1. Chapter 42: Circulatory Systems and Gas Exchange
Take a look at a skeleton and see how well a heart is protected — open heart surgery takes breaking a body to get to the heart.

3. Exchange of materials
Animal cells exchange material across their cell membrane
fuels for energy
nutrients
oxygen
waste (urea, CO2)
If you are a 1-cell organism that’s easy!
diffusion
If you are many-celled that’s harder

4. Overcoming limitations of diffusion
Diffusion is not adequate for moving material across more than 1-cell barrier aa
CO2
NH3 O2 CH
CHO aa O2 CH
CHO
CO2 aa
NH3
CHO CH O2 aa

5. In circulation… What needs to be transported nutrients & fuels
from digestive system
respiratory gases
O2 & CO2 from & to gas exchange systems: lungs, gills
intracellular waste
waste products from cells
water, salts, nitrogenous wastes (urea)
protective agents
immune defenses
white blood cells & antibodies
blood clotting agents
regulatory molecules
hormones

6. Circulatory systems All animals have: circulatory fluid = “blood”
tubes = blood vessels
muscular pump = heart
open
closed
hemolymph
blood

7. Open circulatory system
Taxonomy
invertebrates
insects, arthropods, mollusks
Structure
no separation between blood & interstitial fluid
hemolymph
The fact that open and closed circulatory systems are each widespread among animals suggests that both offer advantages. For example, the lower hydrostatic pressures associated with open circulatory systems make them less costly than closed systems in terms of energy expenditure. Furthermore, because they lack an extensive system of blood vessels, open systems require less energy to build and maintain. And in some invertebrates, open circulatory systems serve a variety of other functions. For example, in molluscs and freshly molted aquatic arthropods, the open circulatory system functions as a hydrostatic skeleton in supporting the body.

8. Closed circulatory system
Taxonomy
invertebrates
earthworms, squid, octopuses
vertebrates
Structure
blood confined to vessels & separate from interstitial fluid
1 or more hearts
large vessels to smaller vessels
material diffuses between blood vessels & interstitial fluid
closed system = higher pressures
What advantages might be associated with closed circulatory systems? Closed systems, with their higher blood pressure, are more effective at transporting circulatory fluids to meet the high metabolic demands of the tissues and cells of larger and more active animals. For instance, among the molluscs, only the large and active squids and octopuses have closed circulatory systems. And although all arthropods have open circulatory systems, the larger crustaceans, such as the lobsters and crabs, have a more developed system of arteries and veins as well as an accessory pumping organ that helps maintain blood pressure. Closed circulatory systems are most highly developed in the vertebrates.

9. Vertebrate circulatory system
Adaptations in closed system
number of heart chambers differs 2 3 4
high pressure & high O2 to body
low pressure to body
low O2 to body
What’s the adaptive value of a 4 chamber heart?
4 chamber heart is double pump = separates oxygen-rich & oxygen-poor blood; maintains high pressure

10. Evolution of vertebrate circulatory system
fish
amphibian
reptiles
birds & mammals
2 chamber
3 chamber
3 chamber
4 chamber
Birds AND mammals!
Wassssup?!
A powerful four–chambered heart was an essential adaptation in support of the endothermic way of life characteristic of mammals and birds. Endotherms use about ten times as much energy as equal–sized ectotherms; therefore, their circulatory systems need to deliver about ten times as much fuel and O2 to their tissues (and remove ten times as much CO2 and other wastes). This large traffic of substances is made possible by separate and independent systemic and pulmonary circulations and by large, powerful hearts that pump the necessary volume of blood. Mammals and birds descended from different reptilian ancestors, and their four–chambered hearts evolved independently—an example of convergent evolution.
Why is it an advantage to get big?
Herbivore: can eat more with bigger gut.
lowers predation
(but will push predators to get bigger as well, although no one east elephant s.) V A A A A A A A V V V V V

11. Evolution of 4-chambered heart
Selective forces
increase body size
protection from predation
bigger body = bigger stomach for herbivores
endothermy
can colonize more habitats
flight
decrease predation & increase prey capture
Effect of higher metabolic rate
greater need for energy, fuels, O2, waste removal
endothermic animals need 10x energy
need to deliver 10x fuel & O2 to cells
convergent evolution

12. Vertebrate cardiovascular system
Chambered heart
atrium = receive blood
ventricle = pump blood out
Blood vessels
arteries = carry blood away from heart
arterioles
veins = return blood to heart
venules
capillaries = thin wall, exchange / diffusion
capillary beds = networks of capillaries
Arteries, veins, and capillaries are the three main kinds of blood vessels, which in the human body have a total length of about 100,000 km.
Notice that arteries and veins are distinguished by the direction in which they carry blood, not by the characteristics of the blood they contain. All arteries carry blood from the heart toward capillaries, and veins return blood to the heart from capillaries. A significant exception is the hepatic portal vein that carries blood from capillary beds in the digestive system to capillary beds in the liver. Blood flowing from the liver passes into the hepatic vein, which conducts blood to the heart.

