21 Respiratory SystemTaft College Human Physiology

Introduction• A steady supply of oxygen-O2 is required for metabolic reactions in

your body that release energy from food you consume and produce ATP in a process known as cellular respiration.

• One waste product of cellular respiration is carbon dioxide -CO2.

• High concentrations of CO2 produce an acid condition that can be toxic to cells and must be removed quickly.

• The cardiovascular and respiratory systems act together to supply O2 and eliminate CO2. The respiratory system provides the gas exchange – O2 in, CO2 out, the cardiovascular system provides transportation of the gases between the lungs and the body cells.

• If either system fails, even for a short time, disruption of homeostasis occurs with rapid cell death from starvation of O2 and a build up of waste products, especially CO2.

Functions of the Respiratory System1. Gas Exchange

• O2 into cells of body , CO2 out of cells.

• Surface for exchange - tiny air sacs = alveoli in the lungs surrounded by a dense network of capillaries.

• The oxygen moves by means of diffusion from high concentration in the alveoli to low concentration in the capillaries. At the same time, carbon dioxide moves by diffusion from high concentration in the blood capillaries to low concentration in the alveoli.

2. Protection

• The respiratory system warms and moistens air-prevents cold damage and drying.

• Respiratory system has two defense mechanisms against foreign materials inhaled in air.

• 1st – The tubing of the respiratory system contains cilia that act to sweep foreign materials up to the throat where they can be swallowed. Nicotine anesthetizes the ciliaand prevents the cilia from performing their function!

• 2nd – The alveoli contain macrophages that feed on foreign particulates.

Cilia

O2

CO2

Macrophages

Gas

Exchange

Functions of the Respiratory System

3. Sense of Smell

• Receptors for sense of smell are located in the nasal cavity.

4. Voice production

• Vocal cords in larynx can be stretched and made to vibrate when air is directed over them.

5. pH regulation

• CO2 is an acid producing compound and toxic in high concentrations.

• pH must be maintained in narrow range.

• CO2 is quickly removed from the body primarily by exhaling, and can be hastened by deep and rapid breathing.

Respiration• The term respiration is used in a number of ways in dealing with the

exchange of gases. We will differentiate between these using these terms:

1. Pulmonary Respiration (Ventilation): Gas exchange between environment lungs

• 2 Phases: Inhalation/Inspiration: intake (inhale)

Exhalation/Expiration: output (exhale)

2. External Respiration: Exchange between

• Lungs Blood

O2 into blood, CO2 into alveoli

3. Internal Respiration: Blood Body Cells

4. Cellular Respiration: Actual utilization of O2 within body cells in metabolic processes to make ATP, which gives off CO2 as a waste product.

Respiration

4. Cellular Respiration: Metabolic process within cells.

• Utilization of O2 in metabolic processes to make ATP, which gives off CO2 as a waste product.

C6H12O6 + 6 O2 6CO2 + 6H2O + 36 ATP

Summary of Terms of Respiration

Components of the Respiratory System

(2 Divisions)

1. Conduction Division

• Function: conducts air and humidifies, cleanses, warms in the process.

• Tubing lined with pseudostratified ciliated columnar epithelium

• Walls are too thick for exchange of gases = dead air (nonexchangeable).

• Anatomical dead space = about 150 ml air. = amount of air taken in with each breath that is not available for gas exchange.

• Structures in descending order:– Nasal Cavities

– Pharynx (throat) (pharyngitis = inflammation)

– Larynx (voice box) (laryngitis = inflammation)

– Trachea (windpipe)

– Bronchi branches into bronchioles

Components of the Respiratory System

(2 Divisions)

2. Respiratory Division = Alveoli of Lungs

• Functions:

• Cleans alveoli using macrophages.

• Gas diffusion.– Lungs with tiny thin walled alveoli.

Alveoli are where the exchange of gases occurs (simple squamous epithelium).

• Human lung = 300 million alveoli with 70 m2 surface area for gas exchange. 40x surface area of body.

