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Primary active transport of hydrogen ions is especially important at two places in the body: (1) in the gastric glands of the stomach; and (2) in the late distal tubules and cortical collecting ducts of the kidneys.
In the gastric glands, the deep-lying *parietal cells* have the most potent primary active mechanism f... | {
"Header 1": "OSMOSIS ACROSS SELECTIVELY PERMEABLE MEMBRANES—\"NET DIFFUSION\" OF WATER",
"Header 2": "Primary Active Transport of Hydrogen lons",
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When sodium ions are transported out of cells by primary active transport, a large concentration gradient of
sodium ions across the cell membrane usually develops, with a high concentration outside the cell and a low concentration inside. This gradient represents a storehouse of energy, because the excess sodium outs... | {
"Header 1": "OSMOSIS ACROSS SELECTIVELY PERMEABLE MEMBRANES—\"NET DIFFUSION\" OF WATER",
"Header 2": "SECONDARY ACTIVE TRANSPORT— CO-TRANSPORT AND COUNTER-TRANSPORT",
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Physiol Rev 2018 98:1493- 1590, 2018.
Kaksonen M, Roux A. Mechanisms of clathrin-mediated endocytosis. Nat Rev Mol Cell Biol 19:313-326, 2018.
Kandasamy P, Gyimesi G, Kanai Y, Hediger MA. Amino acid transporters revisited: new views in health and disease. Trends Biochem Sci 43:752-789, 2018.
Papadopoulos MC, Verk... | {
"Header 1": "OSMOSIS ACROSS SELECTIVELY PERMEABLE MEMBRANES—\"NET DIFFUSION\" OF WATER",
"Header 2": "SECONDARY ACTIVE TRANSPORT— CO-TRANSPORT AND COUNTER-TRANSPORT",
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In Figure 5-1A, the potassium concentration is great inside a nerve fiber membrane but very low outside the membrane. Let us assume that the membrane in this case is permeable to the potassium ions but not to any other ions. Because of the large potassium concentration gradient from the inside toward the outside, there... | {
"Header 1": "Membrane Potentials Caused by Ion Concentration Differences Across a Selectively Permeable Membrane",
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**Figure 5-1 A**, Establishment of a diffusion potential across a nerve fiber membrane, caused by diffusion of potassium ions from inside the cell to outside the cell through a membrane that is selectively permeable only to potassium. **B**, Establishment of a diffusion potential when the nerve fiber membrane is permea... | {
"Header 1": "DIFFUSION POTENTIALS (Anions) Nerve fiber (Anions) Nerve fiber - (Anions) + - + - + (Anions) + - + - + + - + + - + + - + + - + + - + + - + + - + + - + + - + + - + + - + + - + + - + + - + + - + + - + + - + + - + + - + + - + + - + + - + + - + + - + + - + + - + + - + + - + + - + + - + + - + + - + + - + + ... |
The resting membrane potential of large nerve fibers when they are not transmitting nerve signals is about -70 millivolts. That is, the potential *inside the fiber* is 70 millivolts more negative than the potential in the extracellular fluid on the outside of the fiber. In the next few paragraphs, the transport propert... | {
"Header 1": "DIFFUSION POTENTIALS (Anions) Nerve fiber (Anions) Nerve fiber - (Anions) + - + - + (Anions) + - + - + + - + + - + + - + + - + + - + + - + + - + + - + + - + + - + + - + + - + + - + + - + + - + + - + + - + + - + + - + + - + + - + + - + + - + + - + + - + + - + + - + + - + + - + + - + + - + + - + + - + + ... |
**Figure 5-5** shows the important factors in the establishment of the normal resting membrane potential. They are as follows.
#### Contribution of the Potassium Diffusion Potential.
In **Figure 5-5A**, we assume that the only movement of ions through the membrane is diffusion of potassium ions, as demonstrated by ... | {
"Header 1": "DIFFUSION POTENTIALS (Anions) Nerve fiber (Anions) Nerve fiber - (Anions) + - + - + (Anions) + - + - + + - + + - + + - + + - + + - + + - + + - + + - + + - + + - + + - + + - + + - + + - + + - + + - + + - + + - + + - + + - + + - + + - + + - + + - + + - + + - + + - + + - + + - + + - + + - + + - + + - + + ... |
Another important characteristic of the sodium channel inactivation process is that the inactivation gate will not reopen until the membrane potential returns to or near the original resting membrane potential level. Therefore, it is usually not possible for the sodium channels to open again without first repolarizin... | {
"Header 1": "DIFFUSION POTENTIALS (Anions) Nerve fiber (Anions) Nerve fiber - (Anions) + - + - + (Anions) + - + - + + - + + - + + - + + - + + - + + - + + - + + - + + - + + - + + - + + - + + - + + - + + - + + - + + - + + - + + - + + - + + - + + - + + - + + - + + - + + - + + - + + - + + - + + - + + - + + - + + - + + ... |
Like the sodium pump, the calcium pump transports calcium ions from the interior to the exterior of the cell membrane (or into the endoplasmic reticulum of the cell), creating a calcium ion gradient of about 10,000-fold. This process leaves an internal cell concentration of calcium ions of about 10−7 molar, in contrast... | {
"Header 1": "DIFFUSION POTENTIALS (Anions) Nerve fiber (Anions) Nerve fiber - (Anions) + - + - + (Anions) + - + - + + - + + - + + - + + - + + - + + - + + - + + - + + - + + - + + - + + - + + - + + - + + - + + - + + - + + - + + - + + - + + - + + - + + - + + - + + - + + - + + - + + - + + - + + - + + - + + - + + - + + ... |
#### RE-ESTABLISHING SODIUM AND POTASSIUM IONIC GRADIENTS AFTER ACTION POTENTIALS ARE COMPLETED—IMPORTANCE OF ENERGY METABOLISM
Transmission of each action potential along a nerve fiber slightly reduces the concentration differences of sodium and potassium inside and outside the membrane because sodium ions diffuse... | {
"Header 1": "DIFFUSION POTENTIALS (Anions) Nerve fiber (Anions) Nerve fiber - (Anions) + - + - + (Anions) + - + - + + - + + - + + - + + - + + - + + - + + - + + - + + - + + - + + - + + - + + - + + - + + - + + - + + - + + - + + - + + - + + - + + - + + - + + - + + - + + - + + - + + - + + - + + - + + - + + - + + - + + ... |
