BU HC 752 Bio of Disease Fall 2011-Week 6.1

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Cardiovascular System

Describe the Passage Of Blood Through the Heart

1-superior & inferior vena cava carry O2-poor blood from body veins to right atrium
2-right atrium contracts, sending blood through AV valve (tricuspid valve) to the right ventricle
3-right ventricle contracts, pumping blood through the pulminary semilunar valve into the pulmonary trunk
4-pulminary trunk, which carries O2-poor blood, divides into two pulmonary arteries, which go to the lungs
5-pulmonary capillaries within the lungs allow gas exchange. O2 enters the blood, CO2 waste is excreted from blood
6-Four pulmonary veins, which carry O2 rich blood, enter left atrium
7-left atrium pumps blood through an AV valve (tricuspid/mitral) to the left ventricle
8-left ventricle contracts, sending blood through the aortic semilunar valve into the aorta
9-large arteries, smaller arteries, and arterioles supply tissue capillaries, tissue capillaries drain into increasingly larger veins,veins drain into superior and inferior vana cava to start again

Describe pulmonary circulation.

-Blood high in CO2 and low in O2 flows from right heart to lungs
-CO2 off-loaded and O2 on-loaded in pulmonary capillaries
-oxygenated blood flows from lungs to left heart

Describe systemic circulation.

-oxygenated blood flows from left heart to tissues
-nutrients and wastes are exchanged in systemic capillaries, blood O2 exchanged for tissue CO2
-deoxygenated blood flows to right heart

Describe the role of bulk flow and diffusion in the cardiovascular system.

BF: Flow of blood throughout the body is produced by pressure created by pumping heart and all blood constituents move together.
-D: movement of nutrients, metabolic end products between blood and interstitial fluid.
-Diffusion and mediated transport: mechanisms of movement between interstitial fluid and the cell interior

What are the layers of the heart wall?

-Epicardium: outer layer of connective tissue, coronary arteries
-Myocardium: middle layer, muscular, thickest layer, workhorse of heart
-Endocardium: innermost layer, smooth membrane, heart valves part of this, it is continuous with the endothelial layer of blood vessels

What supplies blood to the heart?

Coronary arteries exiting from the aorta provide oxygenated blood to the heart

Describe the cardiac chambers.

-RIght heart (right atrium and ventricle) circulates lung blood to lung (pulmonary pump)
-Left heart (left atrium and ventricle) circulates blood to peripheral tissues (systemic pump)

Describe the cardiac valves.

-Atrioventricular (AV): tricuspid on left, mitral (biscuspid) on right
-Semilunar: pulmonary valve leaving right heart to lungs, aortic valve leaving left heart to systemic circulation

Describe the basics of the internal control of the heart: the cardiac conduction system.

Autorythmic cells in the sinoatrial (SA) node of the right atrium pass electrical impulses (action potentials).
-SA node is the pacemaker of the heart. It initiates the heartbeat and causes atria to contract.
AV node (atrioventricular) conveys the contraction stimulus from the atria to the ventricles. The signal for the ventricles to contract travels from AV node through AV bundle that occurs between the right and left ventricles to the Purkinje fibers.
-Ability of cardiac muscle to depolarize and contract is intrinsic, it doesn't depend on nervous system
SA node--AV node--bundle--Purkinje fibers

Explain how the autonomic nervous systems regulates heartbeat, describe effects of sympathetic and parasympathetic stimulation.

-The ANS is part of peripheral NS. It regulates function of both smooth muscle and cardiac muscle.
-Medulla Oblongata: cardiac control center of brain, regulates HR
Parasympathetic: slows HR
Sympathetic: increases HR

Describe what an ECG is and how it is used.

is the recording of the electrical changes that occur in myocardium during a cardiac cycle.
P Wave-atrial systole
QRS Wave: ventricular systole
T Wave: ventricular diastole
-Can detect cardiac arrhythmias

Describe some cardiac arrhythmias.

-Atrial fibrillation
-Ventricular fibrillation
-Heart block

Describe sequence of events in the cardiac cycle.

Cardiac cycle is all events associated with blood flow during one complete heart beat: a constant contraction then relaxation cycle
Systole: contraction period
Diastole: relaxation period

Atriole sysole--atrial diastole--ventricular systole--ventricular diastole

Explain how stroke volume and heart rate determine cardiac output CO.

CO is volume of blood pumped per minute by each ventricle.
SV: volume of blood ejected with contraction of the ventricle
HR: number of heart beats (ventricular contractions) per minute
CO= SV x HR
SV=EDV - ESV (end diastolic volume-endsystolic volume)

How does the autonomic nervous system regulate multiple heart functions?

Through release of neurotransmitters and and neurohormones.
Sympathetic=fight or flight by norepinephrine and epinephrine=stim HR via SA node, and increase conduction via AV node
Parasympathetic=acetylcholine=decrease HR and decrease conductivity

What are some mechanisms to increase heart rate?

