BIOL 204 – Week 4 Lab

ElectrocardiographyHuman Arteries and Veins

Blood Vessel Histology

Objective 1 ECG An electrocardiogram is a graphical recording of the hearts electrical changes during a cardiac cycle (heart beat)

- Electrical changes initiated and propagated through themyocardium 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 3LA - . 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 thenext R wave and divide that number into 1500

Heart Rate (bpm) = 1500/#small squares

Method #2 locate 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 2 Blood 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, thin Small vein: thin tunica media tunica externa thick tunica

externa

maintains its shape collapsible

Objective 3 Some Human Arteries:

Major Veins of the Body