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Respiratory System (Functions (Water Loss, Acid-Base balance, Metabolism,…
Respiratory System
Functions
Water Loss
Acid-Base balance
Metabolism
Defense
Production of sounds (with motor/nervous system)
Gas exchange
Detect odors (with olfactory receptors in nervous system)
Defense
Alveolar macrophages engulf small particles that reach lungs
Meatuses (narrow passageways) produce turbulence, traps particles in mucus, warms and humidifies incoming air, and brings olfactory stimuli to olfactory receptors
Cilia sweep mucus and trapped debris and microorganisms toward pharynx to be swallowed - mucus escalator
Mucous cells and mucous glands produce mucus that bathes exposed surfaces and helps remove particles and pathogens
Filtration in nasal cavity removes large particles
Efficiency of Gas Exchange
Oxygen and carbon dioxide are lipid soluble
Total surface area is large
Distances involved in gas exchange are short
Blood flow and airflow are coordinated
Differences in partial pressure across blood air barrier are substantial
Types of Tissues
Pseudostratified ciliated columnar epithelium lining upper respiratory tract
Simple cuboidal epithelium lining alveolar ducts
Stratified squamous epithelium lining nasal cavity
Simple squamous epithelium lining pulmonary alveoli
Pressures
Intra-Alveolar Pressure
Varies with phase of respiration
Difference in alveolar pressure and atmospheric pressure drives air flow
Pressure of air in alveoli
Intrapleural Pressure
Varies with phase of respiration
4 mmHg at rest
Negative due to elasticity in lungs and chest wall
Lungs recoil inward as chest wall recoils outward, opposing forces pull on intraplueral space, surface tension of intrapleural fluid prevents wall and lungs from pulling apart
Pressure inside pleural sas
Always negative under normal conditions and less than alveolar pressure
Atmospheric Pressure
Decreases as altitude increases
Increases under water
760 mmHg at sea level
Other lung pressures are given relative to atmospheric pressure
Transpulmonary Pressure
Distending pressure across the lung wall
Increase in transpulmonary pressure, increases distending pressure across lungs, causes lungs (alveoli) to expand, increasing volume
Transpulmonary pressure is equal to alveolar pressure minus intrapleural pressure
Abnormalities
Hypoxia
Low tissue oxygen levels
Anoxia
Complete lack of oxygen in tissues
Pneumothorax
Collapsed lung
Gas Transport
Agents
Blood plasma cannot transport enough oxygen and carbon dioxide to meet physiological needs
Red blood cells transport oxygen to, and carbon dioxide from, peripheral tissues and remove oxygen and carbon dioxide from plasma allowing gases to continue to diffuse into blood
Oxygen
Binds to iron ions in hemoglobin molecules
If blood oxygen pressure is low, oxygen is released from hemoglobin
Occurs at systemic capillaries
If blood oxygen pressure is high, oxygen is bound by hemoglobin
Occurs at pulmonary capillaries
Oxygen combines reversibly with heme portion of hemoglobin
Arterial hemoglobin is more saturated with oxygen
98% of oxygen is carried by hemoglobin
Oxygen bound oxyhemoglobin
No oxygen bound deoxyhemoglobin
Saturation
Percent of heme units containing oxygen
Hemoglobin can bind up to four oxygen molecules
Binding follows Law of Mass Action
More oxygen means more binding
100% saturation means hemoglobin is binded to four oxygens
Saturation Curve
Leftward shift (increased affinity)
Rightward shift (decreased affinity)
Affected by:
Temperature
When temperature decreases, hemoglobin holds oxygen more tightly
Temperature effects are significant only in active tissues that are generating large amounts of heat such as active skeletal muscle
When temperature increases, hemoglobin releases more oxygen
2,3 = BPG
Produced in red blood cells under conditions of low oxygen such as anemia and high altitude
Synthesis is inhibited by oxyhemoglobin
2,3 - BPG - glycolysis intermediate
2,3 - BPG decreases affinity of hemoglobin for oxygen, enhancing oxygen unloading
2,3 - DPG = 2,3 - bisphosphoglycerate
Bohr Effect
Effect of pH on hemoglobin/oxygen dissociation
Higher H+ and lower pH increases oxygen unloading
H+ in the blood causes a decrease in affinity of hemoglobin for oxygen and thus release of oxygen at the tissue because it shifts the equation to the left (Hb + O2 <-- --> HbO2 + H+) and thus less H+
Increase in carbon dioxide causes an increase in release of H+
Active tissues produce more acid which decreases pH in tissues, which causes a rightward shift so that more oxygen is unloaded to tissues
CO2 - Carbamino Effect
HbCO2 has lower affinity for oxygen than Hb
Increased metabolic activity, increases carbon dioxide
Carbon dioxide reacts with hemoglobin to form carbaminohemoglobin
