Respiratory System

• Respiratory System


  A network of tissues and organs responsible for gaseous exchange between the circulatory system and atmosphere

  
• Respiratory system


  • Provides the route by which oxygen in the atmospheric air gain entrance into the body and the route for excretion of the carbon dioxide

  
• Functions of the respiratory system

  • To supply the body with oxygen and eliminate carbon dioxide
  • Involved in regulating blood pH
  • Role in mechanical non-specific immune defences
  • Providing olfactory sensations

  
• Structural classification of the human respiratory system

  • Upper respiratory tract
  • Lower respiratory tract

  
• Upper respiratory tract


  • Nose
  • Pharynx
  • Larynx

  
• Lower respiratory tract


  • Trachea
  • Lungs
  • Carina
  • Right and left pulmonary bronchi
  • Bronchioles
  • Alveoli

  
• Organs of the Respiratory System

  • Pharynx
  • Epiglottis
  • Oesophagus
  • Intercostal Muscles
  • Left Lung
  • Bronchioles
  • Alveoli
  • Nasal Cavities
  • Larynx
  • Trachea
  • Pulmonary Vessels
  • Right Lung
  • Bronchi
  • Heart
  • Pleural membrane
  • Diaphragm

  
• Nose & nasal cavity

  • Primary inlet for air via nostrils or anterior nares
  • Nasal cavity is divided into two equal passages by a septum
  • During inhalation, air enters through the nose to the nasal cavity where it is warmed, moistened and filtered
  • Mucus secreted into epithelial cells – form protective barrier
  • Also contains immune cells, secretory antibodies and antimicrobial enzyme to break down bacterial cell walls
• Pharynx


  • Also known as the throat, about 12-14cm long
  • Connects the nasal and oral cavity with the larynx
  • Divided into nasopharynx, oropharynx, laryngopharynx
  • Nasopharynx lies posterior to the nasal cavity and contains two openings - one leads to the auditory tube while the other leads to the oropharynx and laryngopharynx
  • Tonsils form a ring around the nasopharynx
  • Oropharynx – middle portion of the pharynx
  • Part of both respiratory system and digestive system - food, drink & air all pass through
  • Lined with non-ciliated stratified squamous epithelium to protect it from abrasive effects of swallowing
  • Laryngopharynx – part of both respiratory & digestive system, continuous with the larynx

  
• Larynx (voice box)


  • Formed of 9 pieces of cartilage, connected to laryngopharynx and trachea
  • Largest is thyroid cartilage – Adams apple
  • Epiglottis- Sometimes referred to as the "guardian of the airways", the epiglottis protects the superior opening of the larynx
  • Cricoid cartilage – formed at the base of the larynx
  • Contains vocal cords – vibrate when air passes through them to generate sound

  
• Anatomy of the Respiratory System

  
• Common Upper Respiratory Tract Conditions

  • Common cold
  • Pharyngitis
  • Tonsilitis
  • Hay fever
  • Acute sinusitis

  
• Trachea (windpipe)


  • Approx. 10-12cms long and 2.5 cm in diameter
  • Extends from larynx to carina (the point at which it splits into the right & left bronchi)
  • Dense regular connective tissue and smooth muscle reinforced with C-shaped rings of hyaline cartilage
  • Lined with ciliated columnar epithelium which sweeps contaminated mucus and particulates away from the lungs towards the pharynx

  
• Lungs


  • Conical shaped organs located in the thoracic cavity
  • Wide concave base that rests on the diaphragm with blunt peak (apex) which projects above the clavicle
  • Left lung smaller than the right
  • Left lung has 2 lobes, right lung has 3
  • Lungs surrounded by pleural membrane (visceral)

  
• Pleura


  • Parietal outer layer indirectly connects lungs to thorax & diaphragm
  • Visceral pleura is inner layer covering the lungs
  • Pleural Cavity filled with pleural fluid- lubricates and aid in lung movement during ventilation

  
• Carina, Bronchi, Bronchioles and Alveoli


  • Carina – contains sensory receptors which continually monitor airway for debris
  • Right bronchus - wider, shorter and more vertical compared to the left bronchus, more likely to be obstructed by inhaled foreign bodies
  • Left bronchus - narrower than the right and about 5cm long
  • The bronchi subdivide into bronchioles
  • These subdivide into smaller bronchioles – terminal, respiratory bronchioles, and alveoli
  • Alveoli – provide 70m2 surface area for gaseous exchange, cells elastic allowing the alveolus to inflate during inspiration, alveolar cells secrete pulmonary surfactant, each alveolus contains immune macrophages (dust cells)

  
• Common Lower Respiratory Tract Conditions

  • Pneumonia
  • Tuberculosis (TB)
  • Bronchiolitis
  • Asthma
  • COPD
  • Chronic Bronchitis
  • Interstitial Lung Disease

  
• Pulmonary Ventilation (breathing)


  Include inspiration (air enters) & expiration (air leaves), relies predominantly on the respiratory muscles
• Muscles of inspiration


  • The major muscle of inspiration are the diaphragm and external intercostal muscle
• Inspiration


  1. During inspiration the diaphragm becomes flattened and descends towards the abdomen

  2. The ribs are pulled upwards and outwards and the chest expands

  3. The pressure within the lungs falls and air is drawn in via the trachea

  
• Expiration


  1. The chest returns to its previous dimensions by passive recoil

  2. It is not an active process, muscle contraction is not required as in inspiration

  3. Boyle's law indicates that as the volume of the lungs decreases the pressure inside the lungs increases, this forces air out through the trachea
• Accessory muscles


  • When breathing becomes laboured (high demand) e.g exercise or respiratory dysfunction
  • Forced inspiration – sternocleidomastoid and scalene muscles link the cervical vertebrae to the first two ribs and increase the rib cage expansion
  • Forced expiration – internal intercostal muscles and sometimes the abdominal muscles, increases the pressure in the thorax by squeezing the abdominal contents
  • Serrated anterior pectoralis major and minor, trapezius and others
• Mechanics of breathing
• Control of breathing


  The respiratory centre (formed by group of nerves in the medulla oblongata) controls the rate and depth of breathing and its activity can be influenced by nervous input and chemical input

  
• Chemoreceptors


  • Peripheral chemoreceptors monitor changes in blood
  • Central chemoreceptors monitor PH value of cerebrospinal fluid (CFS)
  • Changes in PH cause chemorecpetors to stimulate inspiration
  • Increased CO2 level stimulates the chemoreceptors and chemosensitive areas of the brainstem
  • An increase in pCO2 is referred to as hypercapnia
  • CO2 increase in the blood is the most powerful stimulus for breathing
  • The centre is not affected directly by low oxygen (O2) levels

  
• Factors Affecting Respiration


  • Physiological
  • Airway resistance
  • Compliance
  • Elasticity
  • Physical exercise
  • Speech/singing
  • Emotional display e.g. crying, laughing , fear etc
  • Drugs e.g. sedatives, alcohol
  • Sleep
  • Dehydration
• Respiration rate in adult

  The average respiratory rate for an adult is 12–20 breaths/min, and each breath consists of three phases: inspiration, expiration, and a pause stage
• Normal respiratory rate for children

  Varies by age, with higher rates in younger children
• Terminology for abnormal breathing

  • Bradypnoea - decreased respiratory rate: abnormally slow
  • Tachypnoea - increased respiratory rate: elevated and rapid
  • Dyspnoea - difficulty in breathing
  • Hyperpnoea - Increase in rate and depth of breathing
  • Apnoea - absence of breathing
  • Orthopnoea – difficulty in breathing when lying flat