e. ALVEOLI (microscopic air sacs)

See Fig 19.15, page 750 & Fig 19.33, page 806.

m wall consist epithelial cells and macrophages

1. Type I Alveolar cells form a continuous simple squamous lining of the alveolar wall

2. Type II Alveolar cells interrupt above lining and secrete surfactant:

a. complex mixture = detergent;

b. lowers surface tension and prevents alveolar collapse.

3. Alveolar Macrophages remove dust particles and other debris from alveolar spaces.

*See scanning electron micrographs of alveoli on page 790.

f. Alveolar-Capillary (Respiratory) Membrane

See Fig 19.33, page 806.

m Composition:

1. simple squamous epithelium of alveolus

2. basement membrane of alveolus

3. endothelium of the lung capillary

4. basement membrane of lung capillary

m Structure = thin (0.5 um in thickness).

m m Function = allows for rapid diffusion of gases (from [high] to [low].

1. External Respiration.

* The lungs contain more than 300 million alveoli = SA of 70m² for gas exchange at one time!

g. Blood Supply to Lungs (two fold):

m pulmonary circuit (deoxygenated blood);

m Oxygenated blood is delivered through bronchial arteries (off thoracic aorta).

LECTURE II Respiratory Physiology

Review: Physical Science/Boyle’s Law

Primary difference between liquid and gas is interactions between the individual molecules of each

- in both molecules are in constant motion

- in a polar liquid molecules held closely together by weak attractions (hydrogen bonds)

- however, electrons tend to repel themselves; because molecules of liquids are close together, liquids tend to resist compression

- in gases, molecules bounce around as totally separate entities

- under normal atmospheric pressure gas molecules are farther apart than in a liquid – density of gas is lower

- the gas molecules are too far apart for weak interactions to occur – so applied pressure pushes gas molecules closer together – compression

- an air filled balloon at atmospheric pressure – pressure within the balloon results from collisions of gas molecules hitting that walls of the balloon; increased collisions = increased pressure

- when volume is reduced = increased collisions/unit time = increased pressure

- increased volume = less collisions/unit time= reduced pressure

- pressure and volume are INVERSELY RELATED; in particular it is reciprocal: double the pressure; volume will drop by half

reduce pressure by ½; volume will double

BOYLE’S LAW: P=1/V

Pressure and Air Flow to the Lungs

- air will flow from an area of higher pressure to an area of lower pressure

- this, along with Boyle’s Law, provides the basis for pulmonary ventilation

- inspiration and expiration involve changes in the volume of the lungs; these changes create pressure gradients that move air into and out of the respiratory tract

Pleural Cavity

Parietal pleura

Visceral pleura

- separated by pleural fluid (serous)

- these membranes are held together by the fluid film between them; as a result the surface of each lung “STICKS” to the inner chest wall and the superior surface of the diaphragm – thus each has a direct effect on the volume of the lungs

Alveoli

- in the alveoli, moist membranes have the opposite effect – water molecules create surface tension and they would stick together and collapse if not for SURFACTANT-lipoprotein produced by certain alveolar cells- reduces surface tension (reducing alveolar collapse)

Muscles of Breathing

- intercostals – between ribs

- diaphragm

- exhalation – abdominals act as accessory muscles

INSPIRATION EXHALATION

-start of breath = equal pressure; no air movement

Compliance of lungs

- indicator of lung expandability (decreased compliance=greater force needed to fill and empty lungs)

Factors Affecting Compliance:

1. connective tissue structure – loss of connective tissue from alveolar damage (emphysema) increases compliance

(oxygen enters more readily, but damage to alveoli restrict gas exchange)

2. amount of surfactant produced ( decreased surfactant, reduces compliance)

3. mobility of thoracic cage – arthritis reduces compliance

Artificial Respiration

- mouth-to-mouth resuscitation – when respiratory muscles no longer functioning

- CPR- cardiopulmonary resuscitation – when cardiovascular system is also nonfunctional

