- Consists of the respiratory and conducting zones
- Respiratory zone
- Site of gas exchange
- Consists of bronchioles, alveolar ducts, and alveoli
- Conducting zone
- Provides rigid conduits for air to reach the sites of gas exchange
- Includes all other respiratory structures (e.g., nose, nasal cavity, pharynx, trachea)
- Respiratory muscles - diaphragm and other muscles that promote ventilation
- Functions of the Respiratory System
- To supply the body with oxygen and dispose of carbon dioxide
- Consists of the following events:
- Ventilation alternate flushing of air into and out of lungs
- Inspiration period of breathing when air enters the lungs
- Expiration - period of breathing when air exits the lungs.
- External Respiration - exchange of gases between alveoli and capillaries
- Transport of Gases - transport of oxygen and carbon dioxide between the lungs and tissues
- Internal Respiration - exchange of gases between capillaries and tissue cells
- Cellular Respiration - use of O2 by cells to make ATP
- Nasal Cavity
- Entrance - External nares (nostrils)
- Functions
- Structures
- Vibrissae - hairs that filter coarse particles from inspired air
- Respiratory mucosa (PCC) and nasal conchae
- Trap particles and push toward pharynx
- Glands secrete mucus containing lysozyme and defensins to help destroy bacteria
- During inhalation the - filter, heat, and moisten air
- During exhalation these structures:
- Reclaim heat and moisture
- Minimize heat and moisture loss
- Paranasal sinuses and nasolacrimal duct drains into
- Pharynx
- Funnel-shaped tube of skeletal muscle that connects to the:
- It is divided into three regions
- Nasopharynx - Strictly an air passageway
- Lined with pseudostratified columnar epithelium
- Closes during swallowing to prevent food from entering nasal cavity
- The pharyngeal tonsil lies high on the posterior wall
- Pharyngotympanic (auditory) tubes open into the lateral walls
- Oropharynx - serves as a common passageway for food and air
- The epithelial lining is protective stratified squamous epithelium
- Palatine tonsils lie in the lateral walls of the fauces
- Lingual tonsil covers the base of the tongue
- Laryngopharynx - serves as a common passageway for food and air
- Lies posterior to the upright epiglottis
- Extends to the larynx, where the respiratory and digestive pathways diverge
- Larynx (Voice Box)
- Attaches to the hyoid bone and opens into laryngopharynx superiorly
- The three functions of the larynx are:
- To provide a patent airway
- Act as a switching mechanism to route air and food into the proper channels
- To function in voice production
- Outer casing of 9 cartilages
- Thyroid the largest (Adam's apple)
- Cricoid - ring shaped (attached to first ring of trachea0
- Epiglottis - closes off airway when swallowing
- Others: artenoid, corniculate, cuneiform cartilages
- Vocal Ligaments
- Attach the arytenoid cartilages to the thyroid cartilage
- Composed of elastic fibers that form mucosal folds called true vocal cords
- The medial opening between them is the glottis
- They vibrate to produce sound as air rushes up from the lungs
- False vocal cords
- Mucosal folds superior to the true vocal cords
- Have no part in sound production
- Sphincter Functions of the Larynx
- The larynx is closed during coughing, sneezing, and Valsalva's maneuver
- Valsalva's maneuver
- Air is temporarily held in the lower respiratory tract by closing the glottis
- Causes intra-abdominal pressure to rise when abdominal muscles contract
- Helps to empty the rectum
- Acts as a splint to stabilize the trunk when lifting heavy loads
