Exam 1 (WRKSHTS) Flashcards
define ganglion
collection of neuron cell bodies outside the CNS
define preganglionic neuron
the first neuron of the 2 neuron autonomic chain; cell body is in the CNS, axon extends into periphery and synapses in autonomic ganglion
define postganglionic neuron
the second neuron of the 2-neuron autonomic chain; cell body is in the autonomic ganglion, axon extends to target cell (smooth muscle, cardiac muscle, or gland cell)
define viscra
organs
define plexus
a network of nerves; for the ANS, contains both sympathetic and parasympathetic nerves
Name the three main cell types in the body innervated by the autonomic nervous system
Smooth muscle, cardiac muscle, glands
Relative to the autonomic nervous system, what do we mean when we say that an organ receives “dual innervation”
Dual innervation means the organ receives both sympathetic and parasympathetic postganglionic axons. Usually sympathetic activation will drive organ function in one direction, and parasympathetic activation in the opposite direction. Organ function at any one time is a balance between sympathetic and parasympathetic release
what happens when an action potential travels down the axon to the terminal
The action potential causes calcium entry into the terminal, which allows vesicles to bind to terminal membrane and release neurotransmitter into the space between the terminal and the target cell; transmitter diffuses to target cell
What happens when neurotransmitter reaches the target cell membrane
Target cell has receptors on its membrane which bind the transmitter. Binding stimulates events in the target cell, which vary depending on the type of target cell : muscles cells can contract or relax, gland cells can secrete, etc
You are given a drug that binds to receptors on the target cell and has the same effect as the neurotransmitter. What would happen to the target cell?
Since the drug has the same effect as the transmitter, the target cell would respond in the same way as if it had bound transmitter
Does the neuron need to fire an action potential to see the effect of a drug that binds to receptors on the target cell
If a drug is binding directly to the target cell, the neuron does NOT need to fire an action potential and release transmitter in order for the target cell to respond. The drug binding to the receptor triggers events in the cell directly.
You are given a different drug that binds to and blocks all the receptors on the target cell, meaning that the drug does not affect the cell but occupies all the receptors so that neurotransmitter cannot bind to the target cell. What would happen to the target cell when you applied the drug?
There would be no effect on the target cell. The drug simply binds to the receptors, but does not stimulate the cell in any way
what kind of receptor (alpha 1, alpha 2, beta 1, beta 2, nicotinic, muscarinic) would you find at the parasympathetic ganglion cell body
nicotinic cholinergic
what kind of receptor (alpha 1, alpha 2, beta 1, beta 2, nicotinic, muscarinic) would you find at the sympathetic ganglion cell body
nicotinic cholinergic
what kind of receptor (alpha 1, alpha 2, beta 1, beta 2, nicotinic, muscarinic) would you find at the smooth muscle cell that contracts when stimulated by norepinephrine
alpha 1 adrenergic
what kind of receptor (alpha 1, alpha 2, beta 1, beta 2, nicotinic, muscarinic) would you find at the smooth muscle cell that relaxes when stimulated by norepinephrine
beta 2 adrenergic
what kind of receptor (alpha 1, alpha 2, beta 1, beta 2, nicotinic, muscarinic) would you find at the postganglionic sympathetic nerve terminal
alpha 2 adrenergic (the autoreceptor for feedback)
what kind of receptor (alpha 1, alpha 2, beta 1, beta 2, nicotinic, muscarinic) would you find at the smooth muscle cell that responds to acetylcholine
muscarinic cholinergic
what kind of receptor (alpha 1, alpha 2, beta 1, beta 2, nicotinic, muscarinic) would you find at the salivary gland cell that responds to acetylcholine
muscarinic cholinergic
what kind of receptor (alpha 1, alpha 2, beta 1, beta 2, nicotinic, muscarinic) would you find at the sweat gland cell
muscarinic cholinergic
what kind of receptor (alpha 1, alpha 2, beta 1, beta 2, nicotinic, muscarinic) would you find at the cell in the adrenal medulla
nicotinic cholinergic
what kind of receptor (alpha 1, alpha 2, beta 1, beta 2, nicotinic, muscarinic) would you find at the target cell in the heart that slows the heart rate when stimulated by acetylcholine
muscarinic cholinergic
what kind of receptor (alpha 1, alpha 2, beta 1, beta 2, nicotinic, muscarinic) would you find at the target cell in the heart ventricle that contracts harder when stimulated by norepinephrine
Beta 1 adrenergic
You are out hiking in the remote woods when a small landslide traps your friends under the trunk of a collapsed tree. You race to their aid and miraculously lift the limb and help them to safety. How were you able to summon this hidden power?
Such an event triggers the “fight or flight” reaction, and gives an adrenaline rush – release of epinephrine (the same hormone that used to be called adrenaline) into the blood stream, and, in addition, activation of sympathetic neurons everywhere in the body
You accidently ingest the wrong kind of wild mushroom, one containing muscarine which stimulates the muscarinic cholinergic receptor. What are some symptoms you would notice?
