Animals - circulatory system long questions

coronary circulation

Circulation of blood through the coronary blood vessels to deliver oxygen and nutrients to the heart muscle tissue

Diastole

relaxation of the heart

Briefly describe 4 functions of the pericardium.

(a) It lubricates the outer heart wall. (b) It holds the heart in place. (c) It acts as a barrier to infections. (d) It helps prevent heart overexpansion.

Describe pacemaker cells. i.e., Where do they originate and discuss their membrane potential.

- Sinoatrial node - Unstable resting membrane potential (‐60 mV) • Pacemaker potential • Threshold (‐40 mV)

What are the six steps of events regarding operation of the atrioventricular (AV) valves?

1 - Blood returning to the atria puts pressure against AV valves, forcing them open. 2 - As the ventricles fill, AV flaps hang limply into ventricles. 3 - Atria contract, forcing additional blood into ventricles. 4 - Ventricles contract, forcing blood against AV flaps. 5 - AV valves close. 6 - Chordae tendineae tighten, preventing valve flaps from everting into the atria.

Pericyte cells

1) Small cells closely associated with small blood vessels 2) Defined by location 3) Heterogeneous pop of cells with different functions - some pericytes stabilize the blood capillary wall - some have "stem-cell" like properties and can give rise to multiple cell types --> iii) Involved in repair and regen. of tissue

Name the steps in heart contraction.

1. SA node depolarizes and the depolarization spreads rapidly via the internodal pathway. 2. The AV node delays the signal. The depolarization spreads through the atria via gap junctions, and causes the atria to contract. 3. The depolarization spreads rapidly through the Bundles of His and Purkinje fibers. 4. The depolarization spreads upward through the ventricle, causing the ventricle to contract.

Describe the steps in the cardiac cycle.

1. Ventricular Diastole - AV valves open - Semilunar valves closed 2. Atrial Systole •Atria contract •Ventricles relaxed •End diastolic volume 3. Ventricular Systole •AV valves close •Semilunar valves closed •Increased pressure 4. Ventricular Systole •Ventricles Contract •Semilunar valves open •End Systolic Volume 5. Ventricular Diastole •Ventricles relaxed •Semilunar valves close

Trace the movement of a drop of blood through the human circulatory system, listing all of the structures it passes (including all of the parts of the heart).

A drop of deoxygenated blood from the systemic circulation comes from the inferior or posterior vena cava, depending on whether it came from the lower or upper body. In enters the right atrium, cross the right atrioventricular (or tricuspid) valve, and enters the right ventricle. From the right ventricle, it will be pumped through pulmonary semilunar valve and enter the pulmonary artery which will bring the drop of blood to the lungs. The drop of blood will travel through pulmonary capillaries where gas exchange will occur, and come back toward the heart in one of the pulmonary veins. This oxygenated blood will enter the left atria, cross the left atrioventricular (or bicuspid) valve, and enter the left ventricle. From there, it will be pumped through the aortic semilunar valve into the aorta, and will be delivered to capillaries in various parts of the body. Deoxygenated blood from the systemic circulation will enter veins that connect to the inferior or posterior vena cava, and the cycle starts again.

Cardiac Cycle

All of the events that occur with one heartbeat.

Compare and contrast the circulatory systems of fish, amphibians, and mammals.

