1. 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

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

3. 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)

4. 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

5. Figure 13.3b

6. 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

7. 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

8. 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

9. 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)

10. 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

11. 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 + O HbO2
HCO3_ + H H2CO CO2+ H2O
(Oxyhemoglobin
is formed)
Bicar-
bonate
ion
Carbonic
acid
Water
Plasma
Red blood cell
Pulmonary capillary
Figure 13.11a

12. 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

13. 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

14. 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 H2CO H++ HCO3_
Water
Carbonic
acid
Bicar-
bonate
ion
HbO Hb + O2
Plasma
Systemic capillary
Red blood cell
Figure 13.11b

15. 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)

16. 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

17. 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

18. 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

19. 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