Circulatory System

1
Circulatory System

• Chapter 42A

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Open vs. Closed Circulatory Systems

• both types have blood, blood vessels, heart
• blood pressure is the motive force for fluid
  movement
• open circulatory system
• blood is NOT confined to vessels and mixes with
  interstitial fluid (forming hemolymph)
• advantage requires less energy to function
• closed circulatory system
• blood is confined to vessels is distinct from
  the interstitial fluid
• advantage more effective at transporting fluids
  in large, active animals

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open
closed
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Blood Vessels

• arteries
• carry blood away from the heart
• thick, elastic walls
• veins
• carry blood back to the heart
• thin walls
• capillaries
• walls one-cell thick which allows for diffusion
  of nutrients between cells blood

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Human Circulatory System Pathway

• R ventricle pumps blood to the lungs (pulmonary
  circuit) via the pulmonary arteries
• blood flows through capillaries in the lungs
  picks up O2/unloads CO2
• O2-rich blood returns to L atrium via pulmonary
  veins
• blood flows from L atrium into L ventricle
• ? cont.

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• L ventricle pumps the blood out to the body
  tissues (systemic circuit) via the aorta which
  branches into arteries ? arterioles ? capillaries
• in capillaries, blood unloads O2 into body
  tissues picks up CO2
• O2-poor blood flows into veins returns to R
  atrium via anterior posterior vena cava
• blood flows from R atrium into R ventricle the
  cycle begins again

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Human Heart A Closer Look
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Heart Contractions

• the heart contracts relaxes in a rhythmic cycle
• SA node (pacemaker) sets rate timing of
  cardiac muscle contractions
• located in wall of R atrium
• self-excitable (doesnt require signal from
  nervous system to contract)
• generates electrical impulses that cause atria to
  contract in unison
• AV node
• located between R atrium R ventricle
• receives signal from SA node delays it for 0.1
  sec before relaying it to ventricles

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Heart Valves

• AV valves
• located between atria ventricles
• close when ventricles contract to prevent
  backflow into atria
• semilunar valves
• located at the 2 exits from the heart
• open when ventricles contract then close as
  they relax to prevent backflow into ventricles

10
Cardiac Cycle Blood Pressure

• cardiac cycle one complete sequence of pumping
  filling
• systole contraction phase (pumps blood)
• diastole relaxation phase (chambers fill
  w/blood)
• blood pressure is a measure of the pressure in
  arteries during both phases
• systolic pressure in arteries when ventricles
  contract
• diastolic pressure in arteries when heart
  relaxes
• normal blood pressure for a resting adult 120/80

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Cardiac Output

• cardiac output volume of blood pumped by L
  ventricle into systemic circuit
• depends on
• heart rate ( beats/min)
• stroke volume (amount of blood pumped by L
  ventricle each contraction)

12
Blood Components
13
Blood Clotting

• begins when blood vessel is damaged
• blood platelets adhere to collagen fibers in
  connective tissue of blood vessel wall to form a
  temporary plug
• clotting factors released from clumped platelets
  convert fibrinogen in the plasma to its active
  form, fibrin, which aggregates into threads that
  permanently block the hole