Muscarinic receptors are found on all target cells of the parasympathetic nervous system, as well as sweat glands (an exception in the sympathetic system). Some symptoms: profuse sweating at the skin, profuse salivation, increased tear production, cramping in the GI tract and maybe diarrhea, constricted pupils, labored breathing, slow heart rate.
A child finds an “epi pen”, a syringe containing a small dose of epinephrine, in a bathroom drawer. What symptoms would you expect to see develop if the child used the syringe on himself?
Epinephrine in the bloodstream would bind to any adrenergic receptor in tissues everywhere in the body. Effects include: increased heart rate and strength of contraction, bronchodilation, dilated pupils, vasoconstriction throughout the system, decreased digestive function, inhibition of bladder and bowel emptying, dry mouth
Describe 4 functions of the blood
Transporting oxygen, carbon dioxide, nutrients, wastes
Regulating pH and ion composition in body tissues
Regulating heat distribution
Prevention of fluid loss (clotting) and defense against disease
What are the two main fractions of blood, and what are their approximate percentages?
Plasma: approximately 55%
Formed elements = red and white blood cells and platelets: 45%
What are the main components of plasma? What approximate percentages do they comprise?
Water – 92%
Proteins – 7%
Everything else – ions, nutrients, wastes – 1%
Where are most plasma proteins produced?
liver
What is the role of plasma proteins?
albumins are largely transport proteins
globulins are transport proteins and also antibodies used to fight disease
fibrinogen and other clotting proteins that can be activated when needed
Describe the life span of a red blood cell (you don’t need to name the intermediate forms, but know what happens as it grows to maturity and beyond), and relate its mature structure to its function. (hint: both shape and contents)
Red blood cells are produced in the marrow; for the first few days of development they produce large amounts of hemoglobin until the cell is little more than a bag of hemoglobin. At that point, the cell extrudes its nucleus
and organelles and is a passive carrier of hemoglobin. The mature cell thus has no nucleus, and has the shape of a biconcave disc – flattened in the middle. This shape gives it a high surface area to volume ratio, maximizing its ability to exchange gases between the hemoglobin in its cytoplasm and the fluid around it.
Describe the structure of a hemoglobin molecule, and relate it to its function in a red blood cell
A hemoglobin molecule consists of 4 subunits assembled into a functional molecule. The two alpha and two beta chains are proteins, made of amino acids. Each protein contains a non-protein heme unit. The heme unit has an iron molecule bound to it, which is the site where oxygen binds. Thus, a hemoglobin molecule has 4 iron units and can bind a maximum of 4 oxygen molecules. When red blood cells are broken down, the 3 parts (protein subunit, heme unit, and iron) are processed differently by the body. The proteins are broken down and the amino acids reused. Iron is transported back to the marrow to make new red cells. Heme is broken down to biliverdin and bilirubin, which is processed by the liver into bile and excreted from the body
Describe some roles for white blood cells in the body
Lymphocytes are responsible for giving the body immunity. Neutrophils and macrophages are major phagocytic cells, engulfing and digesting foreign and abnormal material. Other cells release the chemicals stored in their cytoplasmic granules to cause inflammation (basophils) or attack parasites (eosinophils). All WBCs travel in the blood but may squeeze out of the bloodstream and crawl through tissue to get to sites of injury or disease.
Name the 3 types of granular leukocytes; which is the most common?
Basophils, eosinophils, and neutrophils. Neutrophils comprise approximately 60% of the WBCs
Name the 2 types of agranular leukocytes; which class of cells comprises your immune system?
Monocytes and lymphocytes. Lymphocytes comprise your immune system.
How is a platelet related to a megakaryocyte? What is the function of platelets?
Megakaryocytes are the large marrow cell that gives rise to platelets. Platelets are pieces broken off from the megakaryocyte, membrane bound collections of chemicals that induce the blood clotting process.
Describe the steps in blood clotting.
- In a damaged vessel, the smooth muscle in the wall contracts to reduce the vessel diameter.
- exposed collagen in the damaged wall stimulates platelets to stick and break, and to release their chemicals, which attracts more platelets and through a positive-feedback cycle forms a platelet plug.
- Platelet chemicals initiate the clotting cascade that activates plasma clotting proteins from their inactive to active forms, eventually causing thrombin to turn fibrinogen molecules into fibrin threads, which trap blood cells and form a gel-like clot.
- the clot retracts, pulling the wall of the vessel closed.
- eventually, the clot will dissolve as chemicals in the clot activate plasminogen into plasmin, which digests the fibrin threads.
What is the role of fibrin?
Assembles into threads which form a net and trap blood cells in clot
What is the role of plasmin?
