Ch. 13The Respiratory

System

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Breath of Fresh Air

• Know what is meant by ventilation and where gas exchange occurs in the lungs

• Know the respiratory centers of the brain and how the control respiration

• Know the various lung volumes and lung capacities

• Know how gas exchange is accomplished and the factors that can affect the rate of gas exchange

Respiratory System

• What are some functions of the respiratory system?

• Respiration as a process– Ventilation– External and internal respiration– Cellular respiration

Anatomy

• Principal organs– Nose, pharynx, larynx, trachea, bronchi, and lungs

• Conducting division– Function only in airflow

• Respiratory division– Function in gas exchange

Organs of Respiratory SystemCopyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display.

Nasalcavity

Nostril

Hardpalate

Larynx

Trachea

Right lung

Posteriornasalaperture

Soft palate

PharynxEpiglottis

Esophagus

Left lung

Left mainbronchusLobarbronchusSegmentalbronchus

Pleuralcavity

Pleura(cut)

Diaphragm

Figure 22.1

Lungs• Right lung

– Three lobes divided by horizontal and oblique fissures

• Left lung– Two lobes divided by oblique

fissure

• Pleurae– Visceral– Parietal– Pleural cavity

• Pleural fluid(b) Mediastinal surface, right lung

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Alveoli• ~ 150 million sacs for gas exchange

– Why so many?

• Cells types– Squamous alveolar cells (type I)

• 95% of surface, thinness allows rapid gas exchange

– Great alveolar cells (type II)• Repair alveolar epithelium• Secrete surfactant

– Alveolar macrophages (dust cells)• Phagocytize dust particles, bacteria,

debris

• Respiratory membrane

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Ventilation

• Respiratory cycle– Inspiration– Expiration

• Respiratory muscles– Diaphragm– Intercostals– Accessory muscles of respiration

• Sternocleidomastoids, scalenes, pectoralis muscles, serratus anterior, erector spinae

Sternocleidomastoid(elevates sternum)

Scalenes(fix or elevate ribs 1–2)

External intercostals(elevate ribs 2–12,widen thoracic cavity)

Pectoralis minor (cut)(elevates ribs 3–5)

Internal intercostals,intercartilaginous part(aid in elevating ribs)

Diaphragm(descends andincreases depthof thoracic cavity)

Inspiration

Internal intercostals,interosseous part(depress ribs 1–11,narrow thoracic cavity)

Diaphragm(ascends andreduces depthof thoracic cavity)

Rectus abdominis(depresses lower ribs,pushes diaphragm upwardby compressingabdominal organs)

External abdominal oblique(same effects asrectus abdominis)

Forced expiration

Respiratory Muscles

Figure 22.13

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Neural Control of Breathing• Conscious and sub-conscious control

• Three pairs of respiratory centers in reticular formation of medulla and pons– Ventral respiratory group (VRG)

• Inspiratory (I) neurons• Expiratory (E) neurons

– Dorsal respiratory group (DRG)• External influence of VRG• Integrating center

– Central and peripheral chemoreceptors, stretch receptors, irritant receptors– Pontine respiratory group

• Integrates input from higher brain centers• Influences VRG and DRG• Modifies breathing to sleep, emotional responses, exercise, other

special circumstances

Respiratory Control Centers

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Central chemoreceptors

Spinal integratingcenters

Glossopharyngeal n.

Vagus n.

Diaphragm and intercostal muscles

Accessory musclesof respiration

Ventral respiratorygroup (VRG)

Dorsal respiratorygroup (DRG)

Medulla oblongata

Pontine respiratorygroup (PRG)

Pons

Output fromhypothalamus,limbic system, andhigher brain centers

Phrenic n.

Intercostalnn.

KeyInputs to respiratorycenters of medulla

Outputs to spinal centersand respiratory muscles

Figure 22.14

Taking a Breath• Inspiration

– Boyle’s law• Pressure of a gas inversely proportional to its volume at constant

temp.

– Charles’s law• Volume of a gas directly proportional to its temperature at constant

pressure

• Expiration– Passive process, elastic recoil of thoracic cage

• Resistance to airflow– Diameter of bronchioles– Pulmonary compliance– Surface tension of alveoli

Measurements of Ventilation• Spirometer

• Dead space– Approx. 150 ml of air remain in conductive division– Alveolar ventilation rate (AVR) – volume of air used in gas exchange X breaths/min

• Tidal volume (TV) – one cycle of quite breathing, about 500 ml

• Inspiratory reserve volume (IRV) – amount that can be inhaled beyond TV inhalation, 3000 ml

• Expiratory reserve volume (ERV) – amount that can be forcefully exhaled beyond TV exhalation, 1200 ml

• Residual volume (RV) – volume of air that remains even after maximal expiration, 1300 ml

Lung Volumes and CapacitiesCopyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display.

