Cardiovascular System 2

Cardiovascular System 2

• Cardiac output is the amount of blood pumped from each ventricle, usually referring to the left ventricular output through the aorta.
• Cardiac output is the most crucial factor in the cardiovascular system; the blood flow rate through different body parts depends on cardiac output.
• Arterial blood pressure is defined as the pressure exerted by blood on artery walls.
• Systolic pressure is the maximum pressure during the heart's contraction (systole). Normal systolic pressure is 120 mm Hg.
• Diastolic pressure is the minimum pressure during heart relaxation (diastole). Normal diastolic pressure is 80 mm Hg.
• Mean arterial pressure (MAP) is the average pressure in arteries. Normal MAP is 93 mm Hg (calculated as diastolic pressure + 1/3 pulse pressure).
• MAP = Cardiac Output × Total Peripheral Resistance
• Total peripheral resistance (TPR) is the resistance to blood flow from all systemic vessels, primarily arterioles.
• MAP is regulated by cardiac activity and vascular smooth muscle tone.
• Cardiac output is impacted by heart rate and stroke volume.
• Arteriolar radius affects total peripheral resistance.

Regulation Of Blood Pressure

• Arterial pressure control mechanisms are categorized into two groups:
  • Rapidly acting mechanisms (seconds to minutes).
  • Long-term regulating mechanisms (days, months, years).

Neural Control Mechanisms (Rapidly Acting)

• These mechanisms respond quickly.
• Baroreceptor mechanism and chemoreceptor mechanism are examples of these.

The Baroreceptor Mechanism

• Baroreceptors are pressure-sensitive receptors located in the carotid sinus and aortic arch.
• Increased blood pressure stimulates baroreceptors.
• Impulses travel to the cardiovascular center in the medulla via cranial nerves IX and X.
• This leads to:
  • Dilation of blood vessels
  • Decrease in vasomotor tone
  • Bradycardia (decreased heart rate)
  • Increased vagal tone
• Conversely, a decrease in blood pressure causes:
  • Increased vasomotor tone
  • Increased heart rate
  • Decreased vagal tone
• The nucleus of tractus solitarius integrates baroreceptor signals.

The Chemoreceptor Mechanism

• Chemoreceptors are sensitive to oxygen levels, carbon dioxide levels, and hydrogen ions.
• Located in the carotid bodies and aortic bodies.
• A decrease in blood pressure leads to decreased blood flow to the chemoreceptors, which triggers a response.
• This response stimulates the cardiovascular center, increasing sympathetic output to the heart and blood vessels, leading to increased heart rate and vasoconstriction.

Kidney Regulation of Blood Pressure (Long-Term Regulation)

• Kidneys control arterial pressure in two ways:
  • Regulating extracellular fluid (ECF) volume.
  • Renin-angiotensin mechanism.
• Increased blood pressure causes the kidneys to excrete more water and salt (sodium).
• Decreased blood pressure causes the kidneys to reabsorb more water and salt.
• The renin-angiotensin mechanism increases blood pressure.
  • When blood pressure/ECF volume decreases, the kidneys secrete renin.
  • Renin converts angiotensinogen to angiotensin I.
  • Angiotensin-converting enzyme (ACE) in the lungs converts angiotensin I to angiotensin II.
  • Angiotensin II stimulates the adrenal cortex to secrete aldosterone, which increases sodium and water reabsorption in the kidneys, leading to increased blood volume and pressure.

Pharmacy Applied: Antihypertensive Drugs

• Diuretics reduce body fluid volume. They increase excretion of sodium and chloride ions, increasing urine production.
• ACE inhibitors inhibit the conversion of angiotensin I to angiotensin II. This reduces vasoconstriction and the aldosterone response (sodium retention). This action can increase the effectiveness of diuretics.

The Circulatory Shock

• Circulatory shock is generalized inadequate blood flow leading to tissue damage. This occurs from insufficient oxygen/nutrients to the tissues.
• Shock is usually due to decreased cardiac output or low blood volume.

Types of Shock

• Hypovolemic shock: due to low blood volume (e.g., hemorrhage, dehydration, burns).
• Cardiogenic shock: inadequate pumping action of the heart (e.g., heart attack, heart failure).
• Neurogenic shock: widespread vasodilation due to dysfunction of the autonomic nervous system (e.g., severe emotional stress, spinal cord injury).
• Anaphylactic shock: severe allergic reaction causing widespread vasodilation (e.g., allergic reactions).
• Septic shock: caused by severe bacterial infection with endotoxin/fever, causing widespread vasodilation and inflammation.

Manifestations of Circulatory Shock

• Low blood pressure
• Rapid, weak pulse
• Pale, cold skin
• Low urinary output
• Brain tissue ischemia.

This quiz focuses on the key concepts of the cardiovascular system, including cardiac output, arterial blood pressure, systolic and diastolic pressures, and mean arterial pressure. Test your understanding of how these factors influence blood flow and overall cardiovascular health.