34 Circulation and Gas Exchange

Transcription

1 CAMPBELL BIOLOGY IN FOCUS Urry Cain Wasserman Minorsky Jackson Reece 34 Circulation and Gas Exchange Lecture Presentations by Kathleen Fitzpatrick and Nicole Tunbridge

2 Overview: Trading Places The resources that animal cells require, such as nutrients and O 2, enter the cytoplasm by crossing the plasma membrane In unicellular organisms, these exchanges occur directly with the environment Most multicellular organisms rely on specialized systems that carry out exchange with the environment and transport materials through the body

3 Gills are an example of a specialized exchange system in animals O 2 diffuses from the water into blood vessels CO 2 diffuses from blood into the water Internal transport and gas exchange are functionally related in most animals

4 Figure 34.1

5 Concept 34.1: Circulatory systems link exchange surfaces with cells throughout the body Small, nonpolar molecules such as O 2 and CO 2 move between cells and their immediate surroundings by diffusion Diffusion time is proportional to the square of the distance travelled Diffusion is only efficient over small distances

6 In small or thin animals, cells can exchange materials directly with the surrounding medium In most animals, cells exchange materials with the environment via a fluid-filled circulatory system

7 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 The body wall that encloses the gastrovascular cavity is only two cells thick Flatworms have a gastrovascular cavity and a flat body shape to optimize diffusional exchange with the environment

8 Figure 34.2 Mouth Gastrovascular cavity 1 mm

9 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

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

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

12 Figure 34.3a (a) An open circulatory system Heart Hemolymph in sinuses Pores Tubular heart

13 In closed circulatory systems the circulatory fluid called blood is confined to vessels and is distinct from interstitial fluid These systems are found in annelids, most cephalopods, and all 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

14 Figure 34.3b (b) A closed circulatory system Heart Blood Interstitial fluid Branch vessels in each organ Dorsal vessel (main heart) Auxiliary hearts Ventral vessels

15 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

16 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

17 Arteries and veins are distinguished by the direction of blood flow, not by O 2 content Vertebrate hearts contain two or more chambers Blood enters through an atrium and is pumped out through a ventricle

18 Single Circulation Bony fishes, rays, and sharks have single circulation with a two-chambered heart In single circulation, blood leaving the heart passes through two capillary beds before returning

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

20 Figure 34.4a (a) Single circulation: fish Gill capillaries Artery Heart: Atrium (A) Ventricle (V) Vein Body capillaries Key Oxygen-rich blood Oxygen-poor blood

21 Double Circulation Amphibians, reptiles, and mammals have double circulation Oxygen-poor and oxygen-rich blood is pumped separately from the right and left sides of the heart Having both pumps within a heart simplifies coordination of the pumping cycle

22 Figure 34.4b (b) Double circulation: amphibian Pulmocutaneous circuit Lung and skin capillaries A Right V A Left Systemic circuit Systemic capillaries Key Oxygen-rich blood Oxygen-poor blood

23 Figure 34.4c (c) Double circulation: mammal Pulmonary circuit Lung capillaries A V Right A V Left Systemic circuit Systemic capillaries Key Oxygen-rich blood Oxygen-poor blood

24 In reptiles and mammals, oxygen-poor blood flows through the pulmonary circuit to pick up oxygen through the lungs In amphibians, oxygen-poor blood flows through a pulmocutaneous circuit to pick up oxygen through the lungs and skin Oxygen-rich blood delivers oxygen through the systemic circuit Double circulation maintains higher blood pressure in the organs than does single circulation

25 Evolutionary Variation in Double Circulation Some vertebrates with double circulation are intermittent breathers These animals have adaptations that enable the circulatory system temporarily to bypass the lungs

26 Frogs and other amphibians have a threechambered heart: two atria and one ventricle The ventricle pumps blood into a forked artery that splits the ventricle s output into the pulmocutaneous circuit and the systemic circuit When underwater, blood flow to the lungs is nearly shut off

27 Turtles, snakes, and lizards have a three-chambered heart: two atria and one ventricle Their circulatory system allows control of relative amounts of blood flowing to the lungs and body In alligators, caimans, and other crocodilians a septum divides the ventricle A connection to atrial valves can temporarily shunt blood away from the lungs, as needed

