1. Exchange of materials with the environment
Overview: Trading with the Environment
Every organism must exchange materials with its environment and this exchange ultimately occurs at the cellular level

2. In unicellular organisms the exchange of materials occurs directly with the environment
However, for most of the cells making up multicellular organisms direct exchange with the environment is not possible as they are not in direct contact with the environment.
Multicellular animals thus need structures specialized for exchange with the outside and a means of transporting materials from these structures to all of the body’s cells.

3. Salmon gills
The feathery gills projecting from a salmon are an example of a specialized exchange system found in animals.
Figure 42.1

4. Internal transport systems
Most complex animals have internal transport systems that circulate fluid, providing a lifeline between the aqueous environment of living cells and the exchange organs, such as lungs, that exchange substances with the outside environment.

5. Invertebrate Circulation
The wide range of invertebrate body size and form is paralleled by a great diversity in circulatory systems.
Simple animals, such as cnidarians (corals and jellyfish) have a body wall only two cells thick that encloses a gastrovascular cavity
The gastrovascular cavity functions in both digestion and distribution of substances throughout the body.

6. Cnidarian gastrovascular cavity
Some cnidarians, such as jellyfish have elaborate gastrovascular cavities that funnel substances throughout the body.
Figure 42.2
Circular canal
Radial canal
5 cm
Mouth

7. Open and Closed Circulatory Systems
More complex animals have one of two types of circulatory systems: open or closed
Both of these types of systems have three basic components
A circulatory fluid (blood)
A set of tubes (blood vessels)
A muscular pump (the heart)

8. Open circulatory system
In insects, other arthropods, and most molluscs blood bathes the organs directly in an open circulatory system.
Heart
Hemolymph in sinuses surrounding ograns
Anterior vessel
Tubular heart
Lateral vessels
Ostia
(a) An open circulatory system
Figure 42.3a

9. Closed circulatory system
In a closed circulatory system blood is confined to vessels and is distinct from the interstitial fluid (the fluid that surrounds the cells).
Figure 42.3b
Interstitial fluid
Heart
Small branch vessels in each organ
Dorsal vessel (main heart)
Ventral vessels
Auxiliary hearts
(b) A closed circulatory system

10. Survey of Vertebrate Circulation
Closed systems are more efficient at transporting circulatory fluids to tissues and cells because pressure can be maintained more easily.
Humans and other vertebrates have a closed circulatory system often called the cardiovascular system
Blood flows in a closed cardiovascular system consisting of blood vessels and a two- to four-chambered heart.

11. Arteries carry blood to capillaries the sites of chemical exchange between the blood and interstitial fluid.
Capillaries are extremely thin-walled blood vessels.
Veins return blood from capillaries to the heart.

12. A fish heart has two main chambers
Fishes
A fish heart has two main chambers
One ventricle (the chamber from which blood flows out of the heart) and one atrium (the chamber in the heart blood enters into)
Blood pumped from the ventricle travels to the gills, where it picks up O2 and disposes of CO2

13. Amphibians
Frogs and other amphibians have a three-chambered heart, with two atria and one ventricle
The ventricle pumps blood into a forked artery that splits the ventricle’s output into the pulmocutaneous (lung and skin) circuit and the systemic (rest of the body) circuit.
Because there is only one ventricle a mix of oxygenated and deoxygenated blood is pumped to the tissues.

14. REPTILES (EXCEPT BIRDS) Pulmocutaneous circuit
Vertebrate circulatory systems
FISHES
AMPHIBIANS
REPTILES (EXCEPT BIRDS)
MAMMALS AND BIRDS
Systemic capillaries
Lung capillaries
Lung and skin capillaries
Gill capillaries
Right
Left
Systemic circuit
Pulmocutaneous circuit
Pulmonary circuit
Systemic circulation
Vein
Atrium (A)
Heart: ventricle (V)
Artery
Gill circulation A V
Systemic aorta
Right systemic aorta
Figure 42.4

15. Reptiles (Except Birds)
Reptiles have double circulation with a pulmonary circuit (lungs) and a systemic circuit, but there is still only a single ventricle although it is partially divided reducing mixing of oxygenated and deoxygenated blood.
Turtles, snakes, and lizards have a three-chambered heart.

16. Mammals and Birds
In all mammals and birds the ventricle is completely divided into separate right and left chambers
The left side of the heart pumps and receives only oxygen-rich blood while the right side receives and pumps only oxygen-poor blood

17. Four-chambered heart
A powerful four-chambered heart was an essential adaptation of the endothermic way of life characteristic of mammals and birds.
Keeping oxygen rich and oxygen depleted blood separated enables oxygen to be delivered to the tissues more efficiently.