13. Blood vessels arteries arterioles capillaries venules veins veins
artery
arterioles
venules
arterioles
capillaries
venules
veins

14. Arteries: Built for high pressure pump
thicker walls
provide strength for high pressure pumping of blood
narrower diameter
elasticity
elastic recoil helps maintain blood pressure even when heart relaxes

15. Veins: Built for low pressure flow
Blood flows
toward heart
Veins
thinner-walled
wider diameter
blood travels back to heart at low velocity & pressure
lower pressure
distant from heart
blood must flow by skeletal muscle contractions when we move
squeeze blood through veins
valves
in larger veins one-way valves allow blood to flow only toward heart
Open valve
Closed valve

16. Capillaries: Built for exchange
very thin walls
lack 2 outer wall layers
only endothelium
enhances exchange across capillary
diffusion
exchange between blood & cells

17. Controlling blood flow to tissues
Blood flow in capillaries controlled by pre-capillary sphincters
supply varies as blood is needed
after a meal, blood supply to digestive tract increases
during strenuous exercise, blood is diverted from digestive tract to skeletal muscles
capillaries in brain, heart, kidneys & liver usually filled to capacity
Why?
sphincters open
sphincters closed

18. Exchange across capillary walls
Lymphatic
capillary
Fluid & solutes flows out of capillaries to tissues due to blood pressure
“bulk flow”
Interstitial fluid flows back into capillaries due to osmosis
plasma proteins  osmotic pressure in capillary
BP > OP
BP < OP
Interstitial
fluid
What about edema?
About 85% of the fluid that leaves the blood at the arterial end of a capillary bed reenters from the interstitial fluid at the venous end, and the remaining 15% is eventually returned to the blood by the vessels of the lymphatic system.
Blood
flow
85% fluid returns to capillaries
Capillary
15% fluid returns via lymph
Arteriole
Venule

19. Lymphatic system Parallel circulatory system
transports white blood cells
defending against infection
collects interstitial fluid & returns to blood
maintains volume & protein concentration of blood
drains into circulatory system near junction of vena cava & right atrium

20. Lymph system Production & transport of WBCs Traps foreign invaders
lymph vessels
(intertwined amongst blood vessels)
lymph node

21. Mammalian circulation
systemic
Mammalian circulation
pulmonary
systemic
What do blue vs. red areas represent?

22. Mammalian heart
to neck & head & arms
Coronary arteries

23. Coronary arteries
bypass surgery

24. Heart valves 4 valves in the heart Atrioventricular (AV) valveSL
Heart valves
4 valves in the heart
flaps of connective tissue
prevent backflow
Atrioventricular (AV) valve
between atrium & ventricle
keeps blood from flowing back into atria when ventricles contract
“lub”
Semilunar valves
between ventricle & arteries
prevent backflow from arteries into ventricles while they are relaxing
“dub”
The heart sounds heard with a stethoscope are caused by the closing of the valves. (Even without a stethoscope, you can hear these sounds by pressing your ear tightly against the chest of a friend—a close friend.) The sound pattern is “lub–dup, lub–dup, lub–dup.” The first heart sound (“lub”) is created by the recoil of blood against the closed AV valves. The second sound (“dup”) is the recoil of blood against the semilunar valves.

25. Lub-dub, lub-dub Heart sounds Heart murmur closing of valves “Lub”
recoil of blood against closed AV valves
“Dub”
recoil of blood against semilunar valves
Heart murmur
defect in valves causes hissing sound when stream of blood squirts backward through valve SL AV AV

26. fill (minimum pressure)
Cardiac cycle
1 complete sequence of pumping
heart contracts & pumps
heart relaxes & chambers fill
contraction phase
systole
ventricles pumps blood out
relaxation phase
diastole
atria refill with blood
systolic
________
diastolic
pump (peak pressure)
_________________
fill (minimum pressure)
110
____ 70

27. Measurement of blood pressure
High Blood Pressure (hypertension)
if top number (systolic pumping) > 150
if bottom number (diastolic filling) > 90

28. Gas Exchange Respiratory Systems
alveoli
Gas Exchange
Respiratory Systems
elephant seals
gills

30. Why do we need a respiratory system?
respiration for respiration
Why do we need a respiratory system?
Need O2 in
for aerobic cellular respiration
make ATP
Need CO2 out
waste product from Krebs cycle
food
ATP O2
CO2

31. Gas exchange O2 & CO2 exchange between environment & cells
need moist membrane
need high surface area

32. Optimizing gas exchange
Why high surface area?
maximizing rate of gas exchange
CO2 & O2 move across cell membrane by diffusion
rate of diffusion proportional to surface area
Why moist membranes?
moisture maintains cell membrane structure
gases diffuse only dissolved in water
small intestines
large intestines
capillaries
mitochondria
High surface area? High surface area! Where have we heard that before?

