UNIFYING CONCEPTS OF ANIMAL RESPIRATION• Cells using cellular respiration need a steady supply of

oxygen and must continuously dispose of CO2

• The respiratory system promotes this gas exchange.

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Environment

Cell

Glucose Oxygen Water EnergyCellular

respiration Carbondioxide

C6H12O66 O2 6 CO2 6 H2O ATP

CO2O2

The Human Respiratory System

• Gas exchange occurs at the respiratory surface within the lungs

– A large, moist internal surface folded into the body

– open to the air only through narrow tubes

– The circulatory system transports gases between the respiratory surface (alveoli) and the rest of the body

Lungs(localized

internal organs)

Model of a pair of human lungs

The Human Respiratory System

• The human respiratory system has three phases of gas exchange:

1. breathing, the ventilation of the lungs by alternate

inhalation and exhalation,

2. transport of oxygen from the lungs to the rest of the body via the circulatory system, and

3. diffusion of oxygen from the blood and release of CO2 into the blood by cells of the body.

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Figure 23.UN02

Pulmonaryarteries

CO2

O2-rich blood

O2

PulmonaryveinsPulmonary circuit

O2-poor blood

Capillaries

Systemic circuit

Heart

Capillaries

Aorta

Arteries

Arterioles

Venaecavae

Veins

Venules

The Human Respiratory System

• The human respiratory system:

- has a series of passageways that carry air into and out of the lungs

- It warms & moistens the air moving through it

- It is lined by epithelial cells:

• mucus traps dust and microorganisms

• cilia sweep mucus up toward pharynx

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Air

Nostrils – into nasal cavity

Mouth – into oral cavity

Pharynx

Air filtered by hairs & mucusAir warmed & humidified

common chamber for air & food

Esophagus food to stomach

Larynx (voice box)

Trachea (windpipe)Flexible tube with walls reinforced reinforced

with semicircular bands of stiff with semicircular bands of stiff hyaline cartilagehyaline cartilage

Muscles in the voice box stretch vocal

chords & exhalation passes air over them to produce sounds

Human respiratory system

TracheaBronchus(to right lung)

In the lungs

In the lung the bronchi branch into numerous, even smaller

tubes called bronchioles

Bronchioles

BronchiolesLead to alveoli (pl.)

(air sacs)

(to left lung) Bronchus

Gas exchange

Figure 23.19a

Larynx (voice box)

Trachea (windpipe)

(a) Overview of the human respiratory system

Pharynx

Right lung

Bronchus

Bronchiole

Diaphragm

EsophagusNasal cavity

Left lung

Heart

Figure 23.19b

(b) The structure of alveoli (air sacs) 1.5 to 2.5 million are packed into each lung

Bronchiole

Bloodcapillaries

Fromheart

Toheart

Alveoli

O2-richblood

O2-poorblood

O2

CO2

• Respiratory surface is thin and moist & allows for rapid diffusion

- AlveoliAlveoli: simple : simple squamous epitheliumsquamous epithelium

- Pulmonary Pulmonary capillariescapillaries: simple : simple squamous epithelium squamous epithelium

• Pulmonary capillaries surround alveoli

frompulmonaryartery

alveolarmembrane

respiratorymembrane

to pulmonary vein

(air) CO2

O2

capillary

fluid

Oxygen diffusesinto red blood cells

Carbon dioxidediffuses into alveolus

Gas exchange between alveoli and capillaries

Gases can dissolve & diffuse between the lungs and the circulatory system

Lungs

• Lungs are protected within an airtight chest cavity

• The chest cavity is bound by:

– neck muscles & connective tissue on the top

– muscular thin diaphragm on the bottom

• The rib cage surrounds and protects the lungs

Taking a Breath

• Breathing is the alternating process of inhalation and exhalation.

• During inhalation

– upward movement of the ribs

– downward movement of the diaphragm (contraction)

– volume of the lungs increases/chest is expanded

– Air pressure in lungs drops below air pressure of atmosphere

• Air moves into the lungs by negative pressure breathing (air moves from high to low pressure)

Taking a Breath

• Automatic exhalation of air occurs when muscles that cause inhalation are relaxed and the chest cavity is restricted

– inward movement of the ribs

– upward movement of the diaphragm

– the volume of the lungs decreases

– air pressure in the lungs increases

– air moves out of the respiratory system

Figure 23.20

Inhalation(Air pressure is higher in

atmosphere than in lungs.)

Exhalation(Air pressure is lower in

atmosphere than in lungs.)

Diaphragmrelaxes(moves up)

Diaphragmcontracts(movesdown)

Rib cageexpands asrib musclescontract

Rib cage getssmaller asrib musclesrelax

Airinhaled

Airexhaled

Lung

• Breathing can be controlled

– consciously, as you deliberately take a breath, or

– unconsciously

• Breathing control centers in the brain stem

– automatically control breathing most of the time

– regulate breathing rate in response to CO2 levels in the blood

Taking a Breath

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Figure 23.21-3

CO2 levels in theblood rise as aresult of exercise.

Brain

Breathing controlcenters in the brainmonitor the rising CO2 levels in the blood.

Breathing controlcenters

Nerve signals trigger contraction of muscles to increase breathingrate and depth.

Rib musclesDiaphragm

1

2

3

Signals a need for more oxygen

The Role of Hemoglobin in Gas Transport

• The human respiratory system

– takes in O2

– expels CO2, but

– relies on the circulatory system to shuttle these gases between the lungs and the body’s cells.

AlveolusAir spaces

Capillariesof lung

Tissuecapillaries

CO2-rich,

O2-poor

blood

O2-rich,

CO2-poor

blood

O2 in

inhaled airCO2 in

exhaled air

CO2 O2

Tissue cells throughout body

CO2 O2

Heart

O2

CO

2

O 2CO2

Interstitialfluid

• Oxygen does not readily dissolve in blood.

– Solution: Oxygen is carried in hemoglobin molecules within red blood cells

The Role of Hemoglobin in Gas Transport

Hemegroup

Ironatom

Polypeptide chain

O2 loadedin lungs

O2 unloadedin tissues

O2

O2

How Smoking Affects the Lungs

• Breathing exposes your respiratory tissues to potentially damaging chemicals

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• Tobacco smoke

– damages the cells that line the bronchi and trachea

– interferes with the normal cleansing mechanism of the respiratory system: more toxin-laden smoke particles reach & damage the lungs’ alveoli

• Smoking

– kills half of all people who smoke, about 440,000 Americans every year,

– causes 90% of all lung cancer (one of the deadliest forms of cancer), and

How Smoking Affects the Lungs

(a) Healthy lung (nonsmoker) (b) Cancerous lung (smoker)