Digest fibrin threads and causes clot to break up
Why is tissue plasminogen activator used in the emergency room?
tPA is used in the ER for patients who have had a heart attack or stroke, to speed the breakup of a clot and restore blood flow to heart or brain.
in the pulmonary circuit, blood is pumped from the ___side of the heart to the ___lungs and back to the ___side of the heart.
right
lungs
left
in the systemic circuit, blood is pumped from the ___side of the heart to the ___organs and back to the ____side of the heart
left
organs
right
blood in the pulmonary arteries carries blood ___from the heart. this blood is ___in oxygen and ____in carbon dioxide
away
high
low
from the inner to outer, the three layers in the wall of a blood vessel are the tunica ___, tunica ___, and tunica ___
intima
media
externa
the blood vessel layer that contains smooth muscle and variable amounts of elastic fibers is the
tunica media
the blood vessel layer with cells similar to simple squamous epithelium is the___. the special name given for these cells lining the cardiovascular system is ___
tunica intima
endothelium
the blood vessel layer containing mostly collagen is the
tunica externa
which vessels are categorized as resistance vessels
arterioles
which vessels are categorized as elastic vessels…why
large arteries to the heart
high numbers of elastic fibers in the vessel wall allows vessels to stretch with the pulse of blood from the heart and then recoil to continue to push blood to the organs while the heart is refilling
vessels that distribute blood to organs are categorized as ___ arteries
muscular
why are veins called the capacitance vessels?
vein walls are weaker than arterial walls; they expand to accommodate blood but don’t have the elastic recoil property, so veins have more capacity to hold blood
total blood volume in an adult is about ___liters. must of that blood is found in which class of vessels?
5
systemic veins
explain how venous valves prevent the back flow of blood
Venous valves are created by foldings of the tunica intima into the vessel lumen. As blood moves toward the heart, the valve flaps are pressed along the sides of the vessel out of the way. If blood tries to flow backward in the vein, blood catches in the valve flaps, causing the flaps to expand into the lumen and close off the vessel.Explain how venous valves prevent the backflow of blood
what ar varicose veins? what are hemorrhoids?
Varicose veins are dilated veins visible through the surface of the skin, and are most common in the legs. Hemorrhoids are dilated veins at the anus or within the anal canal. Both are caused by failure of the venous valves to prevent backflow of blood, leading to overstretching of the veins walls and pooling of blood in the veins.
Compare the structure of the three types of capillaries
Capillaries consist of an endothelium with a basal lamina around it. In continuous capillaries, the endothelial cells form a continuous tube with few small gaps between cells letting only the smallest molecules out of the blood. Fenestrated capillaries have endothelial cells with small pores in them, allowing greater exchange of materials, including larger solutes, between the blood and the tissues. Sinuosidal capillaries are the leakiest type of capillary, the endothelial cells are not held together as tightly, so there are large openings between the endothelial cells allowing large solutes – including large proteins – to enter or leave the blood.
Explain how pre-capillary sphincters control the flow of blood through a capillary bed
Pre-capillary sphincters are clusters of smooth muscle cells that surround the small arterioles feeding into a capillary bed. Contraction of the smooth muscle cells constricts the vessel, reducing or preventing flow of blood into the capillary bed and shunting the blood directly into the venules on the other side of the capillary bed.
describe the location of the heart within the thoracic cavity
The heart lies directly behind the sternum in the central compartment of the thorax called the mediastinum, and extends from approximately the second to 4th ribs anteriorly. The apex of the heart, which is the inferior end of the left ventricle, extends to the 5th rib and lies to the left of midline
The pericardial sac outside of the heart comprises two layers. What are they?
The pericardial sac surrounds the heart. Its outer layer is a thick layer of connective tissue, referred to as the fibrous pericardium. The inner layer is a thin, smooth, shiny membrane called the parietal pericardium. Where the sac attaches to the base of the heart, the parietal pericardium folds back over the outer layer of the heart, and is now referred to as the visceral pericardium. If the heart were removed from the sac, its shiny outer visceral pericardial layer would cover its outer surface, the epicardium.
Which two layers of tissue enclose the pericardial cavity? What is normally contained in that space? What is the consequence of abnormal fluid buildup within the pericardial cavity?
The parietal and visceral pericardial layers are two different areas of one continuous membrane and enclose a narrow, fluid filled space called the pericardial cavity. This cavity is external to the heart and surrounds the heart within the pericardial sac. Normally, only a thin layer of slippery (serous) fluid is contained in the cavity, so the surface of the heart (visceral pericardium) slides without friction against the inner side of the pericardial sac (the parietal pericardium). An abnormal accumulation of fluid in this space can compress the heart and limit its ability to fill with blood between beats.
Which major coronary arteries are located on and supply the anterior surface of the heart? The posteriors surface? How does venous blood return from the heart wall to join the blood of the systemic circulation?
