The Cardiovascular SystemSection 1

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Chapter 11 The Cardiovascular System Section 1

Heart Anatomy

Circulation

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The Cardiovascular System

· A closed system of the heart and blood vessels

·

The heart pumps blood

·

Blood vessels allow blood to circulate to all parts of the body

· The primary function of the

cardiovascular system: transportation - - to deliver oxygen, nutrients, hormones,

and to remove carbon dioxide and

other waste products

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The Heart

· Location

·

Thorax between the lungs

·

Pointed apex directed toward left hip - at 5th intercostal space

- rests on diaphragm

·

Base points toward right shoulder

- greater vessels emerge from here - level of 2

^nd

rib

About the size of your fist, weighs less

than a 1 lb.

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The Heart

Figure 11.1

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The Heart: Coverings

· Pericardium – a double serous membrane (continuous with one another)

·

Visceral pericardium

·

Next to heart

·

Parietal pericardium

·

Outside layer

·

Dense connective tissue anchors this layer to surrounding structures

· Serous fluid fills the space between the

layers of pericardium – why?

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The Heart: Heart Wall

· Three layers

·

Epicardium

· Outside layer

· This layer is the visceral pericardium

· Connective tissue layer

·

Myocardium

· Middle layer

· Mostly cardiac muscle (this layer contracts)

·

Endocardium

· Inner layer

· Endothelium – shiny

· Continuous with the lining of blood vessels

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External Heart Anatomy

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The Heart: Chambers

· Right and left side act as separate pumps

· Four chambers

·

2 Atria

· Receiving chambers

· Right atrium

· Left atrium

·

2 Ventricles (“pumps” of the heart)

· Discharging chambers

· Right ventricle –pulmonary circuit pump

· Left ventricle –thicker walled systemic pump

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Blood Circulation

Figure 11.3

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Pulmonary Circulation

• Blood leaves right side, goes to lungs, and returns to left side of heart

- Right atrium receives oxygen poor blood from the veins of the body through the superior and inferior vena cavae

- To right ventricle which pumps it through the

pulmonary trunk (which divides into the pulmonary

arteries) to the lungs where O₂ is picked up and CO₂ is unloaded.

- O₂ rich blood returns through the pulmonary veins to the left atrium

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Systemic Circulation

• From the left side of the heart through the body tissues and back to the right side

- O₂ rich blood in left side of heart is pumped out by the left ventricle and leaves through the aorta - Blood goes to all body tissues and returns to the

right side of the heart

(The left ventricle pumps blood over a greater

distance so the walls are thicker than the walls of the right ventricle)

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The Heart: Valves

· Allow blood to flow in only one direction

· Four valves

· 2 Atrioventricular valves (AV) – between atria and ventricles (also called the cuspid valves)

· Bicuspid valve (left) - (also called mitral valve)

· Tricuspid valve (right)

· AV valves open during relaxation and are

closed when the ventricles are contracting

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Valves (continued)

• 2 Semilunar valves between ventricle and artery

• Pulmonary semilunar valve – between right ventricle and pulmonary artery

• Aortic semilunar valve – between left ventricle and aorta

• Closed during relaxation and forces open

during contraction of the ventricles

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The Heart: Valves

· Valves open as blood is pumped through

· Held in place by

chordae tendineae (“heart strings”) - (keep the AV valves closed during

ventricular contraction)

· Close to prevent backflow

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Operation of Heart Valves

Figure 11.4

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The Heart: Associated Great Vessels

· Aorta (carries blood bound for body)

· Leaves left ventricle

· Pulmonary arteries (carries blood bound for lungs)

· Leave right ventricle

· Vena cava (carries blood returning from body)

· Enters right atrium

· Pulmonary veins (four) (carries blood returning from lungs)

· Enter left atrium

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Coronary Circulation

· Blood in the heart chambers does not nourish the myocardium

· The heart has its own nourishing circulatory system

·

Coronary arteries –branch from the base of the aorta

·

Cardiac veins – drains the myocardium

·

Blood empties into the right atrium via the

coronary sinus

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The Heart: Conduction System

· Intrinsic conduction system (nodal system)

