Heart Anatomy and Function Quiz

Cardiovascular System 1

• Lecture aims: blood flow and circulation, heart structure, heart function

Blood Flow and Circulation

• Systemic and pulmonary circulation
• Blood flow through the heart
• Coronary circulation

Circulation

• Pulmonary circulation: blood travels from the heart to the lungs and back to the heart
• Systemic circulation: blood travels from the heart to the body and back to the heart

Blood flow through the heart

• Path of blood through the heart, including pulmonary capillaries of the right lung, right atrium, right ventricle, pulmonary capillaries of the left lung, left atrium, left ventricle, and capillaries of the trunk and lower limbs
• Key structures: pulmonary capillaries, right atrium, right ventricle, pulmonary capillaries of left lung, left atrium, left ventricle
• Movement of blood through the heart is related to the opening and closing of valves

Coronary Circulation

• Supplies heart muscle with blood
• High demand for oxygen and nutrients
• Diffusion through tissues is insufficient
• Vessels run in sulci (grooves) on the heart surface

Coronary Circulation: The Arteries

• Branches off aorta above aortic semilunar valve (at aortic sinuses)
• High pressure
• Elastic

Coronary Circulation: The Veins

• Run alongside arteries
• Collect waste from cardiac muscle
• Venous drainage mainly via coronary sinus (posterior), emptying into right atrium

Coronary Circulation: If It Goes Wrong

• Myocardial ischemia: reduced blood flow to myocardium
• Angina pectoris: associated pain
• Myocardial infarction (MI): complete obstruction of blood flow to part of myocardium

The Heart (Structure)

• Heart valves and sounds
• Heart tissue

The Heart: Overview

• Pump of the cardiovascular system
• Weighs approximately 250-300g
• Pumps 30 times its own weight (5L) per minute
• Muscular organ that never rests
• Contracts approximately 3 billion times during an average human lifetime

Thickness of Cardiac Walls

• Blood pressure (BP) in aorta is 120mmHg
• BP in pulmonary trunk is 30mmHg
• Why the difference?

Heart Valves

• Valves open to allow blood flow from atria into ventricles (atrioventricular valves: bicuspid (mitral) and tricuspid); and from ventricles into corresponding arteries (semilunar valves)
• Stenosis: narrowing of heart valves, restricting blood flow

Heart Sounds

• Sounds of heartbeat due to turbulence in blood flow and valve closure
• 1st heart sound (lubb) - S1 (closure of AV valves)
• 2nd heart sound (dubb) - S2 (closure of semilunar valves)
• S3 and S4 not usually loud enough to be heard
• Tool: Stethoscope
• Heart murmur: abnormal sounds sometimes due to valve disorder (e.g., mitral stenosis)

The Layers of the Heart Wall

• Endocardium (inner layer): lines chambers and valves, continuous with large blood vessels (thin squamous epithelium)
• Myocardium (muscle layer): specialized cardiac muscle (95% of wall)
• Epicardium (external layer): transparent outer layer, part of pericardium

Pericardium

• Double walled sac surrounding the heart
• Space between inner and outer pericardial membranes filled with pericardial fluid
• Lubrication, prevention of friction during heart beats
• Pericarditis: inflammation of pericardium
  • Causes surfaces to rub together
  • Distinct scratching sound heard through stethoscope
  • Acute or chronic

Myocardium

• Cardiac muscle: muscle fibers swirl/spiral diagonally in interlacing bundles/networks.

The Heart (Function)

• Electrical conduction
• Volume and pressure
• The muscle cells
• Stroke volume and cardiac output

Heart: Electrical Activity, the conducting system

• Heart has intrinsic rhythmical electrical activity (continuous beating)
• Specialized cardiac muscle conducting cells (self-excitable)
• Fire spontaneously due to unstable membrane potential
• Act as pacemakers; set rhythm
• Form networks/path for spread of excitation through the heart

Volume & Pressure: 1. ECG, pressure

• ECG (electrocardiogram) relates to the electrical activity of the heart over time
• Pressure is measured in the heart and blood vessels
• Diagram shows pressure changes relating to the opening and closing of heart valves

Volume & Pressure: 2. Pressure Detail

• Pressure in ventricle higher than aortic and pulmonary trunk – SL valves open
• As ventricle relaxes, pressure drops and AV valves open

Volume & Pressure: 3. Volume Detail

• Pressure in atria higher than in ventricle – passive filling (70% ventricular capacity)
• Volume rises

Volume & Pressure: 4. Heart Sounds

• Heart valves closing produce the lubb-dubb sounds

Myocardium: The Muscle Cells

• Involuntary contractions
• Striated, branching fibers
• Connected by intercalated discs
• Single central nucleus

Myocardium: Histology

• Thick filaments: myosin
• Thin filaments: actin
• Contraction: myosin heads pull thin actin filaments, resulting in shortening of the sarcomere
  • Length of individual thin and thick filaments does not change
  • Shortening of sarcomere = shortening of muscle = contraction

Comparison to Skeletal Muscle

• Shorter (50-100 µm) and exhibit branching
• Usually one central nuclei
• Intercalated discs - contain gap junctions
• Many more mitochondria
• Same arrangement (actin, myosin, bands & discs)
• Less developed sarcoplasmic reticulum with smaller calcium stores

Stroke Volume

• End diastolic volume (EDV): volume in ventricle at end of diastole (approximately 130 mL)
• End systolic volume (ESV): volume in ventricle at end of systole (approximately 60 mL)
• Stroke volume (SV): volume ejected per beat from each ventricle (approximately 70 mL)
  • SV = EDV - ESV

Cardiac Output

• Cardiac output (CO): amount of blood ejected by left ventricle per minute
• Determined by stroke volume and heart rate (CO = SV x HR)
• If SV = 70 mL/beat and HR = 75 beats/min, CO = 5250 mL/min
• Entire blood supply passes through circulatory system every minute
• Cardiac reserve: maximum output – output at rest (average = X4-5, athlete =X7-8)

This quiz tests your knowledge on the anatomy and function of the heart, including the role of heart valves, myocardial contractions, and circulation. Match heart valve actions to states and answer questions about cardiac health and structure. Perfect for students studying cardiovascular anatomy!