Unit 8 - TYU Quiz
Describe the steps in a full cardiac cycle (7 steps)
1. starts -60 mV (resting) increases slowly to gradual depolarization (aka pacemaker potential) 2. this is from Na+ slowly flowing in without the compensation of K+ moving out 3. rate of spontaneous depolarization is fastest in sinoatrial node 4. when pacemaker potential hits -40 mV voltage regulated 5. Ca2+ channels open and Ca2+ come in from ECF and depolarizes 6. once reaches 0 mV then K+ channels open and enter which makes interior plasma membrane increase in negativity and falls (repolarization phase) 7. once repolarized K+ channels close repeat for next heart beat
Identify the types of capillaries and discuss how their structure relates to their function.
3 types: continuous, fenestrated and discontinuous. Continuous - network of capillaries where endothelial cells are closely attached as there are no intracellular pores; this limits movement of substances to very small molecules such as gases and water. Exchange takes place mostly through pinocytosis across the capillary membrane. Located in muscle, adipose tissue, lungs and the central nervous system (including the blood-brain barrier). Fenestrated - endothelial cells are separated by large intercellular pores or 'fenestra' to allow movement of molecules. The pores are lined with a layer of mucoprotein to restrict entry of large molecules (proteins) from entering. Located in areas where there is substantial movement of substance with systemic circulation (i.e. the endocrine glands, kidney and intestines). Discontinuous - mostly found in the liver, spleen and bone marrow. They have the largest opening between the endothelial cells, allowing passing of large molecules such as proteins, red and white blood cells.
Identify the channel(s) and movement of ions which result in myocardial depolarization
A stimulus opens voltage-regulated Na+ gates allowing inward diffusion of Na+ which causes depolarization. low Ca+ channels allow for inward diffusion of Ca+.
Discuss how baroreceptors, chemoreceptors and proprioceptors can influence HR through the cardiac control center.
All 3 send sensory information to the cardiac control center, which in turn will regulate the heart rate accordingly. Baroreceptors: pressure sensors in the aorta and carotid arteries; detect increase in blood pressure and will increase its firing rate to the cardiac control center. Conversely, decrease in blood pressure will cause a decrease in firing rate. Chemoreceptors: pH sensors found in the aortic arch, carotid arteries and medulla oblongata. These sensors detect changes in blood pH, oxygen and carbon dioxide and relays information to the cardiac control centre to increase heart rate if blood pH is low due to slow removal of carbon dioxide. Proprioceptors: receptors found in muscles and joints. These sensors are activated upon start of exercise and will quickly relay information to cardiac centre to increase heart rate.
Define the absolute refractory and relative refractory periods of myocardial action potentials and when they occur
An absolute refractory period is a period of time when a region of the muscle cell membrane cannot be stimulated to produce an action potential. This period occurs during ventricular contraction, and this ensures that the ventricles complete their contraction from the first stimulus. A relative refractory period is when a region of muscle cell membrane can be stimulated to produce an action potential but only by a very strong stimulus. This period begins when the ventricles are finishing contraction.
Define ectopic pacemaker
An ectopic pacemaker is a group of cells that are able to produce action potentials, but this does not include the SA node. An example would be AV node and purkinje fibers.
Identify major vessels of the heart including: aorta, pulmonary trunk, pulmonary arteries, pulmonary veins, superior vena cava and inferior vena cava
Aorta- largest artery receiving blood from left ventricle; takes blood to systemic circulation Pulmonary trunk- connects with pulmonary arteries. collects blood from right ventricle and delivers it to pulmonary arteries where it is sent to pulmonary circulation Pulmonary veins: receives blood from the lungs and sends it to left atrium superior/inferior vena cava: receive systemic blood and take it to right atrium
Identify the layers of an artery and indicate properties of each layer.
