Cardiovascular L4

• Learning objectives


  • To be able to compare and contrast the cardiovascular systems of teleosts, amphibians, reptiles, birds and mammals
  • Describe the factors that led to the evolution of 4 chambered hearts and double circulation
  • Provide examples of cardiovascular plasticity
• Vertebrates have closed circulatory systems
• Vertebrate hearts


  • Show changes with phylogeny

  
• Factors to consider


  • The respiratory medium
  • Blood pressure
  • Any special circumstances (such as changing from water breathing to air breathing)
  • Air (in lungs) is at a low pressure compared with the blood system
  • Water is at a relatively high pressure because of its density
  • In the blood system, pressure is lost at capillaries
• Teleost cardiovascular system: Heart

  • Only two pumping chambers - (atrium and ventricle)
  • Sinus venosus: aids atrial filling by contracting
  • Bulbus arteriosus: flow regulator

  
• Teleost cardiovascular system: Circulation


  • Single circuit ("one loop")
  • Arterial system post-gills is a low pressure system
  • Venous pressure extremely low
• The fish heart is not capable of generating high pressures
• There are problems with oxygen supply to the heart because most hearts derive ALL of their oxygen from venous blood
• Most fish hearts lack a coronary circulation, and current information suggests this has evolved independently (and subsequently lost) several times

  
• Amphibian cardiovascular system: Heart

  • Ectothermic
  • Slow metabolic rate
  • Live in both aquatic and terrestrial habitats
  • Breathing organs: skin and lungs
  • 3 pumping chambers ( 2 atria and 1 ventricle)
  • Atria division driven by appearance of lungs
  • Ventricle is not divided well (some mixing)

  
• Amphibian cardiovascular system: Circulation


  • Separate pulmonary circuit evolved
  • Driven by appearance of lungs
  • Partially achieves double circulation- "two loops"
  • More efficient than a fish heart

  
• Reptilian cardiovascular system (most): Heart

  • Ectothermic
  • Slow metabolic rate
  • Mostly terrestrial habitats (some amphibious)
  • Most breath air (lungs only)
  • Retained two atria that amphibians have
  • Ventricle is weird! (Cavum arteriosum (CA), Cavum pulmonale (CP), Cavum venosum (CV))

  
• Reptilian cardiovascular system (most): Circulation in air

  1. Blood from RA goes through the CV to CP and on to the lungs

  2. Blood from LA goes to CA, then CV, then to systemic arteries (right systemic artery RSA and left systemic artery LSA)

  
• Reptilian cardiovascular system (most): Circulation during diving

  1. Lungs can be bypassed via the cavum venosum (CV)

  2. Blood is shunted from the right side to the left side, thus avoiding the pulmonary circulation

  
• Reptilian cardiovascular system: Crocodilians are special!

  • The foramen of Panizza links left and right aortae
  • Cog-teeth: stiff teeth-like structures which can close during a dive
• Crocodilians: Heart during diving

  1. Cog teeth close

  2. Blood from the RV goes to left aorta

  3. Mixing of oxygenated and deoxygenated blood occurs through the foramen of Panizza

  4. Blood flows from the left aorta to the body and back again

  
• Birds and mammals


  • Four-chambered hearts
  • Ventricle becomes divided by a septum
  • Complete separation of pulmonary and systemic flow
  • No foramen of Panizza or shunts
  • Both groups have a single major distributing artery

  
• Evolution of the vertebrate CV system

  1. Increases from 2 to 4 chambered heart

  2. Moves from single circulation to double circulation
• Cardiovascular comparisons


  • Fish (2 chambers): 1 atrium; 1 ventricle; Single circulation
  • Reptile/Amphibian (3 chambers): 2 atria; 1 ventricle; Oxygenated and deoxygenated blood are somewhat mixed; Double circulation
  • Mammals and birds (4 chambers): 2 atria; 2 ventricles; Oxygenated and deoxygenated blood are separate; Double circulation

  
• Factors that can induce plasticity in the cardiovascular system

  • Exercise training
  • Sexual maturation
  • Food deprivation
  • Environmental conditions (e.g. temperature, hypoxia)
• Sexual maturation - cardiac enlargement in male salmonids

  • Athleticism in salmonids plays an important role in their survival and reproduction
  • Undertake major upstream migrations to spawn
  • Males have fierce territorial disputes over spawning sites
  • Sexual maturity can double heart mass in male rainbow trout
  • Elevated levels of androgens stimulate the cardiac enlargement
• Lizards living at the peak

  • Red tail toad-headed lizard (Phrynocephalus erythrurus)
  • Highest living reptile in the world (4000 – 5000m above sea level)
  • Lives in the Qinghai-Tibetan Plateau
  • Physiological challenges: Reduced oxygen availability (high altitude hypoxia), Low environmental temperatures
• High altitude species


  • Greater blood oxygen carrying capacity (higher haemoglobin and haematocrit)
  • Higher Hb-oxygen affinity

  
• Do these differences in physiological traits reflect fixed, genetically based differences or environmentally-induced acclimatization responses (phenotypic plasticity)?
• Highland and lowland deer mice

  • Deer mice (Peromyscus maniculatus)
  • 4350m above sea level
  • 430m above sea level
• Highland and lowland deer mice: Common garden experiment

  1. 24 highland and 22 lowland mice were transferred to a common garden experiment at 300m above sea level

  2. Left to acclimate for 6 weeks
• Physiological differences disappeared after 6-weeks of acclimation to low altitude conditions