Hearts

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Hearts
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Original parts

• Sinus venosus
• Atrium
• Ventricle
• Bulbus cordis
• 1. conus arteriosus - with conal valves and
  cardiac muscle
• 2. bulbus arteriosus - Teleosts - no conal
  valves, skeletal muscle - absorb some of the
  strength of the heart
• Sinoatrial, atrioventricular, and conal valves
  halt retrograde flow

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Heartbeat

• Self regulation
• pacemaker or sinoatrial (SA) node, present on
  Sinus venosa
• atrioventricular (AV) node and Purkinje fibers -
  modified cardiac muscle cells that look like
  neurons, transmit conduction to ventricles
• Under regulation by nervous and endocrine system
• Tachycardia-increase in heart rate
• Bradycardia-decrease in heart rate

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Primitive vertebrate heart

• branchial heart - no conus arteriosus
• accessory hearts - not hearts, put skeletal
  muscle pumps to help venous sytem along
• Due to drainage being provided by large sinuses,
  venous blood pressure is extremely low and needs
  supplemental pumps to get blood back to heart.
• Pacemaker present on Sinus venosa (SA-node)

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Teleosts

• bulbous arteriosus (not conus arteriorosis)
  perhaps to mitigate force from ventricle to keep
  from damaging gill capillaries

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Lungfishes

• division of labor between left and right halves
• partial interatrial and interventricular septa
• separation incomplete
• conus arteriosus with spiral valve
• deoxygenated blood shunted to aortic arch VI and
  into pulmonary artery
• oxygenated blood through arches III, and IV which
  do not have gills and then to body
• Incomplete septum allows for better switching
  between aerial and aquatic respiration

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Amphibians

• interatrial septum complete
• no ventricular septum, but deep recesses in
  trabeculae carnae - oxygenated blood goes into
  the crevices, deoxygenated goes through the
  middle
• conus arteriosus with spiral valve
• Constrict pulmonary artery so no blood goes to
  lung and more goes to skin during diving

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Squamates (lizards and snakes) and turtles

• Similar to amphibians, but no conus arteriosus
  (no reptiles, birds, or mammals have one)
• Better separation in the Ventricle
• Deep pockets that partition heart into
  semi-distinct chambers (6 in all)
• Can shunt off lungs, good for turtles, snakes
• 60-90 separation of blood flow

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Turtle circulation
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Crocodile Hearts
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Birds and mammals

• same heart, different ontogeny, convergent trait
• complete separation of left and right sides and
  oxygenated and deoxygenated blood
• Why separate? Maybe related to homeothermy.
• Divers cant shunt off lungs, blood flow
  restricted by cutting off microcirculation

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Changing from placental to air breathing