Cardiovascular System: The Heart

Functions of the cardiovascular System

Transports O2, nutrients, CO2, cell wastes, etc. to and from body cells Maintaining body temperature Homeostatic relationships with all body systems With the urinary system, regulation of blood volume and pressure

Location of the heart

Thoracic cavity between two lungs ~2/3 to left of midline Surrounded by pericardium: Fibrous pericardium - Inelastic; anchors heart in place Inside is serous pericardium - double layer around heart Parietal layer fused to fibrous pericardium Inner visceral layer adheres tightly to heart Filled with pericardial fluid - reduces friction during beat.

Heart anatomy

The Heart Wall Epicardium - outer layer Myocardium - cardiac muscle Two separate networks via gap junctions in intercalated discs - atrial & ventricular Networks- contract as a unit Endocardium - Squamous epithelium lines inside of myocardium

The Heart Wall

The Heart Wall

The Heart Wall

Heart Chambers 4 chambers: 2 upper chambers = Atria Between is inter-atrial septum Contains fossa ovalis - remnant of foramen ovalis 2 lower chambers = ventricles Between is interventricular septum Wall thickness depends on work load Atria thinnest Right ventricle pumps to lungs & thinner than left

External Anatomy

External Anatomy

Internal Anatomy

Great Vessels of the Heart Superior & inferior Vena Cavae Delivers O2 depleted blood to R. atrium from body Coronary sinus drains heart muscle veins R. Atrium  R. Ventricle Pumps through Pulmonary Trunk R & L Pulmonary Arteries  lungs

Great Vessels of the Heart Pulmonary Veins from lungs O2 rich blood L. atrium Left ventricle ascending aorta body Between pulmonary trunk & aortic arch is the ligamentum arteriosum fetal ductus arteriosum remnant

Heart Valves Designed to prevent back flow in response to pressure changes Atrio-ventricular (AV) valves are found between the atria and ventricles Right AV valve = tricuspid valve (has three flaps, or cusps) Prevent backflow of blood into the right atrium

Heart Valves Left AV valve = bicuspid, or mitral valve Prevents backflow of blood into left atrium Semilunar Valves are found at the base of aorta and pulmonary trunk Prevent backflow of blood into the ventricles

Heart Valves Chordae Tendinae: Tiny white cords that anchor the AV valve cusps to the wall of the ventricle Help to anchor the flaps to prevent a prolapse

Coronary Circulation Blood flow through vessels in myocardium = coronary circulation Left & right coronary arteries branch from aorta to carry blood throughout muscle O2 - depleted blood collected by coronary sinus (posterior) Empties into right atrium

Coronary Circulation

Heart physiology

Conduction System 1% of cardiac muscle generate action potentials = Pacemaker & Conduction system Normally begins at sinoatrial (SA) node Atria & atria contract AV node – slows the signal, then travels along: AV bundle (Bundle of His) bundle branches Purkinje fibers  apex and up- then ventricles contract

Frontal plane SINOATRIAL (SA) NODE ATRIOVENTRICULAR (AV) NODE Left atrium Left ventricle Anterior view of frontal section ATRIOVENTRICULAR (AV) BUNDLE (BUNDLE OF HIS) RIGHT AND LEFT BUNDLE BRANCHES PURKINJE FIBERS 1 2 3 4 5 Right atrium Right ventricle

Electrocardiogram Recording of currents from cardiac conduction on skin = electrocardiogram (EKG or ECG) P wave = atrial depolarization Contraction begins right after peak Repolarization is masked in QRS QRS complex = Ventricular depolarization Contraction of ventricle T-wave = ventricular repolarization Just after ventricles relax

Cardiac Cycle After T-wave ventricular diastole Ventricular pressure drops below atrial pressure & AV valves open  ventricular filling occurs After P-wave atrial systole Finishes filling ventricle (about 25% of total)

Cardiac Cycle After QRS ventricular systole Pressure pushes AV valves closed Pushes semilunar valves open and ejection occurs Ejection until ventricle relaxes enough for arterial pressure to close semilunar valves Cardiac Cycle Animations

Cardiac Cycle: Flow Terms Cardiac Output (CO) = liters/min pumped Heart Rate (HR) = beats/minute (bpm) Stroke volume (SV) = volume/beat CO = HR x SV Average:

Cardiac Cycle: Control of Stroke Volume Degree of stretch = Frank-Starling law Increase diastolic volume (stretch) increases strength of contraction increased S.V. Increased venous return  increased S.V. Increased sympathetic activity High back pressure in artery  decreased S.V. Slows semilunar valve opening Slow heart rate  increased S.V.

