Functions of Respiratory System • • Protection • Move air – Dehydration, invasion – Respiratory defense • Sound production system • Olfaction • Filtration, mucous, MALT

Bronchi and Lobules • Tissues present… • Functions of each tissue…

1 Alveolar organization

Alveolar cell types • alveolar macrophages • type I alveolar cells – (alveolar epithelium) – gas exchange • type II alveolar cells – (septal cells) – secrete surfactant

• surfactant – coats lining of alveoli – reduces surface tension

Respiratory membrane

• Endothelium – Angiotensin Converting Enzyme (ACE) • Basal laminae • Type I alveolar cells

• Large SA – 35X body surface – 700 - 1500 sq. ft.

2 Pleural cavities & pleural membranes • 2 pleural cavities • visceral layer • pleural fluid • parietal layer

Respiration • external – pulmonary ventilation – gas exchange between alveoli & blood

– transport of O2 & CO2 • internal respiration – gas exchange between blood & tissues • cellular respiration -Chapter 25

Pulmonary Ventilation - topics • Air movement • Pressure changes • Mechanics of • Respiratory rates & volumes

3 Air movement • Pressure differences – Air moves from high P to low P – Pressure is dictated by changes in volume • How do we change the pressure in the pleural cavities?

Mechanism of pulmonary ventilation • Pressure is inversely proportional to volume • P = 1/V; Boyle’s law

Compliance • Compliance: ease of expansion • Changes in compliance – Connective Tissue loss/alteration • alveolar damage, e.g., emphysema increases compliance • Fibrosis decreases compliance – Reduced surfactant causes alveolar collapse, reduces compliance – Thoracic cage mobility changes • Arthritis, ossification…

4 Respiratory Muscles • Normal breathing at rest due to – diaphragm 75% – external intercostals 25%

• Forced breathing requires more muscles Muscles of – diaphragm – external intercostals – *accessory muscles • sternocleidomastoid • scalenes • pectoralis minor • serratus anterior Muscles of Exhalation – internal intercostals – muscles of abdominal wall

Modes of breathing • Quiet breathing – Inhalation active / exhalation passive – Only the diaphragm and external intercostals are active – Two different modes • Diaphragmatic or deep breathing (typical at rest) • Costal or shallow breathing ( h ‘ d abdominal pressure, fluids, masses)

• Forced breathing – Inhalation & exhalation active – Accessory muscles of inspiration are employed – Internal intercostals (and abdominal wall muscles) for exhalation

Respiratory rates & volumes

5 Gas Exchange

• Gas laws – Dalton’s law – Henry’s law • Diffusion & Respiratory function

Dalton’s Law & partial pressures

• Partial pressure of a gas (g); Pg • All gases combined = atmospheric pressure

• PN2 + PO2 + PH2O + PCO2 = 760 mmHg

Calculating the partial

pressure of oxygen; PO2

• P All gases in air = PN2 + PO2 + PH2O + PCO2 • 100% = 78.6% + 20.9% + .5% + 0.04% • atmospheric pressure is 760 mmHg

• So the PO2 of atmospheric air = 21% X 760 mmHg = 159 mmHg

6 PO2 of alveolar air

• Alveolar air is moist, contains water vapor • using the same equation and correcting for the increased water vapor in alveolar air yields a

PO2 of alveolar air of 100 mmHg

Partial pressures

Source N2 O2 CO2 H2O vapor

Inhaled 597 159 0.3 3.7 air mmHg

Alveolar 573 47 air 100 40

Exhaled 569 116 28 47 air

Henry’s Law • the amount of gas that will dissolve in a fluid is • proportional to – its partial pressure and its solubility coefficient

7 Henry’s law in the body…

Allows O2 in alveolar air to diffuse into surfactant

(converse for CO2)

Partial Pressures

Partial pressures in alveoli and alveolar capillaries

8 Partial Pressures in systemic circuit

Gas transport

• Oxygen transport • transport

Oxygen transport • 1.5% dissolved in plasma • 98.5% bound reversibly to Hb (in RBCs) 4 O2 for each Hb Hb + O2 <------> HbO2 • Factors that dictate O2-Hb binding – plasma PO2 – plasma pH – temperature – metabolic activity in RBC ([BPG])

9 O2-Hb saturation curve at pH 7.4

• Cooperative binding

• PO2 of 100 mmHg = saturation _?_%

• What happens at PO2 of 40 mmHg?

