Ch. 16 Respiratory System (Day 1) Flashcards
Ventilation
(Breathing)
Mechanical process that moves air into and out of the lungs
Gas Exchange occurs between?
Blood and lungs; blood and tissues
Cellular Respiration
Oxygen utilization by tissues to make ATP
External Respiration
Ventilation and gas exchange in lungs
Internal Respiration
Oxygen utilization and gas exchange in tissues
Gas Exchange in Lungs
- Occurs via diffusion
- O2 concentration in higher in lungs than in blood, so O2 diffuses into blood
- CO2 concentration in the blood is higher than in lungs, so CO2 diffuses out of blood
Respiratory System Functions (4)
- Exchange of gases between the atmosphere and the blood - brings in O2, eliminates CO2
- Homeostatic regulation of body pH - via selective retention vs excretion of CO2
- Protection from inhaled pathogens and irritating substances - via trapping and either expulsion or phagocytic destruction of potentially harmful substances, pathogens
- Vocalization - vibrations created by air passing over vocal cords
Overall Structure/Anatomy
Trachea –> primary bronchus –> bronchial tree –> terminal bronchioles –> respiratory bronchioles –> alveolar sacs –> alveolus
Conduction Zone function? Includes?
Gets air to the respiratory zone
Trachea –> primary bronchus –> bronchial tree –> terminal bronchioles
Respiratory Zone is the site of? Includes?
Site of gas exchange
Terminal bronchioles –> respiratory bronchioles –> alveolar sacs –> alveolus
Airways
Connect lungs to external environment and warm, humidify, and filter inspired air
Mucus traps small particles, and cilia move it away from the lungs
As progress from trachea through progressive bronchial branchings, total surface area increases by greater than 5 orders of magnetite (greater than 10^5)
Follow the path of air through the airway (starting at nasal cavity)
Nasal cavity –> pharynx –> larynx (through the glottis and vocal cords) –> trachea –> R and L primary bronchi –> secondary bronchi –> tertiary bronchi (more branching) –> terminal bronchioles –> respiratory zone (respiratory bronchioles) –> terminal alveolar sacs
Structure of Lung Lobule
Each cluster of alveoli is surrounded by elastic fibers and a network of capillaries
Respiratory Zone
Alveoli
- -air sacs where gas exchange occurs
- -300 * 10^6; provide large surface area (760 ft^2) to increase diffusion rate
- -each alveolus: one cell layer thick
- -form clusters at the ends of respiratory bronchioles
What are the 2 types of Alveolar Epithelial Cells?
Type 1:
–95-97% total surface area where gas exchange occurs
Type 2:
–secrete pulmonary surfactant and reabsorb sodium and water, preventing fluid buildup
Thoracic Cavity
Contains the heart, trachea, esophagus, and thymus w/in the central mediastinum
The lungs fill the rest of the cavity
Parietal Pleura
Lines thoracic wall
Visceral Pleura
Covers the lungs
Intrapleural Space (Pleural Cavity)
The parietal and visceral pleura are normally pushed together, w/ a fluid-filled space between called the Intrapleural Space
Diaphragm
Dome-shaped skeletal muscle of respiration that separates the thoracic and abdominal cavities
Physical Aspects of Ventilation
Air moves from higher to lower pressure
Pressure differences between the two ends of the conducting zone occur due to changing lung volumes
Compliance, elasticity, and surface tension are important physical properties of the lungs
Types of Pressure
- Atmospheric pressure: pressure of air outside the body
- Intrapulmonary or intra-alveolar pressure: pressure in the lungs
- Intrapleural pressure: pressure w/in the intrapleural space (between parietal and visceral pleura); contains thin layer of fluid to serve as lubricant
Pressure Differences when Breathing
- Inspiration (inhalation): intrapulmonary pressure less than atmospheric pressure
- -pressure LESS than atmospheric = sub-atmospheric or negative pressure (generally about -3mmHg) - Expiration (Exhalation): intrapulmonary pressure GREATER than atmospheric pressure (generally about +3mmHg)
Intrapleural Pressure
Less than P(intrapulmonary) and P(atmospheric) in both inspiration and expiration
P(intrapulmonary) - P(intrapleural) = P(trans pulmonary)
Keeps lungs against thoracic wall, allowing lungs to expand during inspiration
In the normal lung at rest, pleural fluid keeps the lung adhered to the chest wall
Pneumothorax
If the sealed pleural cavity is opened to the atmosphere, air flows in. The bond holding the lung to the chest wall is broken, and the lung collapses, creating a pneumothorax (air in the thorax)
Boyle’s Law
P is proportional to 1/V
- -P = pressure; V = volume
- -assumes temperature constant and closed system
Increased lung volume during inspiration, decreases P(intrapulmonary) to less than P(atmospheric) –> air flows in
Decreased lung volume during expiration –> P(intrapulmonary) greater than P(atmospheric) –> air flows out
Lung Compliance
Physical property of lungs
- Lungs expand when stretched
- Defined as change in lung volume per change in transpulmonary pressure: (delta)V/(delta)P
- Index of the ease w/ which the lungs expand under pressure
- High compliance:
- ->easily stretched
- Low Compliance:
- ->requires more force, restrictive lung diseases, e.g. pulmonary fibrosis, surfactant deficiency
Lung Elasticity
- Return to initial size after being stretched
- Lungs have elastin fibers
- Because the lungs are stuck to the thoracic wall, they are always under elastic tension
- Tension increases during inspiration and is reduced by elastic recoil during expiration
Surface Tension
Exerted by fluid in the alveolus
Resists distention, promotes collapse of alveolar space
Exerted by fluid secreted on the alveoli
Fluid is absorbed by active transport of Na+ and secreted by active transport of Cl-
–any imbalance between these can result in viscous fluid that is difficult to clear –> raises the pressure of the alveolar air as it acts to collapse the alveolus
People w/ cystic fibrosis have a genetic defect that causes such an imbalance of fluid absorption and secretion
So what is surface tension?