All three vertebrates have closed circulatory systems, with a heart that pumps blood, arteries that send blood to tissues, capillaries that allow the diffusion of materials between blood and tissues, and veins that bring blood back to the heart. They differ in the structure of their circuits, which is related to differences in respiratory structures. Water-breathing fish have a single-circuit system in which the heart pumps blood, in series, through the gills and tissues. Tetrapods, that include amphibians and mammals, have a double-circuit system, in which the right side of the heart pumps blood through the pulmonary circuit, while the left side of the heart pumps blood through the systemic circuit. It is important to know that both circuits are in series, that blood leaving the pulmonary circuit enters the systemic circuit, and vice-versa. The left and right sides of the heart are joined as a single organ, but can differ in their degree of separation depending on the animal group. In mammals, the two sides of the heart are completely separated, which allows the pulmonary and system circuits to have very different hydrostatic pressures: the low pressure in the pulmonary circuit prevents fluid loss from the thin pulmonary capillaries, while the high pressure of the systemic circuit is essential to propel blood to all organs of the body. In amphibians, there is incomplete separation of the two circuits: although there are two separate atria, a common ventricle pumps blood to the systemic and pulmocutaneous circulatory circuits. The pulmocutaneous circuit brings blood from the heart to the lungs and skin for oxygenation. Oxygenated blood from the lungs goes directly to the left atrium of the heart, while oxygenated blood from the skin mixes with deoxygenated blood from the systemic circulation before returning to the right atrium.

Name the types of blood vessels and briefly describe them.

Arteries - Carry blood away from the heart Veins - Carry blood to the heart; contain valves Capillaries - Sites of exchange Venules - connect capillaries to larger veins Arterioles - small arteries that connect to capillaries

What is the functional distinction between arteries and veins?

Arteries carry blood away from the heart. Veins return blood to the heart.

Which blood vessels have thicker walls, arteries or veins?

Arteries have thicker walls.

What is the difference between blood and plasma?

Blood is the fluid that circulates within a closed circulatory system. It is a complex tissue with multiple components. Plasma is the fluid component of blood in which the blood cells and proteins are suspended.

What is the importance of the skeletal muscle and respiratory pumps?

Blood pressure in veins is low, meaning that only a small force remains to propel blood back to the heart. The skeletal muscle and respiratory pumps assist the return of blood to the heart. When skeletal muscles contract, they squeeze veins, increasing blood pressure in these vessels. Veins outside the thoracic cavity contain valves that allow blood to go only toward the direction of the heart. Therefore the squeezing of veins by skeletal muscles causes blood to move toward the heart because valves furthest from the heart will close, while those closest to the heart will open. Similarly, the respiratory cycle results in alternating low and high pressures in the thoracic cavity. Low pressures (during inhalation) draw venous blood toward the heart, while high pressure (during exhalation) do not result in backflow because valves outside the thoracic cavity close, and in fact compress the veins so that more blood is pushed towards the heart.

Explain the changes in blood pressure as blood flows through the mammalian circulatory system.

Blood, like any fluid, moves from high pressure to low pressure. Accordingly, the highest pressure must be at the start of the circuits (ventricles) while the lowest must be at the end of the circuits (atria). For the systemic circuit, the highest pressure occurs in the left ventricle, where pressure is generated through ventricular contractions. The pressure in the left ventricle is also highly variable, from near zero during diastole to 100-120mmHg (in humans) during systole. The aorta and subsequent large systemic arteries that receive blood from the left ventricles dampen these variations. This dampening of pressure changes occurs as a result of the storage of mechanical energy in the elastic tissues of the arteries. As blood reaches arterioles, there is a large drop in pressure resulting from the high resistance of these vessels (because of the relative small sizes and numbers). Blood continues to travel through capillaries, venules and veins, and pressure gradually drops until it reaches its lowest level, at the end of the circuit (the right atrium). The same pattern occurs in the pulmonary circuit.

What is the cardiac output equation?

CO = HR x SV

Imagine three identical blood vessels arranged either in series or in parallel. In which case will the total resistance be greatest?

Circulatory systems are analogous to electrical circuits. The total resistance of three vessels in series is equal to the sum of their resistances and is thus less than the total resistance of three vessels in parallel as their total resistance decreases with each additional vessel/resistor.

What is the major factor involved in the evolution of closed circulatory systems? Do all animals fit with this general rule?

Closed circulatory systems have evolved independently from ancestral open systems in several animal lineages. The major factor appears to be the ability of closed systems, as a result of their ability to generate high pressure, controlled and directed blood flow, to more efficiently and effectively deliver oxygen to actively metabolizing tissue. Thus, closed systems are usually seen in highly active organisms and in organisms that live in oxygen-limited environments. Insects are an exception to this rule. They do not, however, use the circulatory system as their primary means of gas transport.

