Info Nqz
FIGURE 6-3 Adrenergic and muscarinic receptors in the heart and blood vessels. Norepinephrine NE released from sympathetic nerve terminals binds to postjunctional adrenoceptors in the heart subtype affinity to NE p1 gt gt p2 and a1 to produce positive inotropy, chronotropy, and dromotropy. In blood vessels, NE binds to postjunctional adrenoceptors subtype affinity to NE a1 gt gt a2 and p2 . NE binding to postjunctional a-adrenoceptors causes vasoconstriction, whereas binding to -adrenoceptors...
Info Wzf
FIGURE 7-4 Reactive hyperemia. Arterial occlusion ischemia followed by reperfusion results in a transient increase in blood flow reactive hyperemia . The magnitude and duration of the reactive hyperemia are directly related to the duration of ischemia. sistance. During the hyperemia, oxygen becomes replenished and vasodilator metabolites are washed out of the tissue, causing the resistance vessels to regain their normal vascular tone and thereby return flow to normal levels. The longer the...
Ecg
FIGURE 4-2 Cardiac cycle. The seven phases of the cardiac cycle are 1 atrial systole 2 isovolumetric contraction 3 rapid ejection 4 reduced ejection 5 , isovolumetric relaxation 6 rapid filling and 7 reduced filling. LV, left ventricle ECG, electrocardiogram a, a-wave c, c-wave y, v-wave AP, aortic pressure LVP, left ventricular pressure LAP, left atrial pressure LVEDV, left ventricular end-diastolic volume LVESV, left ventricular end-systolic volume, S1-S4, four heart sounds. the left...
Of Blood Flow
Tissues and organs have the ability to regulate, to a varying degree, their own blood flow. This intrinsic ability to regulate blood flow is termed local regulation and can occur in the complete absence of any extrinsic neurohumoral influences. For example, if a muscle is removed from the body, perfused under constant pressure with an oxygenated salt solution, and then electrically stimulated to induce muscle contractions, the blood flow increases. The increase in blood flow occurs in the...
Venous Blood Pressure
Venous pressure is a general term that represents the average blood pressure within the venous compartment. A more specific term, central venous pressure, describes the blood pressure in the thoracic vena cava near the right atrium. This pressure is important because it determines the filling pressure of the right ventricle, and thereby determines ventricular stroke volume through the Frank-Starling mechanism as discussed in Chapter 4. Several factors influence central venous pressure cardiac...
Edv 1
FIGURE 4-20 Effects of increased afterload aortic pressure on the steady-state left ventricular LV pressure-volume loop. Heart rate and inotropy are held constant in this illustration. Increased aortic pressure leads to an increase in end-systolic volume ESV , followed by a secondary, but smaller increase in end-diastolic volume EDV . The net effect is a narrower loop and therefore decreased stroke volume. FIGURE 4-21 Effects of increased inotropy on the length-tension relationship for cardiac...
Table 41 Factors Increasing Myocardial Oxygen Consumption
T Heart Rate T Inotropy T Afterload T Preload Changes in preload affect oxygen consumption much less than do changes in the other factors. sion cycles per minute. Increasing inotropy increases oxygen consumption because both the rate of tension development and the magnitude of tension are increased, and they both are associated with increased ATP hydrolysis and oxygen consumption. An increase in af-terload likewise increases oxygen consumption because it increases the tension that must be...
I Map
FIGURE 5-11 Effects of gravity on central venous pressure CVP , cardiac output CO , and mean arterial pressure MAP . Diagram A, supine position. Diagram B an upright position with rigid vessel results in elevated capillary pressure PC owing to hydrostatic forces, but no change in CVP, CO, MAP, or systemic perfusion pressure AP . Diagram C upright position with compliant vessels elevated PC from hydrostatic pressure owing to gravity distends blood vessels particularly veins and increases...
Info Vyt
point on the line is the reciprocal of the compliance, which is sometimes referred to as ventricular elastance or stiffness. The relationship between pressure and volume is nonlinear in the ventricle as in most biological tissues therefore, compliance decreases with increasing pressure or volume. When pressure and volume are plotted as in Figure 4-6, we find that the slope of the filling curve the end-diastolic pressure-volume relationship described in Figure 4-4 increases dramatically at...
The Arrangement Of The Cardiovascular System
The cardiovascular system has two primary components the heart and blood vessels. A third component, the lymphatic system, does not contain blood, but nonetheless serves an important exchange function in conjunction with blood vessels. The heart can be viewed functionally as two pumps with the pulmonary and systemic circulations situated between the two pumps Fig. 1-1 . The pulmonary circulation is the blood flow within the lungs that is involved in the exchange of gases between the blood and...
And Carbon Dioxide
Oxygen diffuses from the blood to the tissues to support mitochondrial respiration. The lipid solubility of oxygen enables it to readily diffuse through tissues however, the distance that oxygen is able to diffuse within a tissue is limited by cellular utilization of oxygen. For example, as oxygen diffuses out of a capillary in skeletal muscle, the muscle cells adjacent to the capillary take up the oxygen for use by the mitochondria. Consequently, little oxygen diffuses all the way through one...
