Why oxygen is import Most animals satisfy their energy requirement by oxidation of food, in the processes forming carbon dioxide and water Oxygen is most abundant element in the earth’s crust (49.2%) In atmosphere Per liter water (150C, 1 atm) O2 20.95% 7.22 ml CO2 0.03% 1019.0 ml N2 78.09% 16.9 ml Argon 0.93% Total 100%

Vacuum 760 mm Pressure exerted by atmospheric air above Earth’s surface Pressure at sea level Mercury (Hg)

Oxygen and carbon dioxide in physical environment Oxygen is added to atmosphere: Photosynthesis (dominant) Photodissociation of water vapor Oxygen is removed from atmosphere: Living organism respiration Oxidizing of organic matter, rocks, gases and fossil fuels

"Global warming" is a real phenomenon: Earth's temperature is increasing. True False

Fig. 11-2, p.464

Oxygen and carbon dioxide in physical environment Solubility of oxygen decreases with increasing water temperature and salinity Temperature Fresh water Sea water ml O2/L water ml O2/L water 0 10.29 7.97 10 8.02 6.35 15 7.22 5.79 20 6.57 5.31 30 5.57 4.46 Normoxic water: 100% saturated with oxygen Hypoxic water contains less oxygen than normoxic water Anoxic water contains no dissolved oxygen

Transport O2 and CO2 in living systems Diffusion is common mechanism for transport both O2 and CO2 across the body surface To maximize the rate of gas transfer Large respiratory surface area Small diffusion distance

The lungs contain many branching airways which collectively are known as the bronchial tree

• The trachea and all the bronchi have supporting cartilage which keeps the airways open. • Bronchioles lack cartilage and contain more smooth muscle in their walls than the bronchi, for airflow regulation • The airways from the nasal cavity through the terminal bronchioles are called the conducting zone. The air is moistened, warmed, and filtered as it flows through these passageways.

The pulmonary arteries carry blood which is low in oxygen from the heart to the lungs. • These blood vessels branch repeatedly, eventually forming dense networks of capillaries that completely surround each alveolus. • oxygen and carbon dioxide are exchanged between the air in the alveoli and the blood in the pulmonary capillaries. • Blood leaves the capillaries via the pulmonary veins, which transports the oxygenated blood out of the lungs and back to the heart.

Alveoli ~ 300 million air sacs. Large surface area (60 – 80 m2). Each alveolus is 1 cell layer thick. Total air barrier is 2 cells across (0.5 mm). 3 types of cells: Alveolar type I: Structural cells. Alveolar type II: Secrete surfactant.

Ventilation Mechanical process to move air in and out of the lungs. O2 of air is higher in the lungs than in the blood, O2 diffuses from air to the blood. C02 moves from the blood to the air by diffusing down its concentration gradient. Gas exchange occurs entirely by diffusion. Diffusion is rapid because of the large surface area and the small diffusion distance.

1. simple epithelium cells 2. alveolar macrophages Three types of cells: 1. simple epithelium cells 2. alveolar macrophages 3. surfactant-secreting cells • The wall of an alveolus is primarily composed of simple epithelium, or Type I cells. Gas exchange occurs easily across this very thin epithelium. • The alveolar macrophages, or dust cells, creep along the inner surface of the alveoli, removing debris and microbes. • The alveolus also contains scattered surfactant-secreting, or Type II, cells.

• Water in the fluid creates a surface tension. Surface tension is due to the strong attraction between water molecules at the surface of a liquid, which draws the water molecules closer together. • Surfactant, which is a mixture of phospholipids and lipoproteins, lowers the surface tension of the fluid by interfering with the attraction between the water molecules, preventing alveolar collapse. • Without surfactant, alveoli would have to be completely reinflated between breaths, which would take an enormous amount of energy.

• The wall of an alveolus and the wall of a capillary form the respiratory membrane, where gas exchange occurs.

Summary • The lungs contain the bronchial tree, the branching airways from the primary bronchi through the terminal bronchioles. • The respiratory zone of the lungs is the region containing alveoli, tiny thin-walled sacs where gas exchange occurs. • Oxygen and carbon dioxide diffuse between the alveoli and the pulmonary capillaries across the very thin respiratory membrane.