- Gross Anatomy of the Lungs
- Lungs occupy all of the thoracic cavity except the mediastinum
- Root - site of vascular and bronchial attachments
- Apex - narrow superior tip
- Base - inferior surface that rests on the diaphragm
- Hilus - indentation that contains pulmonary and systemic blood vessels
- Cardiac notch (impression) - cavity that accommodates the heart
- Left lung - separated into upper and lower lobes by the oblique fissure
- Right lung - separated into three lobes by the oblique and horizontal fissures
- Covered by Pleural Membranes
- Parietal pleura
- Covers the thoracic wall and superior face of the diaphragm
- Continues around heart and between lungs
- Visceral, or pulmonary, pleura - Covers the external lung surface
- Divides the thoracic cavity into three chambers
- The central mediastinum
- Two lateral compartments, each containing a lung
- Trachea
- Flexible and mobile tube extending from the larynx into the mediastinum
- Composed of three layers
- Mucosa - made up of goblet cells and ciliated epithelium
- Submucosa - connective tissue deep to the mucosa
- Adventitia - outermost layer made of C-shaped rings of hyaline cartilage
- Conduction Zone
- The trachea branches at the carina into primary bronchi which leads to each lung and then branches into
- Secondary bronchi which branch to each lobe then to
- Tertiary bronchi to more divisions
- As conducting tubes become smaller, structural changes occur
- Cartilage support structures change
- Epithelium types change
- Amount of smooth muscle increases
- Bronchioles
- Respiratory Zone
- Defined by the presence of alveoli; begins as terminal bronchioles feed into respiratory bronchioles
- Respiratory bronchioles lead to alveolar ducts, then to terminal clusters of alveolar sacs composed of alveoli
- Approximately 300 million alveoli:
- Account for most of the lungs' volume
- Provide tremendous surface area for gas exchange
- Respiratory pressure is described relative to atmospheric pressure (Patm - _________)
- Intrapulmonary pressure (Ppul) - pressure within _________
- Intrapleural pressure (Pip) - negative pressure within _________ cavity
- Must be ______ than intrapulmonary pressure
- Caused by adhesive forces between pleural membranes --> vacuum
- Lung Collapse
- Caused by ______________of the intrapleural pressure with the intrapulmonary pressure (Atelectasis & Pneumothrorax)
- Transpulmonary pressure keeps the airways open
- Transpulmonary pressure - difference between the intrapulmonary and intrapleural pressures (Ppul - Pip)
- Inspiration
- Atmospheric pressure (____ mm Hg) must be ___ intra-alveolar pressure.
- How is pressure decreased in the lungs?
- Inspiration muscles contract ( ___________&___________________)
- Volume of thorax __ lungs _______ less air/volume __ pressure.
- Only a small change needed in a healthy lung (-1mm Hg 759mm Hg)
- Boyle's law the volume of a container decreases, pressure of the gas increases P1V1 = P2V2
- Forced inspiration muscles for maximal inspiration?
- Expiration
- Inspiratory muscles _______ and the rib cage descends due to _________
- Thoracic cavity _________ decreases
- Elastic lungs _______ passively and intrapulmonary volume ____________
- Intrapulmonary pressure rises above _____________ pressure (+1 mm Hg)
- Gases flow ______ of the lungs down the pressure gradient until intrapulmonary pressure is ___
- Forced expiratory muscles?
- Physical Factors Influencing Ventilation
- Airway Resistance
- The amount of gas flowing into and out of the alveoli is directly proportional to change in P, the pressure gradient between the atmosphere and the alveoli.
