The Circulatory System

The Circulatory System

The circulatory system consists of the heart and blood vessels.

Function:

• Heart: Pumps blood throughout the body.

• Blood vessels: Transport blood from the heart to the organs and back.

Pathology:

• Common blood vessel disorders: Hypertension (HTN).

Cardiac Output:

• Cardiac output: The amount of blood pumped by the heart into the aorta with each contraction (about 60ml).

Cardiac Index:

• Formula for calculating cardiac index: Cardiac index = Cardiac output x Heart rate.

• Normal value: (4.2-4.8) = 60 x (60-70)

Work of the Heart:

• Contractile work: Energy consumed to contract the heart muscle.

• Pumping work: Energy consumed to push blood into the aorta.

• Wasted work: Energy consumed due to other factors such as blood friction against the vessel walls.

Blood Pressure:

• Formula for calculating blood pressure: Blood pressure = Cardiac output x Peripheral resistance.

• Peripheral resistance: Elasticity of the vessel wall and blood viscosity affect peripheral resistance.

Cardiac Index:

• Factors affecting cardiac index:

• Heart muscle contractility: Stronger heart muscle contraction, higher cardiac index.

• Blood return to the heart: Greater blood return to the heart, higher cardiac index.

• Cardiac congestion: Cardiac congestion, lower cardiac index.

Heart Failure:

• Compensated heart failure: Stage 1, 2, 3 heart failure.

• Decompensated heart failure: Stage 4 heart failure.

Supporting Heart Activity:

• Sympathetic nervous system: The sympathetic nervous system supports heart activity.

Cardiac Hypertrophy:

• Complications: Angina.

Increased Blood Volume:

• Cause: Reduced blood flow to the kidneys, leading to increased aldosterone secretion, causing salt and water retention, increasing blood volume.

• Complications: Respiratory failure, liver failure.

Congestion:

• Pulmonary congestion: Causes left heart failure.

• Peripheral congestion: Causes right heart failure.

Blood Pressure:

• Decreased arterial blood pressure: Due to decreased cardiac output.

• Increased venous blood pressure: Due to weak heart contractions, causing congestion.

Symptoms of Heart Failure:

• Left heart failure: Acute pulmonary edema, shortness of breath.

• Right heart failure: Impaired liver function, edema, decreased urine output.

Hypertension:

• Complications: Affects the left ventricle (left heart), death from myocardial infarction and congestive heart failure.

Factors related to peripheral resistance (R):

• Vasoconstriction: Related to peripheral resistance (R).

• Increased sympathetic activity: Related to peripheral resistance (R) and cardiac output (CO).

• Aldosterone secretion: Increases cardiac output (CO).

Causes of Hypertension:

• Kidney disease: Causes hypertension.

• Disorders of fat metabolism (LDL): Causes hypertension.

• Endocrine disorders: Causes hypertension.