RESPIRATORY SYSTEM REVIEW

Respiratory System Anatomy 2 lungs + airways + blood vessels + chest wall(Fig.25-1) –Mediastinum – space between lungs Chest wall - protects lungs; muscular support for breathing –Pleura with space between folds Membrane adheres to lungs, folds over itself, attaches to chest wall Space between the folds –Usually filled w/ thin layer of fluid –Important for lubrication; decr friction as membrane layers move against each other –Gas P in pleural space < air P in lungs, airways Impt to gas pressure differential; helps lungs expand, stretch as chest wall moves out

Airways - tracheobronchial tree branches to alveoli (25-3) Alveoli –Tiny, thin-walled sacs at ends of terminal bronchi –About 300 million alveoli in two lungs Mechanical barriers protect –Mucus – holds inhaled particles within tracheobronchi Secretes biochemicals toxic to microorganisms –Cilia – move mucus (w/ trapped particles) –Resident macrophages – phagocytize invaders

–If vent’n decr’d  decr’d ability to clear tract –Two means of support Connective tissue fibers (collagen & elastin) –Allows stretch of tracheobronchi to fill, then return Surfactant - lipoprotein –Detergent-like substance prod’d and held in alveoli –Nec to decr surface tension of alveolar walls –  less gas pressure needed to open alveoli during inspiration

Pulmonary Circulation Nec to gas exchange Blood vessels in lung have thinner walls (Fig.25- 5,6) –Also, alveoli thin-walled M any thin-walled capillaries immediately adjacent to alveoli –Alveoli + blood vessels sep’d by <0.5 microns –Alveoli highly perfused -- large network of cap’s –Alveoli/capillary membranes may fuse  little, no separation between blood in cap’s and air in alveoli

 much surface for gas exchange between blood and air in lungs –Very thin layer of blood lies on large space of alveolus Gas exchange by simple diffusion –Through cells of alveoli and capillaries or through junctions between cells –NOTE: oxygen available at lung must closely match oxygen supply nec to tissues. THIS IS IMPORTANT

Breathing = ventilation Mechanical movement gas/air into/out of lung –Use: chest muscles (Fig.25-7,25-12) – diaphragm – Also, elastic properties of chest wall and lungs impt

Major accessory muscles used for involuntary mechanisms Contraction of diaphragm  diaphragm moves down (Fig.25-13) –  Incr’d vol thoracic cavity –  Decr’d pressure gas in lung Note: If fixed amount of gas in a space, gas exerts pressure on container walls. If container vol incr’s, that same amount of gas will exert less pressure on walls. As thoracic cavity incr’s, lungs expand and see decr’d gas pressure inside lung –Air moves from area of higher pressure (atmosphere) to area of lower pressure (lung) (Fig.25-16)

Contraction intercostal muscles  ribs move outward –  Further increase in thoracic cavity volume –  Further decrease in gas pressure in lung –  Movement of air from area of higher pressure (atmosphere) to area of lower pressure (lung) (Fig.25-16)

Elastic properties of lung/chest wall –Permit expansion followed by return (Fig.25-13) –Recoil Chest wall recoils outward, lungs recoil inward (opposing)  change in thoracic pressures  air taken into lung with inspiration –Compliance = measure of lung, chest wall distensibility If incr'd – lungs abnormally easy to inflate –Lose elastic recoil –Ex: emphysema If decr'd – lungs abnormally stiff, difficult to inflate –Ex: fibrosis, pneumonia, pulmonary edema

Control of breathing both voluntary and involuntary –CNS (Fig.25-11) Through respiratory center at base of brain –Peripheral nervous system (PNS) Receptors in lung sensitive to stretch, irritation –Signals respiratory center, which responds by altering breathing Chemoreceptors in bloodstream sensitive to pH, PaCO 2 and PaO 2 –PaCO 2 = arterial pressure of CO 2 –What do you think happens to breathing when the chemoreceptors signal a decrease in O 2 ? What if there is an increase in acid in the blood?

Gas Exchange Oxygen from gas to blood (Fig.25-16) –P O2 in alveolar gas >>> P O2 in blood Large pressure gradient between O 2 in lung and in blood Promotes movement of O 2 Gas moves by diffusion through alveolar and capillary membr’s (Fig.25-6) – Oxygen transport O 2 dissolves in plasma, binds Hb  increased PaO 2 –Hb has 4 binding sites, binds 4 oxygen (O 2 ) molecules Total blood O 2 = O 2 dissolved in the plasma + O 2 bound to Hb –About 5% of O 2 is gas dissolved in blood; most travels through blood bound to Hb

–Diffusion of O 2 from air to blood stops when pressure of O 2 in alveoli = pressure of O 2 in arterial blood –Hb-O 2 associated at lung dissociates at tissues to Hb + O 2 At tissues, pressure concentration: O 2 pressure in blood >>> O 2 pressure in tissues (Fig.25-16)

CO 2 transport (Fig.25-16) –CO 2 -- byproduct of metabolism Tissue CO 2 pressure >>> venous blood CO 2 pressure Must be eliminated or  respiratory acidosis –CO 2 from tissues dissolves in plasma Diffuses into rbc’s Carbonic anhydrase catalyzes reaction: CO 2 + H 2 O  H 2 CO 3  H+ + HCO 3 - Bicarbonate carried in rbc and dissolved in blood –CO 2 soluble in alveolo-capillary membrane Diffuses quickly from blood to alveolus (concentration gradient), then expired into atmospheric air

Approx. even distribution nec between gas in lungs/blood perfusing the lung –Rate of gas moving into lung = ventilation (V) –Rate of blood perfusing lung = perfusion (Q) Best if V matches Q –V/Q = relationship between ventilation, perfusion Normal V/Q = 0.8 –In healthy lung, ventilation slightly < perfusion If different (with disease, impairment in breathing) –  V/Q mismatch

Signs and Symptoms Cough – protective reflex –“Explosive expiration” –Clears lower airways –From stimulation of irritant receptors –If persistent, indicates disease Nonproductive (no mucus, etc.) indicates: –Bronchitis –Viral pneumonia –Tumor Productive - produces sputum –If purulent: infection

Dyspnea - uncomfortable breathing –Due to incr'd work of breathing with: Diseases of lung tissue Disturbances of: –Ventilation –Gas exchange –Mismatch of V/Q Chemoreceptor stimulation or other reasons Decreased pH or PaO 2, or increased PaCO 2

Cyanosis – blue discoloration of skin due to Hb not associated w/ oxygen –So blood not red color (need O 2 bound for Hb to be red) Can result from decreased PaO2 or decreased cardiac output Does not necessarily indicate respiratory disease

Pain –Originating in pleura usually due to infection –Originating in central chest (pronounced after coughing) May be due to inflammation of bronchi, trachea –Originating in chest wall May be due to rib or muscle injury Possible with excessive coughing