25

• Circulation


  Blood supplies oxygen to muscles
• Muscle is dependent on ATP supply for activity


  During activity muscles depend on oxygen for their supply of ATP
• Oxygen isn't the only thing
• BP is important for

  Urine production
• Thermoregulation or vascular heat exchangers


  • Important for warm or cool weather
• Box 25.1 Figure A

  • Cardiac muscle cells with intercalated disc
• Box 25.1 Figure B

  • Action potentials
• Circulation


  Moves blood, but also O₂, CO₂, nutrients, organic wastes, hormones, immune system products, heat
• Circulation


  Hydraulic pressure for organ roles
• Hearts


  • Muscle tissue of the heart is made of cardiac tissue and is known as the myocardium
• The left side of the human heart

  Has 2 parts: A weakly muscular atrium and a strongly muscled ventricle
• Hearts


  1. They received oxygenated blood from the lungs and send it throughout the body

  2. Blood arrives at the left atrium from the pulmonary veins and leaves the left ventricle via the systemic aorta

  3. Blood returns to the heart via the venae cavae, Entering the heart at the right atrium and on to the left atrium
• The role of the right side of the heart

  To pump deoxygenated blood to the lungs
• Hearts


  1. Blood leaves the right ventricle and enters the pulmonary trunk

  2. From there it moves on to the pulmonary arteries and the lungs
• The heart as a pump


  The action of a heart can be analyzed in terms of the physics of pumping
• During the beating of the heart

  There is a contraction (systole) and a relaxation (diastole)
• During isometric contraction


  The volume of blood in the ventricle is constant
• When the pressure is high enough

  The aortic valve opens, and the blood is pushed from the ventricle
• The blood then


  Enters the aorta
• Ventricular pressure drops and you have

  Isovolumetric relaxation
• Next you have


  Ventricular filling
• The hearts most important feature

  Its' cardiac output, the volume of blood it pumps per unit time
• Cardiac output


  Output of the left ventricle
• The circulation must deliver O₂ to the myocardium
• The ventricular myocardium is second only to the brain in its' need for aerobic catabolism and O₂ demand
• The heart muscle gets blood and O₂ from

  The coronary arteries
• Blood goes to


  The capillaries in the heart muscle and then enters the coronary veins
• Blockage of the coronary artery


  Can cause a heart attack
• O₂ can't get to the heart muscle, so the muscle quickly breaks down
• Figure 25.3


  • Three systems evolved by animals to supply O₂ to the myocardium
• The electrical impulses for heart contraction


  May originate in muscle cells or neurons
• Depolarization of the muscle cell membrane

  Causes the contraction
• Myogenic


  The electrical impulse to contract is in the muscle cells
• Neurogenic


  The impulse comes from nerve cells
• Vertebrates have myogenic hearts
• Muscle cells


  • Electrically coupled by gap junctions
• This occurs in mammals at

  Intercalated discs
• Depolarization spreads from cell to cell


  Causing all to contract together
• The pacemaker in mammals


  Is above the right atrium, the sinoatrial node (SA)
• SA cells


  • Specialized, have a high frequency of depolarization, first cells to depolarize