Heart Review from Day 1 On a whiteboard: 1. Draw and label a diagram of the heart including: The 4 chambers Associated blood vessels Valves The path of blood flow 2. Be prepared to verbally state the path for: Pulmonary circulation Systemic circulation

The Heart: Day 2

Outline the control of the heart beat The heart utilizes myogenic muscle contraction –the cardiac muscle contracts and relaxes without the use of the nervous system *Note: it is very important to control this process and the next slides will tell us how the heart keeps correct timing

sinoatrial node (SA node) aka “pacemaker” – the mass of tissue within the wall of the right atrium (near where the superior vena cava enters the right atrium) It keeps the correct rhythm of the heart Details of Control MechanismDetails of Control Mechanism:

1. The SA node sends out an electrical impulse ( similar to those produced by the nervous system ) which causes the contraction of both atria *Note: for a person with a resting heart rate of 72 bpm, the signal from the SA node is sent out about every.8 seconds 2. Next, the signal is received by the atrioventricular node (AV node)

3. The AV node then delays its signal by about.1 seconds; this is to ensure that the atria will contract first and empty completely before the ventricles contract NOTE: atria empty b/c pressure is lower in ventricles, therefore valves open and blood empties

4. The AV node sends it’s signal to the Purkinje fibers which results in the contraction of both ventricles simultaneously NOTE: the impulses created in the heart can be read by electrodes placed on the skin and connected to an electrocardiogram (EKG)

Factors that Affect Heart Rate 1. Nerves – two sets of nerves oppose each other in adjusting the heart rate; one speeds it up and the other slows it down (signals sent to SA node) Example: You start exercising Decreased O 2 and increased CO 2 result in medulla sensing changes Accelerator nerve increases impulses sent to SA node Heart rate increases

Factors that Affect Heart Rate 2. Hormones – during periods of high stress or excitement, chemicals like adrenaline (aka epinephrine) can speed up the rate Example: You enter a “fight or flight” situation Epinephrine is produced by adrenal glands Hormone travels through bloodstream to SA node Epinephrine increases impulses sent by SA node Heart rate accelerates

Real Life Application: What is the difference between a pacemaker and an implantable defibrillator?

What a pacemaker does is keep the heart beating at the proper rate and from beating too slow. It also will only work if it is needed, it doesn't work all the time. Low-energy electrical impulses for minor irregularities An implanted defibrillator is used for more life- threatening rhythm disturbance often from the lower chambers of the heart; high-energy electrical impulses