- Gas flow is inversely proportional to resistance with the greatest resistance being in the medium-sized bronchi
- As airway resistance rises, breathing movements become more strenuous
- Severely constricted or obstructed bronchioles:
- Can prevent life-sustaining ventilation
- Can occur during acute asthma attacks which stops ventilation
- Epinephrine release via the sympathetic nervous system dilates bronchioles and reduces air resistance
- Alveolar Surface Tension - the attraction of liquid molecules to one another at a liquid-gas interface
- The liquid coating the alveolar surface is always acting to reduce the alveoli to the smallest possible size
- Surfactant, a detergent-like complex, reduces surface tension and helps keep the alveoli from collapsing
- Lung Compliance
- The ease with which lungs can be expanded
- Determined by two main factors
- Factors that diminish
- Scar tissue or fibrosis that reduces the natural resilience of the lungs
- Blockage of the smaller respiratory passages with mucus or fluid
- Reduced production of surfactant
- Decreased flexibility of the thoracic cage or its decreased ability to expand - Examples include:
- Deformities of thorax
- Ossification of the costal cartilage
- Paralysis of intercostal muscles
- Respiratory Volumes
- Spirometry -measurement of air volumes
- Tidal volume (TV) - air that moves into and out of the lungs with each breath (approximately 500 ml)
- Inspiratory reserve volume (IRV) - air that can be inspired forcibly beyond the tidal volume (2100 - 3200 ml)
- Expiratory reserve volume (ERV) - air that can be evacuated from the lungs after a tidal expiration (1000 - 1200 ml)
- Residual volume (RV) - air left in the lungs after strenuous expiration (1200 ml)
- Respiratory Capacities
- Inspiratory capacity (IC) - total amount of air that can be inspired after a tidal expiration (IRV + TV)
- Functional residual capacity (FRC) - amount of air remaining in the lungs after a tidal expiration (RV + ERV)
- Vital capacity (VC) - the total amount of exchangeable air (TV + IRV + ERV)
- Total lung capacity (TLC) - sum of all lung volumes (approximately 6000 ml in males)
- Dead Space (DAS)
- Anatomical dead space - volume of the conducting respiratory passages (150 ml)
- Alveolar dead space - alveoli that cease to act in gas exchange due to collapse or obstruction
- Total dead space - sum of alveolar and anatomical dead spaces
- Minute Ventilation =TV x breaths/min
- Alveolar Ventilation = (TV-DAS) x breaths/min
- Modified respiratory movements
- Cough
- Sneeze
- laugh or cry
- Hiccup
- Yawn
Alveolar Gas Exchange
- Alveoli
- Surrounded by fine elastic fibers
- Contain open pores that:
- Connect adjacent alveoli
- Allow air pressure throughout the lung to be equalized
- House macrophages that keep alveolar surfaces sterile
- Respiratory Membrane
- Alveolar walls:
- Single layer of type I epithelial cells
- Permit gas exchange by simple diffusion
- Secrete angiotensin converting enzyme (ACE)
- Basic Properties of Gases
- Dalton's Law of Partial Pressures
- Total pressure exerted by a mixture of gases is the sum of the pressures exerted independently by each gas in the mixture
- The partial pressure of each gas is directly proportional to its percentage in the mixture
- Partial pressures of gases in the air Pgas
- PO2 = .21 x 760mm Hg =
- PCO2 =.0004 x 760mm Hg =
- PN2= .79 x 760mm Hg =
- Henry's Law
- When a mixture of gases is in contact with a liquid, each gas will dissolve in the liquid in proportion to its partial pressure
- The amount of gas that will dissolve in a liquid also depends upon its solubility
- Various gases in air have different solubilities:
- Carbon dioxide is the most soluble
- Oxygen is 1/20th as soluble as carbon dioxide
- Nitrogen is practically insoluble in plasma
- N2 has the highest pressure why is there very little dissolved in the blood?
- What causes N2 to go into the blood in deep sea diving?
- Partial Pressure Gradients
- Factors influencing the movement of oxygen and carbon dioxide across the respiratory membrane
- Partial pressure gradients and gas solubilities
- Matching of alveolar ventilation and pulmonary blood perfusion
- Structural characteristics of the respiratory membrane
- Gas exchange in alveoli
- Why will CO2 leave blood?
- Why will O2 enter the blood?
- How long will the diffusion rate continue?
- Gas exchange in the tissue cells
- Why will O2 go from the blood to the cells?
- Which way will CO2 go?