Modes of Breathing

- quiet breathing (eupnea)inhalation involves active muscle, exhalation passive

- forced breathing (hyperpnea) – active inhalation and exhalation

Respiratory Cycle

- single cycle of (1) inhalation and (1) exhalation

m Tidal Volume = amount (volume) of air that enters the lungs during normal inspiration and leaves the lungs during normal expiration; approximately 500 ml;

m Inspiratory Reserve Volume (IRV) = the amount of air the can be forcibly inhaled after a normal tidal expiration; approximately 3000 ml;

m Expiratory Reserve Volume (ERV) = the amount of air that can be forcibly exhaled after a normal tidal expiration; approximately 1100 ml;

m Vital Capacity (VC) = the maximum amount of air that can be exhaled after a maximum inhalation;

VC = TV + IRV + ERV = 4600 ml.

m Residual Volume = amount of air that always remains in lungs; 1200 ml;

m Total Lung Capacity = VC + RV; approximately 6 L.

See Summary Table 19.4, page 799.

Pulmonary Function Tests

The above can be measured by a spirometer (except residual air)

Pneumotachometer – measures rate of air movement in respiratory cycle

Peak flow meter- air rate during forced exhale

Respiratory Problems

1. pneumothorax – injury to chest wall that penetrates parietal pleura

a. allows air to enter pleural cavity

b. breaks fluid bond between pleurae

c. allows lungs to recoil -atelectasis (Collapsed Lung)

d. treatment: removal of air and sealing opening

2. Respiratory Distress Syndrome (RDS) in newborns (collapsed lungs) occurs due to the lack of surfactant in the alveoli

Respiratory Rates = #breaths/minute

Resting adult = 12-18 breaths/minute

Children = 18-20 breaths/min.

Respiratory Minute Volume

- amount of air moved per minute (moved through respiratory tract)

respiratory minute volume = respiratory rate X tidal volume

12 X 500ml = 6000ml/minute = 6.0 l/minute

Alveolar Ventilation

- typical inspiration = 500 ml air

- first 350 reaches alveoli, last 150 never makes it (remains in passageways) anatomical dead space – does not participate in gas exchange with blood

- alveolar ventilation – amount of air actually reaching alveoli each minute

- because air (inhale) mixed with that of dead space, air actually reaching alveoli has less oxygen and more carbon dioxide than atmospheric air entering

Nonrespiratory Air Movements

Modified respirattory movements occur in addition to normal breathing; usually the result of reflexes.

a. Cough = sends blast of air through and clears upper respiratory tract;

b. Sneeze = forcefully expels air through nose & mouth;

c. Laugh = a deep breath released in a series of short convulsive expirations;

d. Hiccup = spasmodic contraction of diaphragm;

e. Yawn = deep inspiration through open mouth; (ventilates alveoli?).

CHAPTER 19: RESPIRATORY SYSTEM : Lecture 3

Control of Breathing

A. Normal breathing = rhythmic; involuntary.

B. Nervous Control = Respiratory Center:

1. located in pons & medulla of brain stem;

a. See Fig 19.28, page 802.

2. Rhythmicity area = medulla:

a. composed of dorsal respiratory group which controls the basic rhythm of breathing;

b. ventral respiratory group which controls forceful breathing.

3. Pneumotaxic area = pons:

a. controls rate of breathing.

* See Fig 19.29, page 802 for Summary of Nervous Control of Breathing

C. Chemical Regulation See Fig 19.30, page 803.

1. Chemoreceptors; sensitive to:

a. Low levels of oxygen;

b. High levels of CO₂ ;

- affect chemosensitive areas of respiratory center and breathing rate increases.

c. Effector Sites:

- diaphragm/intercostals

- smooth muscle of terminal bronchioles

d. Hyperventilation

- rapid, shallow breathing increases O₂ level;

- breathing into paper bag rich in CO₂ normalizes gas concentrations

D. Factors that influence breathing:

See Table 19.6, page 804.

1. Stretch of Tissues;

2. Low blood oxygen;

3. High Blood carbon dioxide;

4. Low pH;

5. Others: temperature, pain, irritation of airways.

EXTERNAL RESPIRATION: See Fig 19.33, page 806, and Fig 19.35, page 807.