However, the increased potassium conductance (and the state of hyperpolarization) gradually disappears, as shown after each action potential is completed in the figure, thereby again allowing the membrane potential to increase up to the *threshold* for excitation. Then, suddenly, a new action potential results and the ... | {
"Header 1": "DIFFUSION POTENTIALS (Anions) Nerve fiber (Anions) Nerve fiber - (Anions) + - + - + (Anions) + - + - + + - + + - + + - + + - + + - + + - + + - + + - + + - + + - + + - + + - + + - + + - + + - + + - + + - + + - + + - + + - + + - + + - + + - + + - + + - + + - + + - + + - + + - + + - + + - + + - + + - + + ... |
A new action potential cannot occur in an excitable fiber as long as the membrane is still depolarized from the preceding action potential. The reason for this restriction is that shortly after the action potential is initiated, the sodium channels (or calcium channels, or both) become inactivated, and no amount of exc... | {
"Header 1": "REFRACTORY PERIOD AFTER AN ACTION POTENTIAL, DURING WHICH A NEW STIMULUS CANNOT BE ELICITED",
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In contrast to the factors that increase nerve excitability, *membrane-stabilizing factors* can *decrease excitability*. For example, *a* high *extracellular fluid calcium ion concentration* decreases membrane permeability to sodium ions and simultaneously reduces excitability. Therefore, calcium ions are said to be wh... | {
"Header 1": "REFRACTORY PERIOD AFTER AN ACTION POTENTIAL, DURING WHICH A NEW STIMULUS CANNOT BE ELICITED",
"Header 2": "Inhibition of Excitability—Stabilizers and Local Anesthetics",
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About 40% of the body is skeletal muscle, and perhaps another 10% is smooth and cardiac muscle. Some of the same basic principles of contraction apply to all these muscle types. In this chapter, we mainly consider skeletal muscle function; the specialized functions of smooth muscle are discussed in Chapter 8, and cardi... | {
"Header 1": "**Contraction of Skeletal Muscle**",
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This action causes a local depolarization that in turn leads to the opening of voltage-gated sodium channels, which initiates an action potential at the membrane.
- 5. The action potential travels along the muscle fiber membrane in the same way that action potentials travel along nerve fiber membranes.
- 6. The action ... | {
"Header 1": "**Contraction of Skeletal Muscle**",
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**Troponin and Its Role in Muscle Contraction.** Attached intermittently along the sides of the tropomyosin molecules are additional protein molecules called *troponin.* These protein molecules are actually complexes of three loosely bound protein subunits, each of which plays a specific role in controlling muscle co... | {
"Header 1": "**Contraction of Skeletal Muscle**",
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At this point, the two Z disks of the sarcomere abut the ends of the myosin filaments. Then, as contraction proceeds to still shorter sarcomere lengths, the ends of the myosin filaments are crumpled and, as shown in the figure, the strength of contraction approaches zero, but the sarcomere has now contracted to its sho... | {
"Header 1": "**Contraction of Skeletal Muscle**",
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In the isometric system, the muscle contracts against a force transducer without decreasing the muscle length, as shown in the bottom panel of **[Figure 6-12](#page-85-0)**. In the isotonic system, the muscle shortens against a fixed load, which is illustrated in the top panel of the figure, showing a muscle lifting ... | {
"Header 1": "**Contraction of Skeletal Muscle**",
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Tetany occurs because enough calcium ions are maintained in the muscle sarcoplasm, even between action potentials, so that a full contractile state is sustained without allowing any relaxation between the action potentials.
**Maximum Strength of Contraction.** The maximum strength of tetanic contraction of a muscle o... | {
"Header 1": "**Contraction of Skeletal Muscle**",
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**Hyperplasia of Muscle Fibers.** Under rare conditions of extreme muscle force generation, the actual number of muscle fibers has been observed to increase (but only by a few percent), in addition to the fiber hypertrophy process. This increase in fiber number is called *fiber hyperplasia.* When it does occur, the m... | {
"Header 1": "**Contraction of Skeletal Muscle**",
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"source_pdf": "datasets/websources/biochem/1671268744mpp.pdf"
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#### NEUROMUSCULAR JUNCTION AND TRANSMISSION OF IMPULSES FROM NERVE ENDINGS TO SKELETAL MUSCLE FIBERS
Skeletal muscle fibers are innervated by large myelinated nerve fibers that originate from large motoneurons in the anterior horns of the spinal cord. As discussed in Chapter 6, each nerve fiber, after entering the m... | {
"Header 1": "**Contraction of Skeletal Muscle**",
"Header 2": "**Excitation of Skeletal Muscle: Neuromuscular Transmission and Excitation-Contraction Coupling**",
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However, it is rapidly destroyed by the enzyme *acetylcholinesterase*, which is attached mainly to the spongy layer of fine connective tissue that fills the synaptic space between the presynaptic nerve terminal and the postsynaptic muscle membrane. A small amount of acetylcholine diffuses out of the synaptic space and ... | {
"Header 1": "**Contraction of Skeletal Muscle**",
"Header 2": "**Excitation of Skeletal Muscle: Neuromuscular Transmission and Excitation-Contraction Coupling**",
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Within minutes, some of those affected can begin to function almost normally until a new dose of neostigmine is required a few hours later.