28 Mammals and birds have a four-chambered heart with two atria and two ventricles The left side of the heart pumps and receives only oxygen-rich blood, while the right side receives and pumps only oxygen-poor blood There is no mechanism to vary relative blood flow to the lungs and body Mammals and birds are endotherms and require more O 2 than ectotherms

29 Concept 34.2: Coordinated cycles of heart contraction drive double circulation in mammals The mammalian cardiovascular system meets the body s continuous demand for O 2

30 Mammalian Circulation Blood begins its flow with the right ventricle pumping blood to the lungs via the pulmonary arteries The blood loads O 2 and unloads CO 2 in the capillary beds of the lungs Oxygen-rich blood from the lungs enters the heart at the left atrium via the pulmonary veins and is pumped through the aorta to the body tissues by the left ventricle

31 The aorta provides blood to the heart through the coronary arteries Diffusion of O 2 and CO 2 takes place in the capillary beds throughout the body Blood returns to the heart through the superior vena cava (blood from head, neck, and forelimbs) and inferior vena cava (blood from trunk and hind limbs) The superior vena cava and inferior vena cava flow into the right atrium

32 Animation: Path of Blood Flow Right click slide / Select play

33 Figure 34.5 Superior vena cava Pulmonary artery 7 Capillaries of head and forelimbs Pulmonary artery Capillaries of right lung 9 Aorta 6 Capillaries of left lung Pulmonary vein Right atrium Right ventricle Pulmonary vein Left atrium Left ventricle Inferior vena cava Aorta 8 Capillaries of abdominal organs and hind limbs

34 The Mammalian Heart: A Closer Look A closer look at the mammalian heart provides a better understanding of double circulation When the heart contracts, it pumps blood; when it relaxes, its chambers fill with blood One complete sequence of pumping and filling is called the cardiac cycle

35 Atria have relatively thin walls and serve as collection chambers for blood returning to the heart The ventricles are more muscular and contract much more forcefully than the atria The volume of blood each ventricle pumps per minute is called the cardiac output

36 Figure 34.6 Pulmonary artery Right atrium Aorta Pulmonary artery Left atrium Semilunar valve Semilunar valve Atrioventricular (AV) valve Atrioventricular (AV) valve Right ventricle Left ventricle

37 Figure Atrial and ventricular diastole 0.4 sec

38 Figure Atrial systole and ventricular diastole 1 Atrial and ventricular diastole 0.1 sec 0.4 sec

39 Figure Atrial systole and ventricular diastole 1 Atrial and ventricular diastole 0.1 sec 0.4 sec 0.3 sec 3 Ventricular systole and atrial diastole

40 The heart rate, also called the pulse, is the number of beats per minute The stroke volume is the amount of blood pumped in a single contraction Cardiac output depends on both the heart rate and stroke volume

41 Four valves prevent backflow of blood in the heart The atrioventricular (AV) valves separate each atrium and ventricle The semilunar valves control blood flow to the aorta and the pulmonary artery

42 The lub-dup sound of a heart beat is caused by the recoil of blood against the AV valves (lub) then against the semilunar (dup) valves Backflow of blood through a defective valve causes a heart murmur

43 Maintaining the Heart s Rhythmic Beat Some cardiac muscle cells are autorhythmic, meaning they contract without any signal from the nervous system The sinoatrial (SA) node, or pacemaker, sets the rate and timing at which all other cardiac muscle cells contract The SA node produces electrical impulses that spread rapidly through the heart and can be recorded as an electrocardiogram (ECG or EKG)

44 Figure Signals (yellow) from SA node spread through atria. SA node (pacemaker) ECG

45 Figure Signals (yellow) from SA node spread through atria. 2 Signals are delayed at AV node. SA node (pacemaker) AV node ECG

46 Figure Signals (yellow) from SA node spread through atria. Signals are delayed at AV node. 2 3 Bundle branches pass signals to heart apex. SA node (pacemaker) AV node Bundle branches Heart apex ECG

47 Figure Signals (yellow) from SA node spread through atria. Signals are delayed at AV node. Bundle branches pass signals to heart apex Signals spread throughout ventricles. SA node (pacemaker) AV node Bundle branches Heart apex Purkinje fibers ECG

48 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

49 The pacemaker is regulated by two portions of the nervous system: the sympathetic and parasympathetic divisions The sympathetic division speeds up the pacemaker The parasympathetic division slows down the pacemaker The pacemaker is also regulated by hormones and temperature