• Significance?

O2-Hb saturation curve and pH • effected by pH

• pH changes Hb affinity for O2 • As pH decreases, O2 release increases

• : due to carbonic acid formation

• Carbonic anhydrase activity in RBC

+ - CO2 + H2O <--> H2CO3 <--> H + HCO3

O2-Hb saturation curve and temperature

• At any PO2, an increased temperature

results in decreased O2 affinity

• Only significant for skeletal muscle during heightened activity

10 Hb and bisphosphoglycerate (BPG)

• BPG is a glycolysis GLYCOLYSIS imtermediate (many steps omitted) • As [BPG] increases, more Glucose O is released from Hb 2 • Hormones that increase BPG metabolic rate in RBCs cause an increase in BPG Lactic acid – Thyroid, GH, androgens, catecholamines, high pH

– Improve O2 delivery

Fetal hemoglobin

• Fetal hemoglobin

has a higher O2 affinity than adult hemoglobin • Placental blood has

PO2 of 30 mmHg; note saturation difference…

Carbon Dioxide transport

• Three modes of transport • Bicarbonate ions 70% • Carbaminohemoglobin 23% • Dissolved in plasma 7%

+ - CO2 + H2O <--> H2CO3 <--> H + HCO3 !

11 Summary of gas transport

Control of respiration

• Purpose: control gas exchange… • local regulation dictates – pulmonary capillary diameter – airway diameter • CNS respiratory centers dictate – depth and frequency of ventilation • respiration is coordinated with changes in cardiovascular function

CNS Respiratory centers

• Involuntary control – Pons – – Frequency & depth • Voluntary control – – cerebral cortex – Overrides medulla oblongata and pons

12 Respiratory centers in medulla

• Regulate frequency oblongata • Dorsal Respiratory Group – active every cycle – innervates • Diaphragm & external intercostals • Ventral Respiratory Group – only active during forced breathing – innervates • accessory muscles of inspiration • muscles of expiration • Pacemaker cells – Affected by CNS stimulants and depressants

apneustic center and pneumotaxic center in pons • apneustic center – continues inhalation • pneumotaxic center – promotes exhalation • regulate rate and depth in response to stimuli • input to centers: stimuli monitored by – stretch receptors in bronchioles – in carotid and aortic bodies – baroreceptors in carotid and aortic sinuses

Respiratory reflexes

• reflexes • baroreceptor reflexes • stretch receptors • protective reflexes: irritants in airways • Others

13 Respiratory reflexes: chemoreceptors • peripheral chemoreceptors – Aortic & carotid bodies

– Blood PO2 and pH • – Surface of medulla oblongata

– Monitor PCO2 and pH • stimulation causes increased rate & depth of ventilation

Reflexes based on PCO2

Respiratory reflexes: chemoreceptor sensitivity

• Reflexes are more strongly tied to PCO2 than to PO2 …

– 10% increase in PCO2 doubles respiration – 40% drop in PO2 increases respiration by half

• Explains shallow water blackout…

• Adaptation of chemoreceptors is a significant problem for treating respiratory system disorders…

14 Respiratory reflexes: baroreceptors

• Baroreceptors (monitor blood pressure) – aortic, carotid sinuses • temporary drop in BP causes increased respiration • temporary rise in BP causes decreased respiration

Respiratory reflexes: Hering-Breuer reflexes

• for tidal volumes greater than 1000 ml • receptors are stretch receptors in bronchiolar smooth muscle & alveolar wall – Inflation reflex stops inhalation – Deflation reflex stops exhalation

• prevent overexpansion and stop inhalation during forced breathing

Respiratory reflexes

• Protective Reflexes: irritants in airways – Nasal cavity, larynx, bronchial tree – Sneezing, coughing, laryngeal spasms

• Others: Pain, BT, abnormal visceral sensations stretching anal sphincter

• Voluntary control – Anxiety, emotions, ANS, exercise, speech

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