Transcript Document

Ch. 13
The 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 System
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Nasal
cavity
Posterior
nasal
aperture
Hard
palate
Soft palate
Epiglottis
Nostril
Pharynx
Larynx
Esophagus
Trachea
Left lung
Right lung
Left main
bronchus
Lobar
bronchus
Segmental
bronchus
Pleural
cavity
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
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• Pleurae
– Visceral
– Parietal
– Pleural cavity
• Pleural fluid
(b) Mediastinal surface, right lung
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
Respiratory Muscles
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Inspiration
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)
Forced expiration
Internal intercostals,
interosseous part
(depress ribs 1–11,
narrow thoracic cavity)
Internal intercostals,
intercartilaginous part
(aid in elevating ribs)
Diaphragm
(ascends and
reduces depth
of thoracic cavity)
Diaphragm
(descends and
increases depth
of thoracic cavity)
Rectus abdominis
(depresses lower ribs,
pushes diaphragm upward
by compressing
abdominal organs)
External abdominal oblique
(same effects as
rectus abdominis)
Figure 22.13
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
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Key
Inputs to respiratory
centers of medulla
Outputs to spinal centers
and respiratory muscles
Output from
hypothalamus,
limbic system, and
higher brain centers
Respiratory
Control Centers
Pons
Pontine respiratory
group (PRG)
Dorsal respiratory
group (DRG)
Central chemoreceptors
Glossopharyngeal n.
Ventral respiratory
group (VRG)
Vagus n.
Medulla oblongata
Intercostal
nn.
Spinal integrating
centers
Phrenic n.
Diaphragm and intercostal muscles
Figure 22.14
Accessory muscles
of respiration
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 Capacities
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6,000
Maximum possible inspiration
5,000
Lung volume (mL)
4,000
Inspiratory
reserve volume
Vital capacity
Inspiratory
capacity
Tidal
volume
3,000
Total lung capacity
Expiratory
reserve volume
2,000
1,000
0
Maximum voluntary
expiration
Residual
volume
Functional residual
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 the
capillary beds
– Utilization coefficient – given up 22% of its oxygen load
Systemic Gas Exchange
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Respiring tissue
Capillary blood
7%
Dissolved CO2 gas
CO2
CO2 + plasma protein
Carbamino compounds
23%
CO2
HbCO2
CO2 + Hb
70%
CO2
CO2 + H2O
CAH
H2CO3
Chloride shift
Cl–
HCO3– + H+
98.5%
O2
1.5%
O2
HbO2+ H+
O2 + HHb
Dissolved O2 gas
Figure 22.24
Key
Hb
Hemoglobin
HbCO2
HbO2
HHb
CAH
Carbaminohemoglobin
Oxyhemoglobin
Deoxyhemoglobin
Carbonic anhydrase
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 Exchange
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Alveolar air
Respiratory membrane
Capillary blood
7%
CO2
Dissolved CO2 gas
Carbamino compounds
CO2 + plasma protein
23%
CO2
70%
CO2
CO2 + H2O
CAH
Chloride shift
Cl-
HbCO2
CO2 + Hb
H2 CO3
HCO3- + H+
98.5%
O2
O2 + HHb
HbO2 + H+
1.5%
O2
Dissolved O2 gas
Key
Hb
Figure 22.25
HbCO2
HbO2
HHb
CAH
Hemoglobin
Carbaminohemoglobin
Oxyhemoglobin
Deoxyhemoglobin
Carbonic anhydrase
Concentration Gradients of Gases
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Expired air
Inspired air
PO2 116 mm Hg
PCO2 32 mm Hg
PO2 159 mm Hg
PCO2 0.3 mm Hg
Alveolar
gas exchange
Alveolar air
O2 loading
PO2 104 mm Hg
CO2 unloading
PCO2 40 mm Hg
CO2
Gas transport
O2
Pulmonary circuit
O2 carried
from alveoli
to systemic
tissues
CO2 carried
from systemic
tissues to
alveoli
Deoxygenated
blood
Oxygenated blood
PO2 95 mm Hg
PCO2 40 mm Hg
PO2 40 mm Hg
PCO2 46 mm Hg
Systemic circuit
Systemic
gas exchange
CO2
O2
O2 unloading
CO2 loading
Tissue fluid
PO2 40 mm Hg
PCO2 46 mm Hg
Figure 22.19
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 PO2
•
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 the
Respiratory 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
Effect of Smoking
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Tumors
(a) Healthy lung, mediastinal surface
(b) Smoker's lung with carcinoma
a: © The McGraw-Hill Companies/Dennis Strete, photographer; b: Biophoto Associates/Photo Researchers, Inc.
Figure 22.27 a-b