Three main factors: 1.The surface area and structure of the respiratory membrane. 2. Partial pressure gradients 3. Matching alveolar airflow to pulmonary capillary blood flow

Atmosphere 760 mm Hg Atmospheric pressure (the pressure exerted by the weight of the gas in the atmosphere on objects on the Earth’s surface—760 mm Hg at sea level) Airways (represents all airways collectively) Thoracic wall (represents entire thoracic cage) Intra-alveolar pressure (the pressure within the alveoli—760 mm Hg when equilibrated with atmospheric pressure) 760 mm Hg Pleural sac (space represents pleural cavity) 756 mm Hg Lungs (represents all alveoli collectively) Intrapleural pressure (the pressure within the pleural sac—the pressure exerted outside the lungs within the thoracic cavity, usually less than atmospheric pressure at 756 mm Hg) Fig. 11-17, p.480

(greatly exaggerated) Lung wall 760 Airways Pleural cavity (greatly exaggerated) Lung wall Lungs (alveoli) Thoracic wall 756 756 760 760 760 756 Transmural pressure gradient across lung wall = intra-alveolar pressure minus intrapleural pressure Transmural pressure gradient across thoracic wall = atmospheric pressure minus intrapleural pressure Numbers are mm Hg pressure. Fig. 11-18, p.481

Accessory muscles of inspiration (contract only during forceful Internal intercostal muscles Sternocleidomastoid Scalenus Sternum Ribs Muscles of active expiration (contract only during active expiration) External intercostal muscles Diaphragm Major muscles of inspiration (contract every inspiration; relaxation causes passive expiration) Abdominal muscles Fig. 11-20, p.482

External intercostal muscles (relaxed) Elevated rib cage Elevation of ribs causes sternum to move upward and outward, which increases front-to-back dimension of thoracic cavity Contraction of external intercostal muscles Sternum Contraction of diaphragm Diaphragm (relaxed) Before inspiration Inspiration Lowering of diaphragm on contraction increases vertical dimension of thoracic cavity Contraction of external intercostal muscles causes elevation of ribs, which increases side-to-side dimension of thoracic cavity (a) Fig. 11-21a, p.483

Contraction of internal intercostal muscles flattens ribs and sternum, further reducing side-to-side and front-to-back dimensions of thoracic cavity Relaxation of external intercostal muscles Contraction of internal intercostal muscles Relaxation of diaphragm Contraction of abdominal muscles Position of relaxed abdominal muscles Passive expiration Active expiration Return of diaphragm, ribs, and sternum to resting position on relaxation of inspiratory muscles restores thoracic cavity to preinspiratory size Contraction of abdominal muscles causes diaphragm to be pushed upward, further reducing vertical dimension of thoracic cavity (b) (c) Fig. 11-21bc, p.483

H2O molecules An alveolus Fig. 11-23, p.486

Fig. 11-26, p.489

Fig. 11-27, p.490

Factors affecting the exchange of oxygen and carbon dioxide during internal respiration: 1.The available surface area 2. Partial pressure gradients. 3. The rate of blood flow in a specific tissue.

• These gases are carried in several different forms: Oxygen and Carbon Dioxide Transportation • The blood transports oxygen and carbon dioxide between the lungs and other tissues throughout the body. • These gases are carried in several different forms: 1. dissolved in the plasma 2. chemically combined with hemoglobin 3. converted into a different molecule

Hemoglobin and 02 Transport 280 million hemoglobin/ RBC. Each hemoglobin has 4 polypeptide chains and 4 hemes. Each heme has 1 atom iron that can combine with 1 molecule O2 Each hemoglobin can combine with 4 molecule O2 Combine reversibly with O2 depend on PO2

Hemoglobin's affinity for oxygen increases as its saturation increases the affinity of hemoglobin for oxygen decreases as its saturation decreases

Hemoglobin Oxyhemoglobin: Deoxyhemoglobin: Normal heme contains iron in the reduced form. Reduced form of iron can share electrons and bond with oxygen. Deoxyhemoglobin: When oxyhemoglobin dissociates to release oxygen, the heme iron is still in the reduced form.

