Circulatory System Quiz

The Cardiovascular System

• The cardiovascular system is a closed circuit.
• It contains a pump (the heart) that maintains a pressure gradient.
• This gradient sustains effective blood flow.
• Blood flows from distributing ducts (arteries) to thin vessels (capillaries).
• Blood flows back through collecting ducts (veins).

The Cardiovascular Circuit

• The main circuit has three components:
  • Pump
  • Distributing tubules
  • Thin vessels/Collecting tubules

Main Functions of the Circulatory System

• Transports and distributes essential substances to tissues.
• Removes metabolic by-products.
• Adjusts oxygen and nutrient supply in various physiological states.
• Regulates body temperature.
• Facilitates humoral communication.

Functions of the Heart

• Generates blood pressure.
• Routes blood (separates pulmonary and systemic circulations).
• Ensures one-way blood flow (valves).
• Regulates blood supply (adjusts contraction rate and force to match metabolic needs).

Circuits of the Heart

• Pulmonary circuit: blood flow to and from the lungs
• Systemic circuit: blood flow to and from the rest of the body.
• Vessels carry blood through these circuits:
  • Arteries carry blood away from the heart.
  • Veins carry blood to the heart.
  • Capillaries facilitate exchange.

Cardiac Muscle

• Elongated, branching cells with centrally located nuclei.
• Contains actin and myosin myofilaments.
• Intercalated discs: specialized cell-cell contacts and gap junctions that allow action potentials to move from one cell to the next.
• Cardiac muscle of the atria and ventricles functions as a single unit.
• Mitochondria comprise 30% of the cell volume.

Chambers of the Heart

• Right atrium: Receives blood from systemic circulation. There is no valve between Vena Cava & the Right atrium.
• Left atrium: Receives deoxygenated blood from the lungs.
• Right ventricle: Pumps blood to the lungs via pulmonary arteries.
• Left ventricle: Pumps oxygenated blood to systemic circulation via the aorta.
• The left side of the heart is more muscular than the right side.

Heart Valves

• Atrioventricular (AV) valves are between atria and ventricles:
  • Tricuspid (right side)
  • Bicuspid (left side)
• Semilunar valves prevent backflow into the ventricles:
  • Pulmonary
  • Aortic
• AV valves stop blood from flowing back from the ventricles to the atria.
• Semilunar valves stop blood from flowing back into the ventricles.
• Valves and connective tissue make up the heart skeleton. They do not conduct electrical impulses.

Diastole and Systole

• Cardiac cycle: the electrical and physical events of a complete heartbeat (0.8 seconds).
• Diastole: resting phase, no active contraction.
• Systole: active muscle contraction and electrical impulses.

Cardiac Cycle

• Refers to all events associated with blood flow through the heart, from the start of one heartbeat to the next.
• Each heart chamber goes through systole and diastole.
• Correct pressure relationships depend on careful timing of contractions.

Phases of the Cardiac Cycle

• Atrial diastole and systole: Blood flows passively into the atria. Then atrial systole pumps the remaining blood into the ventricles.
• Ventricular filling (mid-to-late diastole): Heart blood pressure is low, blood passively enters ventricles
• Ventricular systole: Atrial relaxation. Ventricles will contract, pushing blood out into the arteries.

Characteristics of the Heart

• Excitability: cells respond to an electrical stimulus.
• Contractility: specialized cardiac muscle ability to contract.
• Rhythmicity: ability of the cardiac muscle to contract and relax regularly (automaticity: cells can depolarize without outside stimulus).
• Conductivity: cells can propagate electrical impulses from cell to cell.

Action Potentials in Skeletal and Cardiac Muscle

• Action potentials differ in skeletal and cardiac muscle. The plateau phase in the cardiac action potential is absent in skeletal muscle. This plateau differentiates the two and allows for a longer refractory period in the cardiac tissue.

Refractory Periods

• Relative refractory period: the cell can respond to an action potential, but it must be stronger.
• Absolute refractory period: cell does not respond to a re-stimulation, regardless of the strength of the stimulus (occurs during systole and part of diastole).

Contractility

• Frank-Starling law of the heart regulates stroke volume and force.
• The greater the stretch of the heart muscle, the stronger the contraction.
• End-diastolic volume represents measure of the blood flow into and stretch of the ventricles.
• The Frank-Starling law suggests that for normal healthy conditions, the heart pumps all of the blood that returns to it by way of the veins to the greatest extent during a heart beat.
• The heart muscle is stimulated by nerves and is self-excitable (automaticity).
• It contracts as a unit, no motor units.
• Has a long (250ms) absolute refractory period.
• Cardiac muscle contraction similar to skeletal muscle contraction, i.e., sliding filaments.

Rhythmicity

• Factors affecting rhythmicity:
  • Autonomic innervation
  • Electrolytes: Sodium (depolarization), Potassium (repolarization), Calcium (depolarization, myocardial contraction)
  • Temperature
  • Blood pH

Conducting System of the Heart

• SA node (pacemaker): generates spontaneous action potentials and initiates contractions.
• AV node: conducts action potentials more slowly to ensure atria contract before ventricles.
• AV bundle: carries action potentials to the ventricles.
• Bundle branches: extend to the apex of the ventricles.
• Purkinje fibers: conduct action potentials to ventricular muscle cells.
• Auto-rhythmic cells initiate action potentials and they have unstable resting potentials (pacemaker potentials), and use calcium influx rather than sodium for the action potential.

