Pulmonary System Overview

Overview of Pulmonary System

• The function of the pulmonary system is the exchange of gases between environmental air and blood
• Ventilation is the movement of air into and out of the lungs
• Diffusion is the movement of gases between air spaces in the lungs and the bloodstream
• Perfusion is the movement of blood into and out of the capillary beds of the lungs to body organs and tissues
• The pulmonary system carries out ventilation and diffusion
• Cardiovascular system carries out perfusion
• Gas exchange occurs in the Acinus airways, including respiratory bronchioles, alveolar ducts, and alveoli
• Alveoli are primary gas exchange units

Structure of the Pulmonary System

• Structures include upper airways, and two lungs, the left lung (two lobes) and right lung (three lobes)
• Two lungs consist of segments and lobules
• Structures include lower airways, blood vessels, the chest wall or thoracic cage, and the diaphragm
• The diaphragm is dome-shaped muscle, it is involved in ventilation, separates the thoracic and abdominal cavities
• The mediastinum is the space between the lungs, containing the heart, great vessels, and esophagus
• The conducting airways warm and humidifies air, which consist of the upper and lower airways
• The upper airways are the nasopharynx and oropharynx
• The larynx connects the upper and lower airways
• The lower airways includes the trachea, bronchi, and terminal bronchioles
• The carina is a ridge divides the trachea into the right and left bronchi
• The hila is where the right and left bronchi enter the lungs, along with blood and lymph vessels
• Goblet cells produce mucus and cilia are hairlike structures
• Goblet and cilia help propel foreign material upward to enable it to be coughed up

Alveoli

• Alveoli are primary gas exchange units where oxygen enters the blood, and carbon dioxide (CO2) is removed
• Type I alveolar cells provide the alveolar structure
• Type II alveolar cells produce surfactant to prevent lung collapse
• Alveoli contains alveolar macrophages, ingesting foreign material, and remove it through the lymphatic system

Chest Wall and Pleura

• The chest wall includes the skin, ribs, and intercostal muscles
• The chest wall protects the lungs, its muscles and the diaphragm performs the muscular work of breathing
• Containing the thoracic cavity, it is encased by the chest wall
• The serous membrane adheres firmly to the lungs
• It folds over itself, and firmly attaches to the chest wall
• The visceral pleura: Membrane covering the lungs and the Parietal pleura: Lines the thoracic cavity
• The pleural cavity fluid lubricates the pleural surfaces, allowing a sliding movement
• Pressure in the pleural space is negative or sub-atmospheric at -4 to -10 mm Hg

Function of the Pulmonary systems

• Ventilation is the mechanical movement of gas or air into and out of the lungs
• Ventilation is not the same as respirations
• Minute volume is the ventilatory rate multiplied by the volume of air per breath
• Alveolar ventilation must be measured by arterial blood gases
• Ventilation measures partial pressure of carbon dioxide (PaCO2)
• The respiratory center is located in the brainstem
• The respiratory center receives impulses from chemoreceptors in the carotid and aortic bodies
• The respiratory center detects the PaCO2 and the amount of oxygen in the arterial blood

Respiratory Center Modifiers

• The pneumotaxic and apneustic centers are located in the pons
• Modifiers of the inspiratory depth and rate are established by the medullary centers

Lung Receptors

• Irritant receptors are sensitive to noxious substances and when stimulated cause cough, bronchoconstriction, and/or increase respiratory rate
• Stretch receptors protect against excess lung inflation by decreasing respiratory rate and volume
• Juxta pulmonary capillary (J) receptors are sensitive to increased pulmonary capillary pressure

Autonomic Nervous System (ANS)

• Parasympathetic receptors cause smooth muscles to contract and are the main controllers of airway caliber
• Sympathetic receptors relax smooth muscles

Lung Compliance

• Lung compliance consists of elastic properties of the lungs and chest wall
• Compliance measures lung and chest wall distensibility
• Compliance represents the relative ease with which lung structures can be stretched
• Compliance is reciprocal of elasticity
• Low compliance demonstrates increased work of inspiration, meaning stiff lungs
• High compliance demonstrates increased work of expiration, meaning they're easy to inflate, having lost some elastic recoil
• Pulmonary gas exchange includes oxygen delivery to the cells of the body and the removal of CO2

Steps of Gas exchange

• Steps of diffusion the lungs involve: ventilation, diffusion of oxygen from the alveoli into the capillary blood, perfusion of systemic capillaries with oxygenated blood, then diffusion of oxygen from systemic capillaries into the cells
• Diffusion of CO2 then occurs in the reverse order
• Respiration is the movement of gasses across alveoli-capillary membrane AND systemic capillary-cell
• Diffusion is the movement of gases down a pressure gradient from an area of high pressure to an area of low pressure
• Atmospheric pressure (barometric pressure) can be by multiplying concentration of a gas by the atmospheric pressure
• Example: 760 mm Hg x 21% = 150 mm Hg
• Factors affecting diffusion through the alveolar-capillary membrane are: partial pressure of gasses, pressure gradient, lung surface area, membrane thickness, and length of gas exposure

Oxygen Status

• Three major determinants of oxygen status include PaO2 - PaO2 must be obtained from ABG results - PaO2 is considered the partial pressure PP of Oxygen dissolved in arterial blood - PaO2 is 3% of total O2 - PaO2 normal range is 80-100mm Hg
• SaO2 and SpO2 describe the percentage of oxygen bound to Hgb in the blood - SaO2 and SpO2 normal value > 95%, but COPD Pat, 88-93% is satisfactory - O2 qualifies for home use when < 88% SaO2 or SpO2 is required.
• Hemoglobin as the major carrier of O2 is important in tissue oxygenation

Hypoxemia

• Normal levels consist of PaO2 from 80-100 mm Hg
• Moderate Hypoxemia consists of PaO2 from 60-80 mm Hg
• Severe Hypoxemia consists of PaO2 from 40-60 mm Hg
• Very severe Hypoxemia consists of PaO2 < 40 mm Hg

Oxygen and Carbon Dioxide Transport

• The oxyhemoglobin dissociation curve partially determines the affinity of O2 to hemoglobin, affecting diffusion
• The oxyhemoglobin dissociation curve represents the RELATIONSHIP of the pp of arterial O2 (PaO2) and Hgb saturation of O2 (SaO2)
• Ventilation/perfusion is based on Perfusion defined as pumping or flow of blood into tissues and organs, which is altered by cardiac output (CO =SV X HR, CO defined as adequate when it reflects adequate perfusion), and gravity.
• Perfusion defined as pumping or flow of blood into tissues and organs, is altered by CO and gravity
• CO =SV X HR, CO defined as adequate when it reflects adequate perfusion
• CO is also altered by gravity
• CO2 is carried in the blood 3 ways includes: Dissolved in plasma at 10%, transported as Bicarb at 60% (chemically modified), and 30% combined with blood proteins