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Chapter 21 Respiration
Terms in this set (87)
Purpose of Respiratory System
1) oxygen intake to blood for all cells
2) carbon dioxide removal from blood (pH control)
3) vocal sound
4) Increasing pushing pressure - Valsalva
5) chemical detection of odor
collective force of all impacts of all those fluid atoms and molecules.
high pressure -> low pressure
they are inversely proportional
high volume = low pressure
low volume = high pressure
mucous membrane of respiratory wall
-(mucosa) open to outside environment
-contains epithelium, basement membrane and areolar connective tissue
-Moist: secretes mucous from goblet cells/serous glands
bronchi -> bronchiole structure changes
- cartilage rings -> irregular plates (no cartilage at bronchioles
- epithelium: changes from pseudo stratified columnar to cuboidal
- cilia and goblet cells are sparse or absent
- relative amount of smooth muscle increases
breathing; air into and out of the lungs
pulmonary gas exchange
oxygen and carbon dioxide exchange between the lungs and pulmonary circ. blood
oxygen and carbon dioxide in the blood
tissue gas exchange
oxygen and carbon dioxide exchange between systemic blood vessels and tissues
respiratory vs circulatory system
respiratory: pulmonary ventilation & pulmonary gas exchange
circulatory: tissue gas exchange, internal transport & part of pulmonary gas exchange
-~0.5um thick (air-blood barrier)
- alveolar and capillary walls and their fused basement membranes.
- alveolar walls contain a single layer of squamous epithelium (type 1 cells) & elastic fibers
- type 2 cells are scattered and secrete surfactant
-surrounded by fine elastic fibers; contain open pores that connect adjacent alveoli and equalize air pressure throughout lung; macrophages keep alveolar surface sterile
Blood supply systems
1) systemic circulation
2) pulmonary circulation
lungs have "standard" bronchial arteries and veins to provide oxygenated blood to most lung tissue, but do not nourish alveoli cells themselves.
To oxygenate blood for the rest of the body;
low pressure, high volume = low resistance to blood flow;
pulmonary arteries deliver systemic venous blood that branch along with bronchi and feed into pulmonary capillary networks;
pulmonary veins carry oxygenated blood from respiratory areas to the heart
mechanics of breathing
1) inspiration: gases flow into lungs
2) expiration: gases exit lungs
pressure exerted by the air surrounding the body; 760 mm Hg at sea level
-negative respiratory pressure is less than atmospheric pressure
-positive respiratory pressure is greater than atmospheric pressure
- zero respiratory pressure is equal to atmospheric pressure
(air flows towards lower pressures)
pressure in the alveoli, fluctuates during each breath, always eventually equal to atmospheric pressure
pressure in the pleural cavity fluctuates with breathing; ALWAYS NEGATIVE to atmospheric pressure and intrapulmonary pressure; it pulls the lungs open.
2 inward forces promote lung collapse (shrinkage within chest):
a) Recoil of lung elastic connective tissue (stretch)
b) surface tension of alveolar fluid reduces alveolar size
Outward forces of lung inflation
tend to enlarge lungs;
1) pull in both directions (wall out & lungs in) which expands pleural cavity volume, intrapleural pressure declines (vacuum) and lungs pushed out like a balloon; pleural fluid drained away constantly so internal cavity pressure always stays low
2) chest wall is under outward tension. aqueous pleural fluid adheres to visceral and parietal pleurae together, pulling the lungs outward.