There are two coronary arteries branching from the aorta right above the aortic valve before the aorta ascends to its arch; these are the right and left coronary arteries. The right coronary artery mainly supplies the right atrium and ventricle anteriorly; the anterior wall of the left ventricle is supplied almost entirely by the left anterior descending (LAD) branch of the left coronary artery. The posterior part of the heat, including the left atrium and both ventricles, receives two large arteries – the right coronary, and the circumflex branch of the left coronary. All coronary arteries travel on the epicardial surface before diving into the heart wall, and branching into arterioles to feed capillary beds. Blood returning from the capillary beds is collected into venules, and small veins collect back to the epicardial surface to larger cardiac veins. All heart veins ultimately collect into a dilated vessel called the coronary surface on the posterior side of the heart, which returns blood into the right atrium to join the systemic blood returning from the superior and inferior venae cavae
Describe the three layers of the heart wall and the tissue types comprising each layer.
The inner layer of the heart wall is the endocardium; its innermost membrane is the simple squamous endothelium, which rests on a little bit of connective tissue.
The middle layer of the heart wall is the myocardium; it contains mostly cardiac muscle cells, with small amounts of connective tissue (predominantly elastic fibers). This is normally the thickest layer of the heart wall.
The outer layer of the heart is the epicardium; this is a connective tissue layer that also contains the coronary arteries and veins and variable amounts of fat. The outermost part of the epicardium is the single cell thick visceral pericardium, the inner part of the pericardial cavity.
Why do different chambers of the heart have different thickness of myocardium?
The two sides of the heart act as independent pumps. The thickness of the myocardial layer is proportional to the amount of force the chamber can exert to push blood. Both atria are thin walled, as they only need to generate a small amount of pressure to push blood into the ventricles. The left ventricle needs to generate tremendous pressure to push blood through the systemic circuit, so has the thickest myocardium. The right ventricle needs only to push blood through the pulmonary circuit, so typically has a myocardial layer less than half the thickness of the left.
How is the function of semilunar valves different from the function of atrioventricular valves?
Semilunar valves are passive valves, created by infoldings of the tunica intima. They open when the pressure in the ventricle exceeds pressure in the outflow vessel, and close by trapping blood when the pressure gradient reverses. The atrioventricular valves have cordae tendineae attaching them to papillary muscles sticking into the ventricular chamber from the ventricular wall. As the ventricular wall contracts, pushing blood backwards against the AV valve, the papillary muscles also contract, pulling on the cordae tendineae and helping hold the valve flaps into the closed position between the atrium and ventricle.
What kind of cells comprise the conducting system of the heart? Describe the waveform of a pacemaker cell action potential. How does this action potential differ from that of a skeletal muscle cell?
The conducting system is a network of specialized cardiac muscle cells called pacemaker cells. These cells do not contract or generate pressure to move blood, but instead function to generate the electrical signal that starts the contractile cells contracting. Pacemaker cells do not have a stable resting membrane potential: they have a special channel that opens when they are hyperpolarized, and that causes them to immediately start to depolarize again. When they reach threshold, they fire an action potential and then repolarize. In contrast, a skeletal muscle cell maintains a stable resting membrane potential until a nerve releases acetylcholine on it; the Ach opens channels that cause the muscle cell to depolarize to threshold, which causes and action potential. In other words, skeletal muscles require an outside influence – the nerve- to fire an action potential, while pacemaker cells bring themselves to threshold
Describe the pattern of electrical excitation through the heart initiated by the conducting system. Why is the SA node considered the pacemaker for the heart?
The normal pattern of excitation is as follows:
SA node cells send a wave of depolarization to the atrial cells (which spread the signal through their network of gap junctions). This causes the atrial cells to contract.
The signal from the SA node also reaches the AV node cells. These cells have a small delay before passing the signal on to cells of the Bundle of His, which pass the signal to the Purkinje cells in the wall of the ventricle.
The atrial cells get the “go” signal directly from the SA node, so the atrial cells contract as they fire action potentials. But because the AV node cells delay sending the signal on, the atria finish contracting and begin relaxing before the ventricles have even received the signal to contract. This ensures the atria contract first, and the ventricles after, in one cardiac cycle.
Although all the cells of the conducting system have pacemaker activity – they all self-depolarize to threshold – the SA node cells depolarize fastest and therefore fire action potentials first. The other pacemaker cells, still trying to reach threshold, are immediately brought to threshold when the action potential reaches them. In other words, the SA node cells force the other cells to fire action potentials at their pace. If the SA node cells fail, the AV nodes (depolarizing on their own, but more slowly), will eventually reach threshold and fire their own action potential and drive the ventricles to contract – but at a slower rate than if the SA node had been working.
Blood in the inferior vena cava flows directly into the
right atrium
Where would you find the “LAD” artery?
In the epicardium of the anterior wall of the heart
The right atrioventricular valve is called the
Tricuspid valve
Which of the following is true about the conduction system of the heart?
The SA node has the fastest rate of spontaneous depolarization
Papillary muscles are active in which of the following processes?
