Ch 17 Circulatory Function Flashcards
What are the pulmonary and systemic circulations?
Pulmonary consist of the right side of the heart, the pulmonary arteries and arterioles, the pulmonary capillaries and the pulmonary veins. Systemic is the left side of the heart, aorta and its branches, the capillaries and the venous system and the vena cava
Atrium receives blood and the ventricles pump blood either out to the lungs or the body.
What is hemodynamics? Pressure, resistance and flow?
What is Poiseuilles law?
Hemodynamics refers to the principles that govern the flow of blood in the vascular system.
Two factors: the pressure difference oP between the two ends of a vessel or group of vessels and the resistance R that the blood must overcome as it moves through the vessel or vessels. equation : flow
= oP/R
Poiseuilles Law determined that the flow of fluid was determined by the pressure difference between the two ends of a tube P1-P2, the fourth power of the radius r4 of the tube, the viscosity n of the fluid, the tube length l and two constants pie and 8using the following equation flow=oP r4/n
3 areas 1. flow in series and parallel vessels, 2. velocity, cross sectional area and flow. 3 laminar versus turbulent flow. see p 378.
What is wall tension, radius and pressure? Vascular Distensibility?
Wall tension is the force of the vessel wall that opposes the distending pressure inside the vessel. The law of Laplace, P = T/r in which T is the wall tension, P is the intraluminal pressure or the pressure within the vessel and r is vessel radius. The internal pressure expands the vessel until is is exactly balanced by the tension in the vessel wall. The smaller the radius, the greater is the pressure needed to balance the wall tension. Or T = P x r
Distensibility refers to the ability of a blood vessel to be stretched and accommodate an increased volume of blood. Vascular compliance refers to the total quantity of blood that can be stored in a given portion of the circulation for each millimeter of mercury rise in pressure.
What are the layers of the heart?
Pericardium - forms a fibrous covering around the heart, holding it in a fixed position in the thorax and providing physical protection and a barrier to infection. Consists of a tough outer fibrous layer and a thin inner serous layer. Pericardial cavity - potential space that contains 30-50 mL of serous fluid.
Myocardium - or muscular portion of the heart, forms the walls of the atria and ventricles. Cardiac muscles are striated and composed of sarcomeres that contain actin and myosin filaments. They also contain intercalated disks which are fibers that separate neighboring cardiac muscle by dense structures they contain gap junctions that serve as low resistance pathways for passage of ions and electrical impulses.
Endocardium - is a thin three layered membrane that lines the heart and covers the valves.
What are the heart valves?
There are 4 valves, atrio ventricular the tricuspid and mitral valves which are the valves between the atrium and the ventricles. Two semilunar valves - pulmonic and aortic. they control the movement of blood out of the ventricles There are no valves at the atrial sites which means it pushed the blood back in the veins.
What is the electrical activity of the heart? what are the two conduction systems?
It is capable of generating and rapidly conducting its own electrical impulses or action potentials In certain areas of the heart, the myocardial cells have been modified to form the specialized cells of the conduction system. It has 1. the sinoatrial SA node, 2. The internodal pathway which conduct the impulse from the SA node to the AV node. 3. the AV node, in which the impulse from the atria is delayed before passing to the ventricles 4. the AV bundle, which conducts the impulse from the atria to the ventricles 5. left and right bundles of the Parkinje system, which conduct the impulses to all parts of the ventricles.
Atrial and ventricular conduction systems. AV bundle or bundle of his - connects the two systems allowing a pause between which allows the atria to complete their ejection of blood before the ventricular contraction begins.
The purkinje system which supplies the ventricles has large specialized fivers that allow for rapid conduction and almost instantaneous excitation of both the right and left ventricles.
What are the action potentials? What is absolute and relative refractory periods?
Action potentials represents the sequential change in electrical potential that occurs across a cell membrane when excitation occurs. Can be divided into 3 parts; the resting or unexcited state during which the membrane is polarized, depolarization or change in the direction of polarity and repolarization of polarity of the resting membrane potential. Na+, K+ and CA++ are the major electrical charge carriers in cardiac muscle cells.