intrapulmonary pressure minus the intrapleural pressure; keeps the airways open; the greater the transpulmonary pressure the larger the lungs are
the intrapulmonary pressure is equal to the intrapleural pressure. usually air enters the pleural cavity due to a leak from lungs or hole in the thorax
air in cavity
treatment: drain air and reinflate the lung
based on volume changes in the thoracic cavity;
volume changes -> pressure changes -> gases flow until pressures are equalized
an active process;
1) inspiratory muscles contract
2) thoracic volume increases
3) lungs are stretched
4) pressure decreases
5) air flows into the lungs, down its pressure gradient until intrapulmonary pressure is equal to atmospheric pressure
diaphragm and external intercostals
quiet expiration is a passive process;
1) inspiratory muscles relax
2) thoracic cavity volume decreases
3) elastic lungs recoil & volume decreases
4) intrapulmonary pressure increases
5) air flows out of the lungs down its pressure gradient
an active process that uses abdominal and internal intercostal muscles
Factors influencing pulmonary ventilation
3 interrelated factors that hinder airflow and pulmonary ventilation (require energy and effort to overcome)
a) airway resistance
b) alveolar surface tension
c) lung compliance
resistance equals mostly friction;
resistance is usually insignificant because of the large diameters in the superior airways and progressive branching of airways as they get smaller increasing the total cross-sectional area;
no resistance at the terminal bronchioles
relationship of flow, pressure and resistance
F = ΔP / R
ΔP = pressure gradient between the atmosphere and alveoli (less than or equal to 2 mm Hg during normal quiet breathing)
Increased airway resistance
as airway resistance increases, breathing becomes more difficult;
severely contracting or obstructing bronchioles can prevent ventilation such as asthma attacks
Epinephrine dilates bronchioles and reduces air resistance.
Alveolar surface tension
Attraction of polar water molecules to each other at a gas-liquid interface; works to minimize surface area; resists any force that tries to increase the volume of the liquid.
detergent-like lipid and protein complex produced by Type 2 alveolar cells; reduces surface tension of alveolar fluid and fights alveolar collapse.
how well a container changes size because of pressure; measure the change in lung volume that occurs with a given change in transpulmonary pressure.
normally high due to distensibility in elastic tissue of lung tissue and low alveolar surface tension
lung compliance diminished by
nonelastic scar tissue (fibrosis), decreased production of surfactant and decreased flexibility of the thoracic cage from structural issues (arthritis)
used to asses a person's respiratory status
TV; normal air inhaled and exhaled at rest; can force more in and out (reserve) and a tiny bit of air cannot be forced out
physiological dead space
some inspired air does not contribute to gas exchange:
1) anatomical dead space- around 150 ml in volume
2) alveolar dead space- any alveoli that cease to act in gas exchange due to collapse or obstruction
total dead space
sum of all non useful volumes subtracted from inhaled volume
alveolar ventilation rate is use flow of gases into and out of the alveoli within a particular time
AVR (ml/min)= frequency x (TV-dead space)
external and internal respirations
oxygen and carbon dioxide exchange
lungs <--> Blood
Blood <--> tissues
based on physical properties of gases, composition of alveolar gas and environment at tissues
exerted by a mixture of gases = sum of the pressures exerted by each gas
partial pressure (Dalton)
each gas is directly proportional to its percentage in the mixture; each gas goes down its own partial pressure gradient; when a mixture of gases is in contact with a liquid, each gas will push itself into the liquid in proportion to its partial pressure;
the individual gas will move until the partial pressures of the 2 areas are equal.
composition of alveolar gas
alveoli contain less oxygen, more carbon dioxide and more water vapor than atmospheric air:
-gas exchange with blood (losing oxygen and gaining carbon dioxide)
-humidification of air in nose and lungs
partial pressure = force pushing gas into liquid
solubility = ability to interact with liquid molecules and stay inside liquid
The amount of gas that will dissolve in a liquid also depends upon its solubility- carbon dioxide is 24 times more soluble in water than oxygen and very little nitrogen dissolves in water.
exchange of oxygen and carbon dioxide across the respiratory membrane
1) partial pressure gradients and gas solubilities
2) ventilation-perfusion coupling
3) structural characteristics of the respiratory membrane
partial pressure gradient for oxygen
steep in the lungs
venous blood Po2 = 40 mm Hg
alveolar Po2 = 104 mm Hg
blood absorbs oxygen fast- reach 104mmHg in 0.25 seconds, about 1/3 the time of a red blood cell is in a pulmonary capillary
partial pressure gradient for carbon dioxide
less steep in the lungs
venous blood Pco2 = 45 mm Hg
alveolar Pco2 = 40 mm Hg
Carbon dioxide is 20x more soluble in plasma and alveolar fluid than oxygen. Usually, equal amounts of carbon dioxide and oxygen are exchanged.
