C3.8 - Circulatory System

Introduction to Circulatory System

• Responsible for delivering nutrients and oxygen to tissues
• Removes wastes and provides a pathway for hormones and other chemical messengers
• Most multicellular organisms have a fluid-filled vascular system
• Most animals have a vascular system associated with a muscular pump creating a circulatory system

Internal Transport in Simple Organisms

• Unicellular organisms
• Rely on distribution of nutrients through…
  • streaming of circulation of cytoplasm
• i.e. amoeba

Internal Transport in Simple Animals

• A simple body cavity allows materials to be exchanged between

  • the fluid in the body cavity; and

  • the cells of the body cavity itself

  • i.e. sea anemone

    
• Branching of body cavity allows greater surface area for absorption

  • i.e. flatworm

    

Sea anemone cross-section

Flatworm cross-section

Open Transport Systems

• open circulatory system: transport system where blood does not always stay enclosed within blood vessels
• Tubular heart pumps blood through vessels that open into sinuses
• sinus: spongy chamber in system
• Blood bathes tissues directly from sinuses
• It then collects in another set of sinuses and goes back to heart
• i.e. insects

Insect cross-section

Closed Transport Systems

• Blood contained within vessels and pumped around body
• Blood vessels consist of…
  • large vessels for blood collection
  • small vessels for blood distribution
  • capillaries to provide surface area for materials exchange
• More efficient circulation
• Nutrients, gases, and wastes diffuse across thin walls of capillaries
• cardiovascular system: closed circulatory system in humans and other vertebrates
  • humans have network of ~100,000 km of blood vessels

Circulatory system of earthworm

Circulation in Annelids

• Simplest closed circulatory systems
• 2 main blood vessels connected by aortic arches that act as pumps
  • dorsal vessel
  • ventral vessel
• Blood flows from the dorsal vessel, through the aortic arches, to the ventral vessel
• Numerous capillaries found in the skin for gas exchange w/ environ.
• Respiratory pigment hemoglobin assists in absorption and transport of oxygen

Earthworm aortic arches

Circulation in Fish

• 2 chambered heart w/ 2 associated cavities in series (inefficient)
• All chambers are able to contract
• Blood flows in one direction
• Sinus Venosus → Atrium → Ventricle → Conus
• However, pressure is lost over the gills limiting fish’s metabolic rate

Fish heart cross-section

Circulation in Amphibians

• 3-chambered heart: left and right atrium, ventricle
• Blood pumped to lung and then back to the heart → distributed to body
• 3 chambers allow blood to be pumped 2x / cycle
• Only some blood is pumped twice → incomplete double circulation
• Oxygenated and deoxygenated blood mix in ventricle reducing efficiency

Amphibian heart

Circulation in Reptiles

• Non-crocodilians → partially divided ventricle
  • i.e. snakes, turtles, tortoises, lizards
  • more efficient than amphibians but still not very efficient
• Crocodiles → completely divided ventricle
  • functionality similar to mammals

Circulation in Birds and Mammals

• High energy requirements necessitate efficient circulatory system
• Oxygenated and deoxygenated blood kept separate
• 4-chambered heart:
  • left and right atrium
  • left and right ventricle
• Closed, complete, double circulatory system