It’s the force holding fluid molecules together at an air-fluid interface
Surface tension results from?
Strong attractive force of hydrogen bonds between water molecules
Law of Laplace
Pressure is directly proportional to surface tension and inversely proportional to radius of alveolus
Small alveoli would be at greater risk of collapse w/o surfactant
Ex: 2 different sized bubbles in diagram (notes, p.14) have same surface tension. According to Law of Laplace, pressure is greater in the smaller bubble
Surfactant
Surface active agent
Secreted by type II alveolar cells
Consists of hydrophobic protein and phospholipids
Reduces surface tension between water molecules by reducing the number of hydrogen bonds between water molecules
More concentrated as alveoli get smaller during expiration
Prevents collapse
Allows a residual volume of air to remain in lungs
Surfactant reduces? (2 things)
- Surface tension. In the lungs, smaller alveoli have more surfactant per unit surface area, which equalizes pressure between large and small alveoli
- The work of breathing and prevents smaller alveoli from tempting into bigger alveoli
Respiratory Distress Syndrome (RDS)
Production of surfactant begins late in fetal life, so premature babies have higher risk for alveolar collapse - Respiratory Distress Syndrome (RDS); treated w/ surfactant
Similar problems may occur in adults w/ septic shock - decrease in lung compliance, decrease in surfactant - acute RDS; not treatable w/ surfactant
Pulmonary Ventilation
Mechanisms of breathing
Inspiration and Expiration
Accomplished by changing thoracic cavity/lung volume
Inspiration (inhalation)
Breathe in
Expiration (exhalation)
Breathe out
Muscles of Inspiration
- Sternocleidomastoid and Scalenes
- -used for forced inspiration - External Intercostals
- -raises rib cage during inspiration - Parasternal Intercostals
- -works w/ external intercostals - Diaphragm
- -contrats in inspiration - lowers –> enlarging thoracic cavity
- -relaxes in expiration - raises –> thoracic cavity smaller
Muscles of Expiration
Quiet expiration occurs w/ the relaxation of the inspiratory muscles (passive process)
- Internal Intercostals
- -lowers rub cage during forced expiration - External Abdominal Oblique, Internal Abdominal Oblique, Transversus Abdominis, Rectus Abdominis
- -abdominal muscles are also used for forced expiration - Diaphragm
- -relaxes in expiration - raises –> thoracic cavity smaller
Diaphragm at Rest: relaxed or contracted?
Relaxed
Mechanisms of Breathing: Inspiration
Volume of thoracic cavity (and lungs) increases vertically when diaphragm contracts (flattens) and laterally when parasternal and external intercostals raise the ribs
–thoracic and lung volume increase –> intrapulmonary pressure decreases –> air in
Inspiration occurs when alveolar pressure ____?
Decreases
Inspiration: Thoracic Volume Increasing
- Thoracic cage expands outward
2. Diaphragm drops down - contracts and flattens
Inspiration: Side and Front Views
Side: as ribs move up, sternum is pushed up and out, expanding the cage
Front: ribs move up, expanding lateral dimension of rib cage
Expiration
Volume of thoracic cavity (and lungs) decreases vertically when diaphragm relaxes (dome) and laterally when external and parasternal intercostals relax for quiet expiration or internal intercostals contract in forced expiration to lower the ribs
–thoracic and lung volume decreases –> intrapulmonary pressure increases –> air out
Diaphragm and chest wall muscles between ribs relax, and thoracic volume increases
Regulation of Ventilation
Unlike cardiac muscle, skeletal muscles are NOT spontaneously active, so they must be stimulated by nerve signals
Rhythmic pattern of contraction and relaxation of breathing muscles arises from a neural network of spontaneously discharging motor neurons from cerebral cortex (voluntary breathing) and respiratory control centers of Medulla Oblongata and Pons (involuntary breathing)
Motor neurons - innervate diaphragm/other breathing muscles; regulated by descending neurons from the brainstem (Medulla and Pons)
Control of Breathing
Medulla:
- -2 rhythmicity centers: excitatory inspiratory neurons vs neurons which inhibit those inspiratory neurons - intrinsic rhythmicity, but influenced by other factors
- Involuntary breathing (e.g. at rest) - intrinsic to medulla
- Voluntary (“forced,” e.g. exercise) - input from cerebral cortex
Pons: 2 respiratory control centers
- Apneustic (stimulates inspiratory neurons in medulla)
- Pneumotaxic (antagonizes apneustic to inhibit inspiration)
Regulation of Ventilation is controlled by which nervous system?
CNS
