Exam 2 Flashcards
1
Q
How are Purkinje fibers distributed in the ventricles, and how quickly do they spread the impulse to the ventricular muscle mass?
A
After entering the ventricles, the A-V bundle divides into left and right bundle branches, which spread downward toward the apex, dividing into smaller branches. The Purkinje fibers penetrate about 1/3 of the way into the muscle mass and become continuous with cardiac muscle fibers, spreading the impulse almost immediately (0.03 seconds) to the entire ventricular muscle mass
2
Q
How do kidneys contribute to arterial pressure regulation over prolonged periods?
A
Over hours and days, the kidneys regulate arterial pressure by secreting pressure-controlling hormones and regulating blood volume, playing a crucial role in maintaining long-term pressure stability
3
Q
How do pressure differences across the circulatory system facilitate blood flow?
A
Blood is continually pumped by the heart into the high-pressure aorta, flows through the systemic circulation where pressure gradually decreases, and returns to the heart through the low-pressure venous system, ensuring efficient circulation
4
Q
How does acetylcholine affect the A-V junctional fibers?
A
Acetylcholine decreases the excitability of the A-V junctional fibers between the atrial musculature and the A_V node, slowing the transmission of the cardiac impulse into the ventricles
5
Q
How does the pressure difference affect blood flow?
A
Blood flow occurs only if there’s a pressure difference between two ends of a vessel. If the pressure is equal at both ends, no flow will occur despite the presence of pressure
6
Q
How does the viscosity of normal blood compare to water?
A
Normal blood has a viscosity approximately three times greater than that of water
7
Q
How is blood flow to tissues controlled and adjusted to meet tissue needs?
A
Blood flow is controlled according to tissue needs, with microvessels, especially arterioles, monitoring oxygen, nutrients, CO2, and waste products. They can dilate or constrict to adjust local blood flow. Nervous control and hormones also help regulate tissue blood flow
8
Q
How is resistance in blood vessels measured?
A
Resistance, and impediment to blood flow, is calculated from measurements of blood flow and the pressure differences between two points in a vessel, expressed in peripheral resistance units (PRU)
9
Q
How long does blood remain in the capillaries, and why is this time significant?
A
Blood remains in the capillaries for only1-3 secs, a critical period for the diffusion of nutrients and electrolytes
10
Q
What are the average hematocrit values for adult men and woman?
A
The average hematocrit for adult men is about 42, while women is about 38. These values can cary with anemia, physical activity, and altitude
11
Q
What are the functional parts of the circulatory system?
A
Arteries, arterioles, capillaries, venules, and veins
12
Q
What are two main divisions of the circulatory system?
A
Systemic circulation (also called greater or peripheral circulation) and pulmonary circulation
13
Q
What does Ohm’s law state regarding blood flow?
A
Ohm’s law states that blood flow (F) is directly proportional to the pressure difference (delta P=P1-P2) across the vessel and inversely proportional to the resistance (R) of the vessel
14
Q
What happens during phase 0 of the cardiac action potential?
A
During Phase 0, fast sodium channels open, causing Na+ to flow rapidly into the cell. This depolarizes the cell, making the membrane potential more positive, reaching approximately +20 mV before the Na+ channels close
15
Q
What is the refractory period in cardiac muscle?
A
The refractory period is the interval of time during which a normal cardiac impulse cannot re-excite an already excited area of the cardiac muscle
16
Q
What percentage of the body’s blood volume is contained in the heart and pulmonary vessels, respectively?
A
The heart contains 7% of the blood volume, while the pulmonary vessels contain 9%
17
Q
What primarily causes the action potential in skeletal muscle?
A
The action potential in skeletal muscle is caused almost entirely by the sudden opening of large numbers of fast Na+ channels that allow a great quantity of Na+ to enter the cell, followed by abrupt closure leading to re-polarization an the end of the action potential
18
Q
What primarily regulates the rate of blood flow in the circulatory system?
A
Tissue needs for nutrients and removal of waste products are the most important regulators of blood flow. In some organs, like the kidney, blood flow exceeds metabolic requirements due to specific functions such as excretion
19
Q
What would be the venous pressure in the feet of a standing adult without the action of venous valves?
A
Without venous valves, gravitational pressure would cause the venous pressure in the feet to be about +90 mmHg
20
Q
Why does a parabolic velocity profile occur during laminar flow?
A
The parabolic velocity profile during laminar flow is caused by fluid molecules near the vessel wall moving slowly due to adherence, while each subsequent layer slips over the one below it, resulting in progressively faster flow toward the center of the vessel
21
Q
According to the metabolic theory, what causes the blood vessels to constrict and return flow to nearly normal despite increased pressure?
A
Excess flow of O2 and nutrients to the tissues and decreased tissue levels of vasodilators
22
Q
According to the myogenic theory, what causes reactive vascular constriction at high arterial pressure?
