The Circulatory System Part I- The Heart

The Circulatory System Part I- The Heart

Printible copy of assignment: https://docs.google.com/document/d/1JNlJhwfRuTKLi5mvzYGrgtaaBgsMvO6751JThHHEZWU/edit?usp=sharing

The Circulatory System-the body system responsible for carrying blood, nutrients, and waste throughout the body, it includes the heart, the blood vessels, and the blood.  It is a closed system.  There are some animals that use an open circulatory system like arthropods, which includes lobsters, crabs, and spiders. 

The heart- A muscular pump that generate the pressure to keep blood flowing.

Your heart is part of the major organ system called the Circulatory System. The heart is an amazing organ.  By the time a baby growing in the uterus ( fetus) is 8 weeks old, it is the size of a ping pong ball and its organs are very small, but they begin to function. Its tiny heart will begin to beat.  Its heart will beat 100,000 times per day on average, which is about 135 million times per year, and 2.5 billion times over a life time.  The average life span in the US is 76 years.  This means that our hearts beat every minute of every day, without ceasing, without rest, for and average of 76 years and 8 months.  The heart pumps 1.6 gallons of blood every minute, through 60,000 miles of vessels- enough to go around the earth twice.  The adult heart is about the size of two hand clasped together.  All of your 65 trillion cells are fed and cleaned up after by the circulatory system constantly.  The human heart weighs less than one pound, though males have slightly larger hearts, at 1.2 pounds average.  Your heart is very protected, sitting in the middle of your chest, slightly left.  It is surrounded by ribs, a sternum, the diaphragm, and the lungs.  Heart Disease is the leading cause of death in the United States. 

The "Pace" of your heart

A well trained athlete might have a heart rate of 40 beats per minute, but for most of us, our hearts beat about 60-100 beats per minute. Generally a lower heart rate signals good physical health, and its good for your heart that it doesn't have to beat as much.  Its getting more rest than an unhealthy heart.  Sometimes the heart starts to beat too slowly, too quickly, or skip beats.  This is called arrhythmia. When it just flutters ineffectively its called atrial fibrillation.  When it stops beating all together it is called Asystole.

The heart beats because of the Cardiac Conduction System, which is operates on its own.  Even if the nerves to the heart were severed, the heart would continue to beat.  Sometimes we give the heart some help, when it just can't keep a good heart rate. The first implantable pacemaker was made in 1958, and worked so well the woman died of old age.  Los Alamos National Laboratory tried to make a nuclear power source for an artificial heart in the 1970's.  The NTSB and DOE decided it was unsafe to have a person carrying around nuclear material in their chest, because if they got in an accident, the material could be spread. If they got kidnapped the material could be used for terrorism.  Instead they used tiny amounts the highly purified plutonium to power many pace makers, that lasted.

WHY DO WE NEED CIRCULATION? All cells are surrounded by interstitial fluid, where nutrients and Oxygen are dropped off to be taken into the cell, and wastes, like CO₂, are expelled by the cell.  Also, if a cell produces a product that is used elsewhere, that product transported to its destination, often in the blood stream. If we did not exchange the contents of this fluid, soon our cells would die from too much waste. 

The Heart has two Job which are called Circuits:

Circuit One: Systemic Circuit- to get oxygenated blood from the heart out to the body

           The Coronary circuit- gets blood to and from the heart itself- part of the Systemic Circuit

Circuit Two: Pulmonary Circuit- get blood from the heart to the lungs and back to the heart

Vein vs. Arteries and the color of blood

We often see diagrams of the circulatory system and the heart with blue veins and red arteries.  It is easy to assume that deoxygenated blood is blue.  It is not.  Blood in veins is a deeper red, and comes out with less pressure if a vein is cut.  It has dropped off most of the oxygen and is now carrying carbon dioxide back to be expelled by the lungs. Arterial blood is bright red and is high pressure, so if an artery is cut, it may spurt out blood.  Blue in a diagram does not mean it is a vein.  Instead it means it carries deoxygenated blood.  Note in the diagram below, the Pulmonary Artery, a vessel taking blood away from the heart, is blue, because the blood has not yet been oxygenated by the lungs. 

Vein- a vessel going towards the heart        Artery- a vessel going away from the heart

Look at the diagram of a heart and become familiar with its structures.

*Note when looking at the heart directions like right and left are from the standard anatomical position, in other words, from the point of view of the owner of the heart.  Left is this persons left.  Right is this persons right.  It is not from YOUR right or YOUR left.

Chambers of the heart:

Right Atrium-deoxygenated blood returns to the heart through the right atrium, from the  superior and inferior vena cava.

Right Ventricle- Deoxygenated blood pump's from the right atrium into the right ventricle through the tricupid valve then is pumped out though the pulmonary valve to go to the lungs

Left Atrium- oxygenated blood returns from the lungs from the pulmonary veins into the left atrium

Left Ventricle- Oxygenated blood is pumped through the mitral valve (bicuspid valve) into the left ventricle, and then pumped through the aortic valve to the aorta

Valves of the Heart

Valves keep the blood from simply washing back into the chamber it just went through, by shutting the door. It allows the system to keep good pressure. Backwash.  When there is a damaged in malformed valve, a person is said to have a "heart murmur".  The Doctor listening with his stethoscope can hear the blood "whoosh" back.  This can lead to poor circulation, fatigue, swelling in limbs, and even serious bacterial infections.  Each valve consists of two or three flaps that act as a one way door. 

Tricuspid Valve- 3 flaps

Pulmonary Valve- 3 flaps

Mitral Valve- 2 flaps

Aortic Valve- 3 flaps

Veins Entering the heart

The superior and inferior vena cava drop off deoxygenated blood from the body at the right Atrium.  Pulmonary Veins drop of oxygenated blood at the left atrium.

Arteries Exiting the heart

The pulmonary arteries take deoxygenated blood from the heart to the lungs. The Aorta takes Oxygenated blood to the body, including the heart, lungs, and the rest of the body. 

The flow of blood through the heart

Steps:

1. The superior and inferior vena cava bring deoxygenated blood to the right atrium.

2. The blood in the right atrium passes through the tricuspid valve to the Right Ventricle

3. The blood passes through the Pulmonary valve into the pulmonary artery and goes to the lungs

4. Oxygenated blood returns from the lungs in the four pulmonary veins, dropping the blood off in the left atrium

5. blood in the left atrium flows through the mitral valve to the left ventricle.  

6. Blood flows through the aortic valve into the Aorta from the left ventricle

7. blood flows through the arteries, into arterioles, into capillaries, then venules, then veins, and back to the heart

The Cardiac Cycle

The heart muscle beats spontaneously. The nervous system can only adjust the heart rate, but it can't stop it.  Even if all the nerves were severed to the heart, it would continue to beat. It is essentially two pumps, one on the right side and one on the left.  They may have   different circuits but the right and left sides coordinate their "beat".  Cells in the Right Atrium wall called the SA  (sinoatrial) NODE- conduct a signal for the heart to beat.  The signal spreads over both atria to the AV (atrioventricular) Node, where a signal then spreads across the ventricles.  The SA node is considered the "pacemaker" of the heart.  Systole means contraction, and diastole means relaxation of the heart muscle.  You may have heard systolic and diastolic when having your blood pressure taken. When you are told your blood pressure is 120/70, the top number is the pressure in your arteries when your heart contracts, the bottom number is the pressure of your arteries when your heart is relaxed and not beating. 

Watch this video on the cardiac cycle

https://www.youtube.com/watch?v=tqUyazYu3QQ