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Respiratory System
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 gillsLand animals use lungs
© 2012 Pearson Education, Inc.
Nasal cavity
Nostril
Larynx
Right main(primary)bronchus
Trachea
Right lung
Oral cavity
Pharynx
Left main (primary) bronchusLeft lung
Diaphragm
Figure 13.1
Trachea (Windpipe)
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
© 2012 Pearson Education, Inc.
Cribriform plateof ethmoid bone
Sphenoidal sinus
Posterior nasalaperture
Nasopharynx• Pharyngeal tonsil
• Opening of pharyngotympanic
tube• Uvula
Oropharynx• Palatine tonsil
• Lingual tonsil
Laryngopharynx
Esophagus
Trachea
Frontal sinus
Nasal cavity• Nasal conchae (superior,
middle and inferior)
• Nasal meatuses (superior,middle, and inferior)
• Nasal vestibule• Nostril
Hard palate
Soft palate
Tongue
Hyoid bone
Larynx• Epiglottis• Thyroid cartilage• Vocal fold • Cricoid cartilage
(b) Detailed anatomy of the upper respiratory tract
Figure 13.2b
Main (Primary) Bronchi
Formed by division of the tracheaEnters the lung at the hilumRight bronchus is wider, shorter, and
straighter than leftBronchi subdivide into smaller and smaller
branches
Lungs
Occupy most of the thoracic cavity◦Heart occupies central portion called
mediastinumApex 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
Alveolar duct Alveoli
Alveolar duct
Alveolar sac
Alveolar pores
Alveolar duct
Alveolus
(a) Diagrammatic view of respiratory bronchioles, alveolar ducts, and alveoli
Terminalbronchiole
Respiratory bronchioles
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
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
© 2012 Pearson Education, Inc.
HCO3_ + H+ H2CO3 CO2+ H2O
(a) External respiration in the lungs (pulmonary gas exchange)
Oxygen is loaded into the bloodand carbon dioxide is unloaded.
Alveoli (air sacs)
Loading of O2
Unloading of CO2
O2 CO2
(Oxyhemoglobinis formed)
Carbonicacid
Bicar-bonate
ion
Red blood cell
Water
Plasma
Pulmonary capillary
Hb + O2 HbO2
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
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
© 2012 Pearson Education, Inc.
(b) Internal respiration in the body tissues (systemic capillary gas exchange)
Oxygen is unloaded and carbondioxide is loaded into the blood.
Tissue cells
Loading of CO2
Unloading of O2
Water
Plasma
Carbonicacid
Bicar-bonate
ion
Systemic capillary
Red blood cell
O2CO2
CO2+ H2O H2CO3 H++ HCO3_
HbO2 Hb + O2
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
© 2012 Pearson Education, Inc.
Inspired air: Alveoliof lungs:
Pulmonaryveins
Bloodleavinglungs andenteringtissuecapillaries:
Systemicarteries
Tissue cells:
Bloodleavingtissues andenteringlungs:
Externalrespiration
Pulmonaryarteries
Alveolarcapillaries
Heart
Tissuecapillaries
Systemicveins
Internalrespiration
O2 CO2
O2 O2
CO2 CO2
O2 O2
O2
O2
CO2 CO2
CO2
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
© 2012 Pearson Education, Inc.
Ponscenters
Medullacenters
AfferentImpulses tomedulla
Breathing control centers stimulated by:
Efferent nerve impulses frommedulla trigger contraction ofinspiratory muscles
Brain
Breathingcontrolcenters
IntercostalnervesPhrenic
nerves
CO2 increase in blood(acts directly on medullacenters by causing adrop in pH of CSF)
Nerve impulsefrom O2 sensor
indicating O2
decrease
CSF inbrainsinus
O2 sensor
in aortic bodyof aortic arch
Intercostalmuscles
Diaphragm
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
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