ventilation: arount of gas reaching the alveoli
perfusion: blood flow reaching the alveoli
ventilation = perfusion for efficient gas exchange
Po2 ventilation-perfusion coupling
Po2 in the alveoli controls diameters of the pulmonary arterioles; where alveolar oxygen is high, arterioles dilate; alveolar oxygen is low, arterioles constrict
Pco2 ventilation-perfusion coupling
Picot in the alveoli controls diameters of the bronchioles;
where alveolar carbon dioxide is high, bronchioles dilate
where alveolar carbon dioxide is low, bronchioles constrict
0.2-1um thick, large total surface area
if lungs become waterlogged with edema then respiratory membranes thicken and gas exchange decreases.
reduction in surface area with emphysema due to inflammation in alveoli and breakdown of alveolar elastic connective tissue
transport and respiration at body tissue
capillary gas exchange in body tissues (circulatory system); partial pressures and diffusion gradients are reversed compared to external respiration. Po2 in tissue is lower than in systemic arterial blood.
oxygen transport in blood
molecular oxygen is carried in blood: 1.5% dissolved in plasma and 98.5% to hemoglobin in RBCs
globin (protein): 4 polypeptides (2 alpha & 2 beta chains)
heme pigment with iron bonded to each globin chain
up to 4 oxygen per hemoglobin
hemoglobin and oxygen combo
hemoglobin that has released oxygen
Oxygen and hemoglobin
loading and unloading of oxygen is aided by change in shape of hemoglobin molecule.
-as oxygen binds, hemoglobin affinity for oxygen increases, which make is easier to the next oxygen to bind
-as oxygen is released, hemoglobin affinity for oxygen is decreased which makes it easier to release next oxygen
Fully saturated if all 4 heme groups on each Hb molecule have oxygen, partial is 1-3 hemes carrying oxygen.
rate of loading and unloading of oxygen
pressure of oxygen in surrounding environment
BPG concentration-allosteric regulator in RBCs that binds to partially deoxygenated hemoglobin and aids release of remaining oxygen.
Influence of Po2
oxygen-hemoglobin dissociation curve:
Po2 vs hemoglobin saturation is not linear
Po2 affects oxygen binding.
(exercising tissues have low Po2 whereas lungs have high Po2)
Influence of Po2 on arteries
hemoglobin is completely saturated at Po2 = 70 mm Hg
In arterial blood, Po2 = 100 mm Hg and Hb is 98% saturated
Further increases in Po2 produce little increase in oxygen binding. Oxygen loading and delivery to tissues is adequate when Po2 is less than normal levels.
Influence of Po2 on veins
in venous blood:
Po2 = 40 mm Hg, Hb is 75% saturated
Only 25% of bound oxygen is unloaded during one systemic circulation.
If oxygen levels in tissue drop, then more oxygen dissociates from hemoglobin faster and respiratory rate or cardiac output need not increase.
Other factors that increase release of oxygen
1) increased concentration of Pco2 in the blood and increase in hydrogen ions in blood, lowering the pH.
2) increased heat production
factors influencing hemoglobin saturation
increases in temperature, H+, Pco2 and BPG
occur in systemic capillaries at active tissues; change in structure of hemoglobin & decrease its oxygen affinity which ENHANCE oxygen unloading; shift the oxygen-hemoglobin dissociation curve to the right
decrease in these factors shift the curve to the left
Carbon dioxide transport
transported in three forms:
1) dissolved in plasma (7-10%)
2) bound to globin of hemoglobin (20-23%)
3) transported as bicarbonate ions (HCO3-) in plasma (70%)
CO2 transport and exchange
CO2 + water <--> carbonic acid <--> H+ + HCO3-
normally slow process
CO2 + H2) <--> H2CO3
this reaction mostly occurs inside RBCs, where carbonic anhydrase reversibly accelerates both directions of reaction.