Name the three types of capillaries and briefly describe them.

Continuous capillary - Tight junctions Fenestrated capillary - Contain pores Sinusoidal capillary - Fewer tight junctions

What are some possible advantages of a double circulation over a single-circuit circulation?

Double circulation systems allow having vastly different fluid pressures in each circuit. This is important for air breathing vertebrates, because a large pressure in the systemic circuit is essential to insure proper blood flow to all tissues. A low pressure in the pulmonary circuit prevents fluid leakage through the thin pulmonary capillaries, which would lead to reduced gas exchange efficiency.

What are the three types of arteries?

Elastic arteries - Thick tunica externa Muscular arteries Arterioles - Lead into capillaries

Name the layers of the walls of a mammalian heart and describe their structure.

Endocardium: Internal lining of the heart, covering the heart chambers. Made of connective tissue with a layer of epithelial tissues called the endothelium. Myocardium: The thickest layer. The muscular layer that will produce cardiac contractions. Pericardium: Sac enclosing the heart. Composed of two layers separated by a fluid that reduces friction during contraction. The outer layer, or parietal pericardium, is made of connective tissue and anchors the heart to surrounding tissues. The inner layer, or visceral pericardium (also called epicardium), is also made of connective tissue and is continuous with the outer layer of the heart.

chordae tendinae

Fibers attatched to the tricuspid valve which pull it closed when papillary muscles contract, preventing backwash of blood.

After a heart transplant, there is no direct connection between the nervous system and the heart. However, the cardiac output of patients with heart transplants can vary in response to changes in metabolic demand (such as during exercise). How could this be possible? Would you expect this regulation to be as efficient as in a patient with an intact heart?

First, the cardiac muscle is "myogenic" and therefore can undergo spontaneous contractions without any neural or endocrine signals. Second, circulating levels of epinephrine secreted by the adrenal medulla can modulate the force and rate of cardiac contractions during exercise. Because it takes slightly longer for circulating epinephrine to act compared to norepinephrine released by sympathetic nerves, and because of the absence of a circulating antagonist (acetylcholine can affect the heart only by being secreted by parasympathetic neurons), the response is likely to be slower; slower to increase during exercise and slower to decrease after exercise.

Would resistance be higher in an arteriole or a vein, and why?

First, there is a question of size: arterioles have a smaller radius than veins (venules would have a comparable diameter to arterioles) and would therefore offer a much larger resistance (resistance if proportional to the fourth power of the radius). Second, there is a question of compliance: veins are far more compliant than arterioles, which means that in response to an increase in fluid pressure, their diameter will increase, thus reducing resistance.

What physical force causes fluids to flow in circulatory systems?

Fluids are moved via pressure gradients in circulatory systems. All circulatory systems have some type of pumping structure that propels fluid around the system. The pressure generated by this pump may be supplemented by one or more of elastic recoil in the arteries, body movements and/or peristalsis.

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What is the difference between an open circulatory system and a closed circulatory system?

In a closed circulatory system, the circulatory fluid remains within blood vessels at all points in the circulatory system. In an open circulatory system, the circulating fluid enters a sinus at least at one point in the circulating system and thus comes in direct contact with the tissues.

Compare the mechanism of filling of a mammalian heart and an insect heart.

Insects have an open circulatory system, consisting of multiple hearts, most of them along a dorsal vessel, that pump hemolymph toward the anterior part of the body. Body movements refill the hearts with hemolymph from the body cavity. Mammals have a closed circulatory system in which blood is fully enclosed. As a result, there is a constant pressure gradient along the circuit, which is large enough to refill the heart from blood coming back in from the veins.

Name the 4 types of fluids found in circulatory systems and define them.

