Circulation and Cardiovascular System Notes

Circulation: Connecting Blood Pressure to Blood Vessels & the Heartbeat

Review Questions

• What does the ‘P’ peak monitor?
• What does the QRS sequence represent?
• What does the T peak represent?

Application Questions

• What do the repetitive P waves indicate?
• What would a small QRS wave indicate?
• What is arrhythmia?
• Why is ventricular fibrillation dangerous?

Blood Pressure & Blood Vessels

• Blood pressure is related to the blood vessels.
• Fluid pressure decreases the farther blood moves from the heart.

Types of Blood Vessels

• Arteries:
  • Thick-walled.
  • Larger diameter.
  • Elastic.
  • Have muscle fibers embedded in the walls.
  • Stretch to accommodate increased blood pressure.
• Capillaries:
  • Single cell layer thick.
  • Only one red blood cell can get through at a time.
  • Thin walled and easily destroyed
• Veins:
  • Thin-walled.
  • Larger diameter than capillaries.
  • No muscle embedded into the walls of the vessel.
  • Have valves inside that use muscle contractions to squeeze blood back to the heart.
  • Cannot stretch and cannot handle increased blood pressure.

Blood Pressure and Heartbeat Phases

• Blood being pumped through vessels causes pressure changes that correspond with phases of the heartbeat.
• Systolic pressure:
  • Maximum pressure during ventricular contraction.
  • Corresponds to the LUB sound.
• Diastolic pressure:
  • Minimum pressure before ventricles contract again.
  • Corresponds to the DUB sound.
• Normal resting blood pressure: 120/80 (measured using a sphygmomanometer).

Cardiac Output

• The amount of blood that flows from the heart per minute.
• Two factors affect cardiac output:
  • Stroke volume.
  • Heart rate.

Stroke Volume

• Quantity of blood pumped with each beat of the heart.
• The stronger the heart contraction, the greater the stroke volume.
• ~70 mL of blood per beat leaves your ventricles while you are at rest.

Heart Rate

• The number of times the heart beats per minute.

Cardiac Output Equation:

• Cardiac\ output = stroke\ volume \times heart\ rate

• Cardiac output provides a baseline to compare individual fitness.

Regulation of Body Temperature

• Thermoregulation is the maintenance of body temperature within an acceptable range.
• Human’s typical body temperature is ~37 degrees Celsius.
• It is a survival mechanism used to help protect us when we’re in extreme environments of heat or cold.

Responding to Increased Body Temperature

1. The hypothalamus in the brain sends a signal to the sweat glands to initiate sweating, which leads to evaporative cooling.
2. Nerves send a message to the capillaries to dilate, allowing more blood flow to the skin.
3. More blood flow means more heat can be lost through the skin before it returns to our body’s core.
4. Body cools down.

Responding to Decreased Body Temperature

1. The hypothalamus in the brain sends a signal to internal organs to increase body temperature and to initiate shivering.
2. Nerves send a message to the smooth muscles in our arteries to constrict, allowing less blood flow to the skin.
3. Less blood flow means less heat is lost through the skin before it returns to our body’s core.
4. The body warms up.

Heart Disorders

Atherosclerosis

• This condition occurs when excess lipids in someone’s arteries begin to aggregate (clump together) and stick to the inner walls of arteries.
• This limits blood flow and can lead to high blood pressure.
• Sometimes, blood will clot and block the artery completely.

Arteriosclerosis

• Hardening of the arteries due to a buildup of plaque.
• Caused by lack of exercise, smoking, and/or a diet high in fat.
• Leads to decreased blood flow and increased blood pressure.
• Symptoms include chest pain, blood clots, shortness of breath, and heart failure.

Treatments for Arteriosclerosis

• Aspirin (prevents platelets from sticking together, reducing the formation of blood clots).
• Angioplasty (surgical procedure wherein a tube is inserted into a clogged artery and inflated, forcing the artery to open).
• Coronary bypass (segment of a healthy artery/vein is used to create a new pathway from the aorta to an unblocked portion of the blood vessel, thereby “bypassing” the blocked segment).

Congenital Heart Defects

• Structural defects present from birth.
• May be genetic or due to drug/alcohol use during pregnancy.
• Examples:
  • Valve defects (leaky valve leads to heart murmur).
  • Septal defects (hole in septum leads to mixing of oxygenated and deoxygenated blood).
• Congenital heart defects are primarily corrected through surgery.

Aneurysm

• This condition occurs when a bulge forms in the wall of a weakened blood vessel, usually an artery.
• Often occurs due to atherosclerosis.
• It will result in a thinner artery wall and become at risk for a rupture of the artery.

Hypertension

• Caused by increased resistance to blood flow.
• High blood pressure over the long term can:
  • Weaken arterial walls.
  • Destroy capillaries in body tissue (i.e., nephrons in kidneys, coronary arteries, etc.).
• Diet is often a primary factor for susceptible individuals:
  • Increased salt intake can cause blood pressure to rise.

Heart Attack Symptoms

Heart Attack Symptoms in Women

• Neck, shoulder, upper back, or abdominal discomfort - often triggered by stress or anxiety. More likely to occur during rest.
• Shortness of breath
• Nausea or vomiting
• Sweating
• Light-headedness or dizziness
• Unusual fatigue

Heart Attack Symptoms in Men

• Intense chest pain or pressure that may extend to arms - often triggered by physical activity. Tends to go away with rest.
• Shortness of breath
• Cold sweat
• Pain in left arm

Important Note on Heart Attack Symptoms in Women

• The symptoms of a heart attack in women have only recently been studied.
• Women experience symptoms that are often not associated with a heart attack.
• Because women experience more subtle symptoms than men, they are less likely to seek help/call 911 (many don’t even realize they are having a heart attack).
• As a result, women are more likely to die of a heart attack than men.