• If alveoli are non functional in particular area = Physiological Dead Space.

• Physiological Dead Space may be as high as 1-3 liters in conditions of asthma (smooth muscle spasm) and emphysema (alveoli destroyed, elastic tissue destroyed).

1 M

X 70

Other Important Components of Respiratory System

Respiratory Muscles of Inspiration –important muscles for air intake.

Inspiration is an active process.

Inspiration results from contraction of muscles.

• External Intercostals

– Located between ribs. Increase size of thoracic cavity horizontally, by pulling the ribs superiorly and the sternum anteriorly.

• Diaphragm

– Increases size of thoracic cavity vertically.

– Diaphragm is naturally domed.

– When contracted it flattens out, about 1 cm in normal breathing (0.5 L (tidal volume), creates a 1-3 mm Hg difference from atmospheric pressure (760 mm Hg).

– Difference is up to 10 cm in strenuous breathing (2-3 L, 100mm difference).

Other Important Components of Respiratory System

Muscles - Important for inspiration (air intake,

inhalation).

• Diaphragm

– Boyle’s law states that when a container of gas

increases in size the pressure of the gas inside

decreases.

– So atmospheric gas (now at a greater relative

pressure) will move into the container (the lungs).

– The lungs adhere strongly to the expanding plural

cavity the because of subatmospheric pressure

(756 mm Hg) and surface tension created by their

moist adjoining serous membranes.

– The intrapleural space is a closed sac and does

not communicate with the lung space.

– So, it maintains its subatmospheric pressure at all

times.

– In this way the lungs become stretched and

increase in volume as the diaphragm is lowered.

– Accounts for 75% of air movement.

Expanding Lung=

Reduced pressure

Recoiling Lung=

Increased pressure

Other Important Components of Respiratory System

Expiration

Expiration is a passive process which requires no muscular activity.

Expiration results from elastic recoil of lungs and chest wall with

2 contributing factors:

1. Elastic tissue of the lung is stretched during inspiration and

recoils back to resting size.

When the lung is easy to stretch it is termed ‘high compliance’.

2. Surface tension is the inward pull on alveoli due to surface tension of alveolar

fluid. This accounts for 2/3 of recoil.

• Alveolar fluid consists of surfactant (phospholipids and lipoproteins) and water

which are secreted by type II alveolar cells. (Type 1 cells are for gas exchange).

– Without surfactant alveoli would flatten and collapse upon each

expiration and it takes great effort to reopen them during the next inspiration.

– **So, during expiration the alveoli become smaller but do not collapse.

– The air left in alveoli and airway following maximal exhalation is termed the

residual volume of the lungs.

• The decreased volume of the lungs, increases the pressure of the gases

to about 762 mm, so gases move out into atmosphere (760 mm).

<1 Atm = air in

>1 Atm = air out

1 Atmosphere

Pressure =

760 mmHg

• Premature infants tend to have less surfactant and have

difficulty breathing (respiratory distress syndrome (RDS))

due to collapsing alveoli.

– Surfactant starts being made about week 25 and is complete by

week 35 (6 weeks before normal delivery)

– When baby is born with low surfactant, can introduce

pharmaceutical surfactant with assisted ventilation.

– This can be checked by amniocentesis.

• Expiration is normally passive but may be active under

conditions of rapid and forceful breathing.

– The internal intercostals depress the ribs and the abdominal

muscles (rectus abdominis, transverse abdominis, and int. and

ext. obliques) compress the abdomen to raise the diaphragm.

Exchange of AirAdult Male (Female) Lung Volumes and Capacities

500 ml Tidal Volume (TV)– The air exchanged in a single breath during normal breathing.

3100 ml Inspiratory Reserve Volume (IRV) (1900 ml – Female)– The air that can be maximally inhaled over and above tidal volume.

– It is caused by maximal contraction of the diaphragm, external intercostals, and other accessory inspiratory muscles.