Is divided into 5 phases; 0. the upstroke or rapid depolarization. 1 early repolarization 2. the plateau, 3. rapid repolarization, and 4 the resting membrane potential.
The cardiac muscle has 3 types of membrane ion channels 1. fast sodium channels. 2. slow calcium channels, 3. potassium K+ channels.
There is a period in the action potential curve during which no stimuli can generate another action potential. it is known as the absolute refractory period, includes phases 0,1,2 and part of 3
What are arrhythmias and conduction disorders?
2 categories
1. Supraventricular - include those that originate in the SA node, atria, AV node and junctional tissues
2. Ventricular - include those that originate in the ventricular conduction system and ventricular muscle
Are the most serious disorders as they are the pumping chambers of the heart.
Heart block occurs when the conduction of impulses is blocked, often in the AV nodal fibers. the atria and ventricles beat independently of each other. The most serious effect is a slowing of heart rate to the extent that circulation to the brain is compromised
Ectopic pacemaker is an excitable focus outside the normally functioning SA node. A premature ventricular complex PVC occurs when an ectopic ventricular pacemaker initiates a beat.
Fibrillation is the result of disorganized current flow within the atria or ventricle. It interrupts the normal contraction of the atria or ventricles.
What is an ECG?
The electrocardiogram is a recording of the electrical activity of the heart. The deflection points of an ECF are designated by the letters P, Q, R, S, and T. The P wave represents atrial depolarization, the QRS compiles ventricular depolarization; and the t wave, ventricular repolarization. Atrial repolarization occurs during ventricular depolarization and is hidden in the QRS complex.
What is the cardiac cycle? Ventricular systole and diastole?Ca
Which is used to describe the rhythmic pumping action of the heart, is divided into two parts; the systole, the period during which the ventricles are contracting; and diastole, the period during which the ventricles are relaxed and filling with blood.
Ventricular systole is Divided into two periods: the isovolumetric contraction period - begins with the closure of the AV valves and occurrence of the first heart sound, heralds the onset of systole. and the ejection period. The ventricles contract and produce an abrupt inc in pressure. The aortic and pulmonary valves open, signaling the ejection period. At the end of systole the ventricles relax. the blood from the large arteries flow back toward the ventricles, causing the aortic and pulmonic valves to snap shut - the second heart sound.
Diastole is marked by ventricular relaxation and filling The isovolumetric relaxation period, ventricular volume remains the same but ventricular pressure drops until it becomes less than atrial pressure. As this occurs, AV valves open, and the blood that has been accumulating in the atria during systole flows into the ventricles. During this the ventricles inc their volume to approx 120 mL and at the end of systole, approx. 50 mL of blood remains in the ventricles. The difference between the end diastolic and end systolic volumes is called the stroke volume..
What is atrial filling and contraction?
Because there is no valves between the junction of the central veins and the atria, atrial filling occurs during both systole and diastole.
Three main atrial pressure waves occur during the cardiac cycle
- c wave, occurs as the ventricles begin to contract and their inc pressure causes the AF valves to bulge into the atria
- v wave, occurs toward the end of systole when the AV valves are still closed and results from a slow buildup of blood in the atria.
- a wave, occurs during the last part of diastole and is caused by atrial contraction.
What is the regulation of cardiac performance? What is preload? and afterload? Cardiac contractility? Heart Rate?
Cardiac output is the amount of blood the heart pumps each minute. CO is the product of the stoke volume SV or amount of blood that the heart ejects with each beat and the heart rate HR number of times the heart peats each minute CO=SV x HR
Cardiac reserve refers to the maximum percentage of increase in cardiac output that can be achieved above the normal resting level. The heart’s ability to inc its output according to body needs mainly depends on 4 factors:
- Preload - it is the work or lad imposed on the heart before the contraction begins. It is the amount of blood the heart must pump with each beat and represents the volume of blood stretching the ventricular muscle fibers at the end of diastole. It determined by the amount of blood that remains in the ventricle at the end of systole plus the amount of venous blood returning to the heart during diastole Frank starling mechanism - the inc force of contraction that accompanies an inc in ventricular end diastolic volume
- Afterload - is the pressure or tension work of the heart. It is the pressure the heart must generate to move blood into the aorta.
