Functions of Circulatory System

1
Functions of Circulatory System

• Include transportation of respiratory gases,
  delivery of nutrients hormones, waste
  removal
  
• Include roles in temperature regulation,
  clotting, immune function

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Components of Circulatory System

• Include cardiovascular lymphatic systems
• Heart pumps blood thru cardiovascular system
• Blood vessels carry blood from heart to cells
  back
  
• Includes arteries, arterioles, capillaries,
  venules, veins
  
• Lymphatic system picks up excess fluid filtered
  out in capillary beds returns it to veins
  
• Its lymph nodes are part of immune system

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Composition of Blood

• Consists of formed elements (cells) suspended
  carried in plasma (fluid part)
  
• Total blood volume is about 5L
• Plasma is straw-colored liquid consisting of H20
  dissolved solutes
  
• Includes ions, metabolites, hormones, antibodies

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Plasma Proteins

• Constitute 7-9 of plasma
• Three types of plasma proteins albumins,
  globulins, fibrinogen
  
• Albumin accounts for 60-80
• Creates colloid osmotic pressure that draws H20
  from interstitial fluid into capillaries to
  maintain blood volume pressure
  
• Globulins carry lipids
• Gamma globulins are antibodies
• Fibrinogen serves as clotting factor
• Converted to fibrin
• Serum is fluid left when blood clots

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Fig. 13.1
6
Fig. 13.11b
7
Fig. 13.10
8
Fig. 13.11a
9
Conducting Tissues of Heart
Fig 13.20

• APs from SA node spread through atrial myocardium
  via gap junctions
  
• But need special pathway to ventricles because of
  non-conducting fibrous tissue
  
• AV node at base of right atrium bundle of His
  conduct APs to ventricles

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SA Node Pacemaker continued

• Membrane voltage begins at -60mV gradually
  depolarizes to -40 threshold
  
• Spontaneous depolarization is caused by Na
  flowing through channel that opens when
  hyperpolarized (HCN channel)
  
• At threshold V-gated Ca2 channels open, creating
  upstroke contraction
  
• Repolarization is via opening of V-gated K
  channels

Fig 13.18
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11
Fig. 13.22b
12
ECG

• 3 distinct waves are produced during cardiac
  cycle
  
• P wave caused by atrial depolarization
• QRS complex caused by ventricular depolarization
• T wave results from ventricular repolarization

Fig 13.24
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Myocardial APs continued

• Upstroke occurs as V-gated Na channels open
• MP rapidly declines to -15mV stays there for
  200-300 msec (plateau phase)
  
• Plateau results from balance between slow Ca2
  influx K efflux
  
• Repolarization due to opening of extra K
  channels
  

Fig 13.19
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Fig. 13.19
15
Fig. 13.22a
16
Fig. 13.25
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Fig. 13.14
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Fig. 13.13
19
Refractory Periods
Fig 13.21

• Heart contracts as syncytium thus cannot
  sustain force
  
• Its AP lasts about 250 msec
• Has a refractory period almost as long as AP
• Cannot be stimulated to contract again until has
  relaxed

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Heart Murmurs continued

• Mumurs caused by septal defects are usually
  congenital
  
• Due to holes in septum between left right sides
  of heart
  
• Pressure causes blood to pass from left to right

Fig 13.16
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Heart Murmurs

• Are abnormal sounds produced by abnormal patterns
  of blood flow in heart
  
• Many caused by defective heart valves
• Can be of congenital origin
• In rheumatic fever, damage can be from antibodies
  made in response to strep infection

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Heart Murmurs continued

• In mitral stenosis, mitral valve becomes
  thickened calcified, impairing blood flow from
  left atrium to left ventricle
  
• Accumulation of blood in left ventricle can cause
  pulmonary hypertension
  
• Valves are incompetent when don't close properly
• Can be from damage to papillary muscles

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Ectopic Pacemakers

• Other tissues in heart are spontaneously active
• But are slower than SA node
• Are stimulated to produce APs by SA node before
  spontaneously depolarize to threshold
  
• If APs from SA node are prevented from reaching
  these, they will generate pacemaker potentials
  

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Myocardial APs

• Myocardial cells have RMP of 90 mV
• Depolarized to threshold by APs originating in SA
  node
  

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Excitation-Contraction Coupling

• Depolarization of myocardial cells opens V-gated
  Ca2 channels in sarcolema
  
• This depolarization opens V-gated Ca2 release
  channels in SR (calcium-stimulated-calcium-release
  )
  
• Ca2 binds to troponin stimulates contraction
  (as in skeletal muscle)
  
• During repolarization Ca2 pumped out of cell
  into SR
  

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Types of ECG Recordings

• Bipolar leads record voltage between electrodes
  placed on wrists legs (right leg is ground)
  
• Lead I records between right arm left arm
• Lead II right arm left leg
• Lead III left arm left leg

Fig 13.23
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Types of ECG Recordings continued

• Unipolar leads record voltage between a single
  electrode placed on body ground built into ECG
  machine
  
• Limb leads go on right arm (AVR), left arm (AVL),
  left leg (AVF)
  
• The 6 chest leads, placed as shown, allow certain
  abnormalities to be detected

Fig 13.23
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Correlation of ECG with Heart Sounds

• 1st heart sound (lub) comes immediately after QRS
  wave as AV valves close
  
• 2nd heart sound (dub) comes as T wave begins
  semilunar valves close.

Fig 13.25
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