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43 Cards in this Set
- Front
- Back
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Cardiac Cycle What is it? |
Repeating pattern of contraction and relaxation of the heart. • Systole: contraction of heart muscles • Diastole: relaxation of heart muscles (referring to the ventricles) |
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Cardiac Cycle |
Ventricles begin contraction, pressure rises, and AV valves close (lub). Pressure builds, semilunar valves open, and blood is ejected into arteries. 3. Pressure in ventricles falls; semilunar valves close (dub). 4. Pressure in ventricles falls below that of atria, and AV valve opens. Ventricles fill. 5. Atria contract, sending last of blood to ventricles |
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Heart Sounds |
• Produced by closing valves - “Lub” = closing of AV valves (Occurs at ventricular systole)
- “Dub” = closing of semilunar valves
Both are physical sounds of the valves closing |
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ECG and Heart Sounds |
• Lub occurs after the QRS wave. • Dub occurs at the beginning of the T wave.
There are not caused by each other!! |
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Heart Murmur |
• Abnormal heart sounds produced by abnormal blood flow through heart. • Many caused by defective heart valves.
• Mitral stenosis: Mitral valve (bicuspid) calcifies and impairs flow between left atrium and ventricle. |
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Heart Murmur |
• Incompetent valves: do not close properly - May be due to damaged papillary muscles
• Septal defects: holes in interventricular or interatrial septum (Blood crosses sides.) |
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Physical Laws Describing Blood Flow |
Blood flows through vascular system when there is pressure difference (∆P) at its two ends • Flow rate is directly proportional to difference (∆P = P1 - P2) |
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Blood Vessels |
Innermost layer of all vessels is the endothelium Capillaries are made of only endothelial cells Arteries & veins have 3 layers called tunica externa, media, & interna • Externa is connective tissue • Media is mostly smooth muscle • Interna is made of endothelium, basement membrane, & elastin
Although have same basic elements, arteries & veins are quite different |
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Arteries |
Large arteries are muscular & elastic Contain lots of elastin so very elastic Expand during systole & recoil during diastole Helps maintain smooth blood flow during diastole Serve as rapid transit pathway to the tissues and pressure reservoir during diastole |
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Arterioles |
Small arteries & arterioles are muscular • Mostly connect to capillary beds |
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Capillaries: the business end! |
Smallest blood vessel: 7−10 μm in diameter Single layer of simple squamous epithelium tissue in wall Where gases and nutrients are exchanged between the blood and tissues Blood flow to capillaries is regulated by: •No cell is more than 80um away from a capillary WHY? * |
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Capillaries |
• Provide extensive surface area for exchange • Blood flow through a capillary bed is determined by state of precapillary spincters of arteriole supplying it |
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Types of Capillaries |
1. Continuous capillaries, endothelial cells are tightly joined together • Have narrow intercellular channels that permit exchange of molecules smaller than proteins • Present in muscle, lungs, adipose tissue
2. Fenestrated capillaries have wide intercellular pores • Very permeable
3. Discontinuous capillaries have large gaps in endothelium • Are large & leaky • Present in liver, spleen, bone marrow. |
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Exchange of Fluid between Capillaries & Tissues |
• Distribution of ECF between blood & interstitial compartments is in state of dynamic equilibrium
• Movement out of capillaries is driven by hydrostatic pressure exerted against capillary wall - Promotes formation of tissue fluid - Net filtration pressure= hydrostatic pressure in capillary (17-37 mm Hg) - hydrostatic pressure of ECF (1 mm Hg) |
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Capillary filtration
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~ 24 liters/day! ...but only 21 liters enters venous end of capillary Where does the 3 liters go? Lymphatic system! (blood pressure vs osmotic pressure) see figure |
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Cutaneous Blood Flow |
The skin can tolerate the greatest fluctuations in blood flow. The skin helps control body temperature in a changing environment by regulating blood flow = thermoregulation. • Increased blood flow to capillaries in the skin releases heat when body temperature increases. • Sweat is also produced to aid in heat loss. • Vasoconstriction of arterioles keeps heat in the body when ambient temperatures are low. |
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Thermoregulation is aided |
aided by arteriovenous anastomoses, which shunt blood from arterioles directly to venules |
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Veins |
• Contain majority of blood in circulatory system • Capacitance vessels • Contain very low pressure (about 2mm Hg) |
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Venous Return, continued |
Veins hold most of blood in body (70%) & are thus called capacitance vessels • Have thin walls & stretch easily to accommodate more blood without increased pressure (=higher compliance) • Have only 0-10 mm Hg pressure |
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Venous Return |
Is return of blood to heart via veins
Blood is moved toward heart by contraction of surrounding skeletal muscles (skeletal muscle pump) • & pressure drops in chest during breathing
• 1-way venous valves ensure blood moves only toward heart |
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Venous Return dependent on: |
• Blood volume & venous pressure Venoconstriction caused by Symp Skeletal muscle pumps Pressure drop during inhalation
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Venous return controls SV & EDV & CO |
Stroke volume: the blood pumped out of the ventricle with each contraction
End Diastolic Volume: the volume in the ventricles after filling from atrium
Cardiac output: volume of blood
CO = SV x HR (mills p/ min) |
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Functions of the Lymphatic System |
Transports excess interstitial fluid (lymph) from tissues to the veins
Produces and houses lymphocytes for the immune response
Transports absorbed fats from intestines to blood |
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Lymphatic capillaries |
Lymphatic capillaries are closed-end tubes that form vast networks in intercellular spaces -Very porous, absorb proteins, microorganisms, fat
This is the system that moves the ~3Liters that don’t return from capillary bed to veins |
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Vessels of the Lymphatic System |
Lymphatic capillaries: smallest; found within most organsInterstitial fluids, proteins, microorganisms, and fats can enter.