Preventing blood from flowing from the ventricles back into the atria
Blood leaving the right ventricle travels through a type of _____________ valve called the ___________ valve
semilunar; pulmonary
How does the structure of a contractile cardiac muscle cell facilitate the spread of an electrical stimulus through the myocardium?
Contractile cells are branched, so that each cell contacts multiple other cells at points called intercalated discs. Each disc contains gap junctions connecting the cytoplasm of one cell directly with the cytoplasm of its neighbors. When one cell has an action potential, the electrical event is conducted directly to its neighbors. This makes communication faster than if the signal had to spread by a process like synaptic transmission. Thus, the spread of signal through the wall of a chamber is efficient and very rapid
What is the role of calcium in muscle contraction (for any type of muscle)? How does the source of this calcium differ between skeletal and cardiac muscle?
Calcium binds to regulatory proteins that normally block actin-myosin interaction. When calcium is present, the regulatory proteins move out of the way so that actin and myosin are able to bind to each other. Actin and myosin interaction (the crossbridge cycle) is what produces force in the muscle. In cardiac muscles, calcium enters the cell through the plasma membrane during the action potential, and this calcium triggers opening of the sarcoplasmic reticulum, the “bank” of intracellular calcium. Thus, in cardiac muscle there are two important sources of calcium. In skeletal muscle, all the calcium comes from the sarcoplasmic reticulum stores
Describe the action potential of a contractile cardiac muscle cell. Which ions move during each phase? How does the plateau phase help the heart cycle between diastolic and systolic phases?
The AP of a contractile cell has 3 phases. Starting from a stable resting membrane potential, reaching threshold (signaled by other contractile cells via gap junctions) opens voltage gated sodium channels, causes the spike in the AP. As sodium channels close, calcium channels open, and keep the cell in a depolarized state – the “plateau” phase. When the calcium channels close, potassium channels begin to open, causing repolarization and bringing the cell back to resting membrane potential.
The plateau phase extends the duration of the AP and keeps the cell in its absolute refractory state for a long time; this prevents the cell from firing another AP and ensures the cell will undergo and complete contraction before another AP starts the process all over again. This will ensure that the heart is forced to relax between beats, allowing time for it to fill with blood before the next beat. If the heart contracted and could stay contracted (the way skeletal muscles in your can stay contracted for hours while you stand), the heart would not be able to relax and refill, and you would die
P wave
Atrial Depolarization
QRS complex
Ventricular Depolarization (overlapping with atrial repolarization)
T wave
Ventricular Repolarization
In order for blood to move from point A to point B (or chamber A to chamber B), what two factors are important?
A pressure gradient provides the driving force to move blood, blood only moves between chambers if the valve is open
When the aortic valve is open, is the pressure in the ventricle greater or less than the pressure in the aorta?
greater
When the ventricle is in diastole, is the pressure in the ventricle greater or less than the pressure in the aorta?
less (for all but the very beginning of diastole)
Why is there a spike in left atrial pressure during both atrial systole and atrial diastole?
The spike in pressure during systole represents the compression in the chamber due to the atrial cells contracting; closure of the AV valve and backward force from the ventricle gives the spike early in diastole. As the atria fills with returning blood during diastole, its pressure slowly rises until the AV valve opens again`
What causes a heart sound? What event creates the first heart sound? What event creates the second heart sound?
Heart sounds are produced when there is rapid change in the direction of blood flow, causing turbulence when the blood runs into a closed valve. The first sound occurs as the ventricles begin contracting and force blood upward against the AV valve, closing it. The second sound occurs when the ventricles begin relaxing and the ventricular pressure falls below pressure in the pulmonary trunk and aorta; blood moving backward toward the ventricle is caught on the flaps of the semilunar valves, forcing them closed and creating the turbulence
What is the role of desmosomes in an intercalated disc?
physically tie the contractile cells to one another
in the ECG, the P-wave corresponds to
atrial depolarization
What is the correct order for the sequence of electrical excitation of the heart?
SA node, AV node, AV bundle of His, Bundle branches, Purkinje fibers
The mitral valve opens during the stage called ____________ and allows blood to flow into the ____________
ventricular diastole; left ventricle
The first heart sound (“lub”) occurs when the
atrioventricular valves close
Ejection of blood from the left ventricle occurs during
late ventricular systole
What are the 3 factors that determine Cardiac Output? How are they related?
Cardiac Output = Heart Rate X Stroke Volume
An increase in either HR or SV will cause an increase in cardiac output
How does the cardiovascular center in the medulla communicate with the heart? What neurotransmitters are released by the sympathetic and parasympathetic neurons that innervate the heart?
The cardiovascular center has two divisions.
The cardio accelerator region turns up heart activity by increasing the rate of firing of axons in the sympathetic nervous system that innervate the heart. This includes axons to SA and AV nodes as well as to the ventricle walls. Sympathetic axons release norepinephrine on these heart cells. NE speeds up the rate of firing at the SA node to increase heart rate, and increases contractility (gives an increase in cytoplasmic calcium) in the cells of the ventricle wall. Thus, sympathetic axons increase cardiac output by increasing both its parameters – heart rate and stroke volume.
