Chapter 15 - Cardio

Pressure and Volume Changes of a Cardiac Cycle 1:

-During a cardiac cycle, the pressure in the heart chambers rises and falls -Pressure changes open and close the valves

Regulation of the Cardiac Cycle 1:

-Heart rate and volume of blood pumped change to meet requirements -Cardiac center in medulla oblongata performs neural regulation of heart -SA node (pacemaker) normally controls the heart rate, and heart rate changes occur due to factors that influence the SA node -Sympathetic and parasympathetic fibers modify the heart rate in response to changing conditions, such as: • Physical exercise • Body temperature • Fight-or-flight response • Concentration of various ions, such as K+ and Ca+2

Capillary Permeability:

-Openings in walls of capillaries are thin slits found where endothelial cells overlap -Sizes of openings vary among tissues; permeability varies with size of slits

Blood vessels:

-are organs of the cardiovascular system -Blood vessels form a closed circuit, transporting blood from heart to body cells (or lungs) and back to the heart

Heart sounds:

A heartbeat through a stethoscope sounds like "lubb-dupp" -Sounds are due to closing of heart valves, and vibrations associated with a sudden slowing of blood flow during contraction/relaxation of chambers

Murmur:

Abnormal heart sound derived from incomplete closure of cusps of a valve

The deflections in the normal ECG, or waves, include: P wave:

Atrial depolarization; occurs just prior to atrial contraction

Pulmonary circuit:

Carries oxygen-poor blood from heart to lungs, drops off carbon dioxide, picks up oxygen, flows back to heart

(Types of blood vessels) Arteries:

Carry blood away from the ventricles of the heart

Junctional Fibers:

Conduct impulses from SA node to AV node

Internodal Atrial Muscle:

Conducts impulses from SA node to atria

AV (Atrioventricular) Bundle (of His):

Conducts impulses rapidly between SA node and bundle branches

AV (Atrioventricular) Node:

Conducts impulses to AV Bundle; delays impulse, so that atria finish contracting before ventricles contract

Systole:

Contraction of a heart chamber

Purkinje Fibers:

Large fibers that conduct impulses to ventricular myocardium; conduct impulses to apex first; whorled pattern of muscle in ventricles contract with twisting motion

Major Components of the Cardiac Conduction System: SA (Sinoatrial) Node:

Pacemaker; initiates rhythmic contractions of the heart

Arterioles:

Receive blood from the arteries, and carry it to the capillaries

Venules:

Receive blood from the capillaries, and conduct it to veins

Veins:

Receive blood from venules, and carry it back to the atria of the heart

Diastole:

Relaxation of a heart chamber

Capillaries:

Sites of exchange of substances between the blood and the body cells

Cardiac Conduction System:

Specialized group of cardiac muscle cells, which initiate and distribute cardiac action potentials through myocardium

Left and Right Bundle Branches:

Split off from AV bundle, conduct impulses to Purkinje fibers on both sides of heart

Systemic circuit:

Transports oxygen-rich blood and nutrients to body cells, removes wastes from cells, flows back to heart

QRS complex: (3 waves)

Ventricular depolarization; occurs just prior to ventricular contraction • Record of atrial repolarization is "hidden" in the large QRS complex, since ventricular depolarization is a much larger event

T wave:

Ventricular repolarization; occurs just prior to ventricular relaxation

Electrocardiogram (ECG, EKG):

• A recording of electrical changes that occur in the myocardium during the cardiac cycle • Used to assess ability of heart to conduct impulses

Cardiac Cycle (the events that occur during a heartbeat):

• Atria contract (atrial systole) while ventricles relax (ventricular diastole) • Then ventricles contract (ventricular systole) while atria relax (atrial diastole) • Then both chambers relax briefly *The heart chambers function in regulated, coordinated manner

During atrial systole and ventricular diastole:

• Atria contract and ventricles are relaxed • The AV valves open and the semilunar valves close • Atrial systole pushes remaining 30% of blood into the ventricles, causing ventricular pressure to increase

(Regulation of the Cardiac Cycle 3) Example of baroreceptor reflex response:

• Baroreceptors in aortic arch and carotid artery sinuses detect blood pressure • Increased pressure stretches receptors • Parasympathetic cardioinhibitory reflex lowers heart rate and blood pressure

Characteristics of cardiac muscle cells:

• Have 1 central nucleus, and form branching networks • Intercalated discs between cells contain desmosomes for structural support, and gap junctions to spread action potentials through a network of cells • Form a functional syncytium, mass of merging cells that function as a unit

