Histo lec finals

• The respiratory system is the site where respiratory gases O2 and CO2 are exchanged

  
• 4 main functions of the respiratory system

  • Pulmonary ventilation
  • External respiration
  • Internal respiration
  • Respiratory gas transport
• Conducting portion


  Consists of the nasal cavities, nasopharynx, larynx, trachea, bronchi, bronchioles, and terminal bronchioles. Functions to warm, moisten and filter the air before it reaches the respiratory components where gas exchange occurs

  
• Respiratory portion


  Includes the respiratory bronchioles, alveolar ducts, alveolar sacs and alveoli, where the exchange of gases takes place

  
• Nasal cavity


  • Nares (nostrils)
  • Vestibule
  • Olfactory epithelium

  
• Olfactory epithelium


  Tall pseudostratified columnar epithelium consisting of olfactory cells, supporting (sustentacular) cells and basal cells. Contains Bowman's glands that produce a watery secretion

  
• Nasopharynx


  Posterior communication of the nasal cavities, becomes continuous with the oropharynx at the level of the soft palate. Lined with respiratory epithelium and below this up to the laryngopharynx is stratified squamous epithelium

  
• Larynx


  Connects pharynx with the trachea
• Trachea and extrapulmonary (primary) bronchi


  • C shaped hyaline cartilages
  • Respiratory epithelium on the mucosa (ciliated cells, goblet cells, small mucous granule cells, diffuse neuroendocrine cells, short basal cells)
  • Submucosa with seromucous glands
  • Adventitia with C shaped hyaline cartilages

  
• Intrapulmonary bronchi (secondary bronchi)/ lobar bronchi

  • Arise from subdivisions of primary bronchi
  • Divide many times and give rise to segmental bronchi
  • Wall contains irregular cartilage plates
  • Lined by respiratory epithelium
  • Spiraling smooth muscle bundles separate lamina propria from submucosa which contain submucous glands

  
• Primary and terminal bronchioles

  • Lack glands in the submucosa
  • Walls contain smooth muscles rather than cartilage plates
  • Primary bronchioles have ciliated columnar epithelium with goblet cells to ciliated cuboidal with Clara cells
  • Terminal bronchioles have simple cuboidal epithelial lining containing Clara cells

  
• Clara cells


  • Divide and some differentiate into ciliated cells
  • Secrete glycosaminoglycans
  • Metabolize airborne toxins

  
• Asthma is marked by widespread contraction of smooth muscles in the bronchioles causing a decrease in their diameter, associated with extremely difficult expiration of air, accumulation of mucus in the passageways and infiltration of inflammatory cells
• Respiratory bronchioles


  • Transition point between conducting and respiratory zone
  • Lined with simple cuboidal containing mostly Clara cells and some ciliated cells except in area interrupted by alveoli
  • Distally the lining abruptly changes to simple squamous epithelium

  
• Alveolar ducts


  • Linear passageways continuous with respiratory bronchioles
  • Wall consist of adjacent alveoli, separated by an interalveolar septum
  • Most distal portion of the respiratory system – contains smooth muscle cells that rim the opening of adjacent alveoli
  • Lined by type II pneumocytes and highly attenuated simple squamous epithelium of type I pneumocytes

  
• Alveolar sacs


  • Expanded outpouchings of numerous alveoli at the distal ends of the alveolar ducts
• Alveoli


  • Pouch like evaginations about 200um in diameter
  • Separated by interalveolar septa that contains alveolar pores
  • Rimmed by elastic fibers at their openings (except in alveolar ducts where they are rimmed by smooth muscle cells)
  • Lined by type I pneumocytes and type II pneumocytes

  
• Type I pneumocytes


  • Cover 95% of the alveolar surface and form part of the respiratory membrane
  • Extremely thin cytoplasm
  • Form tight junctions with adjacent cells
  • Has phagocytic capabilities
  • Unable to divide

  
• Type II pneumocytes


  • Cuboidal, found near septal intersections
  • Bulge into alveolus, free surface contains microvilli
  • Capable of division and regeneration into both types of pneumocytes
  • Form tight junctions with adjacent cells
  • Synthesize pulmonary surfactant which is stored in cytoplasmic lamellar bodies

  
• Pulmonary surfactant


  Phospholipids and at least 4 proteins. Forms tubular myelin when first released from lamellar bodies, then spreads to produce a monomolecular film over the alveolar surface. Reduces the surface tension of the alveolar surface, permitting the alveoli to expand easily during inspiration and preventing alveolar collapse during expiration

