Respiratory System

I. Overview

Respiration include four processes:

1. Pulmonary ventilation (air in/out, gas exchanged in lungs)
2. External respiration (gas exchanged between blood and alveoli in lungs)
3. Transport of respiratory gases (transport of oxygen and carbon dioxide)
4. Internal respiration (gas exchange between blood and tissues)

II. Functional Anatomy of Respiratory System (Nose, pharynx, larynx, trachea, bronchi, lungs, and alveoli ) Diagram

Consists of two zones:

1. Respiratory zone - actual site of gas exchange (bronchioles, a;veolar ducts, alveoli)
2. Conducting zones - all other respiratory passageways

A. Nose

i. Functions:

• Provides airways for respiration
• Moistens and warms entering air
• Filters inspired air and cleanses it
• Serves as resonating chamber for speech
• Houses the olfactory (smell) receptors

ii. Nose structure Diagram

• External nose composed of dense fibrous connective tissue and cartilage attached to nasal, frontal, and maxillary bone
• External nares (nostrils) lead into nasal cavity which is divided by the nasal septum (composed of hyaline cartilage and vomer bone)
• Nasal cavity entrance contains vestibule with vibrissae
• Nasal cavity lined with olfactory mucosa and respiratory mucosa (mucous and serous glands) and contains lateral projections (superior, middle, inferior nasal conchae)
• Internal nares in posterior nasa cavity lead into the nasopharynx

B. Pharynx Diagram

• Connects nasal cavity and mouth to larynx and esophagus (throat)
  
• Three regions:
  • Nasopharynx - lined with pseudostratified epithelium and houses the pharyngeal tonsil (adenoids)
  • Oropharynx - lined with stratified squamous epithelium, located posterior to oral cavity, include archway (fauces) between uvula and epiglottis, and contain palantine and lingual tonsils
  • Laryngopharynx - lined with stratified squamous epithelium, common passageway for food and air, posterior to epiglottis

C. Larynx Diagram

• Voice box attached to hyoid superiorly and inferiorly with trachea
• Composed of corniculate, arytenoid, cricoid, and thyroid cartilage
  
• Functions:
  • Provide open airway
  • Act as switching mechanism (epiglottis) to route air and food
  • Voice production (vestibular fold or false vocal chord and vocal fold or true vocal cord)

D. Trachea Diagram

• Windpipe
• Descends from larynx through neck into mediastinum and ends by dividing (at carina) into two primary bronchi
• Walls (mucosa, submucosa, hyaline cartilage and adventitia)
• lined with pseudostratified epithelium
  

E. Bronchi and Subdivisions (bronchial tree)

• Conducting zone structures - right and left primary (principle) bronchi branch into:
  • Secondary bronchi (3 on right 2 on left) which branch into
  • Tertiary (segmental) bronchi which branch into
  • 4th, 5th, etc... 23 orders
  • Until bronchioles then terminal bronchioles
    
• Tissue composition of walls of primary bronchi is same as trachea but decreases in size of conducting tubes, then increase in change in composition with each subsequent subdivision:
  • Cartilage rings replaced by irregular plates of cartilage
  • Epithelium: Pseudostratified, then columnar, then cuboidal; cilia and mucus producing cells only in upper bronchioles Diagram
    
  • Smooth muscle increases with decreasing size of bronchioles
    
• Respiratory zone structures - terminal bronchioles divide into respiratory bronchioles with scattered air sac outpocketing from walls, branch into
  • Alveolar ducts with sacs called alveoli (chambers where bulk gas exchange occurs)
  • Alveolar sacs open into a common chamber called an atrium
    
• Air sacs (alveoli) provide surface area for gas exchange Diagram
• Respiratory membrane - Diagram single layer of squamous epithelium (Type I pneumocytes) with pulmonary capillaries
  • Respiratory membrane (air-blood barrier) site of gas exchange (by diffusion)
  • Diffusion requires moist membrane, therefore there are cuboidal epithelium (Type II pneumocytes) that secretes surfactant, coating gas-exposed alveolar surfaces
  • Alveoli contain alveolar macrophages that provide an immunologic defense.