A
A sudden stretch of small blood vessels
23
Q
Besides hematocrit, what other factors affect blood viscosity?
A
Plasma protein concentration and types of proteins in the plasma affect blood viscosity, but their effects are much less significant than that of hematocrit
24
Q
Between arterial pressures of about 70 and 175 mm HG, by how much does the blood flow increase even though the arterial pressure increases 150%?
A
20% to 30%
25
Can potentials be conducted directly from the atrial syncytium to the ventricular syncytium through the fibrous tissue?
No, potentials are not conducted directly from the atrial syncytium to the ventricular syncytium through the fibrous tissue
26
Compare the refractory period of atrial and ventricular muscle
The refractory period of atrial muscle is much shorter than that for the ventricles, being about 0.15 secs for the atria compared with 0.25 to 0.30 seconds for the ventricles
27
Compare the velocity of blood flow in the aorta and capillaries
The velocity averages about 33 cm/sec in the aorta bu tis only 0.03 cm/sec in the capillaries
28
Describe the orientation of the subepicardial and subendocardial layers in the left ventricle.
The subepicardial (outer) layer spirals leftward, while the subendocardial (inner) layer spirals rightwards
29
Describe the overall charges in membrane potential during cardiac action potential.
The action potential in a ventricular muscle fiber averages about 105 millivolts, going from -85 millivolts to a slightly positive value (+20millivolts) for every beat. After the initial spike, the membrane remains depolarized for approximately 0.2 secs (plateau), followed by an abrupt re-polarization
30
Describe the pressure gradient from the aorta to the right atrium.
Pressure falls progressively from 100 mm Hg in the aorta to 0 mmHg at the termination of the superior and inferior venae cavae towards the right atrium
31
Describe the pressure in the venous system and its significance
The pressure in the venous system is low, which allows veins to serve as a major blood reservoir. The venous walls can contract or expand, adjusting the volume of stored blood based on circulation needs
32
Describe the structural difference between arterioles and metarterioles.
Metarterioles (the terminal arterioles) do not have a continuous muscular coat but have smooth muscle fibers encircling the vessel at intermittent points
33
Describe the structure of T-tubules in cardiomyocytes
T-tubules are not a simple transverse system of tubules but consist of non-uniform branching tubules with both transverse and longitudinal elements
34
Describe the structure of capillary walls
Capillary walls are thin and composed of a single layer of highly permeable endothelial cells, allowing for quick and easy interchange of water, nutrients, and waste between tissues and circulating blood
35
Describe the velocity profile during laminar flow in a vessel
During laminar flow, the velocity of blood in the center of the vessel is greater than that near the walls, creating a parabolic velocity profile. This is due to the outer layers of fluid moving slower because of adherence to the vessel wall, while each successive layer toward the center moves more rapidly
36
Describe what occurs during phase 1 of the cardiac action potential
In phase 1, the initial re-polarization phase, fast sodium channels close, leading to the beginning of cell re-polarization as K= exits the cell through open potassium channels
37
Despite having a weaker muscular coat, how can venules still contract considerably?
Despite the weaker muscular coat, venules can still contract considerably because the pressure in them is much less than that in the arterioles
38
Does heart muscle use chemical energy for contraction, like skeletal muscle?
Yes, heart muscle, like skeletal muscle, uses chemical energy for contraction
39
Does the nuclear structure of cardiomyocytes change with age?
The nuclear structure of cardiomyocytes (mononucleated, binucleated, trinucleated) remain constant irrespective of age
40
Composed of endothelial cells and connective tissue, lining the surface of the heart chambers
Endocardium
41
The visceral layer of the serous pericardium, made up of connective tissue. it is the innermost layer of the pericardium
Epicardium
42
The outer layer of connective tissue of the pericardium
Fibrous pericardium
43
How are cardiac muscle fibers organized?
Cardiac muscle fibers are made up of many individual cells connected in series and in parallel with one another
44
How are cardiomyocytes arranged?
Cardiomyocytes are arranged in a lattice work, with the fibers dividing, recombining, and then spreading again
45
How are conductance and resistance related in the context of blood flow through a vessel?
Conductance is the reciprocal of resistance. it measures blood flow through a vessel for a given pressure difference and increases with the vessel's diameter
46
How are potentials conducted from the atria to the ventricles?
Potentials are conducted from the atria to the ventricles by a specialized conductive system called the A-V bundle, which is composed of conductive fibers
47
How are the atria separated from the ventricles in the heart?
The atria are separated from the ventricles by fibrous tissue surrounding the atrioventricular (A-V) valvular openings
48
How are the sympathetic nerves distributed in the heart?
The sympathetic nerves are distributed to all parts of the heart, with strong representation in the ventricular muscle, as well as in all the other areas
49
How can heart disease affect the rhythmical and conductive system of the heart?
