1. Circulation and Gas Exchange34
Circulation and Gas Exchange

2. Do now: What is the purpose of a circulatory system?
What are the different organs of the human circulatory system?
List some organisms that might have circulatory systems different from humans
List some organisms that might not have circulatory systems

3. Main Ideas to know: Different types of circulatory systems
Role of carbon dioxide/pH and homeostasis
Positive feedback of blood clotting
Respiratory pigments

4. Gastrovascular Cavities
Some animals lack a circulatory system
Some cnidarians, such as jellies, have elaborate gastrovascular cavities
A gastrovascular cavity functions in both digestion and distribution of substances throughout the body 4

5. Figure 34.2
Flatworms have a gastrovascular cavity and a flat body shape to optimize diffusional exchange with the environment
Mouth
Gastrovascular
cavity
1 mm
Figure 34.2 Internal transport in the planarian Dugesia (LM) 5

6. Open and Closed Circulatory Systems
A circulatory system has a circulatory fluid, a set of interconnecting vessels, and a muscular pump, the heart
Several basic types of circulatory systems have arisen during evolution, each representing adaptations to constraints of anatomy and environment 6

7. (a) An open circulatory system (b) A closed circulatory system
Figure 34.3
(a) An open circulatory system
(b) A closed circulatory system
Heart
Blood
Heart
Interstitial
fluid
Hemolymph in sinuses
Branch vessels
in each organ
Pores
Dorsal vessel
(main heart)
Figure 34.3 Open and closed circulatory systems
Tubular heart
Ventral vessels
Auxiliary
hearts 7

8. All circulatory systems are either open or closed
circulatory fluid bathes the organs directly in an open circulatory system
Ex: insects, arthropods and molluscs
In an open circulatory system, there is no distinction between circulatory fluid and interstitial fluid, and this general body fluid is called hemolymph 8

9. One or more hearts pump blood through the vessels
In closed circulatory systems the circulatory fluid called blood is confined to vessels and is distinct from interstitial fluid
Ex: annelids (earthworms), vertebrates
One or more hearts pump blood through the vessels
Chemical exchange occurs between blood and interstitial fluid and between interstitial fluid and body cells 9

10. Organization of Vertebrate Circulatory Systems
Humans and other vertebrates have a closed circulatory system called the cardiovascular system
The three main types of blood vessels are arteries, veins, and capillaries
Blood flow is one-way in these vessels 10

11. Artery Vein Red blood cells Valve Basal lamina Endothelium Endothelium
Figure 34.9
Artery
Vein LM
Red blood
cells
100 m
Valve
Basal lamina
Endothelium
Endothelium
Smooth
muscle
Connective
tissue
Smooth
muscle
Connective
tissue
Capillary
Artery
Vein
Figure 34.9 The structure of blood vessels
Venule
Arteriole
15 m
Red blood cell
Capillary LM 11

12. Arteries branch into arterioles and carry blood away from the heart to capillaries
Networks of capillaries called capillary beds are the sites of chemical exchange between the blood and interstitial fluid
Venules converge into veins and return blood from capillaries to the heart
Arteries and veins are distinguished by the direction of blood flow, not by O2 content 12

13. Pulmocutaneous circuit Pulmonary circuit
Figure 34.4
(a) Single circulation: fish
(b) Double circulation:
amphibian
(c) Double circulation:
mammal
Pulmocutaneous
circuit
Pulmonary
circuit
Gill capillaries
Lung
and skin
capillaries
Lung
capillaries
Artery
Heart:
Atrium (A) A A A A
Ventricle (V) V V
Left
Right
Left
Right
Vein V
Systemic
capillaries
Systemic
capillaries
Figure 34.4 Generalized circulatory schemes of vertebrates
Body capillaries
Systemic circuit
Systemic circuit
Key
Oxygen-rich blood
Oxygen-poor blood 13

14. Interstitial fluid Blood capillary Adenoid Tonsils Lymphatic vessels
Figure 34.12
Interstitial
fluid
Blood
capillary
Adenoid
Tonsils
Lymphatic
vessels
Thymus
(immune
system)
Lymphatic
vessel
Tissue cells
Lymphatic
vessel
Spleen
Lymph
nodes
Appendix
(cecum)
Figure The human lymphatic system
Masses of
defensive
cells
Peyer’s patches
(small intestine)
Lymph node 14

15. Cellular elements 45% Number Cell type Functions per L (mm3) of blood
Figure 34.13b
Cellular elements 45%
Number
per L (mm3) of blood
Cell type
Functions
Leukocytes (white blood cells)
5,000–10,000
Defense and
immunity
Lymphocytes
Basophils
Eosinophils
Monocytes
Neutrophils
Figure 34.13b The composition of mammalian blood (part 2: cellular)
Platelets
250,000–400,000
Blood clotting
Erythrocytes (red blood cells)
5,000,000–6,000,000
Transport of O2 and
some CO2 15

16. Stem cells (in bone marrow) Lymphoid Myeloid stem cells stem cells
Figure 34.14
Stem cells
(in bone marrow)
Lymphoid
stem cells
Myeloid
stem cells
B cells
T cells
Figure Differentiation of blood cells
Erythrocytes
Basophils
Neutrophils
Lymphocytes
Monocytes
Eosinophils
Platelets 16

17. Blood Clotting
Coagulation is the formation of a solid clot from liquid blood
A cascade of complex reactions converts inactive fibrinogen to fibrin, which forms the framework of a clot
A blood clot formed within a blood vessel is called a thrombus and can block blood flow 17