Lymph ducts: formed from merging capillariesSimilar in structure to veins Lymph is filtered through lymph nodes
Tonsils, thymus, spleenSites for lymphocyte production
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Why do people faint when they get up too quickly? |
IDK |
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Blood Pressure (BP) |
Needs to be highly controlled -Strong enough to efficiently deliver blood -Not so strong it burdens heart and vessels
Is controlled mainly by Cardiac Output: -Heart rate (HR) -Stroke volume (SV) -Peripheral resistance
An increase in any of these can result in increased BP |
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Regulation of CO: |
Sympathoadrenal activity raises BP via arteriole vasoconstriction & by increased cardiac output
Kidney plays role in BP by regulating blood volume & thus stroke volume -Kidney’s job is to regulate the volume of our circulatory systemToo much blood is bad: more volume = more pressure
-If too much blood, get rid of it by getting rid of the water, make urine!
Less blood volume = less venous return = less EDV |
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Cardiac Output (CO) Equation |
Is volume of blood pumped/min by each ventricle
Stroke volume (SV) = blood pumped/beat by each ventricle
CO = SV (70 ml/beat) x HR (70 beats/min) =4900ml/min
Total blood volume is about 5.5L |
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Regulation of Cardiac Rate |
Sinoatrial Node (SA node) -“pacemaker” (operates on its own) -100-120 beats/min
-Parasympathetic NS –Inhibitory, -dominant influence (vagus nerve) -Sympathetic: -Excitatory, -Slow response
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Regulation of Stroke Volume:
Is determined by 3 variables: |
1. End diastolic volume (EDV) = volume of blood in ventricles at end of diastole 2. Mean arterial pressure (or Total peripheral resistance, TPR) = impedance to blood flow in arteries, the pressure in the arteries that the heart is pumping against 3. Contraction strength = strength of ventricular contractio |
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Regulation of Heart: SV and HR |
Intrinsic Stroke volume -Frank-Starling Law (contractility)
Extrinsic: Heart rate -Parasympathetic and Sympathetic nervous system
Contractility: Sympathetic nervous system
Point of interest: Contractility is controlled both by intrinsic and extrinsic regulation |
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Frank-Starling Law of the Heart |
States that strength of ventricular contraction varies directly with EDV -Is an intrinsic property of myocardium -As EDV increases, myocardium is stretched more, causing greater contraction & SV
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Frank-Starling Law of the Heart cont. (see fig) |
(a) is state of myocardial sarcomeres just before filling Actins overlap, actin-myosin interactions are reduced & contraction would be weak In (b, c & d) there is increasing interaction of actin & myosin allowing more force to be developed |
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CONT. |
As left ventricle fills during diastole, the myocardium stretches causing the sarcomere size to lengthen. This results in optimal length-tension for cardiac muscle cells.
This is very different from muscle tissue which is at optimal length tension when at rest. |
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Extrinsic Control of Contractility |
At any given EDV, contraction depends upon level of sympathoadrenal activity -NE & Epiproduce an increase in HR & contraction ^^Due to increased Ca2+in sarcomeres
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Aerobic Requirements of the Heart |
The coronary arteries supply blood to a massive number of capillaries (2,500–4,000 per cubic mm tissue). Heart is the most perfused tissue in human body -Muscles have about 300 capillaries per mm3
Unlike most organs, blood flow is restricted during systole. Cardiac tissue therefore has myoglobin to store oxygen during diastole to be released in systole. |
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Heart Failure |
Decrease in heart contractility -Damaged cardiac muscle -Prolonged pumping against high pressure**
Changes in SV and CO -Backward failure: Blood pools in veins
Forward failure -Not enough blood to tissues, congestive heart failure
Sometimes treatable by changing extrinsic control; -Sympathetic control -Changing salt reabsorption in kidney
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Blood Pressure (BP) controlled by: |
Is controlled mainly by HR, SV, & peripheral resistance -An increase in any of these can result in increased BP
Sympathoadrenal activity raises BP via arteriole vasoconstriction & by increased CO
Kidney plays role in BP by regulating blood volume & thus stroke volume |
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Regulation of blood volume through kidneys |
Major role is to regulate blood volume! -cirualtory system |
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Antidiuretic hormone (ADH) |
-Made in hypothalamus -Released from posterior pituitary -Causes increased water reabsorption in the kidney -Increases blood volume
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Renin-angiotensin-aldosterone system |
-When blood pressure is low, cells in the kidneys (juxtaglomerular apparatus) secrete the enzyme renin -Causes cascade that results in release of aldosterone from adrenal cortex -Increases salt and water reabsorption in kidney -Increases blood volume |
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Atrial Stretch Receptors |
respons to EDV
-Are activated by increased venous return & act to reduce BP -Stimulate reflex tachycardia (slow HR) Inhibit ADHrelease (antidiuretic hormone, vasopressin) -Promote secretion of ANP (atrial naturieticpeptide)From atrial muscle cells -Decreases blood pressure by
targeting kidney to reduce blood volume Promote water and sodium
excretion |
