1. Chapter 23
Respiratory System

2. Respiration Ventilation: Movement of air into and out of lungs
External respiration: Gas exchange between air in lungs and blood
Transport of oxygen and carbon dioxide in the blood
Internal respiration: Gas exchange between the blood and tissues

3. Respiratory System Functions
Gas exchange: Oxygen enters blood and carbon dioxide leaves
Regulation of blood pH: Altered by changing blood carbon dioxide levels (increase C O2 = decrease pH)
Voice production: Movement of air past vocal folds makes sound and speech
Olfaction: Smell occurs when airborne molecules are drawn into nasal cavity
Protection: Against microorganisms by preventing entry and removing them from respiratory surfaces.

4. Respiratory System Divisions
Upper tract: nose, pharynx and associated structures
Lower tract: larynx, trachea, bronchi, lungs and the tubing within the lungs

5. Nose (Nasus) and Nasal Cavities
External nose (visible part – includes hyaline cartilage plates & nasal bones )
Nasal cavity
From nares (nostrils) to choanae (openings into the pharynx)
Vestibule: just inside nares – lined with stratified squamous epithelium – continuous with skin
Hard palate: floor of nasal cavity – separates nasal cavity from oral cavity – covered by mucous membrane
N asal septum: partition dividing cavity. Anterior cartilage; posterior vomer and perpendicular plate of ethmoid (divides nasal cavity into right & left parts)
C hoanae: bony ridges on lateral walls with meatuses (passageways) between. Openings to paranasal sinuses and to nasolacrimal duct

6. Functions of Nasal Cavity:
Passageway for air (open even if mouth full of food)
Cleans the air [vestibule lined with hair & this traps particles / mucous membrane consists of pseudostratified ciliated columnar epithelium with goblet cells (mucus)]
Humidifies( moisture from mucous membranes & from excess tears that drains into nasal cavity through nasolacrimal duct), warms air ( warm blood flowing through mucous membranes - this prevents damage to respiratory passages caused by cold air)
Smell [superior part of nasal cavity consists of olfactory epithelium (sensory receptors)]
Along with paranasal sinuses are resonating chambers for speech

7. Pharynx:
Common opening for digestive and respiratory systems (connected to respiratory at larynx & to digestive at esophagus)
Three regions
Nasopharynx:
a. Pseudostratified columnar epithelium with goblet cells.
b. Mucous and debris from nasal cavity is swallowed.
c. Openings of Eustachian (auditory) tubes – air that passes through them to equalize air pressure between atmosphere & middle ear.
d. Floor is soft palate (separates nasopharynx from oropharynx), uvula is posterior extension of the soft palate – prevents swallowed materials from entering nasopharynx & nasal cavity
Oropharynx: shared with digestive system (extends from soft palate to epiglottis). Lined with moist stratified squamous epithelium – air, food, & drink passes through.
Laryngopharynx: epiglottis to esophagus. Lined with moist stratified squamous epithelium – food & drink pass through here to esophagus (very little air passes /
too much air = gas)

8. Larynx

9. Larynx - base of tongue to trachea / passageway for air
Unpaired cartilages
Thyroid: largest, Adam’s apple
Cricoid: most inferior, base of larynx (other cartilages rest here)
Epiglottis: attached to thyroid and has a flap near base of tongue. Elastic rather than hyaline cartilage
Paired
Arytenoids: attached to cricoid
Coniculate: attached to arytenoids
Cuneiform: contained in mucous membrane
Ligaments extend from arytenoids to thyroid cartilage
Vestibular folds or false vocal folds
True vocal cords or vocal folds: sound production. Opening between is glottis - laryngitis is an inflammation of mucosal epithelium of vocal folds

10. 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 – during swallowing, epiglottis covers the opening of larynx so, food & liquid slide over epiglottis toward esophagus. Also, closure of vestibular folds can also prevent the passage of air----when person holds breath.
Vocal folds are primary source of sound production. Greater the amplitude of vibration, louder the sound (force of air moving past vocal cords determines amplitude). - Frequency of vibration determines pitch. Also, length of vibrating segments of vocal folds affect ex: when only anterior parts of folds vibrate, higher pitched tones are produced & when longer sections of vibrate, lower tones result.
- Arytenoid cartilages and skeletal muscles determine length of vocal folds and also abduct the folds when not speaking (only breathing) to pull them out of the way making glottis larger (allows greater movement of air).
The pseudostratified ciliated columnar epithelium (lines larynx) traps debris, preventing their entry into the lower respiratory tract.

11. Vocal Folds

12. Trachea - windpipe
Membranous tube of dense regular connective tissue and smooth muscle; supported by hyaline cartilage C-shaped rings (protects & maintains open passageway for air) . Posterior surface is devoid of cartilage & contains elastic ligamentous membrane and bundles of smooth muscle called the trachealis.
Contracts during coughing-----this causes air to move more rapidly through trachea, which helps expel mucus & foreign objects.
Inner lining: pseudostratified ciliated columnar epithelium with goblet cells. Mucus traps debris, cilia push it superiorly toward larynx and pharynx.
Divides to form
Left and right primary bronchi (each extends to a lung)
Carina: cartilage at bifurcation (forms ridge). Membrane of carina especially sensitive to irritation and inhaled objects initiate the cough reflex

13. Tracheobronchial Tree and Conducting Zone
Trachea to terminal bronchioles which is ciliated for removal of debris.
Trachea divides into two primary bronchi. (right is larger in diameter & more in line with trachea than left)
Primary bronchi divide into secondary (lobar) bronchi (one/lobe) which then divide into tertiary (segmental) bronchi.
Bronchopulmonary segments: defined by tertiary bronchi.
Tertiary bronchi further subdivide into smaller and smaller bronchi then into bronchioles (less than 1 mm in diameter), then finally into terminal bronchioles.
Cartilage: holds tube system open; smooth muscle controls tube diameter-----
ex: during exercise, diameter increases, decreases resistance to airflow, increases volume of air moved
during asthma attack, diameter decreases, increases resistance to airflow, decreases volume of air flow
As tubes become smaller, amount of cartilage decreases, amount of smooth muscle increases------ex: terminal bronchioles have no cartilage & only have smooth muscle.