The cardio inhibitory region turns down heart activity by increasing the rate of firing of axons of the parasympathetic nervous system that innervate the heart. It stimulates the vagus nerve axons (parasympathetic preganglionic) to the heart, which synapse on parasympathetic postganglionic axons on the heart. The parasympathetic axons release Acetylcholine on both SA and AV node cells; acetylcholine slows down the rate of firing of these cells, leading to a slowing of heart rate. Thus, parasympathetic axons decrease cardiac output by decreasing heart rate; parasympathetics have no effect on stroke volume
How does acetylcholine affect a pacemaker cell of the SA node? How does norepinephrine affect the pacemaker cell?
Pacemaker cells have an intrinsic rate of spontaneous depolarization leading them to threshold and the firing of an action potential. Aceytylcholine from the parasympathetic nervous system slows down the rate at which the SA node cells depolarize, taking it longer to reach threshold, and thus longer to fire an action potential. This causes fewer action potentials per minute; since each action potential leads to a heartbeat, it slows heart rate.. Norepinephrine from the sympathetic nervous system speeds up the rate at which the SA node cells depolarize, causing them to reach threshold and fire an action potential more quickly, which speeds up heart rate.
What two factors influence end diastolic volume and how are these factors controlled?
End diastolic volume is the amount (volume) of blood in the left ventricle right before it contracts. One factor influencing that volume is how long the heart had to fill between beats, so is related to heart rate (slower heart rate=longer time to fill = increase in EDV). The other factor is the state of the systemic veins returning blood to the heart. Veins are the capacitance vessels, and swell with blood; thus, more blood is contained in the systemic veins than any other part of the circulation. Constricting those veins, or forcing more blood through them by the action of skeletal muscles around them (muscular pump) returns more blood to the heart and increases EDV.
Heart rate and degree of vasoconstriction are controlled by the autonomic nervous system. Skeletal muscle is controlled by the somatic nervous sytem
What three factors influence end systolic volume
Preload
Contractility
Afterload
preload
the volume of blood filling the ventricle during diastole exerts a stretch to the ventricle wall, felt by ever muscle cell in the ventricle. This stretch of the cells stretches their sarcomeres and changes the spacing of the thick and thin filaments that makes it easier for them to interact once the contraction begins. Because this stretch is exerted before contraction begins, it is called the preload. Greater preload gives stronger contraction, greater stroke volume, and increased cardiac output.
Contractility
Contractility is the term describing the effect of intracellular calcium on the contraction. More calcium allows more actin-myosin crossbridges to form, and thus more tension to develop. Numerous factors, including nerve stimulation and circulating hormones, can influence the calcium levels within the cell, and thus increase or decrease the amount of tension that develops. Greater contractility gives stronger contraction, greater stroke volume, and increased cardiac output
Afterload
Afterload describes the forces working against the left ventricle as it tries to push blood out into the systemic circulation. Anything that makes it harder to move blood out means less blood will be ejected. Diseased valves, diseased vessels, and hypertension are all common sources of afterload. It is called afterload because the heart doesn’t feel the problem until it is trying to pump (after contraction begins). Greater afterload gives decreased stroke volume and decreased cardiac output
Why are beta blockers and calcium channel blockers the main drugs used clinically for people with cardiovascular disease?
Beta 1 receptors are the receptors on pacemaker cells and on ventricular wall cells that bind norepinephrine from sympathetic axons. They also bind epinephrine from the adrenal medulla that circulates as a hormone. Since both of these sympathetic signals increase heart activity, beta blockers are used to ease the load on the heart (not to stop it, just to decrease its workload).
Because most beta receptors work by influencing calcium levels in the cells, calcium channel blockers have the same ultimate goal of decreasing heart workload. They just work at a different point in the signaling pathway.
If a patient has an EDV of 120 ml and an ESV of 30 ml, what is the patient’s ejection fraction?
SV = EDV-ESV, so stroke volume is 120ml -30ml = 90 ml. This means the left ventricle ejected 90 ml of blood during one heartbeat.
Ejection Fraction is the percentage of starting blood that was ejected. Since the ventricle started with a volume of 120 ml (the EDV) and pumped 90ml of that (the SV), the ejection fraction is 90/120 =0.75 = 75%
The amount of blood in the ventricle right before it contracts is called the __________.
End diastolic volume
Cardiac output is determined by
multiplying the stroke volume times the heart rate
Which of the following factors most directly affects the end diastolic volume?
venous return
The parasympathetic nervous system _____________ heart rate by _________ the rate of spontaneous depolarization of the SA node cells
slows down; decreasing
An increase in afterload would ________ stroke volume and _________ cardiac output.
decrease; decrease
What two factors determine blood flow to an organ? How does each affect flow?
