Lecture-13-Respiration PDF

 respiration – is the process of obtaining oxygen from the external environment and eliminating carbon dioxide cellular respiration, oxidative processes within cells external respiration, exchange of O2 and CO2 between the organism and its environment Partial Pressure Gradients i...

 respiration – is the process of obtaining oxygen from the external environment and eliminating carbon dioxide cellular respiration, oxidative processes within cells external respiration, exchange of O2 and CO2 between the organism and its environment Partial Pressure Gradients in Gas Exchange Gases diffuse down pressure gradients in the lungs and other organs as a result of differences in partial pressure Partial pressure is the pressure exerted by a particular gas in a mixture of gases Gas diffuses - region of partial pressure to region of partial pressure Lungs and tissues - O2 and CO2 diffuse from where their partial pressures are higher to where they are lower Components of the gas-transfer system in many animals, which involves four basic steps: 1. Breathing movements, which assure a continual supply of air or water to the respiratory surface (e.g., lungs or gills) 2. Diffusion of 0, and C02 across the respiratory epithelium 3. Bulk transport of gases by the blood 4. Diffusion of 0, and C02 across capillary walls between blood and mitochondria in tissue cells  for diffusion to be effective, gas-exchange regions must be: o moist o thin o relatively large o in contact with the environment effectiveness of diffusion is enhanced by vascularization  Respiratory media Animals can use air or water as a source of O2, or respiratory medium In a given volume, there is less O2 available in water than in air Obtaining O2 from water requires greater efficiency than air breathing Types: 1. Unidirectional – in most fish gills continuous ventilation water enters the buccal cavity through the mouth, passes across the gill curtain and exits flowing in one direction 2. Bidirectional or tidal – in lung ventilation with air entering and exiting through the same channel ventilation is not continuous Patterns of gas exchange Countercurrent flow o water flows across the secondary lamellae in one direction and blood flows through capillaries in the opposite direction o gills in some fishes Patterns of gas exchange Crosscurrent flow o airflow and blood flow cross each other obliquely; avian lungs Patterns of gas exchange Uniform pool o lung ventilation keep the partial pressure of gases within the alveolar spaces uniform through frequent breathing, mixing gases, and absence of significant barriers to diffusion  Respiratory Organs Gills or branchia (external or internal)  How a fish ventilates its gills Ventilation moves the respiratory medium over the respiratory surface. countercurrent flow/exchange - exchange of substance between two fluids in opposite directions Copyright © 2002 Pearson Education, Inc., publishing as Benjamin Cummings  Respiratory Organs Lungs - localized organs Respiratory system Branch of Branch of pulmonary pulmonary vein artery (oxygen-rich (oxygen-poor blood) blood) Terminal bronchiole Nasal Pharynx cavity Larynx Alveoli (Esophagus) Left lung Trachea Right lung Bronchus Bronchiole Diaphragm Heart SEM 50 µm Colorized 50 µm SEM system of branching ducts conveys air to the lungs Breathing – alternating inhalation and exhalation or air; ventilates the lungs A frog ventilates its lungs by positive pressure breathing which forces air down the trachea.. Rib cage Rib cage gets expands as Air Air smaller as rib muscles inhaled exhaled rib muscles contract relax Lung Diaphragm INHALATION EXHALATION Diaphragm contracts Diaphragm relaxes (moves down) (moves up) Mammals ventilate their lungs by negative pressure breathing.  