Heart Anatomy and Function Quiz

• The cardiovascular system is also known as the circulatory system
• The text provides an overview into the cardiovascular system for biomedical sciences
• The heart is a four-chambered muscular organ, approximately the size of a clenched fist
• It beats around 100,000 times a day
• It operates as two separate pumps: the right pumps blood to the lungs, and the left pumps blood to the body

Heart Shape and Position

• Found in the thoracic cavity, between the lungs, in the mediastinum region
• The heart is situated behind the sternum (breastbone)
• Most of the heart is located to the left of the midline, with its apex facing downwards
• The base of the heart is the broad, superior end where large vessels attach

Pericardium

• The Parietal pericardium encloses and protects the heart to separate it from other thoracic organs
• It creates a pericardial cavity that contains pericardial fluid
• The parietal pericardium has an outer fibrous layer and an inner serous layer
• The serous layer functions to secrete pericardial fluid

Heart Wall

• The heart wall has three layers
• Epicardium: The outer layer
• Myocardium: The thick middle layer of cardiac muscle
• Endocardium: The smooth inner layer lining the heart

Cardiac Muscle

• Cardiac muscle only exists in the heart
• Cardiac muscle is controlled by the autonomic nervous system
• Cardiac muscle fibers are branched and arranged in a striated pattern
• Cells are connected by intercalated discs which consist of fascia adherens, gap junctions, and desmosomes
• The specialised cell junctions allow the muscle to contract smoothly and repeatedly

Heart Chambers

• The heart has four chambers: the right and left atria, and the right and left ventricles
• The atria are the receiving chambers and they contract and empty into the ventricles
• They are separated by a thin muscular interatrial septum
• The ventricles are the pumping chambers separated by a thick muscular interventricular septum
• Grooved depressions on the heart's surface mark the partitions between chambers and contain cardiac vessels supplying blood to the heart wall

Right Atrium and Ventricle

• The right atrium receives venous blood from the superior and inferior vena cava
• The cardiac cycle involves diastole, where the heart fills with blood, and systole, a period of contraction
• During diastole, blood passes from the right atrium to the right ventricle through the tricuspid valve
• During systole, the right ventricle contracts, closing the tricuspid valve to prevent backflow into the atrium

Left Atrium and Ventricle

• After gas exchange in the lung, oxygenated blood passes to the left atrium from the pulmonary veins
• During diastole, blood passes from the left atrium to the left ventricle through the bicuspid (mitral) valve
• During systole, the left ventricle contracts, closing the mitral valve to prevent backflow into the atrium
• The left ventricle has thicker walls than the right ventricle
• Oxygenated blood leaves the left ventricle through the aorta
• The aortic semilunar valve prevents backflow from the aorta into the left ventricle

Heart Sounds

• When listening to the heart with a stethoscope, the turbulence is noted, created when heart valves close
• S1: First heart sound ('Lub')
• S2: Second heart sound ('Dub')
• Heart murmurs are variations in these sounds that are indicators of problems with the valves

Conduction System

• Consists of the:
• Sinoatrial (SA) node
• Atrioventricular (AV) node
• Bundle of His
• Purkinje fibres

Cardiac Conduction System

• Each heartbeat begins in the SA node
• The SA node is located in the right atrium
• During diastole, the SA node exhibits a spontaneous depolarisation, a "pacemaker potential"
• The wave of depolarisation spreads across the atria, atrial systole, then converges at the AV node
• The AV node delays the impulses to allow the atria time to fully empty into the ventricles
• The Bundle of His conducts impulses to the Purkinje fibres of the ventricles, resulting in ventricular systole

Electrocardiogram (ECG)

• An ECG is a non-invasive test providing data about heart rate and rhythm
• The ECG measures electrical activity generated when the heart contracts, tracing the electrical activity:
• P wave
• QRS complex
• T wave
• The ECG can also help detect abnormal heart rhythms (arrhythmias) and high blood pressure (hypertension) as well as heart attacks (myocardial infarction)

Circulatory System

• The circulatory system is also known as the cardiovascular system
• It circulates blood, transports nutrients, oxygen, and hormones, removes waste products, and controls homeostasis
• The pulmonary circulation transports blood from the right ventricle to the lungs, then to the left atrium
• The systemic circulation consists of all other vessels in the body not part of the pulmonary system

Coronary Circulation

• The heart has its own circulation system known as the coronary circulation
• The right and left coronary arteries are responsible for delivering oxygenated blood to the heart
• After blood passes through capillaries in the myocardium, it enters cardiac veins, which drain into the right atrium

Foetal Circulation

• In utero, the pulmonary circulation is unnecessary because foetal blood is oxygenated by the placenta
• The umbilical cord serves as a connection between the foetus and placenta
• Systemic venous blood returning to the right atrium is deflected through the foramen ovale to the left atrium
• Blood from the left ventricle is diverted away from the pulmonary arteries, to the aorta, through the ductus arteriosus

Blood Vessels

• Consists of:
• Arteries
• Arterioles
• Capillaries
• Venules
• Veins

Arteries

• Consists of oxygenated blood (except in the pulmonary system), carries blood away from the heart
• Having thick elastic muscular walls
• Blood flows under high pressure
• Consist of three layers: tunica externa, tunica media, and tunica intima

Capillaries

• Are the smallest and most abundant blood vessels in the body
• Capillary walls consist of an endothelium, with only one cell layer
• They permit a rapid rate of exchange of oxygen, nutrients, and waste products between blood and tissues
• Capillary beds are networks of capillaries supplying organs
• Blood flow through capillaries is determined by precapillary sphincter muscles and the constriction/dilatation of arteries and arterioles

Veins

• Carry oxygen-depleted blood back to the heart
• Contain valves to prevent backflow/pooling
• Act as a reservoir of blood
• Rely on the skeletal muscle pump and respiratory pump
• Have 3 layered walls but are less muscular and elastic than arteries

Blood-Brain Barrier

• The blood-brain barrier acts as a boundary between circulating blood and the brain and spinal cord
• It is highly selective and protects the brain from 'foreign' substances and maintains a constant environment
• Brain capillaries are not fenestrated and their endothelial cells are tightly packed, preventing large molecules, immune cells, bacteria, and viruses from passing from the blood to the central nervous system

Major Blood Vessels

• Pulmonary artery: Carries blood from the right atrium to the lungs for oxygenation
• Aorta: Originates from the left ventricle as the ascending aorta, forms the aortic arch, then becomes the descending aorta
• Pulmonary vein: Returns oxygenated blood from the lungs to the left atrium
• The superior vena cava receives deoxygenated blood from the upper body
• The inferior vena cava receives the venous return from the lower body
• Both the superior and inferior vena cava drain into the right atrium

Blood Pressure

• Blood pressure measures the force is exerted by circulating blood against the artery walls
• Measured in millimetres of mercury (mmHg)
• The normal blood pressure is Systolic/diastolic e.g. 120/80mmHg

Test your knowledge of the heart's anatomy and physiology. Questions cover heart function and its role as a pump. Topics include the cardiac cycle and valves.