BIOL 1030 – TOPIC 16 LECTURE NOTES

Topic 16: Circulation and Gas Exchange - Circulatory and Respiratory Systems (Ch. 42)

  1. circulation required for all animals that are more than a few cells thick so that cells can get oxygen and nutrients and get rid of wastes
  2. two main types of circulatory systems, open and closed
  3. open systems
  4. no distinction between circulating fluid and extracellular fluid of body (lymph)
  5. hemolymph is the circulating fluid
  6. less efficient for transport (little pressure, slower)
  7. may still have heart(s) for pumping and some vessels
  8. examples: arthropods, mollusks
  9. closed systems
  10. circulating fluid (blood) distinct from lymph
  11. at least one heart always present
  12. blood vessels – tubular network for blood flow from heart of body and back
  13. arteries carry blood away from heart
  14. veins return blood to heart
  15. capillaries between arteries and veins are the thinnest vessel and allow exchanges with body tissues
  16. lymph system - when blood reaches capillaries, liquid seeps out of blood, most is mopped up, but much remains behind and needs to be mopped up or an edema (swelling) will form, lymph vessels return liquid to blood
  17. vertebrate circulatory systems functions
  18. transportation of gasses, nutrients, wastes
  19. regulation of temperature
  20. transportation of hormones
  21. protection (immune defense; blood clotting)
  22. blood plasma
  23. metabolites, wastes and hormones including carbon dioxide
  24. ions - mostly sodium, chloride, and bicarbonate, lower total ion concentration than sea water
  25. proteins - albumin, globulins (carry lipids and steroid hormones and fibrinogen) serum = fluid after fibrinogen clots out
  26. formed elements – blood cells
  27. blood cells
  28. erythrocytes - red blood cells
  29. cell that carries hemoglobin
  30. mammals - anucleate, donut shaped
  31. humans - 5 million/cm3; 45% of blood (hematocrit)
  32. live 120 days before replacement in humans
  33. formed in bone marrow
  34. leukocytes - white blood cells
  35. larger, nucleated, can migrate out of capillaries
  36. humans - 1% of cells in blood
  37. granular leukocyte - neutrophils (most common), eosinophils, and basophils
  38. nongranular leukocytes - monocytes and lymphocytes (T and B cells involved in immune response)
  39. neutrophils accumulate at injury and then joined by monocytes that change into macrophages
  40. phagocytosis by neutrophils and macrophages eliminate disease-causing organisms
  41. platelets
  42. megakaryocytes in marrow break off bits of their cytoplasm to form platelets (actually cell fragments)
  43. accumulate at wound and form a plug by sticking to each other and tissues
  44. plug reinforced by fibrin (formed by fibrinogen in complex chain of events)
  45. blood vessels
  46. structure - endothelium then elastic fibers then smooth muscle layer then connective tissue (except capillaries)
  47. arteries
  48. large ones - very elastic to absorb force of heart
  49. small ones (arterioles) - more muscular - to control blood flow (vasoconstriction and vasodilation)
  50. capillaries
  51. only endothelial lining (one-cell thick)
  52. about one red blood cell wide
  53. all exchange occurs here
  54. little blood pressure after exit
  55. veins and venules (smaller veins, just after capillaries)
  56. less muscular than arteries
  57. blood pressure greatly reduced in venous system - possibility for retrograde (back) flow
  58. valves - present in ascending veins to halt retrograde flow
  59. descending veins - no valves, gravity helps
  60. skeletal muscles help move blood - contract leg muscles to avoid fainting, which is typically caused by blood pooling in the legs
  61. the mammal heart
  62. 4 chambers
  63. right side - atrium receives blood from body, pumps to ventricle, which pumps to lungs
  64. left side - atrium receives blood from lungs, pumps to ventricle, which pumps to body
  65. atria both pump at the same time, then after about 100 ms delay both ventricles pump; both sides must pump the same volume, but the left pumps at greater pressure because it is going through greater resistance
  66. valves prevent backflow
  67. sinoatrial node (SA node) - pacemaker - starts impulse at atria and sends impulse to atrioventricular (AV) node
  68. AV node shunts impulse to the apex (bottom) of the heart through Purkinje fibers - modified cardiac muscle cells that look like neurons (unique to mammals)
  69. shunted impulse squeezes the heart from the bottom up - more efficient just like squeezing the toothpaste from the bottom of the tube is more efficient
  70. heart rate increases under exercise to get enough oxygen to muscles
  1. respiration – general term for use of oxygen and production of carbon dioxide;

cellular respiration – direct biochemical use to break down simple sugars for energy

body respiration (respiratory system) – exchange with environment

  1. components of respiratory systems in vertebrates
  2. air exchange surface – gills and lungs, sometimes skin
  3. transporting system – hemoglobin, red blood cells, and blood plasma
  4. air exchange surfaces
  5. mechanical issues (diffusion)
  6. net movement of molecules is diffusion; parameters involved covered by Fick's Law of Diffusion, which includes that the rate of diffusion:
  7. is proportional to surface area
  8. is proportional to the partial pressure difference
  9. is inversely proportional to travel distance
  10. consequences
  11. air exchange organs have very large surface areas
  12. efficient air exchange mechanics tend to maximize partial pressure difference
  13. air exchange organs and capillaries are thin (1-2 cells thick)
  14. gills
  15. mainly epithelial tissues coated with capillaries for gas exchange
  16. gill arches help spread the tissue
  17. countercurrent flow of blood to water maximizes oxygenation
  18. gills do not work in terrestrial environments
  19. collapse without water to keep them open, greatly reducing surface area for exchange
  20. allow too much water loss– need some sort of enclosure for exchange, or limited to water or moist areas
  21. lungs
  22. primitive versions apparent in early jawed vertebrate fossils; original use for buoyancy in water (swim bladder in modern bony fishes)
  23. air has more oxygen than water, and is easier to get and easier to move than water; however, all exchange surfaces must remain moist
  24. internal placement limits water loss (stays humid inside)
  25. typically has two-way flow, modified in birds to a one-way flow
  26. two-way flow: air enters and exits through same tube system
  27. residual volume of air retained in lung after each breath
  28. diffusion surfaces exposed to mix of fresh and residual air
  29. partial pressure difference far from maximal
  30. less efficient than one-way flow of gills
  31. amphibians
  32. surface area for diffusion not large – large terminal air sacs (alveoli)
  33. alveoli