Adrenal Medulla uses following to increase SA node stimulation
-deliver epinephrine
-release more norepinephrine
-reduce release of acetylcholine

Describe flow of blood through the peripheral vasculature.

arteries--arterioles--capillaries--venules--veins

Contrast the 3 main types of blood vessels: arteries, capillaries, and veins.

-Arteries: Take blood away from heart. Middle layer of arteries consists of smooth muscle that can constrict to regulate blood flow and blood pressure. Thickest to withstand BP.
-Capillaries: walls are only one cell thick and allow exchange of substances with interstitial tissue fluid.
-Veins: venules drain into veins that return blood to the heart. Much less smooth muscle and connective tissue than arteries, have valves that prevent backward flow of blood

How are arteries able to act as pressure reservoirs that can readily stretch and recoil?

Elastic walls of arteries stretch and recoil because they are compliant. They readily distend (increase volume) during systole (time of increased pressure). As a result of large radii, there is little resistance to blood flow.

What is blood pressure?

The pressure of blood against the wall of a blood vessel. Blood flow through any vessel is determined by the change in pressure berween the beginning and end of the vessel. (blood will flow towards areas of decreased pressure) and the resistance to flow (vessel diamter is the main determinant of resistance). Beating of the heart creates the pressure that propels blood in the arteries and arterioles.

Flow=change in pressure/resistance

What is MAP and how is it determined by cardiac output (CO) and total peripheral resistance (TPR)?

Mean Arterial Pressure (MAP) is the average pressure driving blood into tissue during the cardiac cycle.

Describe how arterioles are high resistance conduits for blood and are the major sites of resistence in the systmeic vascular system.

Resistance to blood flow is largely regulated by controlling arteriolar diameter via vasoconstriction and vasodilation. Responsible for determining relative blood flow to the organs at any given time, like a handle on the faucet.

What are some regulators of arteriolar resistance via vasoconstriction and vasodilation?

Intrinsic:
-Active Hyperemia: increased blood flow associated with inc. metabolic activity ex. exercise
-Flow Regulation locally mediated changes in resulting from changes in blood supply due to changes in BP
-Reactive Hyperemia: transient increase in blood flow following arteriolar occlusion ex. response to injury
Extrinsic:
-Autonomic Innervation, hormones, paracrine agents secreted by endothelial cells

Describe how gas, nutrient and waste exchange occurs across tissue capillaries.

Primarily occurs by diffusion. Lipid soluble molecules (O2 and CO2) diffuse via capillary endothelial plasma membranes while ions and polar molecules diffuse via channel in the capillary wall, intercellular clefts between endothelial cells, and fused-vesicle channels through endothelial cells.

Describe how hydrostatic pressure and osmotic pressure determine filtration and absorption and thus distribution of extracellular fluid.

-ECF= interstitial fluid + plasma
ECF movement across capillaries occurs by bulk flow. Fluid is filtered out of capillaries into the insterstitium and absorbed from the interstitium back into the capillaries.
Capillary wall is highly permeable to water and most plasma solutes except plasma protein. Plasma protein is referred to as a non-penetrating solute. Albumin makes up the majority of plasma protein and so accounts for most of the osmotic plasma pressure.
-Filtration: movement of fluid and solutes out of the blood due to pressure differences
-Absorption: movment of fluid and solutes into the blood due to osmosis

What are the Four Forces (Starling Forces) that determine whether fluid is filtered or absorbed into capillaries?

-capillary hydrostatic pressure
-interstitial hydrostatic pressure
-osmotic force due to plasma protein concentration
-osmotic force due to interstitial-fluid protein concentration

What is lymph?

At the arterial end of a capillary, BP is higher than osmotic pressure and water exits a capillary at this end. At the venule end, osmotic pressure is greater than B and water tends to enter capillary. Any excess fluid left behind in capillary tissue beds is collected by lymphatic vessels. This is lymph and it is returned to the circulating blood stream by a one-eay system of lymphatic vessels.

Lymph is formed by slight mismatch between filtration and absorption in the capillaries and returns to blood in the veins

Explain why venous blood flow is unidirectional.

Veins are low resistance vessels for blood flow from tissues to the heart and are dependent upon skeletal muscle contraction, the presence of valves in the veins and respiratory movement. Have one way valves that insure unidirectional blood flow.

Describe the steps of lymphatic circulation.

-Lymphatic capillaries infiltrate capillary beds of most organs
-Excess interstitial fluid enters porous, blind ended ducts of lymphatic capillaries to become lymph fluid
-Lymphatic capillaries converge to form lymph vessels that return lymph fluid to circulation via the subclavian vein

What forces regulate lymph flow?

Propelled by rhythmic contraction of stretch sensitive smooth muscle. One way valves within lymph vessels ensure one way flow towards entry into the circulatory system. Skeletal muscle pumps and respiratory pump enhance lymph flow.

What is edema?

The swelling of tissues with fluid that occurs when excess filtered plasma fluid cannot be returned to the blood stream and interstitial fluid builds up.

What are four causes of edema?

-Reduced concentration of plasma proteins
-Increased capillary permeability
-increase in venous pressure
-blocked or removed lymphatics

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