Heart disease, especially ischemia from inadequate coronary blood flow, can damage the system, leading to abnormal contraction sequences and severely affected pumping efficiency, which can be fatal
50
How can one prevent the increase of venous pressure when standing?
periodically flexing leg muscles and slightly bending the knees activates the venous pump, helping to avoid the buildup of high venous pressure and its associated problems
51
How do L-type calcium channels contribute to the cardiac action potential?
L-type calcium channels are slower to open and remain open for several tenths of a second, allowing a large quantity of both Ca2+ and Na+ to enter the cardiac muscle fiber. This results in a prolonged period of depolarization, known as the plateau phase of the action potential
52
How do alterations in T-tubules structure relate to the function of NCX and SERCA in heart failure?
T-tubule remodeling in non-diabetic HFpEF is accompanied by increased NCX and SERCA function, facilitating Ca2+ removal. However, in diabetic HFpEF and HFrEF, Ca2+ removal by these proteins is decreased
53
How so arterioles regulate blood flow to tissues?
Arterioles regulate blood flow by constricting or dilating. Their strong muscular walls can completely close or open severalfold, altering blood flow in response to tissue needs
54
How do arterioles regulate blood flow to tissues? What substances can pass through capillary walls?
Capillary walls, being thin and having numerous minute pores, are permeable to water and small molecular substances, allowing efficient exchange with the interstitial fluid
55
How do atrial and ventricular muscles contract?
They contract in a similar way as the skeletal muscle
56
How do metarterioles and pre-capillary sphincters interact with the tissues they serve?
The metarterioles and precapillary sphincters are in close contact with the tissues they serve
57
How do venules compare to arterioles in terms of size and muscular coat?
Venules are larger than arterioles and have much weaker muscular coat
58
How do venules function within the circulatory system?
Venules collect blood from capillaries and merge into progressively larger veins, forming the initial segment of blood return to the heart
59
How does Ca2+ contribute to muscle contraction?
Ca2+ released from the SR and diffused from the T-tubules activate ryanodine receptor channels, triggering further release of Ca2+. Ca2+ in the sarcoplasm interacts with troponin to initiate cross-bridge formation and contraction
60
How does an action potential spread to the interior of the cardiac muscle fiber?
When an action potential passes over the cardiac muscle membrane, it spreads to the interior of the fiber along the membranes of the transverse (T) tubules
61
How does body temperature affect heart rate?
Increased body temperature can double the heart rate, while decreased temperature can cause the rate to call to as low as a few beats per minute at body temperature of 60 degrees to 70 degrees
62
How does cardiomyocyte turnover change with age?
Cardiomyocyte turnover decreases exponentially with age and is less than 1 percent per year in adults
63
How does extracellular Ca2+ concentration affect cardiac muscle contraction?
The strength of contraction of cardiac muscle is greatly dependent on the concentration of Ca2+ in the extracellular fluids, as Ca2+ entering from the T tubules enhances the contraction strength
64
How does high extracellular fluid (K+) affect the resting membrane potential in cardiac muscle fibers?
High (K+) partially depolarizes the cell membrane, causing the membrane potential to be less negative, which decreases the intensity of the action potential and weakens heart contraction
65
How does parasympathetic stimulation affect ventricular pumping?
A decrease in heart rate combined with a slight decrease in heart contraction strength can decrease ventricular pumping by 50%
66
How does physical activity affect tissue blood flow and cardiac output?
During activity, tissues require more nutrients, increasing blood flow up to 20-30 times resting levels. However, the heart can only increase its output by 4-7 times. Local regulation in tissues compensates for this by adjusting blood flow to meet their needs
67
How does potassium permeability differ between cardiac and skeletal muscle during an action potential?
Immediately after onset of the action potential, the permeability of the cardiac muscle membrane for potassium decreases about fivefold. This decrease in K+ permeability reduces the efflux of positively charged K+ ions during the plateau phase and prevents an early return of the action potential voltage to its resting level
68
How does sympathetic stimulation affect heart contraction?
It can double the force of heart contraction, thereby increasing the volume of blood pumped and the ejection pressure
69
How does sympathetic stimulation affect the conduction time from the atria to the ventricles?
Sympathetic stimulation decreases the conduction time from the atria to the ventricle making it easier for the action potential to excite each succeeding portion of the conducting fiber bundles, through increased sodium-calcium permeability
70
How does sympathetic stimulation affect the heart at the molecular level?
Norepinephrine stimulates beta-1 adrenergic receptors, increasing permeability to sodium and calcium ions, leading to a more positive resting potential and enhanced excitability and contractility of cardiac muscle
71
How does the Frank-Starling mechanism work?
When an extra amount of blood flows into the ventricles, the cardiac muscle fibers stretch to a greater length, leading to an optimal overlap of actin and myosin filaments, allowing the cardiac muscle to contract with increased force
72
How does the cross-sectional area (CSA) relate to the velocity of blood flow?
The velocity of blood flow is inversely proportional to the vascular CSA. Larger CSAs in veins compared to arteries explain the venous system's larger blood storage capacity
73
How does the diameter of a vessel affect its conductance and blood flow?
