Circulation of the Blood

Circulation of the Blood

• The circulatory system acts as a transport system for the body
• Blood is the fluid medium that carries various substances
• Blood vessels are the tubes that carry blood
• The heart is a two-sided pump that drives the blood along the vessels
• The lymphatic system is part of the circulatory system
• The cardiovascular system includes the heart and blood vessels

Major Systemic Circulation

• The major systemic circulation starts in the left ventricle and ends in the right atrium
• The arterial system is oxygenated in the major systemic circulation
• The venous system is deoxygenated in the major systemic circulation
• The major systemic circulation is high pressure and high resistance

Lesser Pulmonary Circulation

• The lesser pulmonary circulation starts in the right ventricle and ends in the left atrium
• Oxygenated blood is carried from the pulmonary vein to the left atrium
• Deoxygenated blood is carried from the right ventricle to the pulmonary artery
• The lesser pulmonary circulation is low pressure and low resistance

Functional anatomy of the Heart

• The human heart is structurally and functionally divided into right and left halves (right and left heart)
• Each half of the heart consists of two chambers: an atrium and a ventricle
• One-way valves are present between atria and ventricles and at the origin of the aortic and pulmonary arteries

Valves of the Heart

• Right heart: The right heart has a tricuspid valve (atrioventricular valve) and a pulmonary valve (semilunar valve)
• Left heart: The left heart has a mitral valve (atrioventricular valve) and an aortic valve (semilunar valve)
• Atria and ventricles are separated by a single fibrous skeleton
• The fibrous skeleton consists of four interconnected rings of dense connective tissue
• The valves on both sides of the heart open and close simultaneously

Blood flow from the heart

• Atrial Syncytium: Both atria contract simultaneously to push blood into the respective ventricle
• Ventricular Syncytium: Both ventricles contract simultaneously to push blood into the respective artery
• Primer Pump: Atria; Primary Pump: Ventricles

Systole Phase

• Systole phase is the contraction stage
• Contraction increases pressure, opening the valve in front and closing the valve behind
• The chamber empties, decreasing volume after ejection
• Atrial contraction is followed by ventricular contraction

Diastole Phase

• Diastole phase is the relaxation stage
• Relaxation decreases pressure, opening the atrioventricular valve and closing the semilunar valve
• The chamber fills with blood, increasing volume (ventricular filling)
• Filling and emptying occur simultaneously under normal conditions
• If filling does not equal emptying, heart failure occurs
• Heart sounds are produced by closing valves

Phases of Cardiac Cycle

• Stroke volume: The volume of blood pumped by each ventricle per beat (approximately 70 ml)
• Cardiac output: The volume of blood pumped by each ventricle per minute (5–6 L)
• Diastole (Relaxation stage): Includes isovolumetric ventricular relaxation and ventricular filling
• Systole (Contracting stage): Includes isovolumetric ventricular contraction and ventricular ejection

Origin and Spread of Cardiac Excitation/Impulses

• SA Node: The pacemaker
• SA Node signals to the left and right atrium muscle cells
• Left and Right Atrium Muscle cells signal to
• AV Node
• AV Node signals to the
• Bundle of His
• Bundle of His signals to the
• Right and Left Bundle Branches
• Right and Left Bundle Branches signal to the
• Purkinje fibers
• Purkinje fibers signal the
• Ventricular muscle cells

Coronary Circulation

• The aorta gives rise to two coronary arteries:
• Right coronary artery: Supplies the right side of the heart
• Left coronary artery: Branches into left circumflex artery and left anterior descending artery, supplying the left side of the heart
• Blockage in the coronary arteries by atherosclerosis can decrease blood flow to the heart
• Partial blockage can cause chest pain (angina)
• Total blockage can cause a heart attack (infarction), a medical emergency.

Nerve Supply of the Heart

• Normal heart rate: 60-100 beats/min
• Sympathetic nerve stimulation causes release of norepinephrine, increasing the rate and force of contractions
• Parasympathetic nerve stimulation causes release of acetylcholine, decreasing the rate and force of contractions
• Increase in HR: Tachycardia
• Decrease in HR: Bradycardia

Blood Vessels

• Blood vessels are the tubes that carry blood in the body

Arteries (Damping Vessels)

• Arteries have large amounts of elastic tissue (elastic arteries)
• The "Windkessel" effect describes the elastic reservoir of arteries
• Function of the arteries:
  • Dampen huge pressure fluctuations with each cardiac contraction
  • Give a fairly steady driving pressure for tissue perfusion by means of elastic recoil
  • Act as a secondary pump during the diastole phase to maintain forward blood flow

Arterioles (Resistance Vessels)

• Structure of arterioles: Less elastic tissues, more smooth muscles with cholinergic and adrenergic receptors (muscular arteries)
• Function of arterioles:
  • Major site of resistance to blood flow
  • Regulate systemic arterial blood pressure by regulating arteriolar contraction
  • Regulate blood flow to different organs

Capillaries (Exchange Vessels)

• Structure of capillaries: Single layer of endothelial cells
• Function of capillaries:
  • Exchange of materials by diffusion between blood plasma and interstitial fluid (ISF)
  • Exchange of respiratory gases and metabolites

Veins and Venules (Capacitance Vessels)

• Structure of veins and venules: Thinner walls (less elastic tissues and muscles), with larger lumen
• Function of veins and venules:
  • Greater capacity to store blood
  • Shunt blood into systemic arterial circulation by venoconstriction when arterial pressure falls

This quiz explores the intricacies of the circulatory system, covering its components such as the heart, blood vessels, and blood. It also delves into the major systemic and lesser pulmonary circulations, detailing the processes of oxygenation and deoxygenation. Test your knowledge on how blood circulates throughout the body!