Interstitial fluid - extracellular fluid that directly bathes the tissues. Blood - fluid that circulates within a closed circulatory system. Lymph - fluid that circulates in the secondary system of vertebrates called the lymphatic system. Hemolymph - fluid that circulates within an open circulatory system

What is isovolumetric (or isovolumic) contraction?

Isovolumetric contraction represents the initial phase of ventricular contraction. As the AV and semilunar valves are closed, the volume of ventricular blood does not change and the pressure associated with that blood increases sharply.

What would happen if the connection between the AV node and the bundle of His were blocked (in a way that didn't directly affect any other parts of the heart)?

Many cardiomyocytes have pacemaker capacity, the ability to undergo spontaneous and rhythmic depolarizations. If the normal conducting pathway was blocked, the result could be cardiac arrhythmia: the atria may depolarize "normally" as a result of action potentials initiated by the sino-atrial node, while the ventricles may depolarize independently, at their own rhythm, because of action potentials initiated by other cells. The result would be highly inefficient cardiac contractions, because the capacity of the heart to pump blood depends on the coordinated depolarization/contraction events.

Does myogenic autoregulation play an important role in changing blood flow to tissues as oxygen demand increases? (Justify your answer)

Myogenic autoregulation acts as negative feedback loop to maintain blood flow to tissue at a constant level. However, the metabolic activity of a tissue and its demand for oxygen can vary with time, and thus the need for blood flow also varies.

What is the difference between a neurogenic heart and a myogenic heart?

Neurogenic hearts, typical of most arthropods, contract in response to signals from the nervous system. Myogenic hearts, like the mammalian heart, contract in response to signals generated within the muscle.

Name the two types of circulatory systems and define them.

Open - circulatory fluid comes in direct contact with the tissues in spaces called sinuses. Closed - circulatory fluid remains within the blood vessels and does not come in direct contact with the tissues.

What does the P, QRS, and T waves correspond to in an EKG?

P = Atrial contraction, depolarize QRS = Ventricular contraction, ventricles depolarize, atria repolarize. T = Ventricular contraction, ventricles repolarize

Heart Rate (HR)

Rate of contraction

How can substances move across capillaries?

Substances typically move across capillaries via diffusion.

Cardiac Output (CO)

The amount of blood the heart beats per unit time (min)

Stroke Volume (SV)

The amount of blood the heart pumps with each beat

Compare and contrast the heart of an amphibian and a mammal.

The amphibian heart is three chambered with two atria and one ventricle. The ventricle pumps blood into both the pulmonary and systemic circuits. A spiral fold within the conus arteriosus directs the deoxygenated blood to the pulmocutaneous artery. The mammalian heart has four chambers, two atria and two ventricles, with one ventricle pumping blood to the pulmonary circuit via the pulmonary artery and one pumping blood to the systemic circuit via the aorta.

Pulmonary trunk

The artery that carries venous blood from the right ventricle of the heart and divides into the right and left pulmonary arteries

Define heart rate, stroke volume, and cardiac output. Explain how changes in heart rate or stroke volume affect cardiac output.

The cardiac output is the rate of fluid pumping, or the volume of blood pumped per unit of time. It depends on heart rate, the number of contractions per unit of time, and on the stroke volume, the amount of blood pumped per contraction. Changes in either heart rate or stroke volume will alter cardiac output. Norepinephrine from sympathetic neurons and epinephrine from the adrenal medulla can increase heart rate and stroke volume. Heart rate increases as a result of the opening of Na+ (Funny) and Ca++ channels that increase the rate of depolarization of pacemaker cells, and in an increase in the speed of depolarization along the conduction pathway. The rate and the force of contraction increase as a result of four mechanisms triggered by these chemical signals: 1) increased membrane permeability to Ca++ during depolarization 2) increase in the release of Ca++ by the sarcoplasmic reticulum in response to action potentials 3) increase in ATPase activity of myosin heads 4) increase in the Ca++ ATPase activity, which increase the rate of relaxation between contractions. Acetylcholine from parasympathetic neurons can decrease heart rate and stroke volume. Heart rate decreases as a result of the opening of K+ channels that lead to a hyperpolarization of pacemaker cells. The stroke volume decreases as a result of a reduction in the intracellular Ca++ signal.