50 Concept 34.3: Patterns of blood pressure and flow reflect the structure and arrangement of blood vessels The physical principles that govern movement of water in plumbing systems also apply to the functioning of animal circulatory systems

51 Blood Vessel Structure and Function A vessel s cavity is called the central lumen The epithelial layer that lines blood vessels is called the endothelium The endothelium is smooth and minimizes resistance to blood flow

52 Capillaries have thin walls, the endothelium and its basal lamina, to facilitate the exchange of substances Arteries and veins have an endothelium, smooth muscle, and connective tissue Arteries have thicker walls than veins to accommodate the high pressure of blood pumped from the heart

53 LM 15 m LM Figure 34.9 Artery Vein Endothelium Red blood cells 100 m Basal lamina Valve Endothelium Connective tissue Artery Smooth muscle Capillary Smooth muscle Vein Connective tissue Arteriole Venule Red blood cell Capillary

54 Figure 34.9a Connective tissue Artery Endothelium Smooth muscle Capillary Basal lamina Smooth muscle Valve Vein Endothelium Connective tissue Arteriole Venule

55 Figure 34.9b LM Artery Vein Red blood cells 100 m

56 Figure 34.9c LM 15 m Red blood cell Capillary

57 Blood Flow Velocity Blood vessel diameter influences blood flow Velocity of blood flow is slowest in the capillary beds, as a result of the high resistance and large total cross-sectional area Blood flow in capillaries is necessarily slow for exchange of materials

58 Figure Area (cm 2 ) Velocity (cm/sec) Pressure (mm Hg) Aorta Arteries Capillaries Venules Arterioles Veins Venae cavae 4,000 2, Diastolic pressure Systolic pressure

59 Blood Pressure Blood flows from areas of higher pressure to areas of lower pressure Blood pressure exerts a force in all directions

60 Changes in Blood Pressure During the Cardiac Cycle Systole is the contraction phase of the cardiac cycle Pressure at the time of ventricle contraction is called systolic pressure Diastole is the the relaxation phase of the cardiac cycle; diastolic pressure is lower than systolic

61 Maintenance of Blood Pressure Blood pressure is determined by cardiac output and peripheral resistance due to constriction of arterioles Vasoconstriction is the contraction of smooth muscle in arteriole walls; it increases blood pressure Vasodilation is the relaxation of smooth muscles in the arterioles; it causes blood pressure to fall

62 Vasoconstriction and vasodilation help maintain adequate blood flow as the body s demands change Nitric oxide is a major inducer of vasodilation The peptide endothelin is an important inducer of vasoconstriction

63 Fainting is caused by inadequate blood flow to the head Animals with long necks require a higher systolic pressure to pump blood against gravity Gravity is a consideration for blood flow in veins, particularly in the legs One-way valves in veins prevent backflow of blood Blood returns to the heart through contraction of smooth muscle in the walls of veins and venules and by contraction of skeletal muscles

64 Figure Direction of blood flow in vein (toward heart) Valve (open) Skeletal muscle Valve (closed)

65 Capillary Function Blood flows through only 5 10% of the body s capillaries at a time Capillaries in major organs are usually filled to capacity Blood supply varies in many other sites

66 Two mechanisms alter blood flow in capillary beds Vasoconstriction or vasodilation of the arteriole that supplies a capillary bed Precapillary sphincters, rings of smooth muscle at the capillary bed entrance, open and close to regulate passage of blood Critical exchange of substances takes place across the thin walls of the capillaries

67 Blood pressure tends to drive fluid out of the capillaries The difference in solute concentration between blood and interstitial fluid (the blood s osmotic pressure) opposes fluid movement from the capillaries Blood pressure is usually greater than osmotic pressure Net loss of fluid from capillaries occurs in regions where blood pressure is highest

68 Fluid Return by the Lymphatic System The lymphatic system returns fluid, called lymph, that leaks out from the capillary beds Lymph has a very similar composition to interstitial fluid The lymphatic system drains into veins in the neck Valves in lymph vessels prevent the backflow of fluid

69 Figure Thymus (immune system) Adenoid Tonsils Lymphatic vessels Spleen Blood capillary Tissue cells Interstitial fluid Lymphatic vessel Lymphatic vessel Appendix (cecum) Lymph nodes Peyer s patches (small intestine) Lymph node Masses of defensive cells