- Ventilation-Perfusion Coupling
- Ventilation - the amount of gas reaching the alveoli
- Perfusion - the blood flow reaching the alveoli
- Ventilation and perfusion must be tightly regulated for efficient gas exchange
- Changes in PCO2 in the alveoli cause changes in the diameters of bronchioles
- Passageways servicing areas where alveolar carbon dioxide is high dilate
- Those serving areas where alveolar carbon dioxide is low constrict
Transport of Gases
- Oxygen Transport
- Molecular oxygen is carried in the blood:
- Bound to hemoglobin (Hb) within red blood cells
- Dissolved in plasma
- Each Hb molecule binds four oxygen atoms in a rapid and reversible process
- The hemoglobin-oxygen combination is called oxyhemoglobin (HbO2)
- Hemoglobin that has released oxygen is called reduced hemoglobin(HHb)
- Hemoglobin's affinity for O2 decreases as tissue demand for O2 increases and partial pressures decrease
- Hemoglobin's affinity for O2 increase as partial pressures increase.
- Oxygen Unloading
- Factors That Increase Release of Oxygen by Hemoglobin
- As cells metabolize glucose, carbon dioxide is released into the blood causing:
- Increases in PCO2 and H+ concentration in capillary blood
- Declining pH (acidosis), which weakens the hemoglobin-oxygen bond (Bohr effect)
- Metabolizing cells have heat as a byproduct and the rise in temperature increases BPG synthesis
- All these factors ensure oxygen unloading in the vicinity of working tissue cells
- Haldane effect - the lower the PO2 and hemoglobin saturation with oxygen, the more carbon dioxide can be carried in the blood
- Carbon Dioxide Transport
- Carbon dioxide is transported in the blood in three forms
- Dissolved in plasma - 7 to 10%
- Chemically bound to hemoglobin - 20% is carried in RBCs as carbaminohemoglobin
- Bicarbonate ion in plasma - 70% is transported as bicarbonate (HCO3-)
- Carbon dioxide diffuses into RBCs and combines with water to form carbonic acid (H2CO3), which quickly dissociates into hydrogen ions and bicarbonate ions
- In RBCs, carbonic anhydrase reversibly catalyzes the conversion of carbon dioxide and water to carbonic acid
- At the tissues:
- Bicarbonate quickly diffuses from RBCs into the plasma
- The chloride shift - to counterbalance the outrush of negative bicarbonate ions from the RBCs, chloride ions (Cl-) move from the plasma into the erythrocytes
- At the lungs, these processes are reversed
- HCO3- move into the RBCs and bind with H+ to form H2CO3
- H2CO3 is then split by carbonic anhydrase to release CO2 and H2O
- CO2 then diffuses from the blood into the alveoli
- Influence of Carbon Dioxide on Blood pH
- The carbonic acid-bicarbonate buffer system resists blood pH changes
- If hydrogen ion concentrations in blood begin to rise, excess H+ is removed by combining with HCO3-
- If hydrogen ion concentrations begin to drop, carbonic acid dissociates, releasing H+
- Changes in respiratory rate can also change blood pH:
- Hyperventilation - increased depth and rate of breathing that:
- Quickly flushes carbon dioxide from the blood
- Occurs in response to hypercapnia
- Though a rise CO2 acts as the original stimulus, control of breathing at rest is regulated by the hydrogen ion concentration in the brain
- Hypoventilation - slow and shallow breathing due to abnormally low PCO2 levels
- Apnea (breathing cessation) may occur until PCO2 levels rise
Control of Respiration: Medullary Respiratory Centers
- The dorsal respiratory group (DRG), or inspiratory center:
- Appears to be the pacesetting respiratory center
- Excites the inspiratory muscles and sets eupnea (12-15 breaths/minute)
- Becomes dormant during expiration
- The ventral respiratory group (VRG) is involved in forced inspiration and expiration
- Pons centers:
- Influence and modify activity of the medullary centers
- Smooth out inspiration and expiration transitions and vice versa
- The pontine respiratory group (PRG) - continuously inhibits the inspiration center
- Reflexes
- Pulmonary irritant reflexes - irritants promote reflexive constriction of air passages
- Inflation reflex (Hering-Breuer) -stretch receptors in the lungs are stimulated by lung inflation