What is the influence of the skeletal muscle pump on venous return to the heart?

The contraction of skeletal muscle squeezing the veins and forcing the valves that are farthest from the heart to close and those that are closer to open facilitates the movement of blood back to the heart.

What is vasomotor tone?

The degree of contraction of the smooth muscles surrounding the arterioles.

Increased heart rate can greatly reduce diastolic filling time, but has less impact on systolic ejection time. Why?

The diastolic filling time is directly dependent on heart rate, as a faster heart reduced the time between contractions. The systolic ejection time depends mostly on how long it take for ventricles to build up enough pressure to eject blood in arteries, which depends on arterial pressure and cardiac contractility, but not on heart rate.

Explain how the large arteries (such as the aorta) dampen pressure fluctuations and even out blood flow across the cardiac cycle.

The elastic expansion of the aorta and large arteries during systole and the subsequent contraction during diastole reduces the rise in pressure during the former and the fall during the latter, resulting in a more even blood flow across the cardiac cycle.

Which type of animal would you expect to have a higher proportion of spongy myocardium, a fish or a mammal?

The fish would be expected to have a higher proportion of spongy myocardium. Spongy myocardium is poorly vascularized and receives oxygen from blood flowing through the heart. Mammalian myocardium consists largely of compact myocardium which is supplied with oxygen by the coronary arteries.

What are the major factors that determine the resistance of a tube such as a blood vessel?

The major factors that determine the resistance of a tube are its length, its radius, and its viscosity.

Compare and contrast the molecular events of the action potential in the pacemaker cells of the sinoatrial node to those in a ventricular contractile cardiomyocyte.

The membrane of the pacemaker cells of the sinoatrial node is unstable and continuously depolarizes and repolarizes in response to ion transport through voltage-gated K+ and Ca2+ channels and funny Na+ channels. The action potential of a contractile cardiomyocyte is initiated by an electrical stimulus that exceeds the threshold needed to open voltage-gated Na+ channels. Their closure and the opening of voltage-gated K+ channels are counterbalanced by the opening of voltage-gated Ca2+ channels delaying repolarization.

What is the significance of the difference in pressure developed by the right and left atria of a mammalian heart?

The pressure developed during atrial contractions contributes to a small increase in the blood volume contained in ventricles; most of the blood entering the ventricles enters passively, as a result of venous pressure.

Describe the mechanisms that control the radius of the arterioles.

The walls of arterioles contain smooth muscles. Contractions of these smooth muscles will decrease the radius of arteriole, and the reverse when the muscles relax. There are a number of mechanisms that control the activity of these smooth muscles, and therefore that affect the diameter of arterioles. Myogenic autoregulation: smooth muscles can be stimulated to contract in response to stretch, which results in a relatively constant size of arterioles when blood pressure changes. Tissue metabolic activity: Changes in the physical or chemical conditions of a tissue that are associated with an increase in activity (decreased O2 or pH, increased CO2) will result in the relaxation of smooth muscles. As a result, tissues that have greater needs for oxygen, nutrients and waste elimination will receive more blood than tissues with lesser needs. This can be triggered directly by changes in the physicochemical variables, or indirectly through a variety of paracrine signals. Neural and endocrine controls: Norepinephrine from the sympathetic nervous system generally causes vasoconstriction (although local intrinsic controls can override this response); vasopressin (ADH) and angiotensin II generally causes vasoconstriction; atrial natriuretic peptide generally causes vasodilation.

What types of cell walls do arteries have?

Thick tunica externa and tunica media

Why is the lengthy refractory period of a contractile cardiomyocyte important for the function of the mammalian heart?

To be an efficient pump, the heart must constantly alternate between a state of contraction and relaxation; it cannot be in a state of constant contraction, or tetanus, as skeletal muscles can. The refractory period lasts almost as long as the muscle twitch, which prevents a state of tetanus, or sustained contraction, from occurring.