70 Lymph vessels have valves to prevent backflow Lymph nodes are organs that filter lymph and play an important role in the body s defense Edema is swelling caused by disruptions in the flow of lymph The lymphatic system also plays a role in harmful immune responses, such as those responsible for asthma

71 Concept 34.4: Blood components function in exchange, transport, and defense With open circulation, the fluid that is pumped comes into direct contact with all cells and has the same composition as interstitial fluid The closed circulatory systems of vertebrates contain blood, which can be much more highly specialized

72 Blood Composition and Function Blood is a connective tissue consisting of cells suspended in a liquid matrix called plasma The cellular elements occupy about 45% of the volume of blood

73 Video: Leukocyte Rolling

74 Figure Plasma 55% Cellular elements 45% Constituent Major functions Cell type Number per L (mm 3 ) of blood Functions Water Ions (blood electrolytes) Sodium Potassium Calcium Magnesium Chloride Bicarbonate Solvent for carrying other substances Osmotic balance, ph buffering, and regulation of membrane permeability Separated blood elements Leukocytes (white blood cells) Lymphocytes Basophils Eosinophils 5,000 10,000 Defense and immunity Plasma proteins Albumin Fibrinogen Osmotic balance, ph buffering Clotting Neutrophils Platelets Monocytes 250, ,000 Blood clotting Immunoglobulins (antibodies) Defense Substances transported by blood Erythrocytes (red blood cells) 5,000,000 6,000,000 Transport of O 2 and some CO 2 Nutrients (such as glucose, fatty acids, vitamins) Waste products of metabolism Respiratory gases (O 2 and CO 2 ) Hormones

75 Figure 34.13a Constituent Plasma 55% Major functions Water Ions (blood electrolytes) Sodium Potassium Calcium Magnesium Chloride Bicarbonate Plasma proteins Albumin Fibrinogen Immunoglobulins (antibodies) Solvent for carrying other substances Osmotic balance, ph buffering, and regulation of membrane permeability Osmotic balance, ph buffering Clotting Defense Substances transported by blood Nutrients (such as glucose, fatty acids, vitamins) Waste products of metabolism Respiratory gases (O 2 and CO 2 ) Hormones

76 Figure 34.13b Cell type Cellular elements 45% Number per L (mm 3 ) of blood Functions Leukocytes (white blood cells) 5,000 10,000 Defense and immunity Basophils Lymphocytes Eosinophils Neutrophils Monocytes Platelets 250, ,000 Blood clotting Erythrocytes (red blood cells) 5,000,000 6,000,000 Transport of O 2 and some CO 2

77 Plasma Blood plasma is about 90% water Among its solutes are inorganic salts in the form of dissolved ions, sometimes called electrolytes Plasma proteins influence blood ph, osmotic pressure, and viscosity Particular plasma proteins function in lipid transport, immunity, and blood clotting

78 Cellular Elements Blood contains two classes of cells Red blood cells (erythrocytes) transport O 2 White blood cells (leukocytes) function in defense Platelets, a third cellular element, are fragments of cells that are involved in clotting

79 Figure Stem cells (in bone marrow) Lymphoid stem cells Myeloid stem cells B cells T cells Lymphocytes Erythrocytes Neutrophils Basophils Monocytes Platelets Eosinophils

80 Erythrocytes Red blood cells, or erythrocytes, are by far the most numerous blood cells They contain hemoglobin, the iron-containing protein that transports O 2 Each molecule of hemoglobin binds up to four molecules of O 2 In mammals, mature erythrocytes lack nuclei

81 Sickle-cell disease is caused by abnormal hemoglobin that polymerizes into aggregates The aggregates can distort an erythrocyte into a sickle shape

82 Through a person s life, multipotent stem cells replace the worn-out cellular elements of blood Erythrocytes circulate for about 120 days before they are replaced Stem cells that produce red blood cells and platelets are located in red marrow of bones like the ribs, vertebrae, sternum, and pelvis

83 Leukocytes There are five major types of white blood cells, or leukocytes They function in defense by engulfing bacteria and debris or by mounting immune responses against foreign substances They are found both in and outside of the circulatory system

84 Platelets Platelets are fragments of cells and function in blood clotting

85 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

86 Figure Platelet Collagen fibers Platelet plug Fibrin clot Red blood cell 5 m Clotting factors from: Platelets Damaged cells Plasma (factors include calcium, vitamin K) Fibrin clot formation Enzymatic cascade Prothrombin Thrombin Fibrinogen Fibrin