33. Gas exchange in many forms…
one-celled
amphibians
echinoderms
cilia
insects
fish
mammals
size •
water vs. land •
endotherm vs. ectotherm

34. Evolution of gas exchange structures
Aquatic organisms
external systems with lots of surface area exposed to aquatic environment
Terrestrial
Constantly passing water across gills
Crayfish & lobsters
paddle-like appendages that drive a current of water over their gills
Fish
creates current by taking water in through mouth, passes it through slits in pharynx, flows over the gills & exits the body
moist internal respiratory tissues with lots of surface area

35. Gas Exchange in Water: Gills
In fish, blood must pass through two capillary beds, the gill capillaries & systemic capillaries.
When blood flows through a capillary bed, blood pressure — the motive force for circulation — drops substantially.
Therefore, oxygen-rich blood leaving the gills flows to the systemic circulation quite slowly (although the process is aided by body movements during swimming).
This constrains the delivery of oxygen to body tissues, and hence the maximum aerobic metabolic rate of fishes.

36. Counter current exchange system
Water carrying gas flows in one direction, blood flows in opposite direction
Living in water has both advantages & disadvantages as respiratory medium
keep surface moist
O2 concentrations in water are low, especially in warmer & saltier environments
gills have to be very efficient
ventilation
counter current exchange
Why does it work counter current? Adaptation!
just keep swimming….

37. How counter current exchange works
front
back
70%
40%
100%
15%
water
60%
30%
90%
counter-current 5%
blood
water
blood
50%
70%
100%
50%
30% 5%
concurrent
Blood & water flow in opposite directions
maintains diffusion gradient over whole length of gill capillary
maximizing O2 transfer from water to blood

38. Why don’t land animals use gills?
Gas Exchange on Land
Advantages of terrestrial life
air has many advantages over water
higher concentration of O2
O2 & CO2 diffuse much faster through air
respiratory surfaces exposed to air do not have to be ventilated as thoroughly as gills
air is much lighter than water & therefore much easier to pump
expend less energy moving air in & out
Disadvantages
keeping large respiratory surface moist causes high water loss
reduce water loss by keeping lungs internal
Why don’t land animals use gills?

39. Terrestrial adaptations
Tracheae
air tubes branching throughout body
gas exchanged by diffusion across moist cells lining terminal ends, not through open circulatory system
How is this adaptive?
No longer tied to living in or near water.
Can support the metabolic demand of flight
Can grow to larger sizes.

40. Why is this exchange with the environment RISKY?
Exchange tissue: spongy texture, honeycombed with moist epithelium
Lungs
Why is this exchange with the environment RISKY?
Lungs, like digestive system, are an entry point into the body
lungs are not in direct contact with other parts of the body
circulatory system transports gases between lungs & rest of body

41. Alveoli Gas exchange across thin epithelium of millions of alveoli
total surface area in humans ~100 m2

42. Negative pressure breathing
Breathing due to changing pressures in lungs
air flows from higher pressure to lower pressure
pulling air instead of pushing it

43. Mechanics of breathing
Air enters nostrils
filtered by hairs, warmed & humidified
sampled for odors
Pharynx  glottis  larynx (vocal cords)  trachea (windpipe)  bronchi  bronchioles  air sacs (alveoli)
Epithelial lining covered by cilia & thin film of mucus
mucus traps dust, pollen, particulates
beating cilia move mucus upward to pharynx, where it is swallowed

44. Autonomic breathing control
don’t want to have to think to breathe!
Autonomic breathing control
Medulla sets rhythm & pons moderates it
coordinate respiratory, cardiovascular systems & metabolic demands
Nerve sensors in walls of aorta & carotid arteries in neck detect O2 & CO2 in blood

45. Medulla monitors blood
Monitors CO2 level of blood
measures pH of blood & cerebrospinal fluid bathing brain
CO2 + H2O  H2CO3 (carbonic acid)
if pH decreases then increase depth & rate of breathing & excess CO2 is eliminated in exhaled air

