Circulatory System Flashcards
Circulatory System Overview
Components: The human circulatory system consists of blood, blood vessels, and the heart. Blood is a liquid tissue made up of plasma (a watery fluid) and cells (cellular content). The heart is a muscular pump that circulates blood to the lungs and the body. Blood vessels are classified into three types: arteries, veins, and capillaries.
Arteries: Carry blood from the heart to the body.
Veins: Return blood from the body to the heart.
Capillaries: Connect arteries to veins and facilitate material exchange with tissues.
Blood Vessels: Structure and Function
Arteries and Veins Structure: Both arteries and veins consist of three layers:
External Layer: Connective tissue.
Middle Layer: Smooth muscles.
Inner Layer: Endothelium.
Arteries: Smaller lumen, thicker walls, and higher pressure as they carry oxygenated blood (except the pulmonary artery) from the heart to body tissues.
Veins: Larger lumen, thinner walls, and lower pressure. Veins have valves to prevent backflow of blood, particularly in limbs where muscles help move blood upward.
Capillaries: Extremely thin walls (one-cell thick), allowing for material exchange between blood and tissues. They connect arteries and veins.
Function of Blood Vessels
Arteries: Face maximum pressure, carry oxygenated blood (except pulmonary artery). Their thick walls help withstand high pressure.
Veins: Return deoxygenated blood to the heart, face low pressure, and have valves to prevent backflow.
Capillaries: Facilitate nutrient, gas, and waste exchange between blood and tissues, with walls that are only one cell thick.
Human Heart: Structure and Function
Heart Anatomy: The heart is a muscular organ about the size of a clenched fist, located in the chest cavity. It consists of four chambers:
Atria: The upper chambers that receive blood from the body and lungs.
Ventricles: The lower chambers that pump blood to the body and lungs.
Heart Valves: Valves prevent the backflow of blood and ensure proper circulation:
Tricuspid Valve: Between the right atrium and right ventricle.
Bicuspid (Mitral) Valve: Between the left atrium and left ventricle.
Pulmonary Valve: Prevents backflow from the pulmonary artery.
Aortic Valve: Prevents backflow from the aorta.
Left Ventricle: Stronger than the right ventricle, as it pumps blood to the entire body, while the right pumps it to the lungs.
Double Pumping Action of the Heart
Right Side of the Heart: Receives deoxygenated blood from the body via the vena cava, which enters the right atrium. It then passes through the tricuspid valve into the right ventricle. The right ventricle pumps blood into the pulmonary artery for oxygenation in the lungs.
Left Side of the Heart: Receives oxygenated blood from the lungs via the pulmonary veins into the left atrium. Blood passes through the bicuspid valve into the left ventricle, which pumps it into the aorta for distribution throughout the body.
Self-Excitatory System of the Heart
Sinoatrial (SA) Node: The heart’s natural pacemaker, located in the right atrium, generates electrical impulses that stimulate the atria to contract.
Atrioventricular (AV) Node: Receives impulses from the SA node, amplifies them, and sends them to the ventricles to stimulate contraction.
Impulse Spread: This electrical impulse system coordinates heartbeats and ensures both atria contract first, followed by both ventricles.
Cardiac Cycle
The cardiac cycle refers to the sequence of events that occurs during one complete heartbeat:
Diastole: Both atria and ventricles are relaxed, and blood fills the heart.
Atrial Systole: Atria contract, pushing blood into ventricles.
Ventricular Systole: Ventricles contract, pumping blood to the lungs (right ventricle) and the body (left ventricle).
Relaxation: The heart returns to its relaxed state, and the cycle repeats.
Double Circulation in Humans
Human circulatory system is double circulation, meaning blood flows through two circuits:
Systemic Circulation: Oxygenated blood flows from the heart to the body and back.
Carries blood to head, arms, organs, and lower body.
Pulmonary Circulation: Deoxygenated blood flows from the heart to the lungs for oxygenation, then back to the heart.
Involves the pulmonary artery (right ventricle to lungs) and pulmonary vein (lungs to left atrium).
Comparison of Arteries, Veins, and Capillaries
Arteries:
Function: Carry oxygenated blood (except pulmonary artery) from the heart to the body.
Wall Structure: Thick walls with three layers: connective tissue (outer), smooth muscle (middle), and endothelium (inner).
Lumen: Small diameter.
Pressure: High pressure, as blood is pumped directly from the heart.
Valves: Absent.
Blood Flow: Fast and under high pressure.
Veins:
Function: Carry deoxygenated blood (except pulmonary vein) from the body back to the heart.
Wall Structure: Thinner walls compared to arteries, with three layers: connective tissue, smooth muscle, and endothelium.
Lumen: Larger diameter than arteries.
Pressure: Low pressure, as blood flows back to the heart with little force.
Valves: Present to prevent backflow of blood, especially in limbs.
Blood Flow: Slow and under low pressure, assisted by muscle contractions and gravity.
Capillaries:
Function: Facilitate exchange of gases, nutrients, and waste products between blood and tissues.
Wall Structure: One-cell thick walls (endothelium), allowing for easy exchange.
Lumen: Extremely narrow, just wide enough for red blood cells to pass through in single file.
Pressure: Medium pressure, higher than veins but lower than arteries.
Valves: Absent.
Blood Flow: Slow, enabling efficient exchange of materials with tissues.
