Transport in animals

• Transport systems in multicellular animals

  • Link exchange surfaces with cells throughout the body
  • Allow small molecules to move between cells and their surroundings by diffusion
• Circulatory systems

  • Circulatory fluid
  • Set of interconnecting vessels
  • Muscular pump, the heart
• Closed circulatory system

  Cardiovascular system in humans and other vertebrates
• Main types of blood vessels

  • Arteries
  • Arterioles
  • Capillaries
  • Venules
  • Veins
• Order of blood flow from the heart

  1. Capillaries

  2. Venules

  3. Veins

  4. Arteries

  5. Arterioles
• Capillary beds

  Networks of capillaries where chemical exchange between blood and interstitial fluid occurs
• Single vs double circulation

  Mammals have double circulation where oxygen-poor and oxygen-rich blood are pumped separately from the right and left sides of the heart
• Blood vessel structure

  • Cavity is called the central lumen
  • Epithelial layer lining is called the endothelium
• Endothelium is smooth
• Capillaries

  • Only slightly wider than a red blood cell
  • Have thin walls to facilitate exchange of materials
  • Usually filled to capacity in major organs
• Velocity of blood flow in capillary beds

  Slower than in arteries and veins
• Exchange at capillary beds

  • Occurs across the thin endothelial walls
  • Driven by the difference between blood pressure and osmotic pressure
• Most blood proteins and all blood cells are too large to pass through the endothelium
• Mammalian circulation

  1. Blood begins flow in right ventricle to lungs

  2. Oxygen-rich blood from lungs enters left atrium

  3. Pumped by left ventricle to body tissues

  4. Blood returns to heart through superior and inferior vena cava
• Cardiac cycle

  • Contraction phase is systole
  • Relaxation phase is diastole
• Heart rate is the number of beats per minute
• Stroke volume

  Amount of blood pumped in a single contraction
• Cardiac output

  Volume of blood pumped into systemic circulation per minute, depends on heart rate and stroke volume
• Heart valves

  • Atrioventricular valves separate atria and ventricles
  • Semilunar valves control blood flow to aorta and pulmonary artery
• Cardiac muscle cells are autorhythmic and contract without nervous system signals
• Sinoatrial (SA) node

  Sets the rate and timing of cardiac muscle contraction
• Electrocardiogram (ECG or EKG)

  Records the electrical impulses that travel during the cardiac cycle
• Sympathetic and parasympathetic divisions

  Regulate the pacemaker, with sympathetic speeding it up and parasympathetic slowing it down
• Blood

  Connective tissue consisting of cells suspended in plasma
• Plasma constituents

  • Water
  • Ions (electrolytes)
  • Plasma proteins
• Plasma proteins

  • Influence blood pH and osmotic balance
  • Function in lipid transport, immunity, and blood clotting
• Cellular elements of blood

  • Erythrocytes (red blood cells)
  • Leukocytes (white blood cells)
  • Platelets
• Stem cells

  Source of all blood cells in red marrow of bones
• Erythropoietin (EPO)

  Hormone that stimulates erythrocyte production when oxygen delivery is low
• Erythrocytes

  • Most numerous blood cells
  • Contain hemoglobin to transport oxygen
• Hemoglobin

  Iron-containing protein in erythrocytes that transports oxygen
• Oxygen and carbon dioxide transport

  1. Hemoglobin picks up oxygen in lungs

  2. Hemoglobin releases oxygen to body cells

  3. Carbon dioxide diffuses into blood and is transported bound to hemoglobin
• Bohr effect

  Explains why RBCs pick up and release oxygen based on factors like CO2, pH, and temperature
• Carbonic anhydrase

  Enzyme that helps convert CO2 to carbonic acid and bicarbonate ions
• Fetal hemoglobin has a higher affinity for oxygen than adult hemoglobin
• Blood flow


  1. Right ventricle pumps blood to lungs via pulmonary arteries

  2. In lungs, blood loads O2 and unloads CO2

  3. Oxygen-rich blood from lungs enters left atrium via pulmonary veins

  4. Left ventricle pumps blood to body tissues via aorta

  5. Aorta provides blood to heart through coronary arteries

  6. Blood returns to heart through superior vena cava and inferior vena cava

  7. Superior vena cava and inferior vena cava flow into right atrium
• Cardiac cycle


  Ongoing sequence of contraction and relaxation of atria and ventricles that keeps blood continuously circulating
• Cardiac cycle stages


  1. Ventricles relax, atria contract

  2. Atria contract

  3. Ventricles contract
• Cardiac contraction


  • Systole
  • Diastole
• Ventricles relax, atria contract


  • Atria contract, decreasing volume of chambers and increasing pressure inside
  • Pushes blood into ventricles