important activity performed by the respiratory system to satisfy the oxygen needed by all cells in the body. therespiratory muscles are activated to increase and decrease the volume of the thoracic cavity to ventilate the alveoli. consists of inspiration or taking up of air into the lungs and expiration, or expelling air from the lungs  Branching pattern ◦ Trachea ◦ Primary bronchi (left, right) ◦ Secondary bronchi (each lobe) ◦ Tertiary bronchi, bronchioles ◦ Alveoli Vessels accompany respiratory tree to alveoli  Located in pleural cavities ◦ Apex posterior to clavicle ◦ Base lays on diaphragm Root - all vessels, nerves enter each lung ◦ 2 Pulmonary Veins - carries O2 blood from each lung to heart ◦ 1 Pulmonary Artery - carries dO2 blood to each lung ◦ Primary Bronchi ◦ Nerves ◦ Lymph Vessels  Primary muscle of respiration (involuntary) ◦ Contraction during inspiration  Increases volume of thoracic cavity  Decreases pressure of thoracic cavity  Air moves into lungs (high → low pressure) Forced contraction Diaphragm (voluntary) oUsed for defecation, urination, labor ▪ Increases pressure in abdominal cavity ▪Pushes on abdominal organs to move contents out INTERCOSTAL MUSCLES - Lift ribs to expand chest cavity for inspiration Avian lungs no blind ended alveoli in and out of which air moves -Trachea – mesobronchus – dorsobronchi and ventrobronchi – paraboronchi- air sacs  Air sacs – voluminous, thin-walled diverticula of the lungs which penetrate the centra (pneumatic foramina) except in ratites diverticula of the lungs) extensively distributed throughout of the body Air sacs  -Gas transfer takes place in small air capillaries Air Air Anterior air sacs Trachea Posterior air sacs Lungs Lungs Air tubes (parabronchi) 1 mm in lung INHALATION EXHALATION Air sacs fill Air sacs empty; lungs fill  Birds have the most efficient vertebrate lungs Air sacs allow oxygen-rich air to pass respiratory surfaces on both inhalation and exhalation Chemical Dependent on blood CO2 levels ◦ CO2 + H2O →H2CO3 ◦ H2CO3 → HCO3- + H+ pH-dependent Chemoreceptors ◦ Central: monitors CSF ◦ Peripheral: carotid and aortic bodies O2 less important under most circumstances Nervous Voluntary ◦ Cerebral cortex ◦ Protective in nature ◦ Limited control Involuntary (Respiratory center) ◦ Medullary rhythmicity area  Maintains basic rhythm of respiration ◦ Pons  Coordinates transition between inspiration and expiration Control of Breathing in Humans when the control center registers a slight drop in pH, it increases the depth and rate of breathing, and the excess CO2 is eliminated in exhaled air  Involuntary: Brainstem group  This group maintains the basic rhythm of respiration.  The pons coordinates transition between inspiration and expiration. Voluntary: Cerebral cortex group  Influence the timing of inspiratory cut-off by providing a tonic input to the respiratory pattern generators located in the inspiratory center Influences the respiratory Response to stimuli (hypercapnia, hypoxia, and lung inflation) by regulating the duration of inspiration  found in the lower pons source of impulses that terminate inspiration “inspiratory cut-off switch” inactivation of this center results in apneustic breathing (rhythmic respiration with a marked increase in inspiratory time and a short expiration phase)  twogroups: the inspiratory dorsal respiratory group (DRG) of neurons and expiratory ventral respiratory group (VRG) of neurons  DRG is the site of projection of proprioceptive afferents from the respiratory muscles and chest wall. site of origin of the normal rhythmic respiratory drive consisting of repetitive bursts of inspiratory action potentials.  ventral respiratory group (VRG) innervates respiratory effector muscles through the phrenic, intercostal, and abdominal respiratory motoneurons. output increases with the need for forceful expiration such as in exercise or in any condition of increased airway resistance to breathing.  Central: monitors CSF Peripheral: carotid and aortic bodies Respiration is highly dependent on blood CO2 levels as well as pH H+ concentration – most important factor Carbon dioxide aids the H+ concentration by forming carbonic acid.  oxygen diffuses across the respiratory epithelium into the blood - combines with a respiratory pigment - (characteristic color to the blood) Respiratory pigments are complexes of proteins and metallic ions,. The  complexes of proteins and metal ions that transport oxygen, greatly increases the amount of oxygen that blood can carry  each one has a characteristic color  w/o pigment 0.3 vol % O2; w/ pigment 20 vol % Iron Heme  most vertebrates and some Hemoglobin invertebrates use hemoglobin  Bunsen solubility coefficient: ooxygen in blood at 37°C - 2.4 ml oxygen per 100 ml of blood per atmosphere of oxygen pressure Iron oconcentration of oxygen in physical Heme solution (not bound to a respiratory Hemoglobin pigment) in human blood at a normal arterial Po2 - 0.3 ml0, per 100 ml blood, or 0.3 vol % oxygen  Bunsen solubility coefficient: o total oxygen content of human arterial blood at a normal arterial Po - 20 vol % o 70-fold increase - combination of oxygen with hemoglobin Iron color of a respiratory pigment changes Heme with its oxygen content Hemoglobin hemoglobin, which is bright red when it is loaded with 02 becomes a dark maroon-red when deoxygenated.  