87 Figure 34.15a Platelet Collagen fibers Platelet plug Fibrin clot Clotting factors from: Platelets Damaged cells Plasma (factors include calcium, vitamin K) Fibrin clot formation Enzymatic cascade Prothrombin Thrombin Fibrinogen Fibrin

88 Figure 34.15b Fibrin clot Red blood cell 5 m

89 Cardiovascular Disease Cardiovascular diseases are disorders of the heart and the blood vessels Cardiovascular diseases account for more than half the deaths in the United States Cholesterol, a steroid, helps maintain normal membrane fluidity

90 Low-density lipoprotein (LDL) delivers cholesterol to cells for membrane production High-density lipoprotein (HDL) scavenges excess cholesterol for return to the liver Risk for heart disease increases with a high LDL to HDL ratio Inflammation is also a factor in cardiovascular disease

91 Atherosclerosis, Heart Attacks, and Stroke One type of cardiovascular disease, atherosclerosis, is caused by the buildup of fatty deposits within arteries A fatty deposit is called a plaque; as it grows, the artery walls become thick and stiff and the obstruction of the artery increases

92 Figure Endothelium Lumen Blood clot Plaque

93 A heart attack, or myocardial infarction, is the death of cardiac muscle tissue resulting from blockage of one or more coronary arteries Coronary arteries supply oxygen-rich blood to the heart muscle 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

94 Risk Factors and Treatment of Cardiovascular Disease A high LDL to HDL ratio increases the risk of cardiovascular disease The proportion of LDL relative to HDL is increased by smoking and consumption of trans fats and decreased by exercise Drugs called statins reduce LDL levels and risk of heart attacks

95 Inflammation plays a role in atherosclerosis and thrombus formation Aspirin inhibits inflammation and reduces the risk of heart attacks and stroke Hypertension (high blood pressure) contributes to the risk of heart attack and stroke Hypertension can be reduced by dietary changes, exercise, medication, or some combination of these

96 Concept 34.5: Gas exchange occurs across specialized respiratory surfaces Gas exchange is the uptake of molecular O 2 from the environment and the discharge of CO 2 to the environment

97 Partial Pressure Gradients in Gas Exchange Partial pressure is the pressure exerted by a particular gas in a mixture of gases For example, the atmosphere is 21% O 2, by volume, so the partial pressure of O 2 (P O2 ) is 0.21 the atmospheric pressure

98 Partial pressures also apply to gases dissolved in liquid, such as water When water is exposed to air, an equilibrium is reached in which the partial pressure of each gas is the same in the water and the air A gas always undergoes net diffusion from a region of higher partial pressure to a region of lower partial pressure

99 Respiratory Media O 2 is plentiful in air, and breathing air is relatively easy In a given volume, there is less O 2 available in water than in air Obtaining O 2 from water requires greater energy expenditure than air breathing Aquatic animals have a variety of adaptations to improve efficiency in gas exchange

100 Figure Coelom Parapodium (functions as gill) (a) Marine worm Gills (b) Sea star Tube foot

101 Figure 34.17a (a) Marine worm

102 Figure 34.17b (b) Sea star

103 Respiratory Surfaces Gas exchange across respiratory surfaces takes place by diffusion Respiratory surfaces tend to be large and thin and are always moist Respiratory surfaces vary by animal and can include the skin, gills, tracheae, and lungs

104 Gills in Aquatic Animals Gills are outfoldings of the body that create a large surface area for gas exchange Ventilation is the movement of the respiratory medium over the respiratory surface Ventilation maintains the necessary partial pressure gradients of O 2 and CO 2 across the gills

105 Aquatic animals move through water or move water over their gills for ventilation Fish gills use a countercurrent exchange system, where blood flows in the opposite direction to water passing over the gills Blood is always less saturated with O 2 than the water it meets Countercurrent exchange mechanisms are remarkably efficient

106 Figure Gill arch Blood vessels O 2 -poor blood O 2 -rich blood Lamella Water flow Operculum Gill arch Water flow Blood flow Gill filaments Countercurrent exchange P O2 (mm Hg) in water Net diffusion of O 2 P O2 (mm Hg) in blood

