CAMPBELL BIOLOGY IN FOCUS © 2014 Pearson Education, Inc. Urry Cain Wasserman Minorsky Jackson Reece Lecture Presentations by Kathleen Fitzpatrick and Nicole Tunbridge 34 Circulation and Gas Exchange

© 2014 Pearson Education, Inc. Describe the function of the respiratory system.

© 2014 Pearson Education, Inc. 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

© 2014 Pearson Education, Inc. Gases hate to be in mixtures (e.g. gas mixtures, dissolved in liquids, etc.).

© 2014 Pearson Education, Inc. 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 O 2 ) is 0.21  the atmospheric pressure

© 2014 Pearson Education, Inc.  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

© 2014 Pearson Education, Inc. There are 4 requirements a respiratory surface must meet in order to be efficient at gas exchange: 1. Moist 2. Thin membrane 3. Increased surface area 4. Connection to a circulatory system

© 2014 Pearson Education, Inc. As we review the evolution and physiology of the respiratory system, validate the claim made on the last slide. -Where is the respiratory surface? -How does habitat affect the respiratory structure?

© 2014 Pearson Education, Inc. 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

© 2014 Pearson Education, Inc. Figure Coelom Tube foot Gills (b) Sea star (a) Marine worm Parapodium (functions as gill)

© 2014 Pearson Education, Inc. 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

© 2014 Pearson Education, Inc. 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

© 2014 Pearson Education, Inc.  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

© 2014 Pearson Education, Inc. Figure Lamella Water flow Countercurrent exchange O 2 -poor blood Gill filaments Operculum Gill arch Water flow Gill arch Blood vessels O 2 -rich blood Blood flow P O 2 (mm Hg) in blood P O 2 (mm Hg) in water Net diffusion of O

© 2014 Pearson Education, Inc.

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

© 2014 Pearson Education, Inc. Figure TracheolesMuscle fiber Mitochondria Tracheae Air sacs External opening Air sac Tracheole Trachea Air 2.5  m Body cell

© 2014 Pearson Education, Inc. Figure 34.19a Tracheoles Muscle fiber Mitochondria 2.5  m

© 2014 Pearson Education, Inc. 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

© 2014 Pearson Education, Inc. Considering the mammalian system, trace the flow of air from the nasal orifice to the alveoli.

© 2014 Pearson Education, Inc. 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

© 2014 Pearson Education, Inc.  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

© 2014 Pearson Education, Inc.  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 Animation: Gas Exchange

© 2014 Pearson Education, Inc. Figure 34.20a Bronchiole Bronchus Right lung Trachea (Esophagus) Larynx Pharynx (Heart) Left lung Nasal cavity Diaphragm

© 2014 Pearson Education, Inc. Figure 34.20b Terminal bronchiole Capillaries Alveoli Branch of pulmonary vein (oxygen-rich blood) Branch of pulmonary artery (oxygen-poor blood)

© 2014 Pearson Education, Inc. Figure 34.20c Dense capillary bed enveloping alveoli (SEM) 50  m

© 2014 Pearson Education, Inc.  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

© 2014 Pearson Education, Inc. Figure Deaths from other causes RDS deaths Body mass of infant <1,200 g>1,200 g (n  9)(n  0) (n  29)(n  9) Surface tension (dynes/cm) Results

© 2014 Pearson Education, Inc. Breathing is an example of respiration, but not all respiration is described as breathing! Figure that one out…

© 2014 Pearson Education, Inc. Concept 34.6: Breathing ventilates the lungs  The process that ventilates the lungs is breathing, the alternate inhalation and exhalation of air

© 2014 Pearson Education, Inc.  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

© 2014 Pearson Education, Inc. 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 Animation: Gas Exchange

© 2014 Pearson Education, Inc. Figure Inhalation: Diaphragm contracts (moves down). Diaphragm Exhalation: Diaphragm relaxes (moves up). Lung Air inhaled. Air exhaled. Rib cage expands as rib muscles contract. Rib cage gets smaller as rib muscles relax. 1 2

© 2014 Pearson Education, Inc.  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 O 2 in alveoli is considerably less than in the atmosphere ***Making the inhalation of oxygen in air ALWAYS favorable

© 2014 Pearson Education, Inc. How long can you hold your breath? Is it possible to hold it indefinitely? Why?

© 2014 Pearson Education, Inc. 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

© 2014 Pearson Education, Inc. Figure Homeostasis: Blood pH of about 7.4 Stimulus: Rising level of CO 2 in tissues lowers blood pH.

© 2014 Pearson Education, Inc. Figure Carotid arteries Homeostasis: Blood pH of about 7.4 Stimulus: Rising level of CO 2 in tissues lowers blood pH. Sensor/control center: Aorta Cerebro- spinal fluid Medulla oblongata

© 2014 Pearson Education, Inc. Figure Carotid arteries Response: Signals from medulla to rib muscles and diaphragm increase rate and depth of ventilation. Homeostasis: Blood pH of about 7.4 Stimulus: Rising level of CO 2 in tissues lowers blood pH. Sensor/control center: Aorta Cerebro- spinal fluid Medulla oblongata

© 2014 Pearson Education, Inc. Figure Carotid arteries Response: Signals from medulla to rib muscles and diaphragm increase rate and depth of ventilation. Homeostasis: Blood pH of about 7.4 CO 2 level decreases. Stimulus: Rising level of CO 2 in tissues lowers blood pH. Sensor/control center: Aorta Cerebro- spinal fluid Medulla oblongata

© 2014 Pearson Education, Inc.  Sensors in the aorta and carotid arteries monitor O 2 and CO 2 concentrations in the blood  These sensors exert secondary control over breathing

© 2014 Pearson Education, Inc. 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

© 2014 Pearson Education, Inc. Coordination of Circulation and Gas Exchange  Blood arriving in the lungs has a low P O 2 and a high P CO 2 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

© 2014 Pearson Education, Inc. Animation: O 2 Blood to Tissues Animation: O 2 Lungs to Blood Animation: CO 2 Blood to Lungs Animation: CO 2 Tissues to Blood

© 2014 Pearson Education, Inc. Figure Alveolar epithelial cells Alveolar spaces Alveolar capillaries Inhaled air Exhaled air Pulmonary veins Systemic arteries Pulmonary arteries Systemic veins Systemic capillaries Heart CO 2 O2O2 Body tissue cells O 2 CO O 2 CO O 2 CO O 2 CO O 2 CO 2 <40>45 O2O2 CO 2

© 2014 Pearson Education, Inc. 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

© 2014 Pearson Education, Inc.  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 iron- containing heme group  Hemoglobin binds oxygen reversibly, loading it in the gills or lungs and releasing it in other parts of the body

© 2014 Pearson Education, Inc. Figure 34.UN01 Hemoglobin Heme Iron

© 2014 Pearson Education, Inc.  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

© 2014 Pearson Education, Inc. Figure 34.25a Tissues at rest P O 2 (mm Hg) Tissues during exercise Lungs O 2 unloaded to tissues during exercise O 2 unloaded to tissues at rest (a) P O 2 and hemoglobin dissociation at pH 7.4 O 2 saturation of hemoglobin (%)

© 2014 Pearson Education, Inc.  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

© 2014 Pearson Education, Inc. Figure 34.25b pH 7.4 P O 2 (mm Hg) pH 7.2 Hemoglobin retains less O 2 at lower pH (higher CO 2 concentration (b) pH and hemoglobin dissociation O 2 saturation of hemoglobin (%)

© 2014 Pearson Education, Inc. 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 – )

© 2014 Pearson Education, Inc. 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

© 2014 Pearson Education, Inc.  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