- Cardiac contractility - refers to the ability of the heart to change its force of contraction without changing its resting or diastolic length An inotropic influence is one that modifies the contractile state of the myocardium independent of the frank starling mechanism. It inc the Ca available.
- The heart rate influences cardiac output and the work of the heart by determining the frequency with which the ventricles contract and blood is ejected from the heart. Also determines the time spent in diastolic filling. The filling becomes shorter as the heart rate inc.
What is the systemic circulation and control of blood flow? Blood vessels? Arterial system? Venous System?
The systemic vascular system is a closed system of vessels that distributes blood from the heart to the tissues and returns blood to the heart.
Blood vessels - all except capillaries have walls composed of three layers, called tunicae. Outer tunic externa - is loosely woven collagen fibers that protect the blood vessel and anchors it, middle tunica media - largely smooth muscle layer that constricts to regulate and control the diameter of the vessel, innermost tunica intima - consists of a single layer of flattened endothelial cells with minimal underlying subendothelial connective tissue. It provides a smooth slippery inner surface for the vessel prevents platelet adherence and blood clotting.
Arterial system - consists of the large and medium sized arteries and the arterioles. Arteries are thick-walled vessels with large amounts of elastic fibers. The elasticity of these vessels allows them to stretch during cardiac systole and to recoil during diastole. The delivery of blood is dependent on pressure pulsations or waves of pressure that are generated by the intermittent ejection of blood from the left ventricle into the aorta
Venous System - is a low pressure system that returns blood to the heart the valve in the veins and the skeletal muscles move blood back to the heart in a milking motion.
What do the capillaries? lymphatic system? and the microcirculation do?
Capillaries are microscopic single cell thick vessels that connect the arterial and venous segments of the circulation. Intercellular junctions join the capillary endothelial cells are called capillary pores and lipid soluble materials diffuse directly through the cell membrane. Water and water soluble leave and enter through the cell pores.
Lymphatic system - represents an accessory route through which fluid can flow through the tissue spaces into the blood and then back to the heart. Lymphatics can carry proteins and large particulate matter away from the tissue space, it is also the main route for absorption of fats and fat soluble vitamins from the GI tract. Normally along the vessels of the circulatory system.
Microcirculation - is the most important function - consists of the arterioles, capillaries and venules. It is here that transport of nutrients to the tissues and removal of the metabolites takes place. Tissues and organs can regulate their blood flow based on metabolic needs. Autoregulation - is local control mechanism that automatically adjusts tissue blood flow independent of systemic factors. Two factors metabolic and myogenic.
What is endothelial control of blood flow? and Humoral control of blood flow?
One of the important factors of the endothelial cells lining the arterioles and small arteries is the synthesis and release of factors that can affect the degree of relaxation or contraction of the arterial wall. The most important of the endothelial relaxing factors is the release of nitric oxide. It also inhibits platelet aggregation and secretion of platelet contents which causes vasoconstriction. Also produces a number of vasoconstrictor substances angiotensin II, vasoconstrictor prostaglandins, and a family of peptides called endothelins.
Humoral involves the effect of vasodilator and vasoconstrictor substances in the blood. Some formed by special glands, some by local tissues and aid in the control of the flow. Norepinephrine and epinephrine - vasoconstrictor hormone is released due to stress or exercise. Angiotensin II - another powerful vasoconstrictor is part of the renin angiotensin aldosterone system. Normally acts on many arterioles in the same time to inc peripheral vascular resistance.
Histamine - powerful vasodilator and has the ability to inc capillary permeability, allowing leakage of both fluid and plasma proteins into the tissues. Serotonin - is liberated from aggregating platelets during the clotting process causes vasoconstriction and plays a major role in control of bleeding. Bradykinin - are small polypeptides that are liberated from the globulin kininogen cause vasodilation, intense dilation of arterioles, inc capillary permeability, constriction of venules. Thought to plays a major role in regulating blood flow in the skin and salivary and GI glands. Prostaglandins are synthesized from the cell membrane such as tissue injury
