Unit 4 Circulatory system

The cardiovascular system

The cardiovascular system

• Composed of the heart, blood vessels and blood

• Delivers oxygen and other nutrients to all body cells

• Removes carbon dioxide and other waste products from them

• Can be compared to a muscular pump equipped with one-way valves and a system of large and small plumbing tubes within which blood travels

The heart

• Approximately the size of a clenched fist

• Weighs less than one pound

• Located in the medial cavity of the thorax and is flanked by the lungs

• The more pointed apex is directed toward the left and rests on the diaphragm at the fifth intercostal space

Pericardium

• A double-walled sac that encloses the heart

• Keeps the heart contained in the chest cavity

• Prevents the heart from over-expanding when blood volume increases

• Limits heart motion

• Contains lubricating fluid that allows the heart to beat easily

The three layers of the heart’s walls

• Epicardium:

  • Outer layer

• Myocardium:

  • Thick bundles of cardiac muscle

  • The layer that contracts

• Endocardium:

  • Thin sheet that lines the heart chambers

Chambers of the heart

• 4 Chambers:

  • Two atria (left and right)

  • Two ventricles (left and right)

Atria (singular atrium)

• “receiving chambers”

• Blood flows into the atria from the veins under low pressure and then continues on to fill the ventricles

Ventricles

• “discharging chambers”

• When they contract blood is propelled out of the heart and into the circulation

• Right ventricle forms most of the heart’s anterior surface

• Left ventricle forms the apex

• The chambers are divided longitudinally by a septum

External anatomy of the heart

Pulmonary circulation

• Happens in the right side of the heart

• Oxygen-poor blood is transported from the right atrium and ventricle to the lungs for gas exchange

• Then returned to the heart

Systemic circulation

• Happens in the left side of the heart

• Blood moves from the left side through the body tissues and back to the right side of the heart

• It supplies oxygen and nutrient-rich blood to all body organs

The valves

• Allow blood to flow in only one direction through the heart chambers

• From atria through ventricles and out the greater arteries leaving the heart

Atrioventricular Valves

• Located between the atria and ventricles

• Prevent backflow into the atria when the ventricles contract

Left AV valve

• Bicuspid (mitral) valve

• Two flaps of endocardium

Right AV valve

• Tricuspid

• Three flaps of endocardium

The chordae tendineae (“tendinous cords”)

• Anchor the flaps to the walls of the ventricles

• When the heart is relaxed and blood is passively filling its chambers the AV flaps hang limply into the ventricles

• As the ventricles contract, they press on the blood in their chambers and the pressure begins to rise

• This forces the AV flaps upward closing the valves.

Semilunar Valves

• Pulmonary and Aortic Semilunar Valves

• Each has three leaflets

• When the ventricles are contracting, the leaflets are forced open and flatten against the walls of the arteries

• When the ventricles relax, the blood begins to flow backward toward the heart and the leaflets fill with blood closing the valves

The AV valves..

Open during heart relaxation and close during ventricular contractions

The semilunar valves..

Are closed during relaxation and are forced open when the ventricles contract

The Cardiac Cycle

• The heart beats or contracts approximately 70 times per minute. 

• One heartbeat, or cardiac cycle, includes atrial contraction and relaxation, ventricular contraction and relaxation, and a short pause

• Normal cardiac cycles (at rest) take 0.8 seconds

Systole

Contraction of the heart muscle

Diastole

Relaxation of the heart muscle

Auscultation

• The sound of the heart contracting and the valves opening and closing produces a characteristic "lub-dub" sound

• Lub is associated with closure of the AV valves

• Dub is associated with closure of the SL valves

Sinoatrial node (SA node)

Where human heartbeats originate from near the right atrium

Atrioventricular node (AV node)

• Where modified muscle cells contract that send a signal to other muscle cells in the heart to contract

• The signal then spreads to this node

• Signals carried are slightly delayed, through bundle of His fibers and Purkinjie fibers cause the ventricles to contract (almost) simultaneously

Arteries

• Carry blood away from the heart to the tissues of the body

• Composed of (outer layer) connective tissue, (middle layer) smooth muscle, and (inner layer) epithelial cells

• Are strong and elastic to withstand the pressure of the fluid they carry

• Artery expansion is felt as a pulse

Arterioles

• Formed by branching arteries

• Smooth muscle in the arterioles may contract or relax which is controlled by the autonomic nervous system (ANS)

• Important in maintaining constant body temperature

Vasoconstriction

When the diameter of blood vessels decreases

Vasodilation

When the diameter of blood vessels increases

Capillaries

• Branching of arterioles form capillary beds

• Site of fluid and gas exchange

• Extremely small in diameter so that RBC move through in single file

• Extremely high total cross sectional area slows the flow of blood providing time for diffusion

• Capillaries merge in a “mirror image” of the way they branched from the arterioles forming the venous side of a capillary network

Controlling Blood Flow in the Capillaries

• Capillaries lack smooth muscles

• There are pre-capillary sphincter muscles 

• If blood is not needed in a particular capillary network the sphincters contract and reduce blood flow

Veins and Venules

• Return blood to the heart

• Composed of smooth muscle, and one-way valves to return low pressure blood to heart

• Not as thick as arteries and the walls are not as elastic

• The internal diameter of veins is therefore greater than arteries

• Contraction of skeletal muscles help push blood back to heart 

• Gravity pulls blood down and causes pooling, veins may become larger and bulge → varicose veins

Major Vessels of the Body

Blood pressure can be affected by..