- Upon inflation, inhibitory signals are sent to the medullary inspiration center to end inhalation and allow expiration
- Hypothalamic controls act through the limbic system to modify rate and depth of respiration
- Example: breath holding that occurs in anger
- A rise in body temperature acts to increase respiratory rate
- Cortical controls are direct signals from the cerebral motor cortex that bypass medullary controls
- Examples: voluntary breath holding, taking a deep breath
- Depth and Rate of Breathing: PCO2
- Changing PCO2 levels are monitored by chemoreceptors of the brain stem
- Carbon dioxide in the blood diffuses into the cerebrospinal fluid where it is hydrated
- Resulting carbonic acid dissociates, releasing hydrogen ions
- PCO2 levels rise (hypercapnia) resulting in increased depth and rate of breathing
- Hyperventilation - Occurs in response to hypercapnia
- Hypoventilation - abnormally low PCO2 levels may result in Apnea
- Depth and Rate of Breathing: Arterial pH
- Changes in arterial pH can modify respiratory rate even if carbon dioxide and oxygen levels are normal
- Increased ventilation in response to falling pH is mediated by peripheral chemoreceptors
- Acidosis may reflect:
- Carbon dioxide retention
- Accumulation of lactic acid
- Excess fatty acids in patients with diabetes mellitus
- Respiratory system controls will attempt to raise the pH by increasing respiratory rate and depth
Respiratory Adjustments:
- Exercise
- Respiratory adjustments are geared to both the intensity and duration of exercise
- During vigorous exercise:
- Ventilation can increase 20 fold
- Breathing becomes deeper and more vigorous, but respiratory rate may not be significantly changed (hyperpnea)
- Exercise-enhanced breathing is not prompted by an increase in PCO2 or a decrease in PO2 or pH
- These levels remain surprisingly constant during exercise
- As exercise begins:
- Ventilation increases abruptly, rises slowly, and reaches a steady state
- When exercise stops:
- Ventilation declines suddenly, then gradually decreases to normal
- Neural factors bring about the above changes, including:
- Psychic stimuli
- Cortical motor activation
- Excitatory impulses from proprioceptors in muscles
- High Altitude
- The body responds to quick movement to high altitude (above 8000 ft) with symptoms of acute mountain sickness - headache, shortness of breath, nausea, and dizziness
- Acclimatization - respiratory and hematopoietic adjustments to altitude include:
- Increased ventilation - 2-3 L/min higher than at sea level
- Chemoreceptors become more responsive to PCO2
- Substantial decline in PO2 stimulates peripheral chemoreceptors
Homeostatic Inbalance
- Chronic Obstructive Pulmonary Disease (COPD)
- Exemplified by chronic bronchitis and obstructive emphysema
- Patients have a history of:
- Smoking
- Dyspnea, where labored breathing occurs and gets progressively worse
- Coughing and frequent pulmonary infections
- COPD victims develop respiratory failure accompanied by hypoxemia, carbon dioxide retention, and respiratory acidosis
- Asthma
- Characterized by dyspnea, wheezing, and chest tightness
- Active inflammation of the airways precedes bronchospasms
- Airway inflammation is an immune response caused by release of IL-4 and IL-5, which stimulate IgE and recruit inflammatory cells
- Airways thickened with inflammatory exudates magnify the effect of bronchospasms
- Tuberculosis
- Infectious disease caused by the bacterium Mycobacterium tuberculosis
- Symptoms include fever, night sweats, weight loss, a racking cough, and splitting headache
- Treatment entails a 12-month course of antibiotics
- Lung Cancer
- Accounts for 1/3 of all cancer deaths in the U.S.
- 90% of all patients with lung cancer were smokers
- The three most common types are:
- Squamous cell carcinoma (20-40% of cases) arises in bronchial epithelium
- Adenocarcinoma (25-35% of cases) originates in peripheral lung area
- Small cell carcinoma (20-25% of cases) contains lymphocyte-like cells that originate in the primary bronchi and subsequently metastasize
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