  
• Alveolar macrophages


  • Principal mononuclear phagocytes of the alveolar surface
  • Remove inhaled dust, bacteria and other particulate matter trapped in the pulmonary surfactant
  • Migrate to bronchioles after filling with debris and carried to the upper airways – at the oropharynx, they are either swallowed or expectorated
  • May also exit by migrating to the interstitium and leave via lymphatic vessels

  
• Interalveolar septum


  • Wall or partition between 2 adjacent alveoli
  • Outer surface- extremely thin simple squamous epithelium lining the alveoli
  • Contains elastic and reticular fibers in its thicker regions
  • Houses continuous capillaries in its central (interior) region
  • Contains the blood gas barrier (respiratory membrane) which separates the alveolar air space from the capillary lumen

  
• Hyaline membrane disease (infant respiratory distress syndrome) is observed in premature infants (<28 weeks gestational age) who lack adequate amounts of pulmonary surfactant, characterized by labored breathing due to alveoli that are difficult to expand

  
• Emphysema results from destruction of alveolar walls and formation of cyst like sacs, reducing the surface area available for gas exchange. It is marked by decreased elasticity of the lungs, which are unable to recoil adequately during expiration

  
• Hyaline membrane disease


  Can often be prevented by prolonging pregnancy and sometimes by administering glucocorticoids to the expectant mother a few days prior to delivery to help induce the synthesis of surfactant
• Emphysema


  • Results from destruction of alveolar walls and formation of cyst like sacs, reducing the surface area available for gas exchange
  • Marked by decreased elasticity of the lungs, which are unable to recoil adequately during expiration. In time, the lungs expand and enlarge the thoracic cavity (barrel chest)
• Emphysema


  Associated with exposure to cigarette smoke and other substances that inhibit a1- antitrypsin, a protein that normally protects the lungs from the action of elastase produced by alveolar macrophages
• Emphysema


  Can be a hereditary condition resulting from a defective a1 -antitrypsin. In such cases, gene therapy with recombinant a1 -antitrypsin is being used in an effort to correct the problem, and it has recently been successful in boosting the availability of this protective protein
• The digestive system is divided into an alimentary tract and accessory organs of digestion
• The alimentary tract is a continuous passage that starts with the mouth and end in the anus
• Water and food pass through this passage and by mechanical and chemical mechanisms - digestion and absorption of the food products take place
• Accessory organs of the system are made up of the salivary glands, liver and the pancreas

  
• These glands give significant contributions to the process of chemical digestion by producing enzymes, buffers, emulsifiers and lubricants delivered to the alimentary tract via a system of ducts
• Oral cavity


  Internal part of the mouth that function for ingestion, mastication, and lubrication in preparation for deglutition
• Oral vestibule


  The space between inner lips, cheeks, and front surface of the teeth
• Oral cavity


  The space between the upper and lower dental arches, extending from the inner surface of the teeth to the oropharynx

  
• Lining mucosa


  • Covered by non-keratinized stratified squamous epithelium with 2 distinct layers, stratum basale and stratum spinosum only
  • Lines the inner oral surfaces of the lips, cheeks, soft palate, inferior surface of the tongue and the floor of the mouth
  • Less exposed to abrasion than the masticatory mucosa
  • Provides a barrier against the invasion of pathogens and toxic chemicals
  • Contains receptors for sensations and serves immunological functions through diffuse lymphoid tissues, epithelium contains transient antigen presenting cells
  • Also provides lubrication and buffering by minor glands in the submucosal layer

  
• Lamina propria


  • Thin layer of loose connective tissue with many elastic fibers and a few collagen fibers
• Submucosa


  • Thick layer of connective tissue which contains minor salivary glands and is attached to the underlying muscle. Continuously secrete saliva to keep the mucosa wet

  
• Masticatory mucosa


  • Keratinized stratified squamous epithelium
  • Exposed to significant abrasion due to high compression and friction during chewing
  • It has stratum basale, spinosum, granulosum and corneum
  • Lamina propria is thick with a dense network of collagen fibers and a few elastic fibers
  • No submucosa and is directly and rigidly attached to the underlying bone
  • Injection into this area is difficult and painful due to sensitive periosteum
  • Covers the oral surfaces of the gingiva and the hard palate