Cardiovascular system part 2

The cardiac cycle (1)

First sound (lub) is caused by the vibration and closure of the AV valves during contraction of the ventricles

Second sound (dub) is caused by the closure of the semilunar valves during relaxation of the ventricles (think second, semilunar valves)

Heart murmurs: abnormal heart sounds often caused by abnormal valves

The cardiac cycle (2)

1. Ventricular filling

   1. Mostly diastole, blood flows from atria into ventricles

2. Ventricular systole

   1. Ejection, ventricles contract, AV valves are closed (lub sound)

3. Ventricular relaxation

   1. Early diastole, ventricles relax, semilunar valves close (dub sound), AV valves reopen, and cycle begins again

The cardiac cycle (4)

Heartbeat is regular and rhythmic:

• Each complete beat is a cardiac cycle

• Average is about 70 beats per minute

• Each cycle is about 0.85 seconds long

Stages of the cardiac cycle:

• Systole (contraction phase)

• Diastole (relaxation phase) *dying down, diastole

The cardiac cycle (5)

Controlled by nodal tissue

• Combination of cardiac muscle and nervous tissue

• Nodes send electrical impulses through the cardiac muscle to trigger contraction

1. SA (sinoatrial) node; starts: The pacemaker

   1. Regulates heartbeat

2. Atrioventricular node; delays

   1. Delays and relays the impulse

3. AV bundle (bundle of His); delivers: Located in the septum of the ventricle

4. Purkinje fibers; spreads: Located in the walls of the ventricle

Electrocardiography

Study of the electrical system that contracts the heart

The normal ECG has 3 deflections or waves:

1. P wave; SA node gets the go signal:

   1. Associated with SA node impulse to the atria (just before contraction)

2. QRS complex; Ventricles get the go signal:

   1. Associated with the electrical impulse traveling to the ventricles (just before contraction)

3. T wave; Ventricles reset:

   1. Associated with the recovery of the ventricles (just before relaxation)

Blood pressure

Blood pressure: The pressure of blood against the wall of a blood vessel

Systolic pressure:

• The highest pressure against an artery

• Occurs when blood is pumped out of the heart

• Average: 120 mm Hg

Diastolic pressure:

• The lowest pressure against an artery

• Occurs during the relaxation of the ventricles

• Average: 80 mm Hg

Blood pressure

Blood pressure gradient: causes blood to circulate

• Liquids can flow only from the area where the pressure is higher to where the pressure is lower

  • Low or nonexistent blood pressure gradient is fatal if not reversed quickly

    • ex: Shock

  • Hypertension (high blood pressure) can cause a blood vessel to rupture

Factors that influence blood pressure

1. Blood volume: more volume = more pressure

2. Strength of heart contractions: stronger contractions = stronger cardiac output

3. Heart rate: increased heart rate = increased pressure

4. Blood viscosity: thicker blood = higher pressure; harder to move

5. Resistance to blood flow: affected by many factors, including vasomotor mechanism (vessel muscle contraction/relaxation):

   1. Larger diameter (hole) = less resistance

   2. Smaller diameter (hole) = more resistance

Cardiovascular disorders

CV disease is the leading cause of death in the U.S

• 33% of deaths

Heart disease kills about 25% of all men and women in the U.S

Hypertension

High blood pressure:

• Systolic BP: 140+

• Diastolic Bp: 90+

Risk factors:

• High salt, high stress, high fat

• Atherosclerosis: plaques inside of blood vessels

Prevention and treatment:

• Blood pressure checks; lifestyle changes

• Diuretics: increase urine, removes excess fluid

• Medication

Disorders of the arteries

Atherosclerosis: lipids and other matter form plaques and block arteries

• Thrombus: a blood clot caused by a plaque

• Embolus: a dislodged blood clot caused by a plaque (thrombus)

Coronary circulation and coronary heart disease

Blood flows through the left and right coronary arteries:

• Supplies the myocardium with oxygen

Angina Pectoris: Chest pain caused by inadequate oxygen to the heart

Blockage of blood flow through the coronary arteries can cause a myocardial infarction (heart attack)

Heart failure

Heart failure:

• Inability to pump enough returned blood to sustain life

• Can be caused by many different heart diseases

Left-sided heart failure (congestive heart failure):

• Inability of the left ventricle to pump effectively

• Results in congestion of the systemic + pulmonary circulations

Stroke

Cerebrovascular accident (stroke):

• Occurs when a blockage happens in a cranial arteriole

• May cause the arteriole to burst

• Oxygen cannot get to the brain

Symptoms:

• Numbness in the face or hands

• Difficulty speaking

• Temporary blindness in one eye

Brain aneurysm

Aneurysm: Ballooning of a blood vessel

Causes:

• Hypertension

• Antherosclerosis Increases the risk of blood vessels bursting

Increases the risk of blood vessels bursting

Results in life-threatening hemorrhaging

Disorders of veins

Varicose veins (varices): enlarged veins where blood pools

• Hemorrhoids: varicose veins in the rectum

  • Treatment includes supporting affected veins and surgical removal

• Thrombophlebitis:

  • Vein inflammation (phlebitis) accompanied by clot (thrombus) formation

  • May result in fatal pulmonary embolism

Risks

Smoking:

• Nicotine constricts your arterioles

  • Decreases blood flow to the art

  • Increases blood pressure

  • Increases clot formation

Salt:

• High salt diet causes water retention

  • Increases blood volume which increases blood pressure

    • Major risk for CVD and stroke

Fat:

• Cardiac output is greater due to increased tissues

• Increased hypertension

• Increased risk of diabetes

• Plaque formation

• Cholesterol is affected by the fats you eat