#### MUSCLE ACTION POTENTIAL
Almost everything discussed in Chapter 5 regarding the initiation and conduction of action potentials in nerve fibers applies equally to skeletal m... | {
"Header 1": "**Contraction of Skeletal Muscle**",
"Header 2": "**Excitation of Skeletal Muscle: Neuromuscular Transmission and Excitation-Contraction Coupling**",
"token_count": 2008,
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**Figure 7-7.** Excitation-contraction coupling in the muscle, showing (1) an action potential that causes release of calcium ions from the sarcoplasmic reticulum and then (2) re-uptake of the calcium ions by a calcium pump. ATP, Adenosine triphosphate.
whereby anesthetics interact wi... | {
"Header 1": "**Contraction of Skeletal Muscle**",
"Header 2": "**Excitation of Skeletal Muscle: Neuromuscular Transmission and Excitation-Contraction Coupling**",
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#### CONTRACTION OF SMOOTH MUSCLE
Smooth muscle is composed of small fibers that are usually 1 to 5 micrometers in diameter and only 20 to 500 micrometers in length. In contrast, skeletal muscle fibers are as much as 30 times greater in diameter and hundreds of times as long. Many of the same principles of contractio... | {
"Header 1": "**Excitation and Contraction of Smooth Muscle**",
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The slow onset of contraction of smooth muscle, as well as its prolonged contraction, is caused by the slowness of attachment and detachment of the cross-bridges with the actin filaments. In addition, the initiation of contraction in response to calcium ions is much slower than in skeletal muscle, as will be discusse... | {
"Header 1": "**Excitation and Contraction of Smooth Muscle**",
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Then the cycling stops, and contraction ceases. The time required for the relaxation of muscle contraction, therefore, is determined to a great extent by the amount of active myosin phosphatase in the cell.
**Possible Mechanism for Regulating the Latch Phenomenon.** Because of the importance of the latch phenomenon i... | {
"Header 1": "**Excitation and Contraction of Smooth Muscle**",
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**Calcium Channels Are Important in Generating the Smooth Muscle Action Potential.** The smooth muscle cell membrane has far more voltage-gated calcium channels than skeletal muscle but few voltage-gated sodium channels. Therefore, sodium does not participate much in the generation of the action potential in most smo... | {
"Header 1": "**Excitation and Contraction of Smooth Muscle**",
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Berridge MJ: Smooth muscle cell calcium activation mechanisms. J Physiol 586:5047, 2008.
Blaustein MP, Lederer WJ: Sodium/calcium exchange: its physiological implications. Physiol Rev 79:763, 1999.
Brozovich FV, Nicholson CJ, Degen CV, Gao YZ, Aggarwal M, Morgan KG: Mechanisms of vascular smooth muscle contractio... | {
"Header 1": "**Excitation and Contraction of Smooth Muscle**",
"token_count": 843,
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The heart, shown in **[Figure 9-1](#page-109-0)**, is actually two separate pumps, a *right heart* that pumps blood through the lungs and a *left heart* that pumps blood through the systemic circulation that provides blood flow to the other organs and tissues of the body. Each of these is a pulsatile, twochamber pump c... | {
"Header 1": "**Cardiac Muscle; The Heart as a Pump and Function of the Heart Valves**",
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"source_pdf": "datasets/websources/biochem/1671268744mpp.pdf"
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This decreased potassium permeability may result from the excess calcium influx through the calcium channels just noted. Regardless of the cause, the decreased potassium permeability greatly decreases the efflux of positively charged potassium ions during the action potential plateau and thereby prevents early return o... | {
"Header 1": "**Cardiac Muscle; The Heart as a Pump and Function of the Heart Valves**",
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The sodium that enters the cell during this exchange is then transported out of the cell by the sodium-potassium ATPase pump. As a result, the contraction ceases until a new action potential comes along.
**Duration of Contraction.** Cardiac muscle begins to contract a few milliseconds after the action potential begin... | {
"Header 1": "**Cardiac Muscle; The Heart as a Pump and Function of the Heart Valves**",
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This period is called the period of *isovolumic* or *isometric contraction*, meaning that cardiac muscle tension is increasing but little or no shortening of the muscle fibers is occurring.
**Period of Ejection.** When the left ventricular pressure rises slightly above 80 mm Hg (and the right ventricular pressure ris... | {
"Header 1": "**Cardiac Muscle; The Heart as a Pump and Function of the Heart Valves**",
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**Figure 9-10** shows a diagram that is especially useful in explaining the pumping mechanics of the *left* ventricle. The most important components of the diagram are the two curves labeled "diastolic pressure" and "systolic pressure." These curves are volume-pressure curves.
The diastolic pressure curve is determin... | {
"Header 1": "**Cardiac Muscle; The Heart as a Pump and Function of the Heart Valves**",
"Header 2": "GRAPHIC ANALYSIS OF VENTRICULAR PUMPING",
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When systolic pressure is chronically elevated, wall stress and cardiac workload are also increased, inducing thickening of the left ventricular walls, which can reduce the ventricular chamber radius (concentric hypertrophy) and at least partially relieve the increased wall tension. Also, much more chemical energy is e... | {
"Header 1": "**Cardiac Muscle; The Heart as a Pump and Function of the Heart Valves**",
"Header 2": "GRAPHIC ANALYSIS OF VENTRICULAR PUMPING",
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However, they represent function of the entire heart rather than that of a single ventricle. They show the relationship between right atrial pressure at the input of the right heart and cardiac output from the left ventricle into the aorta.
The curves of **[Figure 9-15](#page-120-0)** demonstrate that at any given ri... | {
"Header 1": "**Cardiac Muscle; The Heart as a Pump and Function of the Heart Valves**",
"Header 2": "GRAPHIC ANALYSIS OF VENTRICULAR PUMPING",
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The human heart has a special system for rhythmic self-excitation and repetitive contraction approximately 100,000 times each day or 3 billion times in the average human lifetime. This impressive feat is performed by a system that does the following: (1) generates electrical impulses to initiate rhythmical contraction ... | {
"Header 1": "**Rhythmical Excitation of the Heart**",
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This process continues throughout a person's life.
#### **INTERNODAL AND INTERATRIAL PATHWAYS TRANSMIT CARDIAC IMPULSES THROUGH THE ATRIA**
The ends of the sinus nodal fibers connect directly with the surrounding atrial muscle fibers. Therefore, action potentials originating in the sinus node travel outward into th... | {
"Header 1": "**Rhythmical Excitation of the Heart**",
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Furthermore, it should be recalled that everywhere, except at the A-V bundle, the atrial muscle is separated from the ventricular muscle by a continuous fibrous barrier, a portion of which is shown in **Figure 10-3**. This barrier normally acts as an insulator to prevent passage of the cardiac impulse between atrial an... | {
"Header 1": "The A-V Bundle Is Normally a One-Way Conduction Path. A special characteristic of the A-V bundle is the inability, except in abnormal states, of action potentials to travel backward from the ventricles to the atria. This characteristic prevents re-entry of cardiac impulses by this route from the ventri... |
Once the impulse reaches the ends of the Purkinje fibers, it is transmitted through the ventricular muscle mass by the ventricular muscle fibers themselves. The velocity of transmission is now only 0.3 to 0.5 m/sec, one-sixth that in the Purkinje fibers.