Cardiac Cycle: Control of Heart Rate Pacemaker adjusted by nerves Cardiovascular Center in Medulla Parasympathetic - ACh slows HR via Vagus nerve Sympathetic - norepinephrine speeds HR Sensory input for control: Baroreceptors (aortic arch & carotid sinus)- B.P. Chemoreceptors- O2, CO2, pH

Cardiac Cycle: Other Controls Hormones: Epinephrine & norepinephrine increase H.R. Thyroid hormones stimulate H.R. Called tachycardia (opposite: bradycardia) Ions Increased Na+ or K+ decrease H.R. & contraction force Increased Ca2+ increases H.R. & contraction force

Exercise Aerobic exercise (longer than 20 min) strengthens cardiovascular system Well trained athlete doubles maximum C.O. Resting C.O. about the same but resting H.R. decreased

Blood vessels and circulation

Blood Vessels Arteries: carry blood away from heart Elastic Muscular: Their smooth muscle helps regulate blood pressure, directs flow Arterioles: branches of main arteries; distribution to capillaries

Blood Vessels Capillaries: thin-walled for diffusion Veins: carry blood back to heart Venules: collect blood from capillaries Veins from tissues  vena cavae  heart

Blood Vessel Structure: Arteries, Veins Three Layers: Tunica externa: connective tissue Tunica media: smooth muscle Tunica interna (intima): endothelial tissue

Blood Vessel Structure: Arteries, Veins Arteries: thicker tunica media Elastic tissue and/or muscle Arterioles Arterioles: control blood pressure, blood flow Veins Larger lumen, thinner walls Contain valves to prevent backflow Venules Venules: very thin, no valves

Blood Vessel Structure: Arteries, Veins

Blood Vessel Functions Muscular arteries, arterioles regulate flow Sympathetic activity to smooth muscle  vasoconstriction (narrowing) Decreased sympathetic activity causes relaxation (dilation) Arterioles adjust flow into capillaries Capillaries: sites of gas exchange Systemic venules and veins serve as blood reservoirs (hold ~64% total blood volume)

Venous Return Blood enters veins at very low pressure Inadequate to overcome gravity and return blood to heart Skeletal muscle contractions Contracting skeletal muscles (especially in lower limbs) squeeze veins emptying them Because of venous valves, flow is  heart

Venous Return Respiratory pump has similar action Inhalation decreases thoracic pressure and increases abdominal pressure  blood to heart Exhalation allows refilling of abdominal veins

Venous Return

Blood Flow Through Vessels Blood flow follows a pressure gradient Greater gradient  greater flow BP is highest in aorta: 110/70 mm Hg BP declines as flows through more vessels Capillary beds ~35-16 mm Hg 16 mm Hg at venules  0 at right atrium

Factors Regulating Blood Flow Blood volume and ventricular contraction  cardiac output Vascular resistance: opposition to flow (depends on lumen diameter, vessel length, and blood viscosity) Smaller lumen (vasoconstriction)  greater resistance Greater vessel length (with weight gain)  greater resistance Higher viscosity (as with high hematocrit)  greater resistance

Cardiovascular Center Located in medulla Helps regulate Heart rate Stroke volume Blood pressure Blood flow to specific tissues Mechanisms By neural mechanisms By hormonal mechanisms

Cardiovascular Center Input To inform brain that BP should be altered: Input from different parts of brain Cerebral cortex: thoughts, decisions Limbic system: emotions Hypothalamus: changes in temperature or blood volume Input from sensory receptors and nerves Proprioceptors, baroreceptors, chemoreceptors

Cardiovascular Center Input Proprioceptors: monitor movements of joints and muscles Cause  heart rate as exercise begins   cardiac output (CO)   BP Baroreceptors in aorta and carotid: if BP   sympathetic stimulation   CO   BP  parasympathetic   CO   BP Chemoreceptors in aorta and carotid bodies If low O2, high CO2, or high H+ (acidity)   resistance by  vasoconstriction   BP

Cardiovascular Center Input

Output Effects ANS nerves to heart Vasomotor (sympathetic nerves)  Sympathetic  HR and force of contraction   cardiac output (CO)   BP  Parasympathetic   HR  CO   BP Vasomotor (sympathetic nerves) To arterioles contract smooth muscle   vascular resistance   BP To veins contract smooth muscle  move blood to heart   BP

Circulatory Routes Pulmonary Circulation: from the right side of the heart to the lungs and back to the left side of the heart Systemic Circulation: from the left side of the heart to the tissues and cells of the body and back to the right side of the heart Cardiac Circulation: from the left side of the heart through the coronary arteries and back to the right side of the heart

Circulatory Routes