F. Lungs and Plurae

i. Lungs

• Three lobes on right and two lobes on left Diagram
  
• Occupy the entire thoracic cavity, suspended in its own pleural cavity connected to the mediastinum by vascular and bronchial attachments (roots)
• Lung tissue also referred to as stroma

ii. Pluera

• Thin, double-layered serosa
• Parietal pluera lines the thoracic cavity and visceral pleura covers external lung surface

III. Mechanisms of Breathing (Pulmonary ventilation - inspiration and expiration)

A. Pressure relationships in the thoracic cavity

• Respiratory pressures are always given relative to atmospheric pressure
  
• Thoracic cavity
  • Intrapulmonary pressure - pressure within the alveoli of the lungs; always equal to atmospheric pressure
  • Intrapleural pressure - pressure within pleural cavity; always 4 mm Hg less than atmospheric pressure in alveoli; results from factors holding lungs to thorax wall and those acting to pull lungs away from wall
    
• Negative pressure in the intrapleural space results from the interaction between factors acting to hold the lungs to the thorax wall and factors acting to pull the lungs away
  
  • factors holding lungs to thorax walls:
    1. Adhesive force (surface tension) created by pleural fluid in pleural cavity
    2. Positive pressure within lungs (interpleural pressure is always greater than intrapleural)
    3. Atmospheric pressure acting on thorax (atmospheric pressure pushing on chest is greater than intrapleural pressure, therefore thorax wall tends to be "squeezed" in)
  • Factors forcing the lungs away from thorax wall
    1. Natural recoil tendency of lungs (due to elasticity)
    2. Surface tension of the fluid film in alveoli (draws the alveoli to smallest possible dimension)
    
    
  Question: what is the role of the diaphragm and the role of internal/external costal muscles in regulating pressure differentials?
  

B. Pulmonary Ventilation: Inspiration and Expiration Diagram

• Volume changes lead to pressure changes, which lead to the flow of gases to equalize the pressure
  
• P₁V₁=P₂V₂ (Boyle's Law) pressure of gas is inversely proportional to volume at a constant temperature
  • Inspiration 
    1. Inspiratory muscles (external intercostals) contract; diaphragm descends; rib cage rises
    2. Thoracic cavity volume increases
    3. Lungs stretched; intrapulmonary volume increases
    4. Intrapulmonary pressure decreases
    5. Air (gases) flows into lungs down its pressure gradient until intrapulmonary pressure is zero (equal to atmospheric pressure)
    6. Ribs elevated and sternum flares as external intercostals contract; diaphragm moves inferiorly during contraction
       
  • Expiration 
    1. Inspiratory muscles relax (diaphragm rises, ribcage descends due to gravity)
    2. Thoracic cavity volume decreases
    3. Elastic lungs recoil passively; the intrapulmonary volume decrease
    4. Intrapulmonary pressure rises
    5. Air (gases) flows out of lungs down its pressure gradient until intrapulmonary pressure is zero 
    6. Ribs and sternum depressed as external intercostals relax; diaphragm moves superiorly as it relaxes

C. Respiratory Status

i. Respiratory Volumes: (measured by spirometer) Diagram

• (TV) tidal volume - amount of air inhaled or exhaled with each breath under resting conditions
• (IRV) inspiratory reserve volume - amount of air that can be forcefully inhaled after a normal tidal volume inhalation
• (ERV) expiratory reserve volume - amount of air that can be forcefully exhaled after a normal tidal volume exhalation
• (RV) residual volume - amount of air remaining in the lungs after a forced exhalation

ii. Respiratory Capacities:

• (TLC) total lung capacity - maximum amount of air contained in lungs after a maximum inspiratory effort (TLC = TV + IRV + ERV + RV)
• (VC) vital capacity - maximum amount of air that can be expired after a maximum inspiratory effort (VC = TV + IRV + ERV)
• (IC) inspiratory capacity - maximum amount of air that can be inspired after a normal expiration (IC = TV + IRV)
• (FRC) functional residual capacity - volume of air remaining in the lungs after a normal tidal volume expiration (FRC = ERV + RV)

