Circulatory System

• Circulatory System


  System that transports nutrients, oxygen, water, minerals, and removes carbon dioxide and other metabolic waste products in animal life
• In single-celled animal-like protists, circulatory system is usually absent because simple diffusion from their watery environment allows these activities to take place
• Complex forms of animals rely on a transporting system which consists mainly of heart, blood and blood vessels
• Functions of the circulatory system

  • Transport of nutrients, hormones, gases, and waste materials
  • Protection against blood loss through blood clotting and foreign microbes
  • Regulation and maintenance of body temperature and pH of tissues
• Open (lacunar) circulatory system

  • Characterized by the absence of capillaries
  • Blood is often referred to as hemolymph
  • Hemolymph is pumped by the heart, usually an enlarged blood vessel, in low pressure out into the body cavity, mixes with interstitial fluid and bathes cells of the body then blood is slowly returned to the heart through body spaces known as hemocoel
  • Occurs mostly among invertebrates such as in molluscs, and arthropods such as insects
• Closed circulatory system


  • Blood remains within a completely enclosed system of vessels
  • Never comes in direct contact with tissue cells
  • Materials move between the blood and interstitial fluid through capillaries
  • Blood flows in high pressure
  • Occurs among annelids, squids and mostly among vertebrates such as fishes, amphibians, reptiles, birds, and mammals
• Cardiovascular System


  Composed of blood, blood vessels, and a muscular pump which is the heart
• Lymphatic System


  A pumpless system of vessels that aids the cardiovascular system in its function, composed of lymph, lymphatic vessels, and structures and organs containing lymphatic tissues
• Heart


  • A muscular pump which forces blood out to the tissues of the body through blood vessels
  • The pulsating, contractile organ that provides the energy for moving the blood throughout the body
  • In invertebrates, particularly insects, the heart consists of one longitudinal vessel that runs in the median dorsal of the thorax with no chambers but rather is pierced by series of openings termed as ostia, which serve as entry and exit of the blood
  • In vertebrates, the heart is a muscular organ divided into a number of chambers
• Types of hearts in vertebrates

  • Fishes: two chambers, one atrium and one ventricle, exhibit single pathway or circulation of blood
  • Amphibians and reptiles: three chambers, two atria and one ventricle, exhibit double but incomplete circulation, slight mixing of venous and arterial blood may possibly occur in the ventricles
  • Birds and mammals: four chambers, two atria and two ventricles, exhibit double and complete circulation, no mixing of venous and arterial blood in the ventricle

  
• Blood


  • Complex connective tissue containing plasma and cellular components
  • Called as hemolymph among invertebrates
  • The circulating fluid of the body
  • Characterized by a temperature of about 38°C, pH of 7.35 – 7.45
  • About 8% of total body weight, in humans, 5 to 6 liters (male) and 4 to 5 liters (female)

  
• Functions of blood


  • Transport of nutrients, metabolites, hormones, and waste products
  • Transport of cells (lymphocytes and platelets)
  • Thermoregulation
• Components of blood


  • Plasma: straw-colored liquid portion, about 91.5% water and 8.5% solutes, 55% of the whole blood
  • Formed elements: erythrocytes, leukocytes and platelets, make up about 45% of whole blood
• Erythrocytes (red blood cells)

  • Appear as biconcave discs of 8 um in diameter
  • Contain the oxygen-carrying pigment hemoglobin, which is responsible for the red color of the whole blood
  • Lack nucleus
  • About 5 million cells per cubic millimeter of blood
  • Continuously manufactured in the red bone marrow
  • Have a life span of 120 days which are destroyed after in liver and spleen where they are engulfed by large phagocytic cells
• Types of leukocytes (white blood cells)

  • Granulocytes: basophils, eosinophils and neutrophils (polymorphonuclear leucocytes or PMNs), characterized by the presence of large granules in the cytoplasm and with lobed nuclei
  • Agranulocytes: lymphocytes and monocytes, they lack visible cytoplasmic granules
• Thrombocytes


  • Facilitate blood clotting or coagulation
  • Known as blood platelets in mammals which are fragments of large multinucleate cells called megakaryocytes in red bone marrow
  • About 300,000 per cubic millimeter of blood
  • Produced at a rate of 200 billion a day
• Types of blood vessels