Pressure : an increase in pressure will increase flow
Resistance : an increase in resistance will decrease flow
what is blood pressure
blood pressure is the outward force exerted by blood on the wall of the blood vessel
What is pulse pressure? Which sets of vessels exhibit a pulse pressure? How is pulse pressure related to “pulse points”?
Elastic arteries – the aorta and larger arteries – experience a fluctuation in pressure between systolic and diastolic phases of the ventricle. For someone with the typical arterial pressure of 120/80, the arterial pressure rises to 120mmHg during ventricular systole and falls to 80 during diastole. The difference between these two values - 40mmHg in this example - is the pulse pressure. Where the elastic vessels pass close to the skin, a throb in the vessel wall can be detected by placing the fingers against the skin. These locations are called pulse points
What are the three sources of resistance in the vascular system. What is the main factor determining vascular resistance on a moment-to-moment basis?
the vessels themselves – the total length of the vascular system (fixed on a day-to-day basis) and the diameter of the vessels (adjustable second-by-second by contraction or relaxation of the smooth muscle in the tunica media layer)
viscosity of blood
turbulence in flow (common at branch points in the circulation)
The most important of these in non-disease states is regulation of vessel diameter through the sympathetic nervous system and local chemicals in the tissues surrounding the arterioles in an organ.
Why is blood flow through a capillary bed slower than through an elastic artery? How does this lower velocity contribute to exchange of materials across a capillary wall?
There are only a small number of elastic arteries in the body relative to the huge number of capillaries; if you added up the cross-sectional area of all the elastic arteries vs. all the capillaries, you would see the capillaries offer an area several hundred fold greater for blood to flow through. This means that X volume of blood in the arteries, passes into the capillaries but spreads out over a huge area, leading to slower flow. The slow flow in the capillaries allows time for blood passing through to equilibrate with the environment around them. For all exchange processes involving diffusion, it ensures that substance will diffuse across the capillary membrane until equilibrium is reached.
What are the three forces by which substances move across the wall of a continuous capillary
diffusion
filtration
reabsorption
diffusion
this force is driven by concentration gradients for each substance, so is unaffected by the capillary length.
filtration
this is the effect created by blood pressure within the capillary, called the capillary hydrostatic pressure (CHP). This pressure squeezes fluid and small solutes out through tiny spaces in the capillary wall, regardless of their concentration gradients, into the interstitial fluid around the capillary. The pressure causes substances to filter out through the wall – so the pressure is the force, and filtration is the effect. Because the pressure falls between the arterial and venous ends of the capillary, the filtration force decreases along the length of the capillary
reabsorption
this is the effect created by blood colloid osmotic pressure (BCOP). BCOP is a force causing movement of water (osmosis), and it is created by the presence of large proteins in the blood. This force pulls fluid toward the proteins - into the capillary from the interstitial fluid, which is the opposite direction from the filtration force. These plasma proteins do not pass through capillary walls, so the number of proteins is unchanged between the arterial and venule ends; thus, the reabsorptive force is constant along the length of the capillary.
Why does the net filtration force cause a loss of fluid from the blood into the peripheral tissues in a normal healthy person? How is this fluid recovered in a normal healthy person?
Filtration force pushes water and tiny solutes out of capillaries, driven by capillary blood pressure (called capillary hydrostatic pressure). Fluid is drawn into the capillary toward the large plasma proteins (called the blood colloid osmotic pressure). The difference between those two forces – one pushing out of the capillary and the other drawing in – is the net filtration force. Along a typical capillary bed, more is pushed out by filtration than drawn in by absorption, so there is a net outward loss of fluid from the capillary. This fluid loss, miniscule for any one capillary bed, adds up to about 3 liters of fluid in 24 hours if added up for all the capillary beds in the body. 3 liters of fluid is more than the fluid amount in the blood (all fluid is in the plasma fraction of blood (~55%), so totals less than 3 liters in the body). This fluid is constantly picked up by vessels of the lymphatic system, filtered through lymph nodes, and then returned to the blood close to the heart. So even though there is a net loss of fluid at capillary beds, that fluid is collected and returned by the lymphatic system, and there is no net loss from the blood over the course of the day.
What is edema, and how does it relate to filtration force?
Edema is the accumulation of fluid in the interstitial spaces. It occurs when the net loss of fluid by filtration at capillary beds into the interstitial space is not balanced by return of fluid by the lymphatic system. Two things can lead to edema : damage to the lymphatic system (think of the extreme example of elephantiasis from lecture), or excess net filtration force. Higher than normal blood pressure is one source of high filtration force. Low plasma protein concentration is another; here, the outward filtration force is normal, but the BCOP is decreased, so the imbalance leads to more loss of fluid into the interstitial force than usual, and edema would result.
How would a loss of fluid from the bloodstream change the net filtration force in capillary beds? How does this help recovery?