(brings water and carbon dioxide together quicker than it by themselves)
CO2 transport/exchange in systemic capillaries
carbon dioxide enters RBC; becomes acid; dissociates. HCO3- quickly diffused from RBCs to plasma; the chloride shift occurs: outrush of (-) from RBCs is balanced as Cl- moves in from plasma
CO2 transport/exchange in pulmonary capillaries
HCO3- moves into the RBCs (Cl- out) and binds with H+ to form H2CO3; H2CO3 is split by carbonic anhydrase into carbon dioxide and water; carbon dioxide diffuses into alveoli
Haldane effect (O2 & CO2)
Po2 also affects the amount of CO2 transported by Hb. Low Po2 + low hemoglobin saturation with oxygen gives way to more carbon dioxide that can be carried in the blood (reversible). oxygen and carbon dioxide can both be bound to hemoglobin. As more carbon dioxide enters the blood, more oxygen dissociates from hemoglobin and HbO2 releases oxygen and forms bonds with carbon dioxide.
influence of carbon dioxide on blood pH
plasma HCO2- is the alkaline component of the carbonic acid-bicarbonate buffer system:
-high hydrogen ion concentration in the blood, excess H+ is removed by combining with HCO3- bicarbonate
-low hydrogen ion concentration in the blood, H2CO3 carbonic acid dissociates, releasing H+
influence of CO2 on blood pH
1) changes in respiratory rate can also alter blood pH
ex: slow, shallow breathing allows CO2 to accumulate in the blood, lowering pH.
ex: hyperventilating raises pH
2) changes in ventilation can be used to adjust pH, when it is disturbed by other disease
involves neurons in Medulla
1) ventral respiratory group
2) dorsal respiratory group
ventral respiratory group
rhythm generating and integrative center; inspiratory neurons excite the inspiratory muscles; expiratory neurons inhibit the inspiratory neurons (passive) and connect to expiratory muscles (active)
dorsal respiratory group
some inspiratory stimulation; integrates sensory input from peripheral stretch, irritant and chemoreceptors
Pons integrates with higher brain to match activities.
activation of additional, accessory muscles
modified in response to changing body demands
how long the inspiratory center is active to stimulate the muscles
modified in response to changing body demands
Major breathing custodians
-central chemoreceptors- medulla (pH and CO2)
-peripheral chemoreceptors (pH, Pco2, Po2) carotid bodies at bifurcation of common carotid artery and aortic bodies at aortic arch
conscious brain bypasses respiratory centers completely for direct muscle control
influence of pH by Pco2:
1) if Pco2 levels increase, carbon dioxide accumulates in the brain
2) carbon dioxide -> carbonic acid
3) H+ stimulates the central chemoreceptors of the brain stem
4) chemoreceptors synapse with the respiratory regulatory centers: increase depth and rate of breathing
summary of chemical factors
Rising carbon dioxide levels is the normal respiratory stimulant.
Only when arterial Po2 falls below 60 mm Hg, oxygen becomes the major stimulus for respiration
Arterial pH decreases from carbon dioxide retention or metabolic factors act through the peripheral chemoreceptors.
chemical factors-arterial pH
-Normal breathing signal
-can modify respiratory rate and rhythm even if carbon dioxide and oxygen levels are normal.
-Decreased pH may be due to carbon dioxide retention, accumulation of lactic acid, excess ketone bodies in patients with diabetes.
-respiratory system controls will attempt to raise the pH by increasing hyperventilating.
Depth and rate of breathing
hyperventilation- high depth and rate of breathing from greater need to remove carbon dioxide; carbon dioxide levels decrease which may cause cerebral vasoconstriction and cerebral ischemia
stop breathing- occurs when Pco2 is low
pulmonary irritant reflexes
receptors in the bronchioles responds to irritants (debris or chemicals) causing a reflexive constriction of air passages. receptors in the larger airways mediate the cough and sneeze reflexes.
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