The Cardiovascular System

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The Cardiovascular System

• Andrea McNeilly
• Mcneilly-a_at_ulster.ac.uk

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The Cardiovascular System

• By the end of this session you should be able to
• Describe the structure of the CV system
• Draw and label the components of the system
• Describe the passage of O2 from alveoli to muscle
  mitochondria
• Describe the passage of CO2 from muscle
  mitochondria to alveoli
• Explain the response of the CV system to exercise

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The Cardiovascular System

• Alveoli to Heart
• Heart Structure
• Vascular Structure
• Cardiac Function
• Passage of O2 and CO2
• Exercise

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Blood

• Cells - red white blood cells and platelets
• Red Blood Cells - oxygen carrying
• White Blood Cells fight infection
• Platelets -clotting
• Haematocrit -volume which is cells (38-42)
• Plasma-water, ions, hormones
• Blood volume- approx 5 litres

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Functions of the Blood

• Transports gas, nutrients, and wastes
• Regulates temperature
• Buffers and balances acid base
• Distribution matched to overall metabolic demands
• Autoregulationarterioles within organs or
  tissues dilate or constrict
• Extrinsic neural controlsympathetic nerves
  within walls of vessels are stimulated

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Alveoli - Blood
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CV structure - Heart
w The heart has four chambers left and right
ventricle left and right atrium
w The heart functions as two separate pumps

• The left side pumps oxygenated blood to the body
  (systematic circulation)

• The right side pumps deoxygenated blood to the
  lungs for aeration (pulmonary circulation)

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CV structure - Heart

• Right and Left - septum
• Atria (upper)
• Ventricle (lower)
• Right- tricuspid valve
• Left- Bicuspid valve
• Pulmonary Artery and Aorta - semilunar valves

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Myocardium the heart muscle

• Thickness varies directly with stress placed on
  chamber walls.
• Left ventricle is the most powerful of chambers
  and thus, the largest
• With vigorous exercise, the left ventricle size
  increases.
• Due to intercalated disksimpulses travel quickly
  in cardiac muscle and allow it to act as one
  large muscle fiber all fibers contract together.

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CV function Heart- The outward journey

• After passing through the capillaries of the
  lungs, the blood (oxygenated) returns to the
  heart in the pulmonary veins

• The left atrium receives blood from the pulmonary
  vein

• Blood passes through the mitral valve into the
  left ventricle

• Contraction of the left ventricle pushes blood
  through the aortic semilunar valve into the aorta

• Aorta divides into arteries- taking oxygenated
  blood to all parts the body

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CV structure - Vascular

• Arteries Arterioles
• High pressure tubing that conducts oxygen rich
  blood
• Composed of layers of connective tissue and
  smooth muscle
• Smooth muscle in walls - allows vasoconstriction
  and vasodilation to control or alter blood flow
• Capillaries
• Consist of a single layer of endothelial cells
• Precapillary sphincter (ring of smooth muscle)
  controls capillary diameter

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Oxygen Delivery

• Oxygen dissociates from haemoglobin (Hb)
• Moves across muscle membrane
• Picked up by myoglobin
• Transported to mitochondria
• Used for aerobic metabolism of fats carbohydrates
  and proteins
• Waste product- CO2

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Rest Exercise
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Carbon Dioxide Return

• CO2 binds to myoglobin
• Moves to muscle membrane
• Across membrane picked up by Hb
• Travels back to heart

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Vascular System

• Capillaries
• Venules
• Veins
• Vena Cava
• Heart

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Valves in the veins prevent backward flow
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CV function HeartThe return journey

• Deoxygenated blood returns from the rest of the
  body through the superior and inferior vena cava.

• The right atrium receives the deoxygenated blood.

• Blood then enters the right ventricle through the
  tricuspid valve.

• Contraction of the right ventricle pushes blood
  through the pulmonary semilunar valve into the
  pulmonary arteries in which it travels to the
  lungs.

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Vascular System Summary

• Arteries take blood away from heart
• Smooth muscle to control flow
• Aorta- largest - left ventricle- to body
• Veins take blood toward heart
• Valves to prevent backward flow
• Vena Cava- largest -from body to right atrium

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Heart Contraction

• Heart- cardiac muscle
• Contraction systole- blood pumped out
• Relaxation diastole- refilling of heart
• Intrinsic and extrinsic conduction

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Intrinsic Conduction

• Cardiac rhythm originates at SA node (pacemaker)
• Impulse travels across the atria to the AV node
• From AV node to av bundle (Bundle of His)
• Spreads across the ventricular mass via Pukinje
  fibres

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Extrinsic conduction

• PNS acts through the vagus nerve to decrease
  heart rate and force of contraction.
• SNS is stimulated by stress to increase heart
  rate and force of contraction.
• Epinephrine and norepinephrinereleased due to
  sympathetic stimulationincrease heart rate.

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Electrocardiogram (ECG)

• Records the heart's electrical activity and
  monitors cardiac changes
• PHASES OF THE RESTING ECG

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Cardiac Arrhythmias

• Bradycardiaresting heart rate below 60 bpm
• Tachycardiaresting heart rate above 100 bpm
• Premature ventricular contractions (PVCs)feel
  like skipped or extra beats
• Ventricular tachycardiathree or more consecutive
  PVCs that can lead to ventricular fibrillation in
  which contraction of the ventricular tissue is
  uncoordinated

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Rest vs exercise

• Cardiac cycle- systole and diastole
• Starts with electrical stimulation of sinoatrial
  node - atrium contracts- pushing blood into
  ventricles
• Electrical impulse spreads to atrioventricular
  node- ventricle contracts sending blood into
  systemic and pulmonary system
• 75 bpm- 0.3s systole 0.5s diastole

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Blood Flow During Exercise

• Blood flow- from 4.5l at rest to 30l exercise
• Redistribution-by vasoconstriction and
  vasodilation

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Cardiac Output

• Cardiac Output (CO)
• the volume of blood pumped out of the heart in 1
  min
• Stroke Volume (SV)
• the amount of blood pumped out of the heart in 1
  beat
• Heart Rate (HR)
• the number of beats in 1 minute
• CO SV X HR

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Response to Exercise
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Cardiac Circulation

• The heart is a working muscle and needs a blood
  supply to bring nutrients and oxygen
• Blood passing thorough the inside of the heart is
  not available to cardiac muscle
• 5 of blood leaving the aorta is distributed to
  the heart muscle via the coronary arteries

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Blood Pressure

• Blood Pressure - force exerted by the blood
  against the arterial walls
• Determined by the amount of blood being pumped
  and the resistance in the arteries
• Systolic- pressure during systole (110-130mmHg)
  Diastolic -pressure during diastole (70-90mmHg)

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Essential Reading

• McArdle Katch and Katch
• Section III
• Chapter 9
• The Cardiovascular System and Exercise
• Pages 236-277 (in 1997 paperback version)