A loss of fluid from the bloodstream, such as occurs in hemorrhage, causes a drop in blood pressure. At the capillary beds, this is described as a drop in capillary hydrostatic pressure, which creates a proportional drop in the filtration pressure. The net filtration pressure is the sum of the outward filtration pressure and the inward BCOP pressure. If the filtration pressure drops and the BCOP is unchanged, the net filtration pressure would drop and less fluid would be lost from the capillary than normal. If the drop is severe enough, there would be a negative net filtration pressure, meaning that there is net movement of fluid into the capillary (the reverse of normal). Drawing fluid into the capillaries, and thus into the bloodstream, helps recovery by adding more volume into the blood, raising blood pressure
What is autoregulation of blood flow? What local chemicals are triggers for vasodilation?
Autoregulation of blood flow refers to the process by which a tissue in the body controls its own blood flow. Arterioles within a tissue break up into capillary beds. The arterioles and capillaries travel through a mass of tissue cells and interstitial (=extracellular) fluid. Chemicals in the interstitial fluid can cause the smooth muscle cells in the tunica media to either contract or relax, leading to changes in arteriole diameter and decrease or increase blood flow into the capillary bed.
For example, very active cells use oxygen and nutrients from the interstitial fluid, and release carbon dioxide, acid, adenosine, and potassium into the interstitial fluid. A decrease in oxygen or increase in the other components within the interstitial fluid leads to vasodilation of the arterioles and subsequent increased blood flow through the capillary beds. The increased blood flow brings in more oxygen, and removes wastes.
Describe the anatomy of the baroreceptor reflex. How will this reflex work to return pressure to normal following an increase in blood pressure? Is this a fast or slow response to cardiovascular alterations?
At two places in the body – the aortic arch and the bifurcation of the common carotid arteries – there are specialized receptors that monitor blood pressure. The receptors are called baroreceptors, and they send information through cranial nerves IX and X to the cardiovascular center in the medulla of the brainstem. If pressure increases, they send this information in the form of more action potentials/second; if pressure decreases, they send fewer action potentials/second. The cardiovascular center responds to this ever changing information by altering its output through the autonomic nervous system.
If blood pressure is too high, the cardiovascular system turns up the parasympathetic nervous system to the heart, and turns down the sympathetic nervous system to the heart and blood vessels. Turning UP the parasympathetic signaling to the heart works at the SA node to decrease heart rate, leading to a decrease in cardiac output and a drop in blood pressure. Turning DOWN the sympathetic signaling to the heart decreases heart rate and decreases contractility in the ventricles (decreasing stroke volume), both leading to decreased cardiac output and a drop in blood pressure. Turning down the sympathetic signaling to the blood vessels causes vasodilation (by decreasing the amount of contraction in the smooth muscle cells of the tunica media), which also contributes to a decrease in blood pressure.
Explain why erythropoietin (EPO) is considered a “long term” response to cardiovascular alterations
Erythropoietin is a hormone, produced by the kidney, that tells the bone marrow to make more red blood cells (erythrocytes). Because it takes a week for a new red blood cell to mature and leave the marrow, the end effect of EPO – more oxygen transport- would not be seen for at least a week. This is a very long time frame relative to most homeostatic processes.
Describe the step-by-step changes in the cardiovascular system as you move from a standing to a lying position.
As one stands, immediately gravity acts against blood returning toward the heart from the legs; the capacitance veins of the legs stretch a little with the extra blood. This decrease in venous return to the heart decreases stroke volume, which decreases cardiac output and decreases blood pressure.
But as soon as blood pressure drops a little, the baroreceptors in the aortic arch and carotid sinus decrease their signaling to the cardiovascular center in the medulla. The cardiovascular center then turns UP the sympathetic nervous system activity to the heart (increasing heart rate and ventricle contractility to increase cardiac output) and to the blood vessels (causing vasoconstriction), and turns DOWN the parasympathetic signaling to the heart (less slowing influence for heart rate). All of these actions help to bring blood pressure back to normal within a few beats of standing.
What is atherosclerosis and how does this occur?
Atherosclerosis is an inflammatory disease of the blood vessels, thought to occur when cholesterol enters the wall of the tunica intima. This causes white blood cells to mobilize in the area and initiate inflammation and a release of many chemicals that cause alterations in the normal cells of the vessel wall. The mass that accumulates in the wall – called a plaque – contains cholesterol, white blood cells, abnormal wall cells, and often calcium, which hardens the mass. High cholesterol, genetic influences, stress, and whole-body inflammatory states all hare implicated in formation of plaques
What is pulse pressure?
The difference between the maximum and minimum pressure in the arteries during the cardiac cycle
Mean arterial blood pressure is
closer to the diastolic pressure
The velocity of blood flow is fastest in the __________ and slowest in the ____________.
aorta; capillaries
Which of the following substances does NOT normally leave a fenestrated capillary by diffusion?
plasma proteins
Which of the following types of vessel would exhibit a pulse pressure?
Muscular arteries