1200 ml Expiratory Reserve Volume (ERV) (700 ml – Female)– The air that can be actively exhaled beyond normal tidal volume.

Spirogram =

recording of

lung volumes

and

capacities.

Spirometer =

Apparatus to

measure lung

volumes and

capacities

Exchange of AirLung Volumes and Capacities - Adult Male (Female) Volumes

1200 ml Residual Volume (RV) (1100 ml Female)– The volume of air remaining in lungs after maximal, forced expiration. It

includes the volume of the non collapsible airway plus slightly inflated alveolar volume.

– This volume cannot be directly measured by a spirometer because it does not move in and out of the lungs.

4800 ml Vital Capacity (VC) (3100 ml Female)– The maximum volume of air that can be exhaled in a single breath

following maximal inhalation.

– VC represents the maximal volume change possible within the lungs.• It is rarely used because the contractions involved are so exhausting.

• It is useful to determine the functional capacity of the lungs.

Exchange of Air

Lung Volumes and Capacities (Adult volumes)

4800 ml Vital Capacity (VC) = Inspiratory reserve volume (IRV) + Tidal volume (TV) + Expiratory reserve volume (ERV).

6000 ml Total Lung Capacity (TLC) = 6 Liters (4200 ml Female)

• The maximum volume of air that the lungs can hold.

• TLC = vital capacity (VC) + residual volume (RV).

• Total amount of air in lungs.

• Gives an idea of total lung size.

• Normal Breathing Rate• Normal Breathing Rate x Tidal Volume = Minute Volume of Respiration

(MVR)= amount of air drawn in per minute.

• Normal breathing rate is about 12 breaths/min. Given a tidal volume of 500 ml:

12 x 500 = 6000 ml (6 L)/min of air = respiration minute volume.

• Not all of tidal volume is available for gas exchange (only about 350 ml). About 150 ml/breath remains in anatomical dead space (conducting airways such as the nose, pharynx, larynx, trachea, bronchi, bronchioles, terminal bronchioles).

• Alveolar Ventilation Rate• Normal Breathing Rate x (Tidal volume – Anatomical Dead Space (VD)) =

Alveolar Ventilation Rate (AVR) = amount of air available for exchange per minute.

• 12 breaths/min x 350 ml (tidal volume (500) – anatomical dead space (150)) = 4200ml/min.

• Effect of Exercise• In maximal exercise, increased respiratory rate to 50 breaths/min and

increased depth, > 200 L/min.

Composition of Gases(Atmosphere vs. Body)

Atmosphere

Nitrogen (N2) 78%

Oxygen (O2) 21%

Carbon dioxide (CO2) 0.04%

Rare gases 0.9%

• Gas exchange in the lungs takes place by simple diffusion. No ATP is used.

• Gases are traditionally measured by their pressure rather than by their percentage in the body or atmosphere.

• Dalton’s law states that the pressure created by a mixture of gases is determined by the sum of all the individual gases present. So, the partial pressure of each gas (denoted by a ‘p’) can be easily determined as follows:

• Partial pressure in mm Hg = % of gas present in mixture x total pressure

• Examples:

– pO2 = 0.21 x 760 mm Hg = 160 mm Hg of pressure

– pN2 = 0.78 x 760 mm Hg = 593 mm Hg of pressure

– pCO2 = 0.0004 x 760 mm Hg = 0.3 mm Hg pressure

• The gases diffuse according to the pressure found on each side of a membrane, from higher partial pressure (concentration) to lower partial pressure.

Note: 760 mm Hg is

atmospheric pressure

at sea level

Major idea:

• Oxygen moves from lungs (alveoli) to blood to body tissues by diffusion.

• Carbon dioxide moves from body tissues to blood to alveoli by diffusion.

• In blood, gases move by bulk flow due to blood pressure.

• Gases move in/out of the conducting portion respiratory tubing by bulk flow.