·Heart muscle cells contract, without nerve impulses, in a regular, continuous way

(node-special conduction cells- part nervous tissue, part

muscular tissue)

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The Heart: Conduction System

· Special tissue sets the pace

· Sinoatrial node (SAN)

· Pacemaker

· Atrioventricular node (AVN)

· Atrioventricular bundle

· Bundle branches (right & left)

· Purkinje fibers

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http://www.carolina.com/

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Heart Contractions

· Contraction is initiated by the sinoatrial node –

· Impulse travels through walls of atria causing the atria to contract

· Impulse is reached by the AVN and then travels down the Bundle of His (AV

bundle) and into the AV branches that

supply the ventricles via the Purkinje

fibers

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Filling of Heart Chambers – the Cardiac Cycle

Figure 11.6

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The Heart: Cardiac Cycle

· Atria contract simultaneously

· Atria relax, then ventricles contract 1/10

^th

of a second later

· Systole = contraction

· Diastole = relaxation

· Average heart beats 75 times/minute

· A fluid does not flow if there is no

pressure difference

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http://www.tmc.edu/thi/valves.html

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The Heart: Cardiac Cycle

· Cardiac cycle – events of one complete heart beat; takes about 0.8 seconds

·

Mid-to-late diastole – blood flows into

ventricles through the atria and then the atria contract (P wave)

·

Ventricular systole – blood pressure builds before ventricle contracts, pushing out

blood when pressure becomes higher than the pressure in vessels. This is the first

heart sound that you hear; R wave on EKG.

The atria are relaxed and begin filling with

blood.

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Cardiac Cycle cont.

· Early diastole – atria finish re-filling, ventricular pressure is low, ventricles are relaxed and for a moment, the

ventricles are a completely closed chamber (all valves are closed around it)

-When pressure drops below that of the atria, the AV valves open and the ventricles begin filling with blood

· Then the cycle continues.

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The Heart: Cardiac Output

· Stroke volume (SV)

·

Volume of blood pumped by each ventricle in one contraction

· Cardiac output (CO)

·

Amount of blood pumped by each side of the heart in one minute

·

CO = (heart rate [HR]) x (stroke volume

[SV])

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Monitoring Heart Electrical Activity

•

EKG (ECG)

• Each contraction sends out an electric-like signal

• Three major waves of electrical signals appear

• P wave - 1

^st

wave-records atrial electrical activity (impulse from SA node and depolarization

through both atria)

• QRS wave - largest of the waves & 2

^nd

-records ventricular electrical activity

• T wave - records heart’s return to resting state

(repolarization of ventricles)

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lub-dup sound

• Lub: closing of AV valves during systole

• Dub: semilunar valves close at

end of systole

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Cardiac Output Regulation

Figure 11.7

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Heart Conditions

•

Ischemia – lack of adequate blood supply

•

Bradycardia – slower than normal heart rate (<

60/min)

•

Tachycardia – rapid heart rate (> 100/min)

•

Fibrillation – rapid, uncoordinated, shuddering of the heart muscle

•

Heart block – ventricles begin to beat at their own

rate (not under the control of the SA node)

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Chapter 11 The Cardiovascular System Section 3

blood pressure, blood vessels, and regulation of heart rate

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The Heart: Regulation of Heart Rate

· Stroke volume usually remains relatively constant (70mL/beat, ~ 2oz)

·

Starling’s law of the heart – the more that the cardiac muscle is stretched, the

stronger the contraction

· Changing heart rate is the most

common way to change cardiac output

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The Heart: Regulation of Heart Rate

· Increased heart rate

· Sympathetic nervous system – stimulates the SA and AV nodes

· Hormones

· Epinephrine

· Thyroxine

· Exercise, high fever

· Decreased blood volume

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The Heart: Regulation of Heart Rate

· Decreased heart rate

· Parasympathetic nervous system (vagus nerve mostly)

· High blood pressure or blood volume

· Decreased venous return

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Blood Vessels: The Vascular System

· Taking blood to the tissues and back

·

Arteries

·

Arterioles

·

Capillaries

·

Venules

·

Veins

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The Vascular System

Figure 11.8b

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Blood Vessels: Anatomy

· Three layers (tunics)

