Veins use the milking action of muscles to help move blood

Capillary Beds

Capillary beds consist of two types of vesselsVascular shunt – directly connects an arteriole to a venule

Capillary Beds

True capillaries – exchange vesselsOxygen and nutrients cross to cellsCarbon dioxide and metabolic waste products cross into blood

Diffusion at Capillary Beds

Capillary Exchange
Substances exchanged due to concentration gradients Oxygen and nutrients leave the blood Carbon dioxide and other wastes leave the cells

Capillary Exchange: Mechanisms

Direct diffusion across plasma membranes Endocytosis or exocytosis Some capillaries have gaps (intercellular clefts) Plasma membrane not joined by tight junctions Fenestrations of some capillaries Fenestrations = pores

Major Arteries of Systemic Circulation

Major Veins of Systemic Circulation

Arterial Supply of the Brain

Hepatic Portal Circulation

Pulse

Pulse – pressure wave of bloodMonitored at “pressure points” where pulse is easily palpated

Blood Pressure

Measurements by health professionals are made on the pressure in large arteriesSystolic – pressure at the peak of ventricular contractionDiastolic – pressure when ventricles relaxPressure in blood vessels decreases as the distance away from the heart increases


Measuring Arterial Blood Pressure

Blood Pressure: Effects of Factors

Neural factorsAutonomic nervous system adjustments (sympathetic division)Renal factorsRegulation by altering blood volumeRenin – hormonal control

Blood Pressure: Effects of Factors

Temperature Heat has a vasodilation effect Cold has a vasoconstricting effect Chemicals Various substances can cause increases or decreases Diet

Factors Determining Blood Pressure

Variations in Blood Pressure
Human normal range is variableNormal140–90 mm Hg systolic80–75 mm Hg diastolicHypotensionLow systolic (below 90 mm HG)Often associated with illnessHypertensionHigh systolic (above 140 mm HG)Can be dangerous if it is chronic