sacs one epithelial layer thick

surrounded by capillaries, essentially bathed in blood

surface coated with a surfactant that affects surface tension and stabilizes surface; surfactant in lungs is a complex substance composed of lipid and protein

  • force air into lungs by positive pressure breathing (“mouth breathing” – like bony fish with their gills)
  • much of exchange actually across skin
  • amniotes
  • more advanced than amphibians, greater metabolic need
  • all possess lungs with a larger relative surface area than amphibian lungs, due to many small alveoli (or specialized parabronchi in birds)
  • all gas exchange in lungs occurs at alveoli or parabronchi
  • thoracic breathing

negative pressure in chest due to increasing volume of lungs to draw air into lungs

more efficient than positive pressure breathing

requires connection of lungs to chest wall

  • mammals
  • air taken unto mouth and nose, through larynx (voice box) into trachea (derived from gill arches) that splits into two bronchi, each subdivide into bronchioles that deliver air to alveoli
  • inhalation (aspiration) – contract external rib intercostals (lifts ribs) and diaphragm (pushes on abdomen and expands chest cavity)
  • exhalation – elastic recoil; relaxing muscles snaps ribs and chest cavity back into place, forces air out
  • humans – about 300 million alveoli combine for up to 80 m2 of surface area for gas exchange, 42x body surface area
  • birds
  • flying demands very high metabolism, thus a more advanced respiratory system
  • air flow is unidirectional from posterior to anterior

birds have no residual volume as do mammals

only fresh, fully oxygenated air at diffusing surfaces

thus, bird lungs are more efficient because they increase the partial pressure difference

  • birds can survive at much higher altitudes than mammals
  • avian lung works like a two-cycle pump

air passes through trachea into nondiffusing posterior air sacs with inhalation

air flows into lung with exhalation

air passes from lung to anterior air sacs with next inhalation

air flows out through trachea at next exhalation

  • air flow is different from the flow of blood through the lung

air in lungs flows across parabronchi (tubes instead of sacs, but otherwise like alveoli – only one cell thick for effective diffusion)

parabronchi coated with capillaries

cross-current flow – flow of air and blood at 90 angles to each other

less efficient than countercurrent flow of fish, but more efficient than other amniotes

  1. gas transport and exchange in tissue
  2. simple vs. facilitated diffusion
  3. simple diffusion of gases too slow over more than 0.5 mm
  4. diffusion is facilitated by using carrier proteins in a moving fluid
  5. example: human blood plasma holds only 3mL O2/L, but blood holds 200 m L O2/L because of L O2 bound to the carrier protein hemoglobin
  6. carrier proteins: hemoglobin and hemocyanin
  7. hemoglobin
  8. oxygen carrier protein in blood of all vertebrates, many invertebrates such as echinoderms, annelids, some mollusks, and even some protists
  9. synthesized by and contained within erythrocytes
  10. 4 polypeptides and 4 organic heme groups, iron molecule at center of each heme group
  11. oxygen bound reversible with iron portion of each heme group; thus, each molecule of hemoglobin can bind 4 molecules of O2
  12. CO poisoning: CO actually binds better than O2, quickly compromising O2 transport (quite deadly)
  13. oxyhemoglobin – loaded with O2, bright red
  14. deoxyhemoglobin – O2 released, dark red (veins blue due to tissue colors)
  15. hemocyanin
  16. found in many invertebrates (many arthropods, some mollusks)
  17. not in cells, instead free in hemolymph
  18. uses copper instead of iron
  19. bright blue when bound with O2
  20. oxygen transport (vertebrates)
  21. 95% of O2 bound to hemoglobin in erythrocytes, rest in plasma
  22. partial pressure of oxygen = PO2
  23. if higher in lungs more oxygen will dissolve in blood and combine with hemoglobin
  24. lower at tissues so hemoglobin will give up oxygen to tissues
  25. presence of CO2 at tissues
  26. lowers blood pH at tissues
  27. causes a shape change in hemoglobin that weakens affinity of hemoglobin for oxygen
  28. called Bohr effect – leads to extra unloading of O2 at tissues
  29. normally only about 1/5 of O2 loaded at the lungs is unloaded at tissues
  30. higher metabolic activity at tissues  higher CO2 greater Bohr effect
  31. CO2 transport (vertebrates)
  32. CO2 loading at tissues
  33. as red blood cells unload O2, blood absorbs CO2 from tissues
  34. only 8% of CO2 dissolved in plasma
  35. 20% bound to hemoglobin (different site than where O2 binds)
  36. rest in cytoplasm of red blood cells, where carbonic anhydrase catalyzes formation of carbonic acid (H2CO3)
  37. carbonic acid dissociates to form H+ and bicarbonate (HCO3-)
  38. thus, red blood cells carry most CO2 to lungs as bicarbonate ions
  39. CO2 unloading at lungs
  40. lower concentration of CO2 in alveoli or parabronchi than in blood causes net diffusion of CO2 out of blood
  41. carbonic anhydrase reaction proceeds in reverse

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