107 Tracheal Systems in Insects The tracheal system of insects consists of a network of air tubes that branch throughout the body The tracheal system can transport O 2 and CO 2 without the participation of the animal s open circulatory system Larger insects must ventilate their tracheal system to meet O 2 demands

108 2.5 m Figure Tracheoles Mitochondria Muscle fiber Air sacs Tracheae Air sac Body cell Tracheole Trachea External opening Air

109 Figure 34.19a 2.5 m Tracheoles Mitochondria Muscle fiber

110 Lungs Lungs are an infolding of the body surface, usually divided into numerous pockets The circulatory system (open and closed) transports gases between the lungs and the rest of the body The use of lungs for gas exchange varies among vertebrates that lack gills

111 Mammalian Respiratory Systems: A Closer Look A system of branching ducts conveys air to the lungs Air inhaled through the nostrils is warmed, humidified, and sampled for odors The pharynx directs air to the lungs and food to the stomach Swallowing tips the epiglottis over the glottis in the pharynx to prevent food from entering the trachea

112 Air passes through the pharynx, larynx, trachea, bronchi, and bronchioles to the alveoli, where gas exchange occurs Exhaled air passes over the vocal cords in the larynx to create sounds Cilia and mucus line the epithelium of the air ducts and move particles up to the pharynx This mucus escalator cleans the respiratory system and allows particles to be swallowed into the esophagus

113 Gas exchange takes place in alveoli, air sacs at the tips of bronchioles Oxygen diffuses through the moist film of the epithelium and into capillaries Carbon dioxide diffuses from the capillaries across the epithelium and into the air space

114 Video: Gas Exchange

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

116 Figure 34.20a Pharynx Larynx (Esophagus) Trachea Right lung Nasal cavity Left lung Bronchus Bronchiole Diaphragm (Heart)

117 Figure 34.20b Branch of pulmonary vein (oxygen-rich blood) Terminal bronchiole Branch of pulmonary artery (oxygen-poor blood) Alveoli Capillaries

118 Figure 34.20c 50 m Dense capillary bed enveloping alveoli (SEM)

119 Alveoli lack cilia and are susceptible to contamination Secretions called surfactants coat the surface of the alveoli Preterm babies lack surfactant and are vulnerable to respiratory distress syndrome; treatment is provided by artificial surfactants

120 Figure Surface tension (dynes/cm) Results (n 9) (n 0) (n 29) (n 9) <1,200 g >1,200 g Body mass of infant RDS deaths Deaths from other causes

121 Concept 34.6: Breathing ventilates the lungs The process that ventilates the lungs is breathing, the alternate inhalation and exhalation of air

122 An amphibian such as a frog ventilates its lungs by positive pressure breathing, which forces air down the trachea Birds have eight or nine air sacs that function as bellows that keep air flowing through the lungs Air passes through the lungs of birds in one direction only Passage of air through the entire system lungs and air sacs requires two cycles in inhalation and exhalation

123 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 The tidal volume is the volume of air inhaled with each breath

124 Video: Gas Exchange

125 Figure Rib cage expands as rib muscles contract. Air inhaled. Rib cage gets smaller as rib muscles relax. Air exhaled. Lung Diaphragm 1 Inhalation: 2 Exhalation: Diaphragm contracts (moves down). Diaphragm relaxes (moves up).

126 The maximum tidal volume is the vital capacity After exhalation, a residual volume of air remains in the lungs Each inhalation mixes fresh air with oxygen-depleted residual air As a result, the maximum P O2 in alveoli is considerably less than in the atmosphere

127 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

128 Figure Homeostasis: Blood ph of about 7.4 Stimulus: Rising level of CO 2 in tissues lowers blood ph.

129 Figure Homeostasis: Blood ph of about 7.4 Stimulus: Rising level of CO 2 in tissues lowers blood ph. Sensor/control center: Cerebrospinal fluid Carotid arteries Aorta Medulla oblongata

130 Figure Homeostasis: Blood ph of about 7.4 Response: Signals from medulla to rib muscles and diaphragm increase rate and depth of ventilation. Sensor/control center: Cerebrospinal fluid Stimulus: Rising level of CO 2 in tissues lowers blood ph. Carotid arteries Aorta Medulla oblongata

