 What is the point of the respiring? ◦ Gas exchange provides oxygen for cellular respiration and gets rid of carbon dioxide.  How do gases move from one area to the next? ◦ Gases move down pressure gradients – moving from regions of high pressure to regions of low pressure ◦ In lungs and tissues, O 2 and CO 2 move from areas where the pressure is higher to areas where pressure is lower

 Where can animals get oxygen? ◦ From air and water. In a given volume there is less oxygen in water than in air. So animals who use water as their source of oxygen must be very efficient  What kind of surfaces in animals can be used to obtain oxygen? ◦ All surfaces must be moist ◦ Surfaces include skin, tracheae, gills or lungs

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

 What does ventilation mean to you? ◦ When talking about the respiratory system, ventilation means movement of the respiratory medium over the respiratory surface.  How do fish get oxygen? ◦ They move through water – to move water over their gills ◦ Oxygen moves from the water to the gills to the blood

 What is the name of the system used by fish to get oxygen from gills to the blood? ◦ Counter Current Exchange - 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  What other systems did we learn about that have a counter current exchange system? ◦ Thermoregulation – warm blood from core heating up cold blood returning from the extremities ◦ Excretion – reabsorption of water from nephron to blood

Fig Anatomy of gills Gill arch Water flow Operculum Gill arch Gill filament organization Blood vessels Oxygen-poor blood Oxygen-rich blood Fluid flow through gill filament Lamella Blood flow through capillaries in lamella Water flow between lamellae Countercurrent exchange P O 2 (mm Hg) in water P O 2 (mm Hg) in blood Net diffu- sion of O 2 from water to blood Gill filaments

 What is unique about the respiratory system of insects? ◦ It consists of a tracheal systems made of tubes that branch out supply oxygen to the body cells ◦ It is separate / independent from the circulatory system

Fig Air sacs Tracheae External opening Body cell Air sac Tracheole TracheolesMitochondriaMuscle fiber 2.5 µm Body wall Trachea Air

 What is unique about the respiratory system of mammals? ◦ Mammals have lungs which are infoldings of the body surface ◦ The circulatory systems transports oxygen from the lungs to the rest of the body ◦ A system of branching ducts conveys air to the lungs ◦ Air inhaled through the nostrils passes through the pharynx via the larynx, trachea, bronchi, bronchioles, and alveoli, where gas exchange occurs

Fig Pharynx Larynx (Esophagus) Trachea Right lung Bronchus Bronchiole Diaphragm Heart SEM Left lung Nasal cavity Terminal bronchiole Branch of pulmonary vein (oxygen-rich blood) Branch of pulmonary artery (oxygen-poor blood) Alveoli Colorized SEM 50 µm

 How does oxygen get into the lungs? ◦ Mammals ventilate their lungs by negative pressure breathing, which pulls air into the lungs ◦ Lung volume increases as the rib muscles and diaphragm contract

Fig Lung Diaphragm Air inhaled Rib cage expands as rib muscles contract Rib cage gets smaller as rib muscles relax Air exhaled EXHALATION Diaphragm relaxes (moves up) INHALATION Diaphragm contracts (moves down)

 How is breathing controlled in humans? ◦ In humans, the main breathing control centers are in two regions of the brain, the medulla oblongata and the pons. ◦ 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. ◦ The pons regulates the tempo ◦ Sensors in the aorta and carotid arteries monitor O 2 and CO 2 concentrations in the blood. These sensors exert secondary control over breathing

Fig Breathing control centers Cerebrospinal fluid Pons Medulla oblongata Carotid arteries Aorta Diaphragm Rib muscles

 Why does oxygen move from the lungs to the circulatory system? ◦ Blood arriving in the lungs has a low partial pressure of O 2 and a high partial pressure of 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

Fig Alveolus P O 2 = 100 mm Hg P O 2 = 40 P O 2 = 100 P O 2 = 40 Circulatory system Body tissue P O 2 ≤ 40 mm HgP CO 2 ≥ 46 mm Hg Body tissue P CO 2 = 46 P CO 2 = 40 P CO 2 = 46 Circulatory system P CO 2 = 40 mm Hg Alveolus (b) Carbon dioxide(a) Oxygen

 How does hemoglobin carry oxygen? ◦ A single hemoglobin molecule can carry four molecules of O 2 ◦ The hemoglobin dissociation curve shows that a small change in the partial pressure of oxygen can result in a large change in delivery of O 2 ◦ CO 2 produced during cellular respiration lowers blood pH and decreases the affinity of hemoglobin for O 2 ; this is called the Bohr shift

Fig. 42-UN1  Chains Iron Heme  Chains Hemoglobin

Fig O 2 unloaded to tissues at rest O 2 unloaded to tissues during exercise O 2 saturation of hemoglobin (%) 2060 Tissues during exercise Tissues at rest Lungs P O 2 (mm Hg) (a) P O 2 and hemoglobin dissociation at pH 7.4 O 2 saturation of hemoglobin (%) P O 2 (mm Hg) (b) pH and hemoglobin dissociation pH 7.4 pH 7.2 Hemoglobin retains less O 2 at lower pH (higher CO 2 concentration)

 How does the carbon dioxide produced from cellular respiration exit the body? ◦ Hemoglobin also helps transport CO 2 and assists in buffering ◦ CO 2 from respiring cells diffuses into the blood and is transported either in blood plasma, bound to hemoglobin, or as bicarbonate ions (HCO 3 – ) ◦ CO 2 diffuses from the blood in the pulmonary artery (high CO 2 ) to the lung (low CO 2 ) where the partial pressure is less

Fig Body tissue CO 2 produced CO 2 transport from tissues Capillary wall Interstitial fluid Plasma within capillary CO 2 Red blood cell H2OH2O H 2 CO 3 Hb Carbonic acid Hemoglobin picks up CO 2 and H + CO 2 transport to lungs HCO 3 – Bicarbonate H+H+ + Hemoglobin releases CO 2 and H + To lungs HCO 3 – Hb H+H+ + HCO 3 – H 2 CO 3 H2OH2O CO 2 Alveolar space in lung

Fig. 42-UN2 Inhaled airExhaled air Alveolar epithelial cells Alveolar spaces CO 2 O2O2 O2O2 Alveolar capillaries of lung Pulmonary veins Pulmonary arteries Systemic veinsSystemic arteries Heart Systemic capillaries CO 2 O2O2 O2O2 Body tissue