46. Breathing and Homeostasis
ATP
Homeostasis
keeping the internal environment of the body balanced
need to balance O2 in and CO2 out
need to balance energy (ATP) production
Exercise
breathe faster
need more ATP
bring in more O2 & remove more CO2
Disease
poor lung or heart function = breathe faster
need to work harder to bring in O2 & remove CO2
CO2 O2

47. Diffusion of gases
Concentration gradient & pressure drives movement of gases into & out of blood at both lungs & body tissue
capillaries in lungs
capillaries in muscle O2 O2 O2 O2
CO2
CO2
CO2
CO2
blood
lungs
blood
body

48. Hemoglobin Why use a carrier molecule? Reversibly binds O2
O2 not soluble enough in H2O for animal needs
blood alone could not provide enough O2 to animal cells
hemocyanin in insects = copper (bluish/greenish)
hemoglobin in vertebrates = iron (reddish)
Reversibly binds O2
loading O2 at lungs or gills & unloading at cells
heme group
The low solubility of oxygen in water is a fundamental problem for animals that rely on the circulatory systems for oxygen delivery.
For example, a person exercising consumes almost 2 L of O2 per minute, but at normal body temperature and air pressure, only 4.5 mL of O2 can dissolve in a liter of blood in the lungs.
If 80% of the dissolved O2 were delivered to the tissues (an unrealistically high percentage), the heart would need to pump 500 L of blood per minute — a ton every 2 minutes.
cooperativity

49. Cooperativity in Hemoglobin
Binding O2
binding of O2 to 1st subunit causes shape change to other subunits
conformational change
increasing attraction to O2
Releasing O2
when 1st subunit releases O2, causes shape change to other subunits
lowers attraction to O2

50. O2 dissociation curve for hemoglobin
Effect of pH (CO2 concentration)
Bohr Shift
drop in pH lowers affinity of Hb for O2
active tissue (producing CO2) lowers blood pH & induces Hb to release more O2
PO2 (mm Hg) 10 20 30 40 50 60 70 80 90
100
120
140
More O2 delivered to tissues
pH 7.60
pH 7.20
pH 7.40
% oxyhemoglobin saturation

51. O2 dissociation curve for hemoglobin
Effect of Temperature
Bohr Shift
increase in temperature lowers affinity of Hb for O2
active muscle produces heat
PO2 (mm Hg) 10 20 30 40 50 60 70 80 90
100
120
140
More O2 delivered to tissues
20°C
43°C
37°C
% oxyhemoglobin saturation

52. Transporting CO2 in blood
Dissolved in blood plasma as bicarbonate ion
Tissue cells
Plasma
CO2 dissolves
in plasma
CO2 combines
with Hb
CO2 + H2O
H2CO3
H+ + HCO3–
HCO3–
CO2
Carbonic
anhydrase
Cl–
carbonic acid
CO2 + H2O  H2CO3
bicarbonate
H2CO3  H+ + HCO3–
carbonic anhydrase

53. Releasing CO2 from blood at lungs
Lower CO2 pressure at lungs allows CO2 to diffuse out of blood into lungs
Plasma
Lungs: Alveoli
CO2 dissolved
in plasma
HCO3–Cl–
CO2
H2CO3
Hemoglobin + CO2
CO2 + H2O
HCO3 – + H+

54. Adaptations for pregnancy
Mother & fetus exchange O2 & CO2 across placental tissue
Why would mother’s Hb give up its O2 to baby’s Hb?

55. Fetal hemoglobin (HbF)
HbF has greater attraction to O2 than Hb
low % O2 by time blood reaches placenta
fetal Hb must be able to bind O2 with greater attraction than maternal Hb
Both mother and fetus share a common blood supply. In particular, the fetus's blood supply is delivered via the umbilical vein from the placenta, which is anchored to the wall of the mother's uterus. As blood courses through the mother, oxygen is delivered to capillary beds for gas exchange, and by the time blood reaches the capillaries of the placenta, its oxygen saturation has decreased considerably. In order to recover enough oxygen to sustain itself, the fetus must be able to bind oxygen with a greater affinity than the mother.
Fetal hemoglobin's affinity for oxygen is substantially greater than that of adult hemoglobin. Notably, the P50 value for fetal hemoglobin (i.e., the partial pressure of oxygen at which the protein is 50% saturated; lower values indicate greater affinity) is roughly 19 mmHg, whereas adult hemoglobin has a value of approximately 26.8 mmHg. As a result, the so-called "oxygen saturation curve", which plots percent saturation vs. pO2, is left-shifted for fetal hemoglobin in comparison to the same curve in adult hemoglobin.
Hydroxyurea, used also as an anti-cancer drug, is a viable treatment for sickle cell anemia, as it promotes the production of fetal hemoglobin while inhibiting sickling.
What is the adaptive advantage?
2 alpha & 2 gamma units