Heart and Blood Vessels

Thanks Rebecca and Cait


Anatomy: A four chambered organ. The right side of the heart collects deoxygenated blood from the body and sends it to the lungs. The left side of the heart collects oxygenated blood from the lungs and pumps it to the body cells.

Function: Provides force which moves the blood around the body.

The heart pushes blood by beating. This beat is controlled, in part, by 2 pacemakers. Pacemakers are groups of cells that conduct electrical action potentials in a rhythmic pattern. These pacemakers cause the heart muscle to contract.

The sinoatrial node (SA node) is located at the top of the heart and depolarizes 70-80 times a minute. The atrioventricular node (AV node) is located inferior to the SA node and depolarizes 40-60 times a minute. Under normal operation, the SA node causes the AV node to depolarize faster than it normally would. If the SA node is not functioning the AV node will control the contraction of the heart (although the heart will beat slower).

Electrical Conduction of the Heart


An electrocardiogram (EKG) records the electrical activity of the heart. For our purposes, the EKG has three main features:
P wave: Is the electrical signal that causes the both atria to contract.
QRS complex: Is the electrical signal that causes both ventricles to contract (the atria relax at this point but the electical signal is masked by the size of the QRS complex).
T wave: Is the electrical signal that causes the ventricles to relax.

Cardiac Output

This is a measurement of how much blood a heart moves in one minute. The formula is as follows:

CO = SV * HR

CO = Cardiac Output
SV = Stroke Volume (mL) this is approximately 80 mL for a human heart
HR = Heart Rate (bpm)
bpm = Beats per Minute

Blood Vessels

There are three main types of blood vessels:

Arteries: Handle high pressure blood from the heart. They have thick walls to resist tearing under the high pressure. Due to this they also have a pulse. A pulse is a periodic stretching of the artery that occurs during ventricular systole, right at the highest pressure point when the ventricle contracts.

Capillaries: The smallest blood vessel. These vessels have a very thin wall and allow blood to take in/remove products (oxygen, sugar, water, hormones, carbon dioxide, etc.). These vessels can only fit red blood cells in a single file line they are so small!

Veins: Thin-walled, carry low pressure blood coming out of capillaries back to the heart. Veins have one-way valves in them that prevent blood from flowing away from the heart.

Blood Pressure

Blood pressure is checked with a sphygmomanometer (blood pressure cuff). The procedure, in class, is as follows:
What you do...
What is Happening....
What You Should Hear....
Inflate the cuff until you no longer hear 'rushing' or 'beating' sounds. Do not go more than 30 mmHG over this point!
The cuff is squeezing shut the brachial artery.
The sound of silence.
Slowly turn the knob to release pressure.... watch the pressure gauge and listen!
The cuff pressure is reducing, and at some point the left ventricle of the heart will have enough pressure to force blood through the brachial artery.
You should hear a 'bump' pulse sound. This is the systolic pressure! (note it)
Keep slowly releasing pressure...note when the pressure gauge stops pulsing and you can no longer hear the pulse.
The cuff pressure is reducing, and the pulse sound is going away. Once the pressure is low enough, the brachial artery is no longer pinched shut at any point in the cardiac cycle.
The 'bump' sound gets fainter and fainter. Note the pressure when you cannot hear it anymore. This is the diastolic pressure.