Small changes in vessel diameter cause tremendous changes in conductance and blood flow, with conductance increasing in proportion to the fourth power of the diameter. A fourfold increase in diameter results in a 256-fold increase in flow
74
How does the left ventricle's motion affect its function during systole?
The wringing motion pulls the base downward toward the apex, aiding in the heart's contraction during systole
75
How does the plateau phase of the cardiac action potential affect ventricular contraction?
The plateau in the cardiac action potential causes ventricular contraction to last 15 times longer than in skeletal muscle, which is crucial for the functioning of the heart
76
How does the rate of oxygen usage affect the intermittent periods of capillary blood flow?
When the rate of oxygen usage is great, the intermittent periods of capillary blood flow occur more often, and the duration of each period of flow lasts longer
77
How does the sinus nodal fiber's action potential compare to that of a ventricular muscle fiber?
The resting membrane potential of sinus nodal fibers is about -55 to -60 millivolts, unlike the -85 to -90 millivolts of ventricular muscle fibers. The action potential in the sinus nodal fiber is slower to develop and slower to return to a negative state due to the lower negativity and the inactivity of fast sodium channels at this resting potential
78
How does the structure of cardiac muscle support its function?
The fusion of cell membranes at intercalated discs forms a functional syncytium, enabling efficient propagation of action potentials for coordinated cardiac muscle contraction
79
How far away is any single functional cell of the body from a capillary?
More than 20 to 30 micrometers
80
How is Ca2+ removed from the sarcoplasm at the end of contraction?
Ca2+ in the sarcoplasm is pumped back into the SR via SERCA2 (a calcium-adenosine triphosphatase pump) and out of the cell by a sodium-calcium exchanger, which is coupled to the extrusion of Na+ by the sodium-potassium ATPase pump
81
How is acute control achieved?
By rapid changes in local vasodilation or vasoconstriction of the arterioles, metarterioles, and precapillary sphincters
82
How is arterial pressure regulated independently of local blood flow and cardiac output?
Arterial pressure is controlled by nervous reflexes and the secretion of hormones, especially during significant drops. This includes increasing heart pump force, contracting venous reservoirs, and causing arteriole constriction to raise pressure.Kidneys also regulate pressure by controlling blood volume and hormone secretion over longer periods
83
How is blood flow to each tissue controlled?
Small arterioles control blood flow to each tissue, and the local conditions in the tissues, in turn, control the diameters of these arterioles, allowing each tissue to regulate its own blood flow based on its needs
84
How is the hearts pumping effectiveness controlled by the autonomic nervous system?
The sympathetic and parasympathetic (vagus) nerves can significantly modify the heart's pumping effectiveness. Sympathetic stimulation can increase cardiac output by more than 100%, while parasympathetic stimulation can decrease output to almost zero
85
How is the microcirculation of each organ organized?
The microcirculation of each organ is organized to serve that organs specific needs
86
How is the total blood volume distributed in the body's circulation system?
84% of blood volume is in the systemic circulation, and 16% is in the heart and lungs
87
How long does the impulse delay last in the A-V node before it enters the ventricles?
The impulses experiences a delay of 0.09 seconds in the A-V node itself before it enters the ventricles
88
How long is the normal refractory period of the ventricles?
The normal refractory period of the ventricles is approximately 0.25 to 0.30 seconds, corresponding with the duration of the prolonged plateau phase of the action potential
89
How many capillaries does the peripheral circulation of the entire body have?
About 10 billion
90
How many times do arterioles branch before supplying blood to the capillaries, and what are the diameters at their ends?
Arterioles branch 2-5 times, reaching diameters of 5-9 mm at their ends, where they supply blood to the capillaries
91
How many times do arterioles branch before supplying blood to the capillaries?
2-5 times
92
How many times do nutrients arteries entering an organ branch before becoming arterioles?
6-8times
93
How many times do nutrients arteries entering an organ branch before they become arterioles, and what is the internal diameter of arterioles?
Nutrients arteries entering an organ branch 6-8 times before becoming arterioles, with arterioles having internal diameters of only 10-15 mm
94
How much blood does the heart pump per minute under normal conditions?
The heart pumps 4-6 liters of blood per minute under normal conditions
95
How much blood flow does the kidney require for its function?
Large amounts
96
How much can local muscle blood flow increase during intense exercise due to active hyperemia?
As much as 20-fold
97
How much can sympathetic stimulation increase maximum cardiac output?
Sympathetic stimulation can increase the maximum cardiac output by 2 to 3 times, in addition to the increased output caused by the Frank-Starling mechanism
98
How much can the heart pump increase during intense exercise?
During intense exercise, the heart may pump 4-7 times its normal capacity
99
How much does the blood flow in inactive muscles increase during heavy exercise?
As much as 20 fold
100
How often do cardiomyocytes renew throughout a human's lifetime?
