The Respiratory System

Chapter 11

Respiration

• Physiological process by which oxygen

moves into internal environment and

carbon dioxide moves out

• Oxygen is needed for aerobic

respiration

• Carbon dioxide is produced by same

Respiratory System

• Acts in concert with the circulatory

system to deliver oxygen and remove

carbon dioxide

• Also helps regulate acid-base balance

Human Respiratory System

pharynx (throat)

larynx (voice box)

trachea (windpipe)pleural membrane

intercostal muscle

diaphragm

epiglottis

bronchiole

alveoli

Airways

• Air enters through nose• Moves through pharynx and larynx to

trachea• Trachea branches into two bronchi• Each bronchus branches into

bronchioles• Bronchioles end in alveoli where gas

exchange occurs

Speech Production

• Vocal cords stretch across laryngeal opening; opening between them is glottis

• Position of cords is varied to create different sounds

Glottis closed Glottis open

Pressure Gradients

• Concentration gradients for gases

• Gases diffuse down their pressure

gradients

• Gases enter and leave the body by

diffusing down pressure gradients

across respiratory membranes

Atmospheric Pressure

• Pressure exerted by the weight of the

air on objects on Earth’s surface

• At sea level = 760 mm Hg

• Oxygen is 21% of air; its partial

pressure is about 160 mm Hg

Fick’s Law

• Describes the rate at which a substance (such as oxygen) will diffuse across a membrane (such as a respiratory surface)

• Rate is proportional to the pressure gradient across the membrane and to the surface area of the membrane

Altitude Sickness

• Humans are adapted to lower elevations where oxygen levels are relatively high

• At high altitude

– Hyperventilation leads to ion imbalances in cerebrospinal fluid

– Increased capillary permeability can cause edema

Decompression Sickness

• Pressure increases with water depth

• While diving, pressurized air keeps

lungs from collapsing

• During ascent, pressure decreases

• Bubbles of gaseous nitrogen can form

in blood and block flow

Carbon Monoxide Poisoning

• Colorless, odorless gas

• Binds to hemoglobin 200 times more

tightly than oxygen does

• Even tiny amounts can tie up

hemoglobin and prevent oxygen

delivery

Bronchitis

• Irritation of the ciliated epithelium that lines the bronchiole walls

• Air pollutants, smoking, or allergies can be the cause

• Excess mucus causes coughing, can harbor bacteria

• Chronic bronchitis scars and constricts airways

Emphysema

• An irreversible breakdown in alveolar walls

• Lungs become inelastic

• May be caused by a genetic defect

• Most often caused by smoking

Asthma

• Can be triggered by allergens

• Smooth muscle ringing bronchi contracts

• Mucus is produced by bronchial epithelium

• Result is reduced air flow

• Can be treated with aerosol inhalers

Breathing

• Moves air into and out of lungs

• Occurs in a cyclic pattern called

the respiratory cycle

• One respiratory cycle consists of

inhalation and exhalation

Changes in Pressure

760

756

760

760

754

759

760

756

761

Atmospheric pressure:

Intrapleural pressure:

Intrapulmonary pressure:

Beforeinhalation

During inhalation(lungs expanded)

Duringexhalation

Inhalation

• Diaphragm flattens • External intercostal

muscles contract• Volume of thoracic

cavity increases• Lungs expand• Air flows down pressure

gradient into lungs

Normal (Passive) Exhalation

• Muscles of inhalation relax

• Thoracic cavity recoils

• Lung volume decreases

• Air flows down pressure gradient and out of lungs

Active Exhalation

• Muscles in the abdomen and the internal intercostal muscles contract

• This decreases thoracic cavity volume more than passive exhalation

• A greater volume of air must flow out to equalize intrapulmonary pressure with atmospheric pressure

Lung Volume

• Tidal volume is 500ml of air

• Vital capacity is tidal volume, plus inspiratory

reserve and expiratory reserve

• This is still less than total lung capacity

• Lungs are never fully deflated

Respiratory Membrane

• Area between an alveolus and a pulmonary capillary

• Oxygen and carbon dioxide diffuse across easily

alveolarepithelium

capillaryendothelium

fusedbasementmembranesof bothepithelialtissues

Oxygen Transport

• Most oxygen is carried bound to hemoglobin in red blood cells

• Hemoglobin has a great affinity for oxygen when it is at high partial pressure (in pulmonary capillaries)

• Lower affinity for oxygen in tissues, where partial pressure is low

Carbon Dioxide Transport

• Most carbon dioxide is transported as bicarbonate

• Bicarbonate formation is enhanced by the action of carbonic anhydrase inside red blood cells

• Smaller amounts are transported dissolved in blood and bound to hemoglobin

Bicarbonate Formation: A Two-Step Reaction

• Carbon dioxide combines with water to form carbonic acid

CO2 + H2O ---> H2CO3

(catalyzed by carbonic anhydrase)

• Carbonic acid releases a hydrogen ion

to form bicarbonate

H2CO3 ---> H+ + HCO3-

Breathing Rhythm

• Diaphragm and intercostal muscles

under control of reticular formation

• One cell cluster controls inspiration, the

other expiration

• Resulting rhythm is fine tuned by

centers in the brain stem

Magnitude of Breathing

• Receptors in medulla detect H+

• Signal increase in rate and depth of

breathing

• Carotid bodies and aortic bodies detect

CO2, oxygen, and pH

• Signal increase in rate of breathing

Chemical Controls

• Increase in CO2 causes smooth muscle

of bronchioles to dilate

• Decrease in CO2 causes smooth

muscle of bronchioles to constrict

• Local controls also work on lung

capillaries

Apnea

• Breathing that stops and starts

• Sleep apnea is common in elderly

Effects of Smoking

• Shortened life expectancy

• Increased rates of cancers

• Increased rate of heart disease

• Impaired immune function and healing

• Detrimental to fetus