The cardiac muscle wraps around the heart in a double spiral, w... | {
"Header 1": "The A-V Bundle Is Normally a One-Way Conduction Path. A special characteristic of the A-V bundle is the inability, except in abnormal states, of action potentials to travel backward from the ventricles to the atria. This characteristic prevents re-entry of cardiac impulses by this route from the ventri... |
**Figure 10-4** summarizes the transmission of the cardiac impulse through the human heart. The numbers on the
**Figure 10-4** Transmission of the cardiac impulse through the heart, showing the time of appearance (in fractions of a second after initial appearance at the sinoatrial node... | {
"Header 1": "The A-V Bundle Is Normally a One-Way Conduction Path. A special characteristic of the A-V bundle is the inability, except in abnormal states, of action potentials to travel backward from the ventricles to the atria. This characteristic prevents re-entry of cardiac impulses by this route from the ventri... |
Therefore, the initial rise of the sinus nodal membrane potential caused by inward sodium and calcium leakage requires much longer to reach the threshold potential for excitation. This requirement greatly slows the rate of rhythmicity of these nodal fibers. If the vagal stimulation is strong enough, it is possible to s... | {
"Header 1": "The A-V Bundle Is Normally a One-Way Conduction Path. A special characteristic of the A-V bundle is the inability, except in abnormal states, of action potentials to travel backward from the ventricles to the atria. This characteristic prevents re-entry of cardiac impulses by this route from the ventri... |
When a cardiac impulse passes through the heart, electrical current also spreads from the heart into the adjacent tissues surrounding the heart. A small portion of the current spreads all the way to the surface of the body. If electrodes are placed on the skin on opposite sides of the heart, electrical potentials gener... | {
"Header 1": "**Fundamentals of Electrocardiography**",
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All recordings of ECGs are made with appropriate calibration lines on the display grid. Historically, ECGs were recorded electronically and printed onto paper; ECGs are now usually displayed digitally. As shown in Figure 11-1, the horizontal calibration lines are arranged so that 10 of the small line divisions upward o... | {
"Header 1": "**Fundamentals of Electrocardiography**",
"Header 2": "ELECTROCARDIOGRAPHIC CALIBRATION AND DISPLAY",
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#### Recording Electrical Potentials from a Partially Depolarized Mass of Syncytial Cardiac Muscle
Figure 11-4 shows a syncytial mass of cardiac muscle that has been stimulated at its most central point. Before stimulation, all the exteriors of the muscle cells had been positive, and the interiors had been negative. ... | {
"Header 1": "**Fundamentals of Electrocardiography**",
"Header 2": "FLOW OF CURRENT AROUND THE HEART DURING THE CARDIAC CYCLE",
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Figure 11-5 shows the ventricular muscle lying within the chest. Even the lungs, although mostly filled with air, conduct electricity to a surprising extent, and fluids in other tissues surrounding the heart conduct electricity even more easily. Therefore, the heart is actually suspended in a conductive medium. When on... | {
"Header 1": "**Fundamentals of Electrocardiography**",
"Header 2": "Flow of Electrical Currents in the Chest Around the Heart",
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The different recordings are known as leads $V_1$ , $V_2$ , $V_3$ , $V_4$ , $V_5$ , and $V_6$ .
**Figure 11-9.** Normal electrocardiograms recorded from the six standard chest leads.
**Figure 11-10.** Normal electrocardiograms recorded from the th... | {
"Header 1": "**Fundamentals of Electrocardiography**",
"Header 2": "Flow of Electrical Currents in the Chest Around the Heart",
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From the discussion in Chapter 10 of impulse transmission through the heart, it is obvious that any change in the pattern of this transmission can cause abnormal electrical potentials around the heart and, consequently, alter the shapes of the waves in the electrocardiogram (ECG). For this reason, most serious abnormal... | {
"Header 1": "**Fundamentals of Electrocardiography**",
"Header 2": "**Electrocardiographic Interpretation of Cardiac Muscle and Coronary Blood Flow Abnormalities: Vectorial Analysis**",
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Figure 12-4 shows a partially depolarized heart, with vector A representing the instantaneous mean direction of current flow in the ventricles. In this case, the direction of the vector is +55 degrees, and the voltage of the potential, represented by the length of vector A, is 2 millivolts. In the diagram below the hea... | {
"Header 1": "**Fundamentals of Electrocardiography**",
"Header 2": "VECTORIAL ANALYSIS OF POTENTIALS RECORDED IN DIFFERENT LEADS",
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Thus, the QRS complexes are completed in the three standard bipolar limb leads.
