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

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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

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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

Figure 13.3b

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

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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

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(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

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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

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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