Extrinsic Innervation of the Heart

• Vital centers in the medulla (cardioacceleratory and cardioinhibitory centers): cardiac regulating centers
• Cardioacceleratory center activates sympathetic nerve fibers increasing heart rate.
• Cardioinhibitory center activates parasympathetic nerve fibers, decreasing heart rate.

Regulation of the Heart

• Neural Regulation
  • Sympathetic stimulation is a positive chronotropic factor, increasing heart rate and force of contraction.
  • Supplied by cardiac nerves.
  • Innervates the SA and AV nodes, atrial, and ventricular myocardium.
• Hormonal Regulation
  • Epinephrine and norepinephrine from the adrenal medulla are released.
  • Increased activity, emotions, and stress, cause increased heart rate.
• Parasympathetic stimulation is a negative chronotropic factor, decreasing heart rate.
  • Supplied by the vagus nerve.
  • Secretes acetylcholine.
  • Hyperpolarizes the heart.

Chemical Regulation of the Heart

• Epinephrine and thyroxine hormones increase heart rate.
• Intra- and extracellular ion concentrations must be maintained for healthy heart function.

Heart Rate

• Pulse = surge of pressure in artery
• Infants have high heart rate.
• Young adult females have 72-80 bpm.
• Young adult males avg. 64 to 72 bpm.
• Heart rate rises in the elderly.
• Tachycardia is a resting heart rate above 100.
• Bradycardia is a resting heart rate less than 60.

Regulation of Heart Rate

• Chronotropism: influence on heart rate.
  • Positive chronotropic factors increase heart rate.
  • Negative chronotropic factors decrease heart rate.
• Inotropism: influence on contractility.
  • Positive inotropic factors increase contractility.
  • Negative chronotropic factors decrease contractility.

Factors Affecting Heart Rate

• Cardiovascular control center in medulla (cardioexcitatory and cardioinhibitory centers, autonomic nervous system (ANS))
• Neural reflexes:
  • Atrial stretch receptors reflex
  • Proprioceptor reflex
  • Chemoreceptor reflex
  • Baroreceptor reflex
  • Nociceptor reflex
  • Cerebral Cortex
• Venous return
  • Skeletal muscle pump
  • Muscular contractions squeeze adjacent veins, causing a “milking” action.
  • Valves prevent backward flow.
  • Constriction of veins, through sympathetic stimulation or gravity
• Preload: diastolic volume load before contraction starts (related to venous filling pressure).
• Afterload: systolic load on the left ventricle after contraction (resistance against pumping).

Cardiac Output (CO)

• Amount of blood pumped by each ventricle per minute.
• Calculated as heart rate (HR) multiplied by stroke volume (SV).
• CO = HR x SV (ml/min = beats/min x ml/beat)
• Cardiac reserve is the difference between resting and maximal CO.
• SV = EDV - ESV (End diastolic Volume – End systolic Volume)

Ejection Fraction (EF)

• Fraction of blood pumped out of the ventricles per heartbeat.
• EF = SV/EDV.
• Healthy individuals have an EF between 55%-70%.
• Reduced ejection fraction can manifest as heart failure.

Arterial Blood Pressure (BP)

• Pressure inside large arteries.
• Components: Systolic (maximum pressure) and Diastolic (minimum pressure).
• Normal adult ≈ 120/80 mmHg.

Factors Affecting Arterial Blood Pressure (ABP)

• Sex
• Age
• Emotions
• Exercise
• Hormones
• Gravity
• Race
• Sleep
• Pregnancy

Renin-Angiotensin System

• Important mechanism for sodium retention and maintaining blood volume.
• Any drop in renal blood flow or sodium prompts the juxtaglomerular apparatus in the kidneys to release renin.
• Renin activates the angiotensin system which leads to aldosterone production.

Antidiuretic Hormone (ADH)

• Hypovolemia and dehydration stimulate osmoreceptors in the hypothalamus, leading to ADH release from the posterior pituitary.
• ADH causes water reabsorption in kidney tubules.

Low-Pressure Volume Receptors

• Atrial natriuretic peptide (ANP) hormone regulates sodium excretion from the wall of the right atrium.

Electrocardiogram (ECG/EKG)

• Records electrical events in the myocardium.
• Key components:
  • P-wave: atrial depolarization
  • QRS complex: ventricular depolarization
  • T-wave: ventricular repolarization
• Intervals and segments: indicate timing and health of the conduction system

Laminar vs. Turbulent Flow

• Laminar flow: smooth, orderly flow
• Turbulent flow: disrupted flow, often associated with constrictions.

Jugular Wave Form

• Shows changes in venous pressure related to heart activity

Test your knowledge on the circulatory system and the heart with this quiz. Explore topics such as blood flow, heart structure, and the unique features of cardiac muscle. Challenge yourself to see how well you understand the essential functions and components of this vital system.