1

23-1

Chapter 23Respiratory System

23-2

Respiration

• Ventilation: Movement of air into and out of lungs

• External respiration: Gas exchange between air in lungs and blood

• Internal respiration: Gas exchange between the blood and tissues

• Cellular respiration: “burning” nutrients in mitochondria to get ATP

2

23-3

Nose and Nasal Cavities• External nose• Nasal cavity

– From nares to choanae– Vestibule: just inside nares– Hard palate: floor of nasal

cavity– Nasal septum: partition

dividing cavity. Anterior cartilage; posterior vomer and perpendicular plate of ethmoid

– Conchae: bony ridges or ‘shelves’ with meatusesbetween.

23-4

Functions of Nasal Cavity

• Passageway for air• Cleans the air• Humidifies, warms air• Smell• Along with paranasal sinuses are

resonating chambers for speech

3

23-5

Pharynx• Common passageway for digestive and respiratory systems

• Three regions– Nasopharynx: pseudostratified

columnar epithelium with goblet cells. Mucous and debris is swallowed.. Floor is soft palate, uvula is posterior extension of the soft palate.

– Oropharynx: shared with digestive system. Lined with moist stratified squamous epithelium.

– Laryngopharynx: epiglottis to esophagus. Lined with moist stratified squamous epithelium

23-6

Functions of Larynx• Maintain an open passageway for air movement:

thyroid and cricoid cartilages• Epiglottis and vestibular folds prevent swallowed

material from moving into larynx• Vocal folds are primary source of sound

production. Greater the amplitude of vibration, louder the sound. Frequency of vibration determines pitch.(Arytenoid cartilages and skeletal muscles determine length of vocal folds and also abduct the folds when not speaking to pull them out of the way making glottis larger.)

4

23-7

Vocal Folds

23-8

Tracheobronchial Tree and

Conducting Zone

• Trachea to terminal bronchioles which is ciliated for removal of debris. – Trachea divides into two primary

bronchi. – Primary bronchi divide into

secondary bronchi (one/lobe) which then divide into tertiary bronchi.

– Tertiary bronchi further subdivide into smaller and smaller bronchithen into bronchioles (less than 1 mm in diameter), then finally into terminal bronchioles.

• Cartilage: holds tube system open; smooth muscle controls tube diameter.

• As tubes become smaller, amount of cartilage decreases, amount of smooth muscle increases

5

23-9

Respiratory Zone: Respiratory Bronchioles to Alveoli

• Respiratory zone: site for gas exchange– Respiratory bronchioles

branch from terminal bronchioles. ( Alveolar ducts end as alveolar sacs that have 2 or 3 alveoli at their terminus.)

– No cilia, but debris removed by macrophages. (Macrophages then move into nearby lymphatics or into terminal bronchioles)

23-10

The Respiratory Membrane• Three types of cells in membrane.

– Type I pneumocytes. Thin squamous epithelial cells, form 90% of surface of alveolus. Gas exchange.

– Type II pneumocytes. Round to cube-shaped secretory cells. Produce surfactant. (Discuss later)

– Dust cells (phagocytes)• Layers of the respiratory membrane

– Thin layer of fluid lining the alveolus– Alveolar epithelium (simple squamous

epithelium– Basement membrane of the alveolar

epithelium– Thin interstitial space– Basement membrane of the capillary

endothelium– Capillary endothelium composed of

simple squamous epithelium• Tissue surrounding alveoli contains elastic

fibers that contribute to recoil.

6

23-11

Thoracic WallsMuscles of Respiration

23-12

Pleura• Pleural cavity surrounds each lung and is formed by the pleural membranes. Filled with pleural fluid.

• Visceral pleura: adherent to lung. Simple squamous epithelium, serous.

• Parietal pleura: adherent to internal thoracic wall.

• Pleural fluid: acts as a lubricant and helps hold the two membranes closetogether (adhesion).

• Mediastinum: central region, contains contents of thoracic cavity except for lungs.

7

23-13

Ventilation• Movement of air into and out of lungs• Air moves from area of higher pressure to area of lower

pressure• General Gas Law: PV = nRT, where P = pressure, V =

volume, n = #gram-molecules of gas, R = gas constant, T = temperature.

• Pressure is proportionate to number of molecules and temperature

• P = nRT/V Pressure is inversely proportionate to volume

• (F = P1-P2/R where F = air flow, P1 and P2 are pressures in two different places, and R = resistance to flow.)

• If barometric pressure is greater than alveolar pressure, then air flows into the alveoli.

.

23-14

8

23-15

Alveolar Pressure Changes

23-16

Normal Breathing Cycle

9

23-17

Pulmonary Volumes and Capacities• Spirometry: measures volumes of air that move into

and out of respiratory system. Uses a spirometer• Tidal volume: amount of air inspired or expired with

each breath. At rest: 500 mL• Inspiratory reserve volume: amount that can be

inspired forcefully after inspiration of the tidal volume (3000 mL at rest)

• Expiratory reserve volume: amount that can be forcefully expired after expiration of the tidal volume (100 mL at rest)

• Residual volume: volume still remaining in respiratory passages and lungs after most forceful expiration (1200 mL)

23-18

Spirometer, Lung Volumes, and Lung Capacities

10

23-19

Minute Ventilation and Alveolar Ventilation

• Minute ventilation: total air moved into and out of respiratory system each minute; tidal volume X respiratory rate

• Respiratory rate (respiratory frequency): number of breaths taken per minute

• (Anatomic dead space: formed by nasal cavity, pharynx, larynx, trachea, bronchi, bronchioles, and terminal bronchioles

• Physiological dead space: anatomic dead space plus the volume of any alveoli in which gas exchange is less than normal.)

