D3.1 - Structures of the Circulatory System

Circulatory System Structures

• The circulatory system transports oxygen and nutrients to cells and removes waste.
• It regulates internal temperature and protects from blood loss due to injury or infection.

William Harvey

• He proposed that the heart pumps blood throughout the body.
• He discovered that the blood volume circulates continuously.

The Heart

• The heart is a muscular organ, about the size of a fist.
• Its walls are composed of cardiac muscle.
• Cardiac muscle contraction is involuntary (cannot be consciously controlled).

Heart Chambers

• The heart has four chambers: two atria (top chambers) and two ventricles (bottom chambers).
• The atria receive blood returning from the body and lungs.
• The ventricles pump blood to the body and lungs.
• A septum separates the atria and ventricles.

Circulation Within Heart - Right Side

• Receives deoxygenated blood from the body.
• Pumps this blood to the lungs.
• The superior vena cava collects deoxygenated blood from the head, chest and arms.
• The inferior vena cava collects deoxygenated blood from the rest of the body.
• Deoxygenated blood flows from the right atrium into the right ventricle.
• Blood then flows into the pulmonary trunk and then into the pulmonary arteries.
• Pulmonary arteries are the only arteries in the body containing oxygen-poor blood.

Circulation Within Heart - Left Side

• Receives oxygenated blood from the lungs.
• Pumps this oxygenated blood to the body.
• Oxygenated blood flows from the lungs through the pulmonary veins.
• The pulmonary veins are the only veins (in the body) that contain oxygenated blood.
• The left atrium pumps blood to the left ventricle, which pumps it to the aorta.

Blood Vessel Types

• Arteries: Carry oxygenated blood away from the heart. They have thick, elastic walls to handle the surge of blood during contractions. Rhythmic expansion and contraction of an artery is the pulse.
• Veins: Carry deoxygenated blood toward the heart. They have thinner walls than arteries and contain valves that prevent backflow. Muscle contractions help to propel blood.
• Capillaries: Tiny vessels connecting arteries and veins. Their thin walls allow for gas and nutrient exchange with surrounding tissues. Blood cells pass through these vessels single file.

Valves

• Atrioventricular valves (tricuspid and mitral/bicuspid valves) prevent backflow between atria and ventricles.
• Semilunar valves (pulmonary and aortic valves) prevent backflow from the ventricles into the arteries.

Heart Structure Layers

• Outer: Connective tissue, mixed with elastic tissue
• Middle: Alternating bands of elastic tissue and smooth muscle
• Inner: Single layer of smooth cells reducing friction

The Beating Heart

• Electrical signals control heart rate/strength.
• Sinoatrial node (SA node) stimulates muscle contractions and is often referred to as the pacemaker.
• Generates electrical signals, spread through the atria, causing simultaneous contraction.
• Impulse signals through AV (atrioventricular) node, to specialized AV node fibres (bundle of His).
• The impulse is relayed through two branches that divide into Purkinje fibres, causing almost simultaneous contractions of all cells of the ventricles.

Electrocardiogram (ECG)

• Records the electrical activity of the heart.
• In a healthy heart rhythm, there are three waves: P-wave, QRS complex, T-wave.
• P-wave indicates atrial contraction.
• QRS complex indicates ventricular contraction.
• T-wave indicates ventricular recovery.
• Abnormal peaks and lines indicate potential heart problems.

Heart Sounds

• Heart sounds are due to valve opening and closing.
• "Lub" sound: AV valves closing during ventricular contraction.
• "Dub" sound: Semilunar valves closing during ventricular relaxation.
• A heart murmur is an abnormal sound caused by valve dysfunction.

Blood Pressure (BP)

• Pressure exerted against vessel walls by blood.
• Systolic pressure is the maximum pressure during ventricular contraction.
• Diastolic pressure is the minimum pressure during ventricular relaxation.
• BP is measured with a sphygmomanometer.

Cardiac Output

• Amount of blood pumped by each side of the heart per minute.
• Factors affecting cardiac output include stroke volume and heart rate.
• Stroke volume is the amount of blood pumped with each heartbeat.
• Heart rate is the number of heartbeats per minute.

Cardiac Output Calculation

• Cardiac output is calculated by multiplying heart rate and stroke volume.
• Average cardiac output in a healthy adult is approximately 5 liters per minute.

Pathways of Circulatory System

• Blood vessels form distinct pathways for efficient blood flow.
• The three main pathways are pulmonary, systemic and coronary.

Pulmonary Pathway

• Transports oxygen-poor blood to the lungs.
• Allows for oxygen-carbon dioxide exchange in the alveoli.
• Returns oxygen-rich blood to the heart.

Systemic Pathway

• Transports oxygen-rich blood from the heart to body tissues.
• Oxygen and nutrients are delivered to cells.
• Waste is collected and transported back to the heart.

Tracing Blood Flow

• Oxygen-poor blood returns to the heart, enters the right atrium and is pumped to the lungs for gas exchange.
• Oxygen-rich blood returns to the left side of the heart and is circulated throughout the body.

Coronary Pathway

• Supplies blood to the heart muscle itself.

Cardiovascular Disorders

• Arteriosclerosis: A condition where artery walls thicken and lose elasticity, often due to high fat diets. This blocks the blood flow which leads to several symptoms.
• Atherosclerosis: Buildup of plaque (fatty deposits) in artery walls, potentially leading to angina, blood clots, and heart problems.
• Angioplasty: A surgical procedure that widens blocked arteries.
• Stent: A small metal tube placed in an artery to keep it open.
• Coronary bypass surgery: Uses grafted veins to provide an alternative pathway around blocked coronary arteries.

Test your knowledge on the structures and functions of the circulatory system, focusing on the heart. This quiz covers key concepts from William Harvey's discoveries to the details of heart chambers and circulation. Perfect for students learning about human anatomy and physiology.