Sometimes the QRS complex has a slight negative depression at its beginning in one or more of the leads, which is not shown in **Figure 12-7**; this depression is the Q wave. When it occurs, it is caused by initial depolarization of the... | {
"Header 1": "**Fundamentals of Electrocardiography**",
"Header 2": "VECTORIAL ANALYSIS OF POTENTIALS RECORDED IN DIFFERENT LEADS",
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This preponderant direction of the potential during depolarization from the base to the apex of the heart is called the *mean electrical axis of the ventricles*. The mean electrical axis of the normal ventricles is 59 degrees. In many pathological conditions of the heart, this direction changes markedly, sometimes even... | {
"Header 1": "**Fundamentals of Electrocardiography**",
"Header 2": "VECTORIAL ANALYSIS OF POTENTIALS RECORDED IN DIFFERENT LEADS",
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**Vectorial Analysis of Right Axis Deviation in Right Bundle Branch Block.** When the right bundle branch is blocked, the left ventricle depolarizes far more rapidly than the right ventricle, and thus the left side of the ventricles becomes electronegative as long as 0.1 second before the right. Therefore, a strong v... | {
"Header 1": "**Fundamentals of Electrocardiography**",
"Header 2": "VECTORIAL ANALYSIS OF POTENTIALS RECORDED IN DIFFERENT LEADS",
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Bizarre patterns of the QRS complex are usually caused by two conditions: (1) destruction of cardiac muscle in various areas throughout the ventricular system, with replacement of this muscle by scar tissue; and (2) multiple small local blocks in the conduction of impulses at many points in the Purkinje system. As a re... | {
"Header 1": "**Fundamentals of Electrocardiography**",
"Header 2": "CONDITIONS THAT CAUSE BIZARRE QRS COMPLEXES",
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In Figure 12-17, a small area in the base of the left ventricle is newly infarcted (i.e., there is loss of coronary blood flow). Therefore, during the T-P interval—that is, when the normal ventricular muscle is totally polarized—abnormal *negative* current still flows from the infarcted area at the base of the left ven... | {
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"Header 2": "EFFECT OF CURRENT OF INJURY ON THE QRS COMPLEX",
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One might think that the ECG machines could determine when no current is flowing around the heart. However, many stray currents exist in the body, such as currents resulting from skin potentials and from differences in ionic concentrations in different fluids of the body. Therefore, when two electrodes are connected be... | {
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Insufficient blood flow to the cardiac muscle depresses the metabolism of the muscle for at least three reasons: (1) lack of oxygen; (2) excess accumulation of carbon dioxide; and (3) lack of sufficient food nutrients. Consequently, repolarization of the muscle membrane cannot occur in areas of severe myocardial ischem... | {
"Header 1": "THE J POINT IS THE ZERO REFERENCE POTENTIAL FOR ANALYZING CURRENT OF INJURY",
"Header 2": "CORONARY ISCHEMIA AS A CAUSE OF INJURY POTENTIAL",
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This delayed conduction causes the left ventricle to become depolarized about 0.08 second after depolarization of the right ventricle, which gives a strong mean QRS vector *to the left.* However, the refractory periods of the right and left ventricular muscle masses are not greatly different from each other. Therefore,... | {
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"Header 2": "CORONARY ISCHEMIA AS A CAUSE OF INJURY POTENTIAL",
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Some of the most distressing types of heart malfunction occur because of abnormal rhythm of the heart. For example, sometimes the beat of the atria is not coordinated with the beat of the ventricles, so the atria no longer function to optimize ventricular filling.
The purpose of this chapter is to discuss the physiol... | {
"Header 1": "**Cardiac Arrhythmias and Their Electrocardiographic Interpretation**",
"token_count": 1298,
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#### SINOATRIAL BLOCK
In rare cases, the impulse from the sinus node is blocked before it enters the atrial muscle. This phenomenon is demonstrated in **Figure 13-4**, which shows sudden cessation of P waves, with resultant standstill of the atria. However, the ventricles pick up a new rhythm, with the impulse usuall... | {
"Header 1": "HEART BLOCK WITHIN THE INTRACARDIAC CONDUCTION PATHWAYS",
"token_count": 2029,
"source_pdf": "datasets/websources/biochem/1671268744mpp.pdf"
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periodic fainting spells (syncope) are known as the *Stokes-Adams syndrome.*
Occasionally, the interval of ventricular standstill at the onset of complete block is so long that it becomes detrimental to the patient's health or even causes death. Consequently, most of these patients are provided with an *artificial ... | {
"Header 1": "HEART BLOCK WITHIN THE INTRACARDIAC CONDUCTION PATHWAYS",
"token_count": 1183,
"source_pdf": "datasets/websources/biochem/1671268744mpp.pdf"
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The ECG in **Figure 13-11** shows a series of premature ventricular contractions (PVCs) alternating with normal contractions in a pattern known as *bigeminy*. PVCs cause specific effects in the ECG, as follows:
- 1. The QRS complex is usually considerably prolonged. The reason for this prolongation is that the impuls... | {
"Header 1": "HEART BLOCK WITHIN THE INTRACARDIAC CONDUCTION PATHWAYS",
"Header 2": "PREMATURE VENTRICULAR CONTRACTIONS",
"token_count": 2018,
"source_pdf": "datasets/websources/biochem/1671268744mpp.pdf"
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#### **VENTRICULAR TACHYCARDIA**
**[Figure 13-14](#page-156-1)** shows a typical short paroxysm of ventricular tachycardia. The ECG of ventricular tachycardia has the appearance of a series of ventricular premature beats occurring one after another, without any normal beats interspersed.
Ventricular tachycardia i... | {
"Header 1": "HEART BLOCK WITHIN THE INTRACARDIAC CONDUCTION PATHWAYS",
"Header 2": "PREMATURE VENTRICULAR CONTRACTIONS",
"token_count": 2040,
"source_pdf": "datasets/websources/biochem/1671268744mpp.pdf"
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Then, when each of these impulses reaches another refractory area, it divides to form two more impulses. In this way, many new wave fronts are continually being formed in the heart by progressive *chain reactions* until, finally, many small depolarization waves are traveling in many directions at the same time. Further... | {
"Header 1": "HEART BLOCK WITHIN THE INTRACARDIAC CONDUCTION PATHWAYS",
"Header 2": "PREMATURE VENTRICULAR CONTRACTIONS",
"token_count": 2040,
"source_pdf": "datasets/websources/biochem/1671268744mpp.pdf"
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Numerous small depolarization waves spread in all directions through the atria during atrial fibrillation. Because the waves are weak, and many of them are of opposite polarity at any given time, they usually almost completely electrically neutralize one another. Therefore, in the ECG, one can see either no P waves fro... | {
"Header 1": "HEART BLOCK WITHIN THE INTRACARDIAC CONDUCTION PATHWAYS",
"Header 2": "PREMATURE VENTRICULAR CONTRACTIONS",
"token_count": 1813,
"source_pdf": "datasets/websources/biochem/1671268744mpp.pdf"
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- Passman R, Kadish A: Sudden death prevention with implantable devices, Circulation 116:561, 2007.
- Prystowsky EN, Padanilam BJ, Joshi S, Fogel RI: Ventricular arrhythmias in the absence of structural heart disease, J Am Coll Cardiol 59:1733, 2012.
