BIOL 204 – Week 4 Lab Electrocardiography Human Arteries and Veins Blood Vessel Histology

Objective 1ECG An electrocardiogram is a graphical recording of the hearts electrical changes during a cardiac cycle (heart beat) -Electrical changes initiated and propagated through the myocardium by specialized cells of the heart’s intrinsic conduction system Structures of the Intrinsic Conduction Voltage changes seen System

The voltage changes are recorded by leads which can be placed in different locations on the body We will use limb leads, placed on the appendages to record ECGs in this lab Lead 1: RA -, LA + most sensitive to electrical activity spreading horizontally across the heart Lead 2 RA -, LL + most sensitive to electrical activity spreading vertically (from the base to the apex) Lead 3 LA -. LL + also records electrical activity spreading from the base to the apex, but from a different orientation

When an ECG tracing is recorded using these lead combinations, a series of wave forms are generated which respond to the spread of electricity through the heart after it originates at the SA node

A typical ECG tracing

Y (vertical) axis measure voltage: -typically, 10 squares = 1 mV X axis measures time: -At a chart speed of 25 mm/sec: each small block = 0.04 sec and each large block (5 small blocks) =5 X 0.04 sec. =0.20 sec.

What is the duration of the : P wave? P-R interval? QRS complex? Q-T interval? T wave?

To determine the heart rate from an ECG tracing: Method #1:count the number of small squares from one R wave to the next R wave and divide that number into 1500 Heart Rate (bpm) = 1500/#small squares Method #2locate an R wave on a bold line and identify the next R wave: HR = 72 bpm HR = 37 bpm

In this exercise you will evaluate a baseline ECG, and then identify and discuss changes in the ECG after a period of exercise and after a period of breath holding

Objective 2Blood Vessel Histology Arteries and Veins have three tunics, or tissue layers: Tunica intima (interna) Inner layer of endothelium and subendothelial areolar CT Tunica media smooth muscle and elastic tissue Tunica adventitia (externa) Dense irregular connective tissue

Comparison of arteries and veins: Small artery: thick tunica media, thinSmall vein: thin tunica media tunica externa thick tunica externa maintains its shape collapsible

Objective 3Some Human Arteries:

Major Veins of the Body