• Alveolar ventilation (VA): volume of air available for gas exchange/minute

23-20

Physical Principles of Gas Exchange• Partial pressure

– The pressure exerted by each type of gas in a mixture

– Dalton’s law: in a mixture of gases, the percentage of each gas is proportionate to its partial pressure

– Air in the respiratory system contains humidity because of mucus lining system

• Diffusion of gases through liquids– Henry’s Law: Concentration of a gas in a liquid is

determined by its partial pressure and its solubility coefficient

11

23-21

Physical Principles of Gas Exchange• Diffusion of gases through the respiratory membrane

depends on these things:1. Membrane thickness. The thicker, the lower the

diffusion rate2. Diffusion coefficient of gas (measure of how easily a

gas diffuses through a liquid or tissue). CO2 is 20 times more diffusible than O2, surface areas of membrane, partial pressure of gases in alveoli and blood

3. Surface area. Diseases like emphysema and lung cancer reduce available surface area

4. Partial pressure differences. Gas moves from area of higher partial pressure to area of lower partial pressure. Normally, partial pressure of oxygen is higher in alveoli than in blood. Opposite is usually true for carbon dioxide

23-22

Gas Exchange

12

23-23

Hemoglobin and Oxygen Transport• Oxygen is transported by

hemoglobin (98.5%) and is dissolved in plasma (1.5%)

• Oxygen-hemoglobin dissociation curve: describes the percentage of hemoglobin saturated with oxygen at any given PO2

• Oxygen-hemoglobin dissociation curve at rest shows that hemoglobin is almost completely saturated when PO2 is 80 mm Hg or above. At lower partial pressures, the hemoglobin releases oxygen.

23-24

Curve During Exercise

13

23-25

Effects of CO2 and Temperature

• Increase in PCO2 causes decrease in pH• Carbonic anhydrase causes CO2 and water

to combine reversibly and form H2CO3which ionizes to H+ and HCO3

-

• Increase temperature: decreases tendency for oxygen to remain bound to hemoglobin, so as metabolism goes up, more oxygen is released to the tissues.

23-26

Shifting the Curve

14

23-27

Carbon Dioxide Transport and Chloride Movement(a) Tissue capillaries: as CO2 enters red

blood cells, reacts with water to form bicarbonate and hydrogen ions. Chloride ions enter the RBC and bicarbonate ions leave: chloride shift. Hydrogen ions combine with hemoglobin. Lowering the concentration of bicarbonate and hydrogen ions inside red blood cells promotes the conversion of CO2 to bicarbonate ion.

(b) Pulmonary capillaries: CO2 leaves red blood cells, resulting in the formation of additional CO2 from carbonic acid. The bicarbonate ions are exchanged for chloride ions, and the hydrogen ions are released from hemoglobin.

• Increased plasma carbon dioxide lowers blood pH. The respiratory system regulates blood pH by regulating plasma carbon dioxide levels

23-28

Respiratory Structures in Brainstem

• Medullary respiratory center– Dorsal groups stimulate the

diaphragm– Ventral groups stimulate the

intercostal and abdominal muscles

• Pontine (pneumotaxic) respiratory group– Involved with switching

between inspiration and expiration

15

23-29

Modification of Ventilation• Apnea. Cessation of

breathing. Can be conscious decision, but eventually PCO2 levels increase to point that respiratory center overrides

• Hyperventilation. Causes decrease in blood PCO2 level. Peripheral vasodilation causes decrease in BP. Fainting. Problem before diving.

• Cerebral and limbic system. Respiration can be voluntarily controlled and modified by emotions

• Chemical control– Carbon dioxide is major

regulator, but indirectly through pH change

• Increase or decrease in pH can stimulate chemo- sensitive area, causing a greater rate and depth of respiration

– Oxygen levels in blood affect respiration when a 50% or greater decrease from normal levels exists

• CO2. – Hypercapnia: too much CO2– Hypocapnia: lower than normal

CO2

23-30

Modifying Respiration

16

23-31

Chemical Control of Ventilation• Effect of Carbon Dioxide: small change in carbon

dioxide in blood triggers a large increase in rate and depth of respiration– Hypercapnia: greater-than-normal amount of carbon

dioxide– Hypocapnia: lower-than-normal amount of carbon

dioxide• Chemosensitive area in medulla oblongata is more

important for regulation of PCO2 and pH• Carotid bodies respond rapidly to changes in

blood pH because of exercise

23-32

Regulation of Blood pH and Gases

17

23-33

Modifications of Ventilation

• Activation of touch, thermal and pain receptors affects respiratory center

• Sneeze reflex, cough reflex• Increase in body temperature yields increase

in ventilation• EXERCISE will increase it

23-34

Effects of Aging

• Vital capacity and maximum minute ventilation decrease

• Residual volume and dead space increase• Ability to remove mucus from respiratory

passageways decreases• Gas exchange across respiratory membrane

is reduced