Artery: 1. Tunica externa: connective tissue (collagen) to provide stability 2. External Elastic Membrane: contains elastin fibres to allow for stretching of vessel when under high pressure from ventricular contraction, followed by the ability to recoil, driving blood through the circulatory system during diastole (relaxation phase). 3. Tunica media: smooth muscle 4. Internal Elastic Membrane: contains elastin fibres to allow for expansion of vessel under pressure 5. Tunica interna: includes the endothelium (lines lumen of blood vessel); basement membrane made of glycoproteins and connective tissue; elastin (elastic fiber)
Identify chambers and areas of the heart including: atria, ventricles, auricles, anterior interventricular sulcus, interventricular spectrum, interatrial spetum
Atria- 2 top left and right chambers receiving blood from pulmonary and systemic circulations, respectively. Ventricles- 2 bottom left and right chambers receiving blood from the atria. Auricles- pouches attached to atria that receive blood and send it to ventricles. Anterior interventricular sulcus- groove that separates the right and left ventricles Interventricular spectrum (septum?): wall that separates the ventricles Interatrial septum: wall that separates atria
Correlate the P, QRS, and T wave to phases of the cardiac cycle
Atrial contraction (P wave) occurs at the end of diastole. Ventricular contraction (QRS wave) occurs through the duration of systole and ends at the middle of the T wave (which is repolarization of the ventricles). The plateau that occurs after the T wave is the beginning of diastole (ventricular relaxation).
Define: automaticity, conductivity
Automaticity: the cardiac cells ability to spontaneously depolarize Conductivity: the ability of the heart to transmit electrical activity
Describe the blood flow through the left and right side of the heart and associated vessels
Blood that is low in oxygen is returned to the right side of the heart from systemic circulation via the superior and inferior vena cava where it drains into the right atrium. Blood flows from the right atrium to the right ventricle through the tricuspid valve (right AV valve). The right ventricle will contract, forcing the pulmonary valve (semilunar valve) to open, and blood to flow to the lungs via the pulmonary tract and arteries (pulmonary circulatory system). Pulmonary veins return oxygenated blood to the left side of the heart into the left atrium. Blood flows from the left atrium into the left ventricle through the bicuspid/mitral valve (left AV valve). The left ventricle will contract, forcing the aortic valve (semilunar valve) to open, and blood to be pumped through the aorta where it enters systemic circulation.
Define: chronotropic, inotropic, dromotropic
Chronotropic: mechanisms affecting cardiac rate either positively or negatively. Inotropic: mechanisms that alter the force/energy of contractions either positively or negatively Dromotropic: mechanisms that affect the speed of conduction in the AV node and the rate of electrical impulses
Describe how relaxation occurs after contraction in cardiomyocytes
Contraction occurs via the action of calcium. When an action potential moves through the sarcolemma and T-tubules. T-tubules are surrounded by sarcoplasmic reticulum, and when an action potential travels down these T-tubules, voltage-gated calcium channels open, allowing a large amount of calcium to flood through into the sarcoplasm. Calcium binds troponin which allows the thin and thick filaments to slide across eachother causing a contraction. After contraction, calcium is released from troponin and sequestered back into the sarcoplasmic reticulum. Once calcium is sequestered, troponin changes shape, covering the myosin-binding site on actin. This leads to the relaxation of the muscle.
Identify factors that determine driving forces and resistance and those that affect blood viscosity, length of vessels and vessel radius.
Driving Forces: - Difference in pressure (ΔP) Resistance: - radius of blood vessel - blood viscosity - vessel length Blood Viscosity - Dehydration; Polythemia: (high red blood cell count due to high altitudes/blood doping) will cause an ↑ blood viscosity, ↑ resistance, ↓ blood flow Vessel Length - constant Vessel Radius - Vasoconstriction: ↓ vessel radius, ↑ resistance, ↓ blood flow - Vasodilation: ↑ vessel radius, ↓ resistance, ↑ blood flow
Discuss the importance of ECGs. Describe what makes the waveforms on an ECG
ECG is an important non-invasive procedure to assess cardiac function and identify possible cardiac pathologies. Electric activity generated by the heart (i.e. action potentials and its movement through the conduction system) travels through body tissues and is picked up by sensors located on the body surface. Differences in electrical potential between the sensors is recorded and plotted against time to produce the characteristic waves we see on an ECG. P wave: depolarization/contraction of atria. QRS wave: depolarization/contraction of ventricles. Atrial repolarization takes place in the QRS wave. We do not see a separate wave since it is masked by the contraction of ventricles. T wave: repolarization of ventricles.
Define: end-diastolic volume, stroke volume, end-systolic volume, ejection fraction
End-diastolic volume: total volume of blood in the ventricles at the end of diastole Stroke volume: ⅔ of the blood ejected from the ventricles during ventricular contraction End-systolic volume: ⅓ of the blood remaining in the ventricles after the stroke volume has been ejected. Ejection fraction:ventricular pressure is higher than that of the aorta/pulmonary arteries, forcing the semilunar valve open and ejecting blood into these arteries.
