Respiratory System

1) Introduction

a) Lung Design

i) Thin, delicate moist surface for gas exchange, 0.1 to 1.0 mm thick

ii) Total surface area >35X that of skin (70 to 140 sq. m. est.)

b) Functions

i) Surface area for gas exchange between air and blood

ii) Air movement (ventilation)

iii) Maintain homeostasis of respiratory surface (water, temperature, defense)

iv) Sound production

v) Olfaction

vi) Conversion of angiotensin I to angiotensin II (ACE, p. 831)

c) Organization

i) Gross anatomy

(1) Upper and lower tract

(2) Boundary: larynx begins lower tract

ii) Functional anatomy

(1) Conducting airways: to terminal bronchioles

(2) Respiratory surface: from respiratory bronchioles

iii) Histology

(1) Respiratory mucosa

(a) Warms, moistens, filters

(b) Ciliated epithelium: pseudostratified, to cuboidal, to squamous

(c) Lamina propria

(i) Upper: mucous glands

(ii) Lower: smooth muscle

(d) Defenses

(i) Ciliated movement towards throat

(ii) Increased mucus production

(iii) Alveolar macrophages

(iv) Cystic fibrosis

2) Functional anatomy

a) Upper respiratory system, larynx, trachea

b) Lungs

i) Bronchial tree

(1) Primary bronchus to lung

(2) Secondary bronchus to lobe

(3) Tertiary bronchus to bronchopulmonary segment

(4) Bronchioles

(a) no cartilage

(b) smooth muscle controls diameter: airway resistance

(c) regulated by ANS (sympathetic dilates, parasympathetic constricts)

(d) terminal bronchioles

(i) supply pulmonary lobules

(ii) cuboidal epithelium

(iii) mostly nonciliated

(iv) no goblet cells or mucus glands

ii) Pulmonary lobules

(1) Connective tissue trabeculae connect to septa

(a) Elastic fibers, smooth muscles, lymphatics

(b) Continuous with visceral pleura

(2) Branch of pulmonary artery, vein, nerve, and terminal bronchiole

iii) Respiratory zone

(1) Respiratory bronchioles (branches of terminal bronchiole)

(2) Alveolar ducts, sacs, alveoli

(3) Alveolar (pulmonary) capillaries surrounded by elastic fibers

(4) Alveolus

(a) Macrophages

(b) septal cells: surfactant

(c) pulmonary epithelium

(5) respiratory membrane

(a) pulmonary epithelium

(b) fused basement membranes

(c) capillary endothelium

(d) thickness (normally ~ 0.1 - 1.0 mm; increases with some disorders)

c) Developmental biology

i) Embryology

ii) Changes at birth

iii) Effects of aging

3) Respiratory Physiology

a) Pulmonary ventilation

i) Physical laws

(1) Boyle's law V is inversely proportional to P

(2) Fluids flow from high P to low P

ii) Events

(1) Inspiration

(a) Expansion of thoracic volume (review respiratory muscles)

(b) Decreased intrapleural P

(c) Increased intrapulmonary V

(d) Decreased intrapulmonary P

(2) Expiration: reverse

(3) Forced expiration

iii) Other factors

(1) Lung compliance

(2) Surfactant

(3) Pleural fluid and P

(4) Mobility of thoracic cage

(a) Diaphragmatic

(b) Costal

iv) Lung volumes and capacities

v) Respiratory rate

vi) Alveolar ventilation

(1) Anatomical dead space

(2) Relationships between rate and depth

(a) Rapid shallow

(b) Slow, deep

b) Gas exchange

i) Laws

(1) Dalton's law of partial pressures

(2) Henry's law

(a) Pressure

(b) Solubility

ii) Composition of alveolar air

(1) Oxygen 100 mm Hg

(2) Carbon dioxide 40 mm Hg

iii) Diffusion at the respiratory membrane

(1) Diffusion gradient is large

(2) Distance is small (0.1mm)

(3) Gases are lipid-soluble

(4) Total surface area is large

(5) Blood flow and air flow are matched (perfusion/ventilation coupling)

iv) Composition of blood gases (venous)

(1) Oxygen 40 mm Hg

(2) Carbon dioxide 45 mm Hg

v) Composition of blood gases (arterial)

(1) Oxygen 100 -- 95 mm Hg

(2) Carbon dioxide 40 mm Hg

vi) Transit time

(1) Normally, blood passes through pulmonary capillary in ~ .75 sec

(2) Complete equilibration is accomplished in about 1/3 of that time

c) Transport

i) Oxygen

(1) Each hemoglobin molecule can hold 4 oxygen molecules

(2) If each is saturated, it holds 4

(3) If 75% saturated, it holds 3

(4) If the saturation is 60%, then some hold 3 and some hold 2

(5) Percent saturation is associated with Dissociation curve

(6) Dissociation curve is primarily determined by oxygen pressure

(a) P of 100 mm Hg: 100% saturated

(b) P of 40 mm Hg: 75% saturated

(c) In active tissue, P may be as low as 15 û 20 mm Hg: 15-35% sat.

(7) Dissociation curve is influenced by temperature and pH

(a) High temp, low pH (active tissues) lower affinity of Hb for oxygen

(b) Cooler, higher pH in lungs mean higher affinity

(8) Fetal hemoglobin has a higher affinity for oxygen than adult hemoglobin

ii) Carbon dioxide

(1) Carbonic anhydrase converts ~ 70% of carbon dioxide to bicarbonate

(2) Hemoglobin carries about 25% as carbaminohemoglobin

(3) About 5% is dissolved in plasma

d) Control of respiration

i) Local regulation

(1) Perfusion/ventilation coupling

(2) Bronchodilation/carbon dioxide levels

ii) Brain respiratory centers

(1) Medulla: respiratory rhythmicity centers

(a) DRG: inspiratory center

(b) VRG: expiratory center

(2) Pons: apneustic and pneumotaxic areas

(a) Activated by higher brain centers (hypothalamus, cerebrum)

(b) Apneustic stimulates DRG

(c) Pneumotaxic inhibits apneustic

iii) Reflexes

(1) Stimuli / receptors

(a) High carbon dioxide, low pH, or low oxygen: chemoreceptors

(b) Stretching of lungs: stretch receptors

(c) Irritants: nasal, laryngeal, or bronchial receptors

(d) Other: pain, emotion

iv) Voluntary control