What is transmural pressure?

Transmural pressure is the pressure difference across the wall of a chamber.

Name the three layers of artery and vein walls.

Tunica intima Tunica media Tunica externa

What is the difference between the velocity of the blood and the rate of blood flow? How are these two concepts related?

Velocity is the speed at which a drop of blood travels, in units of distance per time, while the rate of blood flow is the volume of blood passing through a region per unit of time. The relationship between the two is that velocity is equal to flow rate divided by the surface area of the vessel. As a consequence, everything else being equal, increasing velocity in a vessel will increase its flow rate. However, a vessel with a high blood velocity can have a lower flow rate than a vessel with a lower velocity if its surface is smaller. Similarly, everything else being equal, increasing the flow rate in a given vessel will increase its blood velocity, but a vessel with a high flow rate can have a lower velocity than a vessel with lower flow rate if its surface area is larger.

Aortic blood flow starts to increase only some time after the initiation of ventricular contraction. Similarly, aortic blood flow continues at a relatively high level well into the diastolic period. Explain why.

When ventricular contraction occurs, the pressure in the left ventricle is initially below that of the pressure in the aorta. The ventricle must build up enough pressure to exceed aortic pressure before blood is ejected into the aorta; this period is called the isovolumetric contraction, during which time the ventricle contracts but blood does not flow out of the ventricle into the aorta. While blood is flowing through the aorta, during ventricular ejection, the high resistance of the systemic circuit combined with the elasticity of the aorta leads to the storage of mechanical energy in the walls of the aorta. This mechanical energy is released when the ventricle relaxes, which results in the maintenance of a high aortic pressure, allowing blood to continue flowing throughout the diastolic period. This maintenance of a high aortic pressure by the storage of mechanical energy is what will cause the isovolumetric contraction when the next ventricular diastole occurs.

Systole

contraction of the heart

Arteries _____ pressure fluctuations.

dampen

Briefly describe the reptile heart.

• 3 chambers - 2 atria - 1 ventricle • Incomplete septum

Briefly describe the frog heart.

• 3 chambers - 2 atria - 1 ventricle • No septum • Some mixing of blood

Briefly describe the bird and mammal heart.

• 4 chambers - 2 atria - 2 ventricles • Complete septum - Interatrial - Interventricular • No mixing

Name the main parts of the mammalian heart.

• 4 chambers - Right atrium - Right ventricle - Left atrium - Left ventricle • Base • Apex

Name the two main valves of the heart and their subvalves.

• Atrioventricular (AV) valves - Tricuspid valve - Mitral (bicuspid) valve • Semilunar valves - Pulmonary valve - Aortic valve

Name the parts of the left side of the heart.

• Left atrium - 2 right pulmonary veins - 2 left pulmonary veins - Oxygenated blood • Left ventricle - Sends blood to tissues • Aorta

Name the functional circuits of the circulatory system and briefly describe.

• Pulmonary circuit - Right side of the heart - Heart‐ lungs‐ heart • Systemic circuit - Left side of heart - Heart‐ tissues‐ heart

Name the parts of the right side of the heart.

• Right atrium - Superior vena cava - Inferior vena cava - Coronary sinus • Right ventricle - Sends blood to lungs • Pulmonary trunk

Briefly describe the fish heart.

• Single circuit heart - 1 atrium - 1 ventricle

Where is blood velocity the highest and the lowest?

•Highest in arteries •Lowest in capillaries

Describe the blood pressure in the left ventricle and the arterioles.

•Left ventricle -Blood pressure highest and most variable •Arterioles -Blood pressure drops rapidly -Most resistance

Describe the "LUB‐DUB" of the heart.

•Lub - Atrioventricular (tricuspid and mitral) valves close. •Dub - Semilunar (pulmonary and aortic) vales close

Briefly describe cardiac action potentials.

•Sodium gates close •Calcium gates open •Plateau phase •Extended refractory phase