14. Respiratory Z one: Respiratory Bronchioles to Alveoli
Respiratory zone: site for gas exchange
Respiratory bronchioles branch from terminal bronchioles. Respiratory bronchioles have very few alveoli (small, air filled chambers where gas exchange between air & blood takes place). Give rise to alveolar ducts which have more alveoli. Alveolar ducts end as alveolar sacs that have 2 or 3 alveoli at their terminus.
Tissue surrounding alveoli contains elastic fibers (alveoli expand during inspiration & recoil during expiration)
No cilia, but debris removed by macrophages. Macrophages then move into nearby lymphatics or into terminal bronchioles.

15. 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 (makes it easier for alveoli to expand during inspiration).
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.

16. Lungs Two lungs: Principal organs of respiration
Base sits on diaphragm, apex at the top, hilus (hilum) on medial surface where bronchi and blood vessels enter the lung. All the structures in hilus called root of the lung.
Right lung: three lobes. Lobes separated by fissures (deep & prominent)
Left lung: Two lobes
Right lung is larger & heavier than left
Divisions
Lobes (supplied by secondary bronchi), each lobe is subdivided into bronchopulmonary segments (supplied by tertiary bronchi and separated from one another by connective tissue partitions), bronchopulmonary segments are subdivided into lobules (supplied by bronchioles and separated by incomplete partitions).
Note: 9 bronchopulmonary segments present in left lung & 10 present right lung
Note: Individual diseased bronchopulmonary segments can be surgically removed, leaving the rest of lung intact, because major blood vessels & bronchi do not cross connective tissue partitions.

17. Thoracic Wall and Muscles of Respiration

18. Thoracic Wall
Thoracic vertebrae, ribs, costal cartilages, sternum and associated muscles
Thoracic cavity: space enclosed by thoracic wall and diaphragm
Diaphragm separates thoracic cavity from abdominal cavity

19. Inspiration and Expiration
Inspiration: diaphragm, external intercostals, pectoralis minor, scalenes
Diaphragm: dome-shaped with base of dome attached to inner circumference of inferior thoracic cage. Central tendon: top of dome which is a flat sheet of connective tissue.
Quiet inspiration: accounts for 2/3 of increase in size of thoracic volume. Inferior movement of central tendon and flattening of dome. Abdominal muscles relax
Other muscles: elevate ribs and costal cartilages allow lateral rib movement
Expiration: muscles that depress the ribs and sternum: such as the abdominal muscles and internal intercostals.
Quiet expiration: relaxation of diaphragm and external intercostals with contraction of abdominal muscles
Labored breathing: all inspiratory muscles are active and contract more forcefully. Expiration is rapid

20. Effect of Rib and Sternum

21. 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 close together (adhesion).
Mediastinum: central region, contains contents of thoracic cavity except for lungs.

22. Blood and Lymphatic Supply
Two sources of blood to lungs: Pulmonary & Bronchial
Pulmonary artery brings deoxygenated blood to lungs from right side of heart to be oxygenated in capillary beds that surround the alveoli. Blood leaves via the pulmonary veins and returns to the left side of the heart.
Bronchial arteries provide oxygenated systemic blood to lung tissue. They arise from the aorta & run along the branching bronchi. Part of this now deoxygenated blood exits through the bronchial veins to the azygous (drains chest muscles); part merges with blood of alveolar capillaries and returns to left side of heart.
Blood going to left side of heart via pulmonary veins carries primarily oxygenated blood, but also some deoxygenated blood from the supply of the walls of the conducting and respiratory zone.
Two lymphatic supplies: superficial and deep lymphatic vessels. Exit from hilus
Superficial drain superficial lung tissue and visceral pleura
Deep drain bronchi and associated C.T.
No lymphatics drain alveoli
Phagocytic cells within lungs phagocytize carbon particles & other debris from inspired air & move them to lymphatic vessels
Older people & smokers lungs appear gray to black because accumulation of these particles
C ancer cells from lungs can spread to other parts of body through lymphatic vessels.

23. Ventilation Movement of air into and out of lungs
Air moves from area of higher pressure to area of lower pressure (requires a pressure gradient)
If barometric pressure (atmospheric pressure) is greater than alveolar pressure, then air flows into the alveoli.
Boyle’s La w : P = k/V, where P = gas pressure,
V = volume, k = constant at a given temperature
If diaphragm contracts, then size of alveoli increases. Remember P is inversely proportionate to V; so as V gets larger (when diaphragm contracts), then P in alveoli gets smaller.

24. Alveolar Pressure Changes: (Note: Barometric air pressure is
Alveolar Pressure Changes: (Note: Barometric air pressure is always assigned a value of zero)