Describe the HCN channels and how they are influenced by the sympathetic nervous system
HCN channels (hyperpolarization-activated cyclic nucleotide-gated channels) are cardiac pacemaker channels opened by cAMP. Under stimulation of the sympathetic nervous system, diastolic depolarization occurs faster because catecholamines stimulate B1-adrenergic receptors increasing production of cAMP which causes a prolonged duration in open channels. This results in a faster heart rate.
Discuss what produces the heart sounds and when over the cardiac cycle
Heart sounds are detected with a stethoscope. The lub-dub sounds that you hear with a stethoscope correspond to the closing of heart valves during one cardiac cycle. 'Lub': closing of AV valves (isovolumetric contraction) 'Dub': closing of semilunar valve (isovolumetric relaxation)
Relate volume and pressure changes over the cardiac cycle and indicate: isovolumetric contraction, isovolumetric relaxation, ejection, rapid filling
Isovolumetric contraction: Volume (ventricle)- increases to maximum volume; Pressure (ventricle)- huge increase Ejection: Volume(ventricle)- decrease; Pressure (ventricle) increase followed by decrease in pressure Isovolumetric Relaxation: Volume(ventricle)- decrease to lowest volume; Pressure (ventricle)- low pressure (no change) Rapid Filling: Volume(ventricle)- increase in volume; Pressure (ventricle)- low pressure Atrial contraction: Volume(ventricle)- increase in volume; Pressure (ventricle)- increase in pressure
Define isovolumetric contraction, isovolumetric relaxation
Isovolumetric contraction: this is the phase when the ventricles begin to contract, but are neither ejecting blood or filling with blood. Isovolumetric Relaxation: During this phase, volume in the ventricles is not changing. This occurs after blood has been ejected into the arteries, and the greater pressure in the arteries closes the semilunar valves. Pressure in the ventricles is still greater than that of the atria, so the AV valves are still closed.
Identify major values and value components including: mitral, left and right atrioventricular, discuspid, trisuspid, aortic valve, pulmonary valve, chordae tendineae, papillary muscle
Mitral (bicuspid): valve between left atrium and L ventricle Tricuspid: valve between right atrium and L ventricle aortic valve: valve connecting L ventricle with aorta pulmonary valve: valve connecting R ventricle with pulmonary arteries chordae tendinae: rope like structure that connects papillary muscles to tri/bicuspid valves papillary muscle: prevent tri/bicuspids from inverting, ultimately preventing backflow of blood during systole
Indicate the major driving forces of blood throughout the body
Most of the driving force comes from the ventricles contracting (in pulmonary and systemic system) and is dependent on the continuous pressure from the large veins about 25% of the filling of the ventricles is by contraction of the atria and the rest comes from flow of blood into the ventricles under the pressure in the returning venous blood
Describe myocardial excitation-contraction coupling. Discuss calcium induced-calcium release
Myocardial excitation-contraction triggers the contraction of cardiac muscles and depends on the Ca2+ induced- Ca2+ release. Calcium released from the sarcoplasmic reticulum will bind to troponin on the sarcomere fiber, triggering contraction of the cardiac muscle. An action potential will trigger the opening of voltage-gated Ca2+ channels on the plasma membrane of myocytes, causing movement of Ca2+ into the cell. This small influx of intracellular Ca2+ further stimulates opening of Ca2+ channels in the sarcoplasmic reticulum, releasing large quantities of Ca2+ into the cell's cytoplasm.
Describe the myocardial resting membrane potential, depolarization and repolarization
Myocardial resting membrane potential is about -85 mV. Depolarization of these cells occurs when they are stimulated by an action potential reaching a threshold which is about -40mV. This depolarization is maintained for 200-300 ms (which is longer than most muscle membrane potentials). A quick repolarization occurs with K+ diffusing out.
Identify the blood supply to the heart including: opening of coronary arteries, left and right coronary arteries, cardiac veins, coronary sinus
Opening of coronary arteries - The semilunar valve contains three cusps/flaps that contain the opening to the coronary arteries. These flaps are forced shut when the ventricle pushes blood past them. When the heart relaxes between beats (diastole), these openings receive blood gently from the backflow of the aorta
Describe the pacemaker of the mammalian heart
Pacemaker cells directly control the heart rate by contracting the heart through initiating electrical impulses (action potentials).
