breathing

• LUNGS

  • located in thorax, separated by mediastinum and heart
  • extend from neck to diaphragm
  • the diaphragm separates thoracic and abdominal cavities
  • conical shaped with a soft, spongey texture
  • the apex of the lung lies above the clavicle (in the neck)
  • diaphragmatic surface (base)- sits on the diaphragm
  • costal surface- lies adjacent to the ribs
  • mediastinal surface- faces the mediastinium
• RIGHT LUNG

  • wider and shorter than the left lung
  • three lobes: superior; middle; inferior
  • two fissures: oblique; horizontal
• LEFT LUNG

  • narrower and longer than the right lung
  • two lobes: superior; inferior
  • one fissure: oblique
• HILUM OF THE LUNG

  • located on the mediastinal surface
  • the area where the pulmonary vessels, bronchi, bronchial vessels, lymphatics and nerves enter/ leave the lung
• PHYSICAL PROPERTIES OF LUNGS

  • COMPLIANCE (distensibility)

  1. the ability of the lungs to expand
  2. affected by: connective tissue structure of the lungs, level of surfactant, mobility of the thoraic cage

  • ELASTICITY: elastic tissue allows lung expansion during inspiration and recoil during expiration
• THE PLEURA

  • doubled layered serous membrane

  1. visceral pleura adheres to the lungs
  2. parietal pleura attaches to the thoraic wall and diaphragm

  • the pleural cavity is a potential space between the paretiral and visceral layers that contains a thin layer go detours fluid
• FUNCTIONS OF THE PLEURA:

  • reduces friction during breathing
  • creates a pressure gradient which assists in ventilation
  • compartmentalises each lung, therefore reduces spread of infection

  BONY THORAX

  • forms the skeleton of the chest wall
  • consists of:

  1. sternum
  2. ribs (12 pairs)
  3. thoracic vertebrae (12)

  THE STERNUM

  • breast bone
  • consists of:

  1. manubrium
  2. body
  3. xiphisternum
• RIBS

  • attached by the head and tubercle to the thoracic vertebrae
  • slope downwards and forwards
  • ribs 1-10 attached by costal cartilage to the sternum

  1. 7 pairs true
  2. 3 pairs false
  3. 2 floating
• THORACIC VERTEBRAE

  • head of rib articulates with the body of the thoracic vertebra
  • tubercle of rib articulates with the transverse process of the thoracic vertebra
• INTERCOSTAL MUSCLES

  • spans the spaces between the ribs intercostal spaces)

  1. external intercostal muscles (superficial layer)
  2. internal intercostal muscles (middle layer)
  3. innermost intercostal muscles (deep layer)

  • external intercostals: fibres run downwards and forwards
  • internal intercostals: fibres run downwards and backwards
• INTERCOSTAL VESSELS AND NERVES

  • course in the intercostal spaces between the internal intercostal and innermost intercostal muscles
  • supply the muscles, adjacent skin and pleura
• DIAPHRAGM

  • separates the thorax from the abdomen
  • dome-shaped skeletal muscle with central tendon
  • attached to the xiphisternum, costal margin, 11th and 12th ribs, and the lumbar vertebrae
  • openings for the inferior vena cava, oesophagus and aorta
  • fibrous pericardium fused to central tendon
  • innevated by phrenic nerve
• PULMONARY VENTILLATION

  • Inspiration/ inhalation:

  1. movement of air into lungs
  2. occurs when intrapulmonary pressure is lower than atmospheric pressure

  • Expiration/ exhalation

  1. movement of air out of lungs
  2. occurs when intrapulmonary pressure is greater than atmospheric pressure

  • intrapulmonary pressure us altered by changes in thoracic volume, e.g:

  1. changing vertical diameter
  2. anterior posterior (AP) diameter
  3. transverse diameter
• ALTERING VERTICAL DIAMETER:

  • contraction of diaphragm increases vertical diameter
  • relaxation of diaphragm decreases vertical diaphragm
  • contraction responsible for 75% increase in thoracic capacity during inspiration
• INCREASING AP AND TRANSVERSE DIAMETERS

  • Elevation of ribs increases the AP and transverse diameters
  • responsible for 25% increase in thoracic capacity
• TRANSVERSE DIAMETER

  • many of the ribs are lowest near their middle and rise at each end
  • if the middle of the rib rises, it moves away from the midline of the body; making the chest wider from left to right
• ANTERIOR DIAMETER

  • Elevation of ribs at the sternal end makes them more horizontal and pushes sternum forward (pump handle movement) --> increases AP diameter
• MUSCLES OF QUIET INSPIRATION

  • QUIET INSPIRATION- passive process whereby the diaphragm and external intercostal muscles relax
  • occurs at rest
  • the contracted diaphragm flattens to increase the vertical diameter of the thorax
  • the external intercostals elevate the ribs and increase AP and transverse diameters
• MUSCLES OF FORCED INSPIRATION

  1. sternocleidomastoid
  2. pectorails minor
  3. serratus anterior
  4. scalenes
  5. pectoralis major

  • in addition to the diaphragm and external intercostal muscles, these muscles assist in rib elevation, increase the speed and amount of movement
• MUSCLES OF FORCED EXPIRATION

  1. rectus abdominis
  2. external oblique
  3. transversus abdominis
  4. internal oblique

  • internal and innermost intercostals depress the ribs and reduce the size of the thoracic cavity
  • abdominal muscles compress the abdomen and force the diaphragm upwards
• PRESSURE AND VOLUME CHANGES

