The Cardiovascular System

The Cardiovascular System

• A closed system of the heart and blood vessels
• Function: deliver oxygen and nutrients, remove carbon dioxide and waste products

The Heart

• Location: thorax between the lungs, pointed apex directed toward left hip
• Size: about the size of a fist, less than 1 lb
• Coverings: pericardium (double serous membrane) with visceral and parietal layers, and serous fluid fills the space between layers
• Wall structure: epicardium (outside), myocardium (middle), and endocardium (inner) with endothelium

Heart Chambers

• Right and left sides act as separate pumps
• Four chambers: atria (receiving) and ventricles (discharging)

Valves

• Allow blood to flow in one direction only
• Four valves: atrioventricular (between atria and ventricles), and semilunar (between ventricles and arteries)
• Valves open and close with blood flow, held in place by chordae tendineae

Blood Circulation

• Heart pumps blood through the circulatory system
• Associated great vessels: aorta, pulmonary arteries, vena cava, and pulmonary veins

Coronary Circulation

• Heart has its own nourishing circulatory system
• Coronary arteries and cardiac veins supply blood to the myocardium

Cardiac Pathology

• Rapid heart beat (tachycardia) can lead to inadequate blood supply and angina pectoris
• Cardiac damage can lead to arrhythmias and heart failure

Conduction System

• Intrinsic conduction system sets the heart rate
• Special tissue: sinoatrial node, atrioventricular node, atrioventricular bundle, bundle branches, and Purkinje fibers

Heart Contractions

• Heart muscle cells contract without nerve impulses in a regular, continuous way
• Systole (contraction) and diastole (relaxation) phases of the cardiac cycle

Cardiac Output

• Cardiac output (CO) is the amount of blood pumped by each side of the heart in one minute
• CO = heart rate (HR) x stroke volume (SV)
• Normal CO: 5000 ml/min

Regulation of Heart Rate

• Changing heart rate is the most common way to change cardiac output
• Increased heart rate: sympathetic nervous system, hormones, exercise, and decreased blood volume
• Decreased heart rate: parasympathetic nervous system, high blood pressure or volume, and decreased venous return

Blood Vessels

• The vascular system: arteries, arterioles, capillaries, venules, and veins
• Three layers: tunic intima, tunic media, and tunic externa

Capillary Beds

• Consist of two types of vessels: vascular shunt and true capillaries
• Exchange vessels for oxygen and nutrients, and carbon dioxide and waste products

Vital Signs

• Arterial pulse, blood pressure, respiratory rate, and body temperature indicate the efficiency of the system

Pulse

• Pressure wave of blood
• Monitored at pressure points where the pulse is easily palpated

Blood Pressure

• Measurements by health professionals are made on the pressure in large arteries
• Systolic and diastolic pressures
• Pressure decreases as the distance from the heart increases

Blood Pressure Regulation

• Neural factors: autonomic nervous system adjustments
• Renal factors: regulation by altering blood volume and renin hormone control
• Temperature, chemicals, and diet also affect blood pressure

Variations in Blood Pressure

• Normal range: variable, but typically 140-110 mm Hg systolic and 80-75 mm Hg diastolic
• Hypotension: low systolic pressure (below 110 mm Hg)
• Hypertension: high systolic pressure (above 140 mm Hg)