Cardiovascular System – Pulmonary and Systemic Circuits

System Overview System consists of the heart and the blood vessels Function: to bring oxygen and nutrients to all body cells and to remove waste

Heart Location

Coverings of the Heart Pericardium Fibrous pericardium Protects and anchors heart Parietal pericardium and Visceral pericardium Make up the pericardial cavity Pericardial fluid reduces friction

Walls of the Heart Epicardium Same as visceral pericardium Lubricates heart Myocardium Layer that contracts Endocardium Lines heart chambers

Heart Chambers 4 chambers of the heart Atria Thin walls Receive blood returning to the heart Auricles Ventricles Thicker walls Receive blood from atria Force blood out of heart Interventricular Septum Divides chambers

Heart Valves Atrioventricular valves Tricuspid – right Three flaps Bicuspid (mitral) – left Two flaps Semilunar valves Pulmonary – right Aortic – left Chordae tendinae Anchor AV valve flaps

Blood Supply to the Heart Coronary arteries Branch from aorta and nourish heart muscle Cardiac veins Drain blood from heart muscle into the coronary sinus then into right atrium.

Cardiac Cycle Cardiac cycle – series of events that constitute a complete heartbeat Systole – contraction Prior to atrial systole 70% of blood follows into ventricles without contraction Diastole – relaxation

Cardiac Cycle Heart Sounds – “lub-dup” Lub – ventricular systole AV valves close Dup – ventricular diastole SL valves close Murmur – irregular heart sound 1:52

Cardiac Conduction System Coordinates the events of the cardiac cycle Consists of clumps and strands of specialized cardiac muscle that initiate and distribute impulses throughout the myocardium

Nodes of Cardiac Conduction System Sinoatrial node – AKA “pacemaker” Just beneath epicardium Located in right atrium near opening of superior vena cava Initiates impulses without nervous stimulation

Nodes of Cardiac Conduction System Atrioventricular node Located in inferior portion of septum AV bundle (bundle of His) Large fibers run through the interventricular septum Purkinje fibers Spread from septum into papillary muscles Stimulate ventricular contraction 1:00

Regulation of Cardiac Cycle Parasympathetic and sympathetic fibers from medulla oblongata run to the nodes Secrete acetylcholine to decrease heart rate Secrete norepinephrine to increase heart rate

Electrocardiogram (ECG) Recording of the electrical changes in the myocardium during the cardiac cycle P – atrial systole QRS – ventricular systole; covers atrial diastole T – ventricular diastole 1:41

Blood Vessels

Arteries Strong, elastic vessels that carry blood away from the heart Lead to finer branches called arterioles

Artery Layers Tunica intima – simple squamous epithelium for smooth surface Tunica media – largest layer; smooth muscle and elastic CT Tunica externa – CT that attaches artery to surrounding tissues

Capillaries Smallest diameter blood vessels Extensions of inner lining of arterioles (tunica intima) Connect arterioles and venules Allow exchange between blood and tissue fluid More abundant around muscles and nerves Blood flow controlled by precapillary sphincters Exchanges occur by diffusion, osmosis, and filtration

Veins Carry blood back to the right atrium of the heart Form from microscopic venules that are continuous with capillaries Structure similar to arteries, but less developed tunica media Many have valves to prevent blood backflow Act as blood reservoirs when hemorrhage causes decrease in arterial blood pressure

Blood Pressure The force blood exerts against the inner walls of blood vessels Refers primarily to arterial blood pressure Increases during ventricular systole – systolic pressure ( ) Decreases during ventricular diastole – diastolic pressure (70-90) Pulse

Factors that Affect Blood Pressure Heart action – how much blood enters arteries Blood volume Peripheral resistance – friction between blood and vessels Blood viscosity Hypertension and stroke Emotions, exercise, hormones & pain