  • RESPIRATION: exchange of gases (O2 and CO2) between the atmosphere, blood and cells

  1. contributes to homeostasis
  2. regulates the prof internal environment

  • Respiration takes place in 3 stages:

  1. PULMONARY VENTILATION (breathing): inspiration and expiration of air between atmosphere and lungs (alveoli)
  2. EXTERNAL PULMONARY RESPIRATION: exchange of gases between alveoli and blood in pulmonary capillaries
  3. INTERNAL TISSUE RESPIRATION: exchange of gases between blood in systemic capillaries and tissue cells
• PULMONARY VENTILATION (BREATHING)

  • Physical movement of air in and out of alveoli of the lungs
  • Relies on:

  1. BOYLES LAW: when temp of gas = constant, pressure of gas varies inversely with volume
  2. Air flows from an area of high pressure to that of low pressure (lung volume increases, intrapulmonary pressure decreases, air move in)
• INTRAPLEURAL PRESSURE

  • refers to pressure within pleural cavity
  • always lower than atmospheric and intrapulmonary pressures
  • created by elastic recoils of lungs
• RESISTANCE TO BREATHING

  • Forces to overcome

  1. Lung (pulmonary) compliance- ease with which the lungs can be expanded/ distensibility

  -elasticity of lung tissue

  -surface tension of alveoli

  -mobility of chest wall

  2.airway resistance: major non-elastic source

  -elastic recoil of lung opposes inspiration and aids expiration

  -airway resistance opposes both
• 1(a). LUNG COMPLIANCE- ELASTICITY OF LUNG TISSUE

  • measure for elastic recoil
  • a measure of (lung) volume changes resulting from a given change in pressure
• 1(b). LUNG COMPLIANCE- SURFACE TENSION

  • caused by intermolecular forces between molecules in a liquid
  • air-fluid interface surface of a fluid is under tension like a thin membrane being stretched = gas-liquid boundary
  • LAPLACE'S LAW = relationship between pressure, surface tension and radius of an alveolus
  • at equilibrium, the tendency of increased pressure to expand the alveolus balances the tendency of surface tension to collapse it
  • pulmonary surfactant greatly reduces surface tension increasing compliance
  • it equalises the pressure differences between small and large alveoli
• SURFACTANT

  • surfactant helps keep uniform alveolar size

  1. more concentrated in smaller alveoli
  2. lower surface tension helps equalise pressure among alveoli of different sizes
  3. easier to inflate smaller alveoli
  4. work needed to expand alcove with each breath greatly reduced

  • water is composed of highly polar molecules and has high surface tension

  1. if the film coating of alveoli was pure water; then they'd collapse between breaths
  2. as it contains surfactant- a detergent like complex of lipids and proteins reduces surface tension
• NEONATAL RESPIRATORY DISTRESS SYNDROME

  • lack f surfactant secretion in premature babies (28-32 weeks gestation)
  • reduced compliance
  • Alveoli collapse on exhaustion
  • difficult to inflate lungs (50% die without rapid treatment)
• 2. AIRWAY RESISTANCE

  • major non-elastic source of resistance to gas flow = friction
  • factors affecting airway resistance:

  1. LUNG VOLUME- bronchi dilate as lungs expand
  2. BRONCHIAL SMOOTH MUSCLE- parasympathetic nerves bronchoconstrict, sympathetic nerves + adrenaline bronchodilate
  3. STIMULI CAUSING REFLEX BRONCHOCONSTRICTION: smoke, dust irritants, histamine
• MEASURING AIRWAY RESISTANCE

  • FVC- forcibly breathing out vital capacity (usually little difference from VC)
  • FEV1- volume of air expelled in 1 second (assess changes in resistance, less than 80% = increased airway resistance)
• ASSESSMENT OF LUNG FUNCTION

  • Breath sounds

  1. presence of mucous/ fluid
  2. absence of breath sounds: collapsed lungs?

  • Pulmonary function tests

  1. peak flow meter

  • Lung volumes and capacities can be measured via spirometer
• FUNCTIONAL RESIDUAL CAPACITY

  • FRC helps to stabilise the composition of alveolar air
  • volume of air left in the lungs after a normal, passive exhalation
  • cannot be measures by spirometry as it includes the residual volume
• TIDAL VOLUME = volume of air inhaled or exhaled in one quiet breath (males = 500ml, female = 500ml)
• EXPIRATORY RESERVE VOLUME = amount of air that can be forcibly exhaled after a normal tidal volume exhalation (male = 1000ml, female = 700 ml)
• INSPIRATORY RESERVE VOLUME = amount of air that can be forcibly inhaled after a normal tidal volume inhalation (male = 3300ml, female = 1900ml)
• RESIDUAL VOLUME = air remaining in lungs after maximum expiration (male = 1200ml, female = 1100ml)
• VITAL CAPACITY

  VC = TV + IRV + ERV

  • maximum amount of air that can be expired after a maximum inspiratory effect
  • males = 4800ml
  • females = 4200ml
• INSPIRATORY CAPACITY

  IC = TV + IRV

  • maximum amount of air that can be inspired after a normal expiration
• FUNCTIONAL RESIDUAL CAPACITY

  FRC = RV + ERV

  • volume of air remaining in the lungs after a normal tidal expiration
• TOTAL LUNG CAPACITY

  TLC = TV + IRV + ERV + RV

  • maximum amount of air contained in lungs after a maximum inspiratory effect
  • males = 6000ml
  • females = 4200ml