18. REPTILES (EXCEPT BIRDS) Pulmocutaneous circuit
Vertebrate circulatory systems
FISHES
AMPHIBIANS
REPTILES (EXCEPT BIRDS)
MAMMALS AND BIRDS
Systemic capillaries
Lung capillaries
Lung and skin capillaries
Gill capillaries
Right
Left
Systemic circuit
Pulmocutaneous circuit
Pulmonary circuit
Systemic circulation
Vein
Atrium (A)
Heart: ventricle (V)
Artery
Gill circulation A V
Systemic aorta
Right systemic aorta
Figure 42.4

19. Mammalian Circulation: The Pathway
Heart valves dictate a one-way flow of blood through the heart by preventing blood flowing backwards.
Blood begins its flow with the right ventricle pumping blood to the lungs via the pulmonary artery.
In the lungs the blood loads O2 and unloads CO2

20. Mammalian Circulation: The Pathway
Oxygen-rich blood from the lungs travels through through the pulmonary vein and enters the heart at the left atrium. It then is pumped by the left ventricle via the aorta to the body tissues.
Blood returns to the heart from the body via the anterior and posterior venae cavae (singular vena cava) through the right atrium.

21. The mammalian cardiovascular system
Pulmonary
vein
Right atrium
Right ventricle
Posterior
vena cava
Capillaries of
abdominal organs
and hind limbs
Aorta
Left ventricle
Left atrium
artery
Capillaries
of left lung
head and
forelimbs
Anterior
of right lung
Figure 42.5 1 10 11 5 4 6 2 9 3 7 8

22. The Mammalian Heart: A Closer Look
A closer look at the mammalian heart
Provides a better understanding of how double circulation works
Figure 42.6
Aorta
Pulmonary veins
Semilunar valve
Atrioventricular valve
Left ventricle
Right ventricle
Anterior vena cava
Pulmonary artery
Posterior vena cava
Right atrium
Left atrium

23. Cardiac Cycle
The heart contracts and relaxes in a rhythmic cycle called the cardiac cycle
The contraction, or pumping, phase of the cycle is called systole
The relaxation, or filling, phase of the cycle is called diastole

24. Cardiac Cycle
Two sets of valves in the heart are important in controlling blood flow within the heart.
The semilunar valves control the flow of blood from the ventricles into the aorta and the pulmonary arteries.
The atrioventricular (or AV) valves control the flow of blood from the atria to the ventricles.

25. During the cardiac cycle first both atria and ventricles relax and blood flows into the atria and from the atria into the ventricles. The AV valves are open and semilunar valves are closed.
Then the atria contract and the ventricles remain relaxed so the blood from the atria flows into the ventricles.
Finally, the semilunar valves open and the AV valves close. The atria relax and the ventricles contract forcing blood out of the ventricles into the arteries.

26. The cardiac cycle Figure 42.7 Semilunar valves closed AV valves open
AV valves closed
Semilunar valves open
Atrial and ventricular diastole 1
Atrial systole; ventricular diastole 2
Ventricular systole; atrial diastole 3
0.1 sec
0.3 sec
0.4 sec

27. Maintaining the Heart’s Rhythmic Beat
Some cardiac muscle cells are self-excitable meaning they contract without any signal from the nervous system.
A region of the heart called the sinoatrial (SA) node, or pacemaker sets the rate and timing at which all cardiac muscle cells contract
Impulses from the SA node travel to the atrioventricular (AV) node
At the AV node, the impulses are delayed and then travel to the Purkinje fibers that make the ventricles contract

28. The impulses that travel during the cardiac cycle can be recorded as an electrocardiogram (ECG or EKG).
The pacemaker is influenced by nerves, hormones, body temperature, and exercise

29. The control of heart rhythm
Figure 42.8
SA node (pacemaker)
AV node
Bundle branches
Heart apex
Purkinje fibers 2
Signals are delayed
at AV node. 1
Pacemaker generates wave of signals to contract. 3
Signals pass
to heart apex. 4
Signals spread
Throughout ventricles.
ECG

30. Blood Vessel Structure and Function
The “infrastructure” of the circulatory system is its network of blood vessels: arteries, capillaries and veins.
Structural differences in arteries, veins, and capillaries are related to their different functions.

31. Arteries have thick muscular walls because they must withstand the high pressure of blood pumped from the heart.
Veins have thinner walls that can be squeezed by surrounding muscles and also valves that prevent blood flowing backwards.
Capillaries have extremely thin walls to facilitate the transfer of materials across them.

32. In the thinly walled veins blood flows back to the heart mainly as a result of muscle action
Figure 42.10
Direction of blood flow in vein (toward heart)
Valve (open)
Skeletal muscle
Valve (closed)

33. The velocity of blood flow varies in the circulatory system
The velocity of blood flow varies in the circulatory system. It is slowest in the capillary beds as a result of the high resistance and large total cross-sectional area
The critical exchange of substances is between the blood and interstitial fluid. It takes place across the thin endothelial walls of the capillaries.

