Heart and Cardiac Cycle

Heart and Cardiac Cycle Overview

• The central topic is about the heart and the cardiac cycle

Blood Flow Through the Heart

• Deoxygenated blood flows from the right atrium to the right ventricle
• Blood is then pumped to the lungs via the pulmonary artery
• Oxygenated blood returns to the left atrium via the pulmonary vein
• This oxygenated blood then flows to the left ventricle
• Finally, blood is pumped out of the heart through the aorta
• Hepatic Artery is the final step

Artery vs Vein Function

• Arteries generally carry oxygenated blood away from the heart
• Veins generally carry deoxygenated blood towards the heart
• Capillaries are small vessels facilitating the exchange of substances with cells
• Arterioles link arteries to capillaries
• Venules link capillaries to veins

Blood Vessel Structure

• All blood vessels share a similar structure
• A tough, fibrous outer layer resists pressure changes
• A muscle layer can contract to alter blood flow
• An elastic layer stretches and recoils to maintain blood pressure
• A smooth inner endothelium reduces friction
• The lumen is the inside "hole" where blood flows
• In arterioles, thick muscle layers contract to reduce blood pressure before blood enters capillaries, preventing them from bursting

Elastic Layer Function

• The elastic layer prevents bursting and hemorrhages
• Elastic recoil helps maintain blood pressure in arteries
• Blood enters arteries at high pressure, exerting force on the walls
• Elastic potential energy is used to maintain blood flow
• Maintain blood pressure

Cardiovascular System Risks

• Smoking, high blood pressure, and high cholesterol are risk factors for CVD
• A diet high in saturated fat elevates cholesterol
• High salt intake can increase blood pressure

Heart Blood Vessels - Fill in the Blanks

• Deoxygenated blood is pumped through the pulmonary artery to the lungs.
• Oxygenated blood returns via the pulmonary vein
• Oxygenated blood is pumped to the body via the aorta
• Deoxygenated blood returns via the Vena Cava

Structure of the Heart

• The Vena Cava sends blood to the right atrium
• The right atrium sends blood to the right ventricle
• The right ventricle sends blood to the pulmonary artery
• The pulmonary artery sends blood to the lungs
• The pulmonary vein sends blood to the left atrium
• The left atrium sends blood to the left ventricle
• The left ventricle sends blood to the aorta
• The aorta sends blood to the body

Why 2 Pumps?

• Blood spreads out in capillaries within the lungs for gas exchange
• Spreading out into Lung capillaries causes a drop in blood pressure
• Blood returns to the heart to increase pressure for systemic circulation
• Capillaries are one cell thick for short diffusion distance
• They also have a large surface area
• Blood is constantly moving to maintain a concentration gradient

Coronary Arteries

• The heart relies on coronary arteries for oxygen
• Blockage of coronary arteries can lead to myocardial infarction, cutting oxygen to the heart

Heart Circulation

• Deoxygenated blood enters the right atrium through the vena cava.
• The superior vena cava carries blood from the upper body
• The inferior vena cava carries blood from the lower body.
• Blood flows from the right atrium (RA) to the right ventricle (RV) via the right atrioventricular or tricuspid valve
• Blood flows from the right ventricle to the pulmonary artery, splitting into right and left pulmonary arteries, passing through a semilunar valve
• Blood returns from the lungs to the left atrium (LA) via the pulmonary vein.
• The blood moves from the left atrium to the left ventricle through the bicuspid or mitral valve
• Blood exits the left ventricle through a semilunar valve into the aorta
• Remember artery = away from heart

Valves

• Atrioventricular (AV) valves open when atrial pressure exceeds ventricular pressure
• AV valves shut when ventricular pressure exceeds atrial pressure
• Semilunar valves open when ventricular pressure exceeds artery pressure
• Semilunar valves shut when artery pressure exceeds ventricular pressure
• The purpose of all the valves are to maintain unidirectional flow

Cardiac Cycle

• Diastole: the heart muscle is relaxed
• Blood returns from the body and lungs via the pulmonary vein (PV) and vena cava (VC).
• As the atria fill, the pressure increases within them.
• When atrial pressure exceeds ventricular pressure, the bicuspid and tricuspid valves open.
• Blood flows passively into the ventricles.
• Atrial Systole:
• Contraction of the atria
• Atrial walls contract, forcing blood into ventricles
• Most blood has already moved into the ventricles during diastole
• Ventricular Systole:
• Short delay while the ventricles fill
• Ventricle walls contract increasing pressure, this shuts the atrioventricular valves causing first heartbeat thud
• Pressure inside ventricles exceed Aorta and PA, the semilunar valves then open, and blood is forced out
• Valves prevent backflow
• Diastole is when the ventricle muscles relax after ventricular systole, causing recoil. This decreases pressure inside the ventricles
• The pressure lowers in the ventricles more than it is in the aorta and the PA, so the semilunar valves slam shut causing the second heartbeat sound

General Information

• Averages around 70 beats per minute in humans
• It consists of two phases: diastole (relaxation) and systole (contraction)

Cardiac Output

• Amount of blood pumped around the body
• The stroke volume, that is the volume of blood pumped by the left ventricle in each heartbeat
• The heart rate, is the number of times the heart beats per minute
• Formula is cardiac output = stroke volume * heart rate
• A typical volume for an adult at rest is 75ml and 70bpm
• A typical resting cardiac output is 4-6 litres per minute, 40 for trained endurance athletes