131 Figure Homeostasis: Blood ph of about 7.4 Response: Signals from medulla to rib muscles and diaphragm increase rate and depth of ventilation. CO 2 level decreases. Sensor/control center: Cerebrospinal fluid Stimulus: Rising level of CO 2 in tissues lowers blood ph. Carotid arteries Aorta Medulla oblongata

132 Sensors in the aorta and carotid arteries monitor O 2 and CO 2 concentrations in the blood These sensors exert secondary control over breathing

133 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 O 2 and CO 2

134 Coordination of Circulation and Gas Exchange Blood arriving in the lungs has a low P O2 and a high P CO2 relative to air in the alveoli In the alveoli, O 2 diffuses into the blood and CO 2 diffuses into the air In tissue capillaries, partial pressure gradients favor diffusion of O 2 into the interstitial fluids and CO 2 into the blood Specialized carrier proteins play a vital role in this process

135 Animation: CO 2 Blood to Lungs Right click slide / Select play

136 Animation: CO 2 Tissues to Blood Right click slide / Select play

137 Animation: O 2 Blood to Tissues Right click slide / Select play

138 Animation: O 2 Lungs to Blood Right click slide / Select play

139 Figure O 2 CO 2 Exhaled air Inhaled air O 2 CO 2 Alveolar epithelial cells Pulmonary arteries CO 2 O 2 Alveolar spaces Alveolar capillaries Pulmonary veins O 2 CO O 2 CO 2 Systemic veins Heart Systemic arteries Systemic capillaries <40 >45 CO 2 O 2 O 2 CO 2 Body tissue cells

140 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

141 The respiratory pigment of almost all vertebrates and many invertebrates is hemoglobin A single hemoglobin molecule can carry four molecules of O 2, one molecule for each ironcontaining heme group Hemoglobin binds oxygen reversibly, loading it in the gills or lungs and releasing it in other parts of the body

142 Figure 34.UN01 Iron Heme Hemoglobin

143 Hemoglobin binds O 2 cooperatively When O 2 binds one subunit, the others change shape slightly, resulting in their increased affinity for oxygen When one subunit releases O 2, the others release their bound O 2 more readily Cooperativity can be demonstrated by the dissociation curve for hemoglobin

144 O 2 saturation of hemoglobin (%) Figure O 2 saturation of hemoglobin (%) O 2 unloaded to tissues at rest ph 7.4 ph O 2 unloaded to tissues during exercise Hemoglobin retains less O 2 at lower ph (higher CO 2 concentration Tissues during exercise Tissues at rest P O2 (mm Hg) Lungs P O2 (mm Hg) (a) P O2 and hemoglobin dissociation at ph 7.4 (b) ph and hemoglobin dissociation

145 O 2 saturation of hemoglobin (%) Figure 34.25a O 2 unloaded to tissues at rest O 2 unloaded to tissues during exercise Tissues during exercise Tissues at rest P O2 (mm Hg) Lungs (a) P O2 and hemoglobin dissociation at ph 7.4

146 CO 2 produced during cellular respiration lowers blood ph and decreases the affinity of hemoglobin for O 2 ; this is called the Bohr shift Hemoglobin also assists in preventing harmful changes in blood ph and plays a minor role in CO 2 transport

147 Figure 34.25b O 2 saturation of hemoglobin (%) ph 7.4 ph Hemoglobin retains less O 2 at lower ph (higher CO 2 concentration P O2 (mm Hg) (b) ph and hemoglobin dissociation

148 Carbon Dioxide Transport Most of the CO 2 from respiring cells diffuses into the blood and is transported in blood plasma, bound to hemoglobin or as bicarbonate ions (HCO 3 )

149 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

150 Deep-diving air breathers can store large amounts of O 2 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

151 Figure 34.UN02a Percent of individuals Plasma LDL cholesterol (mg/dl) Individuals with an inactivating mutation in one copy of PCSK9 gene (study group) 300

152 Figure 34.UN02b Percent of individuals Plasma LDL cholesterol (mg/dl) Individuals with two functional copies of PCSK9 gene (control group) 300

153 Figure 34.UN03 Exhaled air Inhaled air Alveolar epithelial cells CO 2 O 2 Alveolar spaces Alveolar capillaries Pulmonary arteries Pulmonary veins Systemic veins Heart Systemic arteries CO 2 O 2 Systemic capillaries Body tissue

154 O 2 saturation of hemoglobin (%) Figure 34.UN Fetus Mother P O2 (mm Hg)