ZOOL PPT 6

• Respiratory surface


  Lungs or gills
• Exchanging Materials


  Every organism must exchange materials with its environment. This exchange ultimately occurs at the cellular level.
• Extracellular fluid


  • Interstitial (tissue) fluid
  • Intracellular fluid
  • Blood plasma (if closed circulatory system present)
• Unicellular organisms


  Exchanges occur directly with the environment
• Multicellular organisms


  Direct exchange with the environment is not possible for most of the cells
• Open circulatory system


  Blood (hemolymph) bathes the organs directly
• Closed circulatory system


  Blood is confined to vessels and is distinct from the interstitial fluid
• Closed systems are more efficient at transporting circulatory fluids to tissues and cells
• Invertebrate circulatory systems


  • Wide range of body size and form is paralleled by a great diversity in circulatory systems
• Gastrovascular cavity


  Functions in both digestion and distribution of substances throughout the body
• Vertebrate circulatory system


  • Closed circulatory system called the cardiovascular system
  • Consists of blood vessels and a two- to four-chambered heart
  • Blood flows in a closed cardiovascular system
• Blood flow in closed cardiovascular system


  1. Arteries carry blood to smaller vessels called arterioles, then to the tiny capillaries - the sites of chemical exchange between the blood and interstitial fluid

  2. Blood then flows from capillaries into venules then to larger veins which return blood to the heart
• Fish heart


  • Two main chambers: One ventricle and one atrium
  • Blood pumped from the ventricle travels to the gills, where it picks up O2 and disposes of CO2
• Amphibian heart


  • Three-chambered heart, with two atria and one ventricle
  • The ventricle pumps blood into a forked artery that splits the ventricle's output into the pulmocutaneous circuit and the systemic circuit
• Reptile heart


  • Double circulation with a pulmonary circuit (lungs) and a systemic circuit
  • Turtles, snakes, and lizards have a three-chambered heart
  • Crocodilians have a four-chambered heart
• Mammal and bird heart


  • Ventricle is completely divided into separate right and left chambers
  • The left side of the heart pumps and receives only oxygen-rich blood, while the right side receives and pumps only oxygen-poor blood
• A powerful four-chambered heart was an essential adaptation of the endothermic way of life characteristic of mammals and birds
• Mammalian circulation pathway


  1. Blood begins its flow with the right ventricle pumping blood to the lungs

  2. In the lungs, the blood loads O2 and unloads CO2

  3. Oxygen-rich blood from the lungs enters the heart at the left atrium and is pumped to the body tissues by the left ventricle

  4. Blood returns to the heart through the right atrium
• Anterior vena cava


  Entrance of blood from superior and anterior- blood will meet at the right atrium
• Pulmonary artery


  Carries deoxygenated blood away from the heart
• Arteries


  Carry blood away from the heart, must be oxygenated
• Pulmonary vein


  Carries oxygenated blood to the left atrium
• Mammalian heart


  • Heart contracts and relaxes in a rhythmic cycle called the cardiac cycle
  • Contraction phase is called systole, relaxation phase is called diastole
• Heart rate


  Number of beats per minute
• Cardiac output


  Volume of blood pumped into the systemic circulation per minute
• Maintaining heart's rhythmic beat


  • Some cardiac muscle cells are self-excitable, meaning they contract without any signal from the nervous system
  • Sinoatrial (SA) node, or pacemaker, sets the rate and timing at which all cardiac muscle cells contract
  • Impulses from the SA node travel to the atrioventricular (AV) node, then to the bundle of His and Purkinje fibers
• Electrocardiogram (ECG or EKG)


  Records the impulses that travel during the cardiac cycle
• Pacemaker


  • Influenced by nerves, hormones, body temperature, and exercise
• Blood vessel structure


  • All blood vessels are built of similar tissues and have three similar layers: endothelium, smooth muscle, and connective tissue
• Arteries


  Have thicker walls to accommodate the high pressure of blood pumped from the heart
• Veins


  Have thinner walls, blood flows back to the heart mainly as a result of muscle action
• Blood flow velocity


  Slowest in the capillary beds due to high resistance and large total cross-sectional area
• Blood pressure


  • Hydrostatic pressure that blood exerts against the wall of a vessel
  • Systolic pressure is the highest pressure in the arteries during ventricular systole
  • Diastolic pressure is the lower pressure in the arteries during diastole
• Capillary function


  1. Contraction of smooth muscle layer in arteriole wall constricts the vessel

  2. Precapillary sphincters control the flow of blood between arterioles and venules

  3. Exchange of substances between blood and interstitial fluid takes place across the thin endothelial walls of the capillaries

  4. Difference between blood pressure and osmotic pressure drives fluids out of capillaries at the arteriole end and into capillaries at the venule end
• Capillary Function


  • Two mechanisms regulate the distribution of blood in capillary beds
  • In one mechanism, contraction of the smooth muscle layer in the wall of an arteriole constricts the vessel
  • In a second mechanism, precapillary sphincters control the flow of blood between arterioles and venules
• Critical exchange of substances between the blood and interstitial fluid


  Takes place across the thin endothelial walls of the capillaries
• The difference between blood pressure and osmotic pressure


  Drives fluids out of capillaries at the arteriole end and into capillaries at the venule end
• Lymphatic System


  • Returns fluid to the body from the capillary beds
  • Aids in body defense
• Blood


  A specialized connective tissue in the circulatory systems of vertebrates
• Blood Composition


  • Plasma (55%)
  • Cellular elements (45%)