• Diameter of the vessels

• Physical activity

• Temperature

• Body position

• Diet

• Stress

• Age

• Certain medications

Hypertension

• A condition of consistently elevated blood pressure (i.e. high blood pressure)

• “Silent Killer”

• Dangerous because is forces the heart to work harder to pump the blood around the body

Hypertension can be caused by..

• Kidney disease (causes more fluid to be retained in the blood)

• Some medications

• Age (vessels lose elasticity as we age)

• Diet

Blood

• Whole blood is a mixture of blood cells and plasma.

• Plasma is a yellowish fluid in which the cells are suspended

Components of The Blood

• Red blood cells (RBCs) 

• White blood cells (WBCs) 

• Platelets

Red Blood Cells (erythrocytes)

• Shaped like slightly indented, flattened disks

• Contain the iron-rich protein hemoglobin

• Blood gets its bright red color when hemoglobin picks up oxygen in the lungs

• As the blood travels through the body, the hemoglobin releases oxygen to the tissues

• Life span of about 4 months

White Blood Cells (leukocytes)

• The body's system for defending itself against infection

• Can move in and out of the bloodstream to reach affected tissues

• There are several types and their life spans vary from a few days to months.

• New cells are constantly being formed in the bone marrow

Platelets (thrombocytes)

• Oval-shaped cells made in the bone marrow

• Help in the clotting process

• When a blood vessel breaks, they gather in the area and help seal off the leak

• Survive only about 9 days in the bloodstream and are constantly being replaced by new cells

The Rh System

• “D antigen” (protein) on red blood cells’ surface

  • When present, the person is Rh positive (85% Canadians)

  • When absent, the person is Rh negative (15% Canadians)

If you are Rh positive…

You can receive Rh positive or Rh negative blood

If you are Rh negative…

• You can receive only Rh negative blood

• “Anti-D antibodies”: produced when an Rh-negative person is exposed to red blood cells from an Rh-positive donor

• Creating a transfusion reaction

Arrhythmia

• An abnormal heart rhythm

• Ventricular fibrillation (VF) is the most common type

Bradycardia

Less than 60 beats per minutes

Tachycardia

More than 100 beats per minute

Fibrillation

Uncoordinated contractions

Angina

• When your heart doesn’t get as much blood and oxygen as it needs because one or more of its arteries (coronary arteries) is blocked

• A warning signal that you are at increased risk of a heart attack, cardiac arrest or sudden cardiac death

What is a heart attack?

• When the blood supply to the heart is slowed or stopped because of a blockage

• May also occur when a coronary artery temporarily contracts or goes into a severe spasm, effectively shutting off the flow of blood to the heart 

• The length of time the blood supply is cut off will determine the amount of damage to the heart

Signs of MI (myocardial infarction)

• Pressure in center of chest

• Pain in shoulders, neck, or arms

• Chest discomfort with fainting, sweating, ot nausea

• Pain radiating down left arm

Artherosclerosis

• The narrowing of coronary arteries due to plaque build-up

• Causes more than 90% of heart attacks.

Sudden Cardiac Arrest (SCA)

• A condition in which the heart stops beating suddenly and unexpectedly due to a malfunction in the heart’s electrical system

• Caused by ventricular fibrillation

• It is not a heart attack

• The probability of survival declines by 7% to 10% as time passes

• When CRP and defibrillation are used together, survival rates may increase to more than 50%

How does ventricular fibrillation happen?

• The heart’s rhythm is so chaotic (called “fibrillating”) that the heart quivers, and is unable to pump blood to the body and brain 

• First loses their pulse, then consciousness, and finally the ability to breathe

Causes of cardiac arrest or ventricular fibrillation

• Heart disease

• Drowning

• Stroke

• Electrocution

• Suffocation

• Drug overdose

• Motor vehicle or other injury

Defibrillation

• A heart in ventricular fibrillation must be defibrillated

• To defibrillate the heart an electrical shock must be applied

• Defibrillation administered within the first few minutes after collapse has the highest chance of success

Stroke

• Most are Ischemic

• They are caused by the interruption of blood flow to the brain due to a blood clot.

• The build-up of plaque (fatty materials, calcium and scar tissue) narrows the arteries that supply blood to the brain, interfering with, or blocking the flow of blood

Thrombotic strokes

Are caused by a blood clot that forms in an artery directly leading to the brain

Embolic strokes

Occurs when a clot develops somewhere else in the body and travels through the blood stream to the brain

Signs somebody may have had a stroke

• FAST:

  • FACE: Facial numbness or weakness especially on one side

  • ARM: Arm numbness or weakness especially on one side

  • SPEECH: Difficulty speaking or understanding others or a loss of speech

  • TIME: Call EMS/911 immediately

Heart Disease Prevention

• Quitting smoking

• Healthy diet

• Exercise