34. Blood Composition and Function
Blood is a connective tissue with several kinds of cells suspended in a liquid matrix called plasma
The cellular elements occupy about 45% of the volume of blood.

35. Plasma
Blood plasma is about 90% water
Among its many solutes are inorganic salts in the form of dissolved ions, sometimes referred to as electrolytes and
Plasma proteins which influence blood pH, osmotic pressure, and viscosity.
Various types of plasma proteins also function in lipid transport, immunity, and blood clotting.

36. Suspended in blood plasma are two classes of cells
Cellular Elements
Suspended in blood plasma are two classes of cells
Red blood cells, which transport oxygen
White blood cells, which function in defense
A third cellular element, platelets are fragments of cells that are involved in clotting

37. Number per L (mm3) of blood
The cellular elements of mammalian blood
Cellular elements 45%
Cell type
Number per L (mm3) of blood
Functions
Erythrocytes (red blood cells)
5–6 million
Transport oxygen and help transport carbon dioxide
Separated blood elements
Leukocytes (white blood cells)
5,000–10,000
Defense and immunity
Lymphocyte
Basophil
Eosinophil
Neutrophil
Monocyte
Platelets
250,000 400,000
Blood clotting
Figure 42.15

38. Cellular elements of blood
Red blood cells, or erythrocytes are by far the most numerous blood cells and transport oxygen throughout the body.
White blood cells, or leukocytes function in defense by phagocytizing bacteria and debris or by producing antibodies
Platelets function in blood clotting

39. Stem Cells and the Replacement of Cellular Elements
The cellular elements of blood wear out and are replaced constantly throughout a person’s life.
The spleen is the organ that scrutinizes blood cells and destroys those that have become old and inflexible (and less able to squeeze through capillaries).

40. Erythrocytes, leukocytes, and platelets all develop from a common source
A single population of cells called pluripotent stem cells in the red marrow of bones
B cells
T cells
Lymphoid stem cells
Pluripotent stem cells (in bone marrow)
Myeloid stem cells
Erythrocytes
Platelets
Monocytes
Neutrophils
Eosinophils
Basophils
Lymphocytes
Figure 42.16

41. Blood Clotting
When the endothelium of a blood vessel is damaged the clotting mechanism begins.
Platelets adhere to collagen fibers in the connective tissue and release a substance that makes nearby platelets sticky.
Platelets form a plug in the opening. In addition, a cascade of complex reactions converts fibrinogen to fibrin. Threads of fibrin form a mesh patch that seals the opening

42. Respiratory structures
Animals require large, moist respiratory surfaces for the adequate diffusion of respiratory gases between their cells and the respiratory medium, either air or water.
Gas exchange can occur across the skin, but specialized structures (lungs and gills) and common.

43. Gills in Aquatic Animals
Gills are outfoldings of the body surface specialized for gas exchange.
Many segmented worms have flaplike gills that extend from each segment of their body.
Figure 42.20b
(b) Marine worm. Many polychaetes (marine worms of the phylum Annelida) have a pair of flattened appendages called parapodia on each body segment. The parapodia serve as gills and also function in crawling and swimming.
Parapodia
Gill

44. Countercurrent exchange
The effectiveness of gas exchange in some gills, including those of fishes is increased by ventilation and countercurrent flow of blood and water
Countercurrent exchange
Figure 42.21
Gill arch
Water flow
Operculum
Gill arch
Blood vessel
Gill filaments
Oxygen-poor blood
Oxygen-rich blood
Water flow over lamellae showing % O2
Blood flow through capillaries in lamellae showing % O2
Lamella
100%
40%
70%
15%
90%
60%
30% 5% O2

45. Lungs
Spiders, land snails, and most terrestrial vertebrates including mammals have internal lungs.

46. Mammalian Respiratory Systems: A Closer Look
A system of branching ducts conveys air to the lungs
Branch from the pulmonary vein (oxygen-rich blood)
Terminal bronchiole
Branch from the pulmonary artery (oxygen-poor blood)
Alveoli
Colorized SEM
SEM
50 µm
Heart
Left lung
Nasal cavity
Pharynx
Larynx
Diaphragm
Bronchiole
Bronchus
Right lung
Trachea
Esophagus
Figure 42.23

47. In mammals, air inhaled through the nostrils passes through the pharynx into the trachea, bronchi, bronchioles, and dead-end alveoli, where gas exchange occurs

