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Overview. IntroductionThe Heart and The Circulation SystemThe HeartbeatContractile cellsThe conducting systemThe cardiac cycleHeart DynamicsFactors controlling cardiac output. The Heartbeat. Atria and ventricles contract in coordinated mannerEnsures correct blood flow2 types of cardiac muscle cells involved:Contractile cellsProduce powerful contractions that propel bloodConducting systemControl and coordinate activity of contractile cells.
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1. The Heart Chapter 12
Pgs 368; 375-387
2. Overview Introduction
The Heart and The Circulation System
The Heartbeat
Contractile cells
The conducting system
The cardiac cycle
Heart Dynamics
Factors controlling cardiac output
5. The Heartbeat Atria and ventricles contract in coordinated manner
Ensures correct blood flow
2 types of cardiac muscle cells involved:
Contractile cells
Produce powerful contractions that propel blood
Conducting system
Control and coordinate activity of contractile cells
6. The Heartbeat: Contractile Cells Differs from skeletal muscle:
Action potential
Source of calcium ions
Duration of resulting contraction
7. Cardiac vs. Skeletal Muscle Contraction
9. The Conducting System Cardiac muscle tissue contracts on its own
Does not need hormonal or neural stimulation
These will change the force
Called automaticity or autorhythmicity
Atria contract followed by ventricles
Coordinated by conducting system
Network of specialized cardiac muscle cells
Initiate and distribute electrical impulses
Made up of two types of cells that do not contract:
Nodal cells (responsible for establishing rate of contraction)
Conducting cells (distribute the contractile stimulus to general myocardium)
10. Nodal Cells Cell membranes depolarize spontaneously and generate APs at regular intervals
Electrically coupled to each other, conducting cells, and other cardiac cells
Normal rate of contraction established by pacemaker cells
Located in the SA (sinoatrial) node
Depolarize rapidly and spontaneously
Generate 70-80 APs/min = HR of 70-80 bpm
11. Conducting Cells Stimulus for contraction generated by SA node, but must be distributed so that:
The atria contract together before the ventricles
The ventricles contract together
Wave must begin at apex and spread toward base
This pushes blood toward base into the aorta and pulmonary trunk
Now we will watch the CD!
12. The Cardiac Cycle Cardiac cycle: period between the start of one heartbeat and the beginning to the next
Systole: contraction
Diastole: relaxation
Remember: Fluids move from high pressure to low pressure!
Now we will watch the CD!
14. Heart Dynamics Refers to the movements and forces generated during cardiac contractions
Each time the heart beats the 2 ventricles release = amounts of blood
Stroke Volume (SV)—the amount of blood ejected by a ventricle during a single beat
Can vary from beat to beat
Cardiac Output (CO)—the amount of blood pumped by each ventricle in 1 min
CO = SV x HR
ml/min = ml x bpm
15. Factors Controlling Cardiac Output Highly regulated
Why?
Major factors:
Blood volume reflexes
Autonomic innervation
Hormones
Secondary factors:
Extracellular ion concentration
Body temperature
16. Blood Volume Reflexes Contraction active, relaxation passive
2 heart reflexes respond to changes in blood vol
One occurs in R atrium and affects HR
Atrial reflex
One occurs in the ventricles and affects SV
17. Atrial Reflex Involves adjustments in HR
Triggered by increase in venous return
Walls of RA stretch ? stimulate stretch receptors in wall ? increase in sympathetic activity ? cells of SA node depolarize faster ? increase HR
18. Ventricular Reflex Amount of blood pumped out of each ventricle each beat depends on:
Venous return
Filling time
Frank-Starling principle
Major effect is that the output of blood from both ventricles is balanced under a variety of conditions
19. Factors Controlling CO: Autonomic Innervation ANS can modify HR
Innervated by both parasympathetic and sympathetic divisions
Innervate SA and AV nodes
21. Factors Affecting CO: Hormones Adrenal medulla
NE and E
Result?
Thyroid hormones and glucagon
Secreted by pancreas
Produce similar effects to NE and E
22. Coordination of Autonomic Activity Cardiac centers in medulla
Cardioacceleratory center
Which neurons are activated?
Cardioinhibitory center
Which neurons are activated?
Gets from heart to medulla through vagus nerve
Both respond to changes in bp and arterial concentrations of oxygen and carbon dioxide
Monitored by baroreceptors