Cardiomyocytes renew at rates varying from 1 percent in youth to around 0.3 percent at the age of 75 years
101
How quickly does the reconstruction of tissue vasculature occur in older adults?
Much more slowly, as long as months
102
How quickly does the reconstruction of tissue vasculature occur in young animals?
Rapidly, within days
103
In the brain, what substances play prominent roles in controlling blood flow?
CO2 and H+
104
In what circumstances do metabolic factors appear to override the myogenic mechansim?
When the metabolic demands of the tissues are significantly increased, such as during vigorous muscle exercise
105
Is the cardiomyocyte turnover rate uniform across the heart?
Yes, the cardiomyocyte turnover rate id equal in the main subdivisions of the human heart
106
Layers of the serous pericardium
Comprises the visceral and parietal pericardium, separated by the pericardial space
107
The main constituent of the heart, comprised of muscle cells known as cardiomyocytes
myocardium
108
Name one of the three major types of cardiac muscles
Atrial muscle, ventricular muscle, and specialized excitatory and conductive muscle fibers
109
The inner layer of the serous pericardium, related to the body cavity
Parietal pericardium
110
Contains pericardial fluid (20-60mL) providing mechanical protection for the heart and reducing friction during contraction/heartbeat
Pericardial Space (or Pericardial Cavity)
111
Has two layers: The inner serous pericardium (epicardium) and the outer fibrous pericardium
pericardium
112
Peripheral control:
each peripheral tissue controls its own local blood flow. All combined --> right atrium
113
Specialized excitatory and conductive system of the heart composed of:
1) The sinus node (also called sinoatrial (SA) node) which generates the normal rhythmical impulses- the (natural) pacemaker;
2) The internodal pathways that conduct impulses from the sinus node to the atrioventricular (AV) node;
3)The A-V node in which impulses from the atria are delayed before passing into the ventricles;
4) The A-V bundle, which conducts impulses from the atria into the ventricles
5) The left and right bundle branches of purkinje fibers, which conduct the cardiac impulses to all parts of the ventricles
114
Through what system does the nervous system control the circulation?
Autonomic nervous system
115
To which segments of the circulation are the vasoconstrictor fibers distributed?
Essentially all segments of the circulation
116
Up to what arterial pressure does increasing the aortic pressure not decrease cardiac output?
Increasing the arterial pressure does not decrease cardiac output until the mean arterial pressure rises above about 160mmHg
117
Visceral vs. parietal
Visceral refers to the organ's inner layer, while parietal relates to the body cavity's outer layer
118
What alterations occur in cardiomyocytes T-tubule structure in heart failure?
In heart failure, T-tubule density changes depending on the type of heart failure; it is uncharged in diabetic HFpEF, increased in non-diabetic tubules also dilate in all heart failure entities
119
What are T-tubules, and what is their more recent name?
T-tubules, historically called transverse tubules, are more recently also known as the Transverse- Axial tubule system (TATS)
120
What are caveolins associated with in the endothelial cells?
Molecules of cholesterol and shingolipids
121
What are hypoxia inducible factors (HIFs) and what do they do?
Transcription factors that upregulate gene expression and the formation of vascular growth factors in response to deficiency of tissue oxygen
122
What are intercalated discs?
Intercalated discs are specialized cell membranes that separate individual cardiac muscle cells from one another
123
What are internodal pathways and their role in heart excitation?
Internodal pathways are specialized tracks that conduct impulses from the sinus node to the atrioventricular (A-V) node
124
What are kinins and what do they cause?
Kinins are small polypeptides that cause powerful vasodilation when formed in the blood and tissue fluids of some organs
125
What are mesenchymal cells and where are they located in the heart?
Mesenchymal cells comprise cells residing in the interstitium of the heart, including fibroblasts, pericytes, and smooth muscle cells
126
What are plasmalemmal vesicles also called?
Caveolae (small caves)
127
What are some hormones and locally produced factors that can control circulation?
Some are formed by special glands and transported in the blood throughout the entire body, while others are formed in local tissue areas and cause only local circulatory effects
128
What are some of the specific metabolic needs that tissues control their own local blood flow for?
Delivery of O2, delivery of nutrients, removal of CO2, removal of H+ ions, maintenance of proper ions, transport of various hormones and other substances
129
What are some of the vasodilator substances that diffuse through the tissues to cause dilation?
Adenosine, carbon dioxide, adenosine phosphate compounds, histamine, potassium ions, and hydrogen ions
130
What are basic mechanisms for regulating heart pumping?
1)Intrinsic cardiac pumping regulation in response to changes in the volume of blood flowing into the heart
2) Control of heart rate and strength by the autonomic nervous system
131
What are the benefits of the refractory period in cardiac muscle?
The refractory period helps maintain normal heart rhythm and rhythmic contractions, prevents tetanus (sustained contraction) in the heart, and ensures proper blood flow and effective blood pumping
132
What are the bundle branches and Purkinje fibers, and what role do they play in heart excitation?