- Reed GW, Rossi JE, Cannon CP: Acute myocardial infarction, Lancet... | {
"Header 1": "HEART BLOCK WITHIN THE INTRACARDIAC CONDUCTION PATHWAYS",
"Header 2": "PREMATURE VENTRICULAR CONTRACTIONS",
"token_count": 503,
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The function of the circulation is to serve the needs of the body tissues—to transport nutrients to the tissues, to transport waste products away, transport hormones from one part of the body to another and, in general, to maintain an appropriate environment in all the tissue fluids for survival and optimal function of... | {
"Header 1": "**Overview of the Circulation: Pressure, Flow, and Resistance**",
"token_count": 2033,
"source_pdf": "datasets/websources/biochem/1671268744mpp.pdf"
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Also, nervous control of the circulation from the central nervous system and hormones provides additional help in controlling tissue blood flow.
**Figure 14-3.** Interrelationships of pressure, resistance, and blood flow. P1, Pressure at the origin of the vessel; P2, pressure at the ot... | {
"Header 1": "**Overview of the Circulation: Pressure, Flow, and Resistance**",
"token_count": 2013,
"source_pdf": "datasets/websources/biochem/1671268744mpp.pdf"
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In **[Figure 14-6](#page-166-1)***A*, a vessel contains two fluids, the one at the left colored by a dye and the one
**Figure 14-5.** Ultrasonic Doppler flowmeter.
**Figure 14-6. A**, Two fluids (one dyed red, and the other clear) before flow begins. ... | {
"Header 1": "**Overview of the Circulation: Pressure, Flow, and Resistance**",
"token_count": 2041,
"source_pdf": "datasets/websources/biochem/1671268744mpp.pdf"
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In an adult human, this averages approximately 100 ml/sec. The pressure difference from the systemic arteries to the systemic veins is about 100 mm Hg. Therefore, the resistance of the entire systemic circulation, called the *total peripheral resistance*, is about 100/100, or 1 PRU.
In conditions in which all the blo... | {
"Header 1": "**Overview of the Circulation: Pressure, Flow, and Resistance**",
"token_count": 2044,
"source_pdf": "datasets/websources/biochem/1671268744mpp.pdf"
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Furthermore, *the viscosity of normal blood is about three times as great as the viscosity of water.*
What makes the blood so viscous? It is mainly the large numbers of suspended red cells in the blood, each
**Figure 14-10.** Hematocrit values in a healthy (normal) person and in patie... | {
"Header 1": "**Overview of the Circulation: Pressure, Flow, and Resistance**",
"token_count": 2025,
"source_pdf": "datasets/websources/biochem/1671268744mpp.pdf"
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#### VASCULAR DISTENSIBILITY
A valuable characteristic of the vascular system is that all blood vessels are *distensible.* The distensible nature of the arteries allows them to accommodate the pulsatile output of the heart and to average out the pressure pulsations. This capability provides smooth continuous flow of ... | {
"Header 1": "**Vascular Distensibility and Functions of the Arterial and Venous Systems**",
"token_count": 2042,
"source_pdf": "datasets/websources/biochem/1671268744mpp.pdf"
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In effect, pulse pressure is determined approximately by the *ratio of stroke volume output to compliance of the arterial tree*. Any condition of the circulation that affects either of these two factors also affects the pulse pressure:
Pulse pressure ≈ Stroke volume/arterial compliance
#### ABNORMAL PRESSURE PULS... | {
"Header 1": "**Vascular Distensibility and Functions of the Arterial and Venous Systems**",
"token_count": 387,
"source_pdf": "datasets/websources/biochem/1671268744mpp.pdf"
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When the heart ejects blood into the aorta during systole, only the proximal portion of the aorta initially becomes distended because the inertia of the blood prevents sudden blood movement all the way to the periphery. However, the rising pressure in the proximal aorta rapidly overcomes this inertia, and the wavefront... | {
"Header 1": "**Vascular Distensibility and Functions of the Arterial and Venous Systems**",
"Header 2": "TRANSMISSION OF PRESSURE PULSES TO THE PERIPHERAL ARTERIES",
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It is not equal to the average of the systolic and diastolic pressures because at
**Figure 15-8.** Changes in systolic, diastolic, and mean arterial pressures with age. The *shaded areas* show the approximate normal ranges.
normal heart rates, a greater fraction of the cardiac cycle i... | {
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"Header 2": "TRANSMISSION OF PRESSURE PULSES TO THE PERIPHERAL ARTERIES",
"token_count": 2000,
"source_pdf": "datasets/websources/biochem/1671268744mpp.pdf"
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Consequently, *negative pressure can exist in the dural sinuses of the head;* in the standing position, the venous pressure in the sagittal sinus at the top of the brain is about −10 mm Hg because of the hydrostatic "suction" between the top of the skull and the base of the skull. Therefore, if the sagittal sinus is op... | {
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"Header 2": "TRANSMISSION OF PRESSURE PULSES TO THE PERIPHERAL ARTERIES",
"token_count": 2009,
"source_pdf": "datasets/websources/biochem/1671268744mpp.pdf"
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The heart, for example, shrinks during sympathetic stimulation and in this way can contribute some 50 to 100 ml of blood; the lungs can contribute another 100 to 200 ml when the pulmonary pressures decrease to low values.
#### **THE SPLEEN IS A RESERVOIR FOR RED BLOOD CELLS**
**[Figure 15-13](#page-182-0)** shows t... | {
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"Header 2": "TRANSMISSION OF PRESSURE PULSES TO THE PERIPHERAL ARTERIES",
"token_count": 1229,
"source_pdf": "datasets/websources/biochem/1671268744mpp.pdf"
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The most purposeful functions of the microcirculation are the *transport of nutrients to the tissues* and *removal of cell excreta*. The small arterioles control blood flow to each tissue, and local conditions in the tissues, in turn, control the diameters of the arterioles. Thus, each tissue, in most cases, controls i... | {
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"Header 2": "**The Microcirculation and Lymphatic System: Capillary Fluid Exchange, Interstitial Fluid, and Lymph Flow**",
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"source_pdf": "datasets/websources/biochem/1671268744mpp.pdf"
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In the remainder of this chapter, we are concerned with these averages, although it should be remembered that the average functions are, in reality, the functions of billions of individual capillaries, each operating intermittently in response to local conditions in the tissues.