  • Arteries: with more elastic, thicker walls, carry oxygenated blood away from the heart except for pulmonary artery which carries deoxygenated blood
  • Arterioles: arteries with smaller diameter, walls are mostly covered with smooth muscle which reduces blood flow as it enters capillaries
  • Veins: with thin and less elastic walls, carry deoxygenated blood towards the heart except pulmonary vein which carries oxygenated blood
  • Venules: small veins which collect blood from the capillary beds and deliver it to larger veins
  • Capillaries: network of microscopic vessels which connect arterioles with venules less than 10 um in diameter and its wall is made up of single layer of endothelial cells, allows exchange of nutrients and wastes between blood and tissue cells
• Mammalian heart


  • Located in the center of the chest between the lungs, protected by a breast bone (sternum)
  • Its apex is directed toward the left hip and rests on the diaphragm
  • Has four chambers: left and right atrium, left and right ventricle
  • Contains valves: atrioventricular valves (tricuspid and bicuspid/mitral) and semilunar valves (pulmonary and aortic)
  • Contains transverse septa which prevent mixing of oxygenated from the left side of the heart and deoxygenated blood from the right side

  
• Heart


  • Blood-pumping organ
  • Thick-walled
  • ¾ separated by interventricular septum
  • Left ventricular wall is thicker than the right
  • Contains valves
• Atrioventricular (AV) valves


  • Separate the cavities of the atrium and ventricle in each half of the heart
  • Permit blood to flow from atrium to ventricle
  • Prevent backflow
• Tricuspid valve


  • Three cusps
  • Allow blood to move from right atrium to right ventricle
  • Prevent backflow of blood from right ventricle to right atrium
• Bicuspid (mitral) valve


  • Two cusps
  • Allow blood to move from left atrium to left ventricle
  • Prevent backflow of blood from left ventricle to left atrium
• Semilunar valves


  • Prevent backflow of blood
  • Pulmonary semilunar valve prevents backflow from pulmonary artery to right ventricle
  • Aortic semilunar valve prevents backflow from aorta to left ventricle
• Septa


  • Prevent mixing of oxygenated and deoxygenated blood
  • Interatrial septum separates left and right atria
  • Interventricular septum separates left and right ventricles
• Sinoatrial (SA) node


  • Heart's pacemaker where electrical impulse originates
  • Located in right atrium near entrance of caval veins
• Atrioventricular (AV) node


  • Receives impulses from SA node
  • Excites the bundle of cardiac muscle cells at the base of atria
  • Located at lower middle part of right atrium
• Bundle of His / AV bundle


  • Impulse conducting muscle fibers that divide into right and left bundle branches
  • Only electrical connection between atria and ventricles
• Right and left bundle branches

  Ramify into numerous smaller conduction myofibers or Purkinje fibers
• Diastole


  • Relaxation phase
  • Ventricle walls relax
  • Tricuspid and mitral valves open
  • Blood flows into the heart
  • Pulmonary and aortic valves are closed
• Systole


  • Contraction phase
  • Ventricle walls contract
  • Tricuspid and mitral valves are closed
  • Pulmonary and aortic valves are opened
  • Blood flows away from the heart
• LUB


  Heard when vibrations occur due to closing of atrioventricular valves
• DUP


  Heard when vibrations occur due to closing of semilunar valves
• Adult human heartbeat


  72 beats per minute
• Cardiac output


  Total volume of blood pumped by the heart, 5.0 liters per minute
• Blood flow through the heart

  1. Deoxygenated blood from superior and inferior vena cava enters right atrium

  2. Flows into right ventricle through tricuspid valve

  3. Pumped out through pulmonary semilunar valve into pulmonary arteries

  4. Oxygenated blood returns to left atrium via pulmonary veins

  5. Flows into left ventricle through bicuspid valve

  6. Pumped out through aortic semilunar valve into aorta
• Blood pressure


  • Pressure of blood against the wall of blood vessels, particularly large systemic arteries
  • Measured by sphygmomanometer in millimeter mercury (mmHg)
  • Diastolic is lowest arterial pressure, systolic is highest pressure during ejection
• Normal average blood pressure

  80 to 100 mmHg diastolic, 100 to 120 mmHg systolic
• Pulse


  • Alternate expansion and contraction of arterial wall
  • Indicates heart action, vessel wall elasticity, blood viscosity, and resistance
• Pulse rate


  60 to 80 per minute in adults, 80 to 120 per minute in children
• Pulmonary circulation


  1. Deoxygenated blood flows from right ventricle to lungs

  2. Oxygenated blood returns to left atrium