The left and right bundle branches and Purkinje fibers rapidly conduct cardiac impulses to all parts of the ventricles, ensuring a coordinated and simultaneous contraction of ventricular muscle
133
What are the cardiac events from one heartbeat to the beginning of the next called?
Cardiac cycle
134
What are the characteristics of Purkinje fibers that allow rapid transmission of cardiac impulses in the ventricles?
Purkinje fibers are very large fibers that transmit action potentials at a velocity of .5 to 4.0 meters per second, which is approximately 150times faster than some A-V nodal fibers. This rapid transmission is believed to be due to a very high level of permeability of the gap junctions between successive cells
135
What are the consequences of standing still for extended periods?
Standing still without muscle movement can cause legs to swell and up to 10-20% of blood volume to be lost from the circulatory system within 15 to 30 minutes, possibly resulting in fainting
136
What are the dual systems of control provided by norepinephrine and epinephrine?
Direct nerve stimulation and indirect effects of norepinephrine and/or epinephrine in the circulating blood
137
What are the effects of epinephrine on the circulation?
In some tissues, even causes mild vasodilation. A special example of vasodilation caused by epinephrine is that which occurs to dilate the coronary arteries during increased heart activity
138
What are the effects of excess K+ in the extracellular fluids on the heart?
Excess K+ causes the heart to become dilated and flaccid, slows the heart rate, and can block conduction through the A-V bundle. Elevated (K+) to 2-3x normal can cause heart weakness, abnormal rhythm, and even death
139
What are the four factors that have been best characterized in increasing growth of new blood vessels?
Vascular endothelial growth factor (VEGF), fibroblast growth factor, platelet-derived growth factor (PDGF), and angiogenin
140
What are the four primary functions of the circulatory system?
1) Transport nutrients to tissues
2) Remove waste products
3) Transport hormones
4) Maintain an optimal environment for cell survival and function
141
What are the global functions of nervous control of the circulation?
Redistributing blood flow, increasing or decreasing pumping activity by the heart, and providing rapid control of systemic arterial pressure
142
What are the intercellular clefts at the junction between adjacent endothelial cells called?
Caveolae
143
What are the intrinsic rhythmical rates of the A-V nodal and Purkinje fibers compared to the sinus node?
The A-V nodal fibers have an intrinsic rhythmical rate of 40-60 times/min, and the Purkinje fibers discharge at a rate of 15-40 times/min, compared to the normal rate of the sinus node of 70-80 times/min
144
What are the larger vessels than the arterioles with a weaker muscular coat called?
Venules
145
What are the main functions of the ventricles?
The ventricles provide the main pumping force. The right ventricle propels blood through the pulmonary circulation, and the left ventricle through the systemic circulation
146
What are the most purposeful functions of the microcirculation?
The transport of nutrients to the tissues and removal of cell excreta
147
What are the percentages of blood volume in the systemic circulation's veins, arteries, and arterioles/ capillaries?
in the systemic circulation, 64% is in the veins, 13% is in the arteries, and 7% is in the arterioles and capillaries
148
What are the pores in the capillary membrane?
Two small passageways connecting the interior of the capillary with the exterior. One of these passageways is an intercellular cleft, which is the thin-slitted, curving channel that lies between adjacent endothelial cells
149
What are the primary myosin isoforms in the human heart's ventricles and atria?
In the adult human heart, the primary ventricular myosin isoform is beta-cardiac myosin (gene MYH7), and the primary atrial isoform is alpha-cardiac myosin (MYH6)
150
What are the small oval windows called that penetrate all the way through the middle of the nendothelial cells in the glomerular capillaries of the kidney?
Fenestrae
151
What are the structural units of cardiac muscle?
Cardiac muscle contains similar sarcomeres as found in skeletal muscle
152
What are the three main types of membrane ion channels in cardiac muscle and their effects on the action potential?
The three main types are
(1) fast sodium channels
(2) calcium channels (L-type or slow calcium channels
(3) potassium channels. fast Na+ channels are responsible for the rapid upstroke spike of the cation potential in ventricular muscle. However, these are inactivated at the less negative potential of the sinus fibers, so the slow sodium-calcium channels predominate, leading to a slower action potential in the atrial nodal fibers
153
What are the three major changes that occur simultaneously to help increase arterial pressure?
Most arterioles of the systemic circulation are constricted, the veins and other large vessels of the circulation are strongly constricted, and the heart is directly stimulated in the autonomic nervous system
154
What are the time frames for the acute mechanisms of local blood flow regulation?
A few seconds to a few minutes
155
What are the two main functions of the hearts system for rhythmic self-excitation?
1) it generates electrical impulses for rhythmical contraction
2) It conducts these impulses rapidly through the heart, ensuring atria contract before ventricles, and ventricles contract almost simultaneously
156
What are the two main theories proposed to explain how changes in tissue metabolism or oxygen availability alter tissue blood flow?