Conduction Of Action Potentials Within The Heart
Electrical Conduction within the Heart The action potentials generated by the SA node spread throughout the atria primarily through cell-to-cell conduction Fig. 2-10 . FIGURE 2-10 Cell-to-cell conduction. Cardiac cells are connected together by low-resistance gap junctions between the cells, forming a functional syncytium. When one cell depolarizes, depolarizing currents can pass through the gap junctions and depolarize adjacent cells, resulting in a cell-to-cell propagation of action...
Venous Return And Cardiac Output
The Balance between Venous Return and Cardiac Output Venous return is the flow of blood back to the heart. Previous sections described how the venous return to the right atrium from the abdominal vena cava is determined by the pressure gradient between the abdominal vena cava and the right atrium, divided by the resistance of the vena cava. However, that analysis looks at only a short segment of the venous system and does not show what factors determine venous return from the capillaries....
T Aortic Pulse Pressure
FIGURE 5-5 Factors affecting aortic pulse pressure. Pulse pressure is increased by those factors that increase stroke volume or decrease aortic compliance. mean arterial pressure will be approximately 93 mm Hg. At high heart rates, however, mean arterial pressure is more closely approximated by the arithmetic average of systolic and diastolic pressure because the shape of the arterial pressure pulse changes it becomes narrower as the period of diastole shortens more than does systole....
Autoregulation
, strong , moderate, , weak. 1 Sympathetic vasoconstriction in the coronaries is overridden by metabolic vasodilation during sympathetic activation of the heart. 2 Hypoxia causes vasoconstriction, the opposite of all other organs. imized. Pulmonary capillaries differ from their systemic counterparts in that they form thin interconnecting sheets around and between adjacent alveoli, which greatly increase their surface area and reduce diffusion distances. Unlike other organs, alveolar or...
Cardiac Cell Structure And Function
Cardiac myocytes represent a type of striated muscle, so-called because crossbands or cross striations are observed microscopically. Although cardiac muscle shares some structural and functional similarities with skeletal muscle, it has several important differences. Cardiac myocytes are generally single nucleated and have a diameter of approximately 25 m and a length of about 100 m. In contrast, although some types of skeletal muscle myo-cytes may have a similar diameter, their cell lengths...
Calveolae
FIGURE 3-8 Vascular smooth muscle cell structure. Actin and myosin filaments are connected by dense bodies and dense bands. Each myosin filament is surrounded by several actin filaments. N, nucleus. Enlarged cross-section of actin and myosin FIGURE 3-8 Vascular smooth muscle cell structure. Actin and myosin filaments are connected by dense bodies and dense bands. Each myosin filament is surrounded by several actin filaments. N, nucleus. an arteriole can result in depolarization at a distant...
Ne Aii Et1
FIGURE 3-6 Signal transduction pathways regulating cardiac myocyte contraction. The two major pathways involve formation of either cyclic adenosine monophosphate cAMP or inositol 1,4,5-triphosphate IP3 , both of which affect Ca release by sarcoplasmic reticulum and therefore affect contraction. R, receptor Gs, stimulatory G-protein Gi, inhibitory G-protein Gq, phospholipase C-coupled G-protein AC, adenylyl cyclase PL-C, phospholipase C PIP2, phosphatidylinositol 4,5-bisphosphate DAG,...
Info Eqd
FIGURE 2-7 Changes in ion conductances associated with a sinoatrial SA nodal action potential. Phase 0 depolarization primarily is due to an increase in calcium conductance gCa through L-type Ca channels accompanied by a fall in potassium conductance gK phase 3 repolarization results from an increase in gK and a decrease in gCa . Phase 4 undergoes a spontaneous depolarization owing to a pacemaker current If carried in part by Na decreased gK and increased gCa also contribute to the spontaneous...
Decreasing
Sympathetic stimulation Muscarinic receptor antagonist p-Adrenoceptor agonists Circulating catecholamines Hypokalemia Hyperthyroidism Parasympathetic stimulation Muscarinic receptor agonists p-Blockers Ischemia hypoxia Hyperkalemia tance during phase 4. Cellular hypoxia depolarizes the membrane potential, causing bradycardia and abolition of pacemaker activity. Various drugs used to treat abnormal heart rhythm i.e., antiarrhythmic drugs also affect SA nodal rhythm. Calcium channel blockers, for...
Introduction
The primary function of cardiac myocytes is to contract. Electrical changes within the myocytes initiate this contraction. This chapter examines 1 the electrical activity of individual myocytes, including resting membrane potentials and action potentials 2 the way action potentials are conducted throughout the heart to initiate coordinated contraction of the entire heart and 3 the way electrical activity of the heart is measured using the electrocardiogram ECG . CELL MEMBRANE POTENTIALS Resting...
Case 21
A patient is being treated for hypertension with a -blocker a drug that blocks to 3-adrenoceptors in the heart in addition to a diuretic. A routine ECG reveals that the patient's P-R interval is 0.24 seconds first-degree AV nodal block . Explain how removal of the -blocker might improve AV nodal conduction. Sympathetic nerve activity increases conduction velocity within the AV node positive dromotropic effect . This effect on the AV node is mediated by norepinephrine binding to -adrenoceptors...