Composition of Gases(Atmosphere vs. Body)

Major idea:

Oxygen moves from

lungs (alveoli) to blood

to body tissues by

diffusion.

Carbon dioxide moves

from body tissues to

blood to lungs (alveoli)

by diffusion.

In blood, gases move

by bulk flow due to

blood pressure.

Gases move in/out of

the respiratory tubing

by bulk flow.

• The predominate gas in the air you breathe is Nitrogen (78%).Usually nitrogen gas has little effect as you breathe in 78% nitrogen and exhale 78% nitrogen.

• Nitrogen can be a problem under higher than normal pressures as in deep diving.

• It may cause nitrogen narcosis or ‘rapture of the deep’.

• If a diver comes up faster than the lungs can eliminate it, nitrogen gas bubbles form in the blood and tissues = decompression sickness. Treat by using a decompression (hyperbaric) chamber. Gas bubble formation from the decreased pressure is the same thing that happens when you open a soda (or beer for those of you unfamiliar with soda).

• A hyperbaric chamber can be used for hyperbaric oxygenation.It uses high pressure O2 (3-4x atmospheric pressure, 2280-3040 mm Hg), can be used to treat anaerobic infection (tetanus, gangrene), crush injury, CO poisoning, burns, smoke inhalation, near drowning, and others.

Composition of Gases(Atmosphere vs. Body)

Transport Of The Gases By The Blood

Oxygen Transport• O2 is transported by the hemoglobin molecule found in RBC’s.

• The O2 actually binds to the 4 iron (Fe) atoms found in the hemoglobin

molecule.

• When the binding takes place the hemoglobin molecule changes color.

• This accounts for the bright red color of blood in the systemic arteries vs.

darkish red colors of the blood in the systemic veins.

Fetal Hemoglobin (Hb-F) has a higher affinity for O2 than does maternal Hgb

(Hb-A) so the fetus will pick up O2 in the placenta readily.- helps prevent

hypoxia in fetus.

Carbon Dioxide Transport• CO2 is carried in 3 main forms in the blood:

• 1. Dissolved CO2 – 9%. This is the portion that can diffuse into the

alveoli.

• 2. Carbaminohemoglobin HbCO2- 13%. Binds to globin portion.

• 3. CO2 is primarily carried in blood as Bicarbonate ion HCO3- -78%.

– An enzyme (called carbonic anhydrase) present in RBCs is responsible for the

left side of this reaction.

CA

• CO2 + H2O H2CO3 H+ + HCO3-

Carbonic acid bicarbonate ion

*Notice that C02 and H+ concentrations can be regulated in this manner.

• An increase in CO2 leads to an increase in H+ = Increased Acid

• An increase in H+ can lead to more CO2 which is blown off in the lungs with H2O.

• What will this do to the pH of the blood?— The increase in H+ lowers the pH (more acidic), The elimination of CO2 raises pH (less acidic).,

• ** The lung through its elimination of CO2 is a prime regulator of pH of the blood.

Control of Breathing

• What determines rate and depth of breathing?

• The amount of oxygen present has very little effect on your rate of breathing. – An increase in CO2, decrease in pH, and to

a lesser extent a decrease in oxygen will stimulate the CNS and peripheral (aorta and carotid) chemoreceptors.

• The chemoreceptors will send impulses to the respiratory center of the medulla oblongata that controls the diaphragm via the phrenic nerve. The medulla will act to increase tidal volume and respiratory rate.

Acid Base Balance• The body produces acids during metabolism of glucose, fatty acids, and

amino acids, so a huge excess of H+ is produced that would rapidly lead to death.

The body has 3 mechanisms to remove H+ from body fluids and then eliminate them:

1. Buffer systems.

Buffers bind up reactive H+ to remove them from solution temporarily.

• Proteins are the most abundant buffer with both an amino and acid group,

carbonic acid we have already discussed, and phosphates. Hemoglobin is a

good buffer.

