Chapter 33 Respiration 33 1 Why Exchange Gases The act of breathing is called respiration The process of cellular respiration which converts the energy in nutrients into the ATP used by cells requires a steady supply of oxygen and generates carbon dioxide as a waste product The circulatory system gets oxygen from your lungs carries it to each cell and then picks up CO2 to be expelled from your body by the lungs 33 2 What Are Some Evolutionary Adaptations for Gas Exchange Gas exchange in all organisms ultimately relies on diffusion Cellular respiration increases CO2 levels creating a concentration gradient that favors the diffusion of CO2 out of cells and the diffusion of O2 into them For animals with well developed respiratory systems gas exchange occurs in the following stages Air or water moves past a respiratory surface down a pressure gradient this is usually facilitated by muscular movements such as breathing O2 and CO2 are exchanged through the respiratory surface by diffusion O2 diffuse into the capillaries of the circulatory system and CO2 diffuses out Gases are transported between the respiratory system and the tissues by the flow of blood as it is pumped throughout the body Gases are exchanged between the tissues and the circulatory system by diffusion at the tissues O2 moves out of the capillaries into tissues and CO2 moves from the tissues to the capillaries An Overview of Gas Exchange in Mammals Oxygenated blood Deoxygenated blood Gases move in and out 1 of the lungs by breathing CO2 O2 O2 O2 O2 O2 CO2 alveoli air sacs 2 O2 and CO2 are exchanged in the lungs by diffusion Gases dissolved 3 in the blood are transported by the circulatory system left atrium right atrium right ventricle CO2 left ventricle O2 CO2 CO2 CO2 CO2 4 O2 and CO2 are exchanged in the tissues by diffusion Fig 33 2 Gills facilitate gas exchange in an aquatic environment The simplest type of gill found in amphibians consists of many thin projections of the body surface that protrude into the surrounding water Fish gills are complex structures Fish create a continuous current over their gills by pumping water into their mouths and ejecting over the gills Some land animals use lungs for respiration Lungs are chambers containing moist respiratory surfaces that are protected within the body 33 3 How Does the Human Respiratory System Work The human respiratory system can be divided into two parts The conducting portion a series of passageways that carry air into and out of the gas exchange portion of the respiratory system The gas exchange portion where gases are exchanged with the blood in tiny sacs within the lungs The conducting portion carries air to the lungs and contains the apparatus that makes speaking possible Air enters through the nose or mouth and passes through the nasal or oral cavity into a chamber called the pharynx It then travels to the larynx or voice box where sounds are produced The opening to the larynx is guarded by the epiglottis a flap of tissue supported by cartilage The Human Respiratory System bronchiole pulmonary venule pulmonary arteriole nasal cavity pharynx epiglottis larynx esophagus trachea rings of cartilage oral cavity bronchioles bronchi diaphragm pulmonary veins pulmonary artery capillary network alveoli a Human respiratory system b Alveoli with capillaries Fig 33 7 The epiglottis prevents food from entering the larynx when swallowing During normal breathing the epiglottis is tilted upward allowing air to flow into the larynx During swallowing the epiglottis folds downward and covers the larynx directing substances into the esophagus The Heimlich maneuver If an individual attempts to inhale and swallow at the same time this reflex may fail and food can become lodged in the larynx blocking air from entering the lungs The use of the Heimlich maneuver can clear the obstruction The Heimlich Maneuver Can Save Lives object ejected lungs compressed diaphragm pushed upward 1 Grasp the hands between the navel and breastbone 2 Quickly and forcefully pull upward and toward your body Fig 33 8 Within the larynx are the vocal cords bands of elastic tissue controlled by muscles Exhaled air causes the vocal cords to vibrate producing the tones of speech or song Inhaled air travels past the larynx into the trachea a flexible tube whose walls are reinforced with semicircular bands of stiff cartilage The trachea splits into two bronchi one leading to each lung Inside the lung each bronchus branches repeatedly into ever small tubes called bronchioles Bronchioles lead to microscopic alveoli the tiny air sacs where gas exchange occurs Gas exchange occurs in the alveoli A network of capillaries covers most of the alveolar surface The walls of the alveoli consist of a single thin layer of epithelial cells The respiratory membrane through which gases diffuse consists of epithelial cells of the alveoli and the endothelial cells that form the wall of the capillary across which gas exchange occurs Gas Exchange Between Alveoli and Capillaries to the pulmonary vein from the pulmonary artery capillary alveolar membrane respiratory membrane air CO2 O2 Oxygen diffuses into the red blood cells Carbon dioxide diffuses into the alveolus Fig 33 9 Oxygen transport Nearly all about 90 of the O2 carried by the blood is bound to hemoglobin a large protein that gives red blood cells their color Oxygen Transport surfactant fluid respiratory membrane O2 air in alveolus alveolar wall red blood cells O2 hemoglobin plasma capillary walls extracellular fluid cells of body tissues O2 a O2 transport from the lungs to the tissues Fig 33 10a Carbon dioxide transport CO2 from cellular respiration in the body cells diffuses into nearby capillaries then is carried in the bloodstream to the respiratory membranes of the alveoli Alveolar capillaries have a higher CO2 concentration than that of the alveolar air Carbon dioxide transport continued CO2 is transported in the blood in three ways As bicarbonate ions 70 when CO2 combines with water Bound to hemoglobin 20 Dissolved in plasma as CO2 10 Carbon Dioxide Transport CO2 CO2 1 CO2 2 CO2 CO2 CO2 3 H2O CO2 HCO3 H 5 HCO3 CO2 H2O H HCO3 4 CO2 CO2 b CO2 transport from the tissues to the lungs Fig 33 10b Air is inhaled actively and exhaled passively Breathing occurs in two stages Inhalation when air is drawn into the lungs Exhalation when air is expelled from the lungs The lower boundary of the chest cavity is formed by the diaphragm which domes upward when relaxed During
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