The vasodilator theory
the oxygen demand theory
157
What are the two major types of solid structures found in the interstitial fluid?
Collagen fiber bundles and proteoglycan filaments
158
What are the two mechanisms that could explain acute local blood flow regulation in response to the metabolic needs of the tissues?
Either the vasodilator substance theory or oxygen demand theory
159
What are the two most purposeful functions of the microcirculation?
The transport of nutrients to the tissues and the removal of cell excreta
160
What are the two phases of local blood flow control?
Acute control
Long-term control
161
What are the two separate pumps of the heart?
The right heart pumps blood through the lungs, and the left heart pumps blood through the systemic circulation to other organs and tissues
162
What are the two types of syncytia in the heart?
The heart is composed of two syncytia:
1) atrial syncytium
2) ventricular syncytium
each coordinating contractions in their respective areas
163
What are the two views proposed to explain the acute auto-regulation mechanism?
Metabolic theory
myogenic theory
164
What are the vasoconstrictors?
Norepinephrine
epinephrine
165
What are the walls of the capillaries constructed of?
Single- layer, highly permeable endothelial cells
166
What are two special examples of metabolic control of local blood flow?
Reactive hyperemia and active hyperemia
167
What are ventricular function curves?
Ventricular function curves are expressions of the Frank-Starling mechanism that show how the ventricles fill in response to higher atrial pressures, each ventricular volume and strength of cardiac muscle contraction increase, causing the heart to pump increased quantities of blood into the arteries
168
What can cause direct effects on the vessels to control local blood flow in each small tissue area?
Local conditions of the tissue
169
What can cause large quantities of fluid to leak out of the circulation into the tissues?
In many pathological conditions, the intense arteriolar dilation and increased capillary porosity produced by histamine cause large quantities of fluid to leak out of the circulation into the tissues, inducing edema
170
What can cause the pacemaker of the heart to shift from the sinus node?
Shift in the pacemaker can occur due to blockage of transmission of the cardiac impulse from the sinus node, with the new pacemaker usually occurring at the A-V node or in the Purkinje fibers, leading to an altered beat rate
171
What can most tissues control for their specific metabolic needs?
Local blood flow
172
What can occur if collateral blood vessels are unable to develop quickly enough to maintain blood flow?
Serious heart attacks
173
What can some of the vesicles do in the endothelial cell?
Some of these vesicles may coalesce to form vesicular channels all the way through the endothelial cell
174
What causes a significant increase in NO release from endothelial cells?
Shear stress from then flow of blood through the arteries and arterioles
175
What causes extra blood vessels to open to allow extra flow?
Appropriate local stimuli such as a lack of oxygen, nerve vasodilatory stimuli, or other stimuli
176
What causes the hearts rhythmical beat?
Cardiac rhythmicity, a series of special mechanisms in the heart, transmits action potentials throughout the cardiac muscle to cause the hearts rhythmical beat
177
What causes the increase in local blood flow during active hyperemia?
The increase in local metabolism causes the cells to devour tissue fluid nutrients rapidly and release large quantities of vasodilator substances
178
What causes the slow conduction of excitatory signals through the A-V node?
The slow conduction through the A-V node is caused by diminished numbers of gap junctions between successive cells, resulting in greater resistance to the conduction of excitatory ions
179
What causes vasodilation of the arterioles?
An increase in vasodilator metabolites causes vasodilation of the arterioles
180
What characteristic fo arterioles allows their diameters to change significantly?
The arterioles are highly muscular, allowing their diameters to change by many times
181
What controls blood flow to each tissue?
The small arterioles
182
What determines blood flow through a vessel?
Blood flow is determined by the pressure difference between the two ends of the vessel (pressure gradient) and the vessels vascular resistance
183
What determines cardiac output during normal heart function at systolic arterial pressures of 80-140 mm Hg?
At normal systolic pressures, cardiac output is almost entirely determined by the ease of blood flow through the tissues, controlling venous return to the heart
184
What determines heat loss from the body control of body temperature?
Blood flow to the skin
185
What do epinephrine and norepinephrine usually cause in all parts of the body?
Vasoconstriction
186
What do long-term changes provide?
Better control of the flow in proportion to the needs of the tissues
187
What do norepinephrine act directly on to cause vasoconstriction?
Alpha-adrenergic receptors of the vascular smooth muscle
188
What do the adrenal medulla secrete into the circulating blood?
Epinephrine and norepinephrine
189
What does HFrEF and HFpEF stand for, and how do they differ in terms of T-tubule alterations?
HFrEF stands for heart failure with reduced ejection fraction, and HFpEF stands for heart failure with preserved ejection fraction. T-tubule density is decreased in HFrEF, while in HFpEF, it can be unchanged or increased depending on the presence of diabetes
190
What does a hematocrit value indicate?