Describe how the potassium channels are influenced by the parasympathetic NS
Parasympathetic nervous system decreases diastolic depolarization because ACh released in response to stimulation of the parasympathetic NS results in opening of K+ channels. Outward diffusion of K+ out of pacemaker cells slows the time required for diastolic depolarization to reach threshold, resulting in a slower heart rate.
Predict changes in inotrophy, chronotrophy and dromotrophy after sympathetic and parasympathetic stimulation of the heart
Parasympathetic stimulation negatively affects inotrophy, chronotrophy and dromotrophy. So, cardiac rate would be lowered, force of contractions would be lowered and rate of electrical impulses would be decreased. Sympathetic stimulation has the opposite effect. Cardiac rate, force of contractions and rate of electrical impulses would all be increased under sympathetic stimulation.
Describe the pulmonary and systemic circuits of the mammalian cardiovascular system
Pulmonary circuit distributes blood returning from rest of body into lungs for exchange of oxygen and CO2. systemic circuit distributes oxygenated blood coming from lungs around rest of body
Identify the channel(s) and movement of ions which results in repolarization of the myocardial action potential
Repolarization is produced from the opening of K+ channels and movement out of the cell. Ca2+ concentration is lowered in the cytoplasm via Ca-ATPase pump and Na+-Ca2+ exchanger.
Define rhythmicity, excitability, contractility
Rhythmicity: spontaneous depolarization and repolarization occurring in stable, repeated cycles Excitability: the ability of the cardiac cells to respond to electrical stimulus Contractility: intrinsic ability of the heart to contract
Describe mechanisms that facilitate venous return to the heart. (3 mechanisms)
Skeletal Muscle Pump: contraction of surrounding skeletal muscle compresses veins and propels blood forward in a massaging motion. Venous Valves: closure of valves prevents backflow of blood, ensuring one way flow back to the heart. Breathing: contraction of the diaphragm during inspiration causes a difference in pressure between the abdomen (high pressure) and thoracic cavity (low pressure). This pressure difference in conjunction with squeezing of abdominal veins helps pump blood against gravity as it travels upward towards the heart.
Identify the PR and ST interval and indicate their significance to the cardiac cycle
The PR interval refers to the beginning of atrial depolarization (P wave) and the beginning of ventricular depolarization (Beginning of QRS wave). This is the end of diastole in the cardiac cycle. Normally 0.12-0.2s in duration. Damage to AV node (AV node block) is evident in this interval. First degree block-occurs when rate of impulse conduction through AV node exceeds 0.2s. Second degree block- AV node so damaged that only one of every 2,3 or 4 atrial electrical waves can pass through to ventricles (shows P wave with not associated QRS waves). Third degree block (complete block)- none of atrial waves can pass through to ventricles (ectopic pacemaker, purkinje fibers, still active). The ST interval refers to ventricular depolarization and repolarization. This is systole in the cardiac cycle.
Describe the path of an action potential through the conduction system
The SA node spontaneously depolarizes, and once it reaches a threshold of -40 mV, an action potential is produced and is conducted at about 1m/sec and reaches the AV node in 50 ms. This action potential is spread throughout the atria via Bachmann's bundle causing the atria to contract simultaneously. Once at the AV node, the signal slows down to about 0.05m/sec. The signal is conducted from the AV node down to the bundle of His and finally the purkinje fibers at about 4m/sec. Since the purkinje fibers are embedded within the walls of the ventricles, this causes the ventricles to contract.
Describe the intrinsic rate of the sinoatrial (SA) and atrioventricular (AV) nodes and factors which can increase and decrease the rate
The SA node will spontaneously generate an action potential every 0.8 seconds which translates to resting heart rate of 60-100 beats per minute (bpm). The AV node can also generate an action potential, but at a slower rate than the SA node. Therefore, if the SA node does not fire, the AV node will generate an action potential. This would translate to a lower heart rate (40-50 bpm). Under normal conditions, action potential from the SA node will suppress the action potential from the AV node. Stimulation of the sympathetic nervous system would increase the rate of action potential generation, whereas, stimulation of the parasympathetic nervous system would decrease the rate.