Equation shifts right = more oxygen unloading
Increased oxygen unloading in active tissue
Carbon Dioxide
23% bound to protein portions of hemoglobin molecules in red blood cells forming carbaminohemoglobin
7% transported as dissolved gas molecules in plasma
70% transported as bicarbonate ions (HCO3-)
Hydrogen ions bind to hemoglobin in red blood cells
Bicarbonate ions move into plasma in exchange for chlorine ions (chloride shift)
Most carbon dioxide entering bloodstream diffuses into red blood cells
Carbon dioxide is converted to carbonic acid (H2CO3)
Dissociates into H+ and bicarbonate (HCO3-)
Respiration
Internal
Oxidative Phosphorylation: intracellular metabolic processes using oxygen and producing carbon dioxide in the mitochondria
External
Process by which oxygen moves from atmosphere to alveoli to blood to tissue and carbon dioxide moves from tissue to blood to alveoli to atmosphere
Transport of oxygen and carbon dioxide from lungs to body tissue
Exchange of oxygen and carbon dioxide between air in lungs to blood
Ventilation: the movement of air in and out of the lungs
Exchange of oxygen and carbon dioxide between blood and tissue
Respiratory Tract
Conducting Zone
Anatomy
Nasal cavity, pharynx, larynx, trachea, primary bronchi, secondary bronchi, tertiary bronchi, bronchioles, terminal bronchioles
Physiology
Humidifies air (about 150 mL), mucus secretions via goblet cells, cilia, mucus escalator
Respiratory Zone
Anatomy
Respiratory bronchioles, alveolar ducts, alveolar sacs, alveoli
Type I alveolar cells make up the wall of alveoli
Type II alveolar cells secrete pulmonary surfactant
Physiology
Exchange of oxygen and carbon dioxide via diffusion, epithelial cell of alveoli, endothelial cell of capillaries
Breathing
Inspiration
External intercostal muscles contract, rib cage moves up and out, diaphragm contracts and moves down, pressure in lung decreases, and air comes rushing in
Volume of thoracic cavity increases, which increases lung volume, which causes alveolar pressure to decrease so that atmospheric pressure is greater than alveolar pressure and air flows into lungs
Expiration
Rib cage moves down and in, diaphragm relaxes and moves up, pressure in lungs increases, and air is pushed out
Volume of thoracic cavity decreases, which decreases lung volume, which increases alveolar pressure so that alveolar pressure is greater than atmospheric pressure and air movies out of lungs
Air Flow
Flow is equal to the change in pressure over resistance
If atmospheric pressure does not change, then air flows because of changes in alveolar pressure
Boyle's Law
P1V1 = P2V2
If volume increases, then pressure decreases
If volume decreases, then pressure increases
Gas Exchange
Occurs between blood and alveolar air across blood air barrier
Depends on:
Partial pressures of gases involved
Dalton's Law
Sum of all the individual partial pressures is equal to the total pressure exerted by the gas
21% Oxygen
79% Nitrogen
At sea level the total pressure is 760 mmHg (1 atm)
0.03% Carbon Dioxide
Diffusion of molecules between gas and liquid
Rate of diffusion depends on physical principles, or gas laws
Henry's Law
Concentration is equal to solubility multiplied by the pressure (C = k x P)
As pressure increases, concentration increases
At a given temperature, amount of a gas in solution is proportional to partial pressure of that gas
When gases under pressure contacts a liquid, pressure forces gas molecules into solution
At equilibrium, gas molecules diffuse out of liquid as quickly as they enter it and the number of gas molecules in solution is constant
Regulation
Local Regulation
Neural Regulation
Pulmonary Ventilation
Respiratory system adapts to changing oxygen demands by varying number of breathes per minute (respiration rate) and amount of air moved per breath (tidal volume)
Minute Ventilation
Calculated as respiratory rate multiplied by the tidal volume
Measures pulmonary ventilation
Amount of air moved per minute
Normal minute ventilation = 500 mL x 12 breaths/min = 6000 mL/min
Alveolar Ventilation
Volume of air reaching gas exchange per minute
Calculated as tidal volume multiplied respiration rate minus dead space volume multiplied by respiration rate
Alveolar Ventilation = (TV x RR) - (DSV x RR)
Normal Alveolar Ventilation = (500 mL/breath x 12 breaths/min) - 150 mL/breath x 12 breaths/min) = 4,200 mL/min
Rate of Diffusion
Affected by:
Surface area of membrane
Will be decreased by disease (emphysema)
Diffusion of coefficient gas
Gas's molecular weight and solubility
Carbon dioxide is highly soluble
Oxygen is somewhat soluble
Thickness of membrane
Will be increased with edema (swelling)
Partial pressure difference of gas between two sides of membrane which is affected by altitude