Animal Circulation and Gas Exchange

  • Exchange materials with the environment and transport material between sites of exchange in body

  • limited by animal size and shape→ Cnidarians, sponges have cells in direct contact w/ environment b/c don’t have a base circulatory system

    • instead, they have gastrovascular cavities which also is the same as digestive system

  • Circulatory Systems:

    • a circulatory fluid

    • a set of interconnecting tubes

    • a muscular pump/heart

    • Open (arthropods, mollusks)

      • fluids kept under pressure by animals w/ rigid body coverings

      • no distinction b/w hemolymph and interstitial fluid, open and move everywhere in body

      • lower pressure systems→ deflects fluid back towards the heart, less costly than closed circulatory systems

      • pressure used to generate force for movement

    • Closed (vertebrates, cephalopods, worms)

      • higher blood pressure

      • actual blood vs interstitial fluid

      • blood confined to vessels

      • at least 1 heart that pump blood into small vessels that infiltrate each organ

      • more effective at transporting fluid especially for larger/more active animals

      • exchange occurs at capillaries

  • Blood Vessels (Closed Systems)

    • Cardiovascular system in humans and vertebrates

    • arteries- blood from heart to capillaries (away from heart toward organs)

      • go to arterioles (in organs) to capillaries (small, exchange chemicals via diffusion)

    • Veins- blood from capillaries to heart

      • Capillaries→Venules→Veins

    • Portal veins carry blood b/w pairs of capillary beds outside of heart and lungs

  • Double Circulation- more vigorous flow of blood

  • Fish- single circulation, gills more effective esp not on land

  • Mammals+Birds- Pulmonary circuit is where lungs are

    • right ventricle pumps blood to lungs using arteries→loads O, unloads carbon dioxide, have oxygen rich blood returning on left side…

  • Human Circulatory System:

    • Blood

      • Specialized connective tissue

      • Top layer = plasma, 55% blood volume, mostly water and dissolved ions

      • Middle layer = leukocytes/white blood cells, 1% blood volume, platelets+immune cells

        • white blood cells- resposible for immune responses, diff types perform different functions in the immune system, spend most time outside circulatory system, mainly in lymphatic system

      • Bottom layer = erythrocytes/ red blood cells, transport oxygen

        • Hemoglobin- 1 RBC can carry 4 oxygen molecules

    • Heart

      • Sinoatrial Node = natural pacemaker, specialized muscle cells that do not contract on their own but depolarize to create an electrical signal to tell muscle cells in atria to contract (atrial kick), slowly transmitted to AV node, affects ventricular filling

      • Atrioventricular Node = stimulates contraction in ventricles, controls timing and coordination of ventricular contraction, contractions start at bottom and work anteriorly through purkinje fibers, slows down the system

    • Arteries

    • Veins

      • Connective Tissue allows stretch and recoil, maintain blood flow, provide tough outer coating

      • Smooth Muscle- alters vessel diameter

        • Vasoconstriction = make opening narrower

        • Vasodilation = make opening wider

      • Why are arteries wider? they carry blood away from pumping heart→have to withstand force of contraction→thicker

      • Veins have valves to prevent back flow

    • Capillaries- pressure differences allow materials to move in and out

    • Blood Vessels

  • Lymph Vascular system

    • structure and fluid movement similar to veins

    • fluid recovery and clean up→ collects excess interstitial fluid in capillaries→becomes lymph→returns to blood

    • no heart pumping→rely on body movement and valves

    • lymph passes through lymph nodes (filter and immune response)

    • maintains fluid balance and screen for pathogens→ swell sometimes when sick

  • Respiratory Surfaces- where gas exchange occurs

    • Gills, skin, tracheal systems (insects), lungs all have adapted to help diffusion

    • thin, moist, lots of surface area, concentration gradients, tied to circulation

    • All respiratory surfaces require moist exchange surfaces

    • gas density in air 40 times greater than that dissolved in water→respiratory systems must be larger or more efficient under water

  • Gas Exchange

    • Counter Current Exchange (fish) - water flowing through gills in one direction, blood in opposite directions

      • partial pressure of oxygen in blood always lower than partial pressure of oxygen in water→oxygen moves from water to blood

      • fish extract 80% of oxygen from water

    • Positive Pressure Pumps (amphibians + some reptiles) - folded inside body rather than exposed, don’t dry out

      • air not flowing in/out, have to move it out of body→ need ventilation system

      • inhalation = force air from mouth down the thorax and into lungs (like gulping)

      • exhalation = elastic recoil pushes air up

      • different from humans

    • Negative Pressure Breathing (humans)

      • inhalation = diaphragm contracts (moves down)→ increases volume of chest cavity→pressure goes down→ air rushes in

      • exhalation = diaphragm moves up→ ribcage gets smaller→ volume decreases→ pressure increases, moves back out through nostrils

      • Nasal Cavity - turbinates filter, warm, and moisten air