8/6/2019 CaTOS 43_Resp

1/6

Respiratory SystemOverview: two lungs + series of airways that connect lungs to external environment

Respiration includes 4 major events

1. Breathing: movement of air in and out of the lungs

2. External Respiration: exchange of O2 in inspired air for CO2 in the blood

3. Transport of Gases: conveyance of O2 and CO2 to and from the cells

4. Internal Respiration: exchange of CO2 for O2 in the vicinity of the cells

Functionally

1. Conducting portion

y nose, pharynx, larynx, trachea, bronchi, bronchioles up toand including the terminal bronchioles

2. Resipratory Portion- gas exchange

y respiratory bronchioles, alveolar ducts, alveolar sacsStructurally

A. Upper Resp. System: nose, pharynx, associated structures

Most of air HERE (5-6 L)

B. Lower Resp. System: larynx, trachea, bronchi, lungs

150mL of air here

Airway flow is inversely proportional to resistance

MEDIUM SIZE BRONCHI are the sites ofHIGHEST resistance*K-N-O-W

y smaller airways have parallel arrangementsy total resistance becomes sum inverse of resistancesMechanics of Breathing

Inflow and outflow of air due to:

1. Rib cage

2. DIAPHRAGM muscle (most important)

3. Intercostal muscles

4. Elastic connective tissue of the lung *KNOW

air behaves as fluid, moving from high to low pressure

Conducting Portion

Nose terminal bronchioles

y Airways kept open by rigid or semi rigid walls supported by:bone, cartilage, smooth muscle

y NO GAS EXCHANGE occurs in this portiony Airways purpose is to warm, moisten, filter airy Pseudostratified ciliated columnar epitheliumy THICK basement membrane before lamina propriay 5 cell types, all in contact with basement membraney ENDODERM derived (mostly) *KNOW1. Goblet Cells

y mucus traps particulate matter, moistens airy Cl- secretion *KNOW2. Ciliated Columnar Cells

y effective stroke towards oropharynxy form mucociliary escalator3. Basal Cells

y stem cells4. Brush Cells

y in every airway, function unknown, microvilli5. DNES cells/APUD cells

y small granule cells, release serotonin? Maybe reflex?

8/6/2019 CaTOS 43_Resp

2/6

8/6/2019 CaTOS 43_Resp

3/6

y Below chords, lining becomes respiratory epitheliumE. Trachea

y Begins at cricoid cartilage of larynx, ends when it bifurcatesinto primary bronchi

y Walls supported by C-rings of hyaline cartilage Open ends face posteriorly

Keep trachea from collapsing with inhalation

y Trachealis (smooth) muscle extends between open endscontraction decreases diameter of trachea

= faster airflow, expel lodged objecty Dense fiborelastic CT between adjacent C-rings

allow elongation of trachea during inhalation

1. Mucosa: respiratory epithelium

y thick underlying basement membraney thin lamina propria with longitudinal elastic fibers2. Submucosa: dense, irregular fibroelastic CT

y contains numerous seromucous glands3. Adventitia: fibroelastic CT containing C-rings of hyaline cart

y forms outer layer of trachea, anchors it to adjacentstructures

Bronchial Tree

Begins at bifurcation of trachea, left and right primary bronchiComposed of airways located inside and outside the lungs

Trends (*K-N-O-W)

y Decreasing diameter of lumen, increase total surface areay Decreasing amount of cartilage, increase in smooth muscle

relative to diameter of airway lumen

y Increase in amount of elastic fibers relative to diametery Decreases in height & number of cilia on lining epitheliumy Decrease in number of glandsF. Bronchi

1. Primary/Main bronchi (2)

yMixed glands, O-rings of cartilage

y Accompanying pulmonary arteries, veins, lymph vesselsTogether pierce hilus of lung

y right trifurcates (more vertical), left bifurcates2. Secondary/Lobar bronchi

y intrapulmonary bronchiy supply LOBE of lung; 2 on left, 3 on right3. Tertiary/Segmental bronchi

y subdivisions of secondary bronchiy each goes to bronchopulmonary segmentIntrapulmonary Bronchi

y C rings replaced by irregular plates of hyaline cartilage Completely surround the lumen

y 2 smooth muscle layers spiraling in opposite directionsy increasing number ofelastic fibersy mixed seromucous glandsG. Conducting Bronchioles

yShort, branched tubes, each supplying pulmonary lobuleylack cartilage and glands, smooth musc keeps airways openEPITHELIUM CHANGE: to simple columnar ciliated w goblet