#### EXCHANGE OF WATER, NUTRIENTS, AND... | {
"Header 1": "**Vascular Distensibility and Functions of the Arterial and Venous Systems**",
"Header 2": "**The Microcirculation and Lymphatic System: Capillary Fluid Exchange, Interstitial Fluid, and Lymph Flow**",
"token_count": 1994,
"source_pdf": "datasets/websources/biochem/1671268744mpp.pdf"
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For the short distances between the capillaries and tissue cells, this diffusion allows for rapid transport through the interstitium, not only of water molecules but also of substances such as electrolytes, low-molecular-weight nutrients, cellular excreta, oxygen, and carbon dioxide.
**Free Fluid in the Interstitium.... | {
"Header 1": "**Vascular Distensibility and Functions of the Arterial and Venous Systems**",
"Header 2": "**The Microcirculation and Lymphatic System: Capillary Fluid Exchange, Interstitial Fluid, and Lymph Flow**",
"token_count": 1990,
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Thus, if one remembers that the pressure exerted on the skin is atmospheric pressure, which is considered to be zero pressure, one might formulate a general rule that the normal interstitial fluid pressure is usually several millimeters of mercury negative with respect to the pressure that surrounds each tissue.
In m... | {
"Header 1": "**Vascular Distensibility and Functions of the Arterial and Venous Systems**",
"Header 2": "**The Microcirculation and Lymphatic System: Capillary Fluid Exchange, Interstitial Fluid, and Lymph Flow**",
"token_count": 1816,
"source_pdf": "datasets/websources/biochem/1671268744mpp.pdf"
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**Analysis of Reabsorption at the Venous End of the Capillary.** The low blood pressure at the venous end of the capillary changes the balance of forces in favor of absorption as follows:
| | mm Hg |
|-------------------------------------------------------... | {
"Header 1": "**Vascular Distensibility and Functions of the Arterial and Venous Systems**",
"Header 2": "**The Microcirculation and Lymphatic System: Capillary Fluid Exchange, Interstitial Fluid, and Lymph Flow**",
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"source_pdf": "datasets/websources/biochem/1671268744mpp.pdf"
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The fluid that returns to the circulation by way of the lymphatics is extremely important because substances of high molecular weight, such as proteins, cannot be absorbed from the tissues in any other way, although they can enter the lymphatic capillaries almost unimpeded. The reason for this mechanism is a special ... | {
"Header 1": "**Vascular Distensibility and Functions of the Arterial and Venous Systems**",
"Header 2": "**The Microcirculation and Lymphatic System: Capillary Fluid Exchange, Interstitial Fluid, and Lymph Flow**",
"token_count": 2025,
"source_pdf": "datasets/websources/biochem/1671268744mpp.pdf"
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Therefore, these proteins tend to accumulate in the interstitial fluid, which in turn increases the colloid osmotic pressure of the interstitial fluids.
- 2. The increasing colloid osmotic pressure in the interstitial fluid shifts the balance of forces at the blood capillary membranes in favor of fluid filtration into ... | {
"Header 1": "**Vascular Distensibility and Functions of the Arterial and Venous Systems**",
"Header 2": "**The Microcirculation and Lymphatic System: Capillary Fluid Exchange, Interstitial Fluid, and Lymph Flow**",
"token_count": 1079,
"source_pdf": "datasets/websources/biochem/1671268744mpp.pdf"
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#### LOCAL CONTROL OF BLOOD FLOW IN RESPONSE TO TISSUE NEEDS
A fundamental principle of circulatory function is that most tissues have the ability to control their own local blood flow in proportion to their specific metabolic needs. Some of the specific needs of the tissues for blood flow include the following:
- ... | {
"Header 1": "**Local and Humoral Control of Tissue Blood Flow**",
"token_count": 2025,
"source_pdf": "datasets/websources/biochem/1671268744mpp.pdf"
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For example, minute quantities of adenosine are released from heart muscle cells when coronary blood flow becomes too little, and this release of adenosine causes enough local vasodilation in the heart to return coronary blood flow to normal. Also, whenever the heart becomes more active than normal, the heart's metabol... | {
"Header 1": "**Local and Humoral Control of Tissue Blood Flow**",
"token_count": 2034,
"source_pdf": "datasets/websources/biochem/1671268744mpp.pdf"
} |
Therefore, it has been proposed that when high arterial pressure stretches the vessel, reactive vascular constriction results, which reduces blood flow nearly back to normal. Conversely, at low pressures, the degree of stretch of the vessel is less, so the smooth muscle relaxes, reducing vascular resistance and helping... | {
"Header 1": "**Local and Humoral Control of Tissue Blood Flow**",
"token_count": 2017,
"source_pdf": "datasets/websources/biochem/1671268744mpp.pdf"
} |
Drugs that block endothelin receptors have been used to treat *pulmonary hypertension* but generally have not been used for lowering blood pressure in patients with systemic arterial hypertension.
#### **LONG-TERM BLOOD FLOW REGULATION**
Thus far, most of the mechanisms for local blood flow regulation that we have ... | {
"Header 1": "**Local and Humoral Control of Tissue Blood Flow**",
"token_count": 2025,
"source_pdf": "datasets/websources/biochem/1671268744mpp.pdf"
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Under resting conditions, the blood flow may return to nearly normal, but the new channels seldom become large enough to supply the blood flow needed during strenuous tissue activity. Thus, development of collateral vessels follows the usual principles of acute and longterm local blood flow control; the acute control i... | {
"Header 1": "**Local and Humoral Control of Tissue Blood Flow**",
"token_count": 2048,
"source_pdf": "datasets/websources/biochem/1671268744mpp.pdf"
} |
It is clear that vasopressin could have enormous effects on circulatory function. Yet, because only minute amounts of vasopressin are secreted in most physiological conditions, most physiologists have thought that vasopressin plays little role in vascular control. However, experiments have shown that the concentratio... | {
"Header 1": "**Local and Humoral Control of Tissue Blood Flow**",
"token_count": 2025,
"source_pdf": "datasets/websources/biochem/1671268744mpp.pdf"
} |
Physiology (Bethesda) 28:262, 2013.