Original Oxygenation CO2 Introduction Brick Red Bright red Dull red bright-red with O2 dark maroon- red when deoxygenated  main respiratory pigment in vertebrates MW - 68,000 four iron containing porphyrin prosthetic groups – heme associated with globin - tetrameric protein Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. heme group iron atom beta chain alpha chain © Andrew Syred/Photo Researchers, Inc.  composed of pigment heme, and protein globin heme - iron- containing porphyrin prosthetic groups transports oxygen globin - four folded polypeptide chains of amino acids  globin molecule - two dimers, α1β1, and α2β2, each of which is a tightly cohering unit two dimers - more loosely connected to each other by salt bridges, except that the two β chains do not touch Oxygenation - alters these bridges; conformational changes in the hemoglobin molecule  Chains iron – ferrous state (Fe2+)- bound by porphyrin ring of the heme, forming coordinate links with four pyrrole nitrogens Methemoglobin – Fe2+ is Iron Heme oxidized to Fe3+ ; does not bind oxygen; nonfunctional Chains Hemoglobin RBC with methemoglobin reductase - reduces methemoglobin to the functional ferrous form  Four atoms of iron (Fe2+) associated with a heme Heme group - red color of blood and its oxygen- combining ability one hemoglobin molecule binds four oxygen molecules (oxyhemoglobin) absence of O2, - deoxyhemoglobin  Certain compounds (e.g., nitrites and chlorates) act either to oxidize hemoglobin or to inactivate methemoglobin reductase, thereby increasing the level of methemoglobin and impairing oxygen transport. carbon monoxide (CO) formed from the incomplete combustion of carbon dioxide interferes with the binding of oxygen to hemoglobin has an affinity a higher (200X) affinity to hemoglobin than does oxygen Carboxyhemoglobin – hemoglobin saturated with CO release of CO can cause carbon monoxide poisoning turns blood bright red  Hemerythrin (Priapulida, Brachiopoda, Annelida; (violet, Fe2+) Chlorocruorin (Annelida; (green, Fe2+,) Hemocyanin (Mollusca, Arthropoda; blue; deoxygenated: colorless; not packaged in cells) Oxygen Transport in Blood each hemoglobin molecule can combine with four oxygen molecules (each heme - one molecule of oxygen extent to which oxygen is bound to hemoglobin varies with the partial pressure of the gas, Po2 Oxygen Transport in Blood all sites on the hemoglobin molecule are occupied by oxygen - blood is 100% saturated oxygen content of the blood is equal to its oxygen capacity millimole of heme can bind a millimole of oxygen = represents a volume of 22.4 ml of oxygen Human blood contains about 0.9 mmol of heme per 100 ml of blood oxygen capacity = 0.9 x 22.4 = 20.2 vol %. Oxygen Transport in Blood oxygen capacity of blood increases in proportion to its hemoglobin concentration, the oxygen content = percentage of the oxygen capacity (percent saturation) compare the oxygen content of blood of different hemoglobin content oxygen dissociation curves - relationship between percent saturation and the partial pressure of oxygen.  oxygen dissociation curves of myoglobin and lamprey hemoglobin are hyperbolic sigmoid - oxygen dissociation curves of other vertebrate difference occurs because myoglobin and lamprey hemoglobin have a single heme group hemoglobin molecule - other hemoglobins have oxygenated, it goes four heme groups through a conformational change from the tense (T) state to the relaxed (R) state  Blood arriving in the lungs has a low partial pressure of O2 and a high partial pressure of CO2 relative to air in the alveoli  In the alveoli, O2 diffuses into the blood and CO2 diffuses into the air  In tissue capillaries, partial pressure gradients favor diffusion of O2 into the interstitial fluids and CO2 into the blood  160 120 27 6 Exhaled air Inhaled air 1 0.2 PO 2 PCO 2 PO 2 PCO 2 Alveolar Alveolar spaces 2 epithelial CO2 O2 104 cells 40 Alveolar Blood capillaries entering PO 2 PCO 2 45 alveolar 40 capillaries 5 PO 2 PCO 2 Pulmonary Pulmonary arteries veins and 104 and systemic systemic 3 40 veins arteries PO 2 PCO 2 Systemic >45