2. Exhalation of CO2 and H2O .

Increased ventilation will blow off CO2, which lowers the carbonic acid level and raise the pH.

Where does the H+ go if CO2 has no H? It blows off in the water vapor.

3. Kidney excretion

Slow mechanism (hours to days) but only way to remove acids other than carbonic acid.

Death is caused quickly without the contribution of the kidney in removal of these acids.

Methods of Compensation for Acid ImbalanceCondition Common Cause Compensatory

Mechanism

Respiratory

acidosis

Hypoventilation due to

emphysema, airway

obstruction, muscle

dysfunction, etc.

Renal: increased

excretion of H+ with

resorption of

bicarbonate.

pCO2 stays high.

Respiratory

alkalosis

Hyperventilation due to oxygen

deficiency, pulmonary

disease, anxiety, other

causes.

Renal: decreased H+

excretion with

decreased bicarbonate

resorption. pCO2 low.

Metabolic

acidosis

Loss of bicarbonate ions due to

diarrhea, accumulation of

acid (ketosis), renal

dysfunction.

Respiratory:

hyperventilation, with

loss of CO2.

HCO3- low.

Metabolic

alkalosis

Loss of acid due to vomiting,

gastric suctioning, diuretic

use, intake alkaline drugs.

Respiratory:

hypoventilation with

less CO2 loss.

HCO3- high.

Pulmonary Disorders

• Pulmonary disorders are a major threat to 10% to 15% of persons over age 40, especially to those individuals in a heavily polluted environment.

• Many chronic lung diseases share some degree of obstruction of the airways. The general term COPD (chronic obstructive pulmonary disease) is used to refer to a patient’s condition when the airway is compromised. The Expiratory Reserve Volume will be reduced in these patients.

Pulmonary Disorders

Black lung disease

• Exposure to air with various tiny dust particles: coal, silicates including asbestos, grain, insulation.

• Originally named for coal miner’s lung disease. Very small dust particles accumulate and attract macrophages. The continual activation of macrophages causes local damage which reduces diffusion through the alveolar walls (emphysema).

• The dust can be deposited in the walls of the alveoli and lead to inelasticity of the alveolar walls.

• Bronchioles may become scarred and inflamed which cause airway obstruction.

• Carcinoma may be an outcome depending on the type of dust (asbestos) and coexistent risk (use of cigarettes) exposure.

Pulmonary Disorders

Asthma

• Smooth muscles of the bronchiolesundergo contraction or spasm— it restricts and prevents alveolar ventilation as the airway is partially or completely closed. Often mucous secretion is excessive that further compounds the problem by clogging the respiratory airway.

• Asthma may be due to allergies, exercise, stress, pollutants, or cold air, all of which causes spasms of bronchioles. These can act together, so on a smoggy day, exercise may need to be avoided.

• Relief is achieved from inhaling muscle relaxants (epinephrine, ephedrine & isoproterenol) or steroids (anti-inflammatory) or removing the patient from the polluted environment.

Pulmonary Disorders

Carbon Monoxide Poisoning

• CO, a colorless, odorless, tasteless gas, is produce during combustion. It has an attraction with hemoglobin 200x stronger than O2, so prevents O2 from binding.

• A concentration of only 0.1% will combine with 50% of O2 binding sites which leads to hypoxia.

• Administration of 100% O2 will help recovery.

• So, get a CO detector in your home!

Pulmonary Disorders

Emphysema

• Alveolar walls disintegrate producing larger air spaces that remain filled with air during expiration. Elastic fibers are lost, so elasticity of lung alveoli is reduced with lack of ability to recoil properly.

• Reduced surface area also reduces diffusion of O2 into capillaries.

• Although inhalation is easy, these individuals cannot exhale properly. They must voluntarily exhale to remove more air from the lungs. . A ‘barrel chest’ may develop over time as chest cage is enlarged from repeated exaggerated breathing

• Mild activity or exercise leaves these people breathless as they cannot move enough O2 into the body for metabolic needs.