A. Definition = exchange of oxygen and carbon dioxide between alveoli and lung

B. The pressure of gas determines the rate at which it will diffuse from region to region (Dalton's Law).

C. Air is a mixture of gases:

1. 78% Nitrogen

2. 21% Oxygen

3. .04% Carbon Dioxide

4. .96% other

D. In a mixture of gases, the amount of pressure that each gas creates = partial pressure.

In air: O₂ = 21%; P_O2 = 104 mm Hg

CO₂ = .04%; P_CO2 = 40 mm Hg

E. The partial pressure of a gas is directly related to the concentration of that gas in a mixture.

F. Diffusion of gases through the respiratory membrane proceeds from where a gas is at high pp ------> low pp.

Alveolus

P_CO2 = 40 mm Hg P_O2 = 104 mm Hg

__________________________________________________________________

P_CO2 = 45 mm Hg P_O2 = 40 mm Hg

Capillary

Therefore, CO₂ will flow from lung capillary -------> alveolus &

O₂ will flow from alveolus -------> lung capillary.

G. The rate of diffusion of gases also depends on a number of factors, including the following:

1. gas exchange surface area;

2. diffusion distance;

3. breathing rate and depth.

VI. Internal Respiration

A. Definition = the exchange of oxygen and carbon dioxide between tissue blood capillaries and tissue cells.

B. In tissue cell: pCO₂= 45; pO₂ = 40;

In tissue cap: pCO₂ = 40; pO₂ = 95.

C. Therefore, oxygen moves from the tissue cap into the tissue cell and carbon dioxide moves from the tissue cell into the tissue cap.

Transport of Gases (in Blood)

A. Oxygen

1. binds with hemoglobin (Hb) in red blood cells to form oxyhemoglobin;

2. A weak bond is formed so oxygen can be delivered (released into) to tissues when needed.

3. The release of oxygen from hemoglobin depends on many factors:

a. high blood [CO₂];

b. low blood pH (acidity);

c. high blood temperature.

* To remember these conditions, think of what happens in a skeletal muscle during exercise, when oxygen is required.

4. Carbon Monoxide (CO) binds to hemoglobin more efficiently than oxygen.

a. If the hemoglobin (that is suppose to bind with oxygen) is bound to CO, much less Hb is available to bind and transport oxygen to the tissues; Hypoxia results.

b. See introduction on page 779 and purple box on page 810..

B. Carbon Dioxide (CO₂)

1. CO₂ is transported in 3 forms:

a. dissolved CO₂= 7%

b. carbaminohemoglobin= 23%

c. bicarbonate ions= 70%

2. In tissues, CO₂ is produced by cellular respiration.

a. This CO₂ combines with H₂O to form H₂CO₃ (Carbonic acid)

which then

b. dissociates under the influence of carbonic anhydrase to release

c. H⁺ and bicarbonate ion(HCO₃^-):

CO₂ + H₂O <------> H₂CO₃ <-------> H⁺ + HCO₃^-

* RXN is reversed in lungs & CO₂ is expelled during expiration.

Life Span Changes

A. Exposure to pollutants, smoke, etc, increases the risk of developing respiratory illnesses.

B. Loss of cilia, thickening of mucus, and impaired macrophages increases the risk of infection as one ages.

C. Breathing becomes more difficult as one ages due to:

1. calcified cartilage

2. skeletal changes

3. altered posture

4. replacement of bronchiole smooth muscle by fibrous connective tissue.

D. Vital Capacity decreases with age.

Homeostatic Imbalances: Disorders of the Respiratory System

A. Deviated Septum. See purple box on page 780.

B. Effects of Cigarette Smoking. See Clinical Application 19.1, pages 782-783.

C. Epiglottitis. See purple box on page 785.

D. Cystic Fibrosis. See purple box on page 790.

E. Lung Irritants. See Clinical Application 19.2, page 793.

F. Respiratory Distress Syndrome. See purple box on page 795.

G. Pneumothorax. See purple box on page 796.

H. Respiratory Disorders that Decrease Ventilation. See Clinical Application 19.3, page 801.

I. Altitude Sickness. See purple box on page 807.

J. Disorders Impairing Gas Exchange. See Clinical Application 19.5, pages 808-809.

Other Interesting Topics Concerning the Respiratory System

A. Tracheostomy. See page 785 and Fig 19.11, page 787.

B. Bronchoscopy. See purple box on page 789.

C. Artificial Respiration. See purple box on page 790.

D. Exercise and Breathing. See Clinical Application 19.4, page 805.