Circulation

• Blood is pumped out of the heart by contraction of the cardiac muscle cells.
• These functions are facilitated by the circulatory system
• A circulatory system is necessary in any animal whose body is too large or too complex for such exchanges to occur
• An internal transport system must bring resources close enough to cells for diffusion to be effective
• Diffusion is inadequate for transporting materials over distances greater than a few cell widths
• Internal transport in animals with multiple layers of cells

  Consists of Heart, Circulatory fluid, Vessels
• These needs ultimately extend to every cell in the body
• Types of Internal transport systems

  • Central gastrovascular cavity, True circulatory system
• To sustain life, an animal must acquire nutrients, exchange gases and dispose of waste products
• Types of Circulatory Systems in Animals

  • Open circulatory System, Closed Circulatory System
• Open circulatory System


  • Fluid is pumped through open-ended vessels and flows among the tissues
  • No distinction between the circulatory fluid and the interstitial fluid
• Internal transport in cnidarians and most flatworms

  Serves in digestion and distribution of substances throughout the body
• Animals with Open circulatory System

  • Grasshoppers
• Animals with Closed Circulatory System

  • Vertebrates, Earthworms, Squids, Octopuses
• Closed Circulatory System

  • Circulatory fluid (blood) is confined to vessels keeping blood distinct from the interstitial fluid
  • Has Arteries, Veins, Capillaries
• Closed Circulatory System in fish

  • Heart has Atrium and Ventricle
  • Blood flows to gills via large arteries
  • Oxygen-rich blood flows into large arteries that carry it to all parts of the body
  • Capillaries infiltrate every organ and tissue in the body
  • Chemical exchange between blood and interstitial fluid occurs in capillaries
  • Venules converge into larger veins that return blood to the heart
• The colonization of land by vertebrates was a major episode in the history of life
• Vertebrate Cardiovascular Systems

  • Single circulation
  • Double circulation
• Change from gill breathing to lung breathing


  Occurred as aquatic vertebrates became adapted for terrestrial life
• Capillaries converge into venules which in turn converge into larger veins that return blood to the heart
• As aquatic vertebrates became adapted for terrestrial life, nearly all the organ systems underwent major changes
• Single circulation

  1. Blood passes through the heart only once in each circuit through the body

  2. Blood pumped through the ventricle travels first to the gill capillaries

  3. Blood pressure drops considerably as it flows through the narrow capillaries

  4. An artery carries the oxygen-rich blood from the gills to capillaries in the tissues and organs from which blood returns to the atrium of the heart

  5. The animal’s swimming movements help to propel the blood through the body
• Three Chambered heart

  1. Frogs and other amphibians have a three-chambered heart (one ventricle and two atria)

  2. Right atria receives blood from the systemic capillaries in the body’s organs

  3. Ventricle pumps blood to capillary beds in the lungs and skin

  4. Because gas exchange occurs in both lungs and across the thin moist skin, this is called pulmocutaneous circuit

  5. Oxygen-rich blood returns to the left atrium

  6. Although blood from the two atria mixes in the single ventricle, a ridge diverts most of the oxygen-poor blood to the pulmocutaneous circuit and most of the oxygen-rich blood to the systemic circuit

  7. In the three-chambered heart of turtles, snakes and lizards, the ventricle is partially divided and less mixing of blood occurs

  8. In crocodilians, the ventricle is completely divided
• Double circulation

  1. In terrestrial vertebrates, a single circulation is inadequate to supply enough pressure to move blood through the capillaries of the lungs and then to body capillaries

  2. Evolutionary adaptation of a double circulation results in a vigorous flow of blood to body organs

  3. In double circulation, blood is pumped a second time after it loses pressure in the lungs

  4. Consists of Pulmonary circuit which carries blood between the heart and the gas exchange tissues in the lungs

  5. Systemic circuit which carries blood between the heart and the rest of the body
• Four Chambered Heart

  1. In all birds and mammals, the heart has four chambers (two atria, two ventricles)

  2. This is an evolutionary adaptation to support the high metabolic rates of birds and mammals

  3. The right side of the heart handles only oxygen-poor blood

  4. The left side receives and pumps only oxygen-rich blood
• Blood Vessels

  • Arteries
  • Transport blood from the heart to the lungs and other parts of the body
  • As blood forcefully exits the heart, it enters arteries and then arterioles
  • Has the thickest walls of all the vessels providing strength and elasticity to accommodate the rapid flow and high pressure of blood pumped by the heart
  • Outer layer of connective tissue with elastic fibers enables the vessels to stretch and coil
  • Smooth muscles in the walls of the arteries and arterioles narrow or widen the vessels in response to hormones and signals
• Walls of blood vessels

  • Provide strength and elasticity to accommodate the rapid flow and high pressure of blood pumped by the heart
• Smooth muscles in the walls of arteries and arterioles

  Narrow or widen the vessels in response to hormones and signals from the nervous system
• Constriction or relaxation of blood vessels


  Modulate the blood flow to different parts of the body
• Veins


  • Transport blood from the lungs and other parts of the body to the heart
  • Velocity and pressure are lower in veins than in arteries
  • Large veins have flaps of tissue that act as one-way valves, permitting blood to flow only toward the heart
• Components of Blood

  • Plasma
  • White blood cells/Leukocytes
  • Red blood cells/Erythrocytes
  • Platelets
• Plasma

  • About 90% water
  • Contains inorganic salts in the form of dissolved ions (electrolytes)
  • Functions to keep the pH of blood at 7.4
  • Maintains osmotic balance between blood and interstitial fluid
  • Plasma proteins like albumin act as a buffer and help maintain osmotic balance
  • Fibrinogen functions in blood clotting
  • Immunoglobulins are important in immunity
  • Apolipoproteins escort insoluble lipids which can travel only when bound to proteins
  • Contains a wide variety of substances in transit from one part of the body to another such as nutrients, waste products, O2, CO2, and hormones
• Capillaries


  • Consist of a single layer of epithelial cells wrapped in extracellular matrix
  • Structure fits their unique function which is exchange
  • Exchange facilitated by their intimate connection with the body’s tissues
  • Small diameter and thin walls facilitate the exchange of substances between blood and interstitial fluid
• Outer layer of connective tissue with elastic fibers in blood vessels

  • Enables the vessels to stretch and coil
• Red blood cells/Erythrocytes

  • Function in the transport of oxygen
  • Biconcave disc-shaped, thin in the center than at the sides
  • Small size and shape create a large surface area across which oxygen can diffuse
  • Mature RBCs lack a nucleus, allowing more room to pack in hemoglobin
  • Each RBC contains about 250 million molecules of hemoglobin and can transport about a billion oxygen molecules
  • A single drop of blood (about 50µL) contains about 25 million cells which means you have about 25 trillion RBCs in your 5L of blood
• White blood cells/Leukocytes

  • Five major types: monocytes, neutrophils, basophils, eosinophils, lymphocytes
  • Function collectively to fight infections
  • Monocytes and neutrophils are phagocytes which engulf and digest bacteria
• Platelets


  • Cell fragments involved in blood clotting