IV. Transport of Respiratory Gases by Blood

A. Oxygen Diagram

• Molecular oxygen is carried in blood in two ways:
  1. Bound to hemoglobin within red blood cells (98.5%)
  2. Dissolved in plasma (1.5%)
     
• Oxyhemoglobin (HbO₂) / doexyhemoglon (Hhb)
  
• Hemoglobin - composed of four polypeptide chains each containing and iron (heme) group;
  • Oxygen binding is result of "cooperation"; first oxygen bound to one heme causing change in shape of hemoglobin so that the other peptides will bind more oxygen
  • affinity for oxygen increases with each oxygen bound until saturation; conversely, release of oxygen from hemoglobin increases with each oxygen released

B. Carbon Dioxide Diagram

• Active body cells produce about 200ml of carbon dioxide/minute(released by lungs)
• Carbon dioxide is transported in blood in three forms:
  
  1. Dissolved in plasma (7% to 10%), remainder enter RBCs
  2. Chemically bound to hemoglobin in RBCs (20% to 30%); carried within RBCs as carboaminohemoglobin; carbon dioxide binds to amino acids not heme, therefore does not compete with the oxyhemoglobin transport
  3. As a bicarbonate ion in plasma (60% to 70%), carbon dioxide is converted to bicarbonate ions and transported in plasma
     

C. Respiratory Center Diagram

• Medulla oblongata
  • Inspiratory center - sets the respiratory rhythm
• Pons
  • Contains centers that influence and modify the activity of the medullary neurons
    1. Pneumotaxic center continuously transmits inhibitory impulses to the inspiratory center of the medulla
    2. Apneustic center continuously transmits stimulatory impulses to the inspiratory center of the medulla

Clinical Terms

• Eupnea - quiet breathing
• Tachypnea - rapid breathing
• Costal breathing - shallow
• Diaphragmatic breathing - deep
• Atelectasis - collapse or incomplete expansion of lungs
• Cheyne-Stokes respiration - irregular breathing (increase/decrease in depth and rapidity)
• Laryngitis - inflammation of the vocal cords
• Pleurisy - inflammation of the pleura
• Infant respiratory distress syndrome (IRDS) - insufficient surfactant produced, surface tension forces collapse of the alveoli
• Hypoxia - inadequate amount of oxygen circulated to no oxygen delivered to body cells
  • Hypoxic - lack of oxyen getting from lungs to heart
    
  • Anemic - to few RBCs, or RBCs with inadequate hemoglobin
  • Ischemic (stagnant) - blood circulation is impaired or blocked
  • Histotoxic - interference with gas exchange betweem capillaries and target tissue/organ
    
• Hypercapnia - increase in carbondioxide levels in cerebrospinal fluid, causing pH to decrease, exciting chemoreceptors to make synapses with respiratory centers; depth and rate of breath increases (hyperventilation)
• Hypocapnia - apnea (breathing cessation)
• Chronic Obstructive Pulmonary Disease (COPD), common features:
  1. Patients with history of smoking
  2. Dyspnea - difficult or labored breathing
  3. Coughing and frequent pulmonary infection
  4. Will develop respiratory failure
• COPDs:
  • Obstructive emphysema - permanent enlargement of the alveoli, deterioration of alveolar walls
    • Chronic inflammation leads to lung fibrosis (lungs lose their elasticity)
    • Victims sometimes called "pink puffers" - breathing is labored, but doesn't become cyanotic because gas exchange remains adequate until late in the disease
  • Chronic bronchitis - inhaled irratants lead to chronic excessive mucus production by the mucosa of lower respiratory passageways and inflammation and fibrosis of that mucosa
    • Victims sometimes called "blue bloaters" - hypoxia and cabon dioxide retention occur