Circulatory System

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Circulatory System
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I. Evolution of the Heart

• A. Protochordates - simple tubular heart beating
  by peristalic waves. 1. Arteries - preadapted
  for blood under high pressure because of muscular
  walls 2. Branchial function of aortic arches-
  not for respiration, simply a mechanism for
  getting blood to dorsal aorta through aortic
  arches.

Dorsal Aorta
Aortic arches
Ventral Aorta
Direction of Blood Flow
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B. Fish - gas exchange in gills required
specialized pump - first true heart

• 1. Gill respiration - two operations in gill
  respiration
• a. Collection of blood - collection chambers at
  rear - Sinus venosus
• b. Propulsion of bloodatrium
  ventricle

conus arteriosus
Body
Ant.
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2. Advantages of fish system

• a. Collected blood reached propulsive chambers
  (ventricle and conus arteriosis) via gravity and
  weak contractions of thin-walled atrium.
• b. Thin walls of atrium and sinus venosus offer
  little resistance to blood allowing bulging with
  minimum resistance.
• c. Slight negative pressure in sinus venosus
  exists because of pumping and sino-auricular
  valve which closes
• atrio-ventricular valve between atrium and
  ventricle

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The pumping cycle of the fish heart
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3. Disadvantages of fish systemloss of
pressure in gills because x-section of gill
capillaries is greater than x-sect of vessels
leading to them.No pump from gills to
body in fish and gill-breathing salamanders.
Gills
Body
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C. Lungfish and amphibians 1. Changes required
for air breathing a. Lungs for gas exchange
b. Mechanism of supplying unoxygenated blood to
lungs and aerated blood to body
Lungfish
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2. Modifications in the Amphibian Heart a.
Division of atrium 1. Systemic chamber -
Right - receiving non-aerated blood from sinus
venosus. 2. Pulmonary chamber - left
receiving aerated blood from lungs
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• 2. Pulmonary chamber - receiving aerated bllod
  from lungs
• b. Partial separation of chambers - in conus
  arteriosusDirects aerated blood into vessels of
  systemic aorta or pulmonary arteries
• c. Union of bases of 6th aortic arch separates
  bloood from ventral aorta. Thus - seperate
  exists from conus anteriosus
• d. Reduction of sinus venosus - as collecting
  chamber. Less pressure in air than in H2O.

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D. Later ectothermic state - reptiles 1.
Modifications a. Reduction of sinus venosus. But
never lost - myogenic center (origin of Ht. Beat-
SA node) is here. b. Conus arteriosus
disappears - and forms trunks of large arteries
leaving the Heart - aortae semiluner valves
remain c. Partial subdivision of ventricle
complete in crocodilians
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Blood flow in the reptilian heart
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E. Endotherm state 1. Modifications a.
Separation of ventricles closure of ventricular
septum - no mixing of oxygenated and
unoxygenated blood b. Reduction of
ventricular exits birds - reduction of
ventricular exists from 3 to 2. Loss of left
aortic trunk of the systemic aorta in
mammals, there is a loss of the rt. Aortic
trunk.
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Evolutionary Changes in Vertebrate Hearts
Amphibian Heart
Fish Heart
Endotherm Heart
Reptilian Heart
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