Lung

vol

ume

(mL)

6,000

5,000

4,000

3,000

2,000

1,000

0

Maximum possible inspiration

Inspiratoryreserve volume

Expiratoryreserve volume

Residualvolume

Maximum voluntaryexpiration

Functional residualcapacity

Total lung capacity

Tidalvolume

Inspiratorycapacity

Vital capacity

Spirometry• Restrictive disorders

– Reduce pulmonary compliance– Appear as a reduced vital capacity

• Obstructive disorders– Blockage or narrowing of airway– More difficult to inhale/exhale given amount of air– Measure by forced expiratory volume (FEV)

• Percentage of vital capacity that can be exhaled in a given time interval

– 75-85% in 1 second for healthy adult

Gas Exchange• Involves oxygen and carbon dioxide

• Composition of air– 78.6% N2, 20.9% O2, .04% CO2, 0.5% H2O

• Dalton’s law – total atmospheric pressure is sum of partial pressures of individual gases

• Composition of gases will vary depending on where air is in the respiratory tract– Inhaled air differs from alveolar air differs from exhaled air

Driving Force Behind Alveolar Exchange

• Diffusion down concentration gradient– Have to consider that we are going from air to water

• Henry’s law – for a given temperature, at the air-water interface the amount of gas that dissolves in the water is determined by its solubility in water and its partial pressure in air

• Erythrocytes load O2 and unload CO2

• Efficiency of exchange may be affected by:– Pressure gradients, solubility, membrane thickness

and area, ventilation-perfusion coupling

Gas Transport

• Oxygen binds to hemoglobin (98.5%)– Oxyhemoglobin (HbO2)

• Carbon dioxide– Carbonic acid (90%)– Carbamino compounds (carbaminohemoglobin,

HbCO2)– Dissolved gases

Systemic Gas Exchange• Systemic gas exchange - the unloading of O2 and loading of CO2 at

the systemic capillaries

• CO2 loading– CO2 diffuses into the blood– carbonic anhydrase in RBC catalyzes

• CO2 + H2O H2CO3 HCO3- + H+

– chloride shift• keeps reaction proceeding, exchanges HCO3

- for Cl-

• H+ binds to hemoglobin

• O2 unloading– H+ binding to HbO2 reduces its affinity for O2

• tends to make hemoglobin release oxygen• HbO2 arrives at systemic capillaries 97% saturated, leaves 75%

saturated –

– venous reserve – oxygen remaining in the blood after it passes through thecapillary beds

– Utilization coefficient – given up 22% of its oxygen load

Systemic Gas ExchangeCopyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display.

Respiring tissue Capillary blood

Dissolved CO2 gas

CO2 + plasma protein

CO2

CO2

O2Dissolved O2 gas

Carbamino compounds

Cl–

7%

23%

70%

98.5%

1.5%

CO2 + Hb

CO2 + H2O

O2 + HHb HbO2+ H+

H2CO3 HCO3– + H+

HbCO2

CAH

Key

Chloride shift

CO2

O2

HbCO2 Carbaminohemoglobin

Hb Hemoglobin

HHb Deoxyhemoglobin

CAH Carbonic anhydrase

HbO2 Oxyhemoglobin

Figure 22.24

Alveolar Gas Exchange• Reactions that occur in the lungs are reverse of

systemic gas exchange

• CO2 unloading– As Hb loads O2 its affinity for H+ decreases, H+

dissociates from Hb and bind with HCO3-

• CO2 + H2O H2CO3 HCO3- + H+

– Reverse chloride shift• HCO3

- diffuses back into RBC in exchange for Cl-, free

CO2 generated diffuses into alveolus to be exhaled

Alveolar Gas ExchangeCopyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display.