Fenestrated capillaries:

• Have large openings in cell membranes and between endothelial cells • Found in endocrine glands, kidneys, small intestine

Sinusoidal capillaries:

• Have largest openings; spaces between cells are small cavities • Discontinuous • Found in liver, spleen, and red bone marrow

(Types of capillaries) Continuous capillaries:

• Have small openings • Found in muscle, connective and nervous tissues, and skin

Other factors that affect heart rate:

• Impulses from hypothalamus and cerebrum • Body temperature • Levels of K+ and Ca+2

2 such masses exist in the heart:

• In the atrial walls; called the atrial syncytium • In the ventricular walls; called the ventricular syncytium

Stretch Receptors in venae cavae:

• Increase in blood pressure stretches receptors • Sympathetic cardioaccelerator reflex increase heart rate and force of contraction, to lower venous pressure

Baroreceptor reflexes:

• Involve cardiac control center in medulla oblongata • Balance inhibitory and excitatory effects of parasympathetic and sympathetic fibers • Contains a cardioinhibitor reflex center and a cardioaccelerator reflex center

Blood Flow Through the Heart, Lungs, and Tissues:

• Oxygen-poor blood from venae cavae and coronary sinus enter right atrium • Blood flows from right atrium, through tricuspid valve, into right ventricle • Right atrium contracts, sending remaining blood into right ventricle • Right ventricle contracts • Tricuspid valve closes right atrioventricular orifice • As pressure rises in right ventricle, pulmonary semilunar valve opens • Blood flows into pulmonary trunk • Blood flows to lungs, drops off carbon dioxide, picks up oxygen • Blood returns to left atrium via pulmonary veins • Blood flows from left atrium, though mitral valve, into left ventricle • Left atrium contracts, sending remaining blood into left ventricle • Left ventricle contracts • Mitral valve closes left atrioventricular orifice • As pressure rises in left ventricle, aortic semilunar valve opens • Blood flows into aorta, transporting oxygen-rich blood to body cells

Sympathetic impulses that innervate heart:

• Reach heart on accelerator nerves • Increase heart rate, due to influence on SA and AV nodes, atrial and ventricular myocardium

(Regulation of the Cardiac Cycle 2) Parasympathetic impulses that innervate heart:

• Reach heart via vagus nerves • Lower SA node rate of 100 beats/min to 60 to 80 beats/min • Decrease heart rate, due to influence on SA and AV nodes

Organization of the heart:

• Right side pumps to pulmonary circuit, blood returns to left side • Left side pumps to systemic circuit, blood returns to right side

Arterioles: (depth)

• Smaller and thinner-walled than arteries (same 3 layers or tunics) • Walls of middle and outer layers become thinner as arterioles become smaller *Both arteries and arterioles can undergo vasoconstriction and vasodilation

Capillaries: (depth)

• Smallest-diameter blood vessels • Connect the smallest arterioles and the smallest venules • Extensions of the inner lining of arterioles • Walls consist of endothelium (simple squamous epithelium) only • Semipermeable; exchange substances between blood and tissue fluid • Capillary blood flow regulated mainly by precapillary sphincters: smooth muscle surrounding capillary when it branches off arteriole or metarteriole

Heart sound "Lubb":

• The first heart sound (S1) • Occurs during ventricular systole • Associated with closing of the AV valves

Heart sound "Dupp":

• The second heart sound (S2) • Occurs during ventricular diastole • Associated with closing of the pulmonary and aortic semilunar valves

Arteries: (in depth)

• Thick, strong wall, thicker than walls of veins • 3 layers or tunics: 1. Tunica interna (intima): innermost layer, endothelium 2. Tunica media: smooth muscle and elastic tissue 3. Tunica externa (adventitia): outer layer, connective tissue • Transport blood under high blood pressure • Give rise to smaller arterioles

Early in ventricular diastole:

• Ventricular pressure is lower than atrial pressure • Atria and ventricles are relaxed • AV valves open, and semilunar valves are closed • About 70% of blood flows passively from atria into ventricles

During ventricular systole and atrial diastole:

• When ventricular pressure rises about atrial pressure, AV valves close • Chordae tendineae prevent the cusps of the valves from bulging too far backward into the atria • Atria relax • Blood flows into atria from venae cavae and pulmonary veins • Ventricular pressure continues to increase, and opens the semilunar valves • Blood flows into the pulmonary trunk and aorta