In simple animals, like Platyhelminthes (flatworms), respiration is done by diffusion of oxygen. In annelids, oxygen diffuses from moist soil into skin cells Insects have tiny openings called spiracles and special tubes called tracheae Fish use gills Land animals use lungs Respiratory System

Nasal cavity Oral cavity Nostril Pharynx Larynx Trachea Left main (primary) bronchus Right main (primary) bronchus Left lung Right lung Diaphragm Figure 13.1

Four-inch-long tube that connects larynx with bronchi Walls are reinforced with C-shaped hyaline cartilage Lined with ciliated mucosa Beat continuously in the opposite direction of incoming air Expel mucus loaded with dust and other debris away from lungs Trachea (Windpipe)

Cribriform plate of ethmoid bone Sphenoidal sinus Frontal sinus Posterior nasal aperture Nasal cavity Nasal conchae (superior, middle and inferior) Nasopharynx Pharyngeal tonsil Nasal meatuses (superior, middle, and inferior) Opening of pharyngotympanic tube Nasal vestibule Uvula Nostril Oropharynx Hard palate Palatine tonsil Soft palate Tongue Lingual tonsil Laryngopharynx Hyoid bone Larynx Epiglottis Esophagus Thyroid cartilage Trachea Vocal fold Cricoid cartilage (b) Detailed anatomy of the upper respiratory tract Figure 13.2b

Figure 13.3b

Main (Primary) Bronchi Formed by division of the trachea Enters the lung at the hilum Right bronchus is wider, shorter, and straighter than left Bronchi subdivide into smaller and smaller branches Main (Primary) Bronchi

Lungs Occupy most of the thoracic cavity Heart occupies central portion called mediastinum Apex is near the clavicle (superior portion) Base rests on the diaphragm (inferior portion) Each lung is divided into lobes by fissures Left lung—two lobes Right lung—three lobes Lungs

Respiratory bronchioles Alveolar duct Alveoli Respiratory bronchioles Alveolar duct Terminal bronchiole Alveolar sac (a) Diagrammatic view of respiratory bronchioles, alveolar ducts, and alveoli Alveolar pores Alveolar duct Alveolus Figure 13.5a

Respiratory Membrane (Air-Blood Barrier) Thin squamous epithelial layer lines alveolar walls Alveolar pores connect neighboring air sacs Pulmonary capillaries cover external surfaces of alveoli On one side of the membrane is air and on the other side is blood flowing past Respiratory Membrane (Air-Blood Barrier)

Gas Exchange Gas crosses the respiratory membrane by diffusion Oxygen enters the blood Carbon dioxide enters the alveoli Alveolar macrophages (“dust cells”) add protection by picking up bacteria, carbon particles, and other debris Surfactant (a lipid molecule) coats gas- exposed alveolar surfaces Gas Exchange

Oxygen is loaded into the blood and carbon dioxide is unloaded. (a) External respiration in the lungs (pulmonary gas exchange) Oxygen is loaded into the blood and carbon dioxide is unloaded. Alveoli (air sacs) O2 CO2 Loading of O2 Unloading of CO2 Hb + O2 HbO2 HCO3_ + H+ H2CO3 CO2+ H2O (Oxyhemoglobin is formed) Bicar- bonate ion Carbonic acid Water Plasma Red blood cell Pulmonary capillary Figure 13.11a

Gas Transport in the Blood Oxygen transport in the blood Most oxygen travels attached to hemoglobin and forms oxyhemoglobin (HbO2) A small dissolved amount is carried in the plasma Gas Transport in the Blood

Gas Transport in the Blood For carbon dioxide to diffuse out of blood into the alveoli, it must be released from its bicarbonate form: Bicarbonate ions enter RBC Combine with hydrogen ions Form carbonic acid (H2CO3) Carbonic acid splits to form water + CO2 Carbon dioxide diffuses from blood into alveoli Gas Transport in the Blood

Oxygen is unloaded and carbon dioxide is loaded into the blood. (b) Internal respiration in the body tissues (systemic capillary gas exchange) Oxygen is unloaded and carbon dioxide is loaded into the blood. Tissue cells CO2 O2 Loading of CO2 Unloading of O2 CO2+ H2O H2CO3 H++ HCO3_ Water Carbonic acid Bicar- bonate ion HbO2 Hb + O2 Plasma Systemic capillary Red blood cell Figure 13.11b

Mechanics of Breathing (Pulmonary Ventilation) Two phases Inspiration = inhalation – diaphragm contracts Flow of air into lungs Expiration = exhalation – diaphragm moves superiorly (up) relaxes Air leaving lungs Mechanics of Breathing (Pulmonary Ventilation)

Figure 13.10 Inspired air: Alveoli of lungs: CO2 O2 O2 CO2 O2 CO2 External respiration Pulmonary arteries Alveolar capillaries Pulmonary veins Blood leaving tissues and entering lungs: Blood leaving lungs and entering tissue capillaries: Heart O2 CO2 Tissue capillaries O2 CO2 Systemic veins Systemic arteries Internal respiration CO2 O2 Tissue cells: O2 CO2 Figure 13.10

Neural Regulation of Respiration Activity of respiratory muscles is transmitted to and from the brain by phrenic and intercostal nerves Neural centers that control rate and depth are located in the medulla and pons Medulla—sets basic rhythm of breathing and contains a pacemaker called the self-exciting inspiratory center Pons—appears to smooth out respiratory rate Neural Regulation of Respiration

Brain Breathing control centers Pons centers Medulla centers Afferent Impulses to medulla Efferent nerve impulses from medulla trigger contraction of inspiratory muscles Intercostal nerves Phrenic nerves Breathing control centers stimulated by: CO2 increase in blood (acts directly on medulla centers by causing a drop in pH of CSF) Nerve impulse from O2 sensor indicating O2 decrease Intercostal muscles O2 sensor in aortic body of aortic arch Diaphragm CSF in brain sinus Figure 13.12

Non-Neural Factors Influencing Respiratory Rate and Depth Chemical factors: CO2 levels The body’s need to rid itself of CO2 is the most important stimulus Increased levels of carbon dioxide (and thus, a decreased or acidic pH) in the blood increase the rate and depth of breathing Changes in carbon dioxide act directly on the medulla oblongata Changes in oxygen concentration in the blood are detected by chemoreceptors in the aorta and common carotid artery Information is sent to the medulla Non-Neural Factors Influencing Respiratory Rate and Depth