Circulation of the Heart and Cardiovascular System

Heart Structure and Function

  • Anatomy of the Heart

    • The heart has two main chambers: atria (top) and ventricles (bottom).

    • Location:

    • Dorsal: Base

    • Ventral: Apex

  • Chambers:

    • Atria: Left atrium, right atrium

    • Ventricles: Left ventricle, right ventricle

  • Blood Circulation:

    • Unoxygenated blood returns from the systemic circulation to the heart.

    • Returns to the right atrium via two vessels: cranial and caudal vena cava.

    • Right atrium contracts and sends blood to the right ventricle through the tricuspid valve (right atrioventricular valve).

    • Right ventricle contracts sending blood to the lungs via the pulmonary valve into the pulmonary artery.

  • Lung Function:

    • Blood releases carbon dioxide and picks up oxygen in the lungs.

    • Oxygenated blood returns to the heart through the pulmonary vein to the left atrium.

    • Left atrium contracts, sending blood to the left ventricle through the mitral valve (left atrioventricular valve).

    • Left ventricle contracts, sending blood to the body through the aortic valve into the aorta.

  • Key Vessels:

    • Right atrium: receives unoxygenated blood

    • Right ventricle: pumps to the lungs

    • Left atrium: receives oxygenated blood

    • Left ventricle: pumps to the body

  • Visual Aids:

    • Create diagrams of heart anatomy and blood flow for quizzes and exams.

Coronary Circulation

  • Heart Muscle Blood Supply:

    • Coronary arteries: bring oxygenated blood to heart muscle (myocardium).

    • Coronary veins: drain waste products from the heart muscle.

  • Collateral Circulation:

    • Refers to branching of blood vessels like a tree.

    • Poor collateral circulation in heart, brain, and kidneys: if one vessel is blocked, downstream tissues become ischemic (e.g., heart attack).

  • Blockages:

    • Minor blockage can lead to limited tissue damage; major blockage can cause significant tissue death.

Blood Vessel Anatomy and Function

  • Vascular Hierarchy:

    • Arteries: carry blood away from the heart; branch into smaller arterioles and then capillaries.

    • Capillaries allow exchange of oxygen, nutrients, and waste products.

    • Veins: carry blood back to the heart; join into larger venules and finally veins.

  • Blood Pressure:

    • Highest in the aorta and decreases as blood moves through arterioles to capillaries and into veins (low pressure).

    • Veins have valves to prevent backflow due to low pressure, often assisted by skeletal muscle contractions.

  • Special Notes:

    • Systemic arteries carry oxygenated blood; pulmonary arteries carry deoxygenated blood.

    • Arteries are thicker-walled compared to veins due to higher pressure.

Fetal and Maternal Circulation

  • Fetal Circulation:

    • Unique structures (e.g., umbilical arteries and veins) bypass non-functional organs (lungs, liver) in utero.

  • Key Bypasses:

    • Ductus venosus: bypasses liver, blood from umbilical vein goes directly to the caudal vena cava.

    • Foramen ovale: an opening between right atrium and left atrium, bypassing lungs.

    • Ductus arteriosus: connects pulmonary artery to aorta, bypassing the lungs.

  • Postnatal Changes:

    • After birth, these by-pass structures should close to function normally.

Lymphatic System

  • Purpose:

    • Drains excess interstitial fluid left behind after blood plasma leaves capillaries; prevents edema.

  • Components:

    • Lymph fluid: clear and colorless, transports immune cells (lymphocytes, antibodies).

    • Lymph nodes: filter lymph and produce lymphocytes.

  • Pathway:

    • Lymph fluid collected from tissues via lymph vessels, filtered through lymph nodes, then returned to systemic circulation via the thoracic duct.

Cardiac Function and Physiology

  • Cardiac Cycle:

    • Two phases:

    • Diastole: relaxation and filling of the heart chambers.

    • Systole: contraction and ejection of blood from the heart.

    • Blood pressure is higher during systole than diastole.

  • Heart Sounds:

    • Lub-Dub:

    • Lub: closure of AV valves during systole.

    • Dub: closure of aortic and pulmonary valves during diastole.

  • Cardiac Output:

    • Measured as the volume of blood pumped from the left ventricle per minute, affected by stroke volume and heart rate.

  • Regulation:

    • Heart rate controlled by autonomic nervous system (sympathetic vs. parasympathetic), though heart can contract independently due to intrinsic properties of cardiac cells.

Summary of Cardiac Maintenance

  • Normal Heart Rates:

    • Dogs: approximately 100-130 bpm

    • Cats: approximately 110-140 bpm

    • Horses: slower due to larger size

  • Pathological Heart Conditions:

    • Heart murmurs: abnormal sounds due to valve insufficiency or stenosis - may require further investigation.

    • Listen to heart sounds regularly to familiarize with normal vs. abnormal rhythms.

  • Clinical Implications:

    • Understand variations among species and individual animals when assessing heart rates, output, and potential health issues.

Summary and Suggestions for Study

  • Review diagrams of heart anatomy and blood flow pathways.

  • Create summary tables for the functionality of coronary circulation versus systemic and pulmonary circuits.

  • Practice auscultation with multiple different animals to discern normal and abnormal heart sounds.

  • Familiarize with physiological concepts governing cardiac performance to understand their relevance in clinical practice.

  • Consult textbooks and online resources for visual aids and further illustrations of the cardiovascular system and lymphatic system functions.