- Marshall JM, Ray CJ: Contribution of non-endothelium-dependent substances to exercise hyperaemia: are they O(2) dependent? J Physiol 590:6307, 2012.
- Mortensen SP, Saltin B: Regulation of the skeletal muscle blood flow in humans. Exp Physiol 99:1552, 2014.
- Potente M, Mäkinen T... | {
"Header 1": "**Local and Humoral Control of Tissue Blood Flow**",
"token_count": 477,
"source_pdf": "datasets/websources/biochem/1671268744mpp.pdf"
} |
#### NERVOUS REGULATION OF THE CIRCULATION
As discussed in Chapter 17, adjustment of blood flow in the tissues and organs of the body is mainly the function of local tissue control mechanisms. In this chapter, we discuss how nervous control of the circulation has more global functions, such as redistributing blood fl... | {
"Header 1": "**Nervous Regulation of the Circulation and Rapid Control of Arterial Pressure**",
"token_count": 2027,
"source_pdf": "datasets/websources/biochem/1671268744mpp.pdf"
} |
#### **Control of Heart Activity by the Vasomotor Center.**
At the same time that the vasomotor center regulates the amount of vascular constriction, it also controls heart activity. The *lateral* portions of the vasomotor center transmit excitatory impulses through the sympathetic nerve fibers to the heart when th... | {
"Header 1": "**Nervous Regulation of the Circulation and Rapid Control of Arterial Pressure**",
"token_count": 2034,
"source_pdf": "datasets/websources/biochem/1671268744mpp.pdf"
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This response is called the *alarm reaction*, and it provides an elevated arterial pressure that can immediately supply blood to the muscles of the body that might be needed to respond instantly to enable flight from danger.
#### **REFLEX MECHANISMS FOR MAINTAINING NORMAL ARTERIAL PRESSURE**
Aside from the exercise... | {
"Header 1": "**Nervous Regulation of the Circulation and Rapid Control of Arterial Pressure**",
"token_count": 2004,
"source_pdf": "datasets/websources/biochem/1671268744mpp.pdf"
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Circ Res 32:564, 1973.)*
A primary purpose of the arterial baroreceptor system is therefore to reduce the minute by minute variation in arterial pressure to about one-third that which would occur if the baroreceptor system were not present.
**Are the Baroreceptors Important in Long-Term Regulation of Arterial Press... | {
"Header 1": "**Nervous Regulation of the Circulation and Rapid Control of Arterial Pressure**",
"token_count": 2008,
"source_pdf": "datasets/websources/biochem/1671268744mpp.pdf"
} |
#### **DECREASED BLOOD FLOW TO BRAIN VASOMOTOR CENTER ELICITS INCREASED BLOOD PRESSURE—CNS ISCHEMIC RESPONSE**
Most nervous control of blood pressure is achieved by reflexes that originate in the baroreceptors, chemoreceptors, and low-pressure receptors, all of which are located in the peripheral circulation outsid... | {
"Header 1": "**Nervous Regulation of the Circulation and Rapid Control of Arterial Pressure**",
"token_count": 2019,
"source_pdf": "datasets/websources/biochem/1671268744mpp.pdf"
} |
In this experiment, the cerebrospinal fluid pressure increased to 160 mm Hg, which compressed the cerebral vessels and initiated a CNS ischemic pressure response up to 200 mm Hg. When the arterial pressure rose to such a high value, the brain ischemia was relieved, and the sympathetic nervous system became inactive. As... | {
"Header 1": "**Nervous Regulation of the Circulation and Rapid Control of Arterial Pressure**",
"token_count": 1165,
"source_pdf": "datasets/websources/biochem/1671268744mpp.pdf"
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In addition to the rapidly acting mechanisms for regulation of arterial pressure discussed in Chapter 18, the body also has powerful mechanisms for regulating arterial pressure week after week and month after month. This long-term control of arterial pressure is closely intertwined with homeostasis of body fluid volume... | {
"Header 1": "**Nervous Regulation of the Circulation and Rapid Control of Arterial Pressure**",
"Header 2": "**Role of the Kidneys in Long-Term Control of Arterial Pressure and in Hypertension: The Integrated System for Arterial Pressure Regulation**",
"token_count": 2047,
"source_pdf": "datasets/websources/b... |
Therefore, one can state that if the renal output curve shifts to a new pressure level, the arterial pressure will follow to this new pressure level within a few days.
**[Figure 19-3](#page-221-0)***B* shows how a change in the level of salt and water intake also can change the arterial pressure. In this case, the in... | {
"Header 1": "**Nervous Regulation of the Circulation and Rapid Control of Arterial Pressure**",
"Header 2": "**Role of the Kidneys in Long-Term Control of Arterial Pressure and in Hypertension: The Integrated System for Arterial Pressure Regulation**",
"token_count": 2024,
"source_pdf": "datasets/websources/b... |
One of these is the direct effect of increased cardiac output to increase the pressure, and the other is an indirect effect to raise total peripheral vascular resistance through *autoregulation* of blood flow. The second effect can be explained as follows.
Referring to Chapter 17, let us recall that whenever an exces... | {
"Header 1": "**Nervous Regulation of the Circulation and Rapid Control of Arterial Pressure**",
"Header 2": "**Role of the Kidneys in Long-Term Control of Arterial Pressure and in Hypertension: The Integrated System for Arterial Pressure Regulation**",
"token_count": 2037,
"source_pdf": "datasets/websources/b... |
Subsequently, the autoregulation mechanism returns the cardiac output almost to normal while simultaneously causing a *secondary increase in total peripheral resistance*. (Modified from Guyton AC: Arterial Pressure and Hypertension. Philadelphia: WB Saunders, 1980.)
After these early acute changes in the circulatory ... | {
"Header 1": "**Nervous Regulation of the Circulation and Rapid Control of Arterial Pressure**",
"Header 2": "**Role of the Kidneys in Long-Term Control of Arterial Pressure and in Hypertension: The Integrated System for Arterial Pressure Regulation**",
"token_count": 2004,
"source_pdf": "datasets/websources/b... |
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