Hemoglobin Hemoglobin production controlled by erythropoietin. Production stimulated by P02 delivery to kidneys. Loading/unloading depends: P02 of environment. Affinity between hemoglobin and 02.

Oxyhemoglobin Dissociation Curve Oxygen dissociation curve describes the relation between percent of saturation and the partial pressure of oxygen (S-shape, sigmoid) At high PO2, a large amount of O2 is bound At low PO2, only small amount of O2 is bound

Hemoglobin saturation is determined by the partial pressure of oxygen S-shaped curve

Oxyhemoglobin Dissociation Curve Loading and unloading of 02. Steep portion of the curve, small changes in P02 produce large differences in % saturation (unload more 02). Decreased pH, increased temp., and increased 2,3 DPG, increase CO2 affinity of Hb for 02 decreases. Shift to the right greater unloading. Bohr effect

Muscle Myoglobin Slow-twitch skeletal fibers and cardiac muscle cells are rich in myoglobin. Has a higher affinity for 02 than hemoglobin. Acts as a “go-between” in the transfer of 02 from blood to the mitochondria within muscle cells. May also have an 02 storage function in cardiac muscles.

Human fetal hemoglobin contains g chains, which has a high O2 affinity than adult b hemoglobin In humans, the oxygen affinity of blood decrease for about 3 months after the birth

This reaction is catalyzed by the enzyme carbonic anhydrase.

C02 Transport C02 transported in the blood: HC03- (70%). Dissolved C02 (7%). Carbaminohemoglobin (23%). HCO3- is high in plasma than in erythrocytes CO2 enters and leaves the blood as molecular CO2 rather than HCO3-

Chloride Shift at Systemic Capillaries H20 + C02 H2C03 H+ + HC03- At the tissues, C02 diffuses into the RBC, reaction shifts to the right. Increased [HC03-] in RBC, HC03- diffuses into the plasma with assistance of band III protein. RBC becomes more +. Cl- diffuses in (Cl- shift). HbC02 formed, give off 02.

At Pulmonary Capillaries H20 + C02 H2C03 H+ + HC03- At the alveoli, C02 diffuses into the alveoli, reaction shifts to the left. Decreased [HC03-] in RBC, HC03- diffuses into the RBC. RBC becomes more -. Cl- diffuses out (Cl- shift). Hb02 formed, give off HbC02.

Summary • O2 is transported in two ways: • dissolved in plasma, and • bound to hemoglobin as oxyhemoglobin • The O2 saturation of hemoglobin is affected by: • PO2, pH , temperature, PCO2, and DPG CO2 is transported in three ways: • dissolved in plasma, bound to hemoglobin as carbaminohemoglobin, and converted to bicarbonate ions Oxygen loading facilitates carbon dioxide unloading from hemoglobin. This is known as the Haldane effect. • When the pH decreases, carbon dioxide loading facilitates oxygen unloading. The interaction between hemoglobin's affinity for oxygen and its affinity for hydrogen ions is called the Bohr effect.

Pons Pons Pneumotaxic center respiratory centers Apneustic center Pre-Bötzinger complex Respiratory control centers in brain stem Dorsal respiratory group Medullary respiratory center Medulla Ventral respiratory group Fig. 11-40, p.513

+ + Input from other areas–– some excitatory, some inhibitory Inspiratory neurons in DRG (rhythmically firing) Medulla + Spinal cord Phrenic nerve + Diaphragm Not shown are intercostal nerves to external intercostal muscles. Fig. 11-41, p.513

Sensory Sensory nerve fiber nerve fiber Carotid sinus Carotid bodies Carotid artery Aortic bodies Aortic arch Heart Fig. 11-42, p.514

_ + + Arterial PO2 < 60 mm Hg No effect on Peripheral Emergency life-saving mechanism + No effect on Peripheral chemoreceptors Medullary respiratory center Central + Ventilation Arterial PO2 Fig. 11-43, p.515

Fig. 11-44, p.516