Hematocrit represents the percentage of blood volume that is composed of red blood cells
191
What does blood pressure represent?
Blood pressure represents the force exerted by the blood against any unit area of the vessel wall, quantified by the height (in mm) mercury can be pushed in a manometer
192
What does epinephrine cause in a few tissues?
Vasodilation
193
What does nitric oxide (NO) activate in vascular smooth muscle cells?
Soluble guanylate cyclases
194
What does sympathetic stimulation do to resistance to blood flow?
Increase resistance to blood flow
195
What does sympathetic stimulation do to the heart?
It increases the rate of sinus nodal discharge, conduction rate, excitability in all heart parts, and greatly increases the force of contraction of all cardiac muscle, enhancing overall heart activity
196
What does sympathetic stimulation do to the rate of blood flow through the tissues?
Decrease the rate blood flow through the tissues
197
What does sympathetic stimulation do to the volume of large vessels, particularly veins?
Decrease the volume of these vessels
198
What does the cardiac function curve represent and how is it affected by autonomic stimulation?
Showing that cardiac output increases with sympathetic stimulation and decreases with parasympathetic stimulation. This is due to changes in heart rate and contractile strength
199
what does the parasympathetic nervous system contribute to the regulation of?
Heart function
200
What does the stroke work output curve show?
The stroke work output curve shows that as atrial pressure increases, the stroke work output for that side of the heart increases until it reaches the limit of the ventricles pumping ability
201
What does the ventricular volume output curve indicate?
The ventricular volume output curve indicates that as the right and left atrial pressures increase, the respective ventricular volume outputs per minute also increase
202
What effect does histamine have on the arterioles and capillaries?
Histamine has a powerful vasodilator effect on the arterioles and can increase capillary porosity greatly, allowing leakage of fluid and plasma protein into the tissues
203
What effect does strong sympathetic stimulation have on heart rate?
Strong sympathetic stimulation can increase the heart rate from the normal range of 70 beats/min up to 180
204
What effect does parasympathetic (vagal) stimulation have on the cardiac rhythm and conduction?
Parasympathetic stimulation decreases the rate of rhythm of the sinus node and decreases the excitability of the A-V junctional fibers, thereby slowing transmission of the cardiac impulse into the ventricles
205
What ends the plateau of the cardiac action potential?
The plateau phase ends when the slow calcium-sodium channels close at the end 0.2 to 0.3 seconds, and the influx of Ca2+ and Na+ ions ceases. The membrane permeability for K+ ions increases rapidly, causing a rapid loss of K+ from the fiber and returning the membrane potential to its resting level, thus ending the action potential
206
What function do arterioles serve in the circulatory system?
Arterioles control blood release into capillaries, acting as the final branches of the arterial system with muscular walls that adjust blood flow to tissue needs
207
What happens if there is a greater difference between the concentrations of a substance on the two sides of the capillary membrane?
Greater net movement of the substance in one direction through the membrane
208
What happens to blood flow when the availability of oxygen to the tissues decreases?
The blood flow through the tissues increases markedly
209
What happens to blood viscosity and flow when hematocrit is high?
increases blood viscosity and reduces blood flow
210
What happens to premature babies retinas when they are put into oxygen tents?
Excess oxygen causes almost immediate cessation of new vascular growth and degeneration of some small vessels
211
What happens to the amount of free fluid in tissues when edema develops?
It expands
212
What happens to the hearts rhythm in the case of an A-V block?
the atria continue to beat at the sinus nodes rhythm, but a new pacemaker in the Purkinje system drives the ventricular muscle at a new rate. This is can lead to a temporary failure of the ventricles to pump blood, causing fainting due to lack of blood flow to the brain
213
What happens to the left ventricle at the end of systole?
At the end of systole, the left ventricle is like a loaded spring. it untwists during diastole, allowing rapid entry of blood into the pumping chambers
214
What happens to the need for whole-body blood flow during heavy exercise?
The need for whole-body blood flow often increases to six to eight times the resting blood flow
215
What happens to venous pressure in the lower leg when a person stands still?
Venous pressure increases to about 90 mm HG due to gravity, causing fluid to leak into tissue spaces and potentially leading to swelling and fainting
216
What happens when an artery or vein is blocked in most tissues of the body?
A new vascular channel usually develops around the blockage and allows at least partial resupply of blood to the affected tissue
217
What happens when sympathetic nerves to the heart are inhibited?
Cardiac pumping can decrease to a moderate extent. If the sympathetic nervous system is depressed below normal, both the heart rate and strength of ventricular muscle concentration decrease, potentially reducing cardiac pumping by as much as 30% below normal
218
What happens when the sympathetic nervous system is stimulated in most parts of the body during stress or exercise?
The sympathetic nerve endings in the individual tissues release norepinephrine, which excites the heart and constricts the veins and arterioles
219
What happens with the rates of diffusion through the capillary membranes of most nutritionally important substnaces?
