Circulation and Cardiovascular Systems: Summary Notes

Transport in Vertebrates

  • All vertebrates possess a closed circulatory system known as the cardiovascular system.
  • The vertebrate heart consists of:
    • Atria: receive blood.
    • Ventricles: pump blood out.
  • Vertebrate vessels include:
    • Arteries: carry blood away from the heart.
    • Arterioles: small arteries leading to capillaries, diameter regulated by nervous and endocrine systems.
    • Capillaries: facilitate material exchange with tissue fluid.
    • Venules: join to form veins.
    • Veins: return blood to the heart.
  • Blood Flow:
    • Fish: Single loop; single atrium and ventricle.
    • Amphibians: Double loop (systemic and pulmonary circuits); two atria, single ventricle.
    • Most Reptiles: Partially divided ventricle; minimized blood mixing. Crocodilians have fully separated ventricles.
    • Birds & Mammals: Double loop; divided heart. Right ventricle to lungs, left ventricle to body.

The Human Cardiovascular System

  • Heart Structure:
    • Fist-sized, cone-shaped, located behind the sternum.
    • Composed of cardiac muscle fibers.
    • Enclosed in the pericardium.
    • Septum divides heart into left and right sides, each with two chambers (atria and ventricles).
  • Heart Valves:
    • Atrioventricular:
      • Tricuspid: Between right atrium and ventricle.
      • Bicuspid: Between left atrium and ventricle.
    • Semilunar:
      • Pulmonary: Between right ventricle and pulmonary trunk.
      • Aortic: Between left ventricle and aorta.
  • Blood Pathway:
    • Systemic circuit returns blood to the right atrium via the venae cavae, flows through the tricuspid valve to the right ventricle, then through the pulmonary semilunar valve to the pulmonary circuit.
    • Pulmonary circuit returns blood to the left atrium, flows through the bicuspid valve to the left ventricle, then through the aortic semilunar valve to the systemic circuit.
  • Heartbeat:
    • Systole: Contraction of heart chambers.
    • Diastole: Relaxation of heart chambers.
    • Cardiac cycle: Blood collects in atria (diastole), atria contract, ventricles contract (systole).
  • Pulse and Conduction:
    • Pulse: Wave effect in arterial walls post-ventricular systole.
    • Sinoatrial node (SA): Pacemaker, regulates heartbeat.
    • Atrioventricular node (AV): Signals ventricles to contract.
  • Electrocardiogram (ECG):
    • P wave: Atrial fiber electrical charge, indicates impending atrial contraction.
    • QRS complex: Signals impending ventricle contraction and atrial relaxation.
    • T wave: Electrical changes during ventricular muscle fiber recovery.
  • Circuits:
    • Pulmonary Circuit: Deoxygenated blood to lungs, oxygenated blood to heart.
    • Systemic Circuit: Oxygenated blood to body, deoxygenated blood to heart via venae cavae.
    • Portal System: Blood passes through two capillary beds before returning to the heart (e.g., hepatic portal system).
  • Blood Pressure:
    • Systolic pressure: Pressure during ventricular systole.
    • Diastolic pressure: Pressure during ventricular diastole.
    • Measured in mm of mercury (e.g., 120/80).

Cardiovascular Disease (CVD)

  • Hypertension: High blood pressure, often due to atherosclerosis.
  • Atherosclerosis: Fatty material accumulation in arterial linings, forming plaque.
  • Thrombus: Blood clot on arterial wall.
  • Stroke: Disrupted blood supply to brain.
  • Angina Pectoris: Chest pain due to myocardial oxygen insufficiency.
  • Heart Attack (Myocardial Infarction): Blocked coronary artery.

Blood

  • Functions: Transports gases, nutrients, wastes, antibodies, hormones; combats pathogens; maintains water balance, pH, temperature; facilitates clotting.
  • Composition:
    • Plasma: Water, proteins (albumin, globulins, fibrinogen), salts, gases, nutrients, wastes, hormones.
    • Formed Elements: Red blood cells (erythrocytes), white blood cells (leukocytes), platelets (thrombocytes).
  • Red Blood Cells (RBCs):
    • Small, biconcave disks without a nucleus, containing hemoglobin.
    • Produced in bone marrow.
    • Anemia results from insufficient RBCs or hemoglobin.
  • Blood Types:
    • Determined by surface antigens (ABO and Rh systems).
    • Antibodies cause agglutination if mismatched.
  • Rh System:
    • Rh-negative mothers carrying Rh-positive fetuses may develop anti-Rh antibodies, causing hemolytic disease of the newborn (HDN) in subsequent pregnancies.
  • White Blood Cells (WBCs):
    • Granular: Neutrophils, eosinophils, basophils.
    • Agranular: Monocytes, lymphocytes (T cells, B cells).
  • Platelets:
    • Fragmented megakaryocytes, involved in blood clotting.
    • Form blood clots with RBCs and fibrin.

Capillary Exchange

  • Controlled by osmotic and blood pressure.
  • Nutrients and oxygen diffuse out; carbon dioxide and wastes diffuse in.
  • Excess interstitial fluid is collected by lymphatic capillaries (lymph) and returned to venous blood.