Sympathetic: Epinephrine acts on B2 adrenergic receptors

yRelaxation and increase diameter of airwaysParasympathetic: Vagus N., muscarinic (ACh) receptors

yConstriction and decrease diameter of airways

H. Terminal Bronchioles

yLast portion of conducting airwaysySupply air to lung aciniySimple cuboidal ciliated epithelium, NO GOBLET CELLSNot secreting mucus anymore, still elevating mucus (cilia)

CLARA CELLS- columnar with dome shaped apices

ySecretory cell of terminal bronchioles: surfactant-like productthat prevent collapse during exhalation, proteolytic enzymes to

8/6/2019 CaTOS 43_Resp

4/6

Histamine, Leukotrienes, PGs: bronchiolar constriction break down mucus, protease inhibitor, lysozymes

yAlso act as STEM CELLSRespiratory Portion

A. Respiratory Bronchioles

ySupply an acinusySimple cuboidal epithelium with Clara Cells, some ciliayNumber of ciliated cells decrease, Clara cells increaseyOne side of wall interrupted by alveoliyOpposite wall has branch ofpulmonary arteryB. Alveolar Ducts

yLinear passageway continuous with respiratory bronchioleyLined by highly attenuated simple squamous epithelium

(type 1 pneumocytes) & types II pneumocytes

yAlveoli on both sides, increasing in numberySeparated by interalveolar septumSmooth muscle adjacent to alveolar openings

C. Alveolar Sacs

yExpanded outpouchings of numerous alveoli located at distalend of alveolar ducts

yNO SMOOTH MUSCLED. Alveoli

yThin walled, pouch-like evaginations of resp. bronchioles,alveolar duct, and alveolar sacs (respiratory portion)

yAllows exchange of O2 and CO2ySeparated by interalveolar septa

Contain PORES, permit equalization of pressure

also spread infection

yrimmed by elastic fibers, supported by reticular fibers1. Type 1 Pneumocytes:FLAT, simple squamous

y95% of alveolar surfaceyTHIN cytoplasm gas exchangeyTIGHT JUNCTIONS, cannot divide2. Type II pneumocytes: cuboidal, microvilli

y5% of alveolar surfaceyTIGHT JUNCTIONS, can divide and regenerate both I&IIyMembrane bound lamellar bodies produce & secrete surfactant

Surfactant:

y2 phospholipids- dipalmitoyl phosphatidylchoine (DPPC)yreleased by exocytosis into lumen of alveolusyspreads to form monomolecular film over alveolar surface

lower aqueous phase

superficial lipid phase*REDUCESSURFACE TENSIONof alveolar surface

yexpansion during inspiration, prevent collapse w expiration3. Alveolar Macrophages: aka dust cells

ymonocytes between type 1 pneumocytes, enter lumenyphagocytose particulate matter, surfactantyreleased when debris in lumen, migrate upylast ditch attempt to get rid of foreign materialyproduce elastase (not released in healthy lung)yheart failure cells full of RBCs in CHF

8/6/2019 CaTOS 43_Resp

5/6

E. Interalveolar Septum

Partition lined on both sides by thin alveolar epithelium

1. Thick Regions:

CONTINOUS CAPILLARIES (leaky) K-N-O-W

yinterstitial space btw unfused basal laminasyelastic and reticular fibers, macrophages, MAST CELLS2. Thin Regionsyblood-air barrier site of gas exchangeFour layers: *KNOW

a. Endothelium of continuous capillaries with septum

b. Fused basal lamina of type 1 pn. And endothelial cells

c. Type 1 pneumocytes

d. Surfactant

F. Lung Lobules

yContain single primary bronchi that branches

ySeparated by connective tissue septumyVeins and lymphatics run in septa

G. Vascular Supply

1. Pulmonary Artery: carries deoxygenated blood to lungsyenters lobules, path parallels the bronchioles branching2. Pulmonary Veins: carries oxygenated blood back to left heart

yrun in intersegmental CT, separate from arteriesyafter leaving lobule, run with pulmonary artery3. Bronchiole arteries and veins: nourish nonrespiratory parts

ybranch with bronchiole treeyanastomose with pulmonary vessels near capillary beds

H. Pulmonary Nerve Supply

ANS fibers to smooth muscles of bronchi and bronchioles

Parasympathetic: contraction

Sympathetic: relaxation

*Asthma- constriction of smooth muscle, inability to expire air

yB2 agonists (sym mimic) alleviate

8/6/2019 CaTOS 43_Resp

6/6