18. Fibrin clot formation 1 2 3 Collagen fibers Platelet plug Platelet
Figure 34.15 1 2 3
Collagen
fibers
Platelet
plug
Platelet
Fibrin clot
Red blood cell
5 m
Clotting factors from:
Fibrin clot
formation
Platelets
Damaged cells
Plasma (factors include calcium, vitamin K)
Figure Blood clotting
Enzymatic cascade
Prothrombin
Thrombin
Fibrinogen
Fibrin 18

19. Angina pectoris is caused by partial blockage of the coronary arteries
A heart attack, or myocardial infarction, is the death of cardiac muscle tissue resulting from blockage of one or more coronary arteries
A stroke is the death of nervous tissue in the brain, usually resulting from rupture or blockage of arteries in the head
Angina pectoris is caused by partial
blockage of the coronary arteries
and may cause chest pain 19

20. Concept 34.5: Gas exchange occurs across specialized respiratory surfaces
Gas exchange is the uptake of molecular O2 from the environment and the discharge of CO2 to the environment 20

21. Branch of pulmonary artery (oxygen-poor blood) Branch of
Figure 34.20
Branch of pulmonary
artery (oxygen-poor
blood)
Branch of
pulmonary vein
(oxygen-rich
blood)
Terminal
bronchiole
Nasal
cavity
Pharynx
Left
lung
Larynx
(Esophagus)
Alveoli
Trachea
Right lung
50 m
Capillaries
Bronchus
Figure The mammalian respiratory system
Bronchiole
Diaphragm
(Heart)
Dense capillary bed
enveloping alveoli
(SEM) 21

22. Control of Breathing in Humans
In humans, the main breathing control center consists of neural circuits in the medulla oblongata, near the base of the brain
The medulla regulates the rate and depth of breathing in response to pH changes in the cerebrospinal fluid
The medulla adjusts breathing rate and depth to match metabolic demands 22

23. Homeostasis: Blood pH of about 7.4 Stimulus: Rising level of CO2
Figure
Homeostasis:
Blood pH of about 7.4
Stimulus:
Rising level of CO2
in tissues lowers
blood pH.
Figure Homeostatic control of breathing (step 1) 23

24. Homeostasis: Blood pH of about 7.4 Stimulus: Rising level of CO2
Figure
Homeostasis:
Blood pH of about 7.4
Stimulus:
Rising level of CO2
in tissues lowers
blood pH.
Carotid
arteries
Figure Homeostatic control of breathing (step 2)
Sensor/control
center:
Aorta
Cerebro-
spinal
fluid
Medulla
oblongata 24

25. Homeostasis: Blood pH of about 7.4 Stimulus: Rising level of CO2
Figure
Homeostasis:
Blood pH of about 7.4
Stimulus:
Rising level of CO2
in tissues lowers
blood pH.
Response:
Signals from
medulla to rib
muscles and
diaphragm
increase rate
and depth of
ventilation.
Carotid
arteries
Figure Homeostatic control of breathing (step 3)
Sensor/control
center:
Aorta
Cerebro-
spinal
fluid
Medulla
oblongata 25

26. Homeostasis: Blood pH of about 7.4 CO2 level decreases. Stimulus:
Figure
Homeostasis:
Blood pH of about 7.4
CO2 level
decreases.
Stimulus:
Rising level of CO2
in tissues lowers
blood pH.
Response:
Signals from
medulla to rib
muscles and
diaphragm
increase rate
and depth of
ventilation.
Carotid
arteries
Figure Homeostatic control of breathing (step 4)
Sensor/control
center:
Aorta
Cerebro-
spinal
fluid
Medulla
oblongata 26

27. Concept 34.7: Adaptations for gas exchange include pigments that bind and transport gases
The metabolic demands of many organisms require that the blood transport large quantities of O2 and CO2 27

28. Iron Heme Hemoglobin Figure 34.UN01
Figure 34.UN01 In-text figure, hemoglobin, p. 707
Iron
Heme
Hemoglobin 28

29. Respiratory Pigments
Respiratory pigments circulate in blood or hemolymph and greatly increase the amount of oxygen that is transported
A variety of respiratory pigments have evolved among animals
These mainly consist of a metal bound to a protein
Ex: hemoglobin
A single hemoglobin molecule can carry four molecules of O2, one molecule for each iron- containing heme group 29

30. CO2 produced during cellular respiration lowers blood pH and decreases the affinity of hemoglobin for O2; this is called the Bohr shift
Hemoglobin also assists in preventing harmful changes in blood pH and plays a minor role in CO2 transport 30

31. Carbon Dioxide Transport
Most of the CO2 from respiring cells diffuses into the blood and is transported in blood plasma, bound to hemoglobin or as bicarbonate ions (HCO3–) 31

32. Respiratory Adaptations of Diving Mammals
Diving mammals have evolutionary adaptations that allow them to perform extraordinary feats
For example, Weddell seals in Antarctica can remain underwater for 20 minutes to an hour
For example, elephant seals can dive to 1,500 m and remain underwater for 2 hours
These animals have a high blood to body volume ratio 32

33. Deep-diving air breathers can store large amounts of O2
Oxygen can be stored in their muscles in myoglobin proteins
Diving mammals also conserve oxygen by
Changing their buoyancy to glide passively
Decreasing blood supply to muscles
Deriving ATP in muscles from fermentation once oxygen is depleted 33

34. Exhaled air Inhaled air Alveolar spaces Alveolar epithelial cells CO2
Figure 34.UN03
Exhaled air
Inhaled air
Alveolar
spaces
Alveolar
epithelial
cells
CO2 O2
Alveolar
capillaries
Pulmonary
arteries
Pulmonary
veins
Systemic
veins
Systemic
arteries
Heart
Figure 34.UN03 Summary of key concepts: double circulation
Systemic
capillaries
CO2 O2
Body tissue 34