·

Tunica intima (also called interna) – inner

·

Endothelium (lines the interior of vessels to create a slick surface to decrease friction)

·

Tunica media – middle

·

Smooth muscle – changes the diameter of the vessels called constriction and dilation which changes blood pressure

·

Controlled by sympathetic nervous system

·

Tunica externa (also called adventitia) – outer

·

Mostly fibrous connective tissue to support and

protect the vessels

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Differences Between Blood Vessel Types

· Walls of arteries are the thickest

· Tunica media is thicker to withstand the great changes in blood pressure

· Lumens of veins are larger

· Skeletal muscle “milks” blood in veins toward the heart

· Walls of capillaries are only one cell layer thick (tunica intima only) to allow for exchanges

between blood and tissue

· Larger veins have valves to prevent backflow

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Movement of Blood Through Vessels

· Most arterial blood is pumped by the heart

· Veins use the milking action of muscles to help move blood

Figure 11.9

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Capillary Beds – interweaving network of capillaries

· Microcirculation – flow of blood

through a capillary bed

· Capillary beds consist of two types of vessels

1. Vascular shunt –

directly connects an arteriole to a venule - not a true capillary

2. True capillaries – exchange vessels

- where nutrients and

wastes are exchanged

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Capillary Exchange

· Substances exchanged due to concentration gradients

· Oxygen and nutrients leave the blood

· Carbon dioxide and other wastes

leave the cells

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Capillary Exchange:

Substances take 1 of 4 Routes

1. Direct diffusion across plasma membranes (lipid soluble molecules only)

2. Endocytosis or exocytosis (lipid insoluble) 3. Some capillaries have gaps (intercellular

clefts)

·

Plasma membrane not joined by tight junctions

4. Fenestrations of some capillaries

·

Fenestrations = pores –very permeable

·

Found where absorption is a priority such as…

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Capillary Beds

Figure 11.10

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Major Arteries of Systemic Circulation

Figure 11.11

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Major Veins of Systemic Circulation

Figure 11.12

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Hepatic Portal Circulation

Figure 11.14

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Pulse

· Pulse –

pressure wave of blood

· Monitored at

“pressure

points” where pulse is easily palpated

Figure 11.16

Axillary

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Blood Pressure

· Measurements by health professionals are made on the pressure in large

arteries

·

Systolic – pressure at the peak of ventricular contraction

·

Diastolic – pressure when ventricles relax

· Pressure in blood vessels decreases as the distance away from the heart

increases

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Measuring Arterial Blood Pressure

Figure 11.18

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Blood Pressures in Different Vessels

Figure 11.17

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Any factor that increases peripheral resistance (resistance blood

encounters as it flows through the blood vessels) or increases

cardiac output causes a rise in BP.

Age, weight, time of day, mood, drugs, body position, and

exercise can alter BP.

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Factors that Affect Blood Pressure

· Neural factors

· Autonomic nervous system adjustments (sympathetic division- causes

vasoconstriction)

· Renal factors

· Regulation by altering blood volume through water movement

· Renin (enzyme) – through hormonal

control

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How do the kidneys have an effect on blood pressure?

Renin  cascade of chemical reactions  angiotensin II

(vasoconstrictor)  adrenal cortex releases aldosterone (hormone) 

Na+ reabsorbed by kidneys blood

volume and blood pressure increase

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Factors that affect blood pressure (cont)

· Temperature

·

Heat has a vasodilation effect

·

Cold has a vasoconstricting effect

· Chemicals

·

Various substances can cause increases or decreases (nicotine increases BP causing vasoconstriction, alcohol decreases BP

causing vasodilation)

· Diet

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Factors Determining Blood Pressure

Figure 11.19

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Variations in Blood Pressure

· Human normal range is variable

·

Normal

·

140–110 mm Hg systolic

·

80–75 mm Hg diastolic

·

Hypotension

·

Low systolic (below 100 mm HG)

·

Often associated with illness

·

Hypertension (140/90 or higher)

·

High systolic (above 140 mm HG)

·

Can be dangerous if it is chronic

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