Respiratory membrane Capillary blood

CO2

O2

Alveolar air

Carbamino compounds

7%

23%

70%

98.5%

1.5%

HbCO2

CAH

Key

ClChloride shift

CO2

CO2

O2 Dissolved O2 gas

O2 + HHb HbO2 + H+

HCO3 + H+H2 CO3CO2 + H2O

CO2 + Hb

CO2 + plasma protein

Dissolved CO2 gas

Hb Hemoglobin

HbCO2 Carbaminohemoglobin

HbO2 Oxyhemoglobin

HHb Deoxyhemoglobin

CAH Carbonic anhydrase

Figure 22.25

Concentration Gradients of Gases

Figure 22.19

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Alveolargas exchange

O2 loading

CO2 unloading

Gas transport

O2 carriedfrom alveolito systemictissues

CO2 carriedfrom systemictissues toalveoli

Systemicgas exchange

O2 unloading

CO2 loading

Expired air Inspired air

PO2 116 mm HgPCO2 32 mm Hg

Alveolar air

PO2 104 mm Hg

PCO2 40 mm Hg

Tissue fluid

PO2 40 mm HgPCO2 46 mm Hg

Deoxygenatedblood

PO2 40 mm HgPCO2 46 mm Hg

Oxygenated blood

PO2 95 mm HgPCO2 40 mm Hg

PO2 159 mm Hg

PCO2 0.3 mm Hg

CO2

Pulmonary circuit

Systemic circuit

CO2O2

O2

Adjustment to the Metabolic Needs of Individual Tissues

• Hemoglobin unloads O2 to match metabolic needs of different states of activity of the tissues

• Four factors that adjust the rate of oxygen unloading– ambient PO

2

• active tissue has PO2 ; O2 is released from Hb

– temperature• active tissue has temp; promotes O2 unloading

– Bohr effect• active tissue has CO2, which lowers pH of blood ; promoting O2 unloading

– bisphosphoglycerate (BPG)• RBCs produce BPG which binds to Hb; O2 is unloaded

• Haldane effect – rate of CO2 loading is also adjusted to varying needs of the tissues, low level of oxyhemoglobin enables the blood to transport more CO2

• body temp (fever), thyroxine, growth hormone, testosterone, and epinephrine all raise BPG and cause O2 unloading

• metabolic rate requires oxygen

Blood Gases and theRespiratory Rhythm

• Rate and depth of breathing adjust to maintain levels of:– pH 7.35 – 7.45

– PCO2 40 mm Hg

– PO2 95 mm Hg

• Brainstem respiratory centers receive input from central and peripheral chemoreceptors that monitor the composition of blood and CSF

• Most potent stimulus for breathing is pH, followed by CO2, and least significant is O2

Hydrogen Ions

• Acidosis – blood pH lower than 7.35

• Alkalosis – blood pH higher than 7.45

• Hypocapnia – PCO2 less than 37 mm Hg (normal 37 – 43 mm Hg)

• most common cause of alkalosis

• Hypercapnia – PCO2 greater than 43 mm Hg• most common cause of acidosis

Effects of Hydrogen Ions• Respiratory acidosis and respiratory alkalosis – pH imbalances resulting from a

mismatch between the rate of pulmonary ventilation and the rate of CO2 production

• Hyperventilation is a corrective homeostatic response to acidosis – “blowing off ” CO2 faster than the body produces it

– pushes reaction to the left CO2 (expired) + H2O H2CO3 HCO3

- + H+

– reduces H+ (reduces acid) raises blood pH towards normal

• Hypoventilation is a corrective homeostatic response to alkalosis – allows CO2 to accumulate in the body fluids faster than we exhale it

– shifts reaction to the right– CO2 + H2O H2CO3 HCO3

- + H+

– raising the H+ concentration, lowering pH to normal

Effects of Oxygen

• PO2 usually has little effect on respiration

• Chronic hypoxemia, PO2 less than 60 mm Hg, can

significantly stimulate ventilation

– Hypoxic drive – respiration driven more by low PO2 than by CO2 or pH

– Emphysema, pneumonia

– High elevations after several days

Respiration and Exercise• Causes of increased respiration during exercise

1. When the brain sends motor commands to the muscles• Also sends this information to the respiratory centers

• Increase pulmonary ventilation in anticipation of the needs of the exercising muscles

2. Exercise stimulates proprioceptors of the muscles and joints• Transmit excitatory signals to the brainstem respiratory centers

• Increase breathing because they are informed that the muscles have been told to move or are actually moving

• Increase in pulmonary ventilation keeps blood gas values at their normal levels in spite of the elevated O2 consumption and CO2 generation by the muscles

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(a) Healthy lung, mediastinal surface (b) Smoker's lung with carcinoma

Tumors

a: © The McGraw-Hill Companies/Dennis Strete, photographer; b: Biophoto Associates/Photo Researchers, Inc.

Figure 22.27 a-b