48. How a Mammal Breathes
Mammals ventilate their lungs by negative pressure breathing, which pulls air into the lungs. Lung volume increases as the rib muscles and diaphragm contract.
Air inhaled
Air exhaled
INHALATION Diaphragm contracts (moves down)
EXHALATION Diaphragm relaxes (moves up)
Diaphragm
Lung
Rib cage expands as rib muscles contract
Rib cage gets smaller as rib muscles relax
Figure 42.24

49. How a Bird Breathes
Besides lungs, bird have eight or nine air sacs that function as bellows that keep air flowing through the lungs.
INHALATION Air sacs fill
EXHALATION Air sacs empty; lungs fill
Anterior air sacs
Trachea
Lungs
Posterior air sacs
Air
1 mm
Air tubes (parabronchi) in lung
Figure 42.25

50. In birds air passes through the lungs in one direction only
Every exhalation completely renews the air in the lungs. Air flows in only one direction and a countercurrent blood flow system maximizes oxygen extraction.
As a result, bird lungs are more efficient than mammalian lungs.

51. Control of breathing in humans
The main breathing control centers are located in two regions of the brain, the medulla oblongata and the pons.
The centers in the medulla regulate 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.

52. Control of Breathing in Humans
Figure 42.26
Pons
Breathing control centers
Medulla oblongata
Diaphragm
Carotid arteries
Aorta
Cerebrospinal fluid
Rib muscles
In a person at rest, these nerve impulses result in about 10 to 14 inhalations per minute. Between inhalations, the muscles relax and the person exhales.
The medulla’s control center
also helps regulate blood CO2 level.
Sensors in the medulla detect changes
in the pH (reflecting CO2 concentration)
of the blood and cerebrospinal fluid
bathing the surface of the brain.
Nerve impulses relay changes in CO2 and O2 concentrations. Other sensors in the walls of the aorta and carotid arteries in the neck detect changes in blood pH and send nerve impulses to the medulla. In response, the medulla’s breathing control center alters the rate and depth of breathing, increasing both to dispose of excess CO2 or decreasing both if CO2 levels are depressed.
The control center in the
medulla sets the basic rhythm, and a control center in the pons moderates it, smoothing out the transitions between
inhalations and exhalations. 1
Nerve impulses trigger muscle contraction. Nerves from a breathing control center in the medulla oblongata of the brain send impulses to the diaphragm and rib muscles, stimulating them to contract and causing inhalation. 2
The sensors in the aorta and carotid arteries also detect changes in O2 levels in the blood and signal the medulla to increase the breathing rate when levels become very low. 6 5 4 3

53. Control of breathing in humans
Sensors in the aorta and carotid arteries monitor O2 and CO2 concentrations in the blood and exert secondary control over breathing.

54. O2 and CO2 transport
The metabolic demands of many organisms require that the blood transport large quantities of O2 and CO2
A gas always diffuses from a region of higher partial pressure to a region of lower partial pressure
In the lungs and in the tissues O2 and CO2 diffuse from where their partial pressures are higher to where they are lower

55. Respiratory Pigments
Respiratory pigments are proteins that transport oxygen and they greatly increase the amount of oxygen that blood can carry.
The respiratory pigment of almost all vertebrates is the protein hemoglobin, contained in the erythrocytes.

56. Hemoglobin structure
Like all respiratory pigments Hemoglobin must reversibly bind O2, loading O2 in the lungs and unloading it in other parts of the body
Heme group
Iron atom
O2 loaded
in lungs
O2 unloaded
In tissues
Polypeptide chain O2
Figure 42.28

57. Loading and unloading of O2 depend on cooperation between the subunits of the hemoglobin molecule
The binding of O2 to one subunit induces the other subunits to bind O2 with more affinity

58. Cooperative O2 binding and release is evident in the dissociation curve for hemoglobin
A drop in pH occurs when CO2 reacts with water in red blood cells and forms carbonic acid. The reduced pH lowers the affinity of hemoglobin for O2

59. (b) pH and Hemoglobin Dissociation
O2 unloaded from
hemoglobin
during normal
metabolism
O2 reserve that can
be unloaded from
hemoglobin to
tissues with high
Tissues during
exercise
Tissues
at rest
100 80 60 40 20
Lungs
PO2 (mm Hg)
O2 saturation of hemoglobin (%)
Bohr shift: Additional O2 released from hemoglobin at lower pH (higher CO2 concentration)
pH 7.4
pH 7.2
(a) PO2 and Hemoglobin Dissociation at 37°C and pH 7.4
(b) pH and Hemoglobin Dissociation
Figure 42.29a, b

60. Carbon Dioxide Transport
Hemoglobin also helps transport CO2 and assists in buffering.
Most CO2 diffuses into the blood plasma and then into erythrocytes and is ultimately released in the lungs