resp 2-ANS

• Parasympathetic innervation


  Causes constriction of the airway
• Sympathetic innervation


  Causes relaxation of the airway smooth muscle
• Airway smooth muscle


  • Lines the conducting airways
  • Diameter of the airway can be significantly altered by
• Sympathetic nervous system

  Causes relaxation of the airway smooth muscle
• Beta-2 receptors


  On airway smooth muscle, stimulation induces bronchodilation and decreases airway resistance
• Parasympathetic nervous system


  Innervates airway smooth muscle, triggering contraction when stimulated
• The role of the ANS in regulating airway smooth muscle contraction is more complex than a simplified version
• Lungs


  • Innervated by both sympathetic and parasympathetic nervous systems
  • Activation of adrenergic and muscarinic receptors respectively
• Adrenergic and muscarinic receptors

  1. protein–coupled receptors, widely expressed in the lung
• Receptor expression can vary among species, important to remember when considering regulation of airway smooth muscle in the human lung
• M3 muscarinic receptors


  Located on the airway smooth muscle, activation causes bronchoconstriction
• M2 muscarinic receptors


  Located on the parasympathetic nerves, inhibit release of acetylcholine
• Beta-2 adrenergic receptors


  Expressed on the airway smooth muscle, activation causes bronchodilation
• Adrenergic receptors


  Also on the autonomic nerves, can modulate neurotransmitter release
• There is little evidence of sympathetic innervation of airway smooth muscle in the regulation of human airways
• Sympathetic nerves innervate parasympathetic ganglia, submucosal mucus glands and blood vessels
• There are two distinct parasympathetic pathways: cholinergic (pro-contractile) and non-cholinergic with nitric oxide (NO) and vasoactive intestinal peptide (VIP) which are pro-relaxant
• In the lung, secretion is very important and this is also affected by ANS function
• Submucosal glands


  Complex organs that rapidly produce copious mucus in response to neural signals
• In healthy humans, submucosal glands are estimated to provide more than 95% of upper airway mucus
• Mucus secretion


  Controlled by muscarinic and β2-adrenergic receptors
• Mucus secretion


  1. Acetylcholine release from parasympathetic nerves stimulates

  2. Muscarinic receptors mediate secretion from nasal and submucosal glands and most likely from goblet cells

  3. β-Adrenergic receptors are localized to the submucosal glands
• Mucus secretions


  Complex mix of salts, mucins, other proteins and water
• Mucus secretion


  1. Happens via mucous tubules and serous acini (sacs)

  2. Transported via a ciliary duct (containing ciliated epithelial cells)
• Mucins


  Give mucus its 'gel' like (slime-like??) properties
• More water


  Less viscous the mucous
• Issue with ion (and so water) transport

  Mucins form a more viscous gel
• Lungs


  An intricately designed organ that acts as the body's centre for gas exchange, inhaling and exhaling approximately 6 to 8 L of air per minute while exchanging oxygen for carbon dioxide
• Lungs


  • 300 million alveoli provide a total surface area of around 80 m2 for gas exchange
  • Airways have a surface area of around 2.5 m2
  • Particles landing on these surfaces do not contact the epithelium directly
  • Between the epithelium and the respiratory gases is a continuous film of surface liquid, which increases in depth from 0.1 µm in the alveoli to 10 µm in the trachea
• Gas exchange in lungs

  1. Inspired air being delivered by 23 generations of airways

  2. After about generation 20, the walls become continuously lined with alveoli, and the airways are now known as alveolar ducts

  3. Carbon dioxide and oxygen gas exchange across the wall (blood-air barrier) of pulmonary capillaries and lung alveoli
• Bronchi


  • Extend from the trachea (also called the "windpipe")
  • Together with the trachea, form the tracheobronchial tree of the lungs
  • The first 8 –10 airway generations contain cartilaginous rings or plaques in their walls and are referred to as bronchi
  • From generations 10 to 15, or so, these are referred to as conducting bronchioles
  • After generation 15, alveolar sacs start to bud off their walls, and they become known as respiratory bronchioles
• Bronchi


  • Contain smooth muscle that contract or relax to control the diameter of bronchial airways
• Bronchioles


  • Rely on smooth muscle and elastic fibres to maintain their wall integrity
• Lungs


  • Do not have muscles to expand and contract during respiration
  • Rely on external muscles to enable respiratory movement
• Muscles activated during inspiration

  • Diaphragm (most important)
  • External intercostal muscles
  • Sternocleidomastoid
  • Levator costarum
  • Serratus anterior
  • Scalenus
  • Pectoralis major
  • Pectoralis minor
  • Serratus posterior superior
• Muscles of expiration


  • Muscles of the anterior abdominal wall
  • Internal intercostal muscles
  • Serratus posterior inferior
• Respiratory centre


  Composed of three distinct neuronal groups in the brain: the dorsal respiratory group in the nucleus tractus solitarius, the ventral respiratory group in the medulla, and the pontine respiratory group in the pons
• Pontine respiratory group


  Further classified into the pneumotaxic center and the apneustic centre
• Typically, there are 12-14 breath cycles per minute
• Respiratory cycle


  1. Begins with inspiration

  2. Ends with expiration