Discuss how the autonomic nervous system can alter pacemaker potentials of the SA node
The autonomic nervous system release epinephrine and norepinephrine; this increases the rate of depolarization by stimulating β1-adrenergic receptors and production of cAMP within the cells. This causes opening HCN channels open and influx of Na+ and allows the cell to reach threshold faster; this ultimately causes an increase in heart rate. Alternatively, the release of acetylcholine causes opening of K+ channels, increasing the amount of K+ leaving the pacemaker cell. This slows down depolarization since it takes longer for the cell to reach threshold; this ultimately causes a decrease in heart rate.
Identify the morphology of the P, QRS, and T waves
The beginning of the cardiac cycle begins with a P wave. The P wave is formed from atrial depolarization. It is characterized as a small upright peak. The QRS wave is formed from ventricular depolarization. It is characterized as a small downward peak (Q), a large upward peak (R) and another small downward peak (S). A short plateau occurs after the QRS wave, and finally the T wave is produced from repolarization of the ventricles which forms a small upward peak.
Describe the functional syncytium of the heart and indicate its importance in cardiac physiology
The heart cells are all connected together by gap junctions forming a myocardium, which is a single functioning unit. These gap junctions allow action potentials to be distributed along the entirety of this unit. This is important because portions of the heart (atria and ventricles) need to contract/relax as a unit simultaneously and this is done via the gap junctions.
Identify the significance of the plateau phase of the myocardial action potential
The plateau phase is caused by a slow inward diffusion of calcium occurring at the same time as a slow outward diffusion of K+. This plateau phase occurs at the same time as the refractory period, which prevents summation and tetanus from occurring. This allows the myocytes to contract, which means they have a more sustained contraction which is necessary for expulsion of blood from the heart chambers against pressure in arterial circulation.
Indicate RMP and threshold potentials of the sinoatrial node
The resting membrane potential of the SA node is about -60 mV. The threshold potential is about -40 mV.
Discuss the role of the sarcoplasmic reticulum in myocardial excitation-contraction coupling
The sarcoplasmic reticulum acts as a storage chamber for calcium. When an action potential moves across the sarcolemma and down the T-tubules, the action potential causes voltage-gated calcium channels to open allowing a small amount of calcium in which induces the opening of calcium release channels on the sarcoplasmic reticulum to open allowing a large amount of calcium into the sarcoplasm, ultimately stimulating contraction.
Identify tissues that are capable of automaticity in the heart
Tissues that are capable of automaticity in the heart are: SA node, AV node and purkinje fibers
Identify the layers of a vein and capillary and indicate properties of each layer.
Vein: 1. Tunica externa: connective tissue; 3. Tunica media: smooth muscle 5. Tunica interna: includes the endothelium (lines lumen of blood vessel); basement membrane made of glycoproteins and connective tissue; elastin (elastic fiber) Capillaries are composed of a single layer of endothelium, allowing for rapid exchange between blood and tissues.
Define: venous return, diastole, systole, end diastolic volume, end systolic volume
Venous return: flow of blood from systemic circulation that is returning to the right atrium diastole: the portion of cardiac cycle when the ventricles are relaxed; lasts 0.5s systole:portion of cardiac cycle when ventricles are contracting; lasts 0.3s End diastolic volume: total volume of blood in the ventricles at the end of diastole End systolic volume: last ⅓ portion of blood left in the ventricles during systole; the other ⅔ is ejected as stroke volume
Identify the channel(s) and movement of ions which results in the plateau phase of the myocardial action potential
Voltage-gated slow calcium channels allow for a slow inward diffusion of calcium, and K+ channels allow for slow outward diffusion of K+ during the plateau phase of myocardial action potential.
State the proportion of blood flow due to the ventricles and atria
When ventricles contract, they only eject about ⅔ of the blood they contain. Rapid filling occurs when pressure of ventricles falls below that of atria, which fills the ventricles with blood. Atrial contractions only push about 20% of blood into the ventricles.
Discuss the functional significance of the gap junctions in myocardial cells
the atria and ventricles are a large group of muscle cells electrically coupled by gap junctions, when an ap (action potential) is triggered in either the atria or ventricles it will quickly spread across the entire mass